Home

Datasheets - Jameco Electronics

1. N Ground Test Measurements and Settings The next step for a voltage measurement is to configure the PropScope so that it can display voltage levels in its Oscilloscope screen We will look more closely at what these configurations do in later activities For now just follow these steps using Figure 2 4 as a reference v Click the upper left Oscilloscope tab to navigate to the PropScope s Oscilloscope view Page 30 Understanding Signals with the PropScope Set both Vertical dials to 5 V Set the Horizontal dial to 50 ps Click the Trigger tab and set the Mode slider switch to Off Set both coupling switches under the Vertical dials to DC Test the Run button by clicking it a few times to make it toggle between bright green running and dark green not running Make sure the Run button is bright green showing the oscilloscope is running eo XK Your display should now resemble Figure 2 4 Figure 2 4 PropScope Settings for DC Voltage Measurements 8 PropScope 1 0 6 Fle Edt View Plugins Tools Help Horizontal Oscilloscope Logic Analyzer Analog DSO LSA Oscil z 100ps 200 EA 00s ims Oscilloscope Tab z Square Generate She Freavency joa ___ Set 6 Sawtoo
2. DC AC _ Off DC_AC DAC Off Ip Souare Generate f sre Frequency amz e pi Saetoath Amplitude TY _ i Custom Edt Oftset 2 25 A D Ee e po F Wag AE ee f L Continuous Step qa m Normal In Figure 6 18 the jagged spikes in the lower CH1 trace occur during function generator s low signals in the upper CH2 trace This indicates that a lot of activity is happening on channel 1 when the flow control signal from the function generator is low The actual bit level activity is not visible but it s a good indicator that serial communication occurs during those times For a closer look you can pick a function generator frequency that lets fewer bytes through and then adjust the Horizontal timescale to a smaller value For example you could pick a function generator frequency that only lets two bytes through at a time For two bytes at a time you ll need to set the function generator in terms of some frequency To figure out the frequency the first step is to figure out how much low time is needed for two bytes Next multiply that time by 2 since a square wave has equal high and low times The result is the cycle time or period Then take the reciprocal of the period for the frequency That s your frequency for the function generator Page 198 Understanding Signals with the PropScope Here is how to calculate the function
3. J OOOOOOOOOOS o000000000 6x 1oooN poo000000o00n0000 OO X2 DAC Test Program Figure 8 24 Example Wiring Diagram for Figure 8 23 This program was introduced in Chapter 2 Activity 4 It repeatedly sets the voltage across the RC circuit s capacitor to 1 25 V v Enter Test 1 Channel Dac bs2 into the BASIC Stamp Editor and run it Test 1 Channel Dac bs2 Sert eb LAR capacitor COmler ona SSTAMP BS2 PF SIDBVASINC 2 Sy PAUSE 1000 DEBUG Program running DO PWM 14 64 1 LOOP Target module BASIC Stamp 2 Language PBASIC 2 5 1 ms before first DEBUG command Debug Terminal message Main Loop 1 25 W ite Pid Capacitor Repeat main loop Chapter 8 RC Circuit Measurements Page 295 DAC Test Measurements In Figure 8 25 the CH1 trace shows the DC voltage that the PWM signal establishes across the capacitor The CH2 trace shows signal activity during six repetitions of the DO LOOP in Test 1 Channel Dac bs2 This Horizontal dial setting gives an overview of the program running with 1 ms periods of PWM activity followed by about 1 2 ms of delay between DO LOOP repetitions We would expect 5 V high PWM pulses the sporadic pulse heights are a clue that there isn t enough room in the display to view all the signal activity After this quick ch
4. 1kQ P12 E PropScope CH1 P9 1 KQ P7 PropScope GND P5 X2 Y Click the Generate button to turn off the function generator The button s color should change from bright green to dark green v If you have not already done so set the Channel 1 dial to 1 V div and adjust the trace s position in the oscilloscope display so that it resembles Figure 2 23 v The CH1 trace level should be about half way between the 2 and 3 V Channel 1 division lines indicating 2 5 V v Check the CH1 Average voltage in the Measure tab to verify Page 52 Understanding Signals with the PropScope Figure 2 23 Test the Voltage Divider Output 8 PropScope v2 0 1 File Edt View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA ck th u U 1 divi output in the Oscilloscope Turn off the function generator Dc AC Off DC_AC DAC Off Square Generate Sine Frequency 10kHz Samaai Amplitude Tv A Custom Edt Offset EE i Measure Trigger Measure Channel 1 Keo W 247V Bt acm C ov a Check the Measure tab s Average voltage Not all voltage measurements will be as close as 2 49 V Any measurement in the 2 3 to 2 7 V range indicates that the voltage divi
5. Trigger Channel 1 4 Dt orav j Jaj erent T zav EAE Page 44 Understanding Signals with the PropScope Yr EE r Trigger Measure o M ssov rate JD Mime Figure 2 15 W sa 6rcv La csv M oy Measure Tab DC lt i Voltage Measurements l 375v d Average voltage measurements Floating Cursor vs Measure Tab The floating cursor displays voltage at an instant in time corresponding to your mouse pointer s horizontal position on the Oscilloscope screen The Measure tab s Average voltage displays the calculated average of the measurements over a period of time Since even DC voltage fluctuates slightly the average voltage is typically the more reliable means of obtaining DC measurements However if all you need is a quick and approximate DC voltage measurement the floating cursor may save you a mouse click Your Turn Calculate Set and Test a Voltage with PWM Let s say a device needs to have 3 5 V applied to one of its inputs You may not be able to generate exactly 3 5 V but with PWM you can probably find a digital value that will result in an analog voltage output that is close enough Ideally it should be within about 19 5 mV which is 1 256 of 5 V Knowing that the pwm command charges the DAC circuit s capacitor to voltages in terms of 256 of 5 V we can make a formula for calculating the PwM command s Duty argument for a given voltage in the 0 to 5 V r
6. OOOOOOOO00 O DOOOOOOOOOGS OOOOOOOOOOOOO0O0 BS Chapter 8 RC Circuit Measurements Page 303 DAC Load Test Program Instead of applying the PWM repeatedly at top speed like the example program from the previous activity Test 1 Channel Dac with Delay bs2 applies the PWM signal and then delays for 5 ms before repeating This makes it convenient to use the PropScope to examine the what happens with the 10 kQ resistor attached vy Enter and run Test 1 Channel Dac with Delay bs2 Test 1 Channel Dac with Delay bs2 Seige Pir mca cultsorastOnel Zions Vee S STAMP BS2 Target module BASIC Stamp 2 SPBASIC 2 5 Language PBASIC 2 5 DEBUG Program running Debug Terminal message DO Main Loop ut bal By Ab U O OZS V CO rn mead cubtsona PAUSE 5 t Delay for 5 ms LOOP Repeat main loop DAC Load Test Measurements Figure 8 31 shows the decays that result as the capacitor loses its charge through the 10 KQ resistor Instead of a steady DC voltage the capacitor gets charged to an initial voltage but then it decays through the resistor load Again an op amp buffer aka voltage follower will solve this problem in Chapter 9 Activity 2 y Dial adjustments Horizontal 2 ms div Vertical CH1 0 5 V div CH2 2 Vidiv Vertical coupling switches CH1 DC CH2 DC Trigger tab switches Mode Continuous Edge Rise Level
7. a Em ge D oms 0 F Auto f a 220s 110V v Configure your PropScope s Horizontal dial Vertical dials and coupling switches and Trigger tab settings as shown in Figure 4 22 v Manually adjust the Trigger Voltage Level control to about 2 V v Place an object that will like your hand or a book facing the infrared detector Use Figure 4 20 on page 128 as a guide for object placement v Verify that it results in the irDetectLeft 0 display in the Debug Terminal Chapter 4 Pulse Width Modulation Page 131 v Verify that it results in a brief 0 V signal on CH2 while the FREQoUT command is active in CH1 Figure 4 23 shows the PropScope s Oscilloscope view while no object is detected The FREQOUT signal transmits for 1 ms on the upper CH1 trace but the lower CH2 trace remains at 5 V The BASIC Stamp I O pin interprets the 5 V applied to its P9 I O pin as a binary 1 which results in the irDetectLeft 1 message on the right side of Figure 4 21 v Make sure the Trigger Time control is set to the 2 time division v Repeat the conditions that resulted in the irDetectLeft 1 display from Figure 4 21 and verify that it results in an uninterrupted 5 V signal on CH2 Figure 4 23 Object not Detected PropScope v2 0 1 File Edt View Plugins Tools Help f 3i hig sig inal t WO bject erie Generate PESE TA ced abd A ney IE CH2 lf Ricetters
8. a Most calculators have an e button you can use to calculate the points on y e graphs and it s usually shared with the In function which tells you what x is in e for a given value To save button space the Windows Calculator has the In key and an inverse Inv checkbox that you can click to make the In key calculate e Here is how to calculate e with the Windows calculator s In button Click the 1 button Click to make it 1 Click the Inv checkbox Click the In button The calculator will display the result of e Calculate the value of e Try e e and e and compare them to the points in the graph on the left hand side of Figure 8 1 LAS SA Chapter 8 RC Circuit Measurements Page 269 Figure 8 3 Calculate e with the Windows Calculator B calclator xox zmizi Edit View Help Edit View Help 5 0 36787944117144232159552377016146 C Hep Dec C Oct C Bin Degrees C Radians C Grads l Gace 2 E A e e a ce Jc aa Ee a es a a Te a Pe PE NEVER ES WP ESE pe FS JES HEART AAAA C Hex Dec C Oct Bin Degrees C Radians Grads I Inv I Hyp E Backspace CE C Sum PEE You can create similar graphs to predict a voltage v as it decays from a certain starting value down to zero volts over time t with this version of the RC decay version of the exponential decay equation U R v Vixe VRE
9. Figure 8 15 Example Wiring for Figure 8 14 Potentiometer Sensor Test Code ReadPotWithRcTime bs2 is an example program from What s a Microcontroller Its DO LOOP has code that sets P7 high and then waits for 100 ms which is way more time than necessary for charging capacitor The main reason for the long PAUSE command is to slow down the massages the BASIC Stamp sends to the Debug Terminal to a rate of 10 Hz After the PAUSE the RCTIME command sets the I O pin to input and then waits for the voltage at I O pin P7 to decay to 1 4 V Then it stores the time measurement in terms of 2 us units in a variable named time Before it repeats the DO LOOP the DEBUG command displays the time variable s measurement result in the Debug Terminal v Enter ReadPotWithRcTime bs2 into the BASIC Stamp Editor and run it What s a Microcontroller ReadPotWithRcTime bs2 Read potentiometer in RC time circuit using RCTIME command SSTAMP BS2 Target module BASIC Stamp 2 SPBA5SiIC 2 5 Language PBASIC 2 5 time VAR Word For storing decay times PAUSE 1000 1 s before sending messages Chapter 8 RC Circuit Measurements Page 285 DO Main Loop HIGH 7 T See 127 Inukesa PAUSE 100 Wait 0 1 seconds RET UME Eme RC Decay time measurement DEBUG HOME time DEC5 time
10. Chapter 9 Op Amp Building Blocks Page 335 Non Inverting Amplifier Test Parts 2 Resistors 10 kQ brown black orange 1 Resistor 20 kQ red black orange 1 Op Amp LM358 misc Jumper wires Non Inverting Amplifier Test Circuit Figure 9 10 shows a test circuit for our non inverting amplifier and Figure 9 11 shows an example of the wired circuit The PropScope s function generator will send a test signal to the op amp s non inverting input and CH1 will monitor the resulting signal at the op amp circuit s output STOP Disconnect the CH2 probe from the breadboard first Disconnect the probe from the PropScope s CH2 BNC connector in and connect it to the DAC Card s function generator output See Figure 2 16 on page 46 v Build the circuit in Figure 9 10 using Figure 9 11 as a guide Set the 20 KQ resistor aside for the moment PropScope CH1 Figure 9 10 Rf 10 kQ Non Inverting Amplifier Test Circuit with a Gain of 2 Ri 10 kQ PropScope GND Page 336 Understanding Signals with the PropScope Figure 9 11 Wiring Diagram Example of Figure 9 10 oo ooo odoo wc odoo ow o000 oo o000 T o000 A AK 0o00 0000X 10oe4 o0000 joooo0o o0000 jooooo o0000 00000 o0000 00000 o0000 00000 oo000 00000 Y po A 00000 00000 o 00000 00000
11. PropScope GND OOOo0o0o000000 Was it necessary to move the ground clip connection No the ground clip is still connected to Vss through jumper wires but it could just as easily be left connected to directly to one of the Vss sockets Another Option Connect ground clips to the plated holes at the corners of your board Like the Vss sockets the metal in the plated holes at the each corner of your board are also connected to your board s negative power terminal so they are also Vss connections Chapter 2 DC Measurements Page 55 Potentiometer Voltage Measurement with the PropScope The PropScope s Vertical dial is still set to 50 us That means that the Oscilloscope screen s ten vertical division lines are each 50 millionths of a second apart The trace line crossing the screen that indicates the voltage is actually a graph of voltage measurements over 500 us So no matter how fast you turn the pot the voltage trace on the screen will still display as a straight line crossing the screen The only thing that appears to change as you adjust the pot is the flat trace line s level In Chapter 3 we will use different time division settings to plot voltage variations over time but for now we are just interested in the pot s wiper terminal as a DC voltage level e When you twist the potentiometer s knob make
12. In this activity you will calculate the cutoff frequency for an RC low pass filter and apply that frequency to the filter s input with the PropScope s function generator You will then test the amplitude and phase of the circuit s output to verify the frequency calculation A Corner frequency is another common expression for cutoff frequency When the amplitude e response of a filter is plotted over frequency the amplitude turns a corner and starts why declining at the cutoff frequency These graphs are common in the analysis of filters and amplifiers and they are called Bode plots The name Bode is pronounced bo dee Low pass Filter Test Parts List 1 Resistor 10 KQ brown black orange 1 Capacitor 0 01 WF misc Jumper wires Low pass Filter Test Circuit The circuit schematic in Figure 8 38 and wiring diagram example in Figure 8 39 are repeats of the circuits from Chapter 7 Activity 6 Y Unclip the CH2 probe tip from whatever it s connected to v Disconnect the CH2 probe from the PropScope at its BNC connector and connect it to the DAC Card s function generator output Build the RC circuit shown in Figure 8 38 and Figure 8 39 Connect the function generator output to the RC low pass filter input Connect the CH1 probe to the filter s output SSS Page 314 Understanding Signals with the PropScope Circuit Input Circuit Output PropScope CH1 10 KQ PropScope D
13. Figure 8 11 shows an example with the Horizontal dial adjusted to 200 us div for a zoomed in view of that first one millisecond time constant s worth of decay The vertical A time cursor is lined up with the start of the decay Then the horizontal B voltage cursor is set to as close as possible to 1 47 V which is 36 8 of 4 V You can use the B voltage level measurement in the Cursor display to know the cursor s voltage as you position it to 1 47 V Next the time from the start of the decay to the 36 8 level is measured by aligning the vertical B time cursor with the intersection of the decay trace and the horizontal B voltage cursor The time measurement result will appear in the Measure Display s A field Horizontal Cursors are positioned at voltage levels and measure voltage differences They are commonly referred to as voltage cursors _ 1 _ Vertical Cursors are positioned at times and measure time differences They are w commonly referred to as time cursors Horizontal and Vertical Cursors were introduced in Chapter 3 Activity 5 Set the trigger Level to Normal Make sure the Trigger Voltage control is 2 V on the CH2 vertical scale in the middle of the CH2 DAC square wave in Figure 8 11 v We want to take a close look at that first millisecond of decay so adjust the Horizontal dial to 200 s div Multiply 4 V by 36 8 the result should be about 1 47 V Line the green A vertical cursor up with t
14. 4 6 8 Time ms Triggered Go R E Continuous Step Page 132 Understanding Signals with the PropScope The PBASIC program cannot measure this pulse duration while it is sending the FREQOUT command However you could use a second BASIC Stamp to send IR and then use the first BASIC Stamp to measure the pulse duration with a command called PULSIN You can also use the PropScope to measure the duration of the pulse the IR receiver sends v Set it up so that the IR detector has an object to detect and your PropScope display resembles Figure 4 22 Click the Cursor tab and turn the Vertical time cursors on Line the cursors up along the negative and positive edges of the CH2 low pulse Measure the duration Compare it to the duration of the FREQOUT signal on CH1 KSSS Your Turn Change the Pulse Duration What does infrared object detection with infrared have to do with pulse width modulation The answer is that you can control the duration of the low pulse the IR detector sends by adjusting the FREQOUT command s Duration In other words in FREQOUT Pin Duration Freq1 you can modulate the pulse width by changing the FREQOUT command s Duration argument Try this Change the FREQOUT command in TestLeftIrPair bs2 to FREQOUT 8 2 38500 Place an object that will cause a detection in front of the IR LED and detector Repeat the pulse width measurements on the PropScope See how changing the FREQOUT command s Duration
15. 8 PropScope v2 0 1 sl BS File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Oscillo L morae hniena At3 26 CH1 3 44V CH2 0 73V Pe Vertical cursors DC_AC DAC Off Cursor H Generate t Sine Frequency E ea Amplitude TY pan ms Ga E Ce E Click Vertical button in Cursors subpanel to display the vertical cursors Cursor Display View Cursor measurements Here is how to position cursors to take measurements like those shown in Figure 3 22 v Click the Cursor tab below the Oscilloscope screen v In the Cursors tab click the Vertical button to make the time cursors appear on the oscilloscope They will appear as two vertical lines v Click either the waveform or the CH1 ground line to select CH1 as the active channel in the Cursor display lt lt Chapter 3 Human speed Measurements Page 103 Point at one of the cursor lines with your mouse and it will change to a double arrow that points left and right Click hold and move the cursor left or right to place it over one of the heartbeat signal peaks Repeat with the other cursor and an adjacent heartbeat signal peak Check the f measurement in the Cursor display near the Oscilloscope screen s lower right corner Your Turn Measure Voltage Differences with Horizontal Cursors Figure 3 23 shows horizontal cursors used to measure t
16. Sine Frequency 2 5kHz Sawtooth Amplitude TY 08 4 Time ms Triggered Coena A spectrum analyzer is a device that measures and displays the frequencies and relative amplitudes of a signal s sine wave components The PropScope s analog tab has a built in Spectrum Analyzer Let s try it Page 246 Understanding Signals with the PropScope y Enter D and G Notes bs2 into the BASIC Stamp Editor and load the program into the BASIC Stamp D and G Notes bs2 Play D7 and G7 notes together SSTAMP BS2 Target module BASIC Stamp 2 i TSPBASIC 2 5 Language PBASIC 2 5 DEBUG Program Bunning Debug Terminal message DO Main Loop EPEREOOVUTEO ClO ASS Ssil S36 1 pleg ese rk SIS iz or 1 itt LOOP Repeat main loop v View the waveform in your PropScope s Oscilloscope view using Figure 7 22 as a guide for settings v Click the Analog tab It s in the same group with Logic Analyzer and Oscilloscope Figure 7 23 shows the Analog view which includes three major tools the now familiar oscilloscope the Spectrum Analyzer and XY Plot The Spectrum Analyzer screen makes short work of determining the frequency components that might have looked somewhat confusing in the Oscilloscope screen In contrast to an oscilloscope which plots voltage against time a spectrum analyzer plots sine wave component amplitudes against frequency The heights of the tw
17. gt 1000 PULSIN 9 0 time 0 Measure store data pulses PULSIN 9 0 time 1 PULSIN Gs Wp weenie 72 PULSIN 95 03 seater 3 PULSIN 9 O time 4 PUES 9 0 se wines CS PULSIN 9 0 time 6 PULSIN 9 O time 7 PULSIN 9 0 time 8 PULSIN 9 0 time 9 PULSIN S 5 Canero PULSIN 9 0 time 11 FOR index 0 TO 11 Display 12 pulse measurements DIMBUE CREO Op ar stipvelere Emne IDG atiovelerc AN CRSEXY OQ 4 index DEC time index CELREOL NEXT LOOP Repeat main loop For more information on how the example programs in this activity work download wy and consult the R Remote for the Boe Bot pdf tutorial from www parallax com education Chapter 4 Pulse Width Modulation Page 137 IR Remote Test Measurements with the BASIC Stamp Figure 4 26 shows the BASIC Stamp module s pulse measurements while the remote s 3 button is pressed Point your remote at the IR detector and press and release the 3 button ix Com Port Baud Rate Parity COM1 E 9600 z None z Data Bits Flow Control 1X M DIRT RTS J J0 ZI RK DSR cs time ARRAY PWM MEASUREMENTS Duration Figure 4 26 BASIC Stamp Displays Pulse Measurements 667 from an IR Detector 35i Sei 356 that s receiving infrared signals from a SONY TV 356 remote with the 3 button 666 pressed 355 355 255 356 356 Page 138 Understanding Signals with the Pro
18. Display time in 2 us increments LOOP Repeat main loop Figure 8 16 shows the decay measurement as the number of 2 us units it took the capacitor voltage to decay from its starting voltage down to 1 4 V Since the time displayed in Figure 8 16 is 436 it means that the decay took 436 x 2 us 872 us v Maintain downward pressure on the potentiometer knob as you adjust it to keep it in contact with the breadboard connections v Turn the potentiometer knob to a point about 34 of the way counterclockwise in its range of motion then make fine adjustments for a Debug Terminal value of 436 ixi Com Port Baud Rate Parity Data Bits Flow Control mx DIR RTS J Z RX DSR CTS Figure 8 16 Debug Terminal Pot Measurement time 00436 in 2 us units Macros Pause Clear Potentiometer Sensor Test Measurements Each repetition of ReadPotWithRcTime bs2 takes at least 100 ms because of the PAUSE 100 command In addition there s the time it takes for the RC decay measurement the DEBUG command and some time to process all the commands in the loop All that said 200 ms is a reasonable estimate for a first look at two cycles of the measurement so the Horizontal dial is set to 20 ms div in Figure 8 17 y Dials Horizontal 20 ms div Vertical CH1 1 V div Page 286 Understanding Signals with the PropScope v Vertical coupling switches CH1 DC CH2 Off v Trigger tab switches Mode Continuous Edg
19. Figure 8 28 RC Circuit Converts PWM Signal that s High of the time to 3 75 V 3 4 of 5 V PropScope v1 1 1 Tigi Fie Edt wiew Plugins Tools Help Osciloscoape Logic Analyzer Analog DSO LSA Oscilloscope Dc AC Oft DC_AC DAC Off Square Generate pren an Custom Edit ofset o CH1 DC voltage 3 75V Continuous Step Page 300 Understanding Signals with the PropScope Verifying the RC Circuit s Average Voltage Output When a duty cycle signal s period is much smaller than the RC time constant T lt lt tT the RC circuit s output transmits the average of the voltage input With the PBASIC PWM signal calculating the average is simple because the signal spends its low time at ground So the average voltage is 5 V X thigh teycle More generally the average voltage of a signal is the area between the trace and ground during a cycle divided by the time of a cycle A Area between signal and ground during acycle Cycle Time For example the average voltage in Figure 8 28 is SEES 395 20 us v Apply the average voltage calculation to Figure 8 27 and Figure 8 26 Average Voltage Your Turn Average Voltage for a Different Signal The average voltage of the lower red CH2 trace in Figure 8 29 is the area between one of the triangles in the sawtooth wave and the Ground line divided by the time of one cycle To calculate the area b
20. RX DSR c Figure 8 20 Shorter Decay time 00170 Measurement Macros Pause Clear Close I Echo Off Figure 8 21 shows the corresponding Oscilloscope decay time measurement The main change is that the potentiometer s resistance is smaller so the decay time is shorter for a shorter RCTIME measurement A secondary change is that the capacitor charges to a slightly lower voltage That s because the 220 Q protection resistor value didn t change but the potentiometer is now a smaller value As the BASIC Stamp charges the circuit the slightly lower voltage divider level between the pot and 220 Q resistor limits the capacitor to charging to a slightly lower level 4 56 V instead of 4 8 V vV Repeat the decay cursor time measurement with the vertical cursors It should be in the neighborhood of 340 us v Also repeat the voltage measurement before the decay starts with the green horizontal A cursor and compare it to the level you measured with the other potentiometer setting Chapter 8 RC Circuit Measurements Page 291 Figure 8 21 Shorter Decay Lower Starting Voltage 8 PropScope 1 1 1 File Edit View Plugins Tools Help 10 x DC AC Off DC_AC DAC Off Square Generate Sawtooth TE Custom Edit Otfset 0 Time ms Triggered EY 27ms 4 56 Gq verica Coe A 4 CES Horizontal i 2 a 5 Em Float Trigge
21. s Frequency field Make sure to press the Enter key on your keyboard after typing each new value v How does the appearance of the waveform change with higher and lower frequencies Page 96 Understanding Signals with the PropScope Your Turn Other Waveforms You can make similar adjustments to the Sine Square and Custom waveforms First set the Offset Amplitude and Frequency values V Set Offset to 2 5 V Amplitude to 4 V and Frequency to 20 Hz Next move the slider switch to the different waveforms and observe the change in the display Set the Generator slider to Sine Remember to wait a moment for the screen to refresh V Set the Generator slider to Square Set the Generator to Custom click Edit and draw a waveform in the Waveform Editor with your mouse Click Update to make the DAC Card start transmitting your custom waveform ACTIVITY 5 SIMULATED HEARTBEAT What could be more Human speed than a heartbeat signal Modern heart monitors are oscilloscopes with special features and specialized probes to filter and amplify the very small electrical signals from contact points on the body The BASIC Stamp can be programmed to emulate an amplified heartbeat signal with its PwM command and DAC circuit Displaying and examining a heartbeat signal like the one in Figure 3 20 with the PropScope provides an example of why it s important to understand basic manual measurement techniques and not depend too heavily on
22. s wiper so that the voltage it applies to the ADC0831 s Vin input can be compared to the value the ADC0831 reports to the BASIC Stamp Three of the PropScope DAC Card s four Logic Analyzer inputs are also connected to the lines between the BASIC Stamp I O pins and the Page 152 Understanding Signals with the PropScope ADC0831 CS CLK and DO pins They will be used to monitor the synchronous serial communication between the two devices v Build the schematic in Figure 5 3 using the wiring diagram example in Figure 5 4 as a guide Vdd 220 9 P2 P1 DAC CARD 1 PO DAC CARD 0 DAC CARD 2 F gurea ADC0831 Test E Schematic ADC0831 PropScope CH1 10 KQ Pot PropScope GND DAC CARD G Vss Vss Vdd Vin Vss x3 P15 N NE TA Pi 5s P eid Figure 5 4 aed Wiring Diagram P7 Example for i Figure 5 3 7 P P1 PO X2 Chapter 5 Synchronous Serial Communication Page 153 ACTIVITY 2 WRITE CODE FROM A TIMING DIAGRAM Figure 5 5 shows a timing diagram similar to the one in the ADC0831 datasheet This diagram explains the signaling a microcontroller has to use to get measurements from the chip The little inverted triangles on the CLK signal indicate that the DO line updates its output on the clock pulse s negative edge
23. 2960 DEBUG Done CR Display done END Enter low power mode Play an Individual Note for Oscilloscope Viewing Again One or Two Notes at a Time bs2 makes it possible to play either the D7 note or the F7 note or both at the same time As with the previous activity this program continuously transmits whichever note you leave un commented For now we ll test one note later we ll examine the other note as well as both notes played together v Enter and run One or Two Notes at a Time bs2 as is v After verifying that the note is clearly audible reconnect the capacitor s positive lead to the circuit As before the note s volume may drop considerably but the signal displayed by the PropScope will be much cleaner One or Two Notes at a Time bs2 Select whether to play D7 or F7 or D7 F7 together SSTAMP BS2 Target module BASIC Stamp 2 Y SPBASIC 2 5 Language PBASIC 2 5 DEBUG Program running Debug Terminal message DO Main Loop FREQOUT 9 60000 2489 Play 2489 Hz for 1 minute MAHOU Ys OOOO AMO Commented does not play Y WNT YD CWOOOO As ANG Commented does not play LOOP Repeat main loop Page 240 Understanding Signals with the PropScope AC Couple the Signal Each PropScope Vertical coupling switch has a setting that removes DC offset from a signal it s called AC coupling When you use this setting it causes the sine wave voltages to swing above below the ground lin
24. Chapter 6 Asynchronous Serial Communication Page 211 SUMMARY Microcontrollers can communicate with a variety of devices using asynchronous serial communication Like synchronous serial communication a series of binary values are transmitted and received Unlike synchronous serial communication the devices exchanging data do not depend on a shared clock signal to synchronize when the binary values are transmitted received ASCII codes represent printable characters and some control codes and are often used in conjunction with asynchronous serial communication allowing devices to exchange text like keyboard and display data Asynchronous serial signals can be true or inverted have a baud rate which is a number of bits per second and have other characteristics such as a certain number of data bits parity and a certain number of stop bits The baud rate determines the amount of time each bit lasts the bit time is the reciprocal of the baud rate in bits per second A true signal has a high resting state a low start bit and then a certain number of data bits Like all the other bits each data bit is a signal that lasts one bit time With true signaling a high represents a binary 1 during a certain bit time and a low signal represents a binary 0 Asynchronous serial bytes are transmitted least significant bit first followed by a stop bit which is a resting state that lasts one or more bit times before the next message can be sent Bo
25. Display asynchronous serial messages to make it display text Other useful peripherals that utilize asynchronous serial communication include geographic positioning systems GPS radio frequency identification RFID and radio frequency communication modules that make it possible for microcontrollers to communicate wirelessly This chapter introduces the signaling these devices use to communicate and examines and decodes certain asynchronous serial messages with the PropScope ACTIVITY 1 ASCII CODES ASCII stands for American Standard Code for Information Exchange and it uses numeric codes to represent US alphabet characters It also includes some special codes called control characters for keys on your keyboard like Esc and Backspace When the BASIC Stamp sends messages to display as text on by a PC or serial LCD it uses ASCII codes to send the characters that make up the message Printable ASCII Chart bs2 displays characters and their corresponding ASCII codes for values of 32 through 127 in the Debug Terminal v Enter and run Printable ASCII Chart bs2 Printable ASCII Chart bs2 Display 32 through 127 along with the ASCII characters those values represent SSTAMP BS2 Target module BASIC Stamp 2 PSPBASTC 225 Language PBASIC 2 5 char VAR Word Will store ASCII codes PAUSE 1000 i second delay before messages DEBUG CES V PRINTABLE ASCII CHARACTERS Display chart heading GE TEON SA EO iad FOR c
26. E PropScope v2 0 1 lolx Fie Edt View Plugins Tools Help Oscilloscope Logic Analyzer Analog DS0 LSA 100ps_ 200 E29 Run Ims XV ie X gt DC AC Ofi DC_AC DAC Off PT Squere Generate US Sine Frequency 10kHz a Custom Et Offset o A a Ml Ta Giusy AE 2 am 2 its 4 rn area Ato arms svi or om am gt k d Tigger Eursor Measure Continuous Step Normal Page 124 Understanding Signals with the PropScope With tusuy and tcycue the duty cycle calculation for this signal is t Duty Cycle 2 x 100 CYCLE AAAS 100 17 7 us 25 1 Duty cycle simplifies calculations for the DAC output Just multiply the percentage by the high signal level for a prediction of the DAC output Vpac Duty Cycle x 5V x 25 1 x5V 1 255V The Channel 1 Average voltage measurement in Figure 4 15 and Figure 4 16 is oscillating between 1 22 V and 1 23 V Since this BASIC Stamp feature is not typically used for setting precision voltages a couple hundredths of a volt error is not bad at all Now if error turned out to be in terms of tenths of a volt that might need a closer look Your Turn Try a New Value The command PwM 14 64 5 is probably getting a little old v Pick a target voltage in the 0 to 4 98 V range Y Calculate the number of 256 of 5 V that voltage represents
27. Op amps can be used to perform a variety of operations on signals including compare buffer amplify attenuate invert and many more The op amp has a large open loop gain This chapter demonstrated how the open loop gain can be utilized in a comparator circuit to convert small signal differences into digital outputs Many signal operations rely on negative feedback circuits where the op amp s inverting input senses its output through a circuit When an op amp s inverting input senses the output through a circuit the op amp adjusts its output to make the voltage at the inverting input match the voltage at the non inverting input This behavior was used to demonstrate buffer non inverting amplifier and inverting amplifier circuits Clipping is a form of signal distortion where the op amp s output tries to send a voltage that is outside the limitations of its supply voltages Gain is a measurement of the ratio of output to input signal amplitude This value can be multiplied by the input signal to predict the output signal in an equation called a transfer function For non inverting and inverting amplifier circuits the gain can be set by choosing a ratio of feedback and input resistors according to the gain equation for the circuit Parts and quantities are subject to change without notice Parts may differ from what is shown in this picture If you have any questions about your kit please email education parallax com Wee
28. P1 Sea PO x2 Shorter cathode pin IR Object Detection Test Code TestLeftIrPair bs2 is an excerpt from Robotics with the Boe Bot that displays whether or not an object is detected in the Debug Terminal The command FREQOUT 8 1 38500 sends a 38 5 kHz signal to the IR LED making it a very rapidly blinking flashlight If the IR detector detects this rapidly blinking light reflected off an object it sends a low 0 V signal Otherwise it sends a high 5 V signal The command irDetectLeft INQ stores the IR detector s output in a bit variable named irDetectLeft This command has to immediately follow the FREQOUT command because there is only a brief time window between when the FREQOUT command stops and IR detector s output rebounds to high because it s not seeing the IR reflection any more 4 in Chapter 7 Basic Sine Wave Measurements you will use the PropScope to examine J sine wave signals the BASIC Stamp synthesizes with binary signals using the FREQOUT command Enter and run TestLefIrPair bs2 Chapter 4 Pulse Width Modulation Page 129 Robotics with the Boe Bot TestLeftIrPair bs2 Test IR object detection circuits IR LED connected to P8 and detector connected to PQ SSTAMP BS2 US EBBAS TCRA 58 irDetectLeft VAR Bit DO EREQOUMES il sis irDetectLeft IN9 DEBUG HOME irDetectlheft BINI irDetectLeft PAUSE 100 LOOP IR Object Detection Tests Figure 4 21
29. So when you set the Generator panel s Offset to a value the DC offset average voltage changes and the Page 222 Understanding Signals with the PropScope Trigger Voltage control follows it Up to this point the Generator panel s Offset has been set to 0 V which is where the Oscilloscope has been automatically positioning the Trigger Voltage control v Verify that the Trigger Voltage control s level is 0 V It should be automatically positioned to the left of the Ground line v Change the Generator panel s Offset from 0 to 2 35 V and press Enter Vv Verify that the waveform s average voltage changes to 2 35 V Y Point at but do not click the Trigger Voltage control See Figure 7 9 Verify that the Trigger Voltage control has automatically repositioned to approximately 2 35 V Figure 7 9 Trigger Auto Level Adjusts with DC Offset E PropScope v1 1 0 jol x File F View Plugins Tools Help Oscilloscope Siar Dc AC Oft DC AC DAC Off h theatr Square Generate Point at but 7 Sne Freouency zaz ___ don t click i i h oF ort lt a sie the Trigger f me or ss ir aia Voltage 7 z5 control to see the trigger SRE crosshairs Trigger Auto Continuous Normal Step Average voltage is 2 35 V Chapter 7 Basic Sine Wave Measurements Page 223 The Trigger tab s Edge switch in Figure 7 9 is set to Rise So the Os
30. more of a multipurpose card with DAC being one of its features Other features include external trigger an input that can be used to trigger oscilloscope measurements a video When the DAC Card is in use PropScope CH2 is disabled You can still take Example Program PushbuttonControlOfTwoLeds bs2 This example program from What s a Microcontroller makes the P14 LED blink on off at 10 Hz while the P3 LED is pressed or it makes the P15 LED blink on off at 10 Hz while the P4 button is pressed v Enter and run PushbuttonControlOfTwoLeds bs2 v Verify that the P15 LED blinks while the P4 pushbutton is pressed and held v Verify P14 LED control with the P3 pushbutton Page 88 Understanding Signals with the PropScope What s a Microcontroller PushbuttonControlOfTwoLeds bs2 Blink P14 LED if P3 pushbutton is pressed or blink P15 LED if P4 pushbutton is pressed SSTAMP BS2 SPBASIC 2 5 PAUSE 1000 DO DEBUG HOME DEBUG IN4 DEBUG IN3 if INS 1 TaEN Target module BASIC Stamp 2 Language PBASIC 2 5 Wait 1 second before DEBUG Main loop Top left position in terminal Display IN4 value Display IN3 value If P3 button pressed HIGH 14 P14 LED on PAUSE 50 Wait 1 20th of a second ELSEIF IN4 1 THEN Else if P4 button pressed HIGH 15 P15 LED o PAUSE 50 Wait 1 20th of a second ELSE Else no buttons pressed PAUSE 50 Just wait 1 20 seconds ENDIF No more conditions in c
31. red red brown Test Schematic Figure 7 10 shows a modified version of the test circuit from Figure 7 2 The only difference is the extra 220 Q resistor that connects the function generator s output to a BASIC Stamp I O pin So now the function generator s output goes to both the piezospeaker and the BASIC Stamp I O pin v Add the 220 Q resistor connecting the DAC Card s function generator output to the I O pin input You can also leave it connected to the speaker s input PropScope CH1 PropScope GND Figure 7 10 Audio Tones Test Circuit Modified for BASIC Stamp Monitored Frequency omm000000 o0nmo000000 onm0000000 omom000000000000000 om0000000 om000000000 om000000000 DOONN e 0000 000 X2 Page 226 Understanding Signals with the PropScope Test Code Display Measured Freq bs2 measures the number of sine wave cycles the PropScope applies to P9 during 1 second intervals and displays the result in the Debug Terminal v Enter and run Display Measured Freq bs2 Display Measured Freq bs2 Count signal cycles applied to P9 and display in Debug Terminal SSTAMP BS2 Target module BASIC Stamp 2 SSPBASTIC 2654 Language PBASIC 2 5 cycles VAR Word Stores counted cycles DO E Main loop COUNT S 1000 eyele Store 1 s counted in cycles var DEBUG HOME Input fre
32. s inverting input The potentiometer is connected as a variable voltage divider so turning the knob varies the voltage at its wiper terminal If the potentiometer wiper s voltage is even slightly above the voltage at the comparator s non inverting input the op amp s output will send high signal that s about 3 6 V If the potentiometer wiper s voltage is slightly below the 1 KQ voltage divider output the op amp s output will send a 0 V low signal v STOP If your CH2 probe s BNC end is still connected to the DAC Card s function generator output disconnect it and reconnect it to the PropScope s CH2 BNC input before continuing Build the circuit shown in Figure 9 3 and Figure 9 4 Supply Voltage Plus Headroom When the LM358 sends a high signal it s only 3 6 V instead of the Vdd 5 V applied to its Vcc power input Many op amp outputs require this type of headroom between their maximum output levels and their supply rails Op amps with rail to rail outputs are available but they are typically a little more expensive The added cost is not uusally too steep for projects and prototypes but for products with high sales volumes an extra 50 cents per product could add up very quickly The 220 Q resistor ensures that the DAC Card cannot be damaged if the CH2 probe s BNC end is inadvertently left connected to the function generator output Since no current flows into or out of CH2 it will not have any oth
33. 1 causes the binary number that describes the voltage measurement to store a 1 in its least significant bit If you see LSB in this book it means the rightmost digit in a binary number If AA you see VLsg it means an analog to digital converter voltage increment py Quantize and Quantization If you see the term quantize in A D converter documentation it means that an analog to digital converter quantifies its voltage measurements in terms of a number of Visg increments The A D converter quantizes voltage Quantization is the process of making a conversation from input voltage to a number of Visg increments You might also see the term quantization error which refers to the difference between the actual voltage and the measured quantized value You can use V sg to calculate an analog to digital converter s measurement in terms of volts Simply multiply the value the ADC reports by Visg For example if the ADC0831 reports 170 as it did in the Figure 5 5 timing diagram the voltage applied to the Vin terminal must be Vin adcVal x V sg 170x19 53125mV 3 3203125V 3 32V Chapter 5 Synchronous Serial Communication Page 157 You can also calculate what the ADC will report for a certain voltage measurement by dividing it by Visg For example if you want to know what the ADC0831 will report if 3 32 V is applied to its Vin terminal divide the LSB voltage increment into it Vin Viss 332V 19 531
34. 1 2 Test Equipment Examples ALLL Chapter 1 PropScope Introduction and Setup Page 11 PROPSCOPE MEASUREMENT TOOLS IN A NUTSHELL This section briefly explains each of the PropScope s measurement tools along with some of their most common uses The PropScope is equipped to perform the basic functions of all these pieces of test equipment Voltmeter Oscilloscope Function generator Logic analyzer Spectrum analyzer XY plotter Voltmeter The PropScope s voltmeter features are shown on the lower left and lower right of the Measure display in Figure 1 3 The lower left value can be used to measure DC voltage like across a battery s terminals or the regulated supply voltage for a microcontroller You will take a variety of DC voltage measurements starting in Chapter 2 DC Measurements Time Period High Peak between signal signal voltage N repetitions sie gt E gt ES Peak to Peak 7 sm signal voltage Frequency of signal Figure 1 3 repetitions PropScope Measure Display AC RMS voltage DC voltage or Average voltage Certain voltages that vary with time in a pattern that repeats periodically are called periodic signals The varying voltages in such signals average out to some value When the PropScope is measuring a periodic signal it displays this average in this same field If the voltage is DC that lower left field displays the DC measurement If it s a periodic Page 12 Understanding
35. 2 cycles in the Oscilloscope screen v Divide the amount of time the oscilloscope should display by 10 to get the per division value for the Horizontal dial setting The actual signal period will be slightly longer than predicted because of the time it takes for the BASIC Stamp to process all the commands DO LOOP HIGH LOW PAUSE etc This will also make your measured frequency slightly lower than the one you calculated ACTIVITY 3 MULTIPLE HIGH LOW SIGNALS Many systems have microcontrollers that exchange information with integrated circuits and other microcontrollers using several I O lines The fact that the signals are 5 V when high and 0 V when low isn t in question but the timing of these high and low signals might be causing problems with the data exchange The tool for measuring high low signals on multiple lines is called a logic state analyzer which is abbreviated LSA and often referred to as just a logic analyzer Logic analyzers are especially useful for examining binary communication between devices This type of communication typically involves the exchange of binary values high low signals over multiple signal lines The upcoming chapters on synchronous and asynchronous serial communication will rely on the PropScope s logic analyzer features The signals in those chapters occur at electronic speeds which are much faster than you could observe with say an LED In this activity we ll use the logic analyzer
36. 30 C aa mm Normal Step Figure 6 8 shows samples of the binary patterns for the characters A through E which correspond to ASCII codes 65 through 69 This is a portion of the sequence of asynchronous serial bytes the PropScope should display while Printable ASCII Chart to 10 bs2 is running Page 184 Understanding Signals with the PropScope Figure 6 8 B 66 Byte Values 65 to 96 pe 3 aa asia fel These are the ASCII codes for the characters A through E transmitted at 9600 bps with 8N1 true signaling In the next activity you D 68 will examine these signals bit by bit to ro ZI ese ea determine the ASCII values Your Turn DEBUG vs SEROUT DEBUG is a special case of the SEROUT command It s SEROUT 16 84 arguments For example in Printable ASCII Character Chart to IO bs2 you can replace DEBUG char DEC3 char with SEROUT 16 84 char DEC3 char and the Debug Terminal will behave exactly the same v Try it ACTIVITY 3 A CLOSER LOOK AT A SERIAL BYTE In this activity you will program the BASIC Stamp to send the letter A ASCII 65 using 9600 bps 8N1 true asynchronous serial signaling and decode its value with the PropScope Chapter 6 Asynchronous Serial Communication Page 185 Letter A Test Code Letter A to P11 bs2 transmits the A character via I O pin P11 once every second and it also sends it to the Debug Terminal to verify that characters ar
37. 7 15 Wiring Diagram for Figure 7 14 Unplug the capacitor s positive This capacitor s negative terminal is lead to hear the signal on the the one that comes out of the canister piezospeaker closest to the stripe with the negative sign s Make sure to plug the Reconnect the lead to view the negative terminal in here signal with the PropScope Vdd Vin v X3 P15 Sh aa P14 m P13 P12 P11 P10 oo P9 P8 P7 S odd For BASIC Stamp HomeWork P3 mam Board use a wire in place of ooo the 220 Q resistor PO x2 Page 232 Understanding Signals with the PropScope Listen to the Notes First Two Notes bs2 plays the note D7 2489 Hz followed by F7 2960 Hz As mentioned earlier it uses the FREQOUT command to digitally synthesize sine waves for these notes The command FREQOUT 9 2000 2489 makes I O pin P9 synthesize a 2489 Hz sine wave for 2 seconds Then FREQOUT 9 2000 2960 synthesizes a 2960 Hz sine wave for 2 seconds Enter Two Notes bs2 into the BASIC Stamp Editor and run it Disconnect the 1 uF capacitor s positive lead from the circuit Listen carefully to the two individual notes Press and release the Reset button on your board a couple of times to re run the program SASS Two Notes bs2 Play D7 followed by F7 SSTAMP BS2 Target module BASIC Stamp 2 fSPBABLG 25 Language PBASIC 2 5 PAUSE 1000 Wait
38. Amplitude and Frequency Figure 7 16 shows the BASIC Stamp synthesized D7 note in the Oscilloscope view v v v SS Set the Oscilloscope dials to Horizontal 100 us div Vertical CH1 1 V div Vertical Coupling switches CH1 DC CH2 Off Trigger tab switches Mode Continuous Edge Rise Level Auto and Source CH1 Trigger Time control align with first time division line See in Figure 7 16 Optional Click hold and drag the CH1 ground line downward until it is just above the time division scale values Page 234 Understanding Signals with the PropScope Figure 7 16 FREQOUT 9 60000 2489 in Oscilloscope 8 PropScope 1 1 0 Fale File Edit View Plugins Tools Help Dsciloscope Logic Analyzer Analog DSD LSA Z e Trigger Time control DC_AC DAC Off Generate Amplitude TY Trigger 5 ee Ground line ate dge as Marya sere l f ende Conti z 35 ontinuous a gt E te Step Note that the sine wave in Figure 7 16 has a DC offset like the ones that we added to the PropScope DAC sine waves in Activity 2 You can use the Measure display to get an automated DC offset measurement This same measurement is also displayed in the Oscilloscope view s Measure tab Both are shown in Figure 7 17 v Click the Measure tab and check the CH1 Average voltage It should resemble the example in Figure
39. Channel 1 and now line up with 5 and 5 V on the CH1 voltage scale The red dotted lines near the bottom indicate the maximum input voltages for channel 2 and are still at 10 V v Adjust the Vertical scales for each channel and pay close attention to the maximum and minimum measurement limitations for each setting You may need to adjust each trace up down to see the dotted limit lines at certain settings Page 38 Understanding Signals with the PropScope If you try to measure a voltage that s outside the dotted line limits it won t hurt the PropScope hardware but you will get an incorrect voltage measurement The PropScope will also display a red M5388 warning which means that the measured voltage has been clipped down to the maximum or up to the minimum voltage because it was outside the max or min for the voltage scale setting That s your hint that you need to adjust the Vertical dial to get the correct measurement Let s intentionally clip a voltage measurement so that you can see what happens Y Restore the probes and oscilloscope settings as they were at the beginning of this activity with CH1 connected to Vdd CH2 connected to Vin and both the CH1 and CH2 Vertical dials set to 5 V v Verify that the CH1 trace indicates 5 V and the CH2 trace indicates your board s supply voltage v To cause the signal to clip change the CH2 Vertical scale dial to 2 V The voltage should incorrectly display as 5 V v Verify
40. Inverted Comparison Test Circuit The SEROUT command can be configured to send a true signal followed by an inverted signal one after the other on the same line However that introduces some oddities to the signal that make it difficult for a device to receive and decipher So for a comparison of true and inverted signals the BASIC Stamp will be programmed to send the signals on separate I O pins The PropScope will be used to probe each signal to display on its own channel Connect the probes to the I O socket through the 220 Q resistors shown in Figure 6 13 using Figure 6 14 as a guide True vs Inverted Comparison Test Code True Inverted Comparison bs2 sends the same A character with true signaling we ve been measuring with CH1 on I O pin P11 Then it sends the A character with inverted signaling on I O pin P10 and this will be measured with CH2 v Enter and run True Inverted Comparison bs2 True Inverted Comparison bs2 Transmit A on P11 with true signaling and then on P10 with inverted SSTAMP BS2 Target module BASIC Stamp 2 UES EBBAS TOR2 rS Language PBASIC 2 5 char VAR Word Will store ASCII codes PAUSE 1000 1 second delay before messages DO Main loop SEROUT 11 84 A SEROUT 10 16468 A DEBUG AY PAUSE 1000 Send 9600 bps 8N1 true byte 9600 bps 8N1 inverted byte A to Debug Terminal 1 second delay LOOP Repeat main loop Page 190 Understanding Signals with the PropSco
41. Pitch is usually described in terms of high or low For example a bass guitar tends to play lower pitched notes while a normal guitar plays higher pitched notes Chapter 7 Basic Sine Wave Measurements Page 213 Musical notes are sine waves at specific frequencies and you will experiment with them in the next activity This activity will use more arbitrary frequencies so instead of musical notes they will just be tones The PropScope s function generator will be configured to apply sine waves to a piezospeaker and its oscilloscope will be used to monitor them With this setup you ll be able to see the sine waves with the oscilloscope at the same time that you hear the result played by the speaker The function generator has settings that allow you to control a sine wave s amplitude and frequency So in this activity you will vary a sine wave s amplitude and view its height change in the oscilloscope as you hear the speaker s volume change You will also vary the frequency and view the sine wave s cycle width change in the oscilloscope as you hear the speaker tone s pitch change Audio Tones Parts List 1 Piezospeaker misc Jumper wires Audio Tones Circuit The PropScope s function generator feature can be used to generate sine waves with certain amplitudes and frequencies and those sine waves can be played by a speaker Figure 7 2 shows a schematic and Figure 7 3 shows an example wiring diagra
42. Setup ecceceeceeeeeeeeeeeeeneeeeeeeeeeseaeeseaeeseaeeseeeseeeseaees 18 Activity 2 Configure and Adjust PropScope Probes ccccssecceeseeeeeeseneeeeeseeeesseaeees 19 SUIMMIMANY sees TETTA A EAE A ade ad E N 24 Chapter 2 DC Measurements csseceeseeeeeeeeeseeeeeneeeeseaeseseeenseeeeeseeeseeneenseeeeeeees 25 About Supply and Other DC Voltages eeceeeceeeeeeeeneeeeeeeeeeeeeaeeseaeeseaeeeeaeeseaeeseaeeeeaeeeeaaes 25 Activity 1 Ground Testasin inia e iecdieeecee e ieies a a ECEE ei EE TEESE 27 Activity 2 Vdd and Vin DC Supply Voltages 0 0 0 ceccceeeceeeeeeeeeeeeeneeeeaeeseeeseaeeseaeeseeeeeaees 32 Activity 3 Oscilloscope Voltage Scale Adjustments cccsssccceeeseeeeesseeeessteeesseeeees 34 Activity 4 Digital to Analog DC Voltage eecceeeceeeeeeeeeeeneeeeneeeeneeseaeeseaeeseaeeseaeeseeeseaees 39 Activity 5 Voltage Dividers 20 2 eeeceeeeseeeeeenneeeeeeeeeeseaneeeeesaeeeeesaeeeeseaeeeeeenaeeeeneaeeeeseneees 49 Activity 6 Advanced Topic I O Pin Voltage Vs Current cccesceeeessteeeessteeeeseeeees 58 SUMMARY AAE EEEE cdeguseet ces dnecd eteeg esos lee A cevdes E E ET 66 Chapter 3 Human speed Measurements ccsseccsseceesseeesseeseseeeeeeseeeseeeseseenenseees 67 Human speed Vs Electronic Speed eecceeeceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeseaeeeaeeseaeeeeeeseaeessatens 67 Activity 1 A Potentiometer s Variable Voltage OUutput eeceeeee
43. Synthesizes Sine Waves This activity will use a PBASIC command called FREQouT to make the BASIC Stamp digitally synthesize various sine waves For example FREQOUT 9 60000 2500 uses I O pin P9 to transmit a signal that makes an RC DAC circuit synthesize a 2 5 kHz sine wave for 60 seconds Figure 7 13 shows a single cycle of that sine wave in the lower CH1 trace The upper CH2 trace is the binary signaling the BASIC Stamp transmits with I O pin P9 to make the RC DAC circuit s output voltage increase and decrease in the sine wave voltage pattern Figure 7 13 Varying PWM from I O Pin Converted to Sine Wave with DAC Circuit VO pin sends varying Oscilloscope duty cycle PWM signals DAC circuit output varies as a sine wave PropScope Ch2 PropScope CH1 P9 1 uF PropScope GND Chapter 4 Activity 2 introduced how the PwM command used duty cycle to set DC voltages The FREQOUT command varies the PwM duty cycle to create a sine wave Notice how the PwM signal spends larger portions of time high as the sine wave s voltage increases and more time low as the sine wave s voltage decreases The duty cycle varies like this 2500 times per second to shape the 2 5 kHz sine wave The process the BASIC Stamp uses to set the varying duty cycles is similar to the process it used to synthesize the heartbeat signal in Chapter 3 Activity 5 Instead of a list of values obtained from an electrocardiograph the FREQO
44. THEN remoteCode BIT6 I A Adjust remoteCode so that keypad keys correspond to the value 1 Le Seores remoteCode 1 0 IF remoteCode lt 10 THEN remoteCode IF remoteCode 10 THEN remoteCode RETURN SUMMARY This chapter introduced pulse width modulation PWM and used the PropScope to study PWM signals in several example applications The first application involved positive pulses sent to a servo s control input to set its output horn s position Servo control pulse durations can range from 0 5 ms through 2 5 ms which maps approximately to 0 through 180 servo horn positions Servos are designed to receive pulses at a rate of about 50 Hz but the frequency of the pulses does not have to be precise In contrast the positive pulse durations do have to be precise for good servo horn position control The PWM command for D A conversation uses a duty cycle modulated signal to set voltage across the capacitor in an RC circuit The key attribute of duty cycle modulation is a signal that stays high for a certain proportion of its cycle time Infrared object detection and TV remote control demonstrates how PWM can be used for communication An infrared detector converts brief periods of 40 kHz range infrared signals to brief low signals that contain binary values Chapter 5 Synchronous Serial Communication Page 149 Chapter 5 Synchronous Serial Communication SYNCHRONOUS SERIAL DEVICES Two or more devices can excha
45. Test Measurements The upper DAC trace in Figure 6 18 shows the PropScope DAC Card s function generator sending a 50 Hz square wave Since the function generator s output is connected to BASIC Stamp P10 I O pin for flow control the serial activity on the lower channel 1 trace stops during the square wave s high signals and resumes during low signals Move the Plot Area bar to the far left of the Plot Preview Set the Horizontal dial to 5 ms div and the Vertical dials to 2 V div v Set the Generator panel s Function switch to Square v Set the Generator panel s fields to Frequency 50 Hz Offset 2 25 V Amplitude 4 V then click the Generate button v Set the Vertical CH2 coupling switch to DAC When you set the CH2 coupling switch to DAC it uses the CH2 trace to display the function generator output vIn the Trigger tab set these switches Mode Continuous Edge Rise Level Normal and Source CH2 v Set the Trigger Time control so that the rising edge of the DAC output lines up with the second time division line v Set the Trigger Voltage control to about 2 5 V Make sure it s 2 5 V on the CH2 scale on the right side of the screen See notes in Figure 6 18 Check your PropScope settings and display against Figure 6 18 Chapter 6 Asynchronous Serial Communication Page 197 Figure 6 18 PropScope DAC Card Flow Control of Serial Byte Stream Oscilloscope Logic Analyzer Analog DSO Lsa
46. V is the initial or starting voltage and R and C are the values of the resistor and capacitor The value RC in v Ve is called the RC time constant and is expressed as the Greek letter tau t rhymes with saw but starting with a t So you may see the decay expressed as v Vie The value of t RxC is in units of seconds How did you get seconds out of resistance and capacitance ff 9 Recall that the ohm Q is the unit of resistance the R in RC time constant Also recall that e the farad F is the unit of capacitance C Well it turns out that F s Q If you want to w know why this is so keep studying physics and electronics it s fascinating stuff For now just remember that tT RxC is in units of seconds Another factoid to memorize is that the voltage decays to about 36 8 of its initial value in one Tt time constant and for a reminder just calculate e with your calculator Let s say that C 1 uF and R 1 KQ Then R x C 1 KQ x 1 uF which is 1 000 x 0 000001 0 001 If we assume the capacitor gets charged to 4 V before being allowed to decay through the resistor which would make V 4 V the equation would be t 0 001 v 4x e Page 270 Understanding Signals with the PropScope Figure 8 4 shows a graph of this equation At 1 ms the voltage has decayed to 4 x g 4 x e 4 x 36 8 1 47 V By the time the decay reaches the 5 ms mark it is close enough to its final voltage to
47. Vo This equation is called a transfer function Vo Gain x Vi Page 334 Understanding Signals with the PropScope Gain can also be calculated from the values of the feedback and input resistors For example a non inverting amplifier s gain is Gain aig Ri We already know because of how voltage dividers work that the non inverting amplifier s output will be twice its input if Rf and Ri are equal In other words we expect the amplifier circuit s gain to be 2 Let s try two 10 kQ resistors and calculate the gain Rf Gain 1 R 10kQ _ 10kQ 2 If the gain is 2 we can predict the output for a given input with the transfer function Vo GainxVi 2xVi This activity will start with Rf 10 kQ and Ri 10 kQ and also test with Rf 20 kQ and Ri 10 KQ v Repeat this calculations for Rf 20 KQ and Ri 10 KQ What will the gain be with this different resistor combination Keep in mind that these voltage equations only apply if the output is within the limits set by the op amp s Vcc and Vee power supply rails For the LM358 that s Vee lt Vo lt Vcc 1 4 V If Vo is outside that range it will simply stop at the limit imposed by the supply rail 4 The minimum gain for a non inverting amplifier is 1 So it cannot attenuate a signal only _ J amplify For a gain of 1 Rf has to be 0 Q which is a wire So a voltage follower is really a ww special case of non inverting amplifier
48. a PWM signal to generate an analog voltage as we ve been doing but if we want to use that voltage to do anything we re going to run into trouble The load placed onto the PWM output pin by whatever device we attach will drain the capacitor s charge so that we don t actually get the 1 95 volts or whatever voltage we were expecting to get from our DAC circuit The DAC circuit needs an op amp buffer before a microcontroller application can use the voltage to drive a load The op amp buffer circuit which is also called a voltage follower will be introduced in Chapter 9 Activity 2 In the meantime this activity examines what placing a resistor load across the RC circuit does without the op amp buffer The resistor takes the place of a device we might be trying to power using the output voltage of the DAC circuit Page 302 Understanding Signals with the PropScope Extra Parts for Load Test 1 Resistor 10 kQ brown black orange 1 Resistor 2 KQ red black red Load Test Circuit v STOP Disconnect the CH2 probe s BNC plug from the DAC Card and reconnect it to the PropScope s CH2 BNC jack before continuing here v Modify the circuit from the previous activity to add a resistor load by placing the 10 kQ resistor shown in Figure 8 30 PropScope Ch2 P14 1k PropScope CH1 10 kQ PropScope GND Figure 8 30 PWM DAC Test Circuit with 10 kQ Resistor Load Schematic top Wiring diagram bottom x3
49. an example of SHIFT C Figure 6 28 Inverted C at SIN Pin upper CH2 trace True C at P11 lower CH1 trace DC AC Off DC AC DAC Off BEY Square Generate Bs Frequency 10khz TY i custom OE otse 1 CH1 V Wait for Trigger Trigger gt Eo Cen ME A j au B mE 14 537 Continuous a qe Step O gt Page 210 Understanding Signals with the PropScope If your PC s voltage swings are more than 6 V there might not be enough room to comfortably display both signals Figure 6 29 shows how increasing the voltage per division settings makes more room for larger voltage swings v Try changing the vertical dials from 2 V division to 5 V division Figure 6 29 Increasing Voltage Scales Reduces Trace Heights Change Vertical dials to 5 Vidiv Square Generate Sine Frequency 10khz Sawtooth Amplitude 4 TY dosom Ot onse CH1 V Wait for Trigger Trigger Pica aes f D AEA at f Auta j ICE Continuous m Normal Step Before You Continue The activities in the next chapter are designed for 1x probes none of them utilize the 10x setting Set both probe X1 X10 switches back to X10 v Navigate back to the PropScope software s Manage Probes window and set both probes back to multipliers of 1 v Reattach the probe tip back to CH2 probe
50. and that s because it is almost linear The transistor is like a current valve W and the light level controls how much current it allows through which in turn controls the rate the capacitor discharges The light level is more or less constant during the measurement so the capacitor loses its charge at a linear rate which results in a linear voltage decay Automatic Lighting Condition Adjustments One important difference with the phototransistor is that it s a current conducting device that does not create a voltage divider So the capacitor will charge up to the about the same value regardless of the light level If you take the phototransistor out of the circuit you have an RC DAC circuit for setting voltages With the phototransistor in the circuit you can actually use the PwM command to charge up the capacitor to a certain level followed by the RCTIME command to measure the decay time This makes it possible for the program to adjust to lighting conditions by charging the capacitor to higher or lower voltages before the measuring the decay time For example Test Phototransistor Adjustment bs2 uses the PWM command to charge the capacitor up to about 3 34 V instead of 5 V before starting the RCTIME measurement The result will be a lower light measurement value because the voltage before the decay is lower yY Enter Test Phototransistor Adjustment bs2 into the BASIC Stamp Editor and Run it What s a Microcontroller Test
51. channel to give an at a glance indication of ground voltage the blue dashed line for channel 1 and the red dashed line for channel 2 The bold trace lines should move to new levels that indicate the voltages for each channel The solid blue channel 1 trace should align with the 5 V division line using the left hand CH1 vertical scale The solid red channel 2 trace should indicate the Vin voltage level using the right hand CH2 vertical scale The example in Figure 2 7 shows that Vin is little more than half way between the 5 and 10 V divisions so let s call it 8 V v Check where the voltage trace intersects with the CH1 voltage scale on the left Is it 5 V v Repeat for Vin and the CH2 voltage scale on the right It should be in the 6 V to 9 V range Measured 5 V Figure 2 7 Ground 0 V line DC Signals on the Oscilloscope Channel 2 10 with both Vertical scales set to 5 Vidiv CH1 connected to Vdd and CH2 connected to Vin Ground 0 V line Ss L5 The Oscilloscope view has a Measure tab that automates common signal measurements While these measurements are designed mostly to quantify voltages that vary with time the average voltage measurements circled in Figure 2 8 are essentially DC voltmeter measurements As you will see later the average voltage field can also give you information about DC components in periodic signals Page 34 Understanding Signals wi
52. circuit s output signal on CH1 should be almost the same amplitude as the input signal on the DAC CH2 In contrast if you make the DAC send a frequency that s ten times the cutoff frequency the RC circuit s output signal on CH1 should be much lower in amplitude v Try setting the Generate panel s Frequency field to 159 Hz and compare the RC circuit s output amplitude on CH1 to the DAC CH2 signal amplitude Adjust the oscilloscope display as needed v Repeat for 15 9 kHz the signal s amplitude should be much lower attenuated You can increase the cutoff frequency by decreasing the value of RC If you do this the filter will not reduce the amplitude until the input frequency is higher For example decreasing the resistor by a factor of 10 increases cutoff frequency by a factor of 10 So the value of the 10 kQ resistor is changed to 1 kQ in these cutoff frequency calculations o 1 2aRC fc 1 2x 3 1416 x 1 000 x 0 00000001 z 15 915 Hz Page 320 Understanding Signals with the PropScope v Replace the 10 KQ resistor in Figure 8 38 and Figure 8 39 with a 1 KQ resistor and repeat the calculations and tests in this activity for the higher cutoff frequency You could also reduce the capacitor s value for the same effect except that the Understanding Signals kit does not contain a 0 001 uF 1 nF capacitor You could however leave the resistor alone and swap out the 0 01 uF capacitor for a 0 1 yF capacitor for a cu
53. components starting with a sine wave at the square wave s frequency called the fundamental The next sine wave is smaller amplitude and at three times the fundamental Its called the third harmonic The next higher frequency sine wave is called the fifth harmonic and not surprisingly it is five times the square wave s frequency and has even smaller amplitude This pattern continues for every odd multiple of the square wave s frequency Page 252 Understanding Signals with the PropScope Your Turn Harmonics in a Sawtooth Wave It takes a different set of sine waves to construct a sawtooth wave v Change the Generator panel s Function switch to Sawtooth v What sine wave component frequencies are present in a sawtooth wave that are not present in a square wave ACTIVITY 6 COMPARE TWO SINE WAVES Circuits like filters and amplifiers that process sine waves can be analyzed by comparing a sine wave that enters the circuit s input against the one the circuit transmits at its output The two sine wave attributes that tend to change at the circuit s output are amplitude and phase Amplifiers might create a larger amplitude sine wave and filters might make the sine wave a little or a lot smaller depending on the frequency of the sine wave and certain properties of the filter Filters also tend to introduce a delay in the output signal There s no change in frequency but the output sine wave s points all occur slightly lat
54. consider completely discharged At 1 ms 1 47 Vis 36 8 of 4 V Figure 8 4 2 ahaa oe Eee SS See ee ae eee v At5ms 27mV RC Voltage Decay Graph T 1 I I 34NX E re ate alm pal eae eee l I I I l l I l I bin ae for RxC 0 001 2 3 4 5 Time ms l l i l 0 i 1 ACTIVITY 2 RC GROWTH AND DECAY MEASUREMENTS In this activity you will build an RC circuit and use a square wave from the PropScope s function generator to alternately charge and discharge the RC circuit s capacitor To get good view of the RC decay curves as the capacitor s voltage increases and decreases you will use the RC time constant from the previous activity to calculate an optimal square wave frequency and the oscilloscope s time division settings You will also take measurements to verify the previous activity s RC time constant calculations RC Time Constant Test Circuit Parts 1 Resistor 1 kQ brown black red 1 Capacitor 1 pF misc Jumper wires RC Time Constant Test Circuit Figure 8 5 shows a schematic of the RC decay test circuit and Figure 8 6 shows an example wiring diagram v If your red marked probe is not already connected to the DAC Card s function generator BNC connector do that now see Figure 2 16 page 46 for help Connect the DAC probe to the circuit input shown in Figure 8 5 and Figure 8 6 Connect the blue marked CH1 probe to the RC circuit s output Chapter 8 RC C
55. control up to 2 35 V The sine wave should reappear displayed at the correct level Y Before continuing set the Trigger tab s Level setting back to Auto Offset and Amplitude Tests Up to this point your PropScope is displaying a 3 Vpp sine wave with a 2 35 V offset The sine wave extends to 3 85 V peaks and 0 85 V valleys Your signal is currently in the larger of two function generator voltage ranges 0 to 4 7 V and the waveform s DC offset is currently 2 35 V which is in the middle of that range So you could increase Page 224 Understanding Signals with the PropScope the Generator panel s Amplitude setting all the way to 4 7 Vpp This is a larger amplitude than any of the tests in the 1 5 to 1 5 V range where the maximum amplitude was 3 Vpp v Try setting the Generator panel s Amplitude to 4 7 Vpp v Compare that to Amplitude 3 Vpp Can you hear the volume difference Can you see the difference in the Oscilloscope screen as well With 4 7 Vpp of amplitude there is no room to experiment with DC offset adjustments With 3 Vpp of amplitude and 2 35 Vpc of offset there is some room to experiment but not much 3 Vpp of amplitude makes it possible to adjust the DC offset 0 85 V up or down without exceeding the function generator s 0 to 4 8 V limits By changing the Amplitude to 1 Vpp you ll have more room to adjust the offset In fact 1 Vpp can fit into either the 1 5 to 1 5 V or 0 to 4 8 V ranges So you ll
56. current when a voltage is applied to it Therefore a no load test would be measuring a voltage without any circuits connected that would draw current First let s test an I O pin s high signal voltage with no load applied We ll use I O pin P14 In the previous activity this I O pin had a circuit attached to it that allowed it to use binary signals to control an analog voltage output In this activity we are looking at the voltages of the raw binary high low signals the I O pin transmits No Load Parts misc Jumper wires No Load Circuit Figure 2 28 shows a no load circuit for testing the high signal voltage transmitted by BASIC Stamp via I O pin P14 v Build the test circuit in Figure 2 28 Chapter 2 DC Measurements Page 59 Vdd Vin Vss x3 psy GOoo oooo me P14 CO PropScope CH1 P14 f B l Ji P13 i PropScope GND P12 i l l l i i 5 LO am Oooo oog Vss P9 ooo000 Oo Figure 2 28 P8 o0000 oo B7 00000 oo No Load Test o0000 oo eat Ee Hooo HAR Circuit P4 ooo ooo P3 ooo ooo P2 ooo o000 P1 ooo oooo PO ooo oooo x 000 0000 No Load Test Code High P14 bs2 High P14 bs2 is a test program uses I O pin P14 to transmit a high signal After the HIGH command STOP prevents the BASIC Stamp from automatically going into low power mode after it runs out of commands Enter
57. divide by 10 for Horizontal dial setting in units with a result of 4 ms div The closest value is 5 ms div Figure 4 27 SONY IR Message Initial View PropScope 2 0 1 JA x File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA DC_AC DAC Off Square Generate P 7 Oston Qa ora Time ms Measure Trigger Mode of Continuous O Step Chapter 4 Pulse Width Modulation Page 141 IMPORTANT The timing diagram also showed that the Start pulse begins with a negative edge so it will be important to set the Trigger tab s Edge switch to Fall There are many negative falling edges in the signal but this will increase the likelihood that the first negative edge triggers the display like it did in Figure 4 27 Also the Trigger tab s Level switch should be set to Normal instead of Auto Normal means you will manually adjust the trigger voltage level Auto triggering uses the average voltage of the signal in the Oscilloscope screen but there may be long periods of time between TV remote massages where the signal will stay at 5 V So the average voltage will be 5 V as will the automatic trigger level As the IR detector sends a series of negative pulses to the BASIC Stamp I O pin there will be lots of 0 V low signals So it would be better to manually set the trigger voltage
58. division setting with the Horizontal dial set to 1 ms div This is a good time setting for measuring low pulse times The Vertical time cursors in the figure are measuring a binary 1 pulse v v Adjust the Horizontal dial to 1 ms div Press the 3 button a few times until the Oscilloscope view resembles Figure 4 30 Use the Vertical time cursors to measure the Start 0 and 1 pulse durations for your remote How do they compare to your BASIC Stamp measurements Page 144 Understanding Signals with the PropScope Figure 4 30 Cursor Measurement of a Binary 1 Pulse PropScope 2 0 1 lolx File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Oscilloscope ZOH Jeo DC AC Oft DC_AC DAC Off Generate Seeon Pero i Ca Custom Edit ofset o With the 1 ms div Horizontal setting only half the pulses are visible in Figure 4 30 Figure 4 31 shows an example of the rest of the plot viewed by sliding the plot area bar to the right v Slide the Plot Area bar to the far right of the Plot Preview for a closer inspection of the second half of the IR remote s message Chapter 4 Pulse Width Modulation Page 145 Figure 4 31 Shift Oscilloscope screen right to See the Rest of the Message E PropScope 2 0 1 File Edit view Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Slide the
59. edges are also called positive and negative edges If the Trigger Time control is adjusted so that the second falling edge is not on the Oscilloscope screen the Measure tab will not update the period and frequency information for the signal This can also happen if you reduce the time divisions Horizontal dial too far v Count the number of falling edges visible for in the channel 1 trace There should be 2 v Slowly adjust the Trigger Time control to the right until the Measure tab s Channel 1 period and frequency measurements disappear v Count the number of consecutive falling edges visible for that signal in the Oscilloscope screen v Repeat for channel 2 v When you are done readjust the Trigger Time control so that it makes the vertical trigger crosshair line up with the second time division line Your Turn Increase the Frequency Again Setting the Horizontal dial improperly is a really easy mistake to make and it can lead to incorrect or confusing measurements So it s a good idea to practice the steps in this activity v Save another copy of High Low 100 ms Cycles bs2 y Repeat the process of increasing the frequency again this time by reducing the PAUSE commands to PAUSE 5 v Predict the signal period based on a signal that s low for 5 ms and high for 5 ms before it repeats Chapter 3 Human speed Measurements Page 85 Multiply your predicted signal period by 2 because we want to start by displaying about
60. for the PWM command s Duty argument Modify Test 1 Channel Dac bs2 accordingly and load the modified program into the BASIC Stamp v Check the CH1 Average voltage in the Measure display y Measure and calculate the duty cycle multiply it by 5 V and compare to the CH1 DAC output voltage Chapter 4 Pulse Width Modulation Page 125 ACTIVITY 3 INFRARED OBJECT DETECTION The Parallax Boe Bot Robot in Figure 4 17 uses infrared light emitting diodes IR LEDs as small flashlights and infrared detectors as eyes to check for objects in its path This detection scheme involves just a few inexpensive electronic parts found in common appliances Figure 4 17 Boe Bot Robot The IR LED in the Understanding Signals kit is the kind you might find on the end of a TV remote that you point at the TV to change the channel adjust the volume etc The light it emits is not in the visible spectrum but it s the light that sends signals to the TV Likewise the IR detector is one you might find in a TV that receives and demodulates the remote s infrared messages for the microcontroller in the TV The IR detector is designed to send a low signal if it detects infrared flashing on off at 38 5 kHz Otherwise it sends a high signal In this activity you will program the BASIC Stamp to send a brief 38 5 kHz signal through an IR LED and observe the resulting low pulse at the IR detector s output Page 126 Understanding Signals with the Prop
61. from certain prototyping mistakes The right side of Figure 2 33 shows the LED circuit on the BASIC Stamp HomeWork Board Starting inside the Interpreter chip the LED circuit loads the I O pin driver so it only outputs about 4 6 V instead of a full 5 V The reason the voltage drops to about 3 35 V at the T O pin socket is because the 220 Q resistor built into the HomeWork Board is in series with the 220 resistor on the breadboard The two resistors form a voltage divider and the output of that voltage divider is right at the I O pin socket Recall that the voltage divider output for two equal resistors is 1 2 the voltage applied to both ends of the circuit Half the voltage between 4 6 V at the I O pin driver s output and 2 1 V at the LED s anode is about 3 35 V Chapter 2 DC Measurements Page 63 Figure 2 33 I O Pin Driver and Voltage Divider Responses to Current Load BASIC Stamp HomeWork Board z 2200 Vdd 5V 46V CH1 3 35 V Resistors i VO Pin 0 Pin Socket Driver Circuit Pin 21V a interpreter Chip Resistor built into PIC16 BASIC Stamp Microcontroller HomeWork Baord Interpreter 1O Pin Chip Sockets Your Turn How Much Current Does a Single LED Draw In the BASIC Stamp Manual the BASIC Stamp Model Comparison table states that the BASIC Stamp 2 can source up to 40 mA per 8 I O pin bank or sink up to 50 mA This current could all be supplied by a single I O pin o
62. how two different potentiometer resistances result in two different decay times which the PBASIC RcTIME command would record as two different time measurements If the pot s knob has been adjusted to make the resistance larger the RC time constant will also be larger which means the capacitor will take longer to decay from its starting voltage to 1 4 V If the pot s knob has been adjusted to make the resistance smaller the RC time constant is smaller and the voltage will take less time to decay OM prameni ia ay Pi patsata poseia perso asad E E ae A poe niy cr a h aa a oes ees Figure 8 13 I 1 H 3 t Lesstresistan e pesi SEER How Potentiometer Resistance Or tececced shorter decay time Lae e l Affects Decay Time E a a a a a Excerpt from What s a V E OER Sees Microcontroller Chapter 5 100 ms Opus 100us 200us 300us 400 ps The voltage the capacitor charges to also changes slightly in Figure 8 13 The 220 Q resistor in Figure 8 12 protects the I O pin from current surges as the capacitor starts charging and it also protects the I O pin if the potentiometer s knob is turned to the limit of its range of motion that gives it 0 of resistance Since the BASIC Stamp sends a high signal to the circuit to charge the capacitor that high signal would be shorted to ground if the potentiometer is set to 0 Q So the 220 Q resistor protects the I O pin from this condition However there is a price for the resist
63. in the variable and 2 1 The value stored by Bit 1 determines the number of 2s in the variable and 2 2 The value in Bit 3 determines the number of 4s in the variable and 2 4 More generally Each bit determines whether a binary number has 1 or 0 x 2 Posion Your Turn Pick a Byte Value v Repeat the measurements in this activity with a character or byte value of your choosing ACTIVITY 4 TRUE VS INVERTED When the DEBUG command sends a message to the PC the true signal is inverted by a circuit so that every high portion of the signal becomes low and every low portion becomes high You will take some measurements of the inverted signals going to and coming from the PC in Activity 6 Figure 6 12 shows an example of the same 65 value in an inverted signal In this activity you will program the BASIC Stamp to send the letter A with both true and inverted asynchronous serial signaling and compare the results with the PropScope v Compare the signaling in Figure 6 12 against Figure 6 4 on page 179 Figure 6 12 Timing Diagram of 65 Transmitted with Inverted Signaling 1 0 0 0 0 0 1 a a I l l l l l l l l l I l I I 4 l l I I I I I l l Resting Start Bit BitO Bit 4 Bit5 Bit6 Bit7 Stop Bit Resting State State Chapter 6 Asynchronous Serial Communication Page 189 True vs Inverted Comparison Test Parts 2 Resistors 220 Q red red brown misc Jumper wires True vs
64. in the Projects at the end of the chapter One stop bit means that that the transmitter has to wait at least one bit period tpi before sending another message With 1 start bit 8 data bits and 1 stop bit the total amount of time it takes to send receive a single byte in this format is 10 bit periods Examining Figure 6 4 from left to right the resting state of the signal is high That signal could stay high for an indefinite amount of time if the device transmitting messages doesn t have anything to send When it does have something to send it sends a low Start Bit signal for one bit period Again both transmitter and receiver use the negative edge of this signal for timing The transmitter has to update its output between every bit period and the receiver has to check for a value in the middle of each bit period After the start bit the transmitter sends the least significant bit Bit 0 or LSB followed by Bit 1 during the next bit period Bit 2 in the bit period after that and so on up through Bit Page 180 Understanding Signals with the PropScope 7 during the 8 bit period after the start bit The receiver knows to treat Bit 0 as the number of 1s in the value Bit 1 as the number of 2s Bit 2 as the number of 4s and so on up through Bit 7 which is the number of 128s in the value In Figure 6 4 Bit 0 which is the number of 1s is high and so is Bit 6 which is the number of 64s All the rest of the bits are low so the value this
65. it is about 1 25 V You can either click the CH1 trace or click the CH1 CH2 label in the Measure display s lower right corner to toggle between displaying CH2 and CH1 values Chapter 8 RC Circuit Measurements Page 297 Figure 8 26 RC Circuit Converts Signal High 1 4 of the time to 1 25 V 4 of 5 V E PropScope v1 1 1 JAI Es File Edit View Plugins Tools Help DC_AC DAC Off Square Generate Sine Frequency 40kHz Sawtooth arme Cem Qe ee CHD DC voltage Trigger i i a i 1 25V f Mode Edge Continuous Step PWM Pin Duty Duration of a cycle the signal is high and Duration is the time the BASIC Stamp transmits the PWM Pin is the I O pin the BASIC Stamp sends the PWM signal to Duty is the number of 256 signal Example PWM 14 64 1 sends a PWM signal that s high 64 256 of the time for 1 ms 64 256 is 1 4 so that s why the signal is high 1 4 of the time For now all we want to do is be sure that there really is a relationship between the ratio of high time to cycle time thign teycle that controls the voltage across the capacitor You can do this by varying the PWM command s Duty argument in Test 1 Channel Dac bs2 and checking the duty cycle and CH1 voltage between each adjustment For example Figure Page 298 Understanding Signals with the PropScope 8 27 shows the binary signal for PWM 14 1
66. level to 2 5 V instead of letting it hover around 5 V and hoping it catches the signal transitions that we want to trigger on v Configure your PropScope s Horizontal dial Vertical dials and Coupling switches and Trigger tab settings as shown in Figure 4 27 v Make sure to set the Trigger Edge switch to Fall v Also make sure to set the Trigger Level switch to Normal v Then set the Trigger Voltage control along the left side of the Oscilloscope screen to about 2 5 V v Make sure the Trigger Time control is set half way between the Oscilloscope screen s left margin and the first time division line Careful here in previous activities we always used the second time division line v Press release a number button on your remote while pointing it at the IR detector v Verify that a signal appears that is similar to the one in the Figure 4 27 v Verify that other number buttons result in similar signals Figure 4 28 shows a closer view of the timing with the remote s 1 number button pressed released You may have to press release the button a couple of times to get a display that includes the wider start pulse at the far left v Adjust your PropScope s Horizontal dial to 2 ms div and press the 1 button a few times until you get a display similar to Figure 4 28 Page 142 Understanding Signals with the PropScope Figure 4 28 IR Message 1 button with Decreased Horizontal Scale PropScope 2 0 1 fol x File Edit Vie
67. lt 150 02030 1 20 KQ 1 4 W 5 resistor red black orange Re e 150 01020 2 1KO 1 4 W 5 resistors brown black red aaa aaa ao 150 01030 2 10 KO 1 4 W 5 resistors brown black orange 150 02020 1 2KO 1 4 W 5 resistor red black red SS e i a s 150 02210 4 220 1 4 W 5 resistors red red brown a 150 04710 1 470 Q 1 4 W 5 resistors yellow violet brown P 150 01011 1 100 Q 1 4 W 5 resistors brown black brown 451 00303 1 3 pin single row header 602 0005 1 LM358 DIP op amp ADC0831 1 8 bit A D converter 152 01031 1 10 kQ potentiometer 900 00001 1 Piezo speaker 350 00014 1 Infrared receiver 400 00002 2 Pushbutton normally open i 350 00029 1 Phototransistor 350 00001 f 1 PropScope USB with probes DAC card and USB cable DE a A 350 00003 1 LED Infrared 350 90000 1 LED Standoff 350 90001 1 LED shield for 3560 90000 201 01050 2 1 pF electrolytic capacitors 4 201 01062 1 10 pF electrolytic capacitor 1 Parallax Standard Servo 200 01031 1 0 01 pF poly capacitor 200 01040 2 0 1 uF ceramic capacitor 800 00016 2 3 jumper wires bag of 10
68. musical rhythm Morse code and pulse rate These signals can be quantified either intuitively with some training or in the case of pulse rate with little more than a clock that displays seconds Some signals seem to fall in both categories audio tones for example Different tones played by an audio speaker sound like they have different pitches So using just our ears we can detect fairly subtle variations in the rate at which the speaker vibrates On the other hand it would be difficult to actually count the number of speaker vibrations per second to determine the exact frequency of the tone That would require some specialized equipment You may have already programmed the BASIC Stamp microcontroller to send and measure signals at electronic speeds Examples from What s a Microcontroller and Robotics with the Boe Bot include controlling servo motors measuring light or a dial s position and communicating with a digital integrated circuit The signals in those activities were quantified in terms of 2 microsecond us increments Typical human reaction times might be in tenths or even hundredths of seconds but it takes a microcontroller or some other piece of specialized equipment to send or measure signals in terms of microseconds millionths of seconds If the electronic speed signals don t work as expected it can also be difficult to diagnose without the aid of a signal measuring device and that s where the PropScope proves
69. of Education Serial Rev C and newer USB all revisions The instructions for this board start right after this checklist o BASIC Stamp HomeWork Board Serial Rev C and newer USB all revisions starts on page 110 o All other boards go to www parallax com Go WAM Servo Circuit Connections to find servo circuit instructions for your board v When you are done with the servo circuit instructions for your board go to PWM Signals for Servo Control page 111 Board of Education Serial Rev C and newer USB all revisions There s a jumper that connects two of three pins together between the X4 and X5 servo ports In Figure 4 4 the jumper is shorting the upper two pins to set the servo supply to Vdd regulated 5 V We will use that jumper setting in this activity v Move your board s 3 position switch left to position 0 v Verify the jumper is set to Vdd It should cover the two pins closer to the Vdd label leaving the lowest of the three pins just above the Vin label exposed v Ifthe jumper is instead in the lower position and the Vdd pin is exposed lift the jumper upward to pull it off the pins Then place it as shown in Figure 4 4 15 14 Vdd 13 12 Figure 4 4 oy Power Jumper Baek Between Servo Headers X4 X5 Vin Servo port 14 in the X4 header connects P14 to the servo s white signal line So you can use the P14 socket next to the breadboard to probe the control signals v Plug the servo into servo port 14 as
70. of that signal on the upper blue CH1 trace Note that the sine waves are the same amplitude and phase This indicates that the op amp s output is following the DAC voltage applied to its non inverting input even with the LED current load v Adjust your Oscilloscope s Horizontal Vertical and Trigger settings as to match Figure 9 8 v Verify that the DAC s sine wave is identical to the buffer output s copy of it v Verify that the LED gets brighter and then dimmer at roughly once per second Figure 9 8 Buffer Output DAC Output Oscilloscope Logic Analyzer Analog DSO LSA Oscilloscope ss CHS 200K is a aaa Seen Tee RS Sa gms oE OS i DC_AC DAC Off ip Square Generate kaj Sine Frequency 10khz ie 04 CH1 V Triggered Trigger 5 Gas uen Mode Source g nE aa J Off I Ig Auto CH1 Gee GE Continuous CH2 z Normal Sep Q Page 332 Understanding Signals with the PropScope Your Turn Other RC DAC Waveforms amp Chapter 8 Activity 5 Comparison The LED circuit transmitting the sine wave is interesting because it demonstrates the BASIC Stamp module s ability to control brightness with the op amp buffered DAC circuit However the sine wave is just one example of many that you can create with the BASIC Stamp Programs that cause variations in the PWM command s Duty argument can be
71. of the next second sine wave peak v Check the measurements in the Cursor display by the Oscilloscope screen s lower right corner S N Page 236 Understanding Signals with the PropScope Figure 7 18 Cursor Measurements Align each of the vertical cursors with the centers of adjacent sine wave peaks it Align one of the horizontal cursors with the peaks of the sine wave lt and the other with the valleys CHI v Time ms l Triggered F Man gt Oe BY ABs 2884 lt V4 Fenous 177 V Measure Trigger verica Horizontal Float P Cursors Period gt Mus EEA D Amplitude z il Frequency gt Gas mm Zoom In Figure 7 17 the Measure tab and display reported amplitudes of 1 23 and 1 21 V Since the cursor measurement from Figure 7 18 is 1 19 V it verifies that these measurements are in the right ballpark Likewise with frequency measurements both figures report 2 5 kHz With the BASIC Stamp programmed to transmit 2489 Hz these measurements indicate that the BASIC Stamp module s program and circuit are all working as intended This is the type of intermediate testing step you might see in a design that has an audio tones subsystem The cursors can also provide enough information to verify the average voltage measurement the Measure tab and display reported For a sine wave the half way point between the sine wave s voltages at its peaks and valle
72. one voltage measurement is from one cycle of the signal and the next is from a later cycle the result is often a signal that looks very different from the actual signal being measured This is called aliasing and the PropScope displays a signal that s standing in as an alias for the actual signal The theoretical minimum sampling rate needed to reconstruct a signal is two samples per cycle and it s called the Nyquist rate In practice systems are usually designed to oversample meaning they take many times the Nyquist rate For example it takes 536 voltage samples to construct all the activity in a trace as it crosses the PropScope s Oscilloscope screen The Horizontal dial in Figure 8 26 is adjusted to 5 us division for a detailed view of the PWM signal s binary pulses Since the PWM signal is 5 V for of its cycle it sets a voltage across the capacitor that s 1 25 V which is 1 4 of the 5 V high pulses In review of Chapter 4 Activity 2 the duty cycle is the percent ratio of thigh to teycle The PWM signal in Figure 8 26 is high for 1 4 of its cycle so the duty cycle is 25 Applied to the RC circuit it establishes a voltage that s 25 of the 5 V high signal assuming the low signal is at ground 0 V the other 75 of the time v v v Adjust the Horizontal dial to 5 ps div Check the CH2 signal to verify that it is high for 1 4 of the time Check the CH1 Average voltage in the Measure display and verify that
73. panel is the PropScope s function generator control and it will be used to generate a variety of signals The first one will be a simple DC test voltage Let s try a 3 5 V signal Figure 2 19 shows the settings for a 3 5 Vpc signal F Square Generate D LI Sine Frequency Figure 2 19 mee Ampitude g DC 3 5 V with the i eto Q Ea ofat Function Generator Frequency is set to 10 kHz by default which is fine here Set the wave type switch to Sine Set the Amplitude to 0 and press Enter After every adjustment to a Generator panel Frequency Amplitude or Offset value you have to press Enter Set the Offset to 3 5 Click the Generate button to start the digital to analog conversion RA 44 Page 48 Understanding Signals with the PropScope DC Voltage with the Function Generator A function generator is a device that makes a voltage vary over time according to certain mathematical functions When plotted on graph paper these functions look similar to the square sine sawtooth and other voltage variation patterns that you will see on the Oscilloscope screen when measuring a function generator s output We will experiment with this starting in the next chapter The function generators Amplitude sets the total amount of voltage fluctuation and the Offset sets the average voltage The Frequency sets the rate of voltage fluctuations So if the function generator transmits a 1 V amplitude square wave with a 2
74. plot area ee a right to view the second half of the TAH thout havingto the time division setting change Dc Ac off DC_AC DAC Off Square Generate sre ig Poora O Custom Q Edit Oftset O Page 146 Understanding Signals with the PropScope Your Turn IR Remote Buttons Program Figure 4 32 shows the Debug Terminal after the remote s 3 button was pressed with IrRemoteButtons bs2 running IrRemoteButtons bs2 is an excerpt from IR Remote for the Boe Bot iojxi a E eo M rm comi a0 None E Data Bits Flow Control x M DIRT ATS Figure 4 32 ae E o o ns Debug Terminal Remote Code Display with IrRemoteButtons bs2 running Macros Pause Clear fi Y I Echo Off Download the IR Remote Book Source Code zip from the IR Remote for the Boe Bot Kit and Text page at www parallax com Open IrRemoteButtons bs2 with the BASIC Stamp Editor and load it into the BASIC Stamp Study the codes for buttons like 0 through 9 Power VOL VOL CH CH etc IR Remote for the Boe Bot IrRemoteButtons bs2 Capture and store button codes sent by a universal remote configured to Y COMmEecol 2a SON WY SSTAMP BS2 TA SIDIEVNSIINE RS SONY IrDet SONY Enter ChUp ChDn I O Detiniciome s soseooo ooo SSS TV IR remote declaration input received from IR detector RIN 9 Constants No A E E E EE E TV IR remote c
75. point at which x 1 and at that point the voltage is about 63 2 of the way to its final value Viewed with an oscilloscope this point designates 1 time constant on the oscilloscope s time axis Time constants have many uses For example they can be used to determine resistance and capacitance values in the circuit They can also be used to calculate the amount of time it takes to get close enough to its final decay value for Chapter 8 RC Circuit Measurements Page 267 practical applications even though it never reaches that point mathematically Last but not least RC time constants are also used to predict how RC filters will reduce the amplitudes of sine waves at certain frequencies This activity introduces the exponential decay equation and shows how the values of R and C are used determine an RC circuit s time constant RC Decay Math and Graphing Exercise The equations in question are related to the natural logarithmic constant e The value of e is approximately 2 718 Variations on the exponential growth equation y e are best known for their use in modeling population growth Variations on the exponential decay equation y e also have many uses and one of them is to describe how voltage changes as a capacitor loses or gains charge through a resistor When applied to capacitor as it charges and or discharges through a resistor exponential decay is called RC decay The left side of Figure 8 1 shows a graph of y e Th
76. repetitions That again is because period is the reciprocal of frequency T 1 f Whenever f gets larger T gets smaller and vice versa The PropScope s Frequency field accepts frequencies from 1 Hz to over 1 MHz in increments of 1 10 Hz 1 If the sine wave gets too compressed or too stretched out to fit well in the Oscilloscope W screen just adjust the Horizontal dials time division setting Decrease it for higher frequencies to uncompress the waveform s display or increase it for lower frequencies to get a waveform to fit that would otherwise look stretched Your Turn Test the Piezospeaker s Frequency Response You may have noticed that the tone gets slightly louder as the frequency increases That s because even though amplitude controls volume certain speakers play certain frequencies louder than others All speakers have natural filtering properties that depend on their electromechanical design The woofer midrange and tweeter names for speakers indicate that they play particular frequencies louder and clearer than the others A woofer plays low frequencies and it would be difficult to hear high notes played through it A tweeter plays high frequencies making it difficult to hear the low notes The midrange excels with middle notes You can hear the low and high notes through a midrange speaker but they are quieter With all three speakers working together their signals add up to make a nice full sound Whe
77. resistance from 0 Q to 10 KQ On the left side of Figure 8 12 the microcontroller sets I O pin P7 high The resulting 5 V signal charges the capacitor through the 220 resistor After a brief pause at least 5xt to charge the capacitor the RCTIME command sets P7 to input and the circuit and voltage behave as shown on the right side of the figure As an input the I O pin P7 is invisible to the circuit and it s like the voltage source just disappeared So the capacitor starts losing its charge though the potentiometer As it loses its charge the capacitor s voltage decays So the PBASIC RcTIME command measures the time between when it changed its I O pin P7 to input and when the capacitor s voltage decays to P7 s 1 4 V logic threshold Chapter 8 RC Circuit Measurements Page 281 Figure 8 12 Voltage at P7 through HIGH PAUSE and RCTIME Commands P7 Excerpt from What s a L Microcontroller Vss Invisible to RC Circuit 0 1 uF Chapter 5 HIGH 7 PAUSE 100 RCTIME 7 1 time 100 ms Opus 100us 200us 300us 400 ps Different RC Time Constants for Charging and Discharging Unlike the function generator which applies a high signal to charge and a low signal to discharge the BASIC Stamp applies a high signal to charge the capacitor but then it makes itself invisible as it lets the capacitor discharge through the potentiometer Because of this the capacitor charges more quickly than it discharges The
78. right Debug Termini ox iojxj Com Port Baud Rate Parity Com Port Baud Rate Parity DM1 z g0 E None COM1 z fas00 nf None DataBits_ Flow Cortot Tx M DTR ATS paaBis fowConio rx P DIRT ATS b Af for A em eos R CTS B o I RX DSR CTS Macros Pause Clear Macros Pause i I Echo Off The trick to verifying the approximate threshold voltage is to adjust the pot until you find the point where only a slight adjustment results in a state change Turn it the slightest amount possible to get a transition from 0 to 1 in the Debug Terminal then check the Page 58 Understanding Signals with the PropScope voltage in the PropScope while the Debug Terminal displays State 1 Turn the pot slightly back to transition from State 1 to State 0 and measure the voltage in the PropScope again The approximate threshold voltage is the average of the two values v Try it ACTIVITY 6 ADVANCED TOPIC I O PIN VOLTAGE VS CURRENT A BASIC Stamp I O pin is designed to send a high voltage of 5 V or a low voltage of OV The I O pin can also supply small amounts of current to circuits like indicator lights In this activity you will examine the affect of the current a circuit draws on an T O pin s high signal voltage level You will also test voltages in the circuit and use them to determine the amount of current the I O pin supplies to the circuit No Load Test Recall that a load is a circuit that draws
79. right to 500 ms division 8 PropScope v2 0 1 File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA 100ps_200ps pu S00 ys ims Click the Run button to pause the display after filling the screen with varying voltage measurements DC_AC DAC Off don en Floating curso Plot of potenti f sauece Generate s i Frequency 10kHz we am voltages and ti knob is twisted back 5 6 and forth g CH1 V Time s SS Trigger Cursor Measure Off Continuous Normal Step Page 70 Understanding Signals with the PropScope When the Horizontal dial is set to 100 200 or 500 ms or 1 s div the PropScope displays in datalogging mode which scrolls measurements from right to left The most recent measurements appear on the right and all the older measurements shift to the left The further left on the plot you look the older the measurements This is similar to the way older polygraphs and seismographs draw plots except that they feed paper under a pen that the device moves according to the property it measures The most recent measurements are drawn by the pen and as you look further along the paper that passed underneath it you are looking at older and older measurements To view the most recent PropScope measurements in datalogging mode the second adjustment you ll have to make to get the display in Figure
80. row with the 220 Q resistor Chapter 2 DC Measurements Page 61 Figure 2 30 PropScope Probe Monitoring I O Pin Voltage with LED Circuit Load Vin PropScope CH1 oie jozan ply Sadon wo DP a EE minin oo pA GYooo oo P14 P11 ofiooo oo 0000 oo 220 Q o0000 joo N 00000 oo p7 0000 oo PropScope GND LED P6 000 oo P5 oo oo T o oo Vss oe o oo P2 Be P1 o 00 PO ou oo x OO oo Voltage Measurements The circuit load on the Board of Education reduced the P14 high signal to 4 34 V Figure 2 31 top The same circuit load on the HomeWork Board reduced the voltage to 3 32 V Figure 2 31 bottom Why Keep reading v Make a note of the high signal voltage measurement with load for your board Keep in mind that your measurements may be slightly different Notice that the same siti ne Ey breadboard circuit Channel 1 7 Figure 2 31 resulted in different M sav ati P14 High Signal load measurements M cov s Voltage between the Board of i Measurement Education top and ED ams i with LED Circuit HomeWork Board aD Bo Load bottom This is due Trigger Measure to the additional m Board of resistor that is z Education top surface mounted on gt z the HomeWork E HomeWork Board M iconv MR sav E jom Board bottom Page 62 Understan
81. scale x axis for both channel measurements Page 36 Understanding Signals with the PropScope With the settings from Activity 2 the oscilloscope repeatedly displays 500 us worth of voltage measurements Figure 2 9 shows some examples of the voltage measurements and the times they were taken The top left example is a point on the CH1 trace that s half way between the 0 and 10 V scale values so the voltage is 5 V and the point is above 100 ps on the time scale So the channel 1 voltage at 100 us is 5 V Later on at 350 ps the voltage is still 5 V Of course that s because the CH1 probe is connected to Vdd which is regulated 5 V So every point on the CH1 trace will line up with the 5 V and the result is a flat line In the next chapter the voltage measurements will increase and decrease resulting in traces that rise and fall as they plot the voltage fluctuations over time v Verify the two sample points on the CH2 trace Remember that the voltage scale for CH2 is on the right side of the Oscilloscope screen Also keep in mind that your supply voltage depends on your particular supply and should be in the 6 to 9 V range Adjust Vertical Scales If you change the CH1 Vertical scale dial from 5 V to 2 V each square height for CH1 on the Oscilloscope grid will represent 2 V If you make this change the blue values along the left side of the screen will also change so that they represent the smaller voltage increments The
82. signal transmits is 1 x 1 1 x 64 65 In this activity you will program the BASIC Stamp to use 9600 bps 8N1 true asynchronous serial signaling to transmit the values in the previous activity s ASCII chart using an I O pin A new character will be transmitted once every second and you will use the PropScope to monitor the sequence of ASCII values Asynchronous Serial Test Parts 1 Resistor 220 Q red red brown misc Jumper wires Asynchronous Serial Test Circuit Figure 6 5 shows the test circuit and Figure 6 6 shows a wiring diagram example v Build the circuit in Figure 6 5 using Figure 6 6 as a guide PropScope CH1 P11 o w l Figure 6 5 220 9 Test Circuit for Probing Asynchronous Serial Messages Transmitted PropScope GND by the BASIC Stamp I O pin P11 Chapter 6 Asynchronous Serial Communication Page 181 Vdd ie oo o000 Figure 6 6 Sid oo 0000 re te J SEn Wiring Diagram Example D u i ag pu ooo DOODO for Figure 6 5 5 00000 o PPA oooo0 ooooo P8 00000 00000 p7 00000 00000 3G 00000 00000 55 00000 00000 a 00000 00000 55 00000 00000 m 00000 00000 i 00000 00000 B 00000 00000 xo 00000 00000 Asynchronous Serial Test Code Printable ASCII Chart to IO bs2 sends a character from the ASCII chart to the Debug Terminal once every second At abou
83. sine wave results in zero on the bottom waveform The two values cancel each other out Another example two peaks in the component waveforms get added together to form the highest peak in the bottom waveform Again the BASIC Stamp adds 1 2 of the top waveform amplitude to 1 2 of the middle waveform s amplitude That s why the bottom waveform s peak is not twice as high v Carefully examine Figure 7 20 and make sure you can see how of each component sine wave is added together to make the resulting waveform that contains both musical notes Try opening your screen captures combining them together in a single document and lining them to repeat the comparisons in Figure 7 20 Chapter 7 Basic Sine Wave Measurements Page 243 Figure 7 20 Two Sine Waves Added Together A valley subtracts from a peak Peaks add together Valleys add together Tos 2 3 7 CHL Triggered Times ms CH TIE SOEN ee Sere eee OEE SEREEN DEEE PEN Gree PE EE i For two notes played together adjust the Trigger i Voltage control so that it s just below the top of the highest peak 1 2 ICHI v Triggered Time ms CH Page 244 Understanding Signals with the PropScope Your Turn 100 and 200 Hz Figure 7 21 shows an example of 100 and 200 Hz added together These tones will not be audible with the piezospeaker but you can still measure them with the PropS
84. test circuits and it also makes larger voltage measurements possible In contrast a probe set to X1 does not reduce the signal voltage and improves the resolution of measurements in the ranges we will study in this tutorial The PropScope software needs to know whether the probe is set to X1 or X10 since that setting would make it necessary to either multiply by 1 or 10 before reporting the measurement Since our probes are set to X1 the software has to be configured accordingly v In the PropScope software click Tools and select Manage Probes Set the probe gain to 1 for both probes Tools Help Manage Probes Configure External Trigger Ny Figure 1 10 Configure Probe Gains in Probe 1 Gain fi x PropScope Software Probe 2 Gain 1 x Cancel Page 22 Understanding Signals with the PropScope setting the probe tips and software settings to X10 and performing a one time calibration You will use with the probe s X10 setting in Chapter 6 Activity 6 This will involve with a small screwdriver look for one packaged with your probes Step 4 Connect probes to BNC ports blue to CH1 and red to CH2 By default the software color codes voltage measurements from CH1 as blue and from CH2 as red So the probes should be connected accordingly like in Figure 1 11 v Connect the probe with the blue marker bands to the PropScope s CH1 BNC connector and connect the probe with the red ba
85. that a red warning appears below the oscilloscope display Again remember that this is your warning that the measurement is incorrect because the voltage is outside the measurement set with the Vertical dials Nomenclature Voltage and Time Divisions Most graphs have grid lines for visually aligning a given point in the plot with its x and y axis values The Oscilloscope screen also has gridlines but in oscilloscope terminology they are called division lines The grid lines that run across the screen are called voltage division lines and the ones that run up down are called time division lines Figure 2 11 points out examples of both voltage and time division lines Voltage division lines go across the screen and separate it into ten vertical increments which are called voltage divisions The Vertical dials adjust the size of the voltage increment a voltage division represents For example in Figure 2 11 the CH1 Vertical dial is set to 2 V meaning that each division represents a 2 V increment for Channel 1 The CH2 Vertical dial is set to 5 V meaning that each division represents a 5 V increment for Channel 2 The Vertical dial settings are commonly referred to as voltage settings and are described in terms of volts per division So you could say The channel 1 Vertical dial is set to 2 volts per division Likewise the channel 2 dial is set to 5 volts per division This would commonly be abbreviated to CH1 2 V div and CH2 5
86. that they are not the same Page 166 Understanding Signals with the PropScope Figure 5 13 First Look at the Communication with Missing Clock Pulse PropScope 2 0 1 lolx Fie Edt View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSOLSA Voltage Triggered Logic State Analyzer applied to SS ee Vin is still 3 3V 4 6 Time ms Triggered A closer look at the Logic State Analyzer display in Figure 5 14 shows the problem Instead of 9 pulses there are only 8 The ADC0831 uses the first pulse for its own processing regardless of how many clock pulses it receives and the DO line sends a zero for this pulse which the figure calls a null bit Instead of not paying any attention to that first null bit your modified PBASIC program stores it in adeval bit 7 So a 0 gets stored in bit 7 of adcVal instead of a 1 Then the value that should have represented the number of 128s in bit 7 gets stored in bit 6 So now it represents the number of 64s instead Likewise the value that should have represented the number of 64s got stored in bit 6 so now it represents the number of 32s The end result All the binary digits got shifted to the right in the adeval variable In binary processing this is a shortcut used to divide a number by 2 So the result of 85 which is 1 2 of
87. the total voltage amplitude the Oscilloscope can display Along with the function generator settings Figure 7 24 also shows an example of our square wave measured with CH1 It displays almost five full cycles and fills 34 of the total 1 V amplitude that the Oscilloscope can display with the CH1 vertical dial set to 0 2 V div Remember these limits are indicated by the dotted lines which are visible near the top and bottom of the Oscilloscope screen in Figure 7 24 Page 250 Understanding Signals with the PropScope Set the dials to Horizontal 500 ps div Vertical CH1 0 2 V div Set the Vertical coupling switches to CH1 AC CH2 Off Drag the display up down to position the ground line in the middle of the oscilloscope display v Set the Trigger tab s switches to Mode Continuous Edge Rise Level Auto and Source CH1 SSS Figure 7 25 shows an example of how the Analog View should look when after you configure your Oscilloscope display and then click the Analog view tab The Spectrum Analyzer shows several of the sine wave components that make up the square wave These components are called harmonics When a square wave is transmitted from one circuit to another along a wire the wire can act like a small antenna and broadcasts the harmonics So the 1 kHz square wave might be generating small amounts of radio interference at the 1 kHz 3 kHz 5 kHz 7 kHz 9 kHz and on up the frequency spectrum at odd multiples of
88. to the piezospeaker The Understanding Signals Kit s piezospeaker is not the same as a normal audio speaker it can receive signals with DC offset From the audio standpoint there will be little or no difference in the sound but the signal will look different in the Oscilloscope screen WARNING Only use a piezospeaker here Do not try adding DC offset to audio speaker signals Audio speakers have wound wire coils built in These coils have very low wy resistance compared to piezospeakers DC voltage could result in excessive current demands on the PropScope and its USB port power supply The element in a piezoelectric speaker changes shape with applied voltage and when the voltage oscillates rapidly the piezo element s vibrations create the tones This process a takes only small amounts of current e l_ inan audio speaker an electromagnet acts on a magnet attached to a paper cone to make it vibrate The oscillating voltage applied across the electromagnet s coil results in oscillating current through the coil This oscillating current through the coil creates an oscillating magnetic field that acts on the magnet attached to the paper cone Auto Trigger Follows Average Voltage DC Offset Since the Trigger tab s Level switch is set to Auto the oscilloscope automatically adjusts the Trigger Voltage control to follow the waveform s average voltage Remember that DC offset and average voltage are one and the same
89. used to create other signals Back in Chapter 3 Activity 4 you used the PwM command and an RC DAC circuit to create triangle and sawtooth waves At that point we could only measure the varying voltages because without the buffer the RC DAC circuit could not drive an LED load Now we have a buffer so those programs can actually apply those voltage signals to the LED circuit at the op amp s output v Try Saw Tooth bs2 from Chapter 3 Activity 4 No circuit changes or oscilloscope setting changes are needed just run the program v Repeat the code modifications from that activity that make the sawtooth a triangle wave and examine that too ACTIVITY 3 NON INVERTING AMPLIFIER The previous activity mentioned a rule for op amp circuits with negative feedback that is very important Op Amp Negative Feedback Rule If an op amp s inverting input senses its output through a circuit the op amp adjusts its output to make the voltage at the inverting input match the voltage at the non inverting input The voltage follower circuit in the previous activity was the first example of this rule The op amp s output was connected to its inverting input which forced its output to always match the voltage applied to its non inverting input The non inverting amplifier is another application of the op amp negative feedback rule Take a look at the voltage divider at the op amp s output in Figure 9 9 It sends some fraction of the op amp s ou
90. vertical scales are independent so if you only change the Channel 1 Vertical scale the Channel 2 squares will still represent 5 V per square Let s try it Disconnect your PropScope s probes from Vdd and Vin and reconnect them to Vss like in Figure 2 3 on page 29 v Try adjusting your CH1 vertical scale dial to 2 V You may need to re adjust the positions of the traces if you want it to closely resemble Figure 2 10 vY Look carefully at Figure 2 10 The CH1 V scale is now in units of 2 V while the CH2 V scale is still in units of 5 V Chapter 2 DC Measurements Page 37 Figure 2 10 Channel 1 and 2 with Different Vertical Scales CEE ft Fie Edt View Plugins Tools Help 50 ps div Horizontal Oscilascope Logic Analyzer Analog DSO Scale Dial OS pe 100ps_200ys S00 ps Ams CH1 2V Channel 2 Vertical mum 10 V j Scale Dials CH2 5V Sawtooth i R Square Generate Sine Frequency 10kHz Minimum 10 V are we imum 1 t Efece t no 3 a Ea mene po 2 ETS ES bE iage Continuous Stp Your Turn Examine Measurement Limits and Clippin Another important detail about changing the voltage scale is that certain settings affect the maximum and minimum measurements the channel can display In Figure 2 10 the blue dotted line near the top of the display indicates the maximum and minimum input voltages for
91. 0000000000 oo000000000000000 Chapter 3 Human speed Measurements Page 73 Figure 3 4 PropScope Probes Connected to Two I O Pins Example Program Alternate High Low Signals bs2 The PBASIC program Alternate High Low Signals bs2 contains a loop that starts by sending a high signal to P14 and a low signal to P15 After a 500 ms pause it changes the P14 signal to low and the P15 signal to high After another 500 ms pause the program repeats the same signal sequence Since the HIGH Low and PAUSE commands are all in a DO LOOP the sequence repeats indefinitely y Enter and run Alternate High Low Signals bs2 Alternate High Low Signals bs2 Alternate the high low signals transmitted by P14 and P15 and repeat indefinitely SSTAMP BS2 CEBAS TCE MSI DEBUG Program Running DO HIGH 14 LOW 15 PAUSE 500 1 1 Signal transitions separated by 500 ms pauses Target module BASIC Stamp 2 Language PBASIC 2 5 Program running message Main loop P14 LED on PIS LED off Wait 0 5 seconds Page 74 Understanding Signals with the PropScope LOW 14 VPA EED 06E HIGH 45 Dats LED ON PAUSE 500 Wait 0 5 seconds LOOP Repeat main loop e For more information about this program work through Chapter 2 Activities 1 and 2 of wy What s a Microcontroller from the PDF in the BASIC Stamp Editor Help menu Oscilloscope Voltage Measurements Let s examine the signals th
92. 1 sec before lst message DEBUG 2489 Hz CR FREQOUT 9 2000 2489 DUBEIOKE WC Tela Cat PAUSE 500 DINEIUE UAC O iiza CIR FREQOUT 9 2000 2960 Play display D7 If 2S Fest Play display F7 DEBUG 0 Hz GR 1 2 s rest PAUSE 500 DEBUG Done CR Display done END Enter low power mode Play an Individual Note for Oscilloscope Viewing One Note at a Time bs2 makes the BASIC Stamp play the D note indefinitely You can instead play the F note by commenting FREQOUT 9 60000 2489 by placing an apostrophe to the left of it After that remove the apostrophe to the left of FREQOUT 9 60000 2960 and load the modified program into the BASIC Stamp v v v Chapter 7 Basic Sine Wave Measurements Page 233 Enter and run One Note at a Time bs2 as is After you are satisfied that it plays the note indefinitely plug the capacitor s positive terminal back in using Figure 7 15 as a guide The note should be much quieter maybe even barely audible but the sine wave will look much better on the Oscilloscope screen One Note at a Time bs2 Select whether to play D7 or F7 indefinitely STAMP BS2 Target module BASIC Stamp 2 SP BAS LG 24 3 Language PBASIC 2 5 DEBUG Program running Debug Terminal message DO Main Loop FREQOUT 9 60000 2489 I WPileny BAS BA score Al onune PRT OQ COCO ANG Commented does not play LOOP Repeat main loop w o delay Examine the DC Offset
93. 1000 1 second delay before messages DO Main loop SEROUD J 4 REP TAM 25a Ve Dale eeaterecimts inne Ss meal Ome how eo DEBUG 254 bytes sent CR Debug Terminal message LOOP Repeat main loop Flow Control Test Circuit To test flow control the DAC Card s function generator output needs to be connected to the P10 input Figure 6 16 shows the schematic which is almost identical to the one from the previous activity and Figure 6 17 shows a wiring diagram example The only difference is that the probe has to be disconnected from the PropScope s CH2 BNC connector and connected to DAC Card s function generator output BNC connector v Disconnect the CH2 probe from the PropScope s CH2 BNC connector and connect it to the DAC Card s function generator output For a refresher on which one is the function generator output see Figure 2 16 on page 46 Chapter 6 Asynchronous Serial Communication Page 195 PropScope CH1 P11 o wm 220 9 PropScope DAC Figure 6 16 P10 Pe Oe CH1 Probes P11 Serial Output DAC Output 220 Q Drives P10 Flow Control Input Line PropScope GND 7 Vss Vdd Vin ss x3 P15 P14 a Figure 6 17 P11 Wiring Diagram Example P10 b9 of Figure 6 16 P8 P7 P6 P5 P4 P3 P2 P1 PO X2 Page 196 Understanding Signals with the PropScope Flow Control
94. 170 also provides a clue that there weren t enough clock pulses Chapter 5 Synchronous Serial Communication Page 167 Without the null pulse the null bit value of zero gets stored in the adcVal 1 x64 0x32 1x 16 0x8 1x4 Ox2 1x 1 85 variable s binary digit that should have stored the number of 128s ACTIVITY 5 REFINE AND TEST THE CODE As mentioned earlier the code from ADC0831Test1 bs2 is not optimized Figure 5 15 shows two ways to improve the code The better version uses an index variable and FOR NEXT loop to iteratively load each bit from the ADC0831 into the adeval variable The best version uses a PBASIC command called SHIFTIN to complete the operation including a first null bit pulse in a single command Not only does this command take less code space it is also much faster Page 168 Understanding Signals with the PropScope Figure 5 15 Better and Best Approaches to ADC0831 Communication From ADC0831 Test 1 bs2 LSOUT CLK USE 0 LSOUT CLK LSOUT CLK LSOUT CLK LSOUT CLK LSOUT CLK LSOUT CLK LSOUT CLK Ino ai tae ote tis er nol aly Anal ety tye i tie oly lag Ingll nal a a PA Om Git One One Om Gs Onn Gin Orne mre LSOUT CLK adcVAl1 LOWBIT The syntax for the SHIFTIN command is cVal LOWBIT cVal LOWBIT cVal LOWBIT cVal LOWBIT cVal LOWBIT cVal LOWBIT cVal LOWBIT 200
95. 192 Understanding Signals with the PropScope Your Turn Trigger on CH2 Find the Missing CH1 Signal Let s say you want to take a closer look at the CH2 signal One approach would be to set the Trigger Source to CH2 and the Trigger Edge to Rise This will align the rising edge of the CH2 signal with the second time division but the CH1 signal will mostly if not entirely disappear So where did it go To answer this question you can scroll the Plot Area bar to the center of the Plot Preview and then move the Trigger Time control to adjust the signal positions If you drag it to the approximate center of the Plot Area bar the signals should start to resemble Figure 6 15 again You can also set the units per division to 104 us With adjustments to some combination of the Trigger Time control Plot Area bar Trigger Edge and Trigger Source you can bring either signal into a close up view to examine its bits Remember that with the inverted signal a low is a binary 1 and a high is a binary 0 v Set your display up so that it triggers off the CH2 trace s positive edge and use the Plot Area bar and Trigger Time control to adjust the horizontal positioning of the signals in the Oscilloscope screen v Optional Set the Horizontal timescale to 104 us div See if you can use the Plot Area bar and Trigger Time control to navigate between the CH1 and CH2 bites ACTIVITY 5 HARDWARE FLOW CONTROL Hardware flow control can be an exceedingly us
96. 2 17 Probe DAC Output with Channel 1 Figure 2 18 Wiring Diagram for Figure 2 17 Note that each probe tip is permanently connected to a ground clip Chapter 2 DC Measurements Page 47 Function generator Leads vs Oscilloscope Probes Oscilloscope input probes are not normally used as BNC to Mini Clip Function function generator test leads For best results get a Generator Test Leads set of BNC to alligator clip or BNC to Mini Clip function generator test leads If you have a variety of lengths to choose from get the shortest one available Even set to X1 the probes in your kit still have almost 100 of series resistance between the function generator output and the probe tip contact This is fine for transferring the measured signal to the oscilloscope inputs However if the function generator is driving a circuit that draws current this resistance can cause a 1 10 of a volt per milliamp difference between the function generator s output and the voltage at the probe tip Although it won t affect the measurements in this book it could affect other PropScope measurements X1 for the function generator probe The probe connected to the DAC Card s function generator output should always be set to X1 If you inadvertently set it to X10 it will divide down the voltage to 1 1 0 of what you would expect Set DC Signal with Function Generator Probe with Channel 1 The Oscilloscope view s Generator
97. 200 7 200 6 200 5 200 4 200 3 200 2 200 1 200 0 Dout Dout Dout Dout Dout Dout Dout Dout Best Better index VAR Nib PULSOUT CLE 200 PULSOUT CLK 1 FOR index 7 TO 0 PULSOUT CLK 100 adcVal LOWBIT index Dout NEXT SHIFTIN Dout CLK MSBPOST adcVal 9 SHIFTIN DataPin ClockPin Mode Variable bits Variable bits The DataPin and ClockPin are self explanatory The Mode argument can be one of four values MSBPRE MSBPOST LSBPRE Of LSBPOST significant bit MSB first and updates its DO data output after the clock pulse POST So the correct value to use as the SHIFTIN command s Mode argument is MSBPOST The 9 after adeval applies 9 pulses and shifts in 9 bits But since the adeval variable is a byte it only retains the lowest 8 bits and the null bit is lost which is fine because it didn t hold any meaningful information anyhow Enter and run ADC0831Test2 bs2 The ADC0831 transmits the most Chapter 5 Synchronous Serial Communication Page 169 ADCO831Test2 bs2 Code from the ADC0831 timing diagram SSTAMP BS2 Target module BASIC Stamp 2 L SPBASIG 25 54 Language PBASIC 2 5 ES PIN 0 P 20 gt We CS CLK PIN il PAPI Ss 7NBIC CLI Dout PIN 2 12 lt lt ADO DO adcVal VAR Byte ADC result variable index VAR Nib PAUSE 1000 Delay 1 s before 1st message DEBUG CLS Clear display iphtelst CS I SEAHEC TCS arkeo LO
98. 25mV 169 984 170 adcVal Let s verify the signaling by adjusting the potentiometer until the ADC0831 reports 170 With this value the PropScope should measure a voltage of about 3 3 V Enter and run ADC0831Test1 bs2 v Adjust the potentiometer until the Debug Terminal shows that the ADC0831 is reporting a value of 170 like Figure 5 6 ioii Com Port Baud Rate Parity COMI 9606 z None z Data Bits Flow Control ex 3 RX Figure 5 6 ADC0831 Output with Pot set to 3 3 V 170 Macros Pause Clear Close I Echo Off The PropScope DSO LSA view in Figure 5 7 is great for verifying the voltage measurement and the synchronous serial communication signaling because it shows both the Oscilloscope and Logic State Analyzer screens Remember that the potentiometer s wiper terminal output voltage is connected to the ADC0831 s Vin pin as well as to the PropScope s CH1 probe So we can use the Oscilloscope to verify the voltage the potentiometer applies to the ADC0831 s Vin pin Page 158 Understanding Signals with the PropScope DSO Digital Storage Oscilloscope 4 LSA Logic State Analyzer Mixed Signal Refers to a combination of analog and digital signals The DSO LSA view in Figure 5 7 is a mixed signal view First click the Oscilloscope view and set the Trigger tab s Mode switch to Off Click the DSO LSA view tab to see the Oscilloscope and Logic Sta
99. 28 1 Now the signal is high for half the time and the voltage across the capacitor is 2 5 V which is about half of 5 V In Test 1 Channel Dac bs2 change the PWM command to PWM 14 128 1 Load the modified program into the BASIC Stamp Check the CH2 signal to verify that it is high for about half the time Click the CH1 signal and check its Average voltage in the Measure display to verify that it is about 2 5 V AAAA Figure 8 27 RC Circuit Converts PWM Signal that s High 1 2 of the time to 2 5 V of 5 V 8 PropScope v1 1 1 fol x File Edit View Plugins Tools Help Oscilaseope Logic Analyzet Analog DSO LSA e 2v Click to change tab view DC_AC DAC Off ny Generate D Sine Frequency aaan aee D Tv i Custom Edit otso CH1 DC voltage 225V Measure Continuous Step Q Chapter 8 RC Circuit Measurements Page 299 Figure 8 28 shows the Oscilloscope display with the command PwM 14 192 1 Now the CH2 signal is high about 34 of the time and CH1 shows that the voltage across the capacitor is now about 3 75 V which is of 5 V In Test 1 Channel Dac bs2 change the PWM command to PWM 14 192 1 Load the modified program into the BASIC Stamp Check the CH2 signal to verify that it is high for about 34 of the time Check the Average voltage of the CH1 signal in the Measure display to verify that it is about 3 75 V AK
100. 3 2 is to move the Plot Area bar to the far right of the Plot Preview so that it matches Figure 3 3 The PropScope plots two Oscilloscope screen s worth of measurements and a preview of the entire plot is visible in the Plot Preview See the squiggly line passing through the Plot Preview That s the entire two Oscilloscope screens worth of plotted potentiometer voltages By positioning the Plot Area bar in the Plot Preview you choose the portion of the plot the Oscilloscope screen shows you When you slide the Plot Area bar to the far right you will see the rightmost portion of the two screens worth of plotted measurements At this position the variations in the plotted voltages will be visible at the right side of the Oscilloscope screen as soon as you make adjustments to the potentiometer Figure 3 3 Plot Preview and Plot Area Bar Plot Preview previews all voltage samples JSC mes Ope a SSE ABE E Plot Area bar selects a portion of the preview bar for Oscilloscope screen display v Make sure the CH1 coupling switch is positioned at DC v Turn channel 2 off by moving the CH2 coupling switch to Off The coupling switches are below the Vertical dials Chapter 3 Human speed Measurements Page 71 Set the CH1 Vertical dial to 1 V Set the Horizontal dial to 500 ms Click hold and drag the plot either up or down so that the dashed ground line and dotted maximum voltage line are positioned about as sh
101. 34 Understanding Signals with the PropScope Figure 4 25 SONY TV Remote Protocol Resting state Resting states between message between data pulses packets 20 30 ms 0 6 ms L ka j By f D f ne ni haal Bit 1 Bit 3 Bit 5 Bit 7 Bit 9 Bit 11 t Start pulse Binary 0 Binary 1 duration 2 4 ms data pulse data pulse durations 0 6 ms durations 1 2 ms Extra Parts Equipment and Setup You will use the IR detector and CH2 probe shown in Figure 4 19 and Figure 4 20 on pages 127 and 128 so there is no need to modify your circuit or probe connections The extra equipment you will need is a universal remote 1 Universal remote Parallax 020 00001 for example 1 Instruction sheet booklet for the universal remote Compatible batteries Although a universal TV remote is not included in the Understanding Signals kit most households have one that can be configured to control a SONY TV For those that don t inexpensive universal remotes can also be purchased from local department stores Check the package before you purchase a particular remote to make sure it can be configured to control a SONY TV If the packaging says something like compatible with most all major brands it should work with SONY TVs These remotes are usually packaged with either a piece of paper or a booklet that explains how to configure it to be a SONY TV remote The instructions typically involve e Looking up a number code for SONY TV in t
102. 6 Try 0 125 ms for a 1 kHz signal The correct answer is 45 Some circuits introduce delays between input and output signals For sine waves this delay can be expressed as a phase angle measurement For example all the points in the 1 kHz signal labeled v2 in Figure 7 27 occur 0 125 ms later than the corresponding points in the v1 signal Using phase angle math we can calculate that v2 lags behind v1 by 45 or that vl leads v2 by 45 In oscilloscope terminology the expressions v1 leads v2 and v2 lags v1 are common The angle is negative when measured from a reference sine wave to another that lags or positive when measured to another sine wave that leads So the from v1 to v2 is 45 and from v2 to v1 is 45 Page 256 Understanding Signals with the PropScope Figure 7 27 Identical Sine Waves with Different Phases Phase Shift p _ Degrees 0 45 90 180 270 360 For f 1 kHz 0 ms f 0 25 ms 0 5 MS 0 75 ms 1 0 ms 0 125 ms Amplitude and Phase Angle Test Parts List 1 Resistor 10 KQ brown black orange 1 Capacitor 0 01 uF labeled 103 misc Jumper wires Identifying Capacitors with Three Digit Labels While most larger electrolytic capacitors have their values clearly printed on their sides smaller capacitors such as ceramic capacitors usually have just a three digit code number representing their values Here is how to interpret those code numbers 1 Take the f
103. 7 17 v Repeat using the Measure display Chapter 7 Basic Sine Wave Measurements Page 235 Figure 7 17 Sine Wave DC Offset S measured as the signal s average voltage component DA LO AY AY Kast Trigger Cursor Measure Measure j Channel 1 x Eh 3 G27 e ED ED moge o ar dengem Average voltage is also in the Average voltage Sa Is DC Offset Measure display You can also use the PropScope software s horizontal and vertical cursors to measure amplitude and frequency Figure 7 18 shows an example The amplitude is the peak to peak voltage so place one horizontal cursor at the tops of the sine wave s peaks and the other at the bottoms of its valleys The average voltage is the half way point between the sine wave s peaks and valleys Frequency can be determined from period and the vertical cursors can be used to measure the amount of time it takes the signal to repeat itself One way to do that is to align the vertical cursors with the centers of the sine wave s peaks vIn the Cursor tab click the Vertical and Horizontal buttons to make the vertical and horizontal cursors appear Align the green horizontal cursor A with the tops of the sine wave s peaks Align the purple horizontal cursor B with the bottoms of the sine wave s valleys Align the green vertical cursor A with the center of the top of the sine wave s first peak v Align the purple vertical cursor B with the center
104. 9 against that voltage with a lower potentiometer resistance lt lt Chapter 8 RC Circuit Measurements Page 289 Figure 8 19 Verify the BASIC Stamp module s Decay to 1 4 V Measurement 5 xi 8 PropScope v1 1 1 File Edit View Plugins Tools Help Make a note of the Horizontal A cursor s voltage i DEEN s fi Horizontal B ple Horizontal B voltage cursor set e ae on o aceon _ cursor set to 1 4 V and verticat B time E t 1 4V Sawtooth wv t VERS Custom Q Eat Vertical Horizontal 3 a 7 i c Cursor oto um Measured decay time In Figure 8 19 the cursor A voltage measurement is close to 5 V 4 8 V which indicates that the potentiometer s resistance is large compared to the 220 Q resistor For example if you substitute 7000 Q into the voltage divider equation from Chapter 2 the result would be Vo 5 V x 7000 Q 7000 Q 220 Q 4 84 V Page 290 Understanding Signals with the PropScope Figure 8 20 shows an example the BASIC Stamp module s measurement in the Debug Terminal when the pot is turned to about 3 4 of the way clockwise in its range of motion The decay time is 170 x 2 us 340 us v Turn the potentiometer knob clockwise until the Debug Terminal reports a value in the neighborhood of 170 zimizi Com Port Baud Rate Parity com pa 9600 7 None 7 Data Bits Flow Control 1 I DTR I RTS 8 zj j
105. AC 0 01 uF PropScope GND Vss Vss Figure 8 39 Example Wiring Diagram for Figure 8 38 Calculate the Cutoff Frequency and Phase Shift Figure 8 38 Schematic for RC Low pass Filter Amplitude and Phase Angle Test Measurements The three values we need to know for verifying the filter s behavior are output amplitude frequency and phase shift in terms of time This activity started by mentioning that the output sine wave amplitude will be 0 707 x the input sine wave amplitude and that the phase delay will be 45 The cutoff frequency still needs to be calculated and then that has to be used to calculate a 45 phase delay time Chapter 8 RC Circuit Measurements Page 315 The equation for cutoff frequency is o 1 2aRC fc Substituting our R 10 KQ and C 0 01 uF values the cutoff frequency is 1 z z 1 591 5 Hz 2x 3 1416 x 10 000 x 0 00000001 fe Next we need to figure out what the phase shift time is for 45 at 1591 5 Hz To do this all we need to do is rearrange the terms in one of the two phase angle equations from Chapter 7 Activity 6 and solve for At Since we now know the frequency we can use the phase angle equation with the frequency term and save the 1 T calculation 0 Atxfx360 gt At i f x360 Next solve for At when 9 45 2 78 5 us A
106. AC current flows back and forth through the circuit driven by an AC voltage source that typically alternates between positive and negative voltages many times per second DC voltage is a fairly easy concept to grasp because it s the measurement for typical supplies like batteries and solar panels A common assumption about batteries is that they maintain a constant voltage In contrast to an AC power source like a wall outlet the voltage a battery supplies is constant it s a DC voltage because it does not oscillate back and forth However the DC voltage is not necessarily a fixed value it can vary For example if you measure the voltage across a battery with no current draw it will be close to its rated voltage like 9 Vpc volts DC for an alkaline battery like the one you would use with your BASIC Stamp board When a circuit that draws current is connected to the battery its voltage may drop a little or a lot depending on the electrical properties of the circuit and its current draw The voltage of the battery also decays slowly as it loses its charge A battery in continuous use might start at over 9 Vpc but later it will measure only 8 5 Vpc The voltage will continue to decline as it loses its charge At some point it can no longer power the device and we call it a dead battery Most digital circuits need a steady DC supply voltage to work properly So battery supplies get connected to circuit subsystems called voltage r
107. Auto Source CH2 v Trigger Time control adjust vertical crosshair to first time division line v v Page 304 Understanding Signals with the PropScope Figure 8 31 Voltage Across Capacitor Decays through 10 kQ Resistor between PWM Signals PropScope v1 1 1 jA x File Edit View Plugins Tools Help Oscilloscope kaon sats DI WOH jeug Boome TS DC_AC DAC Off Square Generate a Custom Edit Offset o T enges Auto Continuous Normal Step Q Your Turn Compare to Increased Load and No Load A 2 kQ resistor has less resistance so it conducts more current than a 10 KQ resistor As a result it drains the capacitor more quickly and can be termed a heavier current load on the capacitor With the resistor removed the capacitor should lose its charge very slowly The rate the capacitor loses its charge depends on the insulator that keeps the two metal plates that hold charge apart This insulator is called a dielectric and the small current that flows through the dielectric is called leakage current v Replace the 10 kQ resistor with a 2 KQ resistor v Check the voltage output results with the PropScope Chapter 8 RC Circuit Measurements Page 305 v Disconnect the load resistor the decay should be very small in comparison With a low leakage current capacitor it would be even smaller ACTIVITY 6 PHOTOTRANSIS
108. Build the circuit in Figure 7 14 and Figure 7 15 v The capacitor s negative lead is the one that s closer to the stripe with the minus signs on the capacitor s metal canister Make sure this lead is connected to Vss v Leave the 1 uF capacitor s positive lead disconnected for now CAUTION In some circuits connecting this type of capacitor incorrectly and then connecting power can cause it to rupture or even explode So always make sure to carefully connect its terminals exactly as shown in the circuit diagrams This capacitor has a positive and a negative terminal The negative terminal is the lead that comes out of the metal canister closest to the stripe with a negative sign s Do not apply more voltage to an electrolytic capacitor than it is rated to handle The voltage rating is printed on the side of the canister Safety goggles or safety glasses are recommended Chapter 7 Basic Sine Wave Measurements Page 231 Figure 7 14 BASIC Stamp Controlled Piezospeaker with PropScope Probe and Capacitor for Signal Monitoring For BASIC Stamp HomeWork Board use a wire in place of the 220 Q resistor PropScope CH1 P9 Disconnect this capacitor lead to hear the speaker Reconnect it to view the signal with the 1 uF PorpScope See wiring diagram PropScope GND Vss Figure
109. C0831 timing diagram SSTAMP BS2 Target module BASIC Stamp 2 Y SSP BASLC os 5 Language PBASIC 2 5 CS PIN 0 PO gt ADE CS CERK PIN 0 Pil SS ADC Clix Dout PIN 2 0 2 lt ADC IDO adcVal VAR Byte ADC result variable PAUSE 1000 Delay 1 s before 1st message DEBUG CLS Clear display HIGH CS w Greete CS amoni LOW CLK A Sieaewec CLE IOW NPUT Dout 0 See Doue HO yE Chapter 5 Synchronous Serial Communication Page 155 DO Main Loop LOW CS CS gt low start measurement POIGSOWW Clie ZO First pulse no data follows PAUSE 0 For display time btwn pulses PULSOUT CLK 200 Second pulse adcVal LOWBIT 7 Dout Pe ernie wy oma PULSOUT CLK 200 Third pulse adcVal LOWBIT 6 Dout Get bit 6 PULSOUT CLK 200 Ween eRe adcVal LOWBIT 5 Dout PULSOUT CLK 200 adcVal LOWBIT 4 Dout PULSOUT CLK 200 adcVal LOWBIT 3 Dout PULSOUT CLK 200 adcVal LOWBIT 2 Dout PULSOUT CLK 200 adcVal LOWBIT 1 Dout PULSOUT CLK 200 Ninth pulse adcVA1 LOWBIT 0 Dout Get bit 0 HIGH CS CS gt High disable ADC DEBUG HOME Display measurement Ubgabingeyy elclewerll I NS EveleWelll CIR 4 in binary Decimal adcVal DEC3 adcVal and decimal PAUSE 100 Screen update delay LOOP Repeat main loop ADC0831Testl bs2 might seem inefficient and complicated from the PBASIC programming standpoint especially since PBASIC has a pair of commands named SHIFTIN and SHI
110. CH1 the channel 1 voltage passes through the crosshairs as it transitions from low to high Point at the Trigger Time control to see the trigger crosshairs Click hold and slide left right to adjust the Trigger Time crosshair s position Trigger Voltage crosshair Time crosshair Time ms 160 Triggered Figure 3 10 Adjusting the Trigger Time The vertical and horizontal crosshairs that indicate the trigger time and voltage move when you adjust the Trigger Time and the Trigger Voltage controls Here we are only adjusting the Trigger Time control because the Trigger Level is set to Auto v Ifthe Trigger Time control is not already in the Plot Area bar click and hold the v v Trigger Time control and drag it into the Plot Area bar Point at the Trigger Time control with your mouse A pair of crosshairs should appear in the Oscilloscope screen These crosshairs should intersect at the location of the trigger event Click hold and drag the Trigger Time control left and right but keep it inside the Plot Area bar Page 82 Understanding Signals with the PropScope v As you move the Trigger Time control back and forth the vertical Trigger Time Crosshair should move with it The low to high transition in the channel 1 trace should also move with it Since typical oscilloscope measurements examine what the signal does after the trigger event it s usually
111. CO0831Test1 bs2 find the command u1eH cs that s near the end of the DO LOOP Not the one at the beginning of the program v Comment the HIGH CS that s near the end of the program s Do LooP by placing an apostrophe to its left like this HIGH Cs vV Load the modified program into the BASIC Stamp 2 The potentiometer is still adjusted to 3 32 V but Figure 5 10 shows that the change in the code caused the system to report all zeros instead of the correct values Chapter 5 Synchronous Serial Communication Page 163 2101 x Com Port Baud Rate Parity Data Bits Flow Control ex r Ao E EO Figure 5 10 RX o i Debug Terminal with Zero Measurements Binary adcVal 00000000 because CS was not Decimal adcVal 000 set high between measurements Macros Pause Clear Close I Echo Off If the Binary adcVa1 result in the Debug Terminal shows all ones instead of all zeros it may mean that the first measurement the ADC0831 successfully completed when the program started was an odd number like 169 or 171 instead of 170 So the first and only lan successful measurement left the ADC0831 s DO line high instead of low because odd 1_ numbers always have a 1 in the LSB and the LSB is the last digit the DO line transmits For example the odd decimal numbers 1 3 and 5 have the binary equivalents 001 011 and 101 The rightmost digits are all ones In contrast even decimal numbers like 2 4 and 6
112. DC_AC DAC Off Generate Sine Freeney __ Sarea Amplitude Tv Custom eat oftset 2 Trigger Channel 1 Eh ar 1 B 0 80 e e Ia guna nil o g02v t CH 3 it aea iv Beware of Automated Measurements If we rely on the Measure tab for this patient s heart rate it would be a frequency of 2 19 Hz That s 2 19 beats per second x 60 seconds minute 125 4 beats per minute That s a reasonable heart rate for exercise but if this patient is in a hospital bed it could indicate a problem Fortunately for our patient this measurement is not correct From the PropScope s standpoint it is an understandable measurement because the PropScope correctly calculated the average voltage of this signal to be 1 32 V and it is counting the number of times per second the voltage crosses this level However that s not the right measurement for a heart rate This signal needs to be measured manually Page 100 Understanding Signals with the PropScope Time Division and Vertical Cursor Measurement Examples If we instead measure the time between the highest points in the heart rate signal we can get the correct pulse rate Lets look at two different ways to take the manual measurements by time division and with floating cursor measurements Count Time Divisions The period of the pulse signal can be approximated by counting the number of 200 ms divisions between the signal peaks It looks li
113. FTOUT that automatically do most of this work for you in a single line of code It s still a useful exercise because not all microcontroller programming languages have built in commands that automate synchronous serial communication ADC0831Test1 bs2 shows you how to use lower level commands to implement a timing diagram ACTIVITY 3 VERIFY MICROCONTROLLER SIGNALING The ADC0831 transmits a measurement as a number of least significant bit voltage increments Vrs This voltage increment is just enough to make its measurement step from O to 1 The increment s size depends on the range of the voltage the device is Page 156 Understanding Signals with the PropScope configured to measure The top of this range is set by the voltage applied to Vref and the bottom of this range is set by the voltage applied to Vin Since the ADC0831 splits whatever voltage range it measures into 256 levels the value of Visp is Vref Vin Vise 956 6 Since Vref is connected to Vdd 5 V and Vin is connected Vss 0 V the ADC0831 s measurements will be in terms of 256 of 5 V So that makes one LSB voltage increment 5V 0V 256 0 01953125V 19 53125mV Visp Viss vs LSB Analog to digital converter documentation often just refers to one Visg voltage increment as an LSB LSB also refers to the rightmost binary digit in a binary number The two are related because the voltage that causes an ADC measurement to step from 0 to
114. Figure 9 12 shows a quick amplitude check for a 100 Hz 1 Vpp 0 5 V offset sine wave generated by the DAC Card and displayed in the lower red CH2 trace The amplitude of the output in the upper blue CH1 trace is approximately 2 Vpp so it verifies the gain of 2 with Rf Ri 10 KQ v Configure the PropScope s Horizontal Vertical Generator and Trigger settings according to Figure 9 12 v Make sure to click the Generator button to start the DAC Card s signal Figure 9 13 shows what happens to the output signal when you replace the 10 kQ feedback resistor Rf with a 20 kQ one The gain increased to 3 v Replace the 10 kQ Rf feedback resistor in Figure 9 10 on page 335 with one that s 20 kQ It s the top resistor in the Figure 9 11 wiring diagram v Verify that this resistor change results in gain change from 2 to 3 v Try increasing the input signal s offset to 0 75 and its amplitude to 1 5 in the Generator panel How did the output respond Chapter 9 Op Amp Building Blocks Page 337 Figure 9 12 Non inverting Amplifier Gain Test with Rf Ri 10 kQ Oscilloscope Logic Analyzer Analog DSO LSA DC AC of DC AC DAC Off E Sair Generate 4 4 Sine Frequency 100hz i Sawtooth H Custom O Edit ofse o5s 10 Wait for Trigger Trigger Made Off Continuous Step O Figure 9 13 Gain with Two Different Feedback Resistor Values R
115. High P14 bs2 into the BASIC Stamp Editor and then load the program into your BASIC Stamp High P14 bs2 Sends a high signal to P14 SSTAMP BS2 Target module BASIC Stamp 2 SPBASIC 2 5 Language PBASIC 2 5 DEBUG Program Running Program running message HIGH 14 P14 LED on STOP Halt execution but don t sleep Page 60 Understanding Signals with the PropScope No Load Test Measurements Figure 2 29 shows an example of a high signal measurement with no load 5 01 V Your measurement value may differ slightly v Use your PropScope to measure your I O pin high signal with no load and make a note of it ee ro Trigger Cursor y Measure Channel 1 Channel 2 so D E E M cow soe A A Figure 2 29 M aom E a d P14 High Signal Voltage sory Ma i Measurement No Load P14 I O pin HIGH signal voltage Signal Load Test Circuit Parts 1 LED green 1 Resistor 220 Q red red brown misc Jumper wires LED Load Circuit Figure 2 30 shows a light emitting diode circuit with a probe connected at the junction between P14 and the LED circuit s input When the I O pin sends a high signal to this circuit the light will turn on as a result of electric current flowing from the I O pin through the circuit and into Vss v Build the circuit shown in Figure 2 30 and connect your PropScope probe as shown v Make sure to plug the LED s shorter pin into Vss and its longer pin into the same
116. Il mia m el i Pisces amplitude I ga Ji Horizontal scale is frequency Figure 7 23 also shows a floating cursor measurement As you point your mouse at positions on the screen the floating cursor measurement is displayed in the top left of the Spectrum Analyzer screen In the figure the floating cursor s vertical crosshair is lined up with the left bar and the measurement shows At 2 35 kHz amplitude 0 581V v Use the floating cursor to check the amplitude and frequency of each of the bars in your spectrum analyzer Spectrum Analyzer Units By default the spectrum analyzer displays amplitude in terms of i Vpp and frequency in terms of Hz Both scales are linear If you click the Log Mode button wd the frequency units will increase logarithmically instead of linearly If you click the dB Mode button the amplitude will display as decibels instead of peak to peak volts Page 248 Understanding Signals with the PropScope Sine Waves in a Square Wave It turns out that some varieties of sine waves can be added together to create just about any signal you can display with your Oscilloscope That also means that just about any signal you display in the Oscilloscope is composed of one or more sine waves and the Spectrum Analyzer is your tool determining a signal s component sine waves The PropScope s spectrum analyzer performs a Fast Fourier Transform FFT on the oscilloscope signal to determine its sin
117. O P Chapter 4 Pulse Width Modulation Page 139 Decimal Digits vs Binary Digits Four decimal digits each of which could be a value from 0 to 9 represent the number of Thousands Hundreds Tens Ones i Four binary digits each of which could be a value from 0 to 1 represent the number of w Eights Fours Twos Ones Knowing this you can convert values from binary to decimal For example you could convert binary 1010 do decimal knowing that there an 8 and a 2 which adds up to 10 1x8 0x4 1x2 0x1 10 Variations in SONY TV Remote Communication Pulses Servo control pulses have to be fairly precise because even small variations in pulse durations will be visible as different servo horn positions In contrast TV remote communication protocols tend to leave more room for variations in the pulse durations that represent binary 1s and binary Os The microcontroller inside the TV that receives and deciphers pulses from the IR detector can decide whether a given pulse falls into a range of durations that represents a binary 1 or a range of durations that represents a binary 0 Since universal remotes made by different manufacturers may vary somewhat in their IR signaling times that get converted to pulses by the IR detector leaving room in the protocol for variations in the pulse duration expectations is an important design feature With possible variations in mind your remote s pulse duration values that represe
118. OCL L Ol onari L Ol X2 Figure 9 19 shows the lower DAC trace with an amplitude of 1 Vpp and offset of 2 5 V which is applied to the amplifier s input The upper CH1 trace is the amplifier s output Remember that the gain for this amplifier is Rf Ri 10 KQ 10 kQ 1 That s why the amplifier output signal in the upper CH1 trace is the voltage opposite of the lower DAC trace Look carefully the output signal is an inverted version of the input signal with the top of every peak in the upper trace lined up with the bottom of a valley in the lower trace Chapter 9 Op Amp Building Blocks Page 343 v Adjust the Horizontal Vertical Generator and Trigger settings according to Figure 9 20 v Verify that CH1 shows an inverted version of the DAC output with the same amplitude Figure 9 19 Inverting Amplifier Output with a Gain of 1 Oscilloscope Logic Analyzer Analog DSO LSA 100us 201 Ss Ecos 20 ims Square Generate Sie Frequency _ Sawtooth ou w Oer orap 10 20 30 Custom 4 set 2 5 CH1 V Triggered Time ms Trigger Cursor Made Edge Level off Rise Continuous Fall Step Page 344 Understanding Signals with the PropScope Figure 9 20 compares the 1 gain amplifier circuit against one with Rf 20 k
119. Phototransistor Adjustment bs2 Read phototransistor in RC time circuit using RCTIME command SSTAMP BS2 Target module BASIC Stamp 2 TSP BAS Le oy Language PBASIC 2 5 time VAR Word For storing decay times PAUSE 1000 1 s before sending messages Page 310 Understanding Signals with the PropScope DO Main Loop PAUSE 100 Wait 0 1 seconds PWM 2 171 10 Cherge to 171 256 of 5 V REMI YW i eae RC Decay time measurement DEBUG HOME time DEC5 time Display time in 2 us increments LOOP Repeat main loop Figure 8 36 shows a light measurement in roughly the same lighting conditions as the previous measurement However the result is only half the value with a decay time of 1131 x 2 us 2262 us ini Com Port Baud Rate Parity E M1 z 9600 None z Paa Bits Flow Control 1 DIR FATS 8 Off I RX DSR CTS Figure 8 36 time 01131 Same Light Level PWM Reduced Sensitivity zi Macros Pause Clear I Echo Off Figure 8 37 shows an example of the lower starting voltage which contributes to a smaller decay time However there appears to be something more than just lower starting voltage that s reducing the BASIC Stamp decay time measurement which is 2262 us In contrast the oscilloscope measurement is 2 47 ms 2470 us That s more than 200 us difference between the BASIC Stamp and PropScope measurement Unlike previous measurement differences which were small this is a
120. Q and Ri 10 kQ Gain with the 20 kQ feedback resistor is Rf Ri 20 KQ 10 kQ 2 and this is verified with the upper trace on the right which is an inverted 2 Vpp version of the lower 1 Vpp DAC trace that goes to the amplifier s input v Replace the 10 kQ Rf feedback resistor a 20 KQ verify the 2 gain Figure 9 20 Gain 1 left and 2 right 4 L 10 20 30 40 10 20 30 40 Triggered Time ms Triggered Time ms Your Turn Voltage Offset Response and Other Gain Values With a gain of 2 and if the input signal s offset is 3 V 0 5 V above 2 5 V the output signal should have an offset of 1 5 V That s 1 V below 2 5 V v Test the offset response by adjusting the Offset in the PropScope s Generator panel Is the prediction correct As mentioned earlier the inverting op amp can also attenuate the signal with fractional gains v Adjust the Generator back to 1 Vpp 2 5 V offset v Swap the Rf and Ri resistors Calculate the gain and verify with the PropScope Of course larger magnitude gains are also an option try this Chapter 9 Op Amp Building Blocks Page 345 Rf 10 kQ and Ri 2 KQ Calculate the gain You may need to reduce the DAC signal s amplitude at the op amp circuit s input to prevent clipping at the output v Verify the gain with the Parallax PropScope SSS SUMMARY This chapter introduced the operational amplifier or op amp
121. R Byte PAUSE 1000 Delay before first message DEBUG Program running Debug Terminal message DO Main loop FOR index 0 TO 99 Repeat 99x sweep index var READ heartbeat index dacV Read index value from heartbeat PWM 14 dacv 1 Fetched READ value sets DAC PAUSE 5 Wait 5 ms before next iteration NEXT Next iteration LOOP Repeat main loop Hand digitized values from an ECG printout heartbeat DATA 060 OVS 054 063 070 044 067 063 OSS7 069 061 LSO 075 061 22S O77 061 183 080 061 085 082 061 Oils 082 061 O37 080 061 060 Page 98 Understanding Signals with the PropScope 060 060 060 060 060 060 060 060 060 062 O59 OS OS O86 O80 WS O95 WZ 0967 WY 060 060 060 060 060 060 060 060 060 060 060 060 060 060 060 060 060 060 060 060 O60 W60 O60 C60 O60 060 O60 060 O60 060 W060 O60 O60 O60 O60 O60 O60 060 O60 Wad O60 O60 O60 O60 O60 00 O60 060 O60 060 The pata table in Test Heartbeat bs2 was developed by treating an electrocardiograph printout as a series of values plotted on a graph The graph used a vertical scale of 0 to 255 so that it would fit nicely into the PwM command s Duty argument for generating voltages from 0 to 255 0 255 to 255 255 of 5 V Some head and foot room was incorporated into the vertical scale so that the DAC output did not reach all the way to 0 or 255 The lo
122. RC time constant for the circuit on the left side of Figure 8 12 is 220 Q x 0 1 uF 22 us So only a tiny delay is needed while the capacitor charges The RC time constant for the decay on the right is the potentiometer s resistance Rpot x 0 1 uF Rpot could be as large as 10 kQ Assuming the 1 4 V threshold is less than 2 time constants into the decay an estimate for the longest possible time measurement with generous padding would be 2 x T 2 x 10 000 x 0 1x10 2 ms Decay time vs charge time With RCTIME 7 1 time the command s State argument is set to 1 which configures the command to measure voltage as it decays down to 1 4 V Another way to think about it is that the State argument tells the RCTIME command that IN7 will store a 1 when the measurement starts because the voltage applied will be above 1 4 V Then RCTIME measures the time it takes the voltage to decay to 1 4 V at which point the value IN7 stores transitions from 1 to 0 Page 282 Understanding Signals with the PropScope Keep in mind that different potentiometer knob positions result in different resistances In an RC circuit different resistances result in different decay times that the BASIC Stamp can measure and use to infer the potentiometer knob s position Since your microcontroller can use this to sense the knob s position you can use this technique to incorporate an adjusting knob into your microcontroller designs Figure 8 13 shows examples of
123. S 8 Z Off ZI RX ODSR CTS DC_AC DAC Off Generate Frequency 2 5kHz Amplitude 2 8 0 8 Time ms Triggered ta ENE qg aa m Continuous Step Page 228 Understanding Signals with the PropScope ACTIVITY 3 MEASURE BASIC STAMP MUSICAL NOTES The BASIC Stamp can be programmed to transmit many sine wave frequencies including integer versions of the musical notes shown in Figure 7 12 In this activity you will program the BASIC Stamp to synthesize the D7 pronounced D 7 sharp and F7 notes D7 is the black key below the 2489 0 Hz frequency in Figure 7 12 and F7 is the black key below 2960 0 Hz You will then use the Oscilloscope view s cursor features to measure to examine each sine wave s amplitude frequency and offset Recommended Music with Microcontrollers l What s a Microcontroller Chapter 8 shows how to make sound effects and music with the w BASIC Stamp 2 microcontroller using the same piezospeaker that s in the Understanding Signals kit The book is a free PDF download from www parallax com go WAM Figure 7 12 Rightmost Piano Keys and Their Frequencies 1108 7 1244 5 1480 0 1661 2 1864 7 2217 5 2489 0 2960 0 3322 4 3729 3 B A D 6 6 7 or or or E B E 6 6 7 b b b Chapter 7 Basic Sine Wave Measurements Page 229 How the BASIC Stamp Digitally
124. Scope IR Object Detection Parts List For reference and to make it easier finding the parts in the kit Figure 4 18 shows drawings of the IR LED standoff shield and detector It also shows how to house the IR LED into the standoff and shield USE THIS ONE More Rounded Dom 1 Resistor 220 Q red red brown inane me 1 Resistor 1 KQ brown black red 1 IR LED 1 IR LED Shield NOT THIS ONE Flatter on 1 IR LED Standoff Phototransistor top p 1 IR detector E v Snap the IR LED into the standoff and then place the IR shield on top using v Figure 4 18 as a guide Figure 4 18 IR Detector LED Standoff and Shield 3 a IR LED IR LED r Cia Standoff Shield j IR Detector 4 IR LED will snap in 7 Longer lead ho D I IR LED Flattened edge IR Object Detection Circuit Figure 4 19 shows a schematic of the infrared detection circuit and Figure 4 20 shows an example of the circuit in a wiring diagram With the IR LED in the standoff and shield housing it directs the IR light more like a flashlight Without the housing it s more like a beacon Chapter 4 Pulse Width Modulation Page 127 The IR detector only reports that it sees IR light that has a frequency component in the 38 5 kHz neighborhood Unmodulated infrared from other sources such as a nearby window or indoor lighting normally have little to no effect v v Build the circuit shown in Figure 4 19
125. Signals with the PropScope signal it displays the average voltage A signal s average voltage is also called a DC offset and it s introduced in Chapter 3 Human speed Measurements The RMS voltage on the lower right side of Figure 1 3 is a convenient way of measuring AC wall outlet voltages RMS voltage is explained in the Understanding Signals Supplement which is available as a free PDF online from the Downloads section of www parallax com go PropScope DO NOT TRY TO MEASURE WALL OUTLET VOLTAGE WITH THE PROPSCOPE Electrical shocks that can result from mistakes while attempting to measure wall outlet voltages can be fatal and improper use can also damage equipment and property If you want to learn how to take wall outlet and house factory electrical measurements seek f qualified training in proper measurement procedures and safety precautions and use only equipment that has been designed rated and certified for the measurements you take A stock PropScope cannot be used to measure wall outlet voltage With the probes set to X10 the PropScope can measure up to 200 Vpp PropScope probes and probe settings will be introduced in Activity 2 Since US wall outlet voltage is in the 340 Vpp neighborhood it is well outside this range X20 X50 or X100 probes can be purchased separately and used with the PropScope The other fields in Figure 1 3 summarize other attributes of periodic signals and are components of osci
126. So the BASIC Stamp should wait until it applies a falling clock edge before checking the next binary value from the DO line Figure 5 5 Timing Diagram from ADC0831 Datasheet ADC0831 Timing 1 2 3 4 5 6 7 8 9 10 11 aoxco THT ET t TT TT TTT ti tt LI HJ tur CHIP SELECT CS a te DATA OUT D0 TRISTATE STATE 7 6 5 4 3 2 0 MSB LSB Null bit t t f f Multiply each bit x128 x32 x8 x2 and add up the results to value by x64 x16 x4 x1 get the ADC measurement If you had to send a binary value like 10101010 as a series of high low signals would you send the leftmost digit first and work your way to the right or would you send the rightmost digit first and work your way to the left If you send the leftmost digit first and work your way to the right you would be sending the values in the most significant bit first order MSB first If you instead work from right to left you would be sending values in the least significant bit first LSB first order The ADC0831 transmits the binary values MSB first So the first binary value the DO line transmits is the number of 128s in the measurement The second binary value is the number of 64s in the measurement followed by the number of 32s and so on down to the least significant bit which is the number of 1s in the measurement The example measurement in the timing diagram is 1 x 128 0 x 64 1 x 32 0 x 16 1 x 8 0 x 4 1 x 2 0 x 1 170 Pa
127. TOR LIGHT SENSOR EXAMPLE The phototransistor shown in Figure 8 32 is a light sensor that is also compatible with RCTIME measurements C B and E stand for the phototransistor s terminals which are named collector base and emitter Brighter light shining on the phototransistor s base causes it to conduct more current dimmer light results in less current By measuring how quickly the phototransistor allows the capacitor to discharge in an RC circuit a microcontroller can detect light levels In this activity you will test BASIC Stamp light measurements with the BASIC Stamp and verify the time measurements with the Oscilloscope B gt Z Figure 8 32 Phototransistor Schematic Symbol and Part Drawing USE THIS ONE Flatter on Phototransistor Light Sensor Parts Phoigiransistor j top 1 Phototransistor il 1 Capacitor 0 1 uF 104 7 1 Resistor 10 kQ brown black orange NOT THISONE iore hawhied misc Jumper wires Infrared LED HI Dome Page 306 Understanding Signals with the PropScope Phototransistor Light Sensor Circuit Figure 8 33 shows a schematic and wiring diagram example of the phototransistor in an RC decay circuit Although this is still an RC decay circuit there are several differences First the pot has been replaced with a phototransistor Second the I O pin assignment is different P2 instead of P7 Third the capacitor is ten times the value that was used
128. Try it Use Vertical Cursors to Measure the Period Oscilloscopes including the PropScope have tools called cursors to manually measure waveforms So far we have only used the PropScope s floating cursor feature which gives you an instant readout of each channel s voltage value for a single point in time In contrast to a single point cursors are pairs of horizontal and vertical lines that can be positioned on the Oscilloscope screen over a waveform Instead of simple time and voltage values the Cursor display also gives information about lines relative to each other voltage difference time difference and frequency calculations Figure 3 22 shows an example of the PropScope s vertical time cursors positioned over the heartbeat signal peaks In the Cursor Display on the Oscilloscope view s lower right it shows both the time of each cursor s positions along with automated A and f measurements The A measurement is pronounced delta and is shorthand for the time difference At delta t between the vertical cursor lines When applied to a signal that repeats itself A is also the signal s period T The f measurement is 1 A and is often used to automate the f 1 T calculation Note that the Cursor measurements panel indicates the frequency is 1 18 Hz Multiplied by 60 seconds minute we get 70 8 bpm Page 102 Understanding Signals with the PropScope Figure 3 22 Cursors Placed over Pulse Peaks to Measure Pulse Rate
129. UT command uses a list of values obtained from sine wave graph The BASIC Stamp also has to cycle through the different D A conversions at a much higher rate 2500 cycles per second instead of 70 8 cycles per minute Page 230 Understanding Signals with the PropScope BASIC Stamp Tones Parts List 1 Piezospeaker 1 1 uF Capacitor 1 220 Resistor If you have a BASIC Stamp HomeWork Board use a wire instead misc Jumper wires BASIC Stamp Tones Circuit Figure 7 14 and Figure 7 15 show the schematic and wiring diagram of a circuit that will allow you to alternately play a note with the piezospeaker and then view its sine wave in the Oscilloscope screen With the capacitor in place the PropScope will display a clean sine wave but it will be difficult to hear on the speaker With the capacitor disconnected the tone from the speaker will be easier to hear but instead of a sine wave the PropScope will display the switching activity the I O pin uses to synthesize the sine wave Even with all that binary on off switching the speaker tone still sounds true because the switching frequency is very high compared to what the piezospeaker can broadcast and our ears cannot pick up frequencies that high either So the combination of speaker and eardrum mechanically perform filtering for our brains that is similar to what the RC circuit performs for the PropScope v Make sure the CH2 DAC lead is disconnected from the circuit y
130. Understanding Signals with the PropScope Student Guide VERSION 1 0 PLAX 7 WARRANTY Parallax warrants its products against defects in materials and workmanship for a period of 90 days from receipt of product If you discover a defect Parallax will at its option repair or replace the merchandise or refund the purchase price Before returning the product to Parallax call for a Return Merchandise Authorization RMA number Write the RMA number on the outside of the box used to return the merchandise to Parallax Please enclose the following along with the returned merchandise your name telephone number shipping address and a description of the problem Parallax will return your product or its replacement using the same shipping method used to ship the product to Parallax 14 DAY MONEY BACK GUARANTEE If within 14 days of having received your product you find that it does not suit your needs you may return it for a full refund Parallax will refund the purchase price of the product excluding shipping handling costs This guarantee is void if the product has been altered or damaged See the Warranty section above for instructions on returning a product to Parallax COPYRIGHTS AND TRADEMARKS This documentation is Copyright 2010 2011 by Parallax Inc By downloading or obtaining a printed copy of this documentation or software you agree that it is to be used exclusively with Parallax products Any other uses are not permitted and
131. V div Chapter 2 DC Measurements Page 39 Figure 2 11 Division Lines and Divisions 50 us div Horizontal scale dial sets time division scale increments pu 00ys 200p 500s Ams 4 t l li voltage i voltage divisions D HEA Pii a Chi 2 V div are2VforCHi 5 i J M SETCE TaT Vertical scale dials set fie voltage oe division scale division bees f i j increments voltage divisions E CH2 are 5 V for CH2 n CH2 5 Viiv DC AC Off DC AC DAC Off Square Generate I Sine Frequency 10kHz Figure 2 11 also points out the time division lines that travel up and down the screen separating it into horizontal increments called time divisions The Horizontal dial is set to 50 us which makes each time division represent a 50 us increment With the DC voltages in this chapter it doesn t really matter what time division increment size you chose with the Horizontal dial The DC measurements will still appear as flat lines that cross the Oscilloscope screen In later chapters the voltages will vary with time at certain rates and you will have to adjust the Horizontal dial to get the best view of the signal as it rises and falls across the Oscilloscope screen ACTIVITY 4 DIGITAL TO ANALOG DC VOLTAGE Digital to analog conversion is the process of taking a number a digital value and converting it to a corresponding output voltage an
132. V offset the square wave s high signals would be 2 5 V and its low signals would be 1 5 V Thats a total voltage fluctuation of 1 V with an average value of 2 V If you change the amplitude to zero the signal does not fluctuate any more and you are left with a DC voltage at 2 V So long as the Amplitude is set to zero the function generator will supply DC voltages With Amplitude 0 the frequency can be any value and it doesn t matter whether the function is set to Sine Square or Sawtooth Figure 2 20 shows the measured voltage with the floating cursor and Measure tab Set the CH1 Vertical dial to 1 V div Adjust the CH1 trace s position point at the trace click and drag up down so that it resembles Figure 2 20 Use your mouse to point at the Channel 1 trace to get the CH1 floating cursor measurements Keep in mind that this is an instantaneous measurement that will fluctuate slightly with electrical noise and other factors Check the value in the Measure tab s Channel 1 Average voltage field and keep in mind that this measurement is an averaged value that is more similar to a DC voltmeter s measurement Chapter 2 DC Measurements Page 49 Figure 2 20 Channel 1 Probe of the Function Generator s 3 5 V Output File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA At 374ps CH143 45V CH2 0 86V Floatin gtr a FECH Pee be Pen
133. W terminal voltage has reached the I O pin threshold At that point the PropScope will display the threshold voltage Page 56 Understanding Signals with the PropScope v Add the 220 Q resistor shown in Figure 2 26 to connect the pot s W terminal to BASIC Stamp I O pin P7 Figure 2 26 Potentiometer Voltage Divider Circuit Connected to a BASIC Stamp I O Pin Vdd PropScope CH1 Pot 10 KQ If you are using a HomeWork Board you can use a jumper wire instead of the resistor P7 220 2 PropScope GND Why not just connect W to P7 with a wire The 220 Q resistor protects the I O pin from certain prototyping mistakes For example imagine that the BASIC Stamp was still loaded with a previous program that sent a high signal to P7 so that pin ends up supplying 5 V to gt this circuit If the pot s knob is turned all the way counterclockwise shorting W to Vss ground P7 would try to supply enough current to pull the ground connection up to 5 V and w damage itself in the effort The 220 ohm resistor limits the current from P7 to Vss in this situation protecting the I O pin If you have a BASIC Stamp HomeWork Board there are 220 Q resistors built in to protect the I O pins and you actually could use a
134. W CLK Y Srart CEK Ike INPUT Dout H Ser Douie COLNE DO Main Loop LOW CS CS gt low start measurement SHIFTIN Dout CLK MSBPOST adcVal 9 9 CS pulses keep 8 DO bits HIGH CS 0 CS S ihien CSc ive DEBUG HOME Display measurement Wiglatioveneyy eveleWerll Wi esis eee Veep iy in binary Decimal adcVal DEC3 adcVal and decimal PAUSE 100 Screen update delay LOOP Repeat main loop ase PBASIC has SHIFTOUT too For sending synchronous serial messages to devices wy designed to receive them use the SHIFTOUT command Figure 5 16 shows that the Debug Terminal is still displaying the correct information but the SHIFTOUT command is finishing its job in a fraction of the time In fact it s running so quickly that the current 1 ms division Horizontal dial setting is too large to catch all the signal activity in the Logic State Analyzer v Verify that your Debug Terminal and Logic Analyzer resemble the example in Figure 5 16 Page 170 Understanding Signals with the PropScope Figure 5 16 Debug Terminal Check and SHIFTIN in Logic State Analyzer E PropScope 2 0 1 DI E File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog a LSA MOH je1uo Boome TS Binary adcVal Decimal adcVal gt 4 6 Time ms Triggered Figure 5 17 shows the L
135. a good idea to move the Plot Area bar to the far left of the Plot Preview and to position the Trigger Time control near the left side of the Plot Area bar This will make the signal that follows the trigger event visible on the Oscilloscope screen v v v If it s not already in that position slide the Plot Area bar all the way to the left in the Plot Preview Slide the Trigger Time control to the position shown in Figure 3 11 As you slide the Trigger Time control into the Plot Area bar the pair of crosshairs should that indicate the trigger voltage and time should reappear Adjust the Trigger Time control s position slightly to make the vertical trigger time crosshair and the Channel 1 signal s rising edge align with the 2 time division line Slide Trigger Time control here Slide the plot area bar to the far left division line Trigger Til Time ms 160 Triggered Figure 3 11 Adjusting the Trigger Time control s Position After you slide the Plot Area bar all the way to the left slide the Trigger Time control to the approximate position shown in the Plot Area bar Then slowly adjust it until the vertical trigger time crosshair and the rising edge of the channel 1 trace aligns with the 2 time division line Chapter 3 Human speed Measurements Page 83 If you ever want to check the current Trigger Time or Voltage settings you can use e
136. age 115 Use your Trigger Time control to position the vertical trigger crosshair at the of time division line v Drag the trace down nice and close to the time scale for a better at a glance view of the pulse timing v Check the Oscilloscope s Plot Preview there should be two more pulses off screen and they continue to repeat to keep the servo holding its horn s position Figure 4 10 Servo Control Pulses f PropScope v2 0 1 File Edit View Plugins Tools Help Oscilaseope Logic Analyzer Analog DSO LSA iF DC_AC DAC Off Generate Sine Frequency 40kHz Sawtooth Time ms Aoa k Ea Continuous N a z qe j Normal ae O a ma f sms a l i ge p p CLIPPED CLIPPEL What does this mean It s telling you that the signal voltage exceeded the i voltage limits for the vertical setting In this case it is not a big deal All it indicates that the high signal might have exceeded 5 V maximum voltage by a few millivolts for a short period of time The author prefers to disregard this message and use the 2 V div setting for a better visual representation of the pulses and ease of cursor placement Page 116 Understanding Signals with the PropScope With this initial view of the servo pulses let s check to see if the PWM signal does anything interesting with different PULSOUT Duration values that make the se
137. age rating is printed on the side of the canister CAUTION Safety goggles or safety glasses are recommended Disconnect power from your board v Build the circuits shown in Figure 2 12 and Figure 2 13 v Verify that the negative terminal for each capacitor is connected to Vss before reconnecting power to your board P15 1kQ PropScope Ch2 P14 pee 1kQ Figure 2 12 u tue Dual DAC Circuit PropScope CH1 Schematic PropScope GND Chapter 2 DC Measurements Page 41 Figure 2 13 Wiring Diagram Example of Figure 2 12 Make sure to connect the capacitors negative leads that come out of the metal can by the stripe to Vss WJOOOOOOOR DOOOOOOOOOOOOOOOd x lt N Example Program Test 2 Channel Dac bs2 The PBASIC program Test 2 Channel Dac bs2 uses the PwM command to repeatedly set voltages across the two capacitors in this circuit In effect the program uses the PWM command to make the BASIC Stamp perform D A conversions setting output voltages across the capacitors The pwm command has three arguments Pin Duty and Duration The Pin argument is for selecting which pin sends the PWM signal Duty is the number of 256 of 5 V the capacitor gets charged to and Duration is the time the command has to deliver the signal In Test 2 Channel Dac bs2 the command P
138. air pressure variations from musical instruments playing notes in radio and TV signals and in the voltages supplied by AC electrical outlets Figure 7 1 Sine Wave Two Cycles This chapter introduces basic sine wave measurements using signals that create tones and musical notes as examples Many signals contain more than one sine wave component like musical chords phone tones and even binary on off signals So this chapter also introduces the spectrum analyzer a diagnostic tool that can display a signal s sine wave components Many circuit tests involve comparing a sine wave supplied to a circuit s input against the one at its output So techniques for supplying a sine wave to a circuit and comparing the properties of the input and output signals are also introduced ACTIVITY 1 SINE WAVE AMPLITUDE AND FREQUENCY TESTS When a musical note is played by an instrument like a guitar the guitar string s vibrations cause air pressure variations When a speaker plays a musical note it converts electrical signals into vibrations that cause air pressure variations Regardless of whether it s an actual instrument or a speaker playing the note the eardrum senses the air pressure variations and forwards those signals to the brain via nerve connections Then our brain processes that information and we experience it as a musical note Two properties of a note are volume and pitch Volume is how loud the note sounds
139. aken to ensure systems remain stable An example of a stable system is public address PA system where somebody speaks into a microphone and their voice is amplified and played by a loudspeaker for an audience In a stable PA system the amplifier is properly tuned and the speakers are oriented to minimize the sound energy that goes back into the microphone So the system amplifies the speaker s voice and not what comes from the loudspeakers 1 An example of an unstable system is when the person tries to say something into the PA wg s system s microphone and all the audience can hear is a loud high pitched whine When the person tried to speak into the microphone his her voice was initially amplified by the amplifier and loudspeaker but the microphone picked up the sound from the loudspeaker and amplified it too After that the system gets stuck in an unstable feedback loop of amplifying what the microphone picks up from the loudspeaker The PA system is just one example of a system stability application Ensuring system stability is part of designing many circuits and systems including switching power supplies automated ovens and motor controllers System stability has to be incorporated into many mechanical and electromechanical designs as well including bridges and buildings automobile cruise control and aircraft autopilots You can convert a phase for any frequency to a degree measurement by keeping in mind
140. al of 2 x 1ZV 3 V v Try decreasing the amplitude to 2 V and observe the result v Try decreasing the amplitude to 1 V and observe the result again Chapter 3 Human speed Measurements Page 95 Cece ccepecccccesiccesepececceeace Figure 3 19 Sawtooth Wave with 3 V Amplitude 3 V amplitude en from 1 5 Vto 1 5 V Cee ee Ce 2 40 80 120 CH1 K Time ms The DAC Card can generate signals that fit into one of two ranges e 1 5Vto 1 5V A e OVto47V f e 1 Ifthe amplitude or offset settings exceed the limits the PropScope software will display an w error message For example if you tried to enter a 5 V amplitude and a 3 V offset it would display the error A 5 V amplitude with a 3 V offset means that the signal should swing from 0 5 V to 5 5 V That s the DC offset of 3 V 2 5 V for the top peak and 3 V 2 5 V for the bottom peak The sawtooth wave s Offset setting is currently 0 V DC offset is a DC voltage component that can be added to the signal Let s see what happens when you add a 2 5 V DC offset to the signal v Adjust the Generator panel s Offset to 2 5 v You may need to wait a moment for the display to refresh The frequency adjustment is also simple Let s try these values in the Generate panel s Frequency field 10 Hz 15 Hz 20 Hz 25 Hz 30 Hz v Examine the Oscilloscope display as you enter each successive value into the Generator panel
141. amp of i ol x ol a mfi Here is a program that repeatedly sweeps the PWM command s Duty value from 0 to 255 This in turn sweeps the voltage across the capacitor from 0 to 4 98 V creating a voltage waveform that can be viewed with the Oscilloscope Chapter 3 Human speed Measurements Page 91 v Enter and run Test Saw Tooth bs2 Test Saw Tooth bs2 SSTAMP BS2 Target module BASIC Stamp 2 UTSPBASTE 2 5 Language PBASIC 2 5 dacV VAR Byte Byte variable declaration PAUSE 1000 1 s before DEBUG DEBUG Program running Debug Terminal message DO t Main loop dacV variable sweeps from 0 to 255 DAC output sweeps from 1 0 256 to 255 250 2x B We FOR dacV 0 TO 255 FOR NEXT loop repeats 255x PWM 14 dacv 1 dacV sweeps from 0 to 255 NEXT Next repetition LOOP Repeat main loop Isn t it supposed to be PWM 14 dacv 5 According to the 5 x R x C guideline yes e However this program is repeatedly applying PWM signals in rapid succession and one alL rwm command only varies slightly from the next So this program can get away with a shorter Duration argument in the PWM commands The Oscilloscope screen in Figure 3 17 shows a 2 second time window which means that the oscilloscope s Plot Preview spans 4 seconds This time the Plot Area bar is on the left with the Horizontal dial set to 200 ms div So it may take a
142. an oscilloscope s automated measurements Figure 3 20 BASIC Stamp Generated Heartbeat Signal in the Oscilloscope Chapter 3 Human speed Measurements Page 97 Probe Adjustments This activity relies on the BASIC Stamp DAC circuit from the previous activity v If you have not already done so reconnect the CH1 probe to the P14 DAC circuit output See Set DC Voltages with the PropScope s DAC Card page 45 Example Program Test Heartbeat bs2 Test Heartbeat bs2 emulates a heartbeat signal by fetching successive values from the heartbeat DATA directive near the bottom of the program This DATA is stored in an unused portion of the BASIC Stamp module s EEPROM program memory and the READ command uses an address of heartbeat index to retrieve each value The FOR NEXT loop increments the index variable from 0 to 99 so the READ command fetches the next value in the list each time through the For NExT loop The READ command also places the value it fetched from EEPROM into the dacv variable each time through the FOR NEXT loop Then the PwM command uses the daev variable to modify the voltage across the DAC circuit s capacitor Since the entire FOR NEXT loop is nested in a DO LOOP the signal repeats itself indefinitely v Load Test Heartbeat bs2 into the BASIC Stamp Test Heartbeat bs2 UES CLAMPS SZ i PBASE ASN Target module BASIC Stamp 2 Language PBASIC 2 5 index VAR Byte Variable declarations dacV VA
143. analog value Both the BASIC Stamp and PropScope have digital to analog conversion abbreviated D A or DAC features that allow you to use numbers to generate DC voltages The BASIC Stamp can generate voltages in the 0 to 4 98 V range and the PropScope can generate voltages in the 1 5 to 4 7 V range Page 40 Understanding Signals with the PropScope Dual DAC Parts List 2 Resistors 1 kQ brown black red 2 Capacitors 1 uF misc Jumper wires Dual DAC Circuit Figure 2 12 and Figure 2 13 show two BASIC Stamp resistor capacitor D A conversion RC DAC circuits along with the PropScope probes attached for measuring the DAC output voltages These circuits can be useful for setting DC voltages in projects and prototypes Some D A converter application examples you will see in this book include BASIC Stamp controlled light sensor and amplifier adjustments CAUTION This capacitor has a positive and a negative terminal The negative terminal is the shorter lead that comes out of the metal canister closest to the stripe with a negative sign Always make sure to connect these terminals as shown in the circuit diagrams Connecting one of these capacitors incorrectly can damage it In some circuits f t connecting this type of capacitor incorrectly and then connecting power can cause it to e rupture or even explode CAUTION Do not apply more voltage to an electrolytic capacitor than it is rated to handle The volt
144. and Figure 4 20 Check your work against Figure 4 20 to make sure you connected the IR LED s shorter cathode pin to the right row in the breadboard The cathode pin should be connected to a row that is connected to Vss If your board is sitting on a table point the IR LED upward at an angle of about 30 so that the system does not report the table s reflection as a detected object Make sure other objects are out of the IR LED s beam path so that they won t cause false detections The maximum detection range with a 1 kQ series resistor is usually in the 30 to 40 cm neighborhood Make sure to get the probes out of the way of the IR LED s beam path so that they don t end up reflecting IR and become objects that are inadvertently detected Figure 4 19 Infrared Object Detection Schematic PropScope Ch2 PropScope Ch1 PropScope GND Vdd P9 Pe pra 2202 E oo Vss ae es P8 ee ae 1kQ an j AT Infrared with a 38 5 kHz signal IR N a LED oS Unesi Page 128 Understanding Signals with the PropScope Figure 4 20 Wiring Diagram Example of Figure 4 19 Vdd Vin Vss 7 x3 a 2 j p O uc 2 No Uc 11 g p sen AT P10 gm SA ia P9 g a TS Se P8 ae 22S Son eka oof es oo O P7 NOON COC amin 0 CC ol M P6 a P5 Jasa P4 S TO P3 Daen P2 TASSE
145. and Test v Pick a different potentiometer knob adjustment for a different Debug Terminal decay time and use the PropScope to verify the BASIC Stamp measurements Chapter 8 RC Circuit Measurements Page 293 ACTIVITY 4 RC CIRCUIT S ROLE IN D A CONVERSION In Chapter 4 Activity 2 the relationship between duty cycle and DAC voltage was introduced In this activity you will take a closer look at this relationship After repeating some of the duty cycle and average voltage measurements you will compare the average voltage the PropScope reports against the average voltage at the RC DAC circuit s output You will also calculate the average voltage of a signal DAC Test Parts 1 Resistor 220 Q red red brown 1 Resistor 1 kQ brown black red 1 Capacitor 1 pF misc Jumper wires DAC Test Circuit The circuit in Figure 8 23 and Figure 8 24 should be familiar from the duty cycle measurements in Chapter 4 Activity 2 v STOP If your CH2 probe s BNC end is still connected to the DAC Card s function generator output disconnect it and reconnect it to the PropScope s CH2 BNC input before continuing Build the circuit shown in Figure 8 23 and Figure 8 24 PropScope Ch2 P14 Figure 8 23 DAC Circuit with Probes Attached for P14 PWM Signal and DAC Output Monitoring 1kQ PropScope CH1 PropScope GND Page 294 Understanding Signals with the PropScope
146. and frequencies The oscilloscope s Horizontal time and Vertical voltage display dials were used to adjust the time division and volts division settings The Oscilloscope s divisions were used to measure voltage time and frequency and the measurements were compared to values obtained from the Measure tab and from cursor placement Chapter 4 Pulse Width Modulation Page 105 Chapter 4 Pulse Width Modulation Modulation is the process of varying a signal s properties for communication or control The property that pulse width modulation varies is the amount of time a signal spends at a certain active voltage before returning to a resting voltage When viewed with an oscilloscope a signal that holds a voltage for a certain amount of time has a certain width on the Oscilloscope screen Figure 4 1 shows a few examples of how these voltage pulses might look in an oscilloscope On the left two different positive pulse examples have 0 V resting states and a 5 V active states If the signal spends a brief time at 5 V the pulse looks narrower on the Oscilloscope screen If the signal spends a longer time at 5 V it looks wider On the right the negative version of those same pulses simply have opposite active and resting states Positive Negative i time high gt pulse width 5V Narrower ov Figure 4 1 time low gt pulse width Voltage Pulse Examples 5v Wider ov Active and resting voltages can v
147. ange Vpwm Duty x 5V 256 Duty Vpwm 5V 256 Duty Vpwm 0 01953125 V Next solve for Duty with Vpwm 3 5 V You will have to round to the nearest integer since the PWM command s Duty argument accepts an integer value between 0 and 255 Duty 3 5 V 0 01953125 V 179 2 x 179 Chapter 2 DC Measurements Page 45 So the command PWM 14 179 5 should set a voltage of just under 3 5 V at the P14 DAC circuit s output y Modify the PwM command to P14 in Test 2 Channel Dac bs2 so that it transmits 3 5 V v Test with the PropScope v Repeat for 2 50 V Keep in mind that the PwM command s Duty value represents a certain member of 19 54 mV increments The goal is to get within about 20 mV of the target voltage What does LSB mean For digital to analog D A and analog to digital A D converters an LSB describes the smallest voltage increment the device can work with Under ideal conditions 0 01953125 V is the voltage level across the DAC circuits capacitor when _ Duty 1 in the BS2 command PWM Pin Duty Duration The value 1 would be stored in the least significant bit LSB of the 8 bit Duty argument that controls the voltage output wy Datasheets for D A and A D converters speak in terms of an LSB because their devices may be operating on a scale that s different from 0 to 5 V so they keep it general For example if the scale is instead 0 to 3 3 V the number of levels might still be 256 8 bits
148. argument results in a longer FREQOUT signal in CH1 which in turn causes the IR detector to send a 2 ms low pulse KSSS Chapter 4 Pulse Width Modulation Page 133 ACTIVITY 4 ADVANCED TOPIC PULSES FOR TV REMOTE COMMUNICATION Figure 4 24 shows how a TV remote sends bursts of signals in the 38 to 40 kHz neighborhood to an IR detector The durations of a series of these bursts are coded to communicate which button on the remote is pressed The IR detector on your board converts these brief IR signal durations to brief low pulses which are also called negative pulses The BASIC Stamp can decode these pulses to figure out which button on the remote is pressed in a manner similar to the microcontrollers inside TVs and other entertainment system components In this activity you will use the both the PropScope and BASIC Stamp to examine these signals Figure 4 24 IR Remote Signals to IR Detector gt 2 z Figure 4 25 shows a timing diagram of a SONY TV remote protocol from the standpoint of the IR detector s output After a 2 4 ms start pulse a series of 12 low pulses follow Each low pulse lasts for either 0 6 ms to indicate a binary 0 or 1 2 ms to indicate a binary 1 Just as an 8 bit binary number can contain a value in the 0 to 255 range a 12 bit binary number can contain a value in the 0 to 4095 range So the pulse width modulated signal in Figure 4 25 can be used to transmit 4096 different values Page 1
149. ary from one system to the next For example if the BASIC Stamp transmits pulses it sends 5 V high signals and 0 V low signals but another system might depend on different active and resting state voltages Certain circuits called translators can translate the BASIC Stamp module s outputs to other voltages Circuits called drivers also offer high output current capabilities for motor control and circuits called inverters can change positive pulses to negative pulses Gay w PULSES FOR COMMUNICATION AND CONTROL Pulse width modulation is widely used for both motor control and communication This chapter s activities include PWM examples for each and also examine how to use the PropScope s features to measure these signals Page 106 Understanding Signals with the PropScope ACTIVITY 1 PULSES FOR SERVO CONTROL Hobby servos like the one in Figure 4 2 control the steering and throttle in radio controlled RC cars boats and airplanes They are also useful for a variety of robotic tasks including moving arms legs and grippers The servo can rotate its 4 point star shaped horn 3 in the figure to various positions More importantly the servo can hold its horn in a given position and resist external forces that might try to displace it For example in an RC car the servo has to make the wheels turn left and right for steering The servo has to hold the wheels in a certain position or they would just straighten ou
150. at allows you to draw an arbitrary waveform that can be transmitted by sliding the waveform selector switch to the Custom setting In addition to the signals listed you can set DC voltages by setting the value in the Amplitude field to 0 and then adjusting the value in the Offset field for the desired DC voltage from 1 5 to 4 7 V We will set and measure PropScope function generator voltages starting in Chapter 2 DC Measurements Chapter 1 PropScope Introduction and Setup Page 15 Logic Analyzer When digital devices communicate there may be several signal lines exchanging binary high low voltage signals A logic analyzer plots the binary activity of multiple signal lines over time Figure 1 6 shows an example in which the PropScope is monitoring four BASIC Stamp I O pins which are sending a sequence of four slightly different messages using a form of binary signaling called asynchronous serial communication Figure 1 6 Logic Analyzer 8 PropScope v1 0 6 File Edit View Plugins Tools Help Oscilloscope LogicAnalyzet Analog DSO 100ps_200ps S00 us ims eS 2 4 Triggered Time ms Page 16 Understanding Signals with the PropScope Spectrum Analyzer A spectrum analyzer plots the amplitudes of sine wave components in a signal vs their frequencies Many signals have one or more sine wave components Such signal components are commonly tested when monitoring engi
151. ation arguments will result in the servo horn holding different positions Positive vs Negative Pulses Servo pulses are considered positive pulses because they spend a certain amount of time as high signals before returning to the low resting state A negative pulse would start high and spend a certain amount of time low For negative 1 pulses simply set the I O pin to output high like with the HIGH command before the PULSOUT command and it will send a low pulse instead of a high pulse You will have a chance to measure negative pulses from a sensor in Activity 3 and Activity 4 Examine the Servo Control Signals with the PropScope Back to the two cycles guideline for a first look at any given signal in the oscilloscope We know from the code and timing diagrams that each repetition of the DO LOOP in ServoCenter bs2 takes 20 ms 1 5 ms maybe 1 ms of code overhead 22 5 ms Then multiply by 2 with a result of about 45 ms for two servo pulse signal cycles Next remember that the Horizontal dial selects the time for one division and that the Oscilloscope screen has 10 divisions So divide 45 ms by 10 and the result is the 4 5 ms which is close to 5 ms So select the 5 ms div Horizontal setting in Figure 4 10 v With your BASIC Stamp running ServoCenter bs2 adjust the Horizontal and Vertical dials coupling switches and Trigger tab settings so that they match Figure 4 10 Chapter 4 Pulse Width Modulation P
152. be able to adjust the sine wave s offset to anywhere in the 1 V to 4 2 V range v Change the Generator panel s Amplitude to 1 V v Enter each of these DC offset values into the Generator panel s Offset field 1 0 1 2 3 4 and 4 2 V Keep in mind that the peak amplitude which is 1 2 the peak to peak amplitude is the total excursion above and below the sine wave s DC offset So with a 1 Vpp amplitude when you change the Generator panel s offset to 1 V its voltage oscillates from 0 5 V above that level to 0 5 V below it That s why the DC offset can be adjusted clear down to 1 V because the lowest level the sine wave s valleys reach is the function generator s 1 5 V lower limit Amplitude and Offset for BASIC Stamp Frequency Counting The BASIC Stamp can measure the frequencies of sine waves The PropScope s function generator output needs to be connected to an I O pin to test this Then a program can make the BASIC Stamp count signal cycles over some period of time to measure the frequency For the BASIC Stamp to take these measurements the signal has to have some combination of amplitude and offset that makes it cross the BASIC Stamp I O pin logic input threshold I O pin threshold voltage was tested back in the Determining I O Pin Threshold Voltage section on page 55 and it s typically very close to 1 4 V Chapter 7 Basic Sine Wave Measurements Page 225 Extra Test Parts 1 Resistor 220 Q
153. but the LSB would instead be 3 3 V 256 0 012890625 V Same LSB but a different voltage scale results in a different voltage increment Set DC Voltages with the PropScope s DAC Card The PropScope can also set DC voltages which is useful if a test circuit needs to be examined with a voltage applied To generate test voltages with the PropScope the CH2 Probe should be disconnected from the PropScope s CH2 input and connected to the DAC Card s function generator output Disconnect the CH2 probe from the circuit in Figure 2 13 on page 41 v Disconnect the probe from the PropScope s CH2 BNC connector shown in Figure 2 16 Connect the BNC end of the free probe to the DAC Card s function generator output BNC connector also shown in Figure 2 16 Connect the free probe end which is now the DAC output to the CH1 probe using Figure 2 17 and Figure 2 18 as a guide v If you just now plugged in the DAC Card into the PropScope restart the PropScope software by clicking File and selecting Reset Identify hardware Page 46 Understanding Signals with the PropScope X3 X2 Vdd Vin Vss PropScope Usa Oscilloscope N fi iq PropScope Ch1 iT PropScope GND Vss Figure 2 16 DAC Card function generator Output Figure
154. ches CH1 AC CH2 DAC v Trigger tab switches Mode Continuous Edge Rise Level Auto Source CH2 v Trigger Time control Align vertical crosshair with 2 time division v Generator panel Function switch Sine Frequency 3 kHz Amplitude 2 V Offset 0 V v Waveform Positions Use Figure 7 31 as a guide Position the red CH2 DAC trace slightly above the blue CH1 trace Figure 7 32 shows two different approaches to amplitude measurements with cursors and with the Measure tab v Click the Cursor tab and then click the Horizontal button to start the voltage cursors v Click the CH2 trace to set the lower right Cursor and Measure displays to CH2 DAC output Or click the CH1 CH2 label in the Cursor or Measure display to toggle between CH1 and CH2 DAC v Position one voltage cursor at the tops of the CH2 DAC sine wave s peaks and the other at the bottoms of the valleys Y Record the cursor A measurement and compare it to the automated peak to peak value in the Measure display v Repeat for CH1 Now we know that the circuit reduces the signal s amplitude by Figure 7 32 by almost 1 2 0 867 1 99 0 436 Note that the cursor measurements closely match the automated measurements so for sine wave amplitudes automated measurements will speed up the process Chapter 7 Basic Sine Wave Measurements Page 261 Figure 7 32 Amplitude Comparison Cursor Amplitude Measurement of DAC to Circuit Input on CH2 T 333
155. cilloscope aligns a point where the sine wave rises through the 2 35 V Trigger Voltage crosshair with the Trigger Time crosshair For a sine wave this is the start of its cycle You can see part of a second cycle in the screen starting four time division lines to the right of the trigger event v Try changing the Edge switch in the Trigger tab from Rise to Fall The voltage should now fall through the trigger crosshair intersection instead of rising through it Vv Restore the Trigger tab s Edge switch to Rise If the Trigger tab s Level switch is set to Normal it means that you will manually adjust the Trigger Voltage Level control If the waveform s DC offset or amplitude changes enough so that the signal doesn t cross the Trigger Voltage level the Oscilloscope screen will not refresh There may still be signal activity but it will not be displayed on the Oscilloscope screen Try this v Set the Generator panel s Offset back to 0 V The Trigger Voltage control should automatically reposition to 0 V Y Move the Trigger tab s Level switch to the Normal setting v Change the Generator panel s Offset back to 2 35 V At this point the sine wave should still appear to have a O V offset and a red status warning should appear in the lower right of the Oscilloscope screen WEISGAUFFEI That s because the waveform never crosses the 0 V trigger voltage so the display does not update y Now manually drag the Trigger Voltage
156. color coded servo cable wires line up with the labels in the figure v Plug the PropScope CH1 probe wire into the same row as the servo s signal white line and the ground clip into the same row as the servo s ground black line Vdd x3 a Sones Figure 4 7 minia Wiring Diagram for ooo Figure 4 3 using the Oo BASIC Stamp Po fa HomeWork Board p7 fg G9 F PARALLAX AIEE oy P DI 3 7 www parallax com E P1 m oo Po Oooo oo Chapter 4 Pulse Width Modulation Page 111 PWM Signals for Servo Control The Parallax Standard Servo s horn has a 180 range of motion Figure 4 8 shows timing diagrams for example PWM signals that make the servo hold its horn at 45 90 and 135 positions The pulse high times control the servo s position and they have to be precise PBASIC has a command called puLsout for making the BASIC Stamp deliver precisely timed pulses The pulses also have to be sent repeatedly to make the servo maintain a certain position Repeating the pulses at 50 Hz is ideal but the rate the pulses are delivered does not have to be precise a few Hz faster or slower is fine too Most PBASIC examples use a simple PAUSE 20 inside a loop with a PuLsouT to make the BASIC Stamp send control pulses that repeat at a rate in the 44 Hz neighborhood Figure 4 8 Pulse Width vs Se
157. connected to PropScope CH1 and CH2 d DO NOT leave either probe connected to the DAC Card A o A 10x probe has a built in voltage divider and a bypass capacitor that together minimize the J probe circuits electrical interactions with the test circuit The signal that gets to the Oscilloscope s input circuit is 1 10 the voltage it would be if it was a 1x probe The PropScope software has to know that the signals it measures are coming from 10x probes Reason being these signals are 1 10 the value they would be if they were coming from a 1x probe Figure 6 23 shows how to configure the PropScope software s probe settings to 10x vIn the PropScope software click Tools Manage Probes Set the probe gain to 10 for both probes Tools Help Manage Probes xi NS Probe 1 Geir fio x Figure 6 23 Configure Probe Gain Probe 2 Gain THE w to o Cancel Chapter 6 Asynchronous Serial Communication Page 205 Serial Port Transmit Test Code PC Serial Transmit bs2 sends A to P11 and another A to the BASIC Stamp SOUT pin with the sERouT Pin argument of 16 in the second SEROUT command This test code will make it convenient to compare the true signal transmitted by P1 lagainst the inverted signal transmitted by the SOUT pin v Enter and run PC Serial Transmit bs2 PC Serie Transmit bs2 Sends a true serial byte to Pll as well as to P16 SOUT The byte to SOUT gets inverted by a circu
158. consider the capacitor fully charged or discharged the fact that the signal looks so close to its final voltages is a good sign We can see from the high and low peak voltages in the Measure display that the capacitor charged to 3 92 V then discharged to 39 6 mV We also know from Activity 1 that the capacitor s voltage should charge to about 99 32 of the voltage applied after 5 time constants that it should decay to 0 674 of that voltage after 5 time constants So we d expect the voltage to grow to 0 9932 x 4 V 3 97 V and decay to 0 00674 x 4 V 27 0 mV These measurements are in the right ballpark to confirm that the circuit is working as expected v Click the CH2 trace to set the Measure panel to display its values Or click the CH1 CHz2 label in the Measure display to toggle between measurements for the two traces v Make a note of the CH2 DAC high and low peak voltages v Click the CH1 trace or the CH2 label in the Measure display to switch to displaying values for CH1 and make notes of the high and low peak voltages Examples are shown in Figure 8 7 v Compare them to the predicted 5t values of 0 674 and 99 32 For example 0 674 of 4 V is 4 x 0 00674 0 02696 27 mV v Optional The CH2 DAC signal is an ideal value You can probe the CH2 probe with the CH1 probe to find the actual measured voltage the function generator applies to the circuit s input and then compare those to the measured peak voltages at the circu
159. cope Modify One or Two Notes at a Time bs2 for use with these two frequencies Plot and screen capture the components Plot and screen capture the sum Examine the effect of the peaks and troughs adding together LANA Figure 7 21 Waveform with 100 and 200 Hz Components PropScope v1 1 0 File Edt View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Oscillosco DC_ AC DAC Off A D Square Generate o I Sine Frequency re al rot annsa Custom OE onsa Trigger i Mode Mengs Continuous Step Chapter 7 Basic Sine Wave Measurements Page 245 ACTIVITY 5 SINE COMPONENTS WITH A SPECTRUM ANALYZER What are the frequencies of the sine wave components in the Figure 7 22 waveform Here s a hint they are not D7 and F7 So what are they Could you use the cursors to figure it out Maybe but it might turn out to be difficult and time consuming The answer to the question is that this is FREQOUT 9 60000 2349 3136 which is the BASIC Stamp playing the D7 and G7 notes from Figure 7 12 on page 228 Figure 7 22 Mystery Waveform 8 PropScope 1 1 0 AE File Edt View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA 0 8 ag mior ka J A lan 500n oms 200ns 400ms 0 4 DOMS bathe the E Sons Sodms 0 4 DC AC Oft DC_AC DAC Off H Square Generate
160. couple of seconds before the waveform appears The signal will first be visible in the Plot Preview as it makes its way toward the Oscilloscope screen Your tasks are to Change the Trigger tab s Mode setting from Continuous to Off Slide the Plot Area bar to the far left of the Plot Preview Adjust the Horizontal dial to 200 ms division Adjust the CH1 Vertical dial to 2 V division Set the CH2 Vertical coupling switch to Off Wait a couple of seconds for the waveform to make its way from the right of the Plot Preview and into the Plot Area bar and your Oscilloscope screen Click the Run button to freeze the display and then examine the signal SRA S Kx Page 92 Understanding Signals with the PropScope Figure 3 17 P14 DAC Test Saw Tooth Output on Channel 1 Trace 8 PropScope v2 0 1 eee ltl sd File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA DC Square Generate ve Amoltde 5 Tv gt Custom Edt Oftset a AC Off DC_AC DAC Off 0 8 Time s Trigger 7 Mode due ave puutea Sawa Continuous Step Your Turn Sawtooth vs Triangle Wave The saw tooth function in Figure 3 17 ramps slowly upward from 0 V to 4 98 V and then dives back to 0 V In contrast a triangle wave ramps slowly up and then ramps slowly back down again You can add a second FOR NEXT loop after
161. cts Some that may be pertinent to the reader are e Propeller Chip for all discussions related to the multicore Propeller microcontroller and development tools product line e BASIC Stamp Project ideas support and related topics for all of the Parallax BASIC Stamp models e Education Stamps in Class Students teachers and customers discuss Parallax s education materials and school projects here e Robotics For all Parallax robots and custom robots built with Parallax processors and sensors e Sensors Discussion relating to Parallax s wide array of sensors and interfacing sensors with Parallax microcontrollers e Wireless Topics include XBee WiFi GSM GPRS telemetry and data communication over amateur radio e PropScope Discussion and Technical Assistance for the PropScope USB Oscilloscope e Projects Post your in process and completed projects here made from Parallax products RESOURCES FOR EDUCATORS We have a variety of resources for this text designed to support educators Stamps in Class Mini Projects To supplement our texts we provide a bank of projects for the classroom Designed to engage students each Mini Project contains full source code How it Works explanations schematics and wiring diagrams or photos for a device a student might like to use Many projects feature an introductory video to promote self study in those students most interested in electronics and programming Just follow
162. cuit load like there would be if the voltage follower circuit was replaced with a wire Chapter 9 Op Amp Building Blocks Page 329 Figure 9 6 Voltage Follower Test Circuit PropScope CH2 PropScope CH1 PropScope GND I wey Al Y oOo0 Of x2 The op amp s inputs have very high input resistances in the 200 MQ range This means that its non inverting input will place almost no current load on the capacitor in Figure 9 6 So the capacitor will be able to hold its charge almost exactly the same way it did when no load was connected to it At the voltage follower s output it doesn t matter whether the load is a 10 kQ resistor a 2 kQ resistor or even an LED in series with a 470 Q resistor The op amp will supply whatever current it takes to keep the voltage at its output terminal the same as the voltage the capacitor applies to its non inverting terminal Of course that s provided the load isn t beyond the amount of current the op amp s output is designed to supply Page 330 Understanding Signals with the PropScope How it Works The rule for negative feedback op amps circuits is Op Amp Negative Feedback Rule If an op amp s inverting input senses its output through a circuit the op amp adjusts its output to make the voltage at the inverting input matc
163. d CH2 DAC trace above the blue CH1 positive negative RC decay trace Figure 8 7 5 Time Constant Capacitor Charge and Discharge E PropScope v1 1 0 File Edit View Plugins Tools Help Oscilascope Logic Analyzer Analog ps0 oa Dc AC Oft DC AC DAC Off Square Generate sne Fremvney Toot Sawtooth j gt mea Custom CQEdt otsez Elser High and low peak voltages Level sg SHZ i i n Measure Auto X Continuous ve A ml Normal J Step j Page 274 Understanding Signals with the PropScope In Figure 8 7 the upper red CH2 DAC trace shows a square wave that spends 5 ms at 4 V then 5 ms at O V This is the signal the function generator applies to the RC circuit s input With each voltage level current flows through the resistor and either charges or discharges the capacitor during each 5 ms time period The lower blue CH1 trace shows the capacitor voltage s response which alternates directions of RC decay curves Since the function generator voltage spends 5 ms which is 5 xt in each state the capacitor should charge to almost 4 V and discharge to almost 0 V In the Oscilloscope screen the CH1 voltage charges so close to 4 V and discharges so close to 0 V that it s difficult to tell it hasn t actually reached those values Since the general guideline for practical applications is that 5 time constants is enough to
164. d a trigger An oscilloscope trigger aligns the plot to an instant when the voltage either rises above or falls below a certain level It also makes periodic signals like our square wave signal stay still in the Oscilloscope screen Try this v Click the Trigger settings tab and set the Mode to Continuous the Edge to Rise the Level to Auto and the Source to CH1 The display should now stay still in the Oscilloscope screen Two new controls should have also appeared the Trigger Voltage level control and the Trigger Time control These controls set the time and voltage that the signal has to pass through to trigger a refresh of the display a trigger event The Trigger Voltage control should have appeared to the left of the channel trace as shown in Figure 3 9 and the Trigger Time control should have appeared in the Plot Preview The Plot Area bar may have repositioned to its default position which is all the way to the left of the Plot Preview and the Trigger Time control will probably be positioned most of the way to the left in the Plot Area bar Page 80 Understanding Signals with the PropScope Figure 3 9 Trigger Setting Adjustments A PropScope v2 0 1 izio x Fie Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Dc AC Off DC_AC DAC Off EF Square Generate Sine Frequency 10kHz Sawtooth panna 160 Triggered T
165. d of focusing on the voltage the PWM command sets across the capacitor we ll look at the binary signal the BASIC Stamp transmits that causes the capacitor to charge to that voltage v Enter Test 1 Channel Dac bs2 into the BASIC Stamp Editor and run it Test 1 Channel Dac bs2 T SAC Ckijoelenior aelliceree alin Wi INC WNC eulseewiie Tee M 25 Ww SSTAMP BS2 Target module BASIC Stamp 2 EO PBASTOR2 SI Language PBASIC 2 5 DEBUG Prooram running Debug Terminal message DO Main Loop PWM 14 64 5 P1225 Ww ico Pik eajomeiic ie LOOP Repeat main loop X3 Vin P14 1 kQ PropScope CH1 PropScope GND X2 JO0000 JOOOCOO uoo 0mm00000000 6 0mmm000000006 oo0000000000000 Chapter 4 Pulse Width Modulation Page 121 PropScope Ch2 Figure 4 13 Probes for P14 PWM 1 pF Signal and DAC Output 4 Figure 4 14 Example Wiring Diagram for Figure 4 13 Page 122 Understanding Signals with the PropScope PWM Command Duty Cycle Measurements In Figure 4 15 channel 1 displays the DC voltage across the capacitor That can be considered the DAC circuit s output signal Channel 2 displays the PWM signal the BASIC Stamp applies to the DAC circuit s input This PWM signal has a duty cycle that determines the capacitor s volta
166. d the lower and upper sine wave s features are vertically aligned with no shift to the right or left Certain circuits introduce delays between two signals at their inputs and two ones at their outputs The result is an apparent left or right shift of one of the signals in the oscilloscope In the XY Plot this would produce an elliptical or even circular shape or a line with a different angle instead of the 45 slope shown in Figure 1 8 In addition to quickly determining phase relationships the xy plot can also reveal relationships between signals at different frequencies Figure 1 8 XY Signal Plot TEST EQUIPMENT USES AND PROPSCOPE EXAMPLES The voltmeter oscilloscope function generator logic analyzer and spectrum analyzer are arguably five of the most widely used pieces of test equipment in the electronics industry Many engineers technicians repair specialists students and hobbyists use them to measure signals at various test points in circuits and systems Specialized versions of many of these tools can also be found in the automotive and biomedical industries as well as in many science labs Page 18 Understanding Signals with the PropScope Most of the electronic devices we use on a daily basis were designed by groups of engineers and tested by engineers and or technicians Each subsystem underwent multiple circuit and signal test measurements interleaved with troubleshooting to get to the finish
167. d wire needs to be adjusted A factory mounted servo horn does not necessarily make the wire point in the exact directions shown in Figure 4 9 The horn typically has to be removed rotated slightly and replaced before it ll point a twist tied wire just like it does in Figure 4 9 What s a Microcontroller Chapter 4 Activity 2 explains the procedure in detail The angle vs pulse time values in Figure 4 9 are approximate More precise positioning may require some experimentation Keep the PULSOUT Duration arguments in the 350 to 1150 range PULSOUT command Duration values near the 250 or 1250 limits could cause the servo to push against its built in mechanical limits There are also tips on finding the PULSOUT Duration values just inside these limits in What s a Microcontroller Chapter 4 Center Position Test Program ServoCenter bs2 positions the horn at about the 90 degree mark in Figure 4 9 and holds it there the 90 direction That s okay whatever position the loop points while the program is running you can consider that 90 Another option is to remove the screw that attaches the servo horn pull it off the output shaft rotate it slightly then push it back on to correct the error Make sure to push the horn back onto the output shaft while the program is running That way it ll be as close as possible to the 90 mark v v v Your servo horn will probably not point the twist tied jumper wire straight up in R
168. definite indicator that something is not performing as expected v Try comparing your BASIC Stamp module s measurements using Test Phototransistor Adjustment bs2 against the PropScope decay measurements See the difference between BASIC Stamp and PropScope measurement here Chapter 8 RC Circuit Measurements Page 311 Figure 8 37 How PWM Determines the Starting Voltage S PropScope v1 1 1 File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA 100ps 200ps S500ps Ams DC_AC DAC Off Generate Be a i ona Time rms Triggered Trigger Measure LL T Position h S54ms 3 264 G2 NE 3 verica i Emms iA wa Horizontal el 4 TELNE 5 Float It turns out that the cause of the measurement difference is the fact that the PwM command changes the I O pin direction to input when it s done In D A conversion with no circuit load that change from output to input allows the capacitor to hold its charge and voltage However our light sensor circuit has the phototransistor that starts draining the capacitor as soon as the PWM command is done So after the PwM command finishes we can infer from the measurement that there s about 200 us of capacitor voltage decay time before the RCTIME command starts Page 312 Understanding Signals with the PropScope The Pwm before RCTIME technique is still useful because it does make it po
169. der is working See the Voltage Divider Error Propagation section of the Understanding Signals Supplement which is available as a free PDF online from the Downloads section of www parallax com go PropScope Your Turn Other Resistor Combinations v Repeat the voltage divider tests for the other resistor combinations discussed at the beginning of this activity Chapter 2 DC Measurements Page 53 The Potentiometer an Adjustable Voltage Divider In brief a potentiometer has a resistive element that spans its A and B terminals see Figure 2 24 and a knob on top for adjusting where the W terminal contacts that resistive element As you turn the knob one direction the resistance between W and B decreases while the resistance between W and A increases Turn the knob in the other direction and the resistance between W and B increases as the resistance between W and A increases The sum of these two resistances will always add up to the resistance between A and B which is 10 kQ for the potentiometer in the Understanding Signals kit Figure 2 24 Potentiometer Illustrations from What s a Microcontroller A A 10 KQ F ai 10 KQ WS Pot _ Pot If you connect the potentiometer s A terminal to Vdd and the B terminal to Vss you will have a voltage divider output at the W terminal that you can adjust by turning the knob aN More Stamps in Class Experiments with Potentiometers The potentiometer pot is J introduced as a var
170. dient in negative feedback applications An op amp s open loop gain decreases with LL higher frequency signals and as that gain decreases so does its performance Each tl op amp s datasheet has one or more graphs of its open loop gain s response to frequency When shopping for op amps make sure to check those graphs and verify that the open loop gain is still high in your application s frequency range ACTIVITY 1 COMPARATOR An op amp comparator compares the voltage difference between an op amp s inverting and non inverting inputs If the non inverting input voltage is greater than the inverting input voltage the comparator sends a high signal If the non inverting input voltage is less than the inverting input voltage it sends a low signal With a high open loop gain the comparator will detect even minute differences in voltage and send high or low signals as a result This is useful for converting very small voltage differences into binary values The comparator s high and low signals are like the binary high low signals we 4D programmed BASIC Stamp I O pins to transmit in earlier chapters However the voltages of _ _ the comparator s high and low output signals are not necessarily 5 and 0 V Instead they w are determined by a combination of the op amp s supply voltages and its output characteristics An example of a comparator application is a clock signal The small voltage fluctuations
171. ding Signals with the PropScope Inside With Load Voltage Measurements on the Board of Education The more current a circuit draws the lower the I O pin s high signal voltage Figure 2 32 shows how the I O pin driver circuit inside the BASIC Stamp Interpreter chip is supplied with 5 V With the LED circuit s current draw the I O pin driver s output is only 4 34 V If you replace 220 Q with a larger resistance like two 220 Q resistors in series the LED circuit would draw less current from the I O Pin So the I O pin driver circuit would output a high signal voltage that s closer to 5 V The CH1 measured voltage would probably be in the 4 6 V neighborhood A 1 kQ resistor would make the LED circuit draw even less current and the CH1 voltage measurement would be even closer to 5 V Of course we saw earlier that with no load the high signal voltage is very close to 5 V DoR a CH1 4 3V Vdd 5V E 43V Figure 2 32 I O Pin Driver s Response to Current I O Pin Driver Circuit Pin I O Pin Socket 21V Load TiS eC L Board of Education Microcontroller Vss Inside With Load Voltage Measurements on the HomeWork Board The BASIC Stamp HomeWork Board has 220 Q resistors built into the board between the Interpreter Chip T O pins and the I O pin sockets you use to make connections to the breadboard You can see those resistors on the left of Figure 2 33 As mentioned earlier they help protect the T O pins
172. ding or removing offset from a signal Figure 9 1 shows a picture of the Understanding Signals Kit s LM358 op amp along with a pin map similar to one you might find in the device s datasheet This integrated circuit IC has two op amps shown as triangles labeled A and B The activities in this chapter will focus on using one op amp to perform operations on one or two signals Each op amp can be configured separately and they can both perform operations on signals in parallel They can also be cascaded to perform a series of operations on one or more signals Figure 9 1 LM358 IC Photo and Pin Map Page 322 Understanding Signals with the PropScope Figure 9 2 shows the op amp symbol with each of its connections labeled The numbers by each terminal correspond to the pin map numbers for op amp A in Figure 9 1 The op amp has two supply voltage inputs one positive and one negative It also has two signal inputs The one with a label is called the non inverting input and the one with a label is called the inverting input The notations for some of the terminals in Figure 9 2 might vary from one datasheet to the next as well as from one manufacturer to the next but all the LM358 manufacturers and their datasheets follow the same conventions for the terminals names and their positions around the triangular op amp circuit symbol The one exception to this is that the top bottom positions of the non inverting and inverting input termi
173. dule s r B lt Synchronous Serial EEPROM Program Memory Microcontroller n Interpreter Chip Wi Page 150 Understanding Signals with the PropScope Another example of a synchronous serial device is the ADC0831 analog to digital converter in the Understanding Signals kit This integrated circuit IC is an 8 bit analog to digital converter A D converter or ADC An analog to digital converter measures an analog voltage and expresses it as a digital value 8 bit refers to the number of binary bits in the digital value An 8 bit number has 8 binary digits and can store any value in the 0 to 255 range This ADC is a National Semiconductor NSC product and is designed to communicate with the NSC Microwire synchronous serial protocol The activities in this chapter will chronicle the development and testing of PBASIC code that makes the BASIC Stamp obtain digitalized voltage measurements from the ADC0831 chip using synchronous serial communication ACTIVITY 1 ADC0831 ANALOG TO DIGITAL CONVERTER Figure 5 2 shows a picture of the ADC0831 analog to digital converter chip along with its pin map The pin map is similar to the one you will find in the ADC0831 datasheet s Connection Diagrams section You can download this datasheet from www national com 2 vin CLK Figure 5 2 ADC0831 A D Converter Picture and Pin Map ADC0831 Here is a condensed explanation of the pin map with details that were drawn mainly from the datash
174. e Fall Level Auto Source CH1 v Trigger Time control Adjust vertical crosshair to 2 Time division line Figure 8 17 Two Decay Measurements Separated by a 100 ms Pause 8 PropScope v1 1 1 File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Generate Sine Frequency 10kHz sen a TV 4 80 160 Custom Q Time ms Triggered Measure ode e i 0e e MED ne p cea Continuous j Step In Figure 8 17 it s difficult to see any of the decay measurement because the PAUSE command is 100 ms but the decay is only 872 us That s less than 1 100 of the PAUSE time Figure 8 19 shows an example of a closer look at the decay portion of the signal The fact that the Trigger Edge was set to Fall made it so that reducing the Horizontal dial to 500 ps div zoomed right in on the decay measurement With this view the cursors can be used to measure the decay time and verify the BASIC Stamp module s measurement Chapter 8 RC Circuit Measurements Page 287 The PropScope uses a full cycle to calculate average voltage When the Trigger tab s Level switch is set to Auto it uses this level for positioning the Trigger Voltage control When you zoom in on decay times to take cursor measurements there s no full cycle so it s hard for the PropScope to know what the automatic trigger level should be Also since we are measuring the
175. e 0 V level removing any offset you might see if you viewed it with DC coupling In some measurements DC offset doesn t matter but other properties of the sine wave do In those situations AC coupling can simplify the measurements especially if the two signals have different DC offsets Another important setting is the Trigger tab Level switch s Normal setting This allows you to pick your own voltage level for triggering the display This setting will be useful for aligning the trigger event to a high peak in the signal with two sine waves added together Figure 7 19 shows the AC coupled D7 note from the BASIC Stamp with Normal instead of Auto trigger voltage level It also shows the other settings we ll use to compare the individual frequencies against the frequencies added together v Click the Cursor tab s Horizontal and Vertical buttons to toggle them off v Oscilloscope dials Horizontal 500 us div Vertical CH1 0 5 V div Vertical Coupling Switches CH1 AC CH2 Off v Click and drag the CH1 trace up down and make the CH1 1 V division line up with the bottom of the oscilloscope display Trigger tab switches Mode Continuous Edge Rise Level Normal Source CH1 v If needed adjust the Trigger Voltage control to make the horizontal trigger crosshair line up with the CH1 ground 0 V division line v Trigger Time control Adjust to make one of the sine wave s peaks line up with the middle time divisio
176. e It lists computer system requirements and guides you through installing the PropScope software and connecting the hardware Go to www parallax com go PropScope and find the Downloads section y Download the PropScope Quick Start Guide and follow the instructions v When you get to the step titled Measure continue from here Chapter 1 PropScope Introduction and Setup Page 19 Many of the activities in this book involve measurements of BASIC Stamp 2 microcontroller signaling as it interacts with circuits These circuits are built from parts and components included in the Understanding Signals with the PropScope Kit In these activities you will use the BASIC Stamp Editor to load example programs into the microcontroller The BASIC Stamp Editor software is available for free download from the Parallax web site For best results get the latest version before continuing Go to http www parallax com basicstampsoftware and download and install the latest BASIC Stamp Editor v If you have never used your BASIC Stamp 2 and Board of Education or HomeWork Board before click the BASIC Stamp Editor s Help menu and select Getting Started with Stamps in Class Follow the instructions for connecting your board and testing your BASIC Stamp programming connection If you do not already have a BASIC Stamp Microcontroller Consult the Kit Choices section at www parallax com go WAM If you are new to microcontrollers The Understandi
177. e BASIC Stamp transmits as it runs Alternate High Low Signals bs2 Figure 3 5 shows the Oscilloscope view s representation of the high low voltages transmitted by the BASIC Stamp as it executes the program The channel 1 trace is monitoring the P15 signal and the channel 2 trace is monitoring P14 When the channel 1 voltage is high the voltage is 5 V When it s low its 0 V The same applies to channel 2 except when the channel 2 signal is high the channel 1 signal is low The waveform this signal pattern generates is called a square wave If the plot is currently stopped click the Run button to restart it Restart the Channel 2 trace by moving the coupling switch below the CH2 Vertical dial from Off to DC Verify that the Horizontal dial is still set to 500 ms Set both Vertical dials to 5 V Click and drag the traces up down to arrange them as shown in Figure 3 5 Verify that the high signal for each trace is 5 V and the low signal for each trace is 0 V Remember that the voltage scale for the channel 1 trace is on the left of the Oscilloscope screen and the scale for the channel 2 trace is on the right v v SAMS Figure 3 6 shows the Oscilloscope view s Measure tab which now has more useful voltage information The highest voltage Vmax is 5 01 V and the lowest voltage Vmin is 0 V The peak to peak voltage Vpp is the difference between Vhigh and Vlow and it s 5 01 V The Average voltage no longer represents a DC vol
178. e degree measurements are called phase angles The Greek letter theta 0 is typically used to denote a phase angle and phase angles are also typically expressed in degrees Figure 7 26 shows some examples on a graph of sin 0 vs 8 over 360 Since a full sine wave cycle repeats every 360 any fraction of a full cycle can be measured as a certain number of degrees Even though sine wave cycles take different amounts of time to repeat at different frequencies phase angle measurements give us a way of describing how far into the cycle a certain time is for a sine wave at any given frequency For example 90 is 1 4 of the way into the cycle If the sine wave s frequency is 1 kHz that happens at 0 25 ms into the sine wave If the frequency is 2 kHz that happens at 0 125 ms into the cycle Regardless of the frequency if the time is 1 4 of the way into the sine wave cycle the sine wave is at a phase of 90 Figure 7 26 Sine 8 Vs and Time for 1 and 2 kHz Signals Phase angle 0 0 90 180 270 360 For f 1 kHz 0 ms 0 25 ms 0 5 ms 0 75 ms 1 0 ms For f 2 kHz 0 ms 0 125 ms 0 25 ms 0 375 ms 0 5 ms Page 254 Understanding Signals with the PropScope Phase angle measurements can be used to determine properties of circuits and or the effects they have on signals The next activity will use phase angle tests to determine the delay an RC circuit adds to a sine wave System Stability Phase angle measurements are also t
179. e of that waveform v v v v v In the BASIC Stamp Editor modify One or Two Notes at a Time bs2 by placing an apostrophe to the left of FREQOUT 9 60000 2489 to comment it out Delete the apostrophe to the left of FREQOUT 9 60000 2960 to uncomment it Load the modified program into the BASIC Stamp Use the Trigger Time control to line up one of the peaks of one sine wave with the middle time division line in the screen again Take a screen capture and save it as 2960 Hz bmp Now that the individual notes have been examined and their screen captures stored play both notes together Then examine the resulting signal and take a screen capture of it too KASS sS v In the BASIC Stamp Editor comment out FREQOUT 9 60000 2960 Uncomment FREQOUT 9 60000 2489 2960 Load the modified program into the BASIC Stamp Slide the Trigger Voltage control to make the horizontal crosshair line up near the top of the highest peak in the waveform to keep it from scrolling Use the Trigger Time control to line up the highest peak with the middle time division line For an example see the bottom waveform in Figure 7 20 Take a screen capture and save it as 2489 and 2960 Hz bmp Figure 7 20 conveys the basic idea of how adding two sine waves together works Actually both sine waves are divided by 2 first and then added for the result at the bottom of the figure For example a peak on the top sine wave added to a valley in the middle
180. e of the waveform and the make the square until you get this result HEHHE The CH1 probe adjustment procedure will have to be repeated for CH2 Since the PropScope cannot monitor CH2 while the function generator is running you ll have to connect the probe you would normally connect to CH2 to CH1 wave square v Set the X1 X10 switch in the CH1 probe rod back to X1 Y Disconnect and swap the BNC connectors Now the BNC connector with the red probe marker should be connected to CH1 and the one with the blue probe marker should be connected to the DAC Card s function generator output Chapter 6 Asynchronous Serial Communication Page 203 v Set the switch on the probe connected to the CH1 BNC connector to X10 v Verify that the switch on the probe connected to the DAC Card s function generator BNC connector is set to X1 v Perform the potentiometer adjustment shown in Figure 6 21 for the second probe Now that both probes have the proper trim settings the probe with the blue markers should be reconnected to the PropScope s CH1 BNC port and the other one should be connected to the CH2 BNC port Reconnect the blue marker probe to the PropScope s CH1 BNC port y Reconnect the red marker probe to the PropScope s CH2 BNC port Configure Probes for RS232 Measurements Remember that the RS232 voltages we ll be measuring might exceed the PropScope s 1X probe 10 V measurement limits Although
181. e rod and the other on the BNC connector as shown in Figure 1 9 With this setup when you connect a probe to the circuit all you need to do is check the marker band s color to know which color coded information to check in the PropScope software v Make sure one probe has matching red color bands on its probe rod and BNC connector v Make sure the other probe has matching blue color bands on its probe rod and BNC connector Figure 1 9 Probe Rod and BNC Connector Adjustments BNC stands for Bayonet Neill Concelman Bayonet is name of the latching mechanism and Neill and Concelman are the names of the connector s inventors Chapter 1 PropScope Introduction and Setup Page 21 Step 2 Set the probe gain switch to X1 The probe rod in Figure 1 9 also has a switch labeled X1 X10 These settings can be pronounced times one and times ten Notations of 1x and 10x are also common along with pronunciations of one X and ten X These settings will be explained in more detail later in the book For now it s important to make sure that both probe rod switches are set to X1 v Check each probe rod and make sure it is set to X1 Step 3 Set probe gain in the PropScope software to X1 A probe set to X10 reduces the signal voltage sent to the measuring device to 1 10 of the voltage applied to the probe This voltage scaling is part of a circuit inside the probe that reduces the interactions with
182. e still getting sent once every second The Debug Terminal verification can be useful for situations when you re not sure if the Oscilloscope display should be updating or not v Enter and run Letter A to P11 bs2 Letter A to Pll bs2 Transmit A to P11 and Debug Terminal once every second STAMP BS2 Target module BASIC Stamp 2 TERS PBASTCR2MSN Language PBASIC 2 5 PAUSE 1000 1 second delay before messages DO Main loop SEROUT ii 8A pA LUA Seog Palla DEBUG WA UF Ws ORCIANO A to Debug Terminal BINS MAN CIR PAUSE 1000 1 second delay LOOP Repeat main loop Letter A Test Measurements Figure 6 9 shows the letter A again It s important to verify that your display shows all the transitions and states in the Oscilloscope screen before continuing v Verify your PropScope s Horizontal Vertical and Trigger settings against Figure 6 9 v Verify that your Trigger Voltage control is at about 2 5 V and that the Trigger Time control is at the 2 time division 0 4 ms v Make sure you ve got a good view of this on your PropScope The time per division options on the Horizontal dial are not the only options and this is a case where a custom time per division could come in really handy Remember from Activity 2 that if the baud rate is 9600 bits per second bps then the bit time is tbt 1 9600 bits second 104 17 ps bit Wouldn t it be nice is if the Oscilloscope had a 104 us units per divisio
183. e time cursors Adjust the green A time cursor so that it intersects with where the CH2 DAC sine wave crosses the CH2 ground 0 V line Adjust the purple B time cursor so that it intersects with where the CH1 sine wave crosses the CH1 ground 0 V line Get the phase delay time measurement from the Cursor display s A time difference calculation The example in Figure 7 33 shows a At of about 59 6 us With the measured At of 59 6 us and a period T of 333 us the phase delay is ET ae OM ae ead T 33 us Chapter 7 Basic Sine Wave Measurements Page 263 Figure 7 33 Determine At for Phase Comparison E PropScope v1 1 0 a File Edt View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Cursor A positioned where CH2 DAC signal R crosses OV 2 i ial ursor B position Di See ap i where CHT signal o DC AC Off DC AC DAC Oft j Square Generate P h ase j 2 Sne Frecueney Saz_____ Delay ae amea sd I 5 Time fa sa ee oo ee oe ee ee eee Yew 3 40 s0 120 160 Custom Cheat ra E CH1 v Time ys Trigger i Clrsor Mode Edge Off Rise Continuous Step le In Figure 7 33 you could actually take the measurement by counting time divisions The CH2 DAC sine wave crosses the ground line at the 40 us time division line and three time divisions later the CH1 sine wave crosses the 100 us division line So the time de
184. e wave components A Fourier Series is a sum of sine waves that creates an arbitrary waveform It is named after Joseph Fourier the French mathematician and physicist who developed the technique of describing certain mathematical functions as sums of sine wave equations _ J A Fourier Transform is the inverse of a Fourier Series Given a mathematical function a ew Fourier Transform resolves it into its Fourier Series of sine wave components A Fast Fourier Transform is a widely used technique for determining a signal s sine wave components using fewer steps and less computing time Microcontrollers and other systems that exchange information with high low signals have the potential to cause radio frequency RF interference A radio transmitter applies a sine wave of a certain frequency to an antenna to broadcast A radio receiver tuned for the transmitter s broadcasts detects them as sine wave voltage variations it gets from its own antenna It turns out that binary signals like square waves contain many sine waves with many different frequencies So when a microcontroller applies a square wave to a wire antenna it has the potential to act like a radio transmitter that generates RF interference at many different frequencies Many electronic devices have to be tested to ensure that they do not broadcast at certain frequencies with signals that are strong enough to be received as interference by nearby radio receivers To tes
185. eader who wants to invent or will be faced with a design project at some point down the road All the circuits circuit microcontroller and design technique examples measured in the book are standard ingredients in electronic product designs and can be found in a myriad of products projects and inventions The measurement techniques are also widely used in industry and at various levels in technical and engineering educational programs The measurement techniques in this book are introduced in a variety of courses and grade levels This text leans toward qualitative introductions and when math is required it uses the simplest expressions available This helps keep it compatible with various levels provided by the various disciplines grade levels and their theory textbooks For introductory and survey courses at home students and hobbyists this book can be studied in step by step detail More advanced courses can use this book as a primer or sections of this book can be studied before lab work that requires a particular measurement technique AUDIENCE This text is designed to be an entry point to technology literacy and as an easy learning curve for embedded programming and device design The text is organized so that it can be used by the widest possible variety of students as well as by independent learners Preface Page 7 SUPPORT FORUMS Parallax maintains free moderated forums for our customers covering a variety of subje
186. eak voltages Page 276 Understanding Signals with the PropScope Figure 8 9 zooms in to 2 ms division with the horizontal scale for a closer look at voltage as the capacitor charges Since the Trigger Time control is set to the 2 time division line the positive edge of the CH2 function generator signal lines up with that division line and its negative edge lines up with the 7 time division line Between 5 and 10 ms into the high signal the CH1 RC circuit output voltage changes very little if any This makes sense since 5 ms is the 5 t mark and the capacitor should be charged to 99 32 of the applied voltage At that point there is very little room for it to increase its charge during the remaining 5 ms v Change the Horizontal dial to 2 ms div for the view in Figure 8 9 Figure 8 9 Charging the Capacitor for 10 ms A PropScope v1 1 0 ioj xi File Edt View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Oseili DC AC Oft DC_AC DAC Off Square Generate e Fremency Sire i rs Continuous jl Step Here is a trick to remember You don t have to move the screen back and forth to switch from the view of the capacitor s voltage response as it charges to its voltage response as it Chapter 8 RC Circuit Measurements Page 277 discharges Instead just change the Trigger Edge from Rise to Fall Your display should
187. eck we ll use smaller settings to zoom in on the PWM signal activity v Dial adjustments Horizontal 1 ms div Vertical CH1 1 V div CH2 1 V div v Vertical coupling switches CH1 DC CH2 DC v Trigger tab Mode Continuous Edge Rise Level Auto Source CH2 v Trigger Time control adjust vertical crosshair to second time division E PropScope v1 1 1 iol xi Figure 8 25 File Edt View Plugins Tools Help Overview of Osciloscope Logic Analyzer Analog DSO LSA Signal Activity 100ps_200ys S00ps ims TT DN Since we expect PWM to be a series of 5 V high low signals these sporadic voltage levels are a clue that the Horizontal time division A l E DC_AC DAC Off setting can be ctivity repeats sau J Generate reduced for T 7 T T s T T requency mz OkHz H Py Sawocth are more signal o ae AG DAC Gircult Output Custom Eat otte detail Time Triggered CH2 v j ea Page 296 Understanding Signals with the PropScope Oversampling vs Aliasing The PropScope takes a series of voltage measurements called samples and sends them to the PropScope software to be displayed When there are more than enough samples to represent the signal being measured it is called oversampling lf there are not enough samples to properly display the waveform it is under sampled lf there are so few samples compared to the frequency that
188. econnect power to your board If you have a Board of Education make sure to move its power switch to position 2 so that it supplies power to the servo ports Enter ServoCenter bs2 into your BASIC Stamp Editor and run it What s a Microcontroller ServoCenter bs2 Hold the servo in its 90 degree center position SSTAMP BS2 Us Sey Ns ZA Sy PAUSE 1000 DEBUG Program Running CR DO PULSOUT 14 750 PAUSE 20 LOOP Page 114 Understanding Signals with the PropScope While the program is running the servo should resist light twisting force applied to the horn to maintain its position v Apply light twisting force to the servo horn with only your fingertips DO NOT FORCE IT v The servo should prevent the horn from turning and the motor inside should hum a little bit as it resists and holds the correct position In the ServoCenter bs2 program the DO LOOP repeats the PULSOUT and PAUSE commands indefinitely As mentioned earlier the Duration argument in PULSOUT Pin Duration sets the pulse s duration in terms of 2 us increments So the PULSOUT command sends a pulse brief high signal to P14 that lasts 750 x 2us units That s 750 x 2x10 s 1500 x 10 s 1 5 x 10 s 1 5 ms After the pulse is done the PAUSE 20 command delays for 20 ms Then the DO LOOP repeats beginning with another pulse then another pause then another pulse then another pause and so on Keep in mind that different PULSOUT Dur
189. ed positive and negative edges This particular pulse width measurement was made with PULSOUT 14 1000 Figure 4 12 Cursors for Pulse Width Measurement A PropScope v2 0 1 Fie Edt View Plugins Tools Help Oscilloscope Lovie Anais Analog DS A ees ea ie oi mk a hail ER Ds Pulse Width is 2 ms Continuous Step Measure Set Level to Normal Cursor Settings Page 118 Understanding Signals with the PropScope The PropScope may have difficulty finding the trigger event when there s just one pulse Usually it takes a couple of cycles worth of data to calculate the average voltage used for automatically setting the trigger voltage level So we are going to manually set the trigger voltage for this measurement by setting the Trigger tab s Level switch to Normal and then adjusting the Trigger Voltage Level control v v KSSS Ax In the Trigger tab set the Level switch to Normal Drag the Trigger Voltage Level control up to between the 3 and 4 V division lines as shown in Figure 4 12 Zoom in on the time scale by setting the Horizontal dial to 500 ps div Verify your 2 ms measurement with PULSOUT 14 1000 Change the command to PULSOUT 14 1050 and load the modified program Watch the horn carefully as you load the modified program into the BASIC Stamp It should take a new position slightly counterclockwise of the pos
190. ed product Student and hobby projects often employ similar step by step approaches Many devices also need to be repaired if they malfunction which also involves test measurements There are many different types of signals and measurement techniques employed in the various fields of electronics and design By following the activities in this book you will get some initial hands on experience with many of the more common signals DC supply and AC voltage Binary signal levels and timing for control and communication Digital signals that describe analog voltage measurements Sine waves for audio and analysis of filters and other circuits Sine wave components of audio digital and infrared signals Exponential decay for sensor measurements Amplifier signal conditioning Along the way you will also see a variety of circuit design and microcontroller programming techniques that can be found in common electronic products If you completed What s a Microcontroller Robotics with the Boe Bot or other Stamps in Class texts before starting here you will also have the opportunity to use the PropScope s measurement tools to more closely examine the signaling involved in indicator and motor control sensor monitoring and communication with peripheral integrated circuits and other computers ACTIVITY 1 HARDWARE amp SOFTWARE SETUP The PropScope Quick Start guide is packaged with the PropScope and is also available from the PropScope product pag
191. ed the voltage drop across the resistor Disconnect the BNC connector from the DAC Card s function generator port and connect it to the CH2 port V Set the CH2 coupling switch to DC It s the sliding switch right below the CH2 Vertical dial Connect the CH2 probe as shown in Figure 2 35 Figure 2 35 Measure Voltage at Both Resistor Terminals Vdd Vin hs x3 i P14 vs POO oofoo pal Badon Agoo pA ogoni ogor PropScope CH1 N P12 og Hee oF m 5 f 4 PropScope CH2 LED y 4000 00 PropScope GND Bue 38 P7 ooo ml Vss P6 i ol o P4 P3 o P2 fai C m a DI DI Ooi DI Figure 2 36 shows the resistor voltage measurements and current calculations for the Board of Education and Figure 2 37 shows the same measurements and calculations for the HomeWork Board The voltage Vr across the R 220 Q resistor in the LED circuit was the Measure tab s Channel 1 Average voltage minus the Channel 2 Average voltage measurements Knowing both Vpr and R the calculations for Ir Vg R are shown at the right side of each figure v Measure the voltage at both resistor terminals while the LED circuit is connected to the I O pin and emitting light Chapter 2 DC Measurements Page 65 v Calculate the voltage Vg across the 220 Q resistor by taking the difference of the volta
192. eeeeeeeeeeeeeeeeenteeeneetenees 68 Activity 2 High Low Signal Voltages and Frequencies cccceeeceeeseeeeeeeeeeeeeeneeteneeeeaees 72 Activity 3 Multiple High Low Signals cecccesceeeseeeeeeeeeeeeeeeeeeeeeseaeeeeaeeseaeeseaeeseneeeeaaes 85 Activity 4 D A and function generator Waveforms ceeesceeeeeneeeeeeneeeeeenaeeeeeeneeeeneeeees 90 Activity 5 Simulated Heartbeat ceeccececeeeeeeeeeeeeeeeeeeeeeeaeeseaeeseaeeseaeeseeeseeeeeeeeseeeeeaaes 96 SUMMALY 2 Sisepecensesss A deans uot kalde Abe cence dhnaces A E EN 104 Chapter 4 Pulse Width Modulation scccssscesseeeeeeeeeseeeeeneeeeeeeeeeseeeseseeneneeeeneas 105 Pulses for Communication and Control cecceeseeseeeeeeeeeeneeeeeeseneeeeaeeseeeseaeeseeeseeeenaees 105 Activity 1 Pulses for Servo Control ccecceeesceseeeeeeneeeeeeeeaeeseaeeseaeeseaeeseaeeseaeeseaeeseaeenaas 106 Activity 2 Duty Cycle in PWM DAC eeeceeeeceeeeeeceneeceeeeseaeeeeaeeeeaeeseneeseaeeseaeeseaeessaeenias 119 Activity 3 Infrared Object Detection oo ceeeeeceeeeeeeeneeeeeeeeeeeeeeeeseaeeseaeeeeaeeseaeeseaeeseaeetaas 125 Activity 4 Advanced Topic Pulses for TV Remote Communication ccccceeeeeeees 133 SUMMANY ee aE ote Rett salient i et ee 148 Chapter 5 Synchronous Serial Communication ccssseeneessseeeeeeeceeees 149 Synchronous Serial Devices ceeeeeesceeeseeeeneeeeeeeeeeeeeeseeeesaeeeaeeesaaeseeeeesaesee
193. eeeeneeeeaeees 270 Activity 3 RC Sensor Measurements with a Potentiometer cccscceeeeseeeeeeteeeeees 280 Activity 4 RC Circuits Role IN D A Conversion c cceecceeeeeeeeeeeceneeeeeeeteaeeeeeeeteneeeneeen 293 Activity 5 RC D A Converter Decay from Load eeeeeeeceeeeeeeeeeeeeeeeeeeeeteeseeeeetieeeeaeees 301 Activity 6 Phototransistor Light Sensor Example cccccscceeseeeeeeeeeeeeeeeeeeeeeeeeneeeeneees 305 Activity 7 Low pass Filter ce cceescseeesseeeeeeseneeeeseecenenseneeseseeaeeeseecenseseseeseneneeeeneenenees 312 SUMMALY ost civ aide ee et AA ie earn edi ee esa A N E es 320 Chapter 9 Op Amp Building BIOCKS csssccsseeeeeeeeesseeseseeeenseeeeeeeeeeseeeenseeeeeees 321 Operational Amplifiets minon eiaeia eaaa aE ar neuh oy AEE RENEO ERAN eran leona eae 321 Activity 172 GOmparatotic lt 2 c ceseceste eeesecese eae erena eaaa eee anrea Saip redea aa eaaet diarai 323 Activity 2 Voltage Follower as an Output Buffer ec eeeeceeeeeeeeeeteeeeneeeeeeeeeneeeteeeeaeees 327 Activity 3 Non inverting Amplifier sssesssesseeesrrsssrrssrirrerirrnrtirnstinnssiinnetinnnrtnnnntnnnnnnenn 332 Activity 4 Inverting Amplifier 0 0 2 eee ceeeeeneeeeeseeeeeeaeeeeeeaaeeeseaeeeeeeaeeeeeeaeeeseeneeeeeeeeeees 340 SUIMIMANY fo E E E ETT T E A E esti centereae leeiginee 345 Preface Page 5 Preface The Understanding Signals with the PropScope kit includes the PropScope to c
194. eeeesieeeeneeesieeeeeees 192 Activity 6 Probe the Serial Port ccccecceesceceseeeeeeeteneeeeeeeeeaeeseaeeseaeeeseeeseaeeeeaeeseaeeeeaeee 200 SUMMA Y EEE rA A AA A ATT 211 Chapter 7 Basic Sine Wave Measurements cccssccsseeeeeseeeeeseeeseeeseseeneeeees 212 Sine Wave Examples eaa a ear r a a a aaa e e e eaa E aaa iar aAa anias ENEAS 212 Activity 1 Sine Wave Amplitude and Frequency Tests ccecceeeseeseeeteneeeeeeeteneeeeeeees 212 Activity 2 DC Offset Tests neairt n aA ia e Erara Ano SEAIA KA TEEN aE Eaa 221 Activity 3 Measure BASIC Stamp Musical Notes 0 ccccceseeeeeeeeeeeeeeeeeeneeeeeeeesieeeeeees 228 Activity 4 Summed Sine Waves ccccccecceeeceeeeeeeeeeeeseaeeeeeeeseaeeeeeeeseaeeeneeeseaeesseeeseaeeesates 237 Activity 5 Sine Components with a Spectrum Analyzer ccceeccceeceeeeeeeteeeeeeeeeteeeeneees 245 Activity 6 Compare Two Sine Waves ccccceeceeeeeeeseeeeeeeeeeeeeeeeeeeeeeeeeeseeeeeeeetieeeenees 252 SUMMARY cori cea idiea aire ihe alcatel iad 265 Chapter 8 RC Circuit Measurements ccccceeeeseeeeseeseseeeeneeeeeeeeseeneeeeneeeeesees 266 Resistors Capacitors and RC Circuits cccccecesscceeseeeeeeseneeeeeesneeesseeeeeeseneeeessneeeeseaees 266 Activity 1 RC Growth and Decay Math ecceeesceeeeeeeeeeeeeeeeeeeeteaeeeseeeseaeeseaeeseaeeenaeen 266 Activity 2 RC Growth and Decay Measurements cceccceseceeeeeeeeteeeeaeeeeeeeten
195. eeseaeenseeenaas 149 Activity 1 ADC0831 Analog to Digital Converter eceeceseeeeeseeeeeeeeeneeeteeeeeneeeeeeeeeaes 150 Activity 2 Write Code From a Timing Diagram ceccceesceeeeeeeeeeeseeeseaeesseeeeeaeeseeeetaas 153 Page 4 Understanding Signals with the PropScope Activity 3 Verify Microcontroller Signaling ceccccaceeeeeeeeeeeeeeeteneeeeeeeseaeeeeeeeteaeeeeeten 155 Activity 4 Troubleshooting Examples eccccessceeesneeeeeeneeeseneeeeeesaeeeeeenaeeesenneeeeneeeeess 161 Activity 5 Refine and Test the Code eeccssceeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeseeseeeesieeeneees 167 SUMMA i e aye siediven Get hd esd da stein snare Ain ariel TAN ieies 173 Chapter 6 Asynchronous Serial Communication s cccsssseeeseseeeeees 174 Asynchronous Serial DeViC S eccceeseceeeceeeseeeeneeeeaeeeeaeeeeaeeseaeeseaeeseaeeseaeeseaeeseaeeseeeeeaeees 174 Activity 1 ASCII Codes oc eeeeeccecesceeseeeceeeeeneeeseeeeesaeesaeeesaeessaeseaaeesaaeeesaeesaeeeaeeseaeeeaees 175 Activity 2 First Look at Asynchronous Serial Bytes cceeeeceseseeeeeeeseeeeeeeeeteneeeeeeees 178 Activity 3 A Closer Look at a Serial Byte 0 cc ceeecececeeeeeeeeeeeeeeeeeeeeeeeneeeeaeeeeeeeesneeeeeees 184 Activity 4 True Vs INV rted oo ee eeeeeeeeeneeeeeneeeeeeeneeeeeeaneeeseaeeeeseaeeeeeeaeeesenaeeeeneaeeeesy 188 Activity 5 Hardware Flow Control eeceeeceeeeeeeeeeeeeeeeeeeeeeeeeeaeeeeeee
196. eet s Connection Diagrams Digital Interface and Analog Inputs sections e Vcc and GND power supply and ground connections for the chip e 6Vin the analog voltage input The ADC0831 measures the voltage applied to this pin e Vin and Vref set the limits of the measurement scale For example if 1 V is applied to Vin and 4 V is applied to Vref the Vin voltage will have to fall in the 1 to 4 V range All the ADC0831 s result values would then describe voltages in this range e CS the active low chip select input A transition from high to low starts an analog to digital conversion and the signal applied to this pin has to stay low Chapter 5 Synchronous Serial Communication Page 151 during conversion and communication A high signal to this pin disables the chip While the chip is disabled it will ignore communication and its DO data output pin becomes an input so that it doesn t interfere with other chips that might also use that line for communication with the microcontroller The character is shorthand for active low and an over bar that looks like this CS is a common equivalent notation e CLK the clock signal input This is the input that will receive the signal for synchronizing the binary value exchange e DO the data output that transmits the A D converter measurement as a series of binary 1 0 high low values These values are updated with the negative edge of the synchronizing signa
197. eful feature For example what if two BASIC Stamp modules are connected together and communicating with asynchronous serial communication Robot applications sometimes use a pair of BASIC Stamp modules that exchange data this way Without flow control when one BASIC Stamp is busy with other tasks like servo control and sensor monitoring it could miss serial bytes from the other BASIC Stamp With hardware flow control that BASIC Stamp can send a high signal on a separate line to let the other BASIC Stamp know that it s busy When it s ready for serial messages it can send a low signal The other BASIC Stamp stops sending bytes when it receives a high busy signal and resumes when it receives a low ready signal Systems can also use software flow control With software flow control a receiver sends sequences of serial bytes to tell the transmitter when it is ready or busy This approach is _ J common in systems that automatically buffer store in memory certain numbers of bytes ew and examine portions of them between tasks With BASIC Stamp 2 modules software flow control might save a few I O pins but it tends to take more code and memory to implement Chapter 6 Asynchronous Serial Communication Page 193 In this activity the PropScope will stand in for the BASIC Stamp that receives messages with flow control It might be busy sometimes sending a high signal and ready to receive serial messages other times sendi
198. egulators Figure 2 1 shows an example of a voltage regulator on the Board of Education and another on the BASIC Stamp Homework Board The job of a voltage regulator is to maintain a certain voltage level for the circuits it supplies current to regardless of whether they draw a little current or a lot The voltage of the battery or other source that supplies power to the system is called the unregulated input The voltage regulator s output which stays at a fixed value is called the regulated output The Board of Education and BASIC Stamp HomeWork Board regulators have 5 Vpc regulated outputs meaning they supply the circuits on the boards with a steady 5 Vpc regardless of the current demand Page 26 Understanding Signals with the PropScope Voltage Regulator ICs Figure 2 1 Voltage Regulators Board of Education and BASIC Stamp HomeWork Board voltage regulators each have a regulator integrated circuit IC and a capacitor Capacitors are part of the voltage regulator circuits Since DC supply voltages may vary they sometimes have to be measured before they get connected to certain types of loads a load is a circuit that draws current when voltage is applied Also if a system has a short circuit in it it can sometimes be detected as an unusually low supply voltage likewise with faulty supply sources and dead batteries Some systems even require supplies with certain characteristics like output resistance which can be de
199. end in zeros and their binary equivalents are 010 100 and 110 Figure 5 11 shows that the measured voltage on CH1 is still 3 3 V It would have to be in the 0 to 19 5 mV range for a Debug Terminal to display of all zeros Take a closer look at the BASIC Stamp module s second measurement attempt in the Logic State Analyzer The CS pin has to be set high and then low again to start a measurement In the second measurement the BASIC Stamp sends the clock pulses to CS but the ADC0831 s DO line doesn t reply because the CS line was not set high and then low again to start the measurement Page 164 Understanding Signals with the PropScope Figure 5 11 CS is stays low so DO does not respond to clock pulses after first measurement PropScope v2 0 1 Ez File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Oscille coi CE ESS Ce EM IE et Completed No GS negative Measurement ees eee LEE sae wlio en DC AC Off DC_AC DAC Off Voltage applied to Vin is still 3 3 V Time ms Before examining the next error the example code should be returned to its original state and tested Uncomment HIGH Cs by deleting the apostrophe Uncomment PAUSE 100 by deleting the apostrophe Make sure the potentiometer is still set to 3 3 V Load the corrected program into the BASIC Stamp V
200. enerated by nearby motors and other 1 electrical machines can cause voltage fluctuations in longer cable wires So the larger voltage swings in the signals are one way help ensure that the signals are still correct even when a nearby electric motor is turned on or off Set the PropScope controls as shown in Figure 6 25 and then use the CH2 probe to test the signal on the SOUT pin as shown in Figure 6 24 v Make sure that the Trigger tab s Level switch is set to Normal and the Trigger Voltage control is set to about 2 5 V Figure 6 25 P11 Transmitted Byte on CH1 Followed by Inverted Byte on CH2 Oscilloscope Logic Analyzer Analog DSO LSA DC_AC DAC Off Miar Generate Sine Frequency 10khz Sawtooth TY j 2 14 Et cin Oe ona 1 Wait for Trigger Time ms Trigger D G50 Gez202 Marin go i mE Ge Continuous Ir gt 3 l EA Step Chapter 6 Asynchronous Serial Communication Page 207 Serial Port Receive Test Code PC Serial Receive bs2 receives a byte from the serial port and immediately sends a copy of whatever it receives on P11 v Enter PC Serial Receive bs2 into the BASIC Stamp Editor and then click Run to load it into the BASIC Stamp PC Serial Receive bs2 Receives a byte from the PC s Debug Terminal and transmits it on Pll SSTAMP BS2 Target module BASIC Stamp 2 PSPBAS IC 2 5 Langua
201. er effects on the circuit or probe measurements Chapter 9 Op Amp Building Blocks Page 325 Vdd PropScope CH2 220 Q Pot 10 KQ Figure 9 3 Prop cope CRI Comparator Test Schematic 4 LM358 A PropScope GND Figure 9 4 Wiring Diagram Example of Figure 9 3 do O00 J oo00000 1OO0 JOOOOOODOODOOOOOLA JOooa X2 Comparator Test Measurements Figure 9 5 shows an example of how slight fluctuations at the op amp comparator s non inverting input result in high and low signals at the output The lower red CH2 trace shows the potentiometer wiper terminal s voltage as it is adjusted above and below the Page 326 Understanding Signals with the PropScope 2 5 V threshold and the upper blue CH1 trace shows the op amp comparator s output responding by switching high and low v Adjust the Horizontal Vertical and Trigger settings as shown in Figure 9 5 v Slide the Plot Area bar to the far right of the Plot Preview so you can see immediate voltage changes as you twist the potentiometer s knob v Use the CH2 trace voltage scale on the right as a guide for adjusting the potentiometer s voltage into the 2 to 3 V range v Adjust the potentiometer back and forth in the 2 to 3 V range and verify that the comparator circuit s output res
202. er gas gt Gan i aes am Figure 7 6 Signal Amplitude Compared to Speaker Volume Lowest Highest Volume Volume 2 2 2 o fe o sain oS 2 2 2 Vop 1V Vop 2V Vop 3V Page 218 Understanding Signals with the PropScope Test Frequency s Effect on Pitch Chapter 3 Activity 3 introduced frequency as the number of times a signal repeats itself per second and period as the signal s cycle time Figure 7 7 indicates the start and end of a single sine wave cycle The start of a sine wave s cycle is the point where it passes upward through the half way point on its way from valley to peak The cycle time can be measured to determine the sine wave s period T Then its frequency f can be calculated with f 1 T The PropScope s Measure display also shows the sine wave s measured period and frequency values for a given channel In this case the period can also be measured by counting the number of 100 us divisions in a cycle If the sine wave is exactly 2 5 kHz one cycle should span exactly four 100 yus time divisions Figure 7 7 Period of One Sine Wave Cycle Period T gt 02 0 4 06 08 1 CH1 ty Time ms Triggered a x Frequency LATY 402us Period 1 M nea RASKES E Frequency f 1 400 us 4 4 1 0 0004 s TEE 2500 Hz 2 5 kH R gt Fi
203. er than they do on the input wave This delay is called phase shift The RC circuit we have been using for the BASIC Stamp DAC voltages is a type of filter called a low pass filter Given an input sine wave it will reduce the amplitude and shift the phase of the output signal The amplitude change and phase shift depend on the combination of RC values and the frequency of the input signal In this activity you will measure amplitude and phase shift changes that an RC circuit introduces into a sine wave Later in Chapter 8 Activity 7 you will also use amplitude and phase comparisons to quantify properties of the filter The material in this activity uses certain concepts from Trigonometry v If you have not yet studied trigonometry read the sections in the list below They are in the Sine Wave Math chapter of the Understanding Signals Supplement which is available as a free PDF online from the Downloads section of www parallax com go PropScope o Degree Measurements Angles in Right Triangles and Simple Trigonometry Calculations Sine Calculations for Angles from 0 to 360 A Sine Wave Sine Calculations from 0 to 360 Sine Wave Phase Angle and Phase Shift 0000 Chapter 7 Basic Sine Wave Measurements Page 253 Sine Wave Phase Angle and Phase Shift The degree increments you are probably familiar with for measuring angles can also be used to measure how much of a sine wave cycle has elapsed When applied to a sine wave thes
204. erification that the program is in fact repeating its signals with a period of one second 1 s Since the signal takes about one second to repeat itself the frequency is also close to one repetition per second one hertz 1 Hz Chapter 3 Human speed Measurements Page 77 Figure 3 7 Measure Tab Frequency Info for 1 Hz Binary Signal Period Frequency Trigge TTY fect ANa Measure a Channel 1 Br civ NE ose Tiss mo lee GL 0 252 t MEL 0 95212 J s WM 5oy Mh asav t a W asav A osn Periodic Signal A signal that repeats itself at regular time intervals that is periodically Cycle A repetition of the signal Period The time it takes for one cycle repetition of a periodic signal You will see the terms period and cycle time used interchangeably in this book Frequency They number of times in a second a signal repeats itself Hertz A measurement of frequency in cycles per second Period T is the reciprocal of frequency f and vice versa In other words if you divide period into 1 you get frequency and if you divide frequency into 1 you get period eee and T T F So if you know the period is 100 ms 0 1 second you can use f 1 T to calculate the frequency f 1 0 1 s 10 Hz Likewise if you know the frequency is 10 Hz divide it into 1 and you will get a period of 0 1 s which is 100 ms Adjust the Signal Frequency Adjust the Displa Next let s examine what happens i
205. ering reprogramming or reproducing any data stored in or used with Parallax products Parallax is also not responsible for any personal damage including that to life and health resulting from use of any of our products You take full responsibility for your BASIC Stamp application no matter how life threatening it may be ERRATA While great effort is made to assure the accuracy of our texts errors may still exist Occasionally an errata sheet with a list of known errors and corrections for a given text will be posted on the related product page at www parallax com If you find an error please send an email to editor parallax com Table of Contents Page 3 Table of Contents PROPACG ceiceoenec dice e aE E e a a ee a A ar Ea eaa aN aes 5 ae EIn E EE A A TT TE A A E tees 6 SUpport FOrUMS scp horien eas a a Goliad on SEEE ee die ei ne 7 Reso rces for Educatif Sesani a tie ae p 7 Foreign Translations cs cereals aaa a ara ad ya ea eaae a a anadai 8 About the Author Sat ner etaa ea div eases een ee aaraa a ene 8 Special CONMIDUTOKS aaa a a e ae e T aa aeaa ae aaae a a aa aa eE ERER 9 Chapter 1 PropScope Introduction and Setup ssssssssssnnennnnnnnnnnnnnnnnnn nunne nnmnnn 10 PropScope Measurement Tools in a Nutshell eccceceeeeeeeeeeeeeeeneeeseeeeeeeeeseeeeeseeeseaeesseeen 11 Test Equipment Uses and PropScope Examples cceccceesceseseeeeeeeseeeeeeeeseeeseeeeseaeeesaees 17 Activity 1 Hardware amp Software
206. erity that the Debug Terminal still reports measurements of 170 Return the Horizontal dial to 1 ms div Verify that the synchronous serial communication still displays in the Logic State Analyzer screen like it did in Figure 5 8 AARAA RS Chapter 5 Synchronous Serial Communication Page 165 Recreate and Examine Error 2 Figure 5 12 shows what happens if the first PULSOUT CLK 200 is missing from the program the adcVal variable indicates the measurement is only half of what it should be vV Comment out the very first PULSOUT CLK 200 by placing an apostrophe to its left so that it looks like this PULSOUT CLK 200 Load the modified program into the BASIC Stamp Use the Debug Terminal to verify that your ADC measurement results have been cut in half v Compare the binary pattern in Figure 5 12 to the one in Figure 5 6 on page 157 Would you agree that the binary digits in Figure 5 12 shifted to the right by 1 digit v v alo x Com Port Baud Rate Parity COM1 z 9606 Z None z Data Bits Flow Control ex r M RTS Off AX DSR CTS Figure 5 12 Missing Clock Pulse Causes ADC0831 to 01010101 Return Half the 085 Measured Value Macros Pause Clear Close I Echo Off Figure 5 13 shows that the voltage is still 3 3 V and the signaling in the Logic Analyzer might seem in order but if you examine it closely and compare it to the Figure 5 5 timing diagram on page 153 you ll see
207. error predicted With the measurement of 0 682 Vpp from Figure 8 40 the percent error is 0 67 Vpp 0 707 Vpp 100 0 707 Vpp 5 23 error For more information see the Filter Error Propagation Example in the Understanding Signals Supplement which is available as a free PDF online from the Downloads section of www parallax com go PropScope Although the horizontal voltage cursors were not necessary for amplitude measurements the vertical time cursors are still essential for the phase delay measurement Figure 8 41 shows an example The Horizontal time division setting is reduced for a more precise time difference measurement As in Chapter 7 each signal s O V crossing is a reference point for the beginning of each sine wave s cycle To measure the time difference between the starting points of each sine wave s cycle each vertical time cursors is positioned to intersect with a channel trace where it crosses the 0 V ground line This provides a delay measurement that can be compared to our calculated At value of 77 8 us v Adjust the Horizontal dial to 20 ps div Goto the Cursors tab and turn the Vertical cursors on and the other cursors off v Position the green vertical A time cursor so that it intersects with the CH2 DAC trace as it crosses the 0 V ground line Page 318 Understanding Signals with the PropScope v Position the purple vertical B time cursor so that it intersects with as it c
208. es a teacher or mentor is on hand to provide background information In contrast the lessons in this book are designed so that a beginner can succeed on his or her own Page 6 Understanding Signals with the PropScope Instead of jumping straight from simple DC voltage and current measurements to high speed analog signals Understanding Signals with the PropScope takes incremental steps through measuring human speed signals followed by measuring a variety of binary high low signals first By the time the reader gets to analog signal measurements he or she has already honed many of the skills needed from the earlier work The Human speed Measurements chapter is important because it provides a bridge between DC and high speed signal measurements This chapter guides the reader through measuring signals that he she creates by turning dials pressing buttons and blinking lights Along the way the reader gains hands on experience with measuring time varying signals with the oscilloscope and binary high low signals with both an oscilloscope and logic analyzer The reader also gets hands on experience generating signals with a function generator and with the BASIC Stamp Most chapters include test signals that are generated by the function generator along with similar test signals generated by the BASIC Stamp microcontroller and a circuit Creating similar signals with a microcontroller and one or more circuits is important especially for the r
209. et Ee ee ee ee Function Average Te A i i 4 i voltage 100 200 300 400 Time us Sine Frequency Eee Amplitude custom QE orsaf Generate is button 55us 18 2kHz y 3 46V Your Turn Set and Measure Different Voltages v Try setting the Offset to 3 75 V and repeat the measurements ACTIVITY 5 VOLTAGE DIVIDERS Many electronic products and prototypes have circuits that depend on a DC voltage that may not be available from the device s supply voltages We just finished looking at one way to provide a set voltage for such a device with a microcontroller and DAC circuit However a microcontroller D A conversion can take I O pins processing time and code Provided the DC voltage you need is between two of the supply voltages like Vdd 5 V and Vss 0 V a quick solution for setting a voltage is to use two resistors in series Page 50 Understanding Signals with the PropScope Voltage Divider Parts List 2 Resistors 1 KQ brown black red 2 Resistors 10 kQ brown black orange 1 Resistor 2 kQ red black red Voltage Divider Circuit Two resistors can be connected in series end to end with a voltage applied like V and Vss in Figure 2 21 The voltage at the node where the two resistors meet will be divided according to the voltage divider equation in the figure V R R Figure 2 21 Vo ck ee mae R R Voltage Divider R Ci
210. etween the trace and the ground line for a cycle calculate the area of the triangle half a rectangle and add the area of the rectangle below it v Calculate the average voltage by dividing the time of a cycle into the area for Figure 8 29 v Set up an experiment that sends the signal in Figure 8 29 to the RC DAC circuit o Disconnect the I O pin P14 from the circuit o Move the CH2 probe s BNC connector to the DAC Card s function generator output Repeat the five checklist instructions in the Set DC Voltages with the PropScope s DAC Card section on page 45 o Configure the PropScope s function generator to transmit a 10 kHz 3 Vpp 2 VDC offset Sawtooth wave o Swap the vertical positions of CH1 and CH2 In other words position the Blue CH1 trace in upper region of Oscilloscope and ground line for red CH2 trace just above the horizontal time axis values o Compare your calculated average voltage to the Measured average voltage for both CH1 and CH2 Chapter 8 RC Circuit Measurements Page 301 Figure 8 29 function generator Sawtooth into RC Circuit 8 PropScope v1 1 1 aT ES File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA 100ps_200ps 500 ps ims etween signal and groun triangle Square Sine Sawtooth v ante E Gn a Mao Ls eM aram mm ACTIVITY 5 RC D A CONVERTER DECAY FROM LOAD We can use
211. f 10 kQ Gain 2 Rf 20 kQ Gain 3 20 30 40 Time ms Oo 20 30 AC Time ms w a w Q Page 338 Understanding Signals with the PropScope Op Amp Supply Voltages and Clipping Signal Distortion Remember that the upper limit for the op amp s output signal is 1 5 V less than Vcc and the lower limit is Vee Since Vcc is connected to the your board s Vin supply that maximum voltage would be around 9 V 1 5 V 7 5 V assuming you are using a 9 V battery An output signal that swings from 0 to 4 5 V is well within that range but what happens if you change the op amp s Vcc connection from Vin 9 V to Vdd 5 V Figure 9 14 shows an example Notice that the output signal in the upper CH1 trace reaches the op amp s voltage limit and just levels off It can t go any higher This symptom is a form of signal distortion called clipping because the tops of the sine wave appeared to be clipped off Notice there is no red M amp lai S88 warning unlike Chapter 2 Activity 3 the signal is being clipped by the op amp itself and not by the PropScope software s voltage scale setting v Make sure your Generator panel is set to Offset 0 75 V and Amplitude 1 5 V v Disconnect the end of the jumper wire plugged into Vin and plug it into Vdd instead Y Verify that your trace resembles Figure 9 14 v For clipping at the op amp out
212. f serial bytes from the BASIC Stamp When the signal is low it allows the BASIC Stamp to transmit serial bytes Keep in mind that P10 was used as an output in the previous activity Before connecting the PropScope s function generator output to it you should make sure to run code that sets the I O pin to input Even though there is a 220 Q resistor protecting the I O pin from the function generator output and vice versa it s still a better practice to use code to prevent I O conflicts along with the resistors that protect your hardware from possible coding mistakes Any PBASIC program starts all I O pins as inputs but certain commands can change them to output Examples include HIGH Low and PULSOUT In Test Flow Control bs2 the command SEROUT 11 10 sets P11 to output to make it transmit serial bytes and the optional 10 flow control pin argument sets P10 to input to make it monitor flow control signals So by loading Test Flow Control bs2 into your BASIC Stamp before connecting Page 194 Understanding Signals with the PropScope the function generator output to P10 you are taking an additional step to protect the function generator output and BASIC Stamp I O pin v Enter Test Flow Control bs2 into the BASIC Stamp Editor and run it Test Flow Control pszZ Main loop repeatedly sends 254 copies of A to Pll with P10 flow control SSTAMP BS2 Target module BASIC Stamp 2 PY SPAS eat Language PBASIC 2 5 PAUSE
213. f both PAUSE commands in Alternate High Low Signals bs2 get reduced to PAUSE 50 v Save another copy of Alternate High Low Signals bs2 v In this version change both PAUSE commands to PAUSE 50 Y Load the modified program into the BASIC Stamp Page 78 Understanding Signals with the PropScope Figure 3 8 shows how the higher frequency signals end up looking pretty cramped on the Oscilloscope screen With 500 ms division the Oscilloscope is showing the signal s activity over 5 seconds In that amount of time a signal that repeats every tenth of a second ends up repeating 50 times MANONO AY Figure 3 8 50 Cycles on the Oscilloscope screen 20 ULNA AV AAA INN Looks a little cramped doesn t it el 10 9 10 CH2 Vy When a signal repeats itself too quickly to see clearly in the Oscilloscope screen the horizontal dial should be adjusted to a smaller time increment It s usually best to pick a time increment that accommodates two cycles Since our square wave now has a period of 1 10 of a second 100 ms the ideal setting would be one that makes the Oscilloscope screen 2 10ths of a second or 200 ms wide Remember the Horizontal dial selects the time per division which is 1 10 of the Oscilloscope screen So to display two cycles set the Horizontal dial to 1 10 of 200 ms which is 20 ms Stop here and about the main points in the previous paragraph Ste
214. fect transistors or FETs A typical FET transistor has three terminals wg named drain d gate g and source s When measuring a voltage at a particular transistor s drain the voltage is typically labeled Vd Likewise the voltage measured at a transistor s source is Vs A supply like 5 Vpc that goes to many FET transistor drains in a chip is labeled Vdd and 0 V which tends to be connected to many transistor sources is labeled Vss Page 28 Understanding Signals with the PropScope The PropScope can stand in for a voltmeter for measuring the supply voltages on your board In this activity you will first test the PropScope s probes to verify that they measure Vss as 0 V In the next activity you will use the PropScope to measure and verify that Vdd is 5 Vpc and also to measure Vin These measurements are useful for the sake of making sure your board s voltage supplies are in working order and properly connected They are also useful for verifying that your PropScope is in working order and that you have correctly adjusted the controls for the measurements Steps before between and after measurements Before This is your checklist for getting ready to work on activities in this book v Ifyou have not done so download and install the latest PropScope software from www parallax com go propscope y lf you have not done so download and install the latest BASIC Stamp Editor software from www parallax com basicstamp
215. from oscillator circuits can be passed through comparators to create high low clock signals for computing systems Comparators can also be used with sensors A threshold voltage can be set at one of the comparator s inputs and if the sensor s voltage output rises above the level the comparator sends a high signal otherwise it sends a low signal In this activity an LM358 op amp will be configured to function as a comparator A voltage divider will be used to set the voltage at its non inverting terminal to 2 5 V With no feedback even a small difference above or below 2 5 V will result in the op amp trying to amplify the voltage difference by 100 000 The LM358 s output voltage is limited by its supply voltage so when the output reaches one of those limits it can t go any further The result will be that a voltage that s above the voltage applied to the inverting terminal will make the comparator send a high signal and a voltage that s below it will result in a low signal Page 324 Understanding Signals with the PropScope Comparator Test Parts 1 Potentiometer 10 kQ 103 2 Resistors 1 KQ brown black red 1 Resistor 220 Q 1 Op Amp LM358 misc Jumper wires Comparator Test Circuit Figure 9 3 shows a schematic of a 2 5 V threshold comparator and Figure 9 4 shows a wiring diagram example of the circuit The fixed voltage divider the two 1 KQ resistors applies approximately 2 5 V to the op amp
216. ge PBASIC 2 5 char VAR Word For counting and storing ASCIT PAUSE 1000 1 second delay before messages DEBUGHPxcogmameacunnangeacn Program running message DO Main loop SMRUON US 4h elas Get character from PC SHRO Wi 115 34 Chari Transmit a copy with Pil DEBUG char Echo in back to Debug Terminal LOOP Repeat main loop Figure 6 26 shows the Debug Terminal s Transmit and Receive windowpanes The Receive windowpane receives and displays messages that the BASIC Stamp sends as a result of DEBUG or SEROUT 16 commands The Transmit windowpane is for typing characters that you want to send to the BASIC Stamp The program can receive these characters with either DEBUGIN or SERIN 16 To send a message from the Debug Terminal to the BASIC Stamp you have to first click the Transmit windowpane and then you can start typing v Click the Debug Terminal s Transmit windowpane v Be prepared to repeatedly press a key on your keyboard Page 208 Understanding Signals with the PropScope Figure 6 26 Debug Terminal Transmit and Receive Windowpanes a5 x Com Port Baud Rate ity COM1 9600 Data Bits Flow Control 1 DIRS ats Sty Jot RX e DSR CTS Transmit windowpane Receive windowpane Macros Pause Clear Close I Echo Off Figure 6 27 shows locations for testing the incoming signal from a PC on various boards In both cases the incoming signal test point is adjacent to the outg
217. ge Duty cycle is the ratio of a signal s high time to its cycle time and it is commonly expressed as a percent measurement t Duty Cycle x 100 tCYCLE Figure 4 15 shows the vertical time cursors placed for the turgu measurement Figure 4 15 tyigh Measurement with Cursors PropScope 2 0 1 File Edit View Plugins Tools Help scope SCOPE 100ps_200 ee B00 us Ams AA Vertical cursors Ty N D measure tuah h Cursor time _ measurement DC_AC DAC Off tuian 4 44 us a Cl a Generate ore Penev A TY 4 Custom Edit otsto fF far 1 24 CH1 DC D EAER voltage i D aAA measurement Continuous E 12 V Step Chapter 4 Pulse Width Modulation Page 123 v Configure your PropScope s Horizontal dial Vertical dials and coupling switches and Trigger tab settings as shown in Figure 4 15 Make sure to set the Trigger Source to CH2 v Click the Cursor tab and turn on the vertical time cursors by clicking the Vertical button v Align the vertical time cursors with the pulse s positive and negative edges v Make a note of your tuguy measurement Cycle time tcycig is the signal s period and Figure 4 16 shows the time cursors aligned with successive rising signal edges for this measurement v Use your cursors to get your PWM signal s cycle time which is tcycie Figure 4 16 tcycte Measurement with Cursors
218. ge it is possible to adjust a system to adapt to different light levels So this is an application where placing a load a cross the DAC circuit without the op amp buffer is useful Think about how a property that s considered bad for one application can be good for another Try to keep it in mind as you learn more about how circuits interact with each other Applying an element that s considered bad for one circuit or application might just solve a thorny design problem for a different one ACTIVITY 7 LOW PASS FILTER Chapter 7 Activity 6 introduced a low pass filter example and tests demonstrated that higher frequency sine waves applied to the circuit s input resulted in lower amplitude sine waves with more phase shift at the output In contrast lower frequency sine waves were allowed to pass through the filter with less attenuation and phase shift The value of RxC that we ve been using to characterize RC decay is also a key value for an RC low pass filter You can use it to get the value of the filter s cutoff frequency which is the point at which the output sine wave amplitude is reduced to 70 7 of the input sine wave and the phase is shifted by 45 Another way to say this is that the Chapter 8 RC Circuit Measurements Page 313 output signal amplitude divided by the input signal amplitude is 0 707 This value is the reciprocal of the square root of two Vout 9 797 Vin V2
219. ge 154 Understanding Signals with the PropScope The leftmost digit in a base 2 unsigned integer is most significant because it is the digit that tells how many of the largest power of 2 the number contains In an 8 bit binary _ J number that s how many 2 128 it contains The rightmost digit is the least significant bit because it tells how many of the smallest power of 2 the number contains In an 8 bit binary number that s how many 2 1 it contains From the timing diagram in Figure 5 5 we can make a list of tasks for the BASIC Stamp Step 1 Set the CS line low Step 2 Send the first clock pulse a low high low signal to the ADC0831 s CLK pin Don t worry about collecting any data yet The ADC0831 just sends a low signal the null bit in reply to this first pulse Step 3 Send a second clock pulse and record the binary value the DO pin transmits in bit 7 of the variable that stores the measurement Step 4 Apply a third clock pulse to CLK and store the DO value in bit 6 of the measurement variable Step 5 Repeat 6 more pulses to CLK each time storing the value DO transmits in a successively lower bit in the result variable Step 6 Set CS line high ADC0831Testl bs2 is a program that performs the 6 steps from the datasheet plus a seventh step display the measurement in the Debug Terminal as an 8 digit binary value and as a 3 digit decimal value ADCO0831Testl bs2 Code from the AD
220. ge at both terminals v Use Vp and Ohm s Law to calculate the current draw for your particular circuit and board Figure 2 36 Resistor Voltage Measurements and Current Calculations Board of Education Trigger Cursor Measure Channel 1 e 2 1 Ir Vp sR ED O V 2 27V 2200 M sav T s 1 D 0 01031818 V Q eov e 0 0103 A 10 3mA Resistor Voltage Vr 4 34 V 2 07 V 2 27 V Figure 2 37 Resistor Voltage Measurements and Current Calculations HomeWork Board Trigger Cursor Measure Tp VpitR BY 2 21ms J 1 23V 2200 l eD a Iero av M coy 0 00604545 V Q ul 3 32 0 00605 A 6 05 mA Resistor Voltage Vr 3 32 V 1 99 V 1 33 V The first question was How much current does the I O pin supply one LED circuit The answer is about 10 3 mA on a Board of Education or 6 05 mA on a BASIC Stamp HomeWork Board The second question was Would it be safe to deliver twice that current to supply two LEDs at once The solution is The BASIC Stamp would have to deliver twice as much current as it does to one LED circuit load and still not exceed 40 mA For the Board of Education that would be I 10 1 mA x 2 20 2 mA which is still which is well below the BASIC Page 66 Understanding Signals with the PropScope Stamp Manual s stated 40 mA limit For the BASIC Stamp HomeWork Board it s T 5 59 mA x 2 11 18 mA which is even less and well within the 40 mA limit too So in both case
221. ge sockets above your board s breadboard Figure 2 2 are labeled Vdd Vin and Vss Vdd is regulated 5 Vpc Vin is the unregulated voltage of your board s power supply source which should be in the 6 to 9 Vpc range The sockets labeled Vss are considered 0 V If you are using a battery Vss is the voltage at the battery s negative terminal Vss is commonly referred to as ground and also as a ground reference because the other voltages on your board are measured with reference to Vss Vdd is 5 Vpc because it s 5 V above Vss Likewise Vin should be somewhere in the 6 to 9 Vpc range above Vss Vdd 5 Voc Vin 6 to 9 Voc Vss 0V regulated unregulated ground Vdd Vin Vss x3 5 OO 100 ap OOo aa 100 P13 stat He Figure 2 2 P11 l l l l Your Board s Supply ae 00000 00000 Voltages P8 00000 00000 P7 00000 00000 P6 00000 00000 P5 00000 00000 P4 00000 00000 P3 00000 00000 P2 00000 00000 P1 00000 00000 BO 00000 00000 xq 00000 00000 What do the Vdd and Vss supply voltage labels stand for The labeling convention came from the names of the BASIC Stamp interpreter chip s power supply pins which in turn came from a convention for names of voltage supplies to groups of a particular type of transistor The transistors in the BASIC Stamp module s interpreter chip are called field ef
222. generator frequency for letting two bytes through assuming the baud rate is 9600 bps Since each byte has ten bit times the time for transmitting one byte would be 10 x tbi 10 x 104 us 1040 us 1 04 ms For two bytes that s 2 08 ms so our square wave needs about 2 ms of low time With a square wave there will also be 2 ms of high time for a total cycle time of 4 ms Since frequency is the reciprocal of period f 1 T 1 4 ms 1 0 004 s 250 Hz So the function generator should be configured to send a 250 Hz square wave For a Horizontal timescale we are really interested in the two bytes that get transmitted during the high time not two cycles of the function generator signal We also want to see that the bytes stop transmitting during the function generator s high signal So only one cycle of the function generator square wave needs to be visible in the Oscilloscope screen Since we only want to display one function generator cycle that s a total of 0 004 s 4 ms Remember that to get the Horizontal dial setting for viewing you have to divide the total amount of time you want to view in the plot area by 10 divisions to get the Horizontal dial s time per division setting That s 4 ms 10 400 us which is close to the Horizontal dial s 500 us setting so we ll use that Figure 6 19 shows the result Two A bytes make their way through during each low cycle of the DAC Card s function generator s Square Wave sig
223. generator trace is shown as the red upper CH2 trace and the circuit s output is measured below it with the blue lower CH1 trace The two waves are positioned close together to highlight the differences in the output signal s amplitude and phase Figure 7 31 Visual Phase and Amplitude Check j f PropScope v1 1 0 5 x File Edit View Plugins Tools Help DC_AC DAC Off Generate sre Frewvency amz Sawtooth Amplitude fg T po Fae eo 5 f ii E aa mpe soa mE N e Mode dge eve ource 3 4 MEZEA NE i i D Cee Ga l Continuous a eE Step Q The voltage difference between the output sine wave s peaks and valleys are shorter than the input signal so the amplitude is less In electronics speak you could say the output signal is attenuated Also the output signal is the same frequency as the input signal but the whole sine wave appears to be shifted slightly to the right in the Oscilloscope screen This shift to the right shows that the circuit s voltage output is somewhat Page 260 Understanding Signals with the PropScope delayed running behind the input by roughly 1 100 of a millisecond Again in electronics speak you could say The circuit introduced a phase delay into the output signal v Adjust the PropScope s dials to Horizontal 100ps div Vertical CH1 1 Vidiv CH2 1 V div v Coupling swit
224. gure 7 8 shows how the frequency relates to the tone s pitch A higher frequency results in a higher pitched speaker tone It also results in a more compressed waveform Chapter 7 Basic Sine Wave Measurements Page 219 on the Oscilloscope screen A lower frequency results in a lower pitched tone and it also results in a less compressed or more stretched out waveform on the Oscilloscope screen Figure 7 8 Pitch Compared to Frequency and Period Pitch Frequency Period Highest 3 0 kHz 333 3 us Look carefully at the width of each cycle The widest cycle longest period is at the bottom and they get progressively shorter as the frequencies increase 2 8 kHz 357 1 us 2 6 kHz 384 6 us As frequency increases so does pitch Also as frequency increases period decreases because f 2 4 kHz 416 7 us 42T Lowest 2 2 kHz 454 5 us v Set the Generator panel s Amplitude to 3 Vpp v Type 2200 into the Frequency field and press Enter Page 220 Understanding Signals with the PropScope Y Listen to the pitch of the tone the speaker makes v Make a note of the waveform s period as well as how wide it looks in the Oscilloscope v Repeat with frequency settings of 2400 2600 2800 and 3000 v Try entering the five frequencies in a fairly rapid succession as you listen carefully to identify the increase in pitch In terms of f 1 T the highest frequency waveform has the shortest period time between signal
225. h the voltage at the non inverting input In Figure 9 7 the op amp s output is connected to its inverting input with a wire so the output voltage is applied directly to the inverting input they are the same voltage To enforce the negative feedback rule the op amp has to make its output voltage match the voltage applied to its non inverting input Figure 9 7 Negative Feedback in a Voltage Follower Circuit Vin To make sure the voltage at the non inverting input gt is equal to the voltage at the inverting input the op amp has to make its output voltage the same as the voltage applied to the non inverting input gt Output Feedback wire applies output voltage to inverting input so these two voltages are the same Buffer Test Code One Hz Sine Wave bs2 sends a 1 Hz sine wave to the P14 DAC indefinitely making it convenient to compare the DAC s sine wave output to the voltage follower s output v Enter and run One Hz Sine Wave bs2 One Hz Sine Wave bs2 Transmit a 1 Hz sine wave on P14 indefinitely STAMP BS2 Target module BASIC Stamp 2 SPBASIC 2 5 Language PBASIC 2 5 DEBUG Program Drumming Debug Terminal message DO u Main Loop FREQOUT 14 60000 1 d Plleyy i ily ier 1 mules LOOP Repeat main loop Chapter 9 Op Amp Building Blocks Page 331 Buffer Test Measurements Figure 9 8 shows the RC DAC output on the lower red CH2 trace and the voltage follower s copy
226. hain LOW 14 Tuen P14 and P15 LEDS Off LOW 15 PAUSE 50 Wait another 1 20th second LOOP Repeat main loop Logic Analyzer Measurements Figure 3 15 shows a plot of the binary pushbutton and LED circuit activity in the PropScope software s Logic Analyzer view v Click the Logic Analyzer tab Y Set the Horizontal dial to 500 ms Y Slide the plot area bar to the far right of the Logic State Analyzer s left right range v Try briefly pressing and holding each button and verify that the Logic Analyzer view correctly reports the binary activity you create on your board v Also watch the LED activity as you press and hold a pushbutton and make sure to check the Debug Terminal display too Chapter 3 Human speed Measurements Page 89 Figure 3 15 Pushbutton and LED Activity in the Logic Analyzer View P15 LED i0 blinks while P4 P14 LED i1 blinks while P3 button i2 is pressed and held button i3 is pressed and held IB Propscope vi 0 1 Pugns Took Hele Loge Ang 0S0 LSA oge Slate Analyzer o S Your Turn Find and Fix the Bug PushbuttonControlOffwoLeds bs2 has a bug discussed and fixed in What s a Microcontroller Chapter 3 Activity 4 The bug is that only one LED blinks when both buttons are pressed v Use your PropScope s Logic Analyzer to view this symptom as you press and hold both buttons Only one of the signals monitoring LED circuits should toggle even
227. har 32 TO 127 Character ASCII value loop DEBUG CRSRXY char 32 24 10 char 32 24 3 Position cursor row column DEBUG char DEC3 char Display Character ASCII value NEXT Page 176 Understanding Signals with the PropScope The Debug Terminal display should resemble Figure 6 2 v If the display gets scrambled because there s not enough room in the Debug Terminal make the window larger and restart the program by pressing and releasing the Reset button on your board Figure 6 2 Characters and Decimal Value ASCII Codes Displayed in Debug Terminal Figure 6 3 shows ASCII values the Debug Terminal uses as control characters for operations like Clear Screen Home Backspace Tab Carriage Return and others v In the BASIC Stamp Editor click Edit and select Preferences Then click the Debug Function tab Chapter 6 Asynchronous Serial Communication Page 177 EE Editor Appearance Editor Operation Files amp Directories eration DebugAppesrance Debug Funcion DebugPot Treat ASCII Control Characters As F 0 Clear Screen 7 8 Backspace W 1 Home W 9 Tab F 2 Cursor xy I 10 Line Feed 1 3 Cursor Left F 11 Clear EOL Figure 6 3 7 4 Cursor Right IF 12 ClearDown Debug Terminal Control W Bl CusorUp ta AAT Character Values and Functions Iv 6 Cursor Down I 14 Cursor x WV 7 Bel IV 15 Cursor y Restore Defaults All of the co
228. he asynchronous serial byte now occupies a single time division This makes it much easier to translate an asynchronous serial byte displayed on the Oscilloscope screen into the value that s being transmitted Remember that Bit 0 is the number of 1s in the number Bit 1 is the number of 2s Bit 3 is the number of 4s and so on up through Bit 7 which is the number of 128 Figure 6 11 9600 bps Byte Value 65 Viewed with Timescale set to 104 us Division Oscilloscope Logic Analyzer Analog DSO LS C AC DC o Generate Sine Frequency i Sawtooth zj a S 8 ja P 0 208 0416 0 624 0 832 E custom t iii CHI V Triggered Time ms i Trigger Girsor a gt Gm a ws CE amp D ioe Feri gaye eter ge pe g PCEN EE Continuous C mE Normal Step Page 188 Understanding Signals with the PropScope Bits in a Byte The values in Figure 6 11 get stored in a byte so that it looks like this 01000001 The sign is a PBASIC formatter that tells the BASIC Stamp Editor that it s a binary number In this binary number Bit 0 gets stored in the rightmost position Bit 1 in the om next position to the left and so on up through Bit 7 which is the leftmost digit It s the 1 opposite of the order from the binary digits get transmitted in an asynchronous serial byte w Powers of 2 in a Byte The value stored by Bit O determines the number of 1s
229. he remote s sheet booklet e Pressing and holding a certain remote button until an indicator light comes on e Entering the number code into the remote s keypad Chapter 4 Pulse Width Modulation Page 135 A Gi v An IR Remote Parts Kit is available at www parallax com Just type 29122 into Search field and click Go The remote in this kit is an example of one that costs under 15 US The IR Remote for the Boe Bot Parts Text page Item code 28139 has a link to a free pdf tutorial and another to a zip file with lots of PBASIC code examples for BASIC Stamp IR Remote communication and control These links are in the Downloads amp Resources section near the bottom of the web page Here are example instructions for the TV remote in the IR Remote Parts Kit v v a Remove the battery compartment cover and determine how many and what kind of batteries to use AA AAA etc Load the battery compartment with new or freshly charged rechargeable batteries Do not mix battery types Find the TV setup codes section in the instruction sheet booklet such as Setup Codes for TV Setup Codes for Television TV Code List Find the code for SONY from the TV code list and make a note of it Find the section that explains how to manually program a TV code into your remote such as Programming Your Remote To Manually Program Your Remote Control Programming for TV Follow the instructions in the manual program
230. he start of the decay Set the purple B horizontal cursor as close as possible to 1 47 V Use the B cursor voltage measurement in the Cursor display as a guide v Position the purple B vertical cursor so that it crosses the intersection of the B horizontal cursor and the CH1 trace lt lt SSS Chapter 8 RC Circuit Measurements Page 279 v The Cursor display s A field will show the time difference between the two vertical cursors which is t for your circuit Figure 8 11 Measuring the RC Time Constant 8 PropScope v1 1 1 File Edt View Plugins Tools Help Oseilloscope Logie Analyzer Analog DSO LSA i a Watch this ign gkeen value to make i sure your B Start ofidec horizontal cursor is set to 1 47 V which is approximately T ae ee Y 36 8 of 4 V Position purple B vertical cursor O Ssu Generate g the inter tion of the pur jori Sre p eeney Sore h decay trace a Custom O Eat Decay time is Time ms Triggered C approximately i 1 ms which is T the calculated Gams 1 48Y i RC time 4 09msz constant T oan Sener Predicted vs Measured Differences and Component Tolerances i In Figure 8 11 the measured RC Time constant is 1 09 ms which is within 9 of the calculated t value of 1 ms Since the electrolytic capacitor s tolerance is 20 a difference of up to 20 between the measured and predicted values
231. he voltage difference between the tops of the heartbeat signal s less prominent high points the P and T wave peaks v v v v Click the Horizontal button in the Cursor panel to activate the voltage cursors Click the Vertical button deactivate the time cursors Adjust the horizontal voltage cursors so that they measure the difference between the P and T peaks as shown in Figure 3 23 Check the voltage difference in the cursor display It s near the lower right corner of the Oscilloscope plot It s the value that ends with V by the A symbol in the Cursor display Figure 3 23 Voltage Cursors Measuring Difference between P and T waves Horizonta voltage cursors Also try using both horizontal and vertical cursors at the same time to measure both the voltage and time differences between the peaks of the P and T waves Page 104 Understanding Signals with the PropScope SUMMARY This chapter surveyed a variety of circuit microcontroller programming and measurement techniques for time varying signals Human speed time varying signal measurements were applied to e Binary pushbutton and LED signals viewed with the logic analyzer Varying potentiometer wiper voltage displayed with the Oscilloscope e BASIC Stamp D A and PropScope function generator signals viewed with the Oscilloscope The PropScope s function generator was also used to generate signals with certain amplitudes offsets
232. her way will work fine Y Configure the PropScope o Trigger tab to Mode Continuous Edge Rise Level Auto and Source CH1 o Horizontal 200 us div Vertical 1V div for both CH1 and DAC o Function generator to transmit a square wave with Frequency 1 kHz Amplitude 3 V peak to peak Vpp and Offset 0 V PropScope v1 0 8 1 x Figure 6 20 File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Measuring DAC Card function generator to CH1 With a probe set to 10x a 1 kHz 3 Vpp 0 V offset square wave from the En PropScope s DC AC DAC Off function Square Generate Seo ene generator Men Qe a eed square wave in the CH1 trace before adjustments Page 202 Understanding Signals with the PropScope Your lower CH1 trace may look misshapen compared to Figure 6 20 Figure 6 21 shows some examples of the waveform distortion you might see If the tops and bottoms of the square wave in the CH1 trace are not flat you ll need to adjust the trim potentiometer in the CH1 BNC connector v Using Figure 6 21 as a guide adjust the trim potentiometer in the BNC connector of the probe connected to CH1 to correct the shape of the square wave displayed in the CH1 trace Adjust Trim Potentiometer Figure 6 21 10X Probe Calibration Adjust the trim pot in the CH1 BNC Connector to correct the shap
233. i Ri If we use Rf Ri 1 then the output signal Vo is 1 multiplied by the input signal Substituting Vi 2 or Vi 1 verifies the earlier predictions of Vo 2 V and Vo 1 V Chapter 9 Op Amp Building Blocks Page 341 In contrast to the non inverting amplifier which had a minimum gain of 1 this amplifier can be configured for fractional gains that attenuate the signal by using a value of Ri that s larger than Rf For example if Ri 10 kQ and Rf 1 KQO the output signal will be attenuated to Rf Ri 1 10 the amplitude of the input signal Another difference with possible consequences is the fact that the input signal feeds into a relatively small resistor The signals in the previous two example circuits were fed into the op amp s non inverting input which has resistance in the hundreds of mega ohms The inverting amplifier in Figure 9 16 has input resistance of Ri which might be a comparatively low value like 10 kQ While that s fine for the PropScope s function generator we have already seen how that can cause decay across a DAC circuit s capacitor For a design that needs an inverted signal out of an RC DAC two op amp circuits can be cascaded The DAC s output can be fed into a buffer and then the buffer s output could be fed into an inverting amplifier Inverting Op Amp Test Circuit Parts 2 Resistors 1 KQ brown black red 2 Resistors 10 KQ brown black orange 1 Resistor 20
234. iable resistor in What s a Microcontroller Chapter 5 and as a variable w voltage divider in Basic Analog and Digital Chapters 1 and 3 Potentiometer Voltage Parts List 1 Potentiometer 10 KQ 1 Resistor 220 Q red red brown misc Jumper wires Potentiometer Voltage Test Schematic Figure 2 25 shows a circuit with the pot s A terminal connected to Vdd its B terminal connected to Vss and its W terminal connected to the CH1 probe The divider voltage can be varied simply by turning the potentiometer s knob If you turn the knob counterclockwise the pot s W terminal voltage decreases If you turn it clockwise the voltage increases By twisting the knob back and forth over its 270 range of motion Page 54 Understanding Signals with the PropScope you can set a DC voltage anywhere between O and 5 V Since the CH1 probe is connected to the potentiometer s W terminal you can verify the voltage with the Oscilloscope s trace cursor and or the average voltage in the Measure tab vV Check the potentiometer s legs If the legs have little angular kinks you can squeeze them with pliers to straighten them out to improve the electrical contact the legs make when you plug the pot into the breadboard if needed y Build the circuit in Figure 2 25 Vdd Figure 2 25 L Potentiometer Pot Voltage PropScope CH1 gt 10 KQ Divider Circuit
235. ing voltage signal Potentiometer Voltage Parts List 1 Potentiometer 10 KQ misc Jumper wires Potentiometer Voltage Test Schematic Figure 3 1 is a repeat of Figure 2 25 from Chapter 2 Activity 5 v Rebuild the circuit in Figure 3 1 Vdd Figure 3 1 Potentiometer Boi Voltage Divider o Circuit PropScope CH1 10 kQ PropScope GND Chapter 3 Human speed Measurements Page 69 Potentiometer Voltage Test Procedure Figure 3 2 shows an example of a running history of potentiometer W terminal voltages plotted by the PropScope The wavy line is a plot of W terminal voltages over 5 seconds as the pot s knob is turned back and forth Assuming your PropScope is still configured for Chapter 2 measurements two PropScope settings have to be adjusted for this display The first adjustment is to turn the oscilloscope s Horizontal dial to 500 ms This sets the amount of time between two vertical lines in the oscilloscope display to 500 ms So the PropScope can display 500 ms worth of voltage measurements per time division Since the Oscilloscope screen displays ten time divisions it can display 5 seconds of plotted voltage activity 500 ms div x 10 div 5000 ms 5 s Figure 3 2 Test the Voltage Divider Output Slide the plot area bar to Adjust the Horizontal scale the far
236. ints on the Trace Voltage vs Time A common math and science class activity is plotting x and y values with graph paper a graphing calculator or maybe a spreadsheet In some graphs the x values are equation input values that result in y output values In other graphs the x values are adjusted in lab tests and the y values are the system s measured response to the x values The Oscilloscope screen is like two x y plots on one sheet of graph paper For the PropScope each trace is made from 536 voltage measurements y axis values plotted against the times the measurements were taken x axis values Each channel has its own independent vertical scale for the voltage axis and they both share a common horizontal time scale axis Figure 2 9 points out the scales for both channels along with some example points in each graph To find out the voltage of a given point on a trace just check what value it lines up with on its own voltage scale CH1 on the left CH2 on the right The common time scale goes along the bottom of the plot so to find the time of a point on either trace just check what value the point is above on the time axis Figure 2 9 Scales and Sample Points on the Traces Osc pe 10 At100us At350 us Scale for CH1 10 Cop d eee eae H1 a Scale for CH2 voltage y axis a Channel 2 Trace voltage y axis measurements j measurements AHSO prs At400 Hs ChB is still 8 V Common time
237. ion plot a few sample points and learn about key values called time constants Then in Activity 2 you will use the PropScope s Oscilloscope view test a circuit s time constants and use those values to make adjustments for better view of the voltage as the capacitor charges and discharges Certain sensors vary in either resistance or capacitance which in turn affects how quickly the voltage in an RC circuit decays In addition to using the PropScope to measure these decay times you will also use the BASIC Stamp to automate these measurements which could come in handy for remote sensing projects In Activity 3 you will use RC decay to measure a potentiometer s variable resistance which indicates its knob s position In Activity 6 you will compare the linear decay traces from a light sensor that indicates brightness by the current it conducts to exponential RC decay traces Activity 4 and Activity 5 take a closer look at the signals in the RC circuits that were used for D A conversion in earlier chapters Activity 7 expands on the low pass filter measurements that were introduced in Chapter 7 with a key value called cutoff frequency ACTIVITY 1 RC GROWTH AND DECAY MATH Resistance R and capacitance C values can be incorporated into the exponential decay equation to predict and graph the rate at which voltage increases or decreases as a capacitor is charged or discharged through a resistor For each RC decay graph there is a
238. ircuit Measurements Page 271 Circuit Input Circuit Output PropScope CH1 Figure 8 5 1kQ a PropScope DAC RC Decay Test Circuit 1 uF j PropScope GND With RxC 0 001 Vss Vss Figure 8 6 Wiring Diagram Example of Figure 8 5 Vdd Vin Vss A ooo00000000000r000 OoOoOoo00o0o0000000000 JOOOoOo0O0 Wsiooooo OOOOOOOoOooOoOBUoOoooO OOOOC SOOOL oooooo0g OOOOOOOO0OO0OO00 00000 OOOOOOOOOO0 amp Again the connection to the Vss socket is optional for this test Since the BASIC Stamp is not interacting with this circuit the jumper from the ground clips to the Vss socket is not necessary The ground clips provide a connection to the USB port s ground connection which is also your computer s ground connection If your measurements did involve interaction with the BASIC Stamp connecting the ground clips to Vss would be necessary because the PropScope would need to share a common ground with your development board Page 272 Understanding Signals with the PropScope RC Time Constant Predictions The decay time tests involve a square wave that will charge and discharge the RC circuit s capacitor The first task is to figure out a good frequency for the square wave Since R 1 KQ and C 1 uF the RC time constant T is t RxC 1 kQ x1 pF 1 000 x 0 000001 s 0 001 s ms The squa
239. irst two digits as a two digit number 2 Multiply it by ten raised to the power of the third digit 3 Multiply that result by 1 pF which is 1 x 10 F 4 Express in terms of one or more fractional multipliers pico nano micro etc The top line in Figure 7 28 is an example of the three steps applied to the 0 01 uF capacitor in your kit Chapter 7 Basic Sine Wave Measurements Page 257 Figure 7 28 3 Digit Capacitor Label Fractional Multipliers C 10x 103 x107 F 4 2 3 and Abbreviations i C 10x10 x10 10 000x107 10 000 pF 10x10 10nF 0 01x10 0 01 uF pico p x107 nano n x 10 micro 4 x 10 milli m x10 Why step 4 f e y The reason you may need to express the result with one or more fractional multipliers is eg because you might go shopping for a 10 nF capacitor only to find that the electronics store doesn t carry any but they have a wide selection of 0 01 uF capacitors Amplitude and Phase Angle Test Circuit We ll use the circuit in Figure 7 29 and Figure 7 30 to examine how a circuit can change a sine wave s amplitude and phase The circuit is similar to the DAC circuit for BASIC Stamp D A The PropScope s function generator will apply sine wave signals to the circuit s input and the PropScope s Oscilloscope view will display the function generator signal as well as the output signal measured on CH1 v Set up the CH2 probe hard
240. is graph shows how a capacitor s voltage behaves as it loses its charge through a resistor When x 1 y e 0 368 You could also say that when x gets to 1 y has decayed to 36 8 of its starting value or it s 63 2 of the way to its final value By the time x reaches 5 the y value is only 0 00674 which is less than 1 of its starting value The graph on the right is y 1 e and it describes a capacitor accumulating charge through a resistor The corresponding 63 2 level when x 1 is also important along with the y value when x 5 which is within 1 of its final value of 1 Figure 8 1 Graphs of y and y 1 e 0 9 i get 1 5 0 9932 Page 268 Understanding Signals with the PropScope Let s use the Windows Calculator to verify a few values from the graphs in Figure 8 1 v Run Windows Calculator by clicking Start All Programs Accessories gt Calculator If your calculator looks like the one on the left in Figure 8 2 click View and select Scientific v Figure 8 2 Windows Calculator Hz REE Edt Ven Hep Edit view Help 0 C Hex Dec C Oct Bin le Degrees Radians C Grads e standard 0 l c I Inv D Hyp E a Backspace CE c wef a ef s of AT sof ef ff ef fief of 7 eaf ae wal E E we eo we es e x EE Pe E Smf af ohe wef sf af a un vel ea Be a Bea Jeg ESS es A a VJ VS Va Ty eof fell eel el el
241. it s output Let s try adjusting to cycle high low times that last 10t ten RC time constants instead of 5 t to see if anything interesting happens For this we ll want twice the signal period which would be half the frequency To maintain two cycles in the Oscilloscope display Chapter 8 RC Circuit Measurements Page 275 the time per division will also have to be doubled or in the case of the PropScope adjusted from 2 ms div to the next larger increment which is 5 ms div Figure 8 8 shows the new view In this particular example the high peak in the Measure display is now about 3 98 V which is 20 mV from 4 V and the low peak is at almost 10 mV As before these values are still in the right ballpark Adjust the Horizontal dial to 5 ms div Adjust the Generator panel s Frequency field to 50 Hz Adjust the Trigger Time control to the 2 time division line Repeat the input vs output signal high and low peak measurement comparisons How different are your results after ten RC time constants 10r LAA Figure 8 8 Square Wave Input and Increasing Decreasing RC Decay Output JE PropScope v1 1 0 File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Dc AC Oft DC_AC DAC Off Square Generate oe e wet Anene g Trigger F iode dge Leve j or i Auto Continuous N Step O jormal High and low p
242. it 1x128 Ox64 1x32 0x 16 1x8 0x4 1x2 Ox1 170 Your Turn Try a Different Voltage Pick a target voltage in the 0 to 5 V range Calculate the adeval result Adjust the potentiometer until the Debug Terminal displays your adeval result Verify the approximate voltage with the Measure display Verify the signaling and make sure the DO values during the low clock cycles coincides with the value of adeval displayed in the Debug Terminal Again Figure 5 8 shows an example of how to do this LARA Chapter 5 Synchronous Serial Communication Page 161 ACTIVITY 4 TROUBLESHOOTING EXAMPLES Author s note When I started designing the circuit and code for this chapter I took advantage of the Oscilloscope and Logic Analyzer in the DSO LSA view illustrate common mistakes one might make along the way Here are three errors it would be easy to make 1 Not setting CS high between measurements 2 Not sending a clock pulse for the null bit before the eight pulses for data bits 3 Swapping CLK and DO connections As a result of this error the first test program would send clock signals to the DO pin instead of the CLK pin Since the DO pin also sends signals this could possibly create a situation where the BASIC Stamp I O pin sends a high signal while the DO pin sends a low Without the 220 Q resistor to limit current either the ADC0831 or the BASIC Stamp or both could be damaged The Oscilloscope and Logic State Analyzer a
243. it before it is transmitted y SSTAMP BS2 Target module BASIC Stamp 2 SPBASIC 2 5 Language PBASIC 2 5 PAUSE 1000 1 second delay before messages DO Main loop SEROUT 11 84 A SEROUT 16 84 A PAUSE 1000 LOOP Send A to P11 Send A to P16 SOUT pin 1 second delay Repeat main loop Serial Port Transmit Test Measurements Figure 6 24 shows how to probe the serial port with the CH2 probe while the program is running The CH1 probe is still connected to P11 and the CH2 probe is connected to the signal that the BASIC Stamp sends either to the PC s serial port or to a USB serial converter chip Figure 6 24 CH2 Probe Position for SOUT Signal i 4 4 a A 555 28158 Pr lt A BS2 rec atre tte o Board of Education All BASIC Stamp HomeWork Board Serial Underneath the Serial Port Connecter For other boards get directions from the Supplement at www parallax com go propscope Page 206 Understanding Signals with the PropScope The lower CH1 trace in Figure 6 25 shows the P11 true signal and the upper CH2 trace shows the signal the BASIC Stamp sends to the PC The signal is inverted by a circuit built into the BASIC Stamp and either the PC or USB serial converter chip also has an inverter that converts this signal back to true for processing The inverted signals with higher voltage swings are part of standard computer serial port n designs Electromagnetic interference EMI g
244. it won t actually damage the probes or the PropScope CH1 or CH2 input ports there won t be any way to tell if the PC is transmitting with 12 V for example So the probe that will be used to measure the RS232 communication between the BASIC Stamp and PC should be set to 10x In this section both probes will be set to 10X for the sake of keeping the instructions simple and straightforward It s also important to verify that both probes are connected to the PropScope s CH1 and CH2 inputs WARNING f A probe that s inadvertently left connected to the DAC Card s function generator output but e used to test a serial port could result in damaged equipment Make sure both probes are w connected only to CH1 and CH2 BNC connectors DO NOT connect a probe to the DAC Card s BNC connectors v Make sure the Probes are connected to the CH1 and CH2 BNC connectors on the PropScope v STOP and CHECK No probes should be connected to any DAC Card BNC connector Probes should only be connected to the PropScope s CH1 and CH2 BNC connectors Remove the CH2 probe s tip from the probe rod as shown in Figure 6 22 Set both probe rods switches to X10 lt lt Page 204 Understanding Signals with the PropScope Set switch to 10x on both probe rods Ps SGD Remove the CH2 probe tip Figure 6 22 X1 X10 Switch on the Probe Rod Probe Tip and BNC Connector Make sure BNC connectors are
245. ition it held with PuLsouT 14 1000 If you didn t notice the change try running the PULSOUT 14 1000 version again then switch back to the PULSOUT 14 1050 version Check the new pulse duration in the Oscilloscope Calculate the pulse width for PULSOUT 14 1050 and compare it to your measurement Your Turn Modulated Pulse Width Here is a program from What s a Microcontroller that sweeps the servo s horn back and forth by gradually increasing and then decreasing the pulse width over time v v v Examine the program and try to predict what you would expect to see in the Oscilloscope display Run the program and test your predictions If the display s behavior does not match your predictions study what it does then study the program and try to figure out what s happening Chapter 4 Pulse Width Modulation Page 119 What s a Microcontroller ServoVelocities bs2 Rotate the servo counterclockwise slowly then clockwise rapidly SSTAMP BS2 IP TESIPISYNGHING 2 55 counter VAR Word PAUSE 1000 DO DEBUG Pulse width increment by 8 CR FOR counter 500 TO 1000 STEP 8 PULSOUT 14 counter PAUSE 7 DEBUG DEC5 counter CR CRSRUP NEXT DEBUG CR Pulse width decrement by 20 CR FOR counter 1000 TO 500 STEP 20 PULSOUT 14 counter PAUSE 7 DEBUG DEC5 counter CR CRSRUP NEXT DEBUG CR Repeat CR LOOP ACTIVITY 2 DUTY CYCLE IN PWM DAC A more descriptive name for PBASIC s PwM command w
246. itself to be exceedingly useful Before we move on to measuring electronic speed signals this chapter provides a survey of many of the more commonly used PropScope measurement tools and techniques applied to human speed signals with a variety of circuits Human speed signal measurements provide a nice starting point with the PropScope They make it possible to compare things we can manually initiate and monitor against the PropScope s graphical display and measuring tools Since many of the measurement techniques are the same at both human and electronic speeds taking human speed measurements first provides an opportunity to compare easily verifiable physical quantities against PropScope measurements Having already measured similar signals at human speeds will also make it easier to proceed with confidence with electronic speed measurements in later chapters Page 68 Understanding Signals with the PropScope ACTIVITY 1 A POTENTIOMETER S VARIABLE VOLTAGE OUTPUT In the previous chapter a potentiometer was wired as a voltage divider and its W terminal output was measured as a DC voltage With the same wiring and a simple adjustment of the Oscilloscope s time scale you can instead use the PropScope to plot the W terminal s voltage variations against time as you turn the pot s knob back and forth So instead of viewing the potentiometer s W terminal as an adjustable DC voltage signal we will use the PropScope view it as a time vary
247. itude Output Input Comparison PropScope v1 1 1 File Edit View Plugins Tools Help Oscilloscope ES Dc AC Off DC_AC DAC Off gia Generate Vpp is close ftia amitu __ to 0 707 V ure EN us 124m aay us B Gams oa8y aoa ey fi erie a aoe Continuous Cea Em VE mm Step Trigger Chapter 8 RC Circuit Measurements Page 317 In Chapter 7 the output sine wave from the circuit was positioned below the input sine wave and cursors were used to make the comparisons Since the Measure display s amplitude value always closely matched the horizontal voltage cursor measurements we ll rely on it instead of the cursors for amplitude measurements Chapter 7 also mentioned another common technique of displaying the sine waves with both the CH1 and CH2 ground lines set to the same level It superimposes the sine waves for improved visual comparison So in this chapter we ll rely on that approach How close should the measurement be The tolerances of the resistor and capacitor are 5 meaning that each one s actual value could be 5 smaller or larger than its nominal named value Other sources of error might include the capacitance inside the breadboard clips and the PropScope s 2 voltage measurement tolerance All tolled 7 error is reasonable The percent error equation is d predicted measured predicte 100 Yo
248. ity you will program the BASIC Stamp to transmit PWM control signals to a servo to dictate its horn s position You will then measure and examine the PWM signal s pulse durations with the PropScope W Servo Tutorial There s lots more information about servos and activities that introduce a Why variety of servo control techniques in What s a Microcontroller Chapter 4 Servo Test Parts 1 Parallax Standard Servo 1 3 pin header HomeWork Board only misc Jumper wires Servo Test Circuit Figure 4 3 shows a schematic of the servo and PropScope probe connections The servo s black and red wires provide power to the small DC motor and electronics inside the servo The white wire conveys the PWM signal to control system electronics inside the servo That white wire is connected to BASIC Stamp I O pin P14 and the BASIC Stamp will be responsible for using that pin to send PWM control signals to the servo vda PropScope CH1 Figure 4 3 Servo Schematic PropScope GND Page 108 Understanding Signals with the PropScope The instructions for connecting the circuit depend on your board and revision v If you do not already know which board and revision you have o Open the BASIC Stamp Editor Help v2 5 or newer o Click the Getting Started with Stamps in Class link on the home page o Follow the directions to determine which board you have v Skip to the section in this book that covers your board o Board
249. kQ red black orange 1 Op amp LM358 misc Jumper wires Inverting Op Amp Test Circuit The op amp circuit in Figure 9 16 is typically implemented with a negative supply voltage connected to the op amp s Vee terminal That makes it possible for the output voltage to swing above and below ground in an inverted version of the input signal which also swings above below ground Neither the Board of Education nor the HomeWork Board has a negative supply so our inverting amplifier test circuit in Figure 9 17 and Figure 9 18 will use 2 5 V as a reference voltage instead of 0 V ground A resistor divider with two 1 kQ resistors supplies the non inverting input with 2 5 V So long as the function generator output is configured with a 2 5 V offset the op amp s output will be an inverted version of the input signal The only difference will be that the input and output signals will swing above and below 2 5 V instead of ground y Build the circuit in Figure 9 17 optionally using the example wiring in Figure 9 18 as a guide Page 342 Understanding Signals with the PropScope Ri Rf 10 kQ 10 KQ PropScope CH1 PropScope DAC Figure 9 17 with 2 5 V offset Inverting Amplifier Test Circuit PropScope GND d 000 o 00000 oyoo ow ogd o000 o000 o000 a OOUUY jen 200 rd tfm fo BOO L Ol UOOOL L Ol 00001 L Ol OOOOCL L Ol OOOCL L Ol OOO
250. ke they are just over four 200 ms time divisions apart let s call it 4 This value along with the fact that frequency is the reciprocal of period f 1 T is enough information for the pulse rate s frequency in Hz Then to convert from Hz to the familiar beats per minute just multiply by 60 seconds minute Step 1 Figure out the signal period T based on the number of divisions between peaks T 4 125 divisions x 200 ms division 825 ms Step 2 Use the period to calculate the frequency in Hz f 1 T 1 825 ms 1 825 1000 s 1000 825 s 1 2121 Hz Step 3 Multiply the Hz measurement beats per second by 60 seconds minute get the familiar beats per minute bpm heart rate measurement f bpm f Hz x 60 seconds minute 1 2121 beats s x 60 s m 72 7272 beats m 72 7 bpm Alright our patient isn t so bad off after all Your Turn Take a More Precise Measurement This time division approximation of the heart rate might seem a little vague and imprecise v Try pointing at the top of adjacent peaks with your mouse and record the times with the floating cursor Chapter 3 Human speed Measurements Page 101 Subtract the smaller time from the larger time and use the result to recalculate the pulse rate You can also improve the precision by zooming in on each feature by adjusting the Horizontal dial to smaller values and then moving the screen around to find a more precise time of each event y
251. l applied to the CLK input Getting information out of datasheets can be challenging especially the first few tries The ADC0831 datasheet is no exception to this rule its target readers are electronics engineers and the document covers an entire series of A D converters not just the ADC0831 One of the main things that make it easier to decipher datasheets is practice oN So it s still a good idea to read it and try to understand as much as you can Datasheets for 1 parts you work with are also good to keep on hand for reference because they contain w answers to questions like what s the highest allowable supply voltage for this chip Stamps in Class books how to articles and microcontroller application notes often contain information for getting a given device up and running They also tend to feature lots of useful techniques and helpful background information ADC0831 Test Parts 1 ADC0831 1 Potentiometer 10 kQ 103 3 Resistors 220 Q red red brown misc Jumper wires ADC0831 Test Circuit The schematic in Figure 5 3 and wiring diagram example in Figure 5 4 were set up based on the pin map and pin descriptions accompanying Figure 5 2 To make prototyping easier the Vin pin is tied to Vss 0 V and the Vref pin is tied to Vdd 5 V This sets the bottom of the ADC0831 s input voltage scale to 0 V and the top to 5 V The PropScope s CH1 probe is connected to the potentiometer
252. l as audible Remember that the Oscilloscope screen is a plot of voltage vs time so what you see in the display is a graph of the voltage applied to the speaker as it varies with time in a sine wave pattern v Set the dials Horizontal 100 us div Vertical CH1 1 V div CH2 1 V div v Vertical coupling switches CH1 DC CH2 Off v Chapter 7 Basic Sine Wave Measurements Page 215 Optional Drag the CH1 ground line up down to position it about 2 voltage divisions above the time scale so that it matches Figure 7 4 Trigger tab switches Mode Continuous Edge Rise Level Auto and Source CH1 Generator panel Function switch Sine Frequency 2500 Amplitude 3 and Offset 0 Click the Generator panel s Generate button make the DAC Card start transmitting the signal Make sure you can hear the speaker making an audible tone and that you can see a sine wave in your Oscilloscope screen similar to Figure 7 4 Try using the Run button not the Generate button to freeze the signal and turn the function generator signal sound off Click the Run button again to restart the sound and the display Figure 7 4 Function Generator and Oscilloscope Settings 1 PropScope v1 0 9 lolx File Edit view Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA DC_AC DAC Off Generate Trigger i Eilrsor Step wv n a Gasto
253. lay from just counting time divisions is 60 us which is close enough to 59 6 us for this type of measurement v Turn off the cursors and try counting time divisions to measure the phase delay time Page 264 Understanding Signals with the PropScope Figure 7 34 shows another common practice for comparing sine waves superimposing one over another by positioning their ground lines at the same level in the Oscilloscope screen You will use this setup for amplitude and phase measurements in Chapter 8 Activity 7 Figure 7 34 Sine Waves Superimposed for Comparison 8 PropScope 1 1 0 File Edit View Plugins Tools Help 0 07V DAC i0 32V Generate ies Frenuency amz i ee i Tv nyren J f custom eat otse Triggered eae j Your Turn What s Does a Low pass filter Really Do A low pass filter lets low frequencies through and takes away high frequencies by attenuating them reducing their amplitudes You will see more about this in the next chapter For now let s just examine the filter s behavior by trying a lower frequency and a higher frequency The filter should allow the lower frequency to pass with less attenuation and phase delay It should also remove more from the higher frequency signal and increase the phase delay Chapter 7 Basic Sine Wave Measurements Page 265 v Repeat the amplitude and phase shift measuremen
254. lloscope measurements you will also take starting in Chapter 3 Human speed Measurements Oscilloscope Many voltages that vary over time need to be monitored An oscilloscope which measures and plots voltage vs time is the perfect tool for the job The Oscilloscope screen in Figure 1 4 is plotting two sine wave voltage signals One sine wave the shorter one on the bottom is a signal going into an amplifier circuit The taller sine wave above it is the amplified signal measured at the amplifier s output This amplifier will be introduced in Chapter 9 Op Amp Building Blocks The Oscilloscope in Figure 1 4 has a Horizontal dial for adjusting the amount of time displayed in the x axis the large dial at the top Below it are two Vertical dials for adjusting the amount of voltage displayed by two independent voltage y axes Chapter 1 PropScope Introduction and Setup Page 13 Figure 1 4 PropScope Oscilloscope view Oscilloscope Square Generate Sme Frquecy The Af Amplitude 10 Custom Q Edit Ofiset o5 CH1 V Waitfor Trigger Measure Auto H a Ea Continuous mw CHI ay step Normal The channel 1 voltage scale is on the left side of the plot and the channel 2 voltage scale is on the right The voltage scales can be configured to convenient increments for displaying the signals measured by the PropScope hardware Under the Vertical dials are the vo
255. loating cursor values at the comparator output transitions to approximate the resistor divider s threshold voltage v Compare the averaged instantaneous threshold voltage measurement to the direct measurement v v ACTIVITY 2 VOLTAGE FOLLOWER AS AN OUTPUT BUFFER This activity examines a closed loop op amp circuit called a voltage follower so named because the output voltage follows the input voltage In other words the op amp s output voltage should be the same as the voltage applied to its non inverting input This circuit is also commonly called a buffer That name comes from the fact that the op amp buffers or protects the circuit setting the non inverting input voltage from any load that might be connected to the op amp s output Chapter 8 Activity 5 examined the effect of a resistor load on the RC DAC circuit voltage output After PWM charged the capacitor the load caused the voltage to decay making it an unreliable DC voltage source In this activity you will use the same DAC circuit to create a voltage along with an op amp voltage follower to prevent decay and maintain the voltage across an LED circuit load Page 328 Understanding Signals with the PropScope Buffer Test Parts 1 Resistor 1 KQ brown black red 1 Resistor 470 Q yellow violet brown 1 Capacitor 1 pF 1 Op Amp LM358 1 LED any color misc Jumper wires Voltage Follower Test Circuit Figure 9 6 shows a sche
256. lse Width Modulation Chapter 8 RC Circuit Measurements Chapter 9 Op Amp 1 Building Blocks Further Reading and Program Examples Look up the command in the BASIC Stamp Editor s Help file Also see Basic Analog and Digital Chapter 7 the PDF tutorial is a free download from www parallax com education Measure 2 BASIC Stamp DC Outputs with the PropScope Two good tools for testing DC voltages are the Oscilloscope view s floating cursor shown in Figure 2 14 and the Measure tab s Average voltage fields shown in Figure 2 15 vV Set both of the Vertical dials to 2 V div v Adjust the positions of the traces to match Figure 2 14 Chapter 2 DC Measurements Page 43 v Point at one of the traces with your mouse It will make the floating cursor appear The floating cursor will display the voltage measurements for both traces in the upper left of the Oscilloscope screen Make a note of the measured voltages How close are they to your predictions Click the Measure tab below the Oscilloscope screen Check the average voltage measurements shown in the Average voltage fields KAA Figure 2 14 Floating Cursor DC Voltage Measurements 8 PropScope v2 0 1 View Plugins Oscilloscope Logic Analyzer Analog DSO LSA 100ps_200ps S00 us 4 DH Eup Floating cursor and voltage measurements DC_AC DAC Off r Generate Sine Frequency 10kHz m anme
257. ltage coupling switches When you set the CH2 coupling switch to DAC it uses the CH2 trace to display output from the PropScope s function generator which is introduced in the next section The Oscilloscope also has a Trigger tab for positioning the signal on the screen and a Cursor tab with tools for manually measuring voltage and time differences in the signal s The Measure tab displays measurements for both signals Page 14 Understanding Signals with the PropScope Function Generator A function generator can synthesize a variety of voltage signals These signals can be applied to a circuit input and then the oscilloscope can measure results at a circuit output This technique is useful for testing certain circuit properties and the effects they have on signals It s also useful for verifying that a circuit is functioning properly as well as for tracking down certain malfunctions Figure 1 5 PropScope Function Generator JF Square Generate 4 Generator panel in Y Sine Frequency 4o0Hz PropScope software Sawtooth ga he sa T lt lt TViest signal output PropScope DAC Card A lt amp Logic analyzer inputs Function generator i fi i output 4 lt __ External trigger input Common function generator signals include square waves a series of high low signals sine waves and a triangular pattern called sawtooth The PropScope Generator panel in Figure 1 5 also has an Edit feature th
258. m of the test circuit The function generator sends sine wave voltages to the circuit and the speaker makes it possible to hear to them as tones The CH1 probe is for measuring the signals and the Oscilloscope makes it possible to see them as sine waves Disconnect the probe with the red marker band from the PropScope s CH2 BNC port and connect it to the DAC Card s function generator output For detailed instructions see the Set DC Voltages with the PropScope s DAC Card section starting on page 45 If the piezospeaker has a sticker covering it remove that sticker Build the circuit shown in Figure 7 2 using the wiring diagram in Figure 7 3 as a guide Si Page 214 Understanding Signals with the PropScope PropScope CH1 Figure 7 2 Audio Tones PropScope GND Schematic Figure 7 3 Wiring Diagram for Figure 7 2 om000000 o0onmom000000 o0onm0000000 o0omo000000000 DOOO sOO0O0o00000000 0000 00m0000000000 000000 X2 Audio Test Measurement Settings Figure 7 4 shows the PropScope s Generator panel configured to make the function generator output a sine wave with a frequency of 2 5 kHz a peak to peak voltage of 3 V and a DC offset of 0 V This signal should cause the piezospeaker to make an audible tone The Oscilloscope screen makes the tone visible as wel
259. matic and wiring diagram example of the voltage follower test circuit with an LED circuit load One subtle change to this circuit that s easy to miss is that the op amp s Vcc supply input is now connected to Vin Provided your board s supply is at least 6 5 V this change should make it possible for the op amp s output to follow the BASIC Stamp RC DAC s voltage through its entire 0 to 4 98 V range Build the circuit shown in Figure 9 6 v Make sure the op amp s pin 8 is connected to one of your board s Vin sockets instead of a Vdd socket v A 9 V battery supply is recommended for this activity your supply must be above 6 5 V to give the op amp supply enough headroom to output up to 4 98 V The circuit in Figure 9 6 is called a voltage follower because it forces the op amp s output to follow the voltage applied to its non inverting input The fact that we have made a circuit that matches the input voltage at its output might not seem like a big deal Heck a wire could do that right The thing a wire cannot do is prevent a load from affecting the circuit it draws current from but an op amp voltage follower can With this circuit the BASIC Stamp can use its PWM command to set voltages across the RC DAC circuit to control the LED s brightness The op amp s output supplies the necessary current to make its output voltage match the capacitor voltage applied to the non inverting input but there is no decay from the LED cir
260. may end up having to choose a different Horizontal dial setting In this example the BASIC Stamp RCTIME measurement is 2261 x 2 us 4522 us The PropScope A measurement is 4 52 ms which is 4520 us Especially since the light sensor measurement fluctuates we are not expecting an exact match just oscilloscope verification that the BASIC Stamp measurement is in the right neighborhood So this might be somewhat of a closer match than a typical measurement 8 PropScope v1 1 1 alol xi Fie Edt View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Oscilloscop Figure 8 35 BASIC Stamp Phototransistor Generate Decay Frequency toz Measurement Custom Q Edt otso s gt a z q ms 4s verica li Boims1 4 Horizontal 0 v Use your Debug Terminal time measurement to figure out approximately what Horizontal dial setting will suit your lighting conditions decay times Remember to multiply by 2 to get the number of microseconds Chapter 8 RC Circuit Measurements Page 309 v Use the PropScope to verify the BASIC Stamp module s time measurements in your lighting conditions Depending on your lighting conditions your time scale may have to be significantly different from what s in the figure From RC Decay to Linear Decay The shape of the trace no longer matches the RC decay curve In fact the decay looks _ almost linear
261. may represent a violation of Parallax copyrights legally punishable according to Federal copyright or intellectual property laws Any duplication of this documentation for commercial uses is expressly prohibited by Parallax Inc Duplication for educational use in whole or in part is permitted subject to the following conditions the material is to be used solely in conjunction with Parallax PropScope and BASIC Stamp products and the user may recover from the student only the cost of duplication Check with Parallax for approval prior to duplicating any of our documentation in part or whole for any other use BASIC Stamp Board of Education Boe Bot Stamps in Class and SumoBot are registered trademarks of Parallax Inc HomeWork Board PING Parallax the Parallax logo Propeller and Spin are trademarks of Parallax Inc If you decide to use any of these words on your electronic or printed material you must state that trademark is a registered trademark of Parallax Inc upon the first use of the trademark name Other brand and product names herein are trademarks or registered trademarks of their respective holders ISBN 9781928982548 1 0 0 11 02 27 SCP DISCLAIMER OF LIABILITY Parallax Inc is not responsible for special incidental or consequential damages resulting from any breach of warranty or under any legal theory including lost profits downtime goodwill damage to or replacement of equipment or property or any costs of recov
262. ming section for entering the SONY TV code into your remote IR Remote Test Code RecordAndDisplayPwm bs2 measures the twelve pulses that follow the start pulse in Figure 4 25 and displays their durations in the Debug Terminal The program uses a command called PULSIN which is the inverse of PuLsouT Instead of transmitting a pulse to another device it measures a pulse transmitted by another device and stores the result in a variable This result is a pulse measurement in terms of 2 us units The Debug Terminal displays these results and you can multiply each one by 2 to convert it from a 2 us unit measurement to a number of microseconds y Enter RecordAndDisplayPwm bs2 and run it Remove Sources of IR Interference Depending on the IR detector sunlight from a nearby window could cause a lot of spurious signals Certain fluorescent lights generate 38 5 kHz range inference too For best results close the blinds and turn off nearby fluorescent lights Page 136 Understanding Signals with the PropScope IR Remote for the Boe Bot RecordAndDisplayPwm bs2 t Measure all data pulses from a SONY IR remote set to control a TV SSTAMP BS2 ESP PACH Ca2 oI time VAR Word 12 SONY TV remote variables index VAR Nib Display heading DEBUG time ARRAY CR PWM MEASUREMENTS CR Element Duration 2 us CR DO Beginning of main loop DO Wait for rest between messages PULSIN 9 1 time 0 LOOP UNTIL time 0
263. mo to v In Printable ASCII Chart bs2 try changing 32 TO 127 to A TO Z v Load the modified program into the BASIC Stamp and observe the results v Repeat for a TO z and TO The Debug Terminal has more characters in the 128 to 255 range that you can check too These can be useful for displays in certain languages as well as symbols like degrees and other symbols For example the DEBUG command to display 180 would be DEBUG 180 176 The code 176 makes the Debug Terminal display the symbol v Try this modified For NEXT loop in Printable ASCII Chart bs2 FOR char 128 TO 255 DEBUG CRSRXY char 128 24 10 char 128 24 3 DEBUG char DEC3 char NEXT v Make a note of any character codes that might be useful for displays in future BASIC Stamp projects ACTIVITY 2 FIRST LOOK AT ASYNCHRONOUS SERIAL BYTES Figure 6 4 shows an example timing diagram for the number 65 the letter A transmitted with a widely used format of asynchronous serial signaling The sending device that transmits this byte starts with a transition from high Resting State to low Start Bit Both of the devices use that as the starting point The sending device uses it for updating the bit values it transmits at regular time intervals tpi and the receiving device knows to check for new binary values at those intervals The baud rate determines the time interval which is tpi 1 baud rate For example if the ba
264. n Oea ora Time ms Triggered Measure e IES lt D Ga ass l Auto CHI Continuous CH2 To Mac Normal 4 4 Q X E P inger Page 216 Understanding Signals with the PropScope Run button vs Generate button For this activity the Run button is better than the Generate button for stopping the tone because it freezes the display before it stops the PropScope and DAC Card It turns the sound off while preserving the last sine wave that was displayed in the Oscilloscope screen w If you use the Generate button instead it does toggle the function generator on off which will stop the tone too However the oscilloscope will keep running and there s a chance that the signal activity as the function generator switches off will trigger the display If that happens your sine wave will be replaced by some miscellaneous switching activity Test Amplitude s Effect on Volume A sine wave s amplitude can be measured in several different ways Figure 7 5 shows two examples peak to peak voltage Vpp and peak voltage Vp With an oscilloscope peak to peak amplitude is the voltage difference between the tops of a sine wave s peaks Vmax and the bottoms of its valleys Vmin The PropScope displays Vmax Vmin and Vpp for a given channel in its measure display Another common amplitude measurement is peak voltage Vp which is just the height of a sine wave s peaks measured from the halfway poin
265. n line It doesn t matter where the vertical trigger time crosshair is just make sure a peak in the sine wave is lined up with the middle time division line See example in Figure 7 19 Kx Chapter 7 Basic Sine Wave Measurements Page 241 Figure 7 19 FREQOUT 9 60000 2489 Signal AC Coupled in the Oscilloscope 8 PropScope 1 1 0 File Edit View Plugins Tools Help 100ps_200ps S00 ys Ims align as middle time vision line foo CH1 1 V division line DC_AC DAC Off Generate Frequency 2 5kHz outon Oeae onsa d Gos ans E G2 4H D G18 Gov Continuous Step Compare a Dual Tone Signal to its Component Sine Waves Two Notes Together bs2 played each individual note and then both notes together What do you think the signal will look like when both notes are played together Let s use the PropScope to find out First let s take pictures of the individual D7 and F7 notes and save them for comparison v Make a copy of the Oscilloscope screen for later reference by clicking the Edit Menu and selecting Copy Image Paste it into a program called Paint Start All Programs Accessories Paint v Save the file as 2489 Hz bmp v Page 242 Understanding Signals with the PropScope The next step is to modify One or Two Notes at a Time bs 2 so that it plays the F7 2960 Hz and then take a screen captur
266. n setting Try this Page 186 Understanding Signals with the PropScope VY Right click the Oscilloscope screen The Click on the Value you wish to change window in Figure 6 10 should appear v Shade the value 200 in the timescale Value cell and change it to 104 press the Enter key and close the window This will change the time scale value from the Horizontal dial s 200 ps division setting to 104 us division Oscilloscope Logic Analyzer Analog DSO LSA Og eee Figure 6 9 The Letter A Again TE Square Generate Time per S Fremercy tome division is paron ame aa ae et one 200 us CH1 V Triggered Time ms Trigger Continuous Step Click on the Yalue you wish to change Name Value bool Figure 6 10 Configuring Custom Time per Division Shade the number 200 and change it to 104 Chapter 6 Asynchronous Serial Communication Page 187 Your Oscilloscope will need a few more adjustments before it resembles Figure 6 11 v Adjust the Plot Area bar slightly to the right so that you can view all the bits of the asynchronous serial 65 byte as shown in Figure 6 11 The falling edge of the start bit should align with the first visible time division line v Compare your results to the timing diagram in Figure 6 4 on page 179 The important feature here is that each bit in t
267. n testing the frequency response of a speaker keep the amplitude of the sine wave the same If one tone is louder than the next you know it s a property of the speaker since the amplitude did not change If a tone sounds really loud it may be because the speaker is designed to vibrate at that frequency kind of like when you ring bells of different sizes and shapes Each one has mechanical properties that resonate at a particular frequency This natural frequency is called the resonant frequency The piezospeaker in your Understanding Signals kit is designed with a resonant frequency for smoke alarms so it sounds louder at higher frequencies Chapter 7 Basic Sine Wave Measurements Page 221 Set the Generator panel s Amplitude to 3 V and make sure to press Enter with each adjustment to update the function generator s output v Try 1 2 3 4 5 6 and 7 kHz Can you make it any louder Hint the resonant frequency should be half way between two of the frequencies you have already tested ACTIVITY 2 DC OFFSET TESTS DC offset is useful for certain designs and detrimental to others A useful example would be a signal that is given some DC offset so that every cycle crosses the BASIC Stamp 1 4 V logic threshold A detrimental example would be giving a normal audio speaker a sine wave with DC offset They are designed to receive signals with 0 Vpc offset In this part of the activity we ll add some DC offset to the signal applied
268. n the Understanding Signals kit Listen to Each Note then Play them Together This example program starts off the same as the Two Notes bs2 example from the previous activity it plays the D7 and F7 notes individually After that it plays them simultaneously FREQOUT 9 2000 2489 2960 uses the FREQOUT command s optional Freq2 argument together with the Freq1 argument to play the both sine waves together y Disconnect the capacitor s positive lead from the piezospeaker circuit so that you can hear the notes the piezospeaker plays v Enter Two Notes Together bs2 into the BASIC Stamp Editor and load it into the BASIC Stamp v Listen carefully again to the two individual notes followed by the notes played together v Listen again and try to hear the differences in the three tones by pressing and releasing the Reset button on your board to re run the program Two Notes Together bs2 Play D7 followed by F7 followed by D7 F7 together SSTAMP BS2 Target module BASIC Stamp 2 i TSPBAS IC 25 Language PBASIC 2 5 PAUSE 1000 Wait 1 s before first message DEBUG 2469 2 CR Play display D7 FREQOUT 9 2000 2489 Biase UO iets CIR 1 fe Ss rest PAUSE 500 DEBUG 2960 she ACR Play display F7 PREQOUT 97 2000 7 2960 Chapter 7 Basic Sine Wave Measurements Page 239 DyaeOKE VO tei CIR EIA S Lest PAUSE 500 DEBUG ASOR sp AGO iba ICI Play display D7 F7 FREQOUT 9 2000 2489
269. nal v Adjust the Horizontal dial to 500 ps division v Change the Trigger Edge to Fall and adjust the Trigger Time control so that the DAC trace s negative edge lines up with the first time division line Chapter 6 Asynchronous Serial Communication Page 199 Figure 6 19 Two A Bytes Per Cycle Oscilloscope Logic Analyzer Analog DSO LSA Oscillosco c Generate a plit E Custom C Eat Offset 225 D Ge Cea j emne D Gay gee qr cr Your Turn Does Flow Control Stop at the Bit or the Byte When the flow control signal stops the BASIC Stamp from sending data does the BASIC Stamp stop with the next bit of data to be sent or does it finish sending the current byte before it stops It is difficult to tell from Figure 6 19 If the transition from low to high happened 500 us sooner it would be more obvious because the flow control signal would transition to high in the middle of a byte Then you d be able to tell if the flow control terminates the signal in the middle of a byte or not v Repeat the period to frequency calculations discussed earlier but with high and low times that are 250 ps shorter v Adjust the function generator frequency So does flow control interrupt SEROUT transmit at the bit or the byte Page 200 Understanding Signals with the PropScope ACTIVITY 6 PROBE THE SERIAL PORT In this activity you will
270. nals may be swapped as needed to simplify schematics Positive Supply Vcc F i 8 Non Inverting Input Vit Fi 2 Vo Output pt maj Inverting Input Vi p Amp Terminals se 4 LM358 Vee Negative Supply An operational amplifier s output voltage is the difference between the voltages at the non inverting and inverting inputs multiplied by a very large value For example the Fairchild LM358 datasheet specifies a large signal gain of 100 V mV In other words the output voltage will be 100 000 times the voltage difference between the two inputs This gain is also called open loop gain and will be utilized by a circuit called a comparator in Activity 1 After the open loop comparator operation other operations in the list buffer amplify invert etc require circuits that connect the op amp s output to its inverting input The circuit configuration determines the operation and the values of the components determine the relationship between input and output voltage levels and signal amplitudes In these circuits the output signal is fed back into the inverting input either directly or through a circuit so they are called negative feedback circuits Activity 2 through Activity 4 utilize negative feedback circuits to buffer amplify invert and offset signals Chapter 9 Op Amp Building Blocks Page 323 Op amp shopping tip Open loop gain is not just important for op amp comparator operations it s also an ingre
271. nd measurement ACTIVITY 2 HIGH LOW SIGNAL VOLTAGES AND FREQUENCIES Binary signals can be examined with an oscilloscope to get information about both timing and voltages If only the timing needs to be examined a device called a logic analyzer can be used instead A logic analyzer doesn t plot actual voltage values just high and low signal states In this activity you will use the Oscilloscope view to monitor both the voltages and the timing of two binary signals In Activity 3 you will use the PropScope s DAC Card and the PropScope software s Logic Analyzer view to monitor the high low patterns and timing of four binary signals at once Parts List for Probing I O Pins misc Jumper wires Circuit for Probing I O Pins The next example program will send high and low signals to the P14 and P15 I O pins Figure 3 4 shows how to connect the CH1 and CH2 probes directly to the I O pin sockets so that you can monitor the signals with the PropScope Connect the Probes as shown in Figure 3 4 P15 PropScope CH1 P14 lt PropScope CH2 PropScope GND Vdd Vin Vss x3 Vss P15 rit g0 OOo P14 dl P13 J000 e d P12 g L 000C o0m00 g0 P11 o0mm00000 P10 00000 P9 P8 P7 ODOOOOOOOOgoO P6 L P5 l P4 P3 omo00000
272. nd repair technicians for product development projects diagnostics and repairs PropScope setup involves following the software installation and hardware connection instructions in the PropScope Quick Start Guide Marker bands help make it clear which probe is connected to a given PropScope channel at a glance They should be adjusted to match the colors of the channel information displayed by the PropScope blue for CH1 and red for CH2 Each probe tip has an alligator clip that gets attached to the ground connection of the device under test and a spring loaded retractable probe tip that can grip wires and leads with a hook Grabbing a jumper wire with the hook will simplify probing breadboard sockets As with the color bands use a blue wire with the CH1 probe and a red one with the CH2 probe Chapter 2 DC Measurements Page 25 Chapter 2 DC Measurements ABOUT SUPPLY AND OTHER DC VOLTAGES Voltage is like a pressure that propels electrons through a circuit and the resulting electron flow is called electric current Electric current is often compared to water flow through a pipe or hose If electric current is like the flow of water then DC voltage is like the pressure that causes the water to flow through the pipe The terms DC and AC describe current flow and stand for direct current and alternating current DC current flows directly through a circuit propelled by a voltage that more or less remains constant In contrast
273. nds to CH2 Figure 1 11 Channels and Marker Bands Connect the probe with the blue marker bands to CH1 and the probe with the red marker bands to CH2 Each PropScope probe has two clips shown in Figure 1 12 an alligator clip and a probe tip with a hook Both are spring loaded so that they can grip and hold wires and leads A convenient setup for testing the voltages at breadboard sockets is to grab the stripped end of a jumper wire with a probe tip The other end of the jumper wire can then be inserted into breadboard sockets to test voltages at various points Chapter 1 PropScope Introduction and Setup Page 23 Grab a jumper wire to matches the color of each probe s marker bands o Retract the probe tip gently towards the probe rod to expose the hook as shown in Figure 1 12 Insert a matching colored jumper wire s stripped end into the probe tip hook Release the probe tip to grip the jumper wire ANNAN Figure 1 12 Grab a Stripped Wire End with the Probe Tip Hook Page 24 Understanding Signals with the PropScope SUMMARY The PropScope is a USB hardware peripheral and software tool that allows your computer to perform the functions of several different electronic test equipment components The PropScope can stand in for the basic tasks of the voltmeter oscilloscope function generator logic analyzer spectrum analyzer and XY plotter These devices are used by engineers technicians students hobbyists a
274. nes for unhealthy vibration patterns finding radio signal interference and testing telephone dial tones Diciloscape Logic Analyzer Analog DSO Lsa Timescale 50s gt Figure 1 7 Oscilloscope above Spectrum Analyzer in the PropScope s Analog Spectrum Analyzer View A fourth example of when a signal s sine wave components need to be tested is shown in Figure 1 7 The oscilloscope in the upper portion of the display is monitoring a rapidly switching binary signal that synthesizes two sine waves It would be very difficult to tell Chapter 1 PropScope Introduction and Setup Page 17 what sine waves are being synthesized by looking at the upper Oscilloscope screen The lower Spectrum Analyzer screen shows two prominent vertical bars in a graph revealing two component sine waves one in the 27 kHz neighborhood and the other at about 38 5 kHz Examining such signals will be introduced in Chapter 7 Basic Sine Wave Measurements XY Plot This tool plots two signals voltages against each other One signal s voltages are treated as x values and the other as y values The resulting plots are useful for determining certain relationships between two different signals The line tipping at 45 in Figure 1 8 indicates that the two signals are in phase like the two sine waves in Figure 1 4 Their shape is the same an
275. new name v In the copied program change the first PAUSE command to PAUSE 100 v Change the second PAUSE command to PAUSE 400 v Load the modified program into the BASIC Stamp v Check the Measure tab Is the Channel 2 Average voltage close to 1 V v How about the Channel 1 signal s Average voltage is it now close to 4 V v Compare the amount of high time the Channel 1 and Channel 2 traces spend during their cycle times v Try the high time and cycle time values in this equation for average voltage Average voltage 5 V x high time cycle time v Reload the unmodified version of Alternate High Low Signals bs2 into the BASIC Stamp before you continue Both PAUSE commands should be PAUSE 500 Oscilloscope Frequency Measurements For a signal that repeats itself periodically a periodic signal its cycle time is also called its period Again that s the amount of time it takes a signal to repeat itself A signal s frequency is the number of times it repeats in one second The Measure tab s Period and Frequency measurements for Channel 1 are pointed out in Figure 3 7 The PBASIC code in Alternate High Low Signals bs2 sets each I O pin output state pauses for 500 ms 1 2 a second then inverts the I O pin output states and pauses another 500 ms before repeating Since the program makes the signal repeat after two half second intervals its period should be close to 2 x 2 second 1 second The Measure tab provides a quick v
276. ng RCTIME command SSTAMP BS2 Target module BASIC Stamp 2 SPBASIC 2 5 Language PBASIC 2 5 time VAR Word For storing decay times PAUSE 1000 1 s before sending messages DO T Main Loop HIGH 2 Set P2 high PAUSE 100 Wait 0 1 seconds RCTIME 2 7 tame RC Decay time measurement DEBUG HOME time DEC5 time Display time in 2 us increments LOOP Repeat main loop Figure 8 34 shows the Debug Terminal display for the phototransistor test This measurement should get larger with less light and smaller with more light This circuit was designed for indoor lighting so make sure to stay out of really bright light conditions especially sunlight streaming in through a window v Test your phototransistor by casting a shadow over it with your hand the measurement should increase v Remove the shadow and the measurement should decrease again iix Com Port Baud Rate Parity COM seco z None E tet Bits Flow Control 1x r Dn Pats 7 J Jo RK 6 DSR CTS Figure 8 34 BASIC Stamp Phototransistor Decay Measurement time 02261 xi J Echo Off Page 308 Understanding Signals with the PropScope Figure 8 35 shows an example of the decay measurement It utilizes the same procedure as the potentiometer decay measurement except that the Horizontal dial is adjusted to a coarser time scale of 500 yus div to accommodate the decay time Your lighting conditions may be different and you
277. ng Signals with the PropScope Kit has all the parts you ll need to complete chapters 1 5 7 and 8 in the What s a g Microcontroller tutorial If you have not already completed this text and are new to Wh microcontrollers it s highly recommended before continuing here y Locate the free PDF version of the What s a Microcontroller text in the BASIC Stamp Editor software s Help menu version 2 5 or higher v Complete Chapters 1 5 8 and 9 y Skip Chapter 2 Activity 5 and Chapter 3 Activity 5 ACTIVITY 2 CONFIGURE AND ADJUST PROPSCOPE PROBES The PropScope probes and software may need some small configurations and adjustments to make them compatible with the measurements and instructions in this book This involves four simple steps Marking one probe with blue color bands and the other with red Setting the probe gain switch to X1 Setting probe gain in the PropScope software to X1 Connecting probes to BNC ports blue to CH1 and red to CH2 ak e This activity will guide you through the four steps with some explanations along the way Page 20 Understanding Signals with the PropScope Step 1 Mark one probe with blue color bands and the other with red Since the information in the PropScope software is color coded blue for one channel and red for the other one probe should be marked with blue marker bands and the other with red Each probe should have two marker bands of the same color one on the prob
278. ng a low signal Your actual BASIC Stamp will be the one sending messages to the PropScope It will be programmed to send serial bytes with hardware flow control enabled The program will make your BASIC Stamp send serial bytes using an I O pin connected to the PropScope s CH1 probe Your BASIC Stamp module s program will also monitor another I O pin for hardware flow control high low signals that the PropScope s function generator will transmit The function generator which is emulating a BASIC Stamp receiving serial messages with flow control will transmit a square wave When the square wave s signal is high busy it will cause your BASIC Stamp to wait When the signal is low not busy it will cause your BASIC Stamp to resume transmitting bytes The Oscilloscope will display the function generator s high low signals with its CH2 trace and its CH1 trace will indicate when serial messages are or are not transmitted With this approach you will be able to see how flow control works with high signals on CH2 interrupting serial activity and low signals allowing it to resume Flow Control Test Code In Test Flow Control bs2 the command SEROUT 11 10 84 REP A 254 uses P11 to transmit 254 A bytes in rapid succession and monitors P10 for flow control signals The PropScope s function generator output sends a square wave flow control signal to P10 During the time the square wave signal is high it interrupts the flow o
279. nge binary information with synchronous serial communication The hallmark of this method is that the devices rely on a signal to synchronize the exchange of binary values For example one device might send a series of high low signals with each high signal indicating that it has made a new binary value available on a separate line for the other device to receive Those high low signals synchronize the communication of the series of serial binary values Many electronic devices employ a microcontroller that communicates with other integrated circuits to perform tasks like memory storage analog to digital conversion and sensor measurements Many of these devices are designed to exchange information with the microcontroller using one of a variety of synchronous serial communication protocols A protocol is the set of rules both devices follow for the data exchange to work and they have names like Inter Integrated Circuit I C Serial Peripheral Interface SPD 3 Wire 4 Wire and Microwire The BASIC Stamp Module s EEPROM program memory indicated in Figure 5 1 and it is an example of a synchronous serial peripheral device The BASIC Stamp module s Interpreter chip is a microcontroller that uses the I C synchronous serial protocol to fetch the program tokens it executes from this chip and also to store and fetch values when executing PBASIC WRITE and READ commands I Program Memory i i i i H Figure 5 1 6 BASIC Stamp 2 Mo
280. nt binary 1s and Os might differ from the values in Figure 4 26 For that matter those values differ considerably from the values in the timing diagram in Figure 4 25 on page 134 That timing diagram indicates that binary zeros last 0 6 ms and binary ones last 1 2 ms However in Figure 4 26 the binary 1s appear last for 670 x 2us 1340 us That s 1 34 ms not 1 2 ms Likewise 360 x 2 us 720 us which is 0 72 ms not 0 6 ms How will you be able to tell the difference between your remote s binary 1 and binary 0 pulses Look for longer duration binary 1 pulses that are closer to 1 2 ms and shorter duration binary 0 pulses that are closer to 0 6 ms IR Remote Test Measurements with the PropScope Figure 4 27 shows a first view of the IR detector s output when the 3 button on the remote is pressed The Horizontal dial selection was chosen using the two cycle guideline of a signal in the Oscilloscope screen for a first look In this case we ll call a Page 140 Understanding Signals with the PropScope cycle one infrared message Looking at the timing diagram in Figure 4 25 on page 134 a rough approximation of the time an IR message lasts would be 2 4ms 1x2 4ms start pulse 7 2ms 12x0 6ms highs between low pulses 6 0ms 10x 0 6 ms binary 0 pulses 2 4ms 2x1 2 ms binary 1 pulses 18ms Assuming a message fits in a 20 ms window multiply by 2 for enough room for two cycles which is 40 ms Then
281. ntrol characters listed in Figure 6 3 have symbol names in the PBASIC language For example instead of DEBUG 0 for Clear Screen you can use DEBUG CLS In place of DEBUG 13 for Carriage Return you can use DEBUG CR The DEBUG command documentation in the BASIC Stamp Editor Help s PBASIC Language Reference has a complete list of PBASIC control character symbol names descriptions of their functions and the values they represent v Close the Preferences window and open the BASIC Stamp Editor s Help Click Help and select BASIC Stamp Editor Help v In the PBASIC Language Reference follow the link to the DEBUG command documentation Y Scroll down to the last table It lists the names and ASCII values of the functions in Figure 6 3 along with PBASIC Symbol names you can use as DEBUG command arguments like CLS CR HOME etc Page 178 Understanding Signals with the PropScope Your Turn Display A to Z a to z and_128 to 255 Printable ASCII Chart bs2 uses the char variable in a FOR NEXT loop to count from 32 TO 127 Each time through the loop the DEBUG command transmits the char variable s value to the PC using asynchronous serial communication The Debug Terminal then displays the ASCII value s corresponding character The PBASIC language treats characters in quotes as their ASCII value equivalents so you could actually create a woe myn FOR NEXT loop that counts from A to Z a to z or even
282. o process and execute all the commands in the DO LOOP that switch the I O pins on off apparently add up to an additional millisecond So the 101 ms value displayed in the Measure tab s Period field is verifies that the BASIC Stamp program is doing what it s supposed to Period Frequency Trigger Cursor gt P Figure 3 12 JF Measure tab Frequency Channel 1 hannel 2 s s and Period for Channel 1 bet 501v HED joims HE 102ms A mo a era with High Low 100 ms W sov n o A D Cycles bs2 running bul 2 54 ct 1 Page 84 Understanding Signals with the PropScope A signal that lasts about 1 10 of a second repeats about 10 times in a second If the signal takes a little longer than 1 10 of a second the frequency is going to repeat slightly less than 10 times per second so the 9 87 Hz value in the Measure tab s Frequency field also verifies that the program is working correctly Notice that the Channel 1 frequency displays as 9 87 Hz while the Channel 2 frequency which should be the same displays at 9 78 Hz The Measure tab s automated measurements are for getting a rough idea what the signal is doing a small discrepancy like this is not a big deal Tools and techniques for more precise measurements will be introduced at various points throughout the book Look back at Figure 3 11 on page 82 Notice that each signal has a visible falling edge a rising edge and another falling edge These
283. o vertical bars in the Spectrum Analyzer screen indicate the two sine wave component amplitudes and their left right positions place them over their frequencies For example the left bar in the spectrum analyzer has a height that lines up with about 0 46 V on the vertical scale and is over the 2 35 kHz frequency on the horizontal scale The bar to its right has a height that lines up with about 0 4 V on the vertical scale and is over the 3 14 kHz frequency on the horizontal scale This confirms what we know about D and G Notes bs2 It transmits a signal that is the sum of two sine waves with frequencies of 2349 Hz and 3136 Hz With the ability to indicate a waveform s sine wave component amplitudes and frequencies the spectrum analyzer is quite a handy tool Chapter 7 Basic Sine Wave Measurements Page 247 Figure 7 23 Analog View with frequency components of the signal in Figure 7 22 ia Fie Edt View Plugins Tools Help Gscilascope Logic Analyze Analog DSO LSA Timescale S00ys z CHI jo CH2 j2v b Oscilloscope lee EE ile mal E a ke he ae veedeeede JicHi v E Square Generate Sine Fi y Spectrum Epeli p Analyzer Custom Et orsa ating cursor measurement Vertical NAI T SE S pau scale is kHz component KEAPET i Tea sine wave i TESz
284. ogic State Analyzer with the Horizontal dial set to 200 ps division which is small enough to see the pulses and data values but large enough to still contain the entire CS signal low time v Adjust the PropScope s Horizontal dial to 200 ps division Chapter 5 Synchronous Serial Communication Page 171 Figure 5 17 Closer Look at the Higher Speed SHIFTIN Command E PropScope v2 0 1 iol xi Fie Edt View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSOLSA DC AC Off DC_AC DAC Off S eqs EEr E P OAE an za 18 i re Time ms Triggered Your Turn Pattern Detection When two devices communicate troubleshooting may need to start at a very small time window when a list of certain binary conditions occur The Pattern tab on the left side of the Logic Analyzer can be used to detect a list of conditions like the ones shown in Figure 5 18 By clicking each signal label 10 il i2 and or i3 repeatedly you can toggle through these five trigger conditions es _ Rising positive Edge Ma Low o g Falling negative Edge a No Trigger ON High Page 172 VALAR Understanding Signals with the PropScope Set your PropScope s Horizontal dial to 100 us division Click the Pattern tab on the side of the Logic State Analyzer Set up the pat
285. oing signal s test point v Press the CH2 probe end against the SIN probe point for your board Figure 6 27 CH2 Probe Position for SIN Signal m yu Se Rev a l Sin T T a A h T BASIC Stamp HomeWork Board Serial B fE All caida esucaton Al Underneath the Serial Port Connecter For other boards get directions from the Supplement at www parallax com go propscope Figure 6 28 shows an incoming serial C from the keyboard The inverted incoming signal is shown in the upper CH2 trace and the true version transmitted by P11 is shown in the lower CH1 trace Since the CH2 signal swings from 6 to 6 V we can infer that the voltage rails that connect to the serial driver chip in this particular computer are 6 V Chapter 6 Asynchronous Serial Communication Page 209 The voltage levels you observe may be different but should fall somewhere in the 3 to 25 V range v Adjust your PropScope for the Horizontal Vertical and Trigger settings shown in Figure 6 28 v Make sure the Trigger Voltage control is somewhere in the CH2 trace s 3 V range and the Trigger Time control is aligned with the second time division Keep in mind that even though the Trigger Voltage control is on the left margin when you trigger from the CH2 trace the voltage scale values are shown on the Oscilloscope screen s right margin v Click the Debug Terminal s Transmit windowpane again and try tapping a few keys Figure 6 28 shows
286. oltages with the PropScope s DAC Card section on page 45 v If the Run button is off click it to restart the oscilloscope Figure 3 18 shows a 20 Hz sawtooth waveform generated by the DAC Card s DAC output and monitored and displayed by Channel 1 vIn the Generator panel set the slider to Sawtooth the Frequency to 20 Hz Amplitude to 3 Offset to 0 and then click Generate Vv Set the Horizontal dial to 20 ms and the Vertical CH1 dial to 1 V v Click the Trigger tab and set the Mode to Continuous Edge to Rise Level to Auto and Source to CH1 v Adjust the Trigger Time so that the vertical trigger crosshair aligns with the second time division line Page 94 Understanding Signals with the PropScope Figure 3 18 Sawtooth Waveform PropScope v2 0 1 File Edt View Plugins Tools Help At 181ms CH1 0 68V CH2 DC_AC DAC Off Sawtooth amete Itv lt Cmn Osa ona a FF Square Generate A sre Freqency Zore 160 Time ms Triggered Tages m Measure T Level Source lp a ay Ca ai CET C Continuous C Mey Em ser 9 a CH1 in 20ms The sawtooth wave in Figure 3 18 has a peak to peak amplitude of 3 V True to its name the peak to peak amplitude is the voltage between the top and bottom voltage peaks This waveform swings from about 1 V above the 0 V ground line to about 11 2 V below so its amplitude is a tot
287. onnect to your computer project parts to build circuits on your BASIC Stamp development board and a 350 page book that guides you step by step from the basics through advanced electronic measurement techniques The PropScope has the features of many electronic test bench tools built into one small package that you connect to your computer DC voltmeter to measure voltage levels Oscilloscope to measure and plot voltages that vary with time Logic analyzer to measure and plots digital signal levels Spectrum analyzer to measure and plot sine wave components in signals XY Plotter to plot one signal voltage against another Function generator to synthesize signals for testing circuits and microcontroller projects These tools are used to test circuits microcontroller interactions with circuits and microcontroller communication with other integrated circuits and computers Topics include measuring DC voltages and currents Human speed signals that vary with time and can be observed Pulses for controlling devices and synthesizing signals Digital signaling between microcontrollers and integrated circuits chips Digital signaling between microcontrollers and other microcontrollers or computers Sine waves in signals and how filters and amplifiers affect them RC circuit responses sensor measurements and simple filters Basic amplifier building blocks Many oscilloscope lab manuals present the material in a format that assum
288. onstants for non keypad buttons CON ii CON 16 CON iy Chapter 4 Pulse Width Modulation Page 147 VolUp CON 18 VolDn CON 13 Power CON Fag NS rae DRE rect Co a re aaa a a nl ad a Ge SONY TV IR remote variables irPulse VAR Word remoteCode VAR Byte DO GOSUB Get_Ir_Remote_Code DEBUG CLS Remote code DEC remoteCode PAUSE 100 LOOP SONY TV IR remote subroutine loads the remote code into the remoteCode variable Get_Ir_Remote_Code remoteCode 0 Clear all bits in remoteCode Wait for resting state between messages to end DO RCTIME IrDet 1 irPulse LOOP UNTIL irPulse gt 1000 Measure start pulse If out of range then retry at Get_Ir_Remote_Code ROTIPMETO 0 PRUISE IF irPulse gt 1125 OR irPulse lt 675 THEN GOTO Get_Ir_Remote_Code Get data bit pulses RCTIME IrDet 0 irPulse Measure pulse IF irPulse gt 300 THEN remoteCode BITO 1 Set or leave clear bit 0 RCTIME IrDet 0 irPulse Measure next pulse IF irPulse gt 300 THEN remoteCode BIT1 1 Set or leave clear bit 1 RCTIME IrDet 0 irPulse ecu IF irPulse gt 300 THEN remoteCode BIT2 1 RCTIME IrDet 0 irPulse IF irPulse gt 300 THEN remoteCode BIT3 1 RCTIME IrDet 0 irPulse Page 148 Understanding Signals with the PropScope Il bh IF irPulse gt 300 THEN remoteCode BIT4 RCTIME IrDet 0 irPulse IF irPulse gt 300 THEN remoteCode BIT5 RCTIME IrDet 0 irPulse IF irPulse gt 300
289. or protection In the case of the RC decay measurement the resistor forms a voltage divider with the potentiometer s resistance That voltage divider limits the final voltage the potentiometer can charge up to This shows in the graph as the capacitor charging up to a lower value when the potentiometer s resistance is less which in turn reduces the decay time slightly more than the smaller RC time constant would on its own Chapter 8 RC Circuit Measurements Page 283 Voltage dividers were introduced in Chapter 2 Activity 5 The voltage divider shown below is the 220 resistor in series with the potentiometer with 5 V applied Potentiometer Sensor Test Parts 1 Potentiometer 10 kQ 103 1 Capacitor 0 1 uF 104 1 Resistor 220 Q red red brown If you have a BASIC Stamp HomeWork board use a wire instead of the 220 Q resistor misc Jumper wires Potentiometer Sensor Test Circuit Figure 8 14 shows the potentiometer decay test circuit and Figure 8 15 shows an example wiring diagram vy Build the circuit shown in Figure 8 14 and Figure 8 15 P7 PropScope CH1 Oe Figure 8 14 Potentiometer PropScope GND Test Circuit If you have a BASIC Stamp Schematic HomeWork Board replace 220 Q resistor with a wire Vss Page 284 Understanding Signals with the PropScope If you have a BASIC Stamp HomeWork Board use a wire instead of a 220 Q resistor Vdd Vin Vss
290. osshair to get as close as possible to 1 4 V Slide the Trigger Time control to align the vertical trigger crosshair with the 8 time division line v Adjust the Horizontal dial to 500 us div v Check your display against Figure 8 18 The display is now ready for verifying the BASIC Stamp module s 872 us decay time measurement with a cursor measurement Figure 8 19 shows how the purple B cursors were adjusted to intersect with the CH1 decay trace at 1 4 V Keep in mind that 1 4 V is not 36 8 it s the BASIC Stamp module s threshold voltage Then the Green A cursors were adjusted to intersect at the start of the decay The time measurement in the Cursor display s A field turns out to be 880 us which is close enough to the BASIC Stamp module s 436 x 2 us 872 us time measurement for verification purposes v Set the purple horizontal B voltage cursor to 1 4 V using the Cursor display s B voltage measurement as a guide v Line the vertical B time cursor so that it crosses the intersection of the horizontal B voltage cursor and the CH1 trace Position the green A cursors up to intersect with the start of the decay The Cursor display s A field shows the difference between the two time cursors which should be fairly close to twice the value displayed in by the BASIC Stamp in the Debug Terminal v Make a note of the Horizontal A cursor s voltage level We ll compare the voltage the capacitor charged to in Figure 8 1
291. ould be DCM for duty cycle modulation Duty cycle is a measurement of the ratio of a binary signal s high time to its cycle time When you set the PWM command s Duty argument to a value you are specifying the number of 256 of its cycle time that the signal stays high In this activity you will test to verify this by measuring and calculating the PWM signal s duty cycle for different PwM command Duty arguments DAC Test Parts 1 Resistor 220 Q red red brown 1 Resistor 1 kQ brown black red 1 Capacitor 1 pF misc Jumper wires Page 120 Understanding Signals with the PropScope DAC Test Circuit The circuit in Figure 4 13 is one of the two DAC circuits that were used to set DC voltages in Chapter 2 Activity 4 This circuit was also used to make the PropScope plot a simulated heart monitor display in Chapter 3 Activity 4 A resistor has been added between P14 and the CH2 probe to prevent possible I O pin damage that could happen if the probe is inadvertently left connected to the DAC Card s function generator output v Before you start building this circuit make sure the probe BNC connectors are connected to PropScope CH1 and CH2 There SHOULD NOT be any probes connected to the DAC Card v Build the circuit shown in Figure 4 13 and Figure 4 14 DAC Test Program This program uses the same PWM 14 64 1 to set the voltage across the capacitor to 1 25 V like it did in Chapter 2 Activity 4 Instea
292. own in Figure 3 2 Y Click hold and slide the plot area bar to the far right of the Plot Preview as shown in Figure 3 3 v Check the Run button and make sure it is bright green indicating the oscilloscope is running v Start twisting the potentiometer s adjusting knob back and forth while pressing downward if needed to maintain electrical contact v After the Oscilloscope screen has filled up click the Run button again to stop the plotting and freeze the waveform v Point at various points on the waveform The floating cursor should display the voltage and time of the measurement you are pointing at lt lt Your Turn Adjust the Visible Portion of the Plot with the Plot Area Bar As mentioned earlier the PropScope stores two Oscilloscope screens worth of voltage samples It also previews them at the top of the Oscilloscope display in the Plot Preview shown in Figure 3 3 You can use the Plot Area bar to position the Oscilloscope screen over any portion of the Plot Preview and then view the corresponding portion of the voltage plot in the Oscilloscope screen v Click the Run button to resume plotting voltages v Keep adjusting the potentiometer s knob back and forth until the measurements span the entire Plot Preview v Stop the display again by clicking the Run Button v Try positioning the Plot Area bar at different locations in the Plot Preview Compare the small plot outlined by the Plot Area bar in the Plot P
293. p 1 Figure out how much time a couple of signal cycles will take Step 2 Divide that value by 10 to get your Horizontal dial setting Again the Horizontal dial sets the time division which is 1 10 the width of the Oscilloscope display Set the Horizontal dial to 20 ms Chapter 3 Human speed Measurements Page 79 v Check the time scale at the bottom of the Oscilloscope screen Is it 200 ms wide The PropScope is now plotting in oscilloscope Mode not datalogging mode The PropScope only plots in datalogging mode from right to left for the 200 ms div 500 e ms div and 1 s div w For all other Horizontal dial settings the PropScope plots measurements in oscilloscope mode from left to right In this mode the display does not actually scroll It only updates the display when all the measurements in the plot have been acquired Oscilloscope Trigger and Settings That may have solved cramped display problem but now the signal isn t staying still in the Oscilloscope screen Now that the oscilloscope is at a Horizontal setting below 200 ms div it is functioning in oscilloscope mode refreshing the display only after it has acquired all the measurements and displaying those measurements from left to right So instead of evenly scrolling it now skips each time the display updates Taking measurements on a waveform that jumps around like that could be nerve wracking So oscilloscopes have a built in feature calle
294. pScope Table 4 1 shows approximate measurements of the first four pulses as buttons 1 through 9 are pressed Table 4 1 Pulse Patterns for SONY TV Remote Buttons Pulse Button Variable 1 2 3 4 5 6 7 8 9 time 0 360 670 360 670 360 670 360 670 360 time 1 360 360 670 670 360 360 670 670 360 time 2 360 360 360 360 670 670 670 670 360 time 3 360 360 360 360 360 360 360 360 670 For this remote the 670 values are binary 1s and the 360 values are binary 0s Time 3 through time 0 store pulse durations that represent the lowest four binary digits in the 12 digit binary number the IR remote transmits Table 4 2 shows a sequence of the first five remote buttons their pulse duration patterns the binary values they represent and the decimal equivalent values We ll call these values remote codes v Test your remote buttons 6 7 8 9 and 0 and fill in the rest of the table v Your values may differ but there should be a pattern of values that are closer to 600 that are binary 1s and values that are closer to 300 that are binary Os Table 4 2 Buttons Pulse Patterns Binary amp Decimal Values Button time 3 time 2 time 1 time 0 Binary Value Decimal value 1 360 360 360 360 0000 0 360 360 360 670 0001 1 360 360 670 360 0010 2 360 360 670 670 0011 3 360 670 360 360 0100 4 O10 O N D or R o
295. pScope s Vertical and Horizontal dials using what you have learned If you have a BASIC Stamp HomeWork Board accessing the actual I O pin can be tricky because the 220 Q resistor is built onto the board See Figure 2 33 on page 63 for more info ACTIVITY 4 SUMMED SINE WAVES A piano player presses several keys at a time to make sounds called chords The notes seem to blend and it s an example of a group of sine waves one for each note added together Examples of pairs of sine waves added together can be found in touchtone phones Each key press makes a unique tone that transmits that key s value Since each touchtone is two tones added together it s called dual tone frequency modulation DTMF In addition to individual frequencies the BASIC Stamp can be programmed to transmit two sine wave frequencies at once This makes it possible to play part of a chord In this Page 238 Understanding Signals with the PropScope activity you will compare the D7 and F7 note frequencies from the previous activity against the two notes played together As with the previous activity you will listen to the results on the piezospeaker first and then examine the signals with the PropScope s Oscilloscope view ON DTMF Tones The BASIC Stamp can also play DTMF tones with the DTMFOUT command ol Although they can be viewed with the PropScope the tones frequencies are typically too w low to be audible through the piezospeaker i
296. pe PropScope CH1 P11 D w l 2202 PropScope CH2 Figure 6 13 Both Channel Probes P10 Connected to I O Pin 220 Q Sockets through Protection Resistors PropScope GND ae i X3 Figure 6 14 Wiring Diagram Example of Figure 6 13 X2 Chapter 6 Asynchronous Serial Communication Page 191 True vs Inverted Comparison Test Measurements Figure 6 15 shows the true signal on the lower CH1 trace and the inverted signal on the upper CH2 trace Note that the inverted signal is simply the opposite level from the true signal for all bits and resting states v v AAA Slide the Vertical CH2 coupling switch from Off to DC Click hold and drag the red CH2 trace and position it so that its O V ground line is slightly above the top of the CH1 trace In Figure 6 15 it s 1 5 voltage divisions above the top of the CH1 trace Adjust the Horizontal dial to 500 ms division Slide the Plot Area bar to the far left If needed adjust the Trigger Time control so that it aligns the CH1 signal s first negative edge with the second time division Figure 6 15 True Signal on CH1 lower trace Inverted on CH2 upper trace C Generate Frequency 10khz Triggered TY Hoson Ot orem 7 Trigger Page
297. play for one second about 34 seconds into the program That s 33 seconds worth or characters and the 1 second PAUSE command at the very beginning Keep in mind that the signaling shown by the PropScope will change once every second as the BASIC Stamp transmits a new ASCII value Also notice that the Trigger in Figure 6 7 has been set to Fall since the message begins with a negative transition from high resting state to low start bit v Drag the CH1 trace downward so that 0 V is only slightly above the time scale In Figure 6 7 the 0 V ground line is 1 voltage division above the time scale v Configure the PropScope s Horizontal Vertical and Trigger controls according to Figure 6 7 v Set the Trigger Voltage control to about 2 5 V and the Trigger Time control to the second time division v Watch the counting pattern in the Oscilloscope and use the Debug Terminal as a reference for seeing how the ASCII codes correspond to the signals in the Oscilloscope v Verify that the pattern displayed by the PropScope changes once every second Chapter 6 Asynchronous Serial Communication Page 183 Figure 6 7 ASCII 65 Capital A Osciloscoape Logic Analyzer Analog D80 LSA om square Generate Sine Frequency pomen ame j t 5 Custom D Edt otso CH1 V Wait for Trigger Time ms Trigger Cursor Off gy auto Eo GE Continuous C
298. ponds with high low signals Figure 9 5 2 5 V Threshold Crossings Cause High Low Signals at Comparator Output Oscilloscope Logic Analyzer Analog DSO LSA SRA Swot wea SaaS SEES ES EE SEE DC_AC DAC Off E Square Generate Sine Frequency 10khz J ee P Amplitude 1 e Custom _ Edit Ofset o Trigger CH1 7 ERT mm eE Continuous CH2 P E Iq 1617 Sep 7 az Y CHT in V 05s Chapter 9 Op Amp Building Blocks Page 327 Your Turn Verify the Threshold Voltage The gold bars on the 1 KQ resistors indicate a 5 tolerance That means their actual values may be up to 5 above or below their nominal named values These variations from 1 KQ typically cause the voltage divider s output to be close to but not exactly 2 5 V In Figure 9 5 the mouse is pointing at one of the transitions and the floating cursor info near the top of the Oscilloscope screen is reporting the CH2 voltage as 2 49 V This voltage will vary from one transition to the next but an average of these measurements can be taken to approximate the threshold This value can be compared to a direct measurement of the threshold voltage v Use the CH2 probe to test the voltage at the LM358 pin 2 This is the resistor voltage divider output and it s the actual threshold voltage You may need to click the Run button to get the display to hold still Try averaging the f
299. put s lower power supply limit try Amplitude 1 V and Offset 0 25 V v Reconnect the op amp s Vee positive supply input to Vin before continuing Figure 9 14 Output Signal Clipping Oscilloscope n lt _ lt T Square Generate Sine Frequency m Sawtooth P 0 20 e a Wait for Trigger Time ms Chapter 9 Op Amp Building Blocks Page 339 Your Turn How the Op Amp Translates Offset Voltage Figure 9 15 shows an example of how a non inverting op amp circuit amplifies both the offset and the amplitude The offset of the input sine wave is 1 1 V Since the gain of the circuit is 3 the amplitude of the sine wave is about 3 V peak to peak and the offset is almost 1 1 x 3 3 3 V v Change the Generator settings back to Amplitude 1 V and Offset 0 5 V v Increase the Offset from 0 5 to 1 2 V in increments of 0 1 V and observe the signal after each increase The signal s amplitude should stay at 3 Vpp but the offset should increase by 0 3 V for every 0 1 V increase in your input signal s offset Figure 9 15 1 1 V Offset Amplified to almost 3 3 V Oscilloscope E Square Generate Sine Frequency 100hz Custom Edt omea 7 v Set the Trigger Mode to Off v Change the Generator Amplitude to 0 V v Apply different DC voltages to the amplifier s input by entering values into the Offset field Try 0 5 to 1 2 V in increments of 0 1 V again TH 4 56V r
300. quency Display result DEGoaNeyecles a Hz LOOP Repeat main loop Test Procedure The function generator should be adjusted to make the sine wave cross the BASIC Stamp module s 1 4 V I O pin input threshold v Set the function generator s amplitude to 2 8 V and the offset to 1 4 V Remember to press the Enter key to make the PropScope update its function generator output v Verify that the frequency the BASIC Stamp reports to the Debug Terminal agrees with the one in the PropScope Measure display as shown in Figure 7 11 Your Turn Amplitude Offset Options to Maintain 1 4 V Crossings Since the BASIC Stamp is just counting the number of times the signal crosses its 1 4 V threshold for a frequency measurement the amplitude does not have to be 2 8 V Since the offset is 1 4 V the sine wave will still crosses the I O pin threshold with each cycle regardless of whether the amplitude is 2 8 V 2 V 1 V or even 0 5 V v Try a few different signal amplitudes with the 1 4 V offset and verify that the BASIC Stamp continues to count signal cycles Chapter 7 Basic Sine Wave Measurements Page 227 v Set the amplitude to 2 Vpp before continuing With a 2 Vpp sine wave the offset can be increased to somewhere in the neighborhood of 2 4 V before the sine wave no longer passes the 1 4 V threshold y Try it Figure 7 11 BASIC Stamp Frequency Measurement Compared to PropScope lo x Data Bits Flow Conto tx M DTR AT
301. r communicating with synchronous serial devices Provided the command s arguments and features are used correctly they can make short work of synchronous serial communication code and they are also much faster than loops that store individual bits in a variable Page 174 Understanding Signals with the PropScope Chapter 6 Asynchronous Serial Communication The previous chapter introduced synchronous serial communication which relies on a separate clock signal to synchronize the exchange of a series of values In contrast asynchronous serial communication is the exchange of a series of values without the synchronizing clock signal ASYNCHRONOUS SERIAL DEVICES Figure 6 1 shows some examples of devices that use asynchronous serial communication to exchange information When a BASIC Stamp executes a DEBUG command it uses asynchronous serial communication to send information to the PC either through a serial cable or to a chip that converts the serial message to the USB protocol Figure 6 1 Asynchronous Serial Device Examples BS2 to PC on Serial BS2 to Parallax Serial LCD Board of Education Asynchronous Serial s Communication BS2 to USB Serial Converter on USB Board of Education Chapter 6 Asynchronous Serial Communication Page 175 Another example the BASIC Stamp sends the Parallax Serial LCD Liquid Crystal
302. r educational use exclusively with Parallax BASIC Stamp products and the student is charged no more than the cost of duplication The PDF files are not locked enabling selection of texts and images to prepare handouts transparencies or PowerPoint presentations FOREIGN TRANSLATIONS Many of our Stamps in Class texts have been translated into other languages these texts are free downloads and subject to the same Copyright Permissions for Educational Use as our original versions To see the full list click on the Tutorials amp Translations link at www parallax com Education These were prepared in coordination with the Parallax Volunteer Translator program If you are interested in participating in our Volunteer Translator program email translations parallax com ABOUT THE AUTHOR Andy Lindsay joined Parallax Inc in 1999 and has since authored a dozen books and numerous articles and product documents for the company Much of the material Andy develops is based on observations and educator feedback that he collected while traveling the nation and abroad teaching Parallax Educator Courses and events Andy studied Electrical and Electronic Engineering at California State University Sacramento Preface Page 9 SPECIAL CONTRIBUTORS The Parallax team assembled to prepare this textbook includes Lesson design and technical writing by Andy Lindsay cover art by Jen Jacobs graphic illustrations by Rich Allred and Andy Lindsay technical re
303. r evenly distributed across several T O pins within a given bank of eight The I O pin banks are P0 P7 and P8 P15 Two questions to ask before turning on both LEDs at once are 1 how much current does the T O pin supply one LED circuit and 2 would it be safe to deliver twice that current to supply two LEDs at once 4 _ Source and Sink When an I O pin sends a high signal it acts as a current source applying Vdd 5 V to the circuit When an I O pin sends a low signal it acts as a current sink ww applying Vss 0 V to the circuit If you can measure the voltage across a resistor you can use the resistor s value and Ohm s Law to calculate the current passing through the resistor Ohm s Law states that the voltage measured across a resistor V is equal to the current I passing through the resistor multiplied by its resistance R Depending on which two terms you know or have measured you can rearrange the terms in Ohm s Law to calculate the third V V IxR i 1 V R Figure 2 34 R R V Ohm s Law for a Resistor Page 64 Understanding Signals with the PropScope We know the resistance R in the LED circuit it is 220 Q So the only other value we need to calculate the current through the resistor is the voltage V across it One quick way to measure the voltage across the resistor is to measure the voltages at both ends of the resistor and then subtract The difference between the two voltages is call
304. r i Cuid i Measure Zoom In on the Shorter Time Value Figure 8 22 shows how reducing the Horizontal dial to a smaller time division makes it possible to zoom in and get a more precise measurement Take a look at the time A value in the Cursor panel Ironically it s 346 us is a little further off than the 336 us from Figure 8 21 Still the PropScope is now reporting a more precise measurement with the higher Horizontal time division setting Furthermore a 6 us difference is not cause for concern It s only 1 76 off the BASIC Stamp measurement which can be attributed to a combination of possible differences in the two devices clock frequencies slight alignment errors with the cursors and slight deviations of the actual threshold voltage from the 1 4 V level v Carefully adjust the pot s knob to make the Debug Terminal report 170 Page 292 Understanding Signals with the PropScope v Reduce your time division to 50 us and repeat the cursor time and voltage measurements Figure 8 22 Adjust the Horizontal Dial to Zoom in on the Decay Time PropScope v1 1 1 File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO Pisi DC_AC DAC Off Generate set ama 4 400 Custom Q Triggered Measure Sy 7 GVyge Vertical ode gt BED Horizontal Float Trigger Your Turn Pick a Decay Time
305. r on this event You can do this by setting the Logic State Analyzer s i0 trace to negative edge trigger After that you will also have to adjust the horizontal scale so that the entire serial exchange is visible in the Oscilloscope screen To match Figure 5 8 the Trigger Time control should also be adjusted to align the i0 trace s negative edge with the first time division line v Set the Horizontal dial to 1 ms division v Repeatedly click the i0 signal label on the left side of the Logic State Analyzer screen until it displays a negative edge symbol v Adjust the Logic State Analyzer s Trigger Time control y so that it aligns its vertical crosshair with the first time division line This should in turn cause the i0 trace s negative edge to line up with the first time division line v Compare the signaling in Figure 5 8 to the timing diagram in Figure 5 5 v Check i2 in the Logic State Analyzer to verify that the 1s and Os transmitted by the ADC0831 s DO line are the correct sequence for the binary number 10101010 decimal 170 Figure 5 8 shows an example of how to do this Page 160 Understanding Signals with the PropScope Figure 5 8 Verify Value Transmitted by ADC0831 with Logic Analyzer After setting i0 to negative edge set the Trigger Time control so that the CS signal s negative edge lines up with the first time division Click i0 twice to set to negative edge trigger Null b
306. r with a vertical height amplitude and horizontal position frequency Two sine waves often have to be compared to each other for amplitude and phase differences These comparisons are fundamental to numerous circuit analysis and system stability test procedures As an example of amplitude and phase comparison the PropScope s function generator was used to apply a signal to the input of an RC low pass filter circuit Then the amplitude and phase of a sine wave at the circuit s output was compared to the function generated signal applied to its input These tests were also performed at several frequencies to examine how the filter lets certain frequencies pass through while blocking others by reducing the signal amplitude at its output Page 266 Understanding Signals with the PropScope Chapter 8 RC Circuit Measurements RESISTORS CAPACITORS AND RC CIRCUITS A resistor resists the flow of current and a capacitor has the capacity to store charge kind of like a tiny rechargeable battery These two components form the building blocks for a variety of resistor capacitor circuits commonly called RC circuits The voltage waveform created by a capacitor charging or discharging through a resistor has a characteristic shape Like a sine wave this characteristic shape can be described by a mathematical equation It s called an exponential decay equation In Activity 1 you will examine a graph of an exponential decay equat
307. rcuit and Equation Vss The circuit in Figure 2 21 is designed to supply voltage but not current The RC DAC you experimented with has a similar limitation Many devices have voltage inputs that are called high impedance inputs they do not draw current and are compatible with voltage dividers and RC DACs A i Op amp buffer circuits will be introduced in Chapter 9 Op amp is a shortened version of the component s real name operational amplifier A buffer s output voltage can be determined by a voltage divider or an RC DAC and it can maintain its output voltage and still supply current to circuits For example the PropScope DAC Card s function generator output is buffered by an op amp making it possible to drive DC current loads up to about 1 mA minimal without any measurable reduction in output voltage If you substitute Vj Vdd 5 V and Ry Ro 1 KQO the result of Vo should be 2 5 V v Try substituting the values into the voltage divider equation Do your calculations agree What happens if you use two 10 kQ resistors instead How about R 1 KQ and R 2 KQ Also try Ri 2 KQ and R3 1 KQ Chapter 2 DC Measurements Page 51 Figure 2 22 shows a test circuit to verify the voltage divider output with Ry R 1 KQ and V Vdd 5 V v Build the circuit shown in Figure 2 22 Figure 2 22 Voltage Divider Measurement Schematic and Wiring Diagram Vdd Vin Vso X3 Vdd P15
308. re useful diagnostic tools for finding and fixing errors In this activity we ll examine how the DSO LSA view s Oscilloscope and Logic Analyzer can be used to diagnose problems 1 and 2 Recreate and Examine Error 1 Before we recreate error 1 it s important to zoom out a little to see multiple ADC communications Figure 5 9 shows an example with the PAUSE 100 command in the commented out of the example code and the Horizontal dial adjusted to 10 ms division In the Logic State Analyzer the CS line stays high between measurements and there are two measurements visible v Remove the PAUSE 100 from ADC0831Test1 bs2 by placing an apostrophe to its left so that it reads PAUSE 100 v Load the Modified program into the BASIC Stamp v Change the Horizontal dial setting in the PropScope s DSO LSA view to 10 ms division Page 162 Understanding Signals with the PropScope Figure 5 9 Two ADC0831 Measurements in Logic Analyzer Oscilloscope Logic Analyzer Analog DSOLSA Hae one 400ps 200s Run 50 p S00 ps i t 20p tins DC_AC DAC Off El D GS 257 yess qa ae LG i Ga IzcHz nv tO 20 Triggered Time rms Now that we know what to expect when it s working right let s try disabling the command that sets CS high between measurements v In AD
309. re wave s high signal has to last at least 5 time constants 5t for the capacitor to charge and the low signal also needs to last 5t for the capacitor to discharge So the minimum value of one signal cycle period Tmin to the RC circuit s input has to last for a total of ten RC time constants Tmin 10t 10 x 1 ms 10 ms This means the input frequency has to be at most the reciprocal of Tmin fmax 1 Tmin 100 Hz For a first view it s always good to see at least two full cycles which means that the display has to be two cycles wide Oscilloscope screen widthmin 2 X Tmin 2 x 10 ms 20 ms Remember that the Horizontal dial specifies the width of a time division which is 1 10 of the Oscilloscope screen s width so Horizontal dial settingmin Oscilloscope screen widthmin 10 20 ms 10 2 ms Chapter 8 RC Circuit Measurements Page 273 Examine the Capacitor Voltage as it Charges and Discharges Figure 8 7 shows two cycles of the square wave the function generator applies to the RC circuit along with the RC decays at the circuit s output v Ae aS Generator panel Function switch Square Frequency 100 Hz Amplitude 4 V Offset 2 V Dials Horizontal 2 ms div Vertical CH1 2 V div CH2 2 V div Vertical coupling switches CH1 DC CH2 DAC Trigger tab Mode Continuous Edge Rise Level Auto Source CH2 Trigger Time control Set to 1 time division line Position the re
310. review to the full size one in the Oscilloscope display The portion of the plot outlined by the Plot Area bar should be a miniature of the one in the oscilloscope display What if you want to check the voltage of the pot s W terminal once every second While the Run button is stopped you can use the time division lines as a guide for where to point the floating cursor to get measurements that are one second apart Since each time division is 500 ms two time divisions add up to 1 second s worth of plotted voltage measurements So use the floating cursor to point at the plot at every other vertical time division line to check the voltage at one second intervals Page 72 Understanding Signals with the PropScope Now what if you want to check voltages once every second for 10 seconds You can treat 0 seconds as the leftmost edge of the Oscilloscope screen when the plot area bar all the way to the left and treat 10 seconds as the rightmost edge when the plot area bar is all the way to the right You will have to reposition the Plot Area bar at least once to check all ten measurements v The Run button should still be stopped so that you have a frozen plot of potentiometer measurements v Use the Floating Cursor to check the W terminal s voltages at seconds 0 1 2 3 and up to second 10 Reposition the Plot Area bar as needed At the far right of the plot the measurements may end at a value like 9 97 s you can use that as your 10 seco
311. rigger Mode eve Source qo qa _ ean EEN Let s talk about what each of those Trigger tab settings and the two trigger controls do The Source is CH1 meaning that the PropScope monitors channel 1 for a trigger event Since Edge has been set to Rise that trigger event happens when the voltage rises above a certain voltage What voltage With the Level set to automatic the oscilloscope uses the signal s average voltage to set that voltage Yes it s the same average voltage you would see in the Measure tab s Average voltage field As proof notice on the left that the Trigger Voltage control has been automatically positioned at the halfway point between the channel 1 high and low signals The Trigger tab s Mode is Continuous which means as soon it s done plotting measurements it will start checking for another trigger event Chapter 3 Human speed Measurements Page 81 As soon as the PropScope is done with its current plot it starts looking for another trigger event Since the Trigger Voltage level is set to automatic that ll be at about 2 5 V for the signal we are currently plotting By adjusting the Trigger Time control you ll be able to see where the trigger event occurs Figure 3 10 shows an example of the crosshairs that appears as you point at the Trigger Time control These crosshairs indicate the Trigger Time and Voltage level Since the Trigger tab s Edge has been set to Rise with a Source of
312. rosses the CH1 0 V ground line the CH1 trace v Check the A measurement in the Cursors display and compare to the calculated 78 5 us value Figure 8 41 Phase Output Input Comparison 8 PropScope v1 1 1 File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA 100ps_200ps S00 ps Ims 08 i ign green A K time cursor with ne j 0 4 e F i o N a Align purple Bo time cursor with ESDS En CH1 signal s DC_AC DAC Off a i 0 8 ifm Generate F Penance pescsesheess sid seses lees th gee se patton ihiihi pleas ampitude T gt 40 80 120 160 200 Custom QEdt osef Time us Triggered Trigger Vertical Horizontal Float Get the resulting A time measurement from this field in Cursor display Chapter 8 RC Circuit Measurements Page 319 Again how close should the measurement be For the phase delay 6 is reasonable Comparing the 79 6 us measurement from Figure 8 41 against the predicted value of 78 5 us we have measured predicted oerror x 100 la predicted 79 78 T See OU ae 78 5 us 1 4 Your Turn Test Other Frequencies and Time Constants Keep in mind that a low pass filter lets low frequency sine waves through and filters out higher frequency sine waves If the DAC is set to 1 10 the cutoff frequency the RC
313. rvo Horn Angle Vdd 5 V Excerpt from What s a Vss 0 V Microcontroller v3 0 Vdd 5 V Vss 0 V Page 112 Understanding Signals with the PropScope Figure 4 8 shows just three servo horn positions in a range of motion that spans from 0 to 180 Figure 4 9 shows a map of the servo s range of horn positions with some example pulse durations that will make the servo point in certain directions You can use this map to make the servo point to an angle of your choosing For example you could choose to make the servo point to the 30 position by sending 0 834 ms pulses That pulse duration was calculated using the fact that 30 is 30 45 between the pulse durations for 0 and 45 The corresponding PULSOUT Pin Duration command for that angle is PULSOUT 14 417 That command tells the BASIC Stamp to transmit a 417 x 2 us 0 834 ms pulse using I O pin P14 For other puLsout Duration arguments just divide 2 pus into the millisecond pulse duration round to the nearest integer and use that result for the Duration argument Figure 4 9 Pulse Width vs Servo Horn Angle Excerpt from What s a Microcontroller v3 0 Oo 75 PULSOUT 14 1 5 ms S i lt Q oy Oy m n gt 4 EA amp E 90 Sa Sof ys Bi 5 st 60 03 wah s 3 0 o PULSOUT 14 1250 180 2 5 ms 0 PULSOUT 14 250 0 5 ms standard servo www parallax com Chapter 4 Pulse Width Modulation Page 113 The twist tie
314. rvo hold different positions Figure 4 11 shows traces for PULSOUT 14 500 PULSOUT 14 750 and PuLSOUT 14 1000 With the larger PULSOUT Duration values the period of the signal gets a little longer because the PAUSE in the program does not get any shorter to compensate for the longer pulse durations So the frequency of the pulses drops slightly with larger PULSOUT Duration values As mentioned earlier the pulse durations have to be precise but the frequency of the pulses just has to be in the neighborhood of 50 Hz So small differences like the ones caused by different pulse durations do not affect the servo s performance PULSOUT 14 500 Servo horn to 459 PULSOUT 14 750 Servo horn to 909 4 PULSOUT 14 1000 _ ES Servo horn to 1359 2 i 10 20 30 40 CH Time rns Triggered v Modify ServoCenter bs2 so that it reads PULSOUT 14 500 v Run the modified program and note the width of the pulses v Repeat for PULSOUT Duration values of 750 and 1000 and verify that the pulse width increases each time Chapter 4 Pulse Width Modulation Page 117 For more precise pulse time measurements the Horizontal dial can be adjusted to a lower value that makes the pulse fill more of the Oscilloscope screen Figure 4 12 shows an example with the Horizontal dial set to 500 us division The Vertical cursors are placed at the pulse s rising and falling edges They are also call
315. s the BASIC Stamp can safely deliver current to two LEDs at once Your Turn More Current Measurements v Repeat by replacing the 220 Q resistor with a 1 KQ resistor Could your BASIC Stamp safely drive eight LEDs with a bank of 8 I O pins using 1 kQ resistors SUMMARY This chapter examined power supply voltages and surveyed a variety of circuits and measurement techniques for fixed DC voltages DC voltages that were measured included Vdd Vin Vss voltage dividers outputs and DAC circuit outputs set by the BASIC Stamp and the PropScope DAC Card s DAC output The Oscilloscope s voltage divisions floating cursor and Measure tab were used to measure these voltages The effects of circuit load on I O pin high signal voltages were examined Higher current draws resulted in lower I O pin driver output voltages Ohm s Law was used to determine the current through a circuit by measuring the voltage at each of the resistor s terminals The voltage across the resistor and its resistance can be used in I V R to calculate the current passing through the resistor Chapter 3 Human speed Measurements Page 67 Chapter 3 Human speed Measurements HUMAN SPEED VS ELECTRONIC SPEED Human speed and electronic speed are not really technical terms but they can be useful for describing the differences between signals we can and cannot quantify without specialized equipment Examples of human speed signals include street lights
316. shown in Figure 4 5 SS Make sure that the color coded servo cable wires line up with the White Red Black labels shown in Figure 4 5 Connect the PropScope CH1 probe to P14 and the probe s ground clip to Vss Skip to the PWM Signals for Servo Control section it starts on page 111 White gt Red gt Black gt E Figure 4 5 pal D P13 5 o pni 2 P10 bs A o P7 J PARALLAX re H o Pa i Ae fl P2 P1 PO 1 x2 Chapter 4 Pulse Width Modulation Page 109 Wiring Diagram for Figure 4 3 using the Board of Education Page 110 Understanding Signals with the PropScope BASIC Stamp HomeWork Board Serial Rev C and newer USB all revisions Disconnect power from your board v Build the servo port as shown in Figure 4 6 Vdd Vin Vss x3 none Ca Cocos N i pA DOOOO NA J pA GOOG Yopi pu A COooo Baga r ne ooono gogo Figure 4 6 o00000 D0000 Po aana Ionan BASIC Stamp Be ooooo 00000 HomeWork Board Ho000 00000 Servo Port Wirin 00000 jooooo 9 OOOCL P4 OOOCL P3 00001 P2 P1 OOOCL B0 00000 00000 o 00000 00000 v Connect the servo to the port as shown in Figure 4 7 making sure the
317. shows the Debug Terminal s reports for object detected 0 and object not detected 1 v With an object like a book or your hand about 10 cm in front of where the IR LED is pointing verify that the Debug Terminal displays irDetectLeft 0 v With no objects in the IR LED s line of sight verify that the Debug Terminal reports irDetectLeft 1 Figure 4 21 Debug Terminal IR Detection Tests Object detected No object detected iojxi iojxi Se oe oe Soe ae ae Data Bits Flow Control Data Bits Flow Control ata Le wee rol ohx r DTR ats ala a for i 1x M DIR ATS I AX DSR CTS AX DSR CTS Macros Pause Clear Close J Echo Off Page 130 Understanding Signals with the PropScope Figure 4 22 shows the Oscilloscope view while an object is detected The 1 ms FREQOUT signal is shown by the upper blue CH1 trace The lower red CH2 trace sends a low signal during that time which indicates that it detected reflected infrared with a 38 5 kHz component The BASIC Stamp I O pin interprets the 0 V applied to its P9 I O pin as a binary 0 which results in the irDetectLeft 0 message on the left side of Figure 4 21 Figure 4 22 Object Detected E PropScope v2 0 1 Fie Edt View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA z 4 IR Receiver DC AC Oft DC_AC DAC Off Sends tow signal to P9 F Square Generate Sentan Amplitude TV 4
318. sible to view plots of the binary signal exchange between the circuits and the BASIC Stamp I O pins with the PropScope software s LSA logic state analyzer feature v Build the circuit and make the DAC Card connections shown in Figure 3 13 and Figure 3 14 The DAC Card s 1 to 4 inputs will be to your boards Vss ground This gives The socket labeled G is the logic analyzer s ground connection and it should be connected analyzer has a 0 V reference to compare the voltage signals it measures displayed as logic analyzer channels 1 through 4 the systems a common ground so that the logic Figure 3 13 Pushbutton and LED Circuit with Logic State Analyzer Connections DAC CARD 1 DAC CARD 0 P15 P14 2202 DAC CARD G DAC CARD 2 P4 P3 220 Q DAC CARD 3 Chapter 3 Human speed Measurements Page 87 Logic State Analyzer Inputs 0 3 and Common Ground G DAC CARD Figure 3 14 Wiring Example for the Figure 3 13 Schematic generator signal output and a 4 channel logic analyzer input measurements with CH1 just not CH2 The DAC in DAC Card stands for Digital to Analog Conversion and refers to the card s ability to set voltages and synthesize signals with the function generator This card is really
319. software v Connect your PropScope to your computer with a USB cable v Run the PropScope software and the BASIC Stamp Editor software v Connect your BASIC Stamp development board to your computer and power an supply and run a test program If you have never used your BASIC Stamp 1 development board before open the BASIC Stamp Editor Help follow the Getting py Started directions to connect your hardware to your computer and test your programming connection Between If instructed to modify a circuit on your board or build a different circuit y Disconnect power from your board before modifying any circuit v Reconnect power after you have modified the circuit After If you are done for the day or leaving your circuit unattended for a while v If your board has a 3 position switch move it to position 0 v Disconnect the board s power source Even if the 3 position switch is off it s still a good idea to disconnect the power source when the board is unattended Ground Test Parts List 3 Jumper wires Chapter 2 DC Measurements Page 29 Ground Test Circuit Figure 2 3 shows how to connect the PropScope s probes to verify that they measure 0 V at Vss Disconnect power from your board Connect the PropScope probes as shown in Figure 2 3 Reconnect power to your board Figure 2 3 ProoScope Ground Test Schematic and Wiring Diagram PropScope Ch2 PropScope CH1 I PropScope GND
320. ssible to adjust the system s light sensitivity With additional testing a better estimate of time between PWM and RCTIME can be determined Then the program can just add that value to the measurements In other applications this time difference doesn t even matter For example there s an application for the Boe Bot robot that makes it compare two of these light sensor measurements to figure out which one detects brighter light This works well for light source following activities The Boe Bot robot s program doesn t care about precise measurements it just wants to know which measurement is larger Since the extra time would be identical for both sensors the comparison of the two measurements still supplies the information the BASIC Stamp needs for determining the direction of the light source A current load on a DAC circuit without an op amp has its uses this is one of them The previous activity demonstrated how a resistive load prevented the capacitor in a DAC circuit from holding its charge which in turn prevented it from maintaining an output voltage If the goal is to maintain an output voltage under load the load poses a problem that an op amp will be used to fix in the next chapter In this automatic light level adjustment activity the goal was not to maintain a voltage output l it was to charge a capacitor with a light sensor load to a certain voltage before measuring w the decay With control over the volta
321. sure to press it downward onto the wh breadboard so that it keeps electrical contact v Rotate the pot s adjustment knob back and forth from one end of its 270 range of motion to the other If needed push down on the pot as you adjust it to maintain its electrical contacts v In the Oscilloscope screen observe how the CH1 trace moves up and down v As you adjust the pot s knob slowly from one end of its range to the other monitor the voltage with the floating cursor and or the Measure tab s Average voltage measurement How does the voltage relate to the pot s adjusting knob s position Determining I O Pin Threshold Voltage A BASIC Stamp I O pin set to input interprets voltages above 1 4 V as binary 1 and below 1 4 V as binary 0 The 1 4 volt level is called the I O pin s logic threshold This threshold voltage level can vary slightly from one I O pin to the next as well as from one BASIC Stamp to the next These variations are typically small and are unlikely to exceed a tenth of a volt You can use the PropScope to determine your BASIC Stamp module s I O pin threshold voltage The circuit will need to be modified so that the pot s W terminal is connected to an I O pin Then run a program to display the voltage state the I O pin detects As the pot is adjusted you can monitor the I O pin state in the Debug Terminal When the pot reaches a position that causes the Debug Terminal to report a change in state the
322. t 1591 5Hz x 360 Now we know to that the cutoff frequency for our RC filter is 1591 5 Hz If we supply the filter with a sine wave at this frequency we ll expect the output to be 70 7 of the input signal amplitude with a phase shift if 45 which corresponds to a time shift of 78 5 us Test the Amplitude and Cutoff Frequency First let s check to find out if the filter s output signal is about 70 7 of the input signal from the function generator To make this measurement easy the PropScope s function generator can supply the RC circuit s input with a 1 5915 kHz sine wave that s 1 Vpp Then the output signal s amplitude should be about 0 707 Vpp Figure 8 40 shows an example Page 316 Understanding Signals with the PropScope v Set the Generate switch to Sine with a Frequency of 1591 5 Hz an Amplitude of 1 V an Offset of 0 V and remember to click the Generate button v Adjust the dials coupling switches and Trigger tab settings to match Figure 8 40 v Adjust the trace positions as shown in the Oscilloscope display with both the CH2 DAC trace and CH1 circuit output trace in the middle of the screen Their ground lines should be right on top of each other Vv Set the Measure display to CH1 If its channel indicator is set to CH2 click it to toggle back to CH1 v Use the Measure display to verify that the CH1 measurement of the output sine wave s amplitude is in the 0 707 V neighborhood Figure 8 40 Ampl
323. t 10 V So if your computer s serial port uses signal voltages outside 10 V you ll still be able to measure the values One Time 10x Probe Calibration The PropScope Probe Kit came with instructions for a one time probe calibration that should be done before taking measurements with the probes set to 10x While monitoring a 1 kHz square wave trace with a probe set to 10x a screwdriver that also came with the probe kit is used to adjust a potentiometer inside the BNC connector The goal of the adjustment is to make the measured square wave in the CH1 trace as square as the wave it receives This compensates for electrical interactions between the 10x probe circuit and the Oscilloscope input circuit The source of the 1 kHz square wave will be the PropScope s function generator and the trace will be measured on CH1 v Set the switch in the CH1 probe rod to X10 and update the PropScope software s Tools Manage Probes settings so that the Probe 1 Gain is 10X Chapter 6 Asynchronous Serial Communication Page 201 Connect your PropScope probes so that the function generator sends a signal to the CH1 probe For this particular task you do not need to connect clips to your board yjust connect the ground clips to each other and the DAC Card s function generator output probe to the CH1 input probe Another option is to follow the connection instructions in the Set DC Voltages with the PropScope s DAC Card section on page 45 Eit
324. t Peak amplitudes are more common in equations that describe sine waves In contrast peak to peak amplitudes are more common in oscilloscope measurements If you ever need the peak amplitude measurement for an equation just take the peak to peak measurement from your oscilloscope and divide by 2 Larger sine wave amplitudes result in louder piezospeaker volumes smaller amplitudes result in quieter speaker volumes Figure 7 6 shows how a cycle of the sine wave looks at three different amplitudes As the amplitude increases the sine wave s height in the oscilloscope increases and so does the volume Try these adjustments to the signal s amplitude v If your tone and display are paused click the On button again to resume viewing the live signal and playing the tone v Type into the Generator panel s Amplitude field and press Enter v Listen to volume from the speaker and make a note of the sine wave s amplitude in the Oscilloscope screen v Repeat by entering values of 2 and then 3 into the Generator panel s Amplitude field The tone should get a little bit louder with each adjustment Listen to the volume and make a note of the Oscilloscope amplitude after each adjustment Chapter 7 Basic Sine Wave Measurements Page 217 Figure 7 5 Peak to Peak vs Peak Amplitude 0 2 0 4 0 6 0 8 KCH1 v Time ms Triggered Measure Vmax gt AM O2us Vpp Vmax Vmin Vp Vpp 2 une Of s
325. t and the car would go forward again Likewise an RC boat rudder has to push against the water flowing around it to make the boat turn in the water 2 Figure 4 2 Servo 1 Plug 2 Cable 3 Horn 4 Mounting Flange PARALLAX www parallax com Driving an RC vehicle usually involves manipulating joysticks on a radio transmitter As the joysticks are moved to certain positions the servos in the vehicle rotate their horns to positions that mirror the joystick positions For example a joystick moved left and right in the radio control transmitter unit might make the steering servo in an RC car rotate left and right Also if the joystick is held in a certain position the servo holds its horn at the corresponding position and resists opposing forces Chapter 4 Pulse Width Modulation Page 107 The radio transmitters in these systems code the joystick s position into bursts of radio activity The durations of the bursts indicate the joystick positions On the RC vehicle a radio receiver converts these bursts of radio activity into binary high low signals The signal is high while the radio bursts last and low when there is no radio activity The brief high signals are called pulses and the radio receiver sends these binary pulses to the various servos in the vehicle to control them The process of adjusting pulse durations that get sent to a servo to control its horn position is an example of pulse width modulation In this activ
326. t the same time it sends a copy of that character to T O pin P11 using 9600 8N1 true serial signaling v Open the BASIC Stamp Editor s Help and look up the sERroUT command in the PBASIC Language Reference v Read the Syntax and Function sections v Find the Common Baud Rates and Corresponding Baud mode Values table for the BS2 and verify that 84 is the Baud mode in SEROUT 11 84 char that will make it send its characters using true signaling at 9600 8N1 vV Enter and run Printable ASCII Chart to IO bs2 Printable ASCII Chart to 10 bs2 Display another value in the ASCII character chart once every second Transmit a copy of that value to Pll using 9600 bps 8N1 with true signaling SSTAMP BS2 Target module BASIC Stamp 2 SPBASIC 2 5 Language PBASIC 2 5 Page 182 Understanding Signals with the PropScope char VAR Word X PAUSE 1000 DO DEBUG CLS n PRINTABLE ASCII CHARACTERS CRPI from 32 CE 127 HOR Cline 32 Wo IZ DEBUG CRSRXY char 32 24 10 char 32 24 3 SEROUE dik Sl CRAT x DEBUG FENA E DECS CNAE t PAUSE 1000 r NEXT 1 LOOP Asynchronous Serial Test Measurements Kor counting and Storing ASCTI 1 second delay before messages Main loop Table heading Count from 32 CO LA Posie lon cursor Send 9600 bps 8N1 true byte Display byte in Debug Terminal 1 second delay Repeat FOR NEXT loop Repeat main loop Figure 6 7 shows an example of the A character which will dis
327. t this the PropScope DAC Card s function generator can generate the square wave and then the Spectrum Analyzer can display the frequency components v Set up your PropScope s hardware to transmit signals from the DAC Card s function generator to the CH1 probe Instructions and circuit for this were first introduced in the Set DC Voltages with the PropScope s DAC Card section starting on page 45 v Configure the Generator panel to make the DAC Card s function generator output transmit a 1 kHz 1 5 Vpp O V offset square wave You can use the Generator panel settings in Figure 7 24 as a guide Chapter 7 Basic Sine Wave Measurements Page 249 Figure 7 24 1 kHz 1 5 Vpp 0 Vpc Offset Square Wave 8 PropScope 1 1 0 BME Fie Edt View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA DC_AC DAC Off Generate Anotuse Ts ___ Hf Tv E Time ms Triggered Measure Next even though the Analog view has variations on most of the controls you ve been using in Oscilloscope view it s better to set up the measurement in the Oscilloscope view and then switch over Then you can make minor adjustments in the Analog view to get the information you need For the clearest spectrum analysis it s best to have four to eight cycles of the signal displayed in the Oscilloscope and the voltage scale should make the waveform fill at least half of
328. tage Now it represents the average of the channel s voltage over time which is 2 52 V in the figure Since the signal is 5 V half the time and O V the other half of the time it stands to reason that the average voltage of half way between these two values would be about 2 Y volts v Click the Measure tab Chapter 3 Human speed Measurements Page 75 v Check the voltages for each channel in the Measure tab and make sure they agree with what you see on the Oscilloscope screen Figure 3 5 Binary Signals in the Oscilloscope view File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA DC_AC DAC Off Generate a Custom _ Edit Orset o Trigger Cursor Measure Mode ge eve Source cots d mgee m dpi hal Trigger y t Measure Channel 1 pores Figure 3 6 Vmax W 501v l M ross Measure tab Vmin Mo A 0 95212 Voltage Info for Vop W so sw O ng Binary Signal A EZP Average is now 1 2 of Vmax Vmin Page 76 Understanding Signals with the PropScope Your Turn A Closer Look at Average Voltage What happens to the Average voltage if the P14 signal is high less than half the time Try making it high 1 5 of its cycle time the cycle time is the amount of time a signal takes to repeat itself and see what happens to the Average voltage measurement v Save a copy of Alternate High Low Signals bs2 under a
329. te Analyzer screens at the same time v Set the CH1 Vertical dial to 1 V division and the Vertical coupling switch to DC v Verify that the CH1 voltage measures 3 3 V lt s Figure 5 7 Check Voltage and Communication with DSO LSA View A PropScope v2 0 1 iol xi File Edit View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA Approximate sal ax Confirmation DC AC Off DC _ AC DAC Off of the 3 3 V measurement in the Oscilloscope screen 6 Time ms Triggered Chapter 5 Synchronous Serial Communication Page 159 The Logic State Analyzer screen in Figure 5 8 is useful for synchronous serial signaling verification The ADC0831Testl bs2 code example from Activity 2 implements the timing diagram in Figure 5 5 and the Logic State Analyzer display in Figure 5 8 verifies that it s doing it right In Activity 1 you connected the PropScope DAC Card s Logic State Analyzer input 0 to the ADC0831 s CS line So the CS signal will be displayed by the trace labeled 10 The first thing the program s main loop does is set the CS line low to start a measurement and communication It also sets CS high again when it s done Since the first communication event is the CS line s negative edge transition from high to low the Logic State Analyzer can be configured to trigge
330. termined by supply voltage and current tests Other devices rely on DC voltages to adjust how they operate One example is a voltage controlled oscillator A voltage supplied by a device like the BASIC Stamp causes the oscillator to transmit a signal at a certain frequency Another example some amplifiers have to be fine tuned with DC voltages which are called trim voltages These voltages do not have to supply any power to the devices they are just there to set some level Because of this they can be simpler circuits involving resistors or a digital to analog converter D A converter or DAC Both supply and other DC voltages are typically measured with a device called a voltmeter Some voltmeters stand alone and others are built into devices called multimeters A multimeter can also measure resistance current and sometimes other electrical properties like capacitance and transistor gain In this chapter you will use the PropScope in place of a voltmeter to measure your board s supply voltages You will also build and test circuits that can generate DC voltages that could be used to adjust how other devices operate trim voltages Additionally you will use voltage measurements at different points in circuits to determine the current passing through them and also to determine whether a BASIC Stamp I O pin can safely supply current to a given circuit Chapter 2 DC Measurements Page 27 ACTIVITY 1 GROUND TEST The supply volta
331. tern of trigger conditions shown in Figure 5 18 Try creating a signal pattern that never happens For example set i0 to high and il to positive edge What happens to the screen activity and what message appears The Logic State Analyzer keeps waiting for a trigger event that doesn t occur Try setting 10 to trigger on low and il to trigger on rising edge The rising edge will line up with the fist division line because the i0 Low condition was satisfied but the display still has to wait for a rising edge on il Experiment with clicking through different options on different channels and examine any changes in signal edge alignment with the first time division line Figure 5 18 Pattern Triggering i pal w oO I Low Signal Level 2 High Signal Level 22S GE EE EE GE EE EE EE 0 4 0 6 1 2 Triggered Time ms More ADC0831 Projects Basic Analog and Digital and Process Control are two Stamps in Class textbooks kits with activities and projects that utilize the ADCO831 A D converter Both textbooks are free pdf downloads from www parallax com education Chapter 5 Synchronous Serial Communication Page 173 SUMMARY A variety of inexpensive special purpose integrated circuits are available to perform tasks like memory storage coprocessing and analog to digital conversion to name a few and many of them are designed to exchange information with a microcontroller
332. th aa s T E mE De lt Pe agi i a magen Continuous Step Figure 2 5 shows a close up of the oscilloscope display after some adjustments Note that there are two bold colored lines called traces which cross the Oscilloscope screen Chapter 2 DC Measurements Page 31 You can grab these traces with your mouse pointer and drag them up and down so that their locations match Figure 2 5 v In your PropScope software use your mouse to point at click and hold the blue channel 1 trace v Drag the channel 1 trace either up or down to position it in your Oscilloscope display roughly matching the location in Figure 2 5 As you move the channel 1 trace the numbers in the voltage scale on the left should move with it The 0 on the left which indicates 0 V should move to keep level with the trace as it moves v Make a similar adjustment to the red channel 2 trace so that it also matches the figure The scale on the right side should move with the channel 2 trace as you drag it up down with your mouse and the 0 V indicator on the right should also stay level with it as you make your adjustments Channel 1 Tracey t Measured 0V Figure 2 5 Voltages on the Oscilloscope with both Vertical scale dials set to 5 V Alright so what are the traces in the Figure 2 5 Oscilloscope screen telling us Since the probes are connected to Vss along with
333. th devices rely on the negative edge of the start bit to determine when to send receive the next binary value in the series Inverted serial communication is the voltage opposite of true serial communication with all highs changed to lows and all lows changed to highs RS232 serial communication is inverted and is the type of signaling between a PC and device s connected to its serial port s The high signals can be in the 3 to 25 V range and low signals in the 3 to 25 V range High and low voltages will vary with computer hardware but tend to be determined by their built in power supply voltage rails The PropScope s time units per division can be customized by right clicking the Oscilloscope screen and filling in a number in the Timescale Value cell This is useful for setting the units per division so that each one lasts a single bit time which in turn is very useful for translating asynchronous serial messages into the values they represent Setting the correct trigger edge is also important for aligning the start bit s edge with a time division For trigger settings keep in mind that a true signal initiates its start bit with a negative edge and an inverted signal with a positive edge Page 212 Understanding Signals with the PropScope Chapter 7 Basic Sine Wave Measurements SINE WAVE EXAMPLES Figure 7 1 shows two cycles of a sine wave Examples of this gradual up down pattern can be found in waves in a pool or at sea in
334. th the PropScope Click the Oscilloscope view s Measure tab v Examine the average voltage values Measure Tab a noo C Trigger Meastire Channel 1 z Figure 2 8 M sov EA Measure Tab Information Nl M sov d VCE The Average voltage IEO NEEE UE D e fields display DC values bu 4 ggy j Average DC Voltages Your Turn Battery Tests The voltage across a 9 V battery s terminals can give you an indication of how much charge is left If the supply in Figure 2 8 is an alkaline battery it has already supplied a significant portion of its charge but still has some life left v Obtain a new 9 V alkaline battery one that has been in service for a while but is still good and a dead one v Plug each battery into your Board and make notes of the Vin voltage for each e Testing battery voltage directly You can also connect a ground clip directly to a battery s 1 negative terminal and the probe hook to the positive terminal to measure its voltage ACTIVITY 3 OSCILLOSCOPE VOLTAGE SCALE ADJUSTMENTS Now that you ve tried a few simple DC voltage measurements with the oscilloscope this activity takes a closer look at what each trace really represents It also demonstrates how to adjust each channel s voltage scale to accommodate the voltage measurement and how to check the voltage measurement limits for a given voltage scale adjustment Chapter 2 DC Measurements Page 35 Po
335. that the ratio of 0 to 360 is the same as the ratio of the time t to the cycle s period T From that a phase angle equation is simple Just multiply both sides of the equation by 360 to solve for 8 I ENR RIOT T 360 T The equation 90 t T x 360 is saying that the phase angle 0 is equal to the time t of a point on the sine wave divided by its period T and multiplied by 360 For example let s say we have a 2 kHz sine wave That s a frequency but we need to know its period T Remember the period is the reciprocal of frequency so you can use T 1 f to calculate the period 1 1 T gt T f 2000 Hz 0 0005 s 0 5 ms Chapter 7 Basic Sine Wave Measurements Page 255 Let s say we want to know the phase angle of a point that s t 0 375 ms into a cycle of the 2 kHz sine wave Since we know its period is 0 5 ms we have all the values we need to calculate the phase angle b x 360 375S lt 360 270 S TIP Since f 1 T you could replace t T with txf for this equation 0 tx f x360 fe 1 This can save you the frequency to period conversion calculation For example If t 0 375 ins and f 2 kHz 6 0 000375 s x 2000 Hz x 360 270 v Take a look at Figure 7 26 Does the 0 375 ms match with 270 for a 2 kHz signal v Repeat this exercise for 0 125 ms in a 2 kHz signal and 0 25 ms in a 1 kHz signal Make sure to check your results against Figure 7 2
336. the Stamps in Class Mini Projects link at www parallax com Education Educators Courses These hands on intensive 1 or 2 day courses for instructors are taught by Parallax engineers or experienced teachers who are using Parallax educational materials in their classrooms Visit www parallax com Education Educators Courses for details Page 8 Understanding Signals with the PropScope Parallax Educator s Forum In this free private forum educators can ask questions and share their experiences with using Parallax products in their classrooms Supplemental Education Materials are also posted here To enroll email education parallax com for instructions proof of status as an educator will be required Supplemental Educational Materials Select Parallax educational texts have an unpublished set of questions and solutions posted in our Parallax Educators Forum we invite educators to copy and modify this material at will for the quick preparation of homework quizzes and tests PowerPoint presentations and test materials prepared by other educators may be posted here as well Copyright Permissions for Educational Use No site license is required for the download duplication and installation of Parallax software for educational use with Parallax products on as many school or home computers as needed Our Stamps in Class texts and BASIC Stamp Manual are all available as free PDF downloads and may be duplicated as long as it is fo
337. the first one to make the waveform ramp back down for a triangle wave v Save Test Saw Tooth bs2 as Test Ramping bs2 v Insert this For NEXxT loop after the first one This loop should occupy new lines between the NEXT and LOOP commands in the existing program FOR dacV 254 TO 1 FOR NEXT loop repeats 255x PWM 14 dacv 1 dacV sweeps from 0 to 255 NEXT Next repetition Chapter 3 Human speed Measurements Page 93 v Load the modified program into the BASIC Stamp and remember to give the new waveform a couple of seconds to make its way across the Plot Preview and into the Oscilloscope screen ___Why does the second FoR NEXT loop count from 254 down to 1 On the way up the _ first FOR NEXT loop took the dacv variable from 0 to 255 so on the way down the second loop only needs to step from 254 down to 1 PropScope Function Generator Waveforms The PropScope s DAC Card and Generator panel can be used to generate square sine and saw tooth waves The Generator panel also has a custom setting that you can use to draw your own waveform with the Edit feature Many circuit tests involve applying a signal and examining the effect on the output So the PropScope s function generator feature is exceedingly useful for applying a signal to the circuit s input Then the circuit s output can be examined with the oscilloscope channel 1 v Repeat the five checklist instructions in the Set DC V
338. the ground clips both traces should indicate 0 V measurements The blue trace should be level with the blue 0 on the left side of the Oscilloscope screen indicating that the voltage measured by the channel 1 CH1 probe Page 32 Understanding Signals with the PropScope is zero volts The voltage at the channel 2 CH2 probe is also 0 V so the red CH2 trace should be level with a red 0 on the right side of the Oscilloscope screen ACTIVITY 2 VDD AND VIN DC SUPPLY VOLTAGES Next let s verify that Vdd 5 Vpc and measure your particular battery or DC supply voltage by probing Vin We ll measure Vdd with channel 1 and Vin with channel 2 Figure 2 6 shows how to connect your probes The ground clips don t move because they are tied to a reference voltage of Vss 0 V Supply Voltage Test Circuit Disconnect power and plug the CH1 and CH2 probes into the Vdd and Vin sockets as shown in Figure 2 6 Reconnect power to your board Figure 2 6 Probe Supply Voltages with the PropScope Vdd Vin PropScope Ch2 PropScope CH1 PropScope GND Vss N Chapter 2 DC Measurements Page 33 Supply Voltage Measurement Settings When you reconnect your board s power dashed lines will still remain at the 0 V levels for each
339. the square wave s frequency Note that as the frequency of the harmonic increases its amplitude decreases v Click the Analog tab The Spectrum analyzer will probably display a horizontal frequency scale of 0 to 5 kHz So only the first three sine wave harmonics will be visible You can adjust the Spectrum Analyzer s frequency scale with your mouse Just point at the Spectrum Analyzer screen and then click hold and drag either right or left Dragging left increases the frequency scale dragging right decreases it v To increase the frequency scale for viewing more harmonics point at the Spectrum Analyzer screen with your mouse then click hold and drag left v Adjust the Spectrum Analyzer plot so that it resembles the lower portion of Figure 7 25 with a frequency scale of 0 to 10 kHz Chapter 7 Basic Sine Wave Measurements Page 251 Figure 7 25 Sine Wave Components in a Square Wave fie Ede ew Mgs Tok hib Crcaaicane Lage Anata Ansion 050 LSA Tonevewle anny Frogen tana angos 15 Otter T rey ones aan Point at the Spectrum Analyzer screen with your mouse Then click hold and drag left until the Spectrum Analyzer s frequency scale displays from 0 to 10k called harmonics add to make the square wa f The result should look like this gt A square wave is made up of an infinite number of sine wave
340. then resemble Figure 8 10 With that change it causes the function generator signal s negative edge to line up with the 2 time division The 10 ms of the function generator s low signal becomes visible in CH2 and the RC circuit s output voltage response as the capacitor discharges becomes visible in CH1 v Change the Trigger Edge setting from Rise to Fall Your view should now resemble Figure 8 10 Figure 8 10 Toggle Trigger Edge from Rise to Fall to See the 10 ms Discharge E PropScope v1 1 0 AE File Edt View Plugins Tools Help Osciloscope Logic Analyzer Analog DSO LSA Start Dc AC Oft DC_AC DAC Off ort 3 m E discharging M 5 suare Generate j Eee Frequency soz Sawtooth Amplitude T 4 Continuous j Step Page 278 Understanding Signals with the PropScope RC Time Constant Measurements In an RC decay trace if 1 time constant has elapsed the voltage will have decayed from 100 to 36 8 The converse is also true if the voltage has decayed to the 36 8 level one time constant has elapsed With this in mind the trick to measuring an RC circuit s time constant from its decay response is to set a horizontal voltage cursor at a level that s 36 8 above the final voltage Then use the time cursors to measure from the start of the decay to the point where the voltage cursor that s at the 36 8 level intersects with the trace
341. though both i3 and i4 signals are high Correct the problem in the PBASIC code and load the modified code into the BASIC Stamp Hint Either break the IF THEN ELSE ENDIF block into two separate IF THEN ELSE blocks or look up the other solution near the end of Activity 4 in What s a Microcontroller Chapter 3 v Use your PropScope s Logic Analyzer view to demonstrate that the modified code corrected the problem Page 90 Understanding Signals with the PropScope ACTIVITY 4 D A AND FUNCTION GENERATOR WAVEFORMS The same digital to analog conversion features we used to set DC voltages in Chapter 2 Activity 4 can also be used to synthesize time varying waveforms DAC Parts List 1 Resistor 1 KQ brown black red 1 Capacitor 1 pF misc Jumper wires DAC Circuit Figure 3 16 shows a schematic and wiring diagram of one BASIC Stamp D A conversion DAC circuit along with a PropScope probe attached for measuring the DAC output voltages v Build the circuit shown in Figure 3 16 v Verify that the negative terminal of the capacitor is connected to Vss before reconnecting power to your board Vdd Vin x3 P14 P15 z Jaa 1kQ r1 DI a ol Figure 3 16 1uF gt O8 00 OO PropScope CH1 a a One DAC PropScope GND a SCR P7 P6 Vss P5 i P4 P3
342. time it takes the voltage to decay to the BASIC Stamp module s 1 4 V logic threshold it s a good idea to set the set the Trigger tab s Level setting to Normal and then manually adjust the Trigger Voltage control to 1 4 V The trace will cross this at the end of the measurement so it s also a good idea to adjust the Trigger Time control to somewhere near the right of the oscilloscope display like maybe the 8 time division line Figure 8 18 Adjustments for Verifying BASIC Stamp RC Decay Measurements Brropscopevitt eee Fie Edt View Plugins Tools Help Set Horizontal dial to 200 us div Oscilloscope Logic Analyzer Analog DSO LSA Set Trigger Time control to make vertica Fie es line up with 8 time givisjo on DCAC Off DC_AC DAC Off Square Generate Sine Frequency 10kHz Set Trigger Voltage control to p See re ee oes ee izontal Ci ir at i V 0 4 0 8 1 2 Time ms Triggered O rs Cursor Level Auto Normal Change Trigger tab s Level switch to Normal Page 288 Understanding Signals with the PropScope v Change the Trigger tab s Level switch from Auto to Normal v Slide the Trigger Voltage control to 1 4 V The Trigger display in the bottom right corner of the window shows your manually adjusted trigger voltage value Watch it as you adjust the Trigger Voltage control s horizontal trigger cr
343. toff frequency that s ten time lower instead of higher SUMMARY This chapter introduced RC circuits and their relationship to the exponential decay equation This relationship was examined with oscilloscope measurements verifying the importance of the RC time constant This understanding of RC circuits is useful for measuring the output of devices that vary in resistance or capacitance Using the PBASIC RcTIME command the position of a potentiometer dial a variable resistor was measured The same programming technique was also used to measure a phototransistor s output current which resulted in a more linear decay We took a closer look at some circuits used in previous chapters The RC DAC s role in D A conversion was examined along with its susceptibility to resistive loads The low pass filter was also revisited this time with attention to testing its cutoff frequency Chapter 9 Op Amp Building Blocks Page 321 Chapter 9 Op Amp Building Blocks OPERATIONAL AMPLIFIERS Operational amplifiers op amps are versatile electronic building blocks that can be configured with circuits to perform a wide variety of operations on signals Examples in this chapter include e Comparing two voltages e Buffering a voltage signal that cannot drive a resistive load directly like the RC DAC circuit from Chapter 8 Activity 5 Amplifying an input voltage Inverting an input voltage Attenuating and invert an input voltage Ad
344. tput voltage back to the inverting input So to get the voltage at the inverting input to match the voltage at the non inverting input the op amp s output has to send a larger voltage The net effect is that it amplifies the output signal For example if Rf and Ri are the same value the voltage between Rf and Ri would be of Vo So to make the voltage at the inverting terminal match the voltage at the non inverting terminal the op amp has to make Vo twice the value of Vi the voltage applied to the non inverting terminal Chapter 9 Op Amp Building Blocks Page 333 Input Vi Rf Vi Output Signal O Signal 3 a Figure 9 9 Ri Non Inverting Amplifier Feedback and Input Resistors Rf is called the feedback resistor and Ri is called the input resistor Common Textbook Version of the Same Circuit Compare the circuit below to the one in Figure 9 9 They are the same circuit just drawn differently Ri Rf Output Vo Signal lt n n lt n on lt n n Understanding and Applying Gain The amount an amplifier amplifies voltage is measured as gain and it s the ratio of output voltage Vo to input voltage Vi You can also think about it as the ratio of output signal amplitude to input signal amplitude Gain J Vi Gain is a convenient value for predicting output voltage based on input voltage Simply multiply both sides of the Gain ratio by Vi and you get an equation that predicts
345. ts in this activity for 1 kHz and 6 kHz You may need to choose different Horizontal and Vertical settings to accommodate the different amplitudes and frequencies Record the output signal amplitudes and phase delays for both frequencies The pattern your measurements should fall into is lower frequency less output attenuation and phase delay higher frequency more attenuation and phase delay v v SUMMARY In this chapter sine waves were displayed with the PropScope and their basic properties of amplitude frequency DC offset and phase shift were studied Practical applications of amplitude and frequency were demonstrated in a tone s volume and pitch While DC offset doesn t necessarily affect the way a tone sounds in a piezospeaker it can be problematic for audio speakers DC offset can also be adjusted to position a sine wave so that it crosses a microcontroller s I O pin threshold with each cycle making it possible for the BASIC Stamp to count cycles and determine frequency Musical notes are sine waves of specific frequencies and the PropScope was used to study the sine waves of individual notes as well as notes played together In terms of sine waves two notes played together is equivalent to adding two sine waves together point by point Given an arbitrary waveform it can be difficult to determine its sine wave components The spectrum analyzer is a tool that graphs each of a signal s component frequencies as a ba
346. u A0imS M qe 297 3 av Cc m It s also useful to look at just a DC signal amplified Page 340 Understanding Signals with the PropScope ACTIVITY 4 INVERTING AMPLIFIER The input signals up to this point have been fed to the op amp s non inverting input In contrast the inverting amplifier circuit feeds the input signal to the amplifier s inverting input Figure 9 16 shows the inverting amplifier circuit This is still a negative feedback amplifier because the inverting input is still connected to the output through Rf Ri Rf Output Figure 9 16 Input 3 a a Vi Y Signal Inverting Amplifier Vss Vss lt n n Remember the rule of negative feedback with op amps the output will adjust to keep the voltage at the inverting input equal to the voltage at the non inverting input Let s say the resistors are equal and Vi 2 V In that case the output would have to transmit 2 V to keep the voltage at the inverting input equal to 0 V which is the value at the non inverting input Another example with Rf Ri if Vi is 1 V Vo has to be 1 V to keep the voltage at the inverting input at O V so that it is equal to the non inverting input These are two examples where the op amp s output inverts the signal More generally the gain for an inverting amplifier is R Gain oa Ri The negative sign in the gain comes into play when expressing the relationship of output to input signal R Vo x V
347. ud rate is 9600 bits per second bps it means that each bit period has to be 1 9600 of a second In other words the bit time is tpi 1 9600 bits second 104 17 us bit So the transmitting device Chapter 6 Asynchronous Serial Communication Page 179 updates its binary values every 104 17 us and the receiving device checks in the middle of each of those time periods for the next binary value in the byte Figure 6 4 Number 65 Transmitted with 8 Bit True No Parity Asynchronous Serial Signaling 1x1 0x2 0x4 0x8 0x16 0x32 1x64 0x128 65 gt 0o ee ot ao ee ep SS SS Seis ee no 0o Resting Start Bit BitO Bit1 Bit2 Bit3 Bit4 BitS Bit 6 Bit7 Stop Bit Resting State State l ton 7 Baud rate 1 tpit in bits per second bps l l l l l l l l l l t t A device that transmits or receives the asynchronous serial signal in Figure 6 4 is using a format called True signaling 8 bits no parity and one stop bit The shorthand for this is 8N1 and it is usually preceded by a baud rate like this 9600 bps 8N1 or just 9600 8N1 With true signaling also called non inverted a high signal sends a binary 1 and a low signal sends a binary 0 8 bits means that the signal contains 8 binary values bits No parity indicates that this signal does not contain a parity bit an option that the transmitter and receiver use to help detect communication errors Parity bits will be examined
348. us With Automated Cursors a2 0 4 OE Os 1 Cursor Amplitude Measurement of Circuit Output on CH1 0 2 0 4 0 6 0 8 1 Page 262 Understanding Signals with the PropScope Next let s examine the phase delay the circuit introduces by measuring the phase shift First we need to measure the time difference At between waveforms and then express it as a number of degrees The time difference can be measured by picking a point that s common to both signals With the CH1 coupling set to AC and CH2 with zero offset a convenient reference point is where each wave crosses the zero volt line Figure 7 33 shows the measurement The Horizontal dial is adjusted to 20 ps for a closer look at the times that the waveforms cross their 0 V lines Then cursors are used to measure the time difference v SASS s Before adjusting the display make a note of the signal s period T Example in top right of Figure 7 32 is 333 us Set the Horizontal dial to 20 us div In the Trigger tab change the Level switch from Auto to Normal Adjust the Trigger Voltage control to align with the CH2 ground line Adjust the Trigger Time control so that the CH2 DAC sine wave rises through the intersection of the ground line and the second time division In the Cursor tab click the Horizontal button to remove the voltage cursors then click the Vertical button to start th
349. use one of the probes to test the signals a BASIC Stamp transmits to and receives from the PC via the serial port It doesn t matter if your board is USB the BASIC Stamp still uses serial signaling to exchange data with the USB board s serial USB converter chip and you can measure those signals PC serial ports typically send serial signals with peak to peak voltages that are outside the 0 to 5 V range that BASIC Stamp I O pins transmit These ports adhere to a standard called RS232 which allows for high signals in the 25 to 3 V range and low signals in the 3 to 25 V range RS232 driver chips in computer serial ports typically get their signal voltages from the computer s power supply So a serial driver chip s high and low voltages will typically be the same as a pair of its power supply voltages commonly called power supply rails or just supply rails Supply rail values of 5 V and 12 V are common but they do vary from one system to the next For example one system might have a pair of rails at 12 V and another at 5 V while a different system might have a pair of rails at 5 V and another at 3 3 V Probe Setup With probes set to 1x the maximum voltage range the PropScope can measure is 10 V Your computer s serial port voltages might be outside that range so the best thing to do is adjust your probes and PropScope software to the 10x setting Then the PropScope will be able to measure up to 100 V instead of jus
350. using synchronous serial communication Synchronous serial devices use a variety of protocols with a common denominator of a clock signal that synchronizes the exchange of a series of binary values The ADC0831 8 bit A D converter is an example of a synchronous serial device that transmits a number from 0 to 255 to represent measured voltages This device s datasheet provides pin maps and timing diagrams that can be used to develop a test circuit and test code Communication takes signals on three lines chip select clock and data out Chip select has to be held low for the duration of the communication and pulses applied to the chip s clock pin result in successive binary values that represent the measurement value transmitted by its data out pin The PropScope s DSO LSA View has an Oscilloscope and Logic Analyzer This arrangement makes it possible to verify both the voltage applied and the synchronous serially communicated measurement The oscilloscope can be used to view the voltage applied to the ADC0831 s Vin analog input while the Logic Analyzer monitors the communication lines to verify that the signaling is correct One incorrect microcontroller coding error can change the signaling in ways that prevent communication or cause incorrect values Two such errors were studied in this chapter and the digital signal oscilloscope and logic state analyzer were used to diagnose each error PBASIC has SHIFTIN and SHIFTOUT commands fo
351. view by Joshua Donelson editing and layout by Stephanie Lindsay Thank you to Ken Gracey Stamps in Class program founder Aristides Alvarez Education Manager Hanno Sander of Hannoware com PropScope Software Developer Jeff Martin BASIC Stamp Editor Software Developer David Carrier PropScope hardware developer Thank you also to our customer reviewers for their questions recommendations and corrections Paul Smith of Alverno College Lisa Quackenbush and Ingolf Sander Page 10 Understanding Signals with the PropScope Chapter 1 PropScope Introduction and Setup The PropScope USB hardware and software shown in Figure 1 1 make it possible to take a variety of electrical and electronic test and diagnostic measurements with your computer Figure 1 1 PropScope USB Hardware and Software H A HEMEL LT Many of the PropScope s capabilities used to require a test bench full of measurement equipment Figure 1 2 shows examples left to right including the voltmeter function generator mixed signal oscilloscope a combination oscilloscope and logic analyzer and a spectrum analyzer The PropScope provides the basic functionalities of these tools along with an affordable starting point for learning to take test measurements Armed with the PropScope and the techniques this book introduces you ll be able to test and troubleshoot many of the circuits and signals in your future electronics and or robotics projects Figure
352. w Plugins Tools Help DC AC Off DC_AC DAC Off Square Generate a Ce Custom Edit otso idie n Measure f Mode Level Source S i OT lt of Rise i Auto cui mM erige gi CH2 M a gt all Normal f Ste a rp O igy xxo I 7 mi ras ws Te l With the Horizontal dial set to 2 ms you ll be able to see the low pulse durations change as you press release different numbers on the remote Figure 4 29 shows patterns that represent the 2 3 and 4 buttons v Remember to point the remote at the IR detector before you press its buttons v Press release the 2 button on your remote a few times until the start pulse s negative edge lines up with the 1 time division The pattern of low pulses should resemble the signal labeled 2 Button in Figure 4 29 Repeat for the 3 and 4 buttons and compare to Figure 4 29 lt 4 Keep an eye on the three negative pulses that follow the start pulse They are the ones that carry the binary values 001 010 and 011 which are the binary remote codes for the 2 3 and 4 buttons Chapter 4 Pulse Width Modulation Page 143 Figure 4 29 Pulse Patterns for the 2 3 and 4 Buttons 2 Button 3 Button Wait for Trigger 4 Button Time ms Wait for Trigger Figure 4 30 shows the Oscilloscope zoomed in another time
353. wM 15 64 5 sets the voltage across the capacitor in the circuit connected to P15 to 64 256 of 5 V That s 1 25 V Likewise PWM 14 192 5 sets the voltage across the capacitor in the P14 circuit to 192 256 of 5V That s 3 75 V The Duration argument in both PwM commands is 5 which gives the command 5 ms to charge the capacitor You will learn more about why it needs 5 ms in Chapter 8 RC Circuit Measurements Page 42 Understanding Signals with the PropScope v The PwM command should charge the capacitor in the P15 DAC circuit to 64 256 of 5 V which is 1 25 V Use a calculator to verify this voltage prediction v Repeat for the P14 pwm command and capacitor voltage to verify the 3 75 V prediction v Load Test 2 Channel Dac bs2 into your BASIC Stamp Now that the program is running the next step will be to test and verify the voltages across the capacitors with the PropScope Test 2 Channel Dac bs2 cect Pomc apdGclEormvoluagemeOmlne Oo V anad ml mccdpcdlcitt Ort OMmSrN Ome SSTAMP BS2 Target module BASIC Stamp 2 SPBASIC 2 5 Language PBASIC 2 5 DEBUG Program cunning Debug Terminal message DO Main Loop PWM 15 64 5 1 25 W ice PIS eajeeuicer PM I ie amp 0 Sols W ice Pi capaci Cor LOOP Repeat main loop More about how PWM works and how to use it Different facets of setting voltages with PWM and a resistor capacitor RC DAC circuit will be explored later in this book Chapter yom 4 Pu
354. ware to be a function generator output See Set DC Voltages with the PropScope s DAC Card on page 45 for step by step instructions vy Build the circuit in Figure 7 29 optionally using Figure 7 30 as a guide Page 258 Understanding Signals with the PropScope Figure 7 29 Schematic for Phase Angle Measurement Test Circuit Input Circuit Output PropScope CH1 10 KQ PropScope DAC 0 01 uF PropScope GND Vss Vss Figure 7 30 Example Wiring Diagram for Figure 7 29 The connection to the Vss socket is optional for this test Since the BASIC Stamp is not interacting with this circuit the jumper from the ground clips to the Vss socket is not necessary The ground clips provide a connection to the USB port s ground connection which is also your computer s ground connection If your measurements did involve interaction with the BASIC Stamp connecting the ground clips to Vss would be necessary because the PropScope would need to share a common ground with your Board of Education HomeWork board Chapter 7 Basic Sine Wave Measurements Page 259 Amplitude and Phase Angle Test Measurements Figure 7 31 shows a sine wave the PropScope DAC Card s function generator output applies to the RC circuit s input along with the sine wave measured at the circuit s output The function
355. west value is 13 and the highest is 229 Measure the Simulated Heartbeat Signal Figure 3 21 shows the PropScope settings to display the heartbeat Remember that you can adjust the waveform s vertical position by sliding it up down with your mouse Just point at either the waveform or the dashed ground line for that channel then click hold and drag v Update your PropScope settings to match Figure 3 21 Pay close attention to the Horizontal and CH1 Vertical scales the Plot Area bar s position and the vertical position of the waveform If the Run button is off click it to restart the display Locate the frequency for Channel 1 in the Measure tab What s the patient s heart rate according to the automated Measure tab SS The Trigger tab s Mode setting automatically turns off when the Horizontal dial is set to 200 ms or larger That s because the oscilloscope goes into datalogging mode with time scales of 200 ms div or larger and datalogging mode is not compatible with triggers A Why trigger aligns the rest of the plot around some trigger condition in oscilloscope mode In datalogging mode the oscilloscope scrolls continuously so it cannot be forced to align with a particular trigger event Chapter 3 Human speed Measurements Page 99 Figure 3 21 Pulse Rate in Measure Tab is Not Correct ix Fie Edt View Plugins Tools Help Oscilloscope Logic Analyzer Analog DSO LSA
356. wire instead of the 220 Q resistor The next step in testing the I O pin s threshold voltage is to write a program that displays the binary state the I O pin detects above threshold binary 1 or below threshold binary 0 Test Threshold Voltage bs2 does this with a DEBUG command that displays the value of the BASIC Stamp IN7 register IN7 stores the state I O pin P7 detects v Enter Test Threshold Voltage bs2 into the BASIC Stamp Editor and load it into the BASIC Stamp Chapter 2 DC Measurements Page 57 Test Threshold Voltage bs2 Display P7 state for testing threshold voltage SSTAMP BS2 Target module BASIC Stamp 2 Y HSPBASIC 2 55 Language PBASIC 2 5 PAUSE 1000 Wait 1 s before values display DO t Main loop DEBUG HOME State BIN1 IN7 Display state of signal at P7 PAUSE 100 Wait 100 ms LOOP Repeat main loop i For more information about this program work through Chapter 3 Activities 1 and 2 of Lb What s a Microcontroller from the PDF in the BASIC Stamp Editor Help menu Figure 2 27 illustrates that when you run the program it makes the BASIC Stamp send the Debug Terminal the State 1 message when the pot s W terminal voltage is above the threshold voltage left or the State 0 message when the voltage is below the threshold right v Test this with your potentiometer Figure 2 27 Debug Terminal State Displays above threshold left below threshold
357. with the previous circuit Fourth and finally this circuit has a 10 kQ resistor instead of a 220 Q resistor This is not for increased I O pin protection it s for a light level compensation feature that will be examined after the basic measurements v Build the circuit shown in Figure 8 33 P2 PropScope CH1 0 1 uF PropScope GND Vss Figure 8 33 Phototransistor Vi in Vs Circuit X3 a8 Schematic top P14 Isao Wiring diagram P13 a l bottom a 00000 opoo 00000 JN H 00000 COON hi 00000 ooon a ooooo fooooo 55 o0000 00000 se ooooo jooooo ies ooooo jooogs D ooog p1 oo og 7 o0000 dad 0 oo T X2 TestPhototransistor bs2 tests the phototransistor in much the same fashion as Activity 3 s example program tested the potentiometer Chapter 8 RC Circuit Measurements Page 307 Enter TestPhototransistor bs2 into the BASIC Stamp Editor and run it Make sure the lighting conditions are low no bright lights or sunlight from a nearby window v Ifthe Debug Terminal measurement is 0 it indicates that he time measurement exceeded the RCTIME command s 65535 maximum value which in turn indicates that it s either too dark or there is a wiring mistake lt 4 What s a Microcontroller TestPhototransistor bs2 Read phototransistor in RC time circuit usi
358. with a human speed example that involves the pushbutton and LED circuits from What s a Microcontroller Chapter 3 The PBASIC program for the BASIC Stamp will monitor the pushbutton circuits and blink one of two indicator lights when one of two pushbuttons is pressed and held The logic analyzer will be used to monitor and display the signal activity buttons pressed not pressed and lights on off as the application runs For more information about this circuit and program work through Chapter 3 Activities 1 4 of What s a Microcontroller from the PDF in the BASIC Stamp Editor Help menu Page 86 Understanding Signals with the PropScope Pushbutton and LED Parts 2 Pushbuttons normally open 2 Resistors 10 KQ brown black orange 4 Resistors 220 Q red red brown 2 LEDs any color misc Jumper wires Pushbutton and LED Circuit Figure 3 13 shows a schematic of four binary circuits two LED indicator lights and two pushbuttons It also shows connections between these circuits and the PropScope DAC Card s four logic analyzer channel inputs which are the sockets labeled 1 through 4 There is also a mandatory common ground connection which is the wire between Vss on your board and G on the DAC Card Vss is your board s ground and G is the DAC Card s Logic Analyzer ground connection Figure 3 14 shows a wiring diagram example for the same circuit These connections will make it pos
359. would still be reasonable Page 280 Understanding Signals with the PropScope Your Turn Repeat for RC Decay from 0 to 4 V For RC decay from 0 to 4 V all you have to do is toggle the Trigger Edge from Fall to Rise and then use cursors to measure the time difference between when the capacitor starts charging and when it passes 63 2 of the way to its final voltage level v Try it Your value should be almost identical to your decay time since it s a measurement of the RC time constant for the same circuit ACTIVITY 3 RC SENSOR MEASUREMENTS WITH A POTENTIOMETER The BASIC Stamp can measure RC decay with a command called RcTIME Since a wide variety of sensors either vary in resistance or capacitance it s an extremely useful feature It can also be used with sensors that vary in conductance allowing more or less current to flow with changes in the physical property the sensor measures Examples include visible light infrared light humidity potentiometer knob position temperature presence or absence of a flame and the presence of certain gasses These are just a few entries in a larger list if the sensor varies in resistance or capacitance it s a candidate for the techniques you will examine in this activity Figure 8 12 shows how the PBASIC RcTIME command works with a potentiometer With its B and W terminals connected as shown the pot functions as a variable resistor The adjusting knob can be turned to vary the
360. your mouse to point at the Plot Preview or any of the scales numbers around the plot 1 When you do that it makes the Trigger Crosshairs appear The vertical crosshair indicates the trigger time and the horizontal crosshair indicated the trigger voltage level With the Trigger Level set to Auto the PropScope software positions the trigger voltage level control icon at the signal s average voltage which is currently half way between the channel 1 low and high voltage levels Inside the trigger voltage level control icon is a line that transitions from low to high This indicates that the Trigger Edge has been set to Rise which in turn means that the PropScope software will wait until it detects a voltage passing through the voltage crosshair s level as it is increasing The display then aligns that rising edge with the vertical time and horizontal voltage trigger crosshair intersection and it positions the rest of the plot accordingly v Try adjusting the Trigger Edge to Fall You can do this by setting the Edge switch in the Trigger tab What happened to the Channel 1 trigger edge v Change the Trigger Edge back to Rise See the difference Figure 3 12 shows the Measure tab with the modified program still running The period it displays is 101 milliseconds ms Both PAUSE command Duration arguments in the program were reduced from 500 to 50 so the signal should repeat itself about every 100 ms The time it takes the BASIC Stamp t
361. ys is the average of the two voltages To calculate this average just add the two cursor measurements which are VA and VB in Figure 7 18 and divide by two DC Offset Average voltage Va Vg 2 Chapter 7 Basic Sine Wave Measurements Page 237 For the cursor measurements in Figure 7 18 that s DC Offset 2 88 V 1 7 V 2 2 29V The calculated DC offset value of 2 29 V from the cursor measurements is close enough to confirm the measured value of 2 32 V back in Figure 7 17 Your Turn Examine the F7 Sine Wave Try taking a closer look at the F7 sine wave Start by modifying One Note at a Time bs2 and then examine the new signal Because of the way the signal interacts with the resistor and capacitor it may be of slightly lower amplitude Since it s a higher frequency signal you can also expect the period to be slightly shorter v In the BASIC Stamp Editor modify One Note at a Time bs2 by placing an apostrophe to the left of FREQoUT 9 60000 2489 Then delete the apostrophe to the left of FREQOUT 9 60000 2960 v Load the modified program into the BASIC Stamp v Repeat this activity s offset amplitude and frequency measurements If you want to replicate the measurement in Figure 7 13 after completing this activity you PN can modify the FREQOUT command in One Note at a Time bs2 so that it reads FREQOUT e 9 60000 2500 You will also need to connect the CH2 probe to I O pin P9 and adjust ey the Pro

Datasheets - Jameco Electronics

Contents

Download Pdf Manuals

Related Search

Related Contents