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1. a ROM THE BENCH Energy Extraction Powering Up with Heat Transfer ae i i y S n t W _ p al 5 Q 09 by Jeff Bachiochi USA If you can generate the right amount of heat you can produce electricity for a variety of purposes Here you learn how to use fire a Peltier device and little ingenuity to power up small devices very time I had a propane tank delivery the pilot light went out on my gas fired hot water heater To relight this small gas flame and keep it lit the thermocouple which protrudes into the center of the pilot lights flame had to be hot As a safety feature if this thermocouple wasn t hot the gas valve would cut off the gas flow Thermo couples produce a small voltage when heated This Signal tells the valve it can keep the gas flowing A homeowner who doesn t understand this require ment may be frustrated THERMOELECTRICITY In 1821 physicist Thomas Seebeck discovered that a continuous current is generated in a circuit composed of two wires of dissimilar metals joined at both ends when one end is heated Today thermo couple probes are standardized by the alloys used in fabrication When attempting to measure a thermo couple s output any dissimilar metal used in the measurement leads will in effect become a thermal couple junction and destroy the measurements integrity Special compensation is needed to derive the temperature of interest using
2. It is important to understand reliability to plan product support warranty costs Spare parts availability and so forth Sys tem availability can be established by estimating MTTR by performing and tim ing various repairs This is also a balanc ing act The shorter the MTTR the more expensive its achievability usually becomes If availability and MTTR are a part of the specification as they often are you may have to go back and modi fy the design either to meet the availabil ity requirements or if there is sufficient margin to reduce costs The iterative design process is the only way to achieve the best performance at the lowest cost To put it bluntly no designer can be truly successful without understanding and applying reliability concepts il George Novacek gnovacek nexicom net is a professional engineer with a degree in Cybernetics and Closed Loop Control Now retired he was most recently president of a multinational manufacturer for embedded control systems for aerospace applications George wrote 26 feature articles for Circuit Cellar between 1999 and 2004 RESOURCES Advanced Logistics Development Free MTBF calculator www ald service com en reliability software free mtbf calculator html I Bazovsky Reliability Theory and Practice Prentice Hall 1961 G Novacek Diode ORing Circuit Cellar 263 2012 Environmental Stress Screening Circuit Cellar 255 ZAG Quanterion So
3. R 0 which as you just saw can barely handle the on board circuitry A single 20 mA LED adds 140 mW to the regulator s power dis sipation when it operates from a 12 V sup ply a few cheerful LEDs can push the reg ulator into thermal shutdown The specs in Figure 1 do not mention that the current through the chips Voc and ground pins must not exceed 200 mA probably because theres no easy way to measure that value You can work around the Vc limit by powering LEDs and other loads from an off board 5 V regulator but the return current through the digital pins adds to the microcon trollers ground pin current In fact a project with just 10 full brightness LEDs can exceed the ground pin current limit Ill have more to say about I O pin characteristics in upcoming columns Until then pay attention to both the regulator power limits and the chip current limits MAKING CONNECTIONS Everyone myself included has poked round hookup wires into those square header sockets even though that s a very very bad idea The tuning fork contacts within the sockets firmly grip 25 mil 0 64 mm square header pins and work best with pin strips firmly soldered into PCBs Typical 24 AWG solid hookup wire fits loosely because its only 20 mil 0 51 mm Ed Nisley is an EE and author in in diameter and doesn t provide flat con tact surfaces If you must use hookup wire find some 22 AWG solid wire its 25 mil diameter fits much
4. Photo 1 These heavy duty alarm contacts determine whether the garage doors are open or closed D2 a pair of back to back Zener diodes to prevent overvolt age and is fed to the DS 1487 differential driver where it is translated to a 5 V Serial signal and supplied to a Microchip Technology PIC18F2221 s UART The microcontroller s output RA2 is used to switch the driver between transmit and receive The system normally remains in Receive mode and is switched to Transmit mode when it needs to reply to another device on the network Receive enable RE and output enable OE are tied together on the DS 1487 When the unit needs to enter Transmit mode the receiver becomes dis abled This prevents half duplex echo where the UART picks up its own transmissions The interface that monitors whether the door is opened or closed is connected to J4 and uses an external pull up resistor to maintain a high state Photo 3 The two boards one for each garage door are mounted on opposite sides of the case The RS 485 harness the position sensors and the door opened contact are terminated on the barrier strip at the rear This location also represents the end of one side of the RS 485 line so the termination resistor is also on the barrier strip www circuitcellar com CIRCUIT CELLAR 0010384132 158 29444 Photo 2a The reader is connected to a breadboard that reads the data and clock signals I used two chips the Microchip 28 pin PIC
5. lt A Standard Development ools 10 Year Life guarane Royalty fred kTOS M NAA WE The gridARM System on a Chip SOC is a high performance low cost low power highly integrated single chip with 10 100 1000 Mbps Ethernet USB CAN Serial SRAM Memory SPI I2C RTC and internal peripherals designed to provide a complete solution for embedded applications THE NETWORKING EXPERTS Leaders in the embedded and networking marketplace providing network hardware high quality software and services f Qridconnect 800 975 4743 USA 1630 245 1445 gridconnect com gridarm html www circuitcellar com CIRCUIT CELLAR 1 R Brown Non Continuous Events in the Telephone Outside Plant Telecommunication Industry Association TR 30 3 99 04 620 1999 gplEDA www gpleda org gputils GNU PIC Utilities http gputils sourceforge net Microchip Technology Inc PIC12F508 509 16F505 Data Sheet 8 14 Pin 8 Bit Flash Microcontrollers 2009 ww1 microchip com downloads en devicedoc 41236e pdf PICkit 2 Programmer Debugger Users Guide 2008 ww1 microchip com downloads en devicedoc 51553e pdf STMicroelectronics L293D L293DD Push Pull Four Channel Driver With Diodes 2003 www st com internet com TECHNICAL_RESOURCES TECHNICAL_LITERATURE DATASHEET CD00000059 pdf PIC16F505 Microcontroller and PICkit 2 Development programmer debugger Microchip Technology Inc www micro
6. EXtensive Interfaces y UART FIFO SPI FC FT1248 4 EXtended Features m Battery charger detection Low active power 8 mA typical Internal MTP memory Expandable clocking clock generation and system clock out Exceptional Drivers Windows MacOS Android and Linux Power of the Quoting Revolution in the palm of your hand At a click of a button we will find the best price in the market compiled in one easy to read spreadsheet Just like your BOM NIK ARAVA oh a GU Y te gt ax Y P WWW AVe 4 zw
7. Issue 269 N w December 2012 Issue 269 Main screen Toggle Backlight Set speed override Clear power y Leftand Power screen items right Hold i Set Amps left override Right Sub screen timeout Sub screen timeout 3 s Clear trip Left and Speed distance items right screen 4 az Toggle Left backlight Throttle override screen Sub screen timeout Left and right 5 Toggle Left backlight Recent log files screen Figure 6 This diagram shows how the user push button EBikeMeter LCD screens navigation and function selection works subscreen timeout and the throttle override control values The LCD backlight is normally off One of the push buttons can be used to turn it on When the LCD backlight is turned on and the bicycle is moving it will stay on but when the bicycle stops moving the LCD backlight will turn off after a configured timeout period The LCD backlight brightness is adjustable for nighttime operation and should be unneces sary for daytime operation The LCD contrast is temperature sensitive and requires temperature based adjustment to remain visible at various temperatures The configuration setting sets the temperature at which the adjustment begins At every 0 5 C above this temperature the on board digital potentiometer is adjusted one step to change the contrast setting Of the five LCD screens shown in Photo 2 only the Main screen with the speedomete
8. or product availability can be expressed as MTTF MTTF _ gt MTTF MTTR 2 Availability MTBF MTTF is often used instead of the MTBF when the product is not repairable e g light bulbs space vehicles weapons etc Under some circumstances MTTF MTBF Alternatively MTBF is redefined by some companies as mean time before failure This can be confusing It is highly advisable to clarify the terminology before starting work Besides the most popular exponential failure distribution other distributions e g Weibull are used This is because a failure rate can be a function of the product s or system s age With some repairable products the time to the first failure can be longer than the time to subsequent failures Assume for example a devices calculated failure rate A 20 Therefore the MTBF is 50 000 h This doesn t mean the product will last 50 000 h without a failure The MTBF once again is a cal culated statistical average Therefore 10 devices will exhibit the CS328A XS 100MHz Mixed Signal Oscilloscope Signal Generator What other scope can log 30 hours with 600ns resolution Ours can Check us out e HARA EM Z GZ HI Off B Off Chart scroll 2 Divisions Chan A 2 000 V ChanB 200 0mV Time 10 00s Frame 1 Trigger time 09 Mar 11 14 50 21 962100982 Chan A V 14 0 12 0 10 0 8 0 6 0 These are 1 i duration pul s 2 0 7 f i 0 0 10 0 20 0
9. BOVE THE GR PLANE Arduino Sumival ee Power Supply Ed Nisley THE DARKER SIDE Locked In Synchronous Detection Explained Robert Lacoste I THIN SLICES Concurrency in Embedded Systems Part 4 Introducing Linux and Concurrency Bob Japenga EMBEDDED IN THII THE CONSUMMATE ENGINEER Product BA Part 2 The Meaning of Failure Rate George Novacek FROM THE BENCH Energy Extraction Powering Up with Heat Transfer Jeff Bachiochi Programmable Logic Electrostatic Cleaning Robot TA CLI LAA Al A y e a R A 2 R IYI LA N ZA 1 K A i Pie Ew ALW FANS a m Break Through Designer s Block C J Abate NEW PRODUCT NEWS LO EMBE TILE 14 TES UR EQ SOLUTION gt QUES NS 8 ANSWERS 4 2 Engineering SE Entao amp Explanation An Interview with Stuart Ball Nan Price CROSSWORD 7 PRIORITY INTERRUPT 3 O Onward and pana Steve Ciarcia CIRCUIT CELLAR www circuitcellar com components for design engineers mouser com Distributing semiconductors and electronic Authorized Distributor mouser com Tne widest selection of the newest products MOUSER The Newest Products for Your Newest Designs ELECTRONICS a tti company r Electronics are registered trademarks of Mouser Electronics Inc Steve Ciarcia C J Abate Nan Price Jeff Bachiochi Bob Japenga Robert Lacoste George Martin Ed Nisley George Novacek Patrick Schaumont
10. nician in the U S Navy He enjoys reverse engineering and documenting electronic device hardware and firmware from the 1980s and 1990s He is a charter subscriber who has every issue of Circuit Cellar magazine and has been reading Steve Ciarcia s Circuit Cellar articles since the late 1970s Dan s website is at http dlkeng cwahi net PROJECT FILES To download the code go to ftp ftp circuitcellar com pub Circuit_Cellar 2012 269 RESOURCES Arduino Forum BIG Numbers from a Little LCD 2008 http arduino cc forum index php topic 245 0 html CIRCUIT CELLAR www circuitcellar com Atmel Corp Studio Archive www atmel com tools STUDIOARCHIVE aspx AVR103 Using the EEPROM Programming Modes 2005 www atmel com images doc2578 pdf AVR318 Dallas 1 Wire Master 2004 www atmel com images doc2579 pdf J Bachiochi Electric Movement and Control Circuit Cellar 199 2007 ConhisMotor Technology Co Ltd Standard Controller 48 V 1 000 W www conhismotor com ProductShow asp id 49 FreePCB www freepcb com Future Technology Devices International Ltd FTDI USB TTL Serial Cables www ftdichip com Products Cables USBTTLSerial htm Grin Technologies Homepage of the Cycle Analyst www ebikes ca drainbrain shtml D Karmann DLK Engineering http dlkeng cwahi net EBikeMeter htm MCS Electronics MCS BootLoader Application Note 143 w
11. 1 l I 1 I 1 U 1 I Ls 30 0 40 0 500 600 70 0 80 0 90 0 100 0 110 0 120 0 Time s 14 Bits 100 MSPS Mso UEH www cleverscope com December 2012 Issue 269 0 UT December 2012 Issue 269 probability of one failure every 5 000 h per formula as shown in Equation 1 The probability of the device operating without failure during time t can be calculated T R t e MTBF 3 Therefore if a device is fault free at the beginning of a 3 h mission the mis sion has a 99 994 probability of suc cess no matter how many hours the device already operated see my article Diode ORing Circuit Cellar 263 2012 Substituting t MTBF the probability of a device surviving its entire MTBF in continuous operation without failure is merely 36 8 RELIABILITY amp ACCURACY Reliability is statistics The calculated results can be 100 accurate for an infi nitely large population of products only The failures during the useful life i e after infant mortality and before wear out are random and unavoidable The only way to reduce the probability of those failures is to reduce the A and to ensure the device operates well away from the infant mortality and wear out regions FEFE a 4 q 4 2 q u rp Ja age DB DOWNLOAD our free CAD software DESIGN your two or four layer PC board SEND us your design with just a click RECEIVE top quality boards in just days exbresspcb com 0
12. 250MHz ARM93 or 800MHz ARM9 or Cortex A8 CPU Sr H U i ja pa zi l L E ka va i Fast startup under 3 seconds a starts at gt nuan ponm Ba a cej Fanless operation from 20 C to 70 C es 22 1 99 User programmable opencore FPGA qty 100 Program in Ladder Logic or C Debian Linux Modbus support PoE capable 10 100 Ethernet USB 2 0 Host Ports j picture of T5 8820 BOX Industrial screw down connectors Opto lsolated DIO Digital Counters Quadrature Technologic Systems now offers three powerful computers targeting industrial process control Up to 46 DIO with PWM Implement an intelligent automation system at Opto lsolation available for RS 232 RS 485 and CAN low cost with a minimal number of components s DIN mount option 3 Technologic Systems We use our stuff Visit our TS 7800 powered website at www embeddedARM com December 2012 Issue 269 ZUMO SHIELD FOR ARDUINO The Zumo Shield is an Arduino shield with a Zumo tracked chassis The shield includes dual motor drivers a buzzer to play simple sounds and music and a three axis accelerometer and compass It mounts directly onto the Zumo chassis with the Arduino plugged face down into the shield The Zumo Shield s battery voltage powers the Arduino It breaks out the Arduino reset button user LED and I O lines for convenient accessibility and to accommodate additional sensors Using a Zumo Shield and an Arduino Uno or an Arduino L
13. An LM7808 linear regulator in a TO220 case with a heatsink reduces the load on the Arduino s tiny SMD regulator by supplying a constant 8 V entire Arduino board you know its time for a different solution CURRENT LIMITS Figure 1 includes a frequently ignored specification the DC current at any micro controller pin must not exceed 40 mA The maximum current for a typical 5 mm LED is 20 mA one Arduino digital output pin can drive only two LEDs in parallel to full brightness Even a small mechanical relay may require more current than one pin can safely deliver The microcontroller s output pin drivers do not include current limiters which means the external circuit must limit its current to no more than 40 mA from a low impedance 5 V source New users may connect a bare LED directly to a digital out put pin and depend on the Arduino to limit its current a technique that makes an LED Shine very brightly while the microcon troller dissipates far more heat than it Should You must always use a current lim iting resistor with any low impedance load to protect the microcontroller s circuitry The pin current going to the load comes from the Arduino s power supply regulator mbed mbed NXP LPC11U24 Microcontroller Rapid prototyping for USB Devices Battery Powered designs a 32 bit ARM Cortex M0 applications http mbed org Nazza T5 PA December 2012 Is
14. For cooking you want to burn wood until you can pull out a nice bed of coals and use this as your cooking source With wood fire temperatures being so erratic and Peltier devices having maximum temperature issues I think it would be a good idea to monitor temperatures on both sides of the Peltier device To do so I ll use a microcontroller to measure two temperatures communicate with the SPV1020 using a SPI channel to extract voltage and current measurements and dis play those results In addition I ll add a cooling fan control and piezoelectric beeper as an auditory warning device The SPV1020 uses two references On the input side the Voe i e open circuit must be scaled using a resistor divider for the Vin sng Input where RI V OC R2 125 A second resistor divider is used to scale down the output voltage Vaxour fOr input Voyr gs where Atom D525 Touch PG NEW PPC 080T 525 Intel Atom D525 Dual core 1 8 Ghz 2GB DDR3 800MHz SODIMM RAM 16GB SATA SSD Hard Drive 8 Color LCD Screen 800x600 Analog Resistive Touchscreen 10 100 1000 Base T Ethernet Wireless 802 11 b g n 4 External USB 2 0 Ports External ESATA Port External RS 232 Port External VGA Port Audio Line In amp Line Out Windows 2W Stereo Internal Speakers A s Embedded 12V DC in Dimensions 8 5 x 7 20 x 1 77 m 2 6 KERNEL The PPC 080T 525 Touch PC comes ready to run with the Operating System installed on
15. You could try to build a narrower filter for example by digitizing the received signal and designing a precise digital filter But this will significantly increase the projects budg et and power requirements and make it difficult to significantly improve the performance Are there other options SYNCHRONOUS DETECTION As you may have anticipated a lock in amplifier built around a synchronous detection is exactly what you need The idea behind such a detector is simple As we have generated the excitation signal ourselves here the 100 kHz modulation we know its exact frequency This information enables the building of a band pass filter as in the previous example but it can now be built as narrowly as desired Figure 3 shows the concept Here the received signal multiplied by the excitation signal and low pass filtered This is exactly like a radio frequency down converter more precisely a zero IF converter as the local oscillator is at the same frequency as the input signal Remem ber my article Radio Frequency Mixers Circuit Cellar 263 2012 Multiplying two sine signals of frequencies f1 and f2 provides the sum of two signals at respective frequencies Synchronous detector Measurement Preamplifier Multiplier Low pass filter 1Hz Signal 10 mV Noise 1 V Signal 10 mV Noise 1 mV Figure 3 A synchronous detector uses the excitation signal and multiplies it to the received signal This translates the desire
16. and R15 along with a current limiting resistor added to the connection between the throttle and the motor con troller to protect the throttle s circuitry When a set speed current or voltage limit is reached the throttle override sig nal overrides the control signal from the Initialize I O Enable interrupts Load config from EEPROM Initialize file system New prompt Emit serial prompt Y Sub screen timeout Select Main screen Y Screen update time X Rotating items time Y Speedometer input Y Pwr fail PB Interrupt 5 Process pin change Y PB Processing 7 Process push button i Y Read temp time Read temperature Y Data logging time E Log data to SD card WE Y Throttle override time a Process throttle override gt Process serial input Y Heartbeat LED update a Update heartbeat LED Figure 4 Here is the EBikeMeter firmware s start up and main processing loop An expanded view of the charts highlighted section is available on Circuit Cellars FTP site N Update current screen on LCD Update rotating item on LCD throttle preventing it from controlling the motor controller This is a one way override sig nal i e it can only cause the motor controller to slow down not speed up If there is a speed control override the bicycle speed should be limited to a certain maximum value with electric assistance Although the motor con troller cannot increase the bicyc
17. and heater It transfers heat from one side of the device to the other through electrical energy con sumption On the plus side a Peltier cooler has no moving parts or circulating liquid is relatively small in size and can be manufactured in a variety of Shapes While it is not efficient if you have a sur plus of heat it can generate electricity from that heat Let s take a closer look at the thermocooling device s construction In semiconductors doping is used to change sil icon s conduction properties Silicon by itself is not a good conductor as its four valence i e outer Shell electrons are shared with neighboring silicon atoms creating a stable crystalline structure When doped i e infused with a material that has five CIRCUIT CELLAR www circuitcellar com Electron current gt Cool side Electron current gt Hot side Figure 1 N and P type materials are used in pairs to create an electrical path where current flows from the hot side to the cold side in N material and from cold to the hot in a P material On the other hand heat flows from the hot side to the cold side in both materials via the majority carriers which are electrons in the N material and holes in the P material valance electrons e g arsenic this extra electron doesn t have anywhere to fit into the crystalline structure The extra electron is pushed about by a voltage potential becoming the charge carrier of current in t
18. attached to the front fork with a companion magnet attached to a front wheel spoke The speedometer s wiring was routed from the front fork to the handlebar mounted EBikeMeter The power and throttle control signal wires were routed from the handlebar mounted EBikeMeter along the bicycle frame under the rider s seat to behind the rider where a small box was placed that contained the voltage current and throttle control connections to the battery and motor controller Before using the EBikeMeter several items need to be con figured to the bicycle on which it is installed This configuration can be accomplished using a serial connection to a PC at 19 200 bps using your favorite terminal emulation software As I previously stated in the Hardware section the EBikeMeter s serial interface is not RS 232 but is typically called a TTL inter face It requires an RS 232 to TTL converter or possibly a USB to TTL converter such as those from FTDI Note that most FTDI converters do not supply the DTR signal so they will work for configuration but not firmware upgrade The most important configuration item is the wheel s circum ference on which the speedometer sensor is installed This con trols the accuracy of the speed trip distance and odometer readings Other configuration settings include the initial odometer setting the LCD backlight timeout and brightness the LCD contrast adjustment base temperature value the LCD December 2012
19. audio GRESS E ng tarba in m dae 3 ww fl L Hisz HL e W 7 RSA Seo y LI La X Gay Tech the Future explores the solutions for a sustainable future provided by technology i creativity and science a United Kingdom Wisse Hettinga z 31 0 46 4389428 w hettinga elektor com USA Hugo Van haecke 1 860 875 2199 h vanhaecke elektor com Germany Ferdinand te Walvaart 49 0 241 88 909 0 f tewalvaart elektor de France Denis Meyer 31 0 46 4389435 d meyerQelektor fr Netherlands Harry Baggen 31 0 46 4389429 h baggenQelektor nl lz l IE Issue 269 December 2012 ISSN 1528 0608 CIRCUIT CELLAR ISSN 1528 0608 is publisned monthly by Circuit Cellar Incorporated 4 Park Street Vernon CT 06066 Periodical rates paid at Vernon CT and additional offices One year 12 issues subscription rate USA and possessions 50 Canada 65 Foreign ROW 75 All subscription orders payable in U S funds only via Visa MasterCard international postal money order or check drawn on U S bank Cover photography by Chris Rakoczy www rakoczyphoto com Spain Eduardo Corral 34 91 101 93 85 e corralQelektor es Italy Maurizio del Corso 39 2 66504755 m delcorsoQGinware it Sweden Wisse Hettinga 31 0 46 4389428 w hettinga elektor com Brazil Joao Martins 351214131600 joao martins editorialbolina com Portugal Jo o Martins 351214131600 joao martinsQeditorialbolina
20. countries Not a member yet MCC Micro Computer Control 77 Microchip Technology Inc 19 Microengineering Labs Inc 78 Mosaic Industries INC 111 78 Mouser Electronics Inc 0005 5 ETB Ul ep acy oe sei E eee TEA C2 Newark element14 21 POOE OP Rado Sa oh ee ee AW i EE 25 Reach Technology Inc 77 Saelig Co INC chau ta vite 404 we eas 48 Technologic Systems 8 9 TOU LG 2 5 G 0 5 om A ae ee Re ee ae 17 Triangle Research International Inc 79 AP OMCUNS Oona ou t2a cew Cute ae we 60 ARM ioe Act dh i free nak i Pee 47 Beta Layout Ltd 00005 65 BusBoard Prototype Systems 19 Butterfly Network INC aaau aaaea 29 Circuit Cellar 25th Anniversary USB 53 Cleverscope anaana aaa aaa 65 Comfile Technology onanan anaana 49 Custom Computer ServiceS 19 DesignSpark esa Ga G EG tae GER ee 1 Cl ae ee ee ee eee 62 63 E EEE ee Uae sxe eee ake 74 75 EIDFOURONIG Caesar wom care eae dee bow ce eae ESEE ME ay gu 6 open ene Eee i 5 EMAC IE ra testasesiinataa ea 71 EXDIESSPOB tawseaca ca wso oe a 66 POL SST 6 Mag oder oe be C3 Grid Connect INC 4 445224 lt s004 e484 29 NEDDOWAIE eaa a etm Aes a a om Bt 78 Holtek Semiconductor Inc 37 H mandata Ltd osesa sers cee ba wa x 13 Imagineering INC 444a4441111 C4 Ironwood Electronics 7
21. his curiosity figured out how things work and designed useful projects We recently discussed some of his early microprocessor designs his interest with Atmel s AVR C coding and his dream project which involves enabling future engineers to learn through experimentation Nan Price Associate Editor C coding And I just like the way it works I tend to stick with things that work as long as they fit the application Some years ago I introduced DSPs to the engineering organization where I was working At that time I was using Ana log Devices s parts but I was using them as very fast microcontrollers instead of as DSP blocks I designed a lot of hardware using those parts some of which they are still using now after 15 years Like a lot of engineers I can get really focused on some thing Once I decide to do a project I tend to pursue it to completion even if it takes multiple approaches NAN Your article Inside a Digital Joystick Circuit Cellar 139 2002 describes how you designed a poten tiometer free joystick Tell us a little about the design Do you still use the joystick STUART At the time I was just experi menting with contactless joystick ideas and got focused on the idea of a joystick that did not use potentiometers but also didn t require any complicated fabricated CIRCUIT CELLAR www circuitcellarcom parts like molded plastic reflec tors or precision bearings I exper imen
22. ing time is critical you may need to rapid prototype your archi tecture and see what actually happens for your application Slight advantage Threads Resources Since each process uses its own instance of mem ory for program and data child processes are different a thread can use significantly less virtual memory than a process In addition semaphores timers and file handles are all shared between the same process threads Advantage Threads Libraries Linux enables you to use static or dynamic libraries A static library is linked into your code space and everything I have said concerning your code space i e text segment Thread 3 December 2012 Issue 269 UT December 2012 Issue 269 applies to any static library For dynamic or shared libraries all threads share the same dynamic library in their virtual address space Dynamic libraries add an additional requirement for the designer concerning a library functions thread safety With processes you dont need to be concerned about whether or not the library is thread safe since you have a completely sep arate library instantiation Resource wise advantage Threads Ease of use advantage Processes Dynamic starting and stopping Many times a design has a requirement to start and stop a task The overhead for stopping and starting a process is significantly greater i e a factor of 10 than starting and stopping a thread Advantage Threads
23. notification of system shutdown so appropriate logging and EEPROM storage can be completed before power is lost THE HARDWARE Figure 2 is the EBikeMeters schematic Most of the parts came from my electronics stockpile The SD card socket was salvaged from an old digital camera The ATmega328P IC1 controls the EBikeMeter s oper ation and uses every pin The inter nal 8 MHz internal RC oscillator is CIRCUIT CELLAR www circuitcellar com 4x20 CD Contrast Back light 48 to 5V 5 to 3 3 V Figure 1 An Atmel ATmega328P microcontroller is at the heart of the EBikeMeter The EBikeMeters main compo nents and the interfaces to the speed sensor battery motor controller and throttle are also shown Digital potentiometer ATmega328P Motor controller M Motor thot THROTTLE OVERRIDE SPEED i Speed sensor used so no external crystal is required The EBikeMeter oper ates at 3 3 V from the low dropout LDO regulator 1C4 from the 5 V power from the voltage converter VM1 from the 48 V battery The speed sensor input from a magnetically activated reed switch or equivalent is input to the ATmega328PS INTO input General purpose input output GPIO pins PC2 and PC3 monitor the user push button switches SW1 left and SW2 right Other GPIO pins PB6 PB7 and PD4 PD7 are used to interface to the LCD The LCD backlight is controlled with the Timer2 PWM output using an external transistor Q
24. stack and heap segments However the program memory is shared by the parent and child and is set to read only by the ker nel s memory manager Think of the program CIRCUIT CELLAR www circuitcellar com memory as the read only DNA inherited from the parent and think of data stack and heap as life s experiences You are stuck for better or worse with what you get for DNA but your life experiences are your own and can be shaped independently of your par ents experience A child process is free to modify variables and use resources however it wishes with no possibility of interfering with the parents memory and resources With child processes similar tasks that use a common code base can maintain data inde pendence and still share the same code Each process parent or child can create separate execution threads These threads share the same code base as the child processes do with their parents in a read only memory segment but they also share all memory except the stack and thankfully errno i e the global variable that indicates the type of error that occurs with certain function calls Thus one thread of the same process can stomp all over another thread s heap and data variables Or to put it nicely they can share each others data Initial i e minimum stack sizes can be separately set for each process and thread Think of threads as old time multitasking with some useful additions SCHEDULING
25. Arduino project I always verify the power sup ply first THE SOURCE OF ALL POWER Photo 1 shows the power supply components on an Arduino UNO board Input power can come from any of four different sources e coaxial DC jack center e USB jack e Vin header socket e 5V header socket When you plug in both DC power and a USB cable the circuitry automatically draws power from the higher voltage source The small FET just to the left of the 16 MHz crystal isolates the USB cable from the Arduino power supply to prevent backfeeding the PC s USB port A series diode pre vents reverse polarity on the DC jack from destroying the circuitry IA TL RX NIEDA ARDUINO ri amp ab C O Gmt tom tu Photo 1 The power section of an Arduino UNO board auto matically selects the higher input voltage Thermal vias around the voltage regulator conduct heat to a copper area on the bottom of the board Photo adapted from http arduino cc en uploads Main ArduinoUno_R3_Front jpg CIRCUIT CELLAR www circuitcellar com Microcontroller ATmega328 Operating Voltage 5V 7 12V Input Voltage limits 6 20V Digital I O Pins 14 6 PWM Analog Input Pins 6 DC Current per I O Pin 40 mA DC Current for 3 3 V Pin 50 mA Input Voltage recommended Figure 1 The Arduino UNO board specification summary gives you the broad outlines but you must dig into the datasheets and hardware layout to keep your pr
26. Board AFastI O Rich Single Board Computer ih T 159 100s Low cost2 5 x4 R ards C programmable computer 16 bit HCS12 processor clocked at 40 MHz 8 PWM 8 counter timer and 8 digital I O 16 10 bit A D inputs Dual RS232 485 ports SPI and 1 C ports 512K on chip Flash 512K RAM with Flash backup e Plug in I O expansion including Ethemet Wi Fi GPS 24 bit data acquisition UART USB Compact Flash card relays and more fae Mosaic Industries Inc LF tel 510 790 1255 fax 510 790 0925 kid www mosaic industries com microEngineering Labs Inc www melabs com 888 316 1753 Programmers for Microchip PIC Microcontrollers p PC Tethered USB Model shown Standalone software Command line operation melabs mE U2 Programmer miercEagincarng Labs Me ae i as Corr E Starting at 79 95 Hide GUI for automated use Override configuration with drop downs Stand Alone Field Programmer la Power from target device or adapter ta Program file stored on SD CARD Programming options stored in file Single button operation Program in circuit or use adapters for unmounted chips Zero Insertion Force Adapters available for DIP SOIC SSOP TQFP and more PIC is a registered trademark of Microchip Technology Inc in the USA and other countries N CC Electronic Toolbox App Databases schematics calculators 8 more For iPad iPhon
27. CELLAR www circuitcellar com Figure 1 A Microchip Technology PIC16F505 microcontroller is at the heart of the phone bell ringer s circuit BUILDING THE BELL RINGER You ve got to hand it to the engineers who designed the orig inal telephone system Using only two wires they were able to provide power to the handset detect when the handset was on and off the hook provide full duplex voice communication decode pulse dialing and ring a phone bell all with tubes and relays One result of combining all these capabilities is that a telephone bell is not rung by a simple low voltage DC current as you may expect Instead the phone bell requires a 20 Hz alternating current at 90 V This is in North America bells in other countries have other standards l Many people have taken on the challenge of ringing a phone bell for many pur poses As a result there are many circuits available to ring the bell Some are made entirely from discrete parts while most use one or more 555 timers to generate the ring tone itself as well as the ring cadence i e how long the bell rings and the time between rings As I was starting to breadboard a circuit I found based on a single 555 timer and a power transistor it occurred to me that it had a high parts count for what it accomplished I thought it should be possible to significantly reduce the count by using a microcontroller to generate the signal rather than using the 555 timer a
28. Flash Disk Just apply power and watch either EMAC OE Linux or Windows Embedded appear on the vivid 8 color resistive touch screen Suitable for use in a variety of work environments the PPC 080T 525 uses a robust aluminum housing and has no moving parts Quantity 1 pricing begins at 795 www emacinc com panel _pc ppc_080t_d525 htm ENSE EQUIPMENT IMONITC Phone 618 529 4525 e Fax 618 457 0110 e Web www emacinc com Since 1985 YEARS OF SINGLE BOARD SOLUTIONS www circuitcellar com CIRCUIT CELLAR R3 _ V Se MAXOUT _ R4 l The SPV1020 s evaluation board is set up for a V of about 38 V and a regulated V of about 36 V so I need to modify the resistor values to use a 16 V V and a 13 5 V Vur using these formulas A constant 13 5 V supply can keep a 12 V gel cell bat tery charged without causing long term overcharging To monitor the Peltier device and run a 12 V fan to ensure proper device cooling you must start with a charged battery Im not sure I can depend on the Peltier device to begin producing sufficient power without sustaining any damage if it is not being actively cooled And in my case that s with the 12 V fan Referring to the schematic in Figure 4 the fan is controlled by a simple transistor from the microcontrollers PWM output At this stage I m not using the PWM for fan speed control but that option is available Honeywell TD5A temperature dependant resistors TDRs are used to sense
29. Peltier device which has a 16 V plus input voltage However the SPV1020 is a similar device that can handle inputs up to 40 V Figure 3 is a block diagram of the STMicroelectronics device Its SPI can be used to retrieve the device s voltage and current data Note that this diagram shows only one of the four phase interleaved switching converters that are used to elimi nate the need for output electrolytics I used an STMicroelectronics STEVAL ISV009 which is based on the SPV1020 to make a Peltier to 13 5 V supply I used this supply to charge 12 V lead acid batteries These types of lead acid cells even the small ones are great for recharging cell phones and operating other electronic equipment for example when you lose power for extended periods of time or when you need the convenience of technology while backpacking and or Thermal z a DLA ME M Haft iia ja ni LEJ a i i ii a p a a ay Photo 1 To create this series string of N and P type elements Peltier devices are manufactured in a matrix of vertical connections on one surface and horizontal connections on the other surface Photo courtesy of Steve J Knole 2003 December 2012 Issue 269 9 December 2012 Issue 269 Figure 2 A device such as CUI s CP85 was designed to cool a CPU This graph shows the high currents necessary to support a constant flow of heat away from the CPU Note the tradeoff between
30. R Ul December 2012 Issue 269 Photo 4 The Arduino Pro Mini board uses a voltage regulator in a minus cule SOT23 5 package that cannot dissipate more than a few hundred milli watts and will overheat when supplying very small load currents together Photo 3 taken from the Arduino UNO R3 Eagle PCB layout file gives a better view of the top and bottom copper layers around the regulator and the thermal vias connecting the two layers My rule of thumb for ordinary electronics is that if you cant compel yourself to hold your thumb on it for more than a few seconds its too hot That translates to about 65 C 150 F which is far less aggressive than most industrial design limits On the other hand an Arduino isn t intended for long term high temperature industrial applications no component on the board should raise an instant blister on an errant finger The NCP1117 datasheet sets 6 the thermal coefficient between the junction and the case at 15 C W Subtracting the two thermal coefficients gives a very rough estimate of the case to ambient thermal coefficient Oca 0 Oe 75 C W 15 C W 50 C W It will actually be somewhat lower due to heat loss through the epoxy case but that s close enough My rule of thumb limits the case temperature to 65 C and the ambient temperature won t be much more than 40 C That temperature difference limits the maximum power dissipation in the NCP1117 to
31. SYSTEMS WZ United States W i 4 scott potterQ jasperwireless com l EF 4 EXOSITE W P i SIAR 7 SYSIEMS Micrium p 4 a w 2 4 OKAYA ir fo TOTALPHASE Kaj Electrostatic Cleaning Robot F z Second Prize Cloud Electrofusion Machine Using approximately 400 times less energy than commercial electrofusion machines the Cloud Electrofusion Machine is designed for welding 0 5 to 2 polyethylene fittings The RL78 controlled machine is designed to read a barcode on the fitting which deter mines fusion parameters and trace ability Along with the barcode data the system logs GPS location to an SD card if present and transmits the data for each fusion to a cloud database for tracking purposes and quality control Third Prize The Sun Chaser A GPS Reference Station Michael Hamilton United States mike a dtechnologies com The Sun Chaser is a well designed solar based energy harvesting system that automatically recalculates the direction of a solar panel to ensure it is always facing the sun Mounted on a rotating disc solar panel s orientation is calculated using the registered GPS position With an external compass the internal accelerometer a DC motor and stepper motor you can determine the solar panel s exact position The system uses the Renesas RDKRL78G13 evaluation board running the Micrium pC OS HI real time kernel Sjoerd Brandsma Netherlands
32. VxWorks RTOS and the Linux operating system OS The toolchain combines a global real time thread scheduler with aicas s parallel and concurrent fully preemptive thread distributed garbage collector QNX VxWorks and Linux developers can use Multicore JamaicaVM to develop hard real time applications on multicore CPU architectures using the Java programming language Applications can be scaled from single core CPUs to large multicore CPU architectures without recompiling Java language source code For scalability and performance the QNX VxWorks or Linux OSes can be used with JamaicaVWM s embedded optimizing compiler the Realtime Specification for Java API and multicore runtime Contact aicas for pricing gy TRON Lina se Lill oe MGS oe Merl oe 05 4 0 P GO oe OE oo RTEMS Saket oo Demet Min CE aicas Intend ecm MADA 2 Candie 4 ERT o Nene RRM MOC MPS Peer 4 GK oe SHE oo Speer oe Ex oo dh www alcas com N CIRCUIT CELLAR www circuitcellar com 0 HUMANDATA AET Boards from JAPAN O i W SAVING COST TIME with readily FRGA CPLD stamp Module PLCC68 Series D q Va q bi F P G A b Od rd S Easy and Quickly Mountable Module z u BBE and AMP CAULES MIE power supply operation FPGA Module IC socket mountable T Quality and reliability is provided by years of sales 50 I Os External clock inputs gag D Same board size and connector layout ACM
33. What about profiling tools Tools are available for profiling both threads and processes so I see no clear advantage of either From the command line processes are a little easier to profile than threads Slight advantage Processes Software updates Since processes are separate executables that can be separately updated there is some advantage to making every task a process Slight advantage Processes What about multiprocessing Some time in the near future I expect to design our first embedded system with a multicore processor But to date it is only a feature we appreciate on our desktops and servers One huge advantage of using Linux for embedded systems is that the Linux community is getting the kinks out of this OS feature on desktops and servers When I am ready to incorporate it into my first embedded design it will have had years of experience The OS can run any thread on any core of course under careful guidance No advantage AP CIRCUITS PCB Fabrication Since 1984 D As low as 9 95 each Two Boards Two Layers Two Masks One Legend Unmasked boards ship next day www apcircuits com gt Q QUESTIONS amp ANSWERS Since I m not usually afraid to go where angels fear to tread I ll share my opinion concerning processes and threads in embedded real time systems I think you need to start with some questions How important is keeping the data isolated There are some designs where t
34. XCM series SE EWC Suet A ejj All stocked items are ready to be shipped immediately operation Voltage HE for awdlary power supply are built in u Over 100 varieties of FRGA CPLD boards are available e Cre WOU am Customizing speed grade and or any features are possible JTAG signal All PLCC68 series have common vin SEM Free download technical documents before purchasing assignment High quality and highly reliable FRGA CPLD boards from Japan Very small size 25 3 x 25 3 mm O RoHS compliance Almost all products are ROHS compliance MADE IN JAPAN e ALTERA FPGA Board XILINX FPGA Board XILINX PLCC68 Series Cyclone IV E F780 FPGA board Spartan 6 FGG484 FPGA board Spartan 6 PLCC68 FPGA Module Lo ACM 204 series uw XCM 018 018Z series XP68 03 EP4CE30F29C8N Br p m aise XC6SLX45 2FGG484C RRFREEFERFE ENTA I 5 EP4CE40F29C8N mi XC6SLX75 2FGG484C H p 3 3V single power supply operation N EP4CE115F29C8N XC6SLX100 2FGG484C On board oscillator 50MHz V Credit card size 86 x 54 mm E XC6SLX150 2FGG484C RoHS compliant RoHS compliant a Credit card size 86 x 54 mm sze RoHS compliant K T Spartan 3AN PLCC68 FPGA Module Arriall GX F572 FPGA board XP68 02 ACM 025 series Spartan 6 FGG484 FPGA board i m XCM 110 110Z series XC3S200AN 4FTG256C EP2AGX45DF25C6N HE HH 4 Spartan 6 MRAM DDR2 FPGA internal configuration ROM EP2AGX65DF25C6N 40 XC6SLX45 2FGG484C FI Two User LEDs EP
35. about 1 V at moderate load currents which requires a DC input over 6 5 V to ensure 5 V out The Arduino specs suggest 6 to 20 V with a recommended range of 7 to 20 V Most users expect quite reasonably that the board will operate correctly from any power supply within those limits Unfortunately there s another limit that the Arduino specs mention only in passing If using more than 12 V the voltage regulator may overheat and damage the board In fact the regulator has internal over temperature protec tion and will shut down when the junction temperature exceeds 175 C 350 F It will resume operation after the temperature drops producing baffling periodic failures as the microcontroller restarts The NCP1117 is a linear regulator basi cally a transistor acting as a variable resist ance so the device power dissipation equals the input to output voltage differ ence times the load current The junction temperature T increases almost linearly as a function of the power dissipation P T P x 6 Ty The datasheet gives the junction to ambient thermal resistance coefficient 8 160 C W with a minimum copper area under the SOT 223 package Increasing the copper area decreases 0 but it exceeds 75 C W for a Square about 15 mm on each side A close look at Photo 1 shows that the Arduino UNO board includes several thermal vias that con nect the top and bottom copper planes December 2012 Issue 269
36. and intuitive During track placement the route will follow the mouse wherever possible and will intelligently move around obstacles while obeying the design rules All versions of Proteus also include an integrated world class shape based auto router as standard PROTEUS DESIGN SUITE reatures Hardware Accelerated Performance Board Autoplacement amp Gateswap Optimiser Unique Thru View Board Transparency Direct CADCAM ODB IDF amp PDF Output Over 35k Schematic amp PCB library parts Integrated 3D Viewer with 3DS and DXF export Integrated Shape Based Auto router Mixed Mode SPICE Simulation Engine Flexible Design Rule Management Co Simulation of PIC AVR 8051 and ARM7 Polygonal and Split Power Plane Support Direct Technical Support at no additional cost www labcenter com Electronics Labcenter Electronics Ltd 411 Queen St Suite 201 Newmarket Ontario Canada Toll Free 866 499 8184 www labcenter com or Email info labcenter electronics com December 2012 Issue 269 1G 2G 3 O 3 B z L lt A a L gt lt December 2012 e Build an MCU Based Bicycle Computer Dan Karmann Electrically Actuated Sound Effects A Circuit and Firmware to Ring a Phone Bell Joe Pfeiffer RL78 Green Energy Challenge Winners Controlling Access with a Proximity Card Open the Door to Manchester Encoding Scott Weber
37. and the eight pin DS 1487 driver shown above it to connect it to the network for testing b The numeric values encoded in the RFID are preprinted on the card The 5 bytes I read from the card in hexadecimal are 34 00 9E 73 04 The 34 is the manufacturer ID Of the remaining 4 bytes 93 is 134 in decimal fol lowed by 73 04 or 29444 in decimal Alternately 9E 73 04 is 10384132 in decimal both of which match the card s preprinted values when the door contact is open Almost any resistance will suf fice as the contact will ground the input line when the door is closed I used heavy duty garage door alarm contacts that screw into the concrete and have an armored wire harness see Photo 1 Interface to the proximity card reader is done through five lines on J3 two of which supply power to the reader device The remaining lines are connected to the microcontroller s RB port to take advantage of the separate interrupt 0 and inter rupt 1 feature I can monitor the data signal to determine when a card becomes present and track the clock signal to decode the datastream The data is processed by bit banging the data line and the clock lines in software Photo 2 shows the prototype bread boarding of the proximity card reader to the PIC microcontroller The J2 connector is simply a dry contact relay that is con nected across the garage door s Activate button The micro controller will activate the relay for approximately 1 s The relay
38. as stage manager and sound effects technician during performances N 0 I was only too happy to oblige Fortu nately I d recently retired so I had time The majority of the sound effects needed were completely mechanical e g a rain drum passing dried peas over nails to create the sound of rain clapboards slapped together to mimic gun shots orchestral chimes loaned to us by New Mexico State University s Department of Music for clock bells etc We also used a few sampled sound effects Incidental music was played by an organ on stage This music was recorded by cast member Robert Senecal and played from a lap top hidden in the organ console using the same sound effects software we normally used from the light booth Finally there were a few effects that were electrically actuated some alarm bells a car horn a tick tock to mimic a clock running at several different speeds and a telephone bell This last sound effect is the subject of this arti cle Photo 1a is my microcontroller based bell ringer Photo 1b shows the design mounted in the theatre ON AIR APPLAUSE Photo 1a Here is the completed phone bell ringer with the cover removed The bell is exposed to show the audience that this is the sound source and to make the sounds easier to hear The power ground and input connections are on the bottom of the box b The design is mounted and ready for use CIRCUIT
39. encoded data signal I used the device s UART to com municate on the RS 485 net work The signal decoding and interfacing to the card reader is w R accomplished by bit banging the clock and data lines This article describes how this is done As it is installed today the microcontroller that controls the doors is in place and the code works well However I have not settled on an adequate weatherproof enclosure for the reader RAO ANO RAT AN1 RA2 AN2 VREF CVREF RAS AN3 VREF RA4 TOCKI C1 OUT RAS AN4 SS LVDIN C2OUT OSC2 CLKO RAS OSC1 CLKI RA7 J3 O O O O O J5 O O O O O 5 DS1487 Low RX High TX RBO AN12 INTO FLTO HARDWARE amp ASSEMBLY Figure 1 shows the circuits schematic The unit connects to the network through J1 obtaining power and com munication via the differential signal The power is fused for protection and fil tered with C1 to clean up any noise The differential signal is bounded by D1 and RCO T1OSO T18CKI RC1 T1OSICCP2 UOE RC2 CCP 1 RC3 SCK SCL RC4 SDI SDA RC5 SDO RC6 TX CK RC7 RX DT MCLR VPP RE3 BVO RL1 as p 400 ohm N 9 1N4747 4 83 ohm p 60 mA R2 Q1 2N2222 6 8k Figure 1 A Microchip Technology PIC18F2221 microcontroller controls my garage doors The differential driver section around U2 is identical to devices I have used for other projects The proximity card reader attaches to J3 CIRCUIT CELLAR www circuitcellar com
40. format 2010 2011 A USB memory upgrade from 16 GB to a whopping 32 GB Free gift Circuit Cellar 25 anniversary hat Order today at www cc webshop com Design Challenge add ons Atmel AVR Design Contest 2006 WlZnet iEthernet Design Contest 2007 Microchip Technology 16 Bit Embedded Control Contest 2007 Texas Instruments DesignStellaris Contest 2010 WiZnet IMCU Design Contest 2010 December 2012 Issue 269 AC Power Transmitter source Oa Medium loss medium Receiver Preamplifier Moderate attenuation and noise Unknown phase shift Synchronous I Q detector Multiplier Low pass filter Figure 6 A phase locked loop PLL can be used when there is no way to directly use the excitation signal as a reference Such a PLL regenerates a local oscillator which is in phase with the excitation but requires a signal strong enough to lock called synchronous detection It works but only if the receiver is kept exactly in phase with the excitation source which was not a problem here IMPROVEMENTS In the previous discussion I assumed the phase shift between the excitation source and the receiver is null What about situations where this phase shift cant be neglected With the solution shown in Figure 3 the measured value will be reduced by the phase shift s cosine The higher the shift the more erroneous the result As shown in Figure 4 the first solution is simply to add a man
41. here this method works well because it uses the excitation signal itself as a reference fed to the multiplier along with the noisy signal This means the detector is using a signal with the same continuous frequency and phase as the signal to be detected which is required for this method Imagine you design the same detector but with a locally generated 100 kHz oscillator to replace using the excitation source Even if this oscillator is precise it will never stay exactly in phase with the excitation source for a long time which would drastically limit the detected signals performance This is why this method is Synchronous I Q detector Multiplier Low pass filter Receiver Preamplifier Phrase tan 5 Figure 5 This is the architecture of the ubiquitous I Q synchronous demodulator Using two detectors fed by two signals in quadrature it is possible to use simple math to simultaneously measure the received signals amplitude and phase Ul N CIRCUIT CELLAR www circuitcellar com ONE POWERFUL OOL FOR YOU m i T 7 a a u y g Here s what s included Special anniversary USB drive or our traditional CC GOLD USB drive Your choice PDFs of all Circuit Cellar magazine issues in print through date of purchase oy Article code Design Challenge projects Two years of Elektor magazine issues in PDF format 2010 2011 Two years of audioXpress magazine issues in PDF
42. in this type of application in his article Electric Movement and Control Circuit Cellar 199 2007 Note The eight pin MAX4081T device IC2 is shown in the schematic superimposed on a six pin DIP outline This is because the MAX4081T is only available as a sur face mount device and is soldered to a six pin DIP socket as a through hole component Also note IC2 has two sources of Voc power one from the 5 V supply and one from the current shunt resistor s positive side This was needed for initial testing when using an external 5 V supply without the 48 V battery I noticed the IC2 REF1A pin was acting as a short circuit to ground with out an IC2 V voltage By supplying both voltages via D10 and D11 if the 48 V battery voltage is ever lost due to a blown fuse or broken connection the 3 3 V voltage supply will not be affected and the rest of the circuit will continue operation The throttle override mechanism intent is for the EBikeMeter to act as a governor to limit operation of the bicycle electric assist motor to a maximum speed maximum motor current and or minimum operating battery voltage This is accomplished by overriding the throttle control signal from the throttle to the December 2012 Issue 269 jos N w ae 250mA PA Without a VCC REF1A is a short to GND 1N4148 BV D10 MW I I I i D11 m Rs RS l k gt vcc REF1A 1N4148 N C REF1B H i i GND OUT I I MAX4081 2N7008 Spee
43. is compared to the device s address If there is no match the state returns to the condition of waiting for an SOH Otherwise subsequent char acters are placed in the receive buffer and an index is incremented If the buffer becomes full before it sees an EOT the entire buffer is discarded and the state returns to the condition of watching for an SOH When an EOT is received I know an entire message has been received and the state is set to indicate a message has arrived From there the main processing loop examines the message and reacts accordingly Once the message is processed the main loop sets the state back to wait for another SOH The main program loop simply clears the watchdog timer and tests to see if a new message has arrived from the UART When that occurs it will examine the command byte and take the appro priate action I previously discussed the basic commands in my article about the RS 485 network The specialized com mands the unit understands are shown in Table 1 Payload Purpose Switch interrupt to GLK Back up 16 Collect 64 clocks samples 64 bits all correct Finding 9 1s preamble Collect 5 bytes Figure 3 This is the state machine that decodes the Manches ter datastream from the proximity card reader The detection begins when the data line becomes active When the main program loop processes an incoming message an empty reply buffer is created in case a response is need
44. must furnish digital files that meet our specifications www circuitcellar com advertise ALL TEXT AND OTHER ELEMENTS MUST FIT WITHIN A 2 x 3 FORMAT E mail adcopy circuitcellar com with your file or send it to IDEA BOX Circuit Cellar 4 Park Street Vernon CT 06066 For current rates deadlines and more information contact Peter Wostrel at 978 281 7708 or peter smmarketing us The Vendor Directory at www circuitcellar com vendor is your guide to a variety of engineering products and services 7C SMB us e Bus Monitors 7 dm 4 e Protocol Analyzers e Host Adapters e Multiplexers e Battery Applications e Software Tools Micro Computer Control www mcc us com Giga snaP BGA sockets and Adapters Giga snaP BGA SMT Adapters allow _attordable socketing UIS tow insertion torce 4 C H7bandwidm Same CTE as PCB nullor 7 TOUrT est sot Ironwood 0204 ELECTRONICS www ironwoodelectronics com www circuitcellar com CIRCUIT CELLAR Our Display Module Add a Touch Screen to Your Embedded Produc No special OS or Library Required Programming GUI is Simple Development Kit Up and Running in Days Learn more at www reachtech com or contact us at 510 770 1417 or sales reachtech com ment Kits include serial LOD controller board display touch screen cable IR Z Pe G mi images coce owe supply su r TECHNOLOGY INC 100 Satisfaction Guaranti Disk On Chip Rea
45. pmr Diz Development Kit for MOD54415 Part No NNDK MOD54415 KIT 99 00 for a limited time Development Kit for NANO54415 Part No NNDK NANO54415 KIT 99 00 2a freescale PE WITT YYY Alliance y i al fem se Ja LEA A 2 in A E DESIGNSPARK NEW FREE DESIGNSPARK PCB VERSION 4 COMPREHENSIVE NEW LIBRARIES EASIER COMPONENT SELECTION amp QUOTATION New FCB PROTOTYFINS SUPPORT DIKSON O Ne i SC Stele www designspark com RESOURCES BY December 2012 Issue 269 MANAGER Before I introduce the articles in this issue I want to take the opportunity to thank Steve Ciarcia for bringing the electrical engi neering community 25 years of innovative projects essential content and industry insight Since 1988 he s devoted himself to the pursuit of EE innovation and publishing excellence and we re all better off for it I encourage you to read Steve s final Priority Interrupt editorial on page 80 I m sure you ll agree that there s no better way to begin the next 25 years of innovation than by taking a moment to understand and celebrate our past Thanks Steve Break Through Designer s Block re you experiencing designer s block Having a hard time starting a new project You arent alone After more than 11 months of designing and programming which invariably involved numerous successes and failures many engineers are simply spent But don t worry Just like every other
46. power features for extended battery lifetime The RC1700HP MBUS4 module includes an extended feature set to meet time critical requirements in two way communication It can detect and receive both frame formats in parallel and support encryption on the extended link layer and the application layer The RF module can be used in the meter side at the concentrator side or as a standalone repeater The small module saves space in size critical applications When used at the meter side the RC1700HP MBUS4 provides low current con sumption in all operating modes e g sleep transmit and receive The module automatically handles reception time windows and automatically enters Sleep mode for low power consumption When used at the concentrator side the RC1700HP MBUS4 can handle 256 meters internally storing individual encryption keys and several thousand meters by using an external host controller for expanded key memory The module automati cally detects and checks ELL and APL encryption An automatic message generator helps streamline the two way communi cation with the meters enabling the module to communicate with thousands of meters from one concentrator Contact Radiocrafts for pricing Radiocrafts www radiocrafts com DEVELOPMENT TOOLCHAIN COMPATIBLE WITH MANY OSes The Multicore JamaicaVM is a development toolchain and runtime compatible with QNX Software Systems s QNX real time operating system RTOS Wind River Systems s
47. sbrandsma gmail com www circuitcellar com RenesasRL 8Challenge Rora Honorable Mention Water Heater by Solar Concentration This solar water heater is powered by the RL78 evaluation board and designed to deflect concentrated amounts of sunlight onto a water pipe for continual heating The deflector armed with a counterweight for easy tilting automatically adjusts the angle of reflection for maximum solar energy using the lowest power consumption possible Pierre Berquin France Honorable Mention Air Quality Mapper Want to make sure the air along your daily walking path is clean The Air Quality Mapper is a portable device designed to track levels of CO and CO gasses for constructing Smog Maps to determine the healthiest routes Constructed with an RDKRL78G13 the Mapper receives location data from its GPS module takes readings of the CO and CO concentrations along a specific route and stores the data in an SD card Using a PC you can parse Air Quality Mapper the SD card data plot it and upload it automatically to an online MySQL database that presents the data in a Google map Raul Alvarez Torrico Bolivia raul at hotmail com www circuitcellar com RenesasRL 8Challenge Rora High Altitude Low Cost Experimental Glider HALO Honorable Mention High Altitude Low Cost Experimental Glider HALO The HALO experimental glider project consists of three main parts A weather ba
48. series can be used to create higher volt ages see Figure 1 The construction technique for fabricating thermoelectric devices using Peltier and Seebeck technology uses alternating N and P type materials in a zig zag of rows to produce a hot side cold side sandwich as shown in the unassembled module in Photo 1 While the alternating N and P type material may look like diode junctions the materials are separate i e not dif fused and dont act like diodes In fact reversing the heat flow direction also reverses the current flow direction The amount of heat that moves from one side to the other is dependent on the temperature differential between the two sides If both sides are at an ambient temperature no heat current flows If one side is heated and the other side is somehow kept at an ambient tem perature then a stable differential temperature is maintained The larger the differential temperature the more heat i e watts will be transferred from the hotter side to the cooler side When using a thermoelectic device to generate energy it is important to note the device s maximum temperature On the CUI CP85 I purchased this is 80 C the melting point is 138 C www circuitcellar com CIRCUIT CELLAR Electron current gt Electron current gt This creates a safety margin so the device will never reach the solder melt ing temperature for obvious reasons Large heatsink masses can prevent hot spots from forming
49. the next byte reader cardBytej 0 if cardByte Oxff 64 9 start 1 end state STATE _MSG_COMPLETE break State STATE_START_OVER INTCONDits INTOIF 0 Back to INTO INTCONDIits INTOIE 1 INTCON3bits INTLE 0 And stop the INT 1 s T_DONE SERVICE_UART if RCS TAbits FERR PIRIbits RCIF 0 cmd_state CMD WAITING ch RCREG goto INT_DONE lf RCS RCSTAbits CREN RCSTADits CREN TAbits O0ERR 0 l PIRIbits RCIF 0 cmd_state CMD _WAITING ch RCREG goto INT_DONE ch RCREG Switch cmd_state case CMD_WAITING if ch 0x01 cmd_state CMD_READ ADDR break case CMD _READ_ADDR if ch gaddr cmd_state CMD READ CMD msgbyte 0 else cmd_state CMD_WAITING break case CMD READ _CMD PIRIbit INT_DONE return R if ch 0x04 cmd_state CMD_COMPLETE else commandlmsgbyte ch msgbyte if msgbyte gt 10 cmd_state CMD WAITING break s RCIF 0 ROOM TO GROW Obviously there are many applications for decoding proximity cards this way and the code I provided should be easy to migrate to other microcontrollers There is also room for other enhance ments e g forwarding card access activity to a dedicated recorder which would enable tracking of entrances and by whom I would also like to place a unit by the regular house doors a
50. theyre not direct physical replacements even though they re almost software compatible Pop Quiz The Arduino Pro Mini shown in Photo 4 has a Micrel MIC5205 linear regulator in a tiny SOT23 5 package with 8 220 C W Find the maximum load current for 6 9 12 and 16 V DC inputs given a 5 V output Because the Arduino project applies Open Hardware licenses to their designs other manufacturers can duplicate or adapt the boards This can introduce unexpected differences between PCBs bearing almost the same names For example the EkKitsZone UNO PCB in Photo 2 does not include thermal vias so its regula tor will probably run hotter than the one on the Arduino UNO PCB It also draws about 65 mA while running Blink quite a bit more than you d expect from the datasheet estimates I used Voltage regulator power dissipation will pose a problem for all but the smallest projects For example driving a single LED with 20 mA from a digital output burns another 140 mW in a regulator dropping 7 V from a 12 V supply Even if you run the regulator hot ter than I do just a few LEDs can heat it up and shut it down The same restrictions apply to the 3 3 V regulator in the ATmega16U3 or FTDI USB interface chip Its powered from the regulated 5 V supply and drops only 1 7 V but chips 0 limits the current available at the 3 3V output Homework Figure out the maximum current available for your 3 3 V logic Hint also consider the additional powe
51. this article when I use the word task I am talking about either a process or a thread I ll start by defining terms and looking at the differences and similarities DEFINITIONS Processes and threads fall under my old defini tion of tasks A task can be defined as an instance of a software program that utilizes CPU resources to accomplish some purpose These resources include memory I O the file system s and net working In Linux a process is a task that obtains these resources from the kernel All processes have their own memory allocated to them These consist of program memory sometimes called the text or code segment data memory where variables are kept heap i e dynamic memory and the stack The kernels memory manager prevents processes from having any access to other processes memory This encap Sulation is an extremely valuable feature that enables us to isolate the process from problems created by hardware or software memory corrup tion If one process goes amuck there is no chance of corrupting memory in other processes If hardware or software never failed this separa tion would be unnecessary Figure 1 shows how a process with multiple threads uses virtual memory Here is where things get a little tricky A process can create a separate process called a child process The creating process is called the parent process The child process inherits copies of all the parent s data
52. unavoidable and the P in PVT is an attempt to account for their effects in the timing analysis The idea is to make the analysis conservative enough so your design will work reliably despite these variations What s your EQ The answers are posted at www circuitcellar com eq Contributed by David Tweed You may contact the quizmasters at eq circuitcellar com ye ew aes Ar ee S LEARN FROM THE EXPERTS Newnes Press has the resources you need to get started SAVE 30 on all titles when you order from www newnespress com Enter promotional code Newnes30 at checkout y N J jy FAST AND EFFECTIVE 1 TRA H EMBEDDED SYSTEMS EMBEDDED EMBEDDED PEN DESIGN j i THE HANDS ON Applying th Abak SOFTWARE XBEE LAB MANUAL ARM med secure Software and Systems The Works Experiments that Teach Development you XBEE Wirelesss wc Communications ByColin Walls By lon Titus By Rob Toulson and ISBN 9780124158221 ISBN 9780123914040 Tim Wilmshurst ISBN 9780080977683 Join our free membership page at www newnespress com s Printo stook enews updates Receive our best discounts Hear about books before they publish m i Access to free sample chapters video tutorials and more ote m Mik her ISBN 9780123868862 Newnes Find us on Facebook f Follow us on Twitter Scan to access WWW NEWNESPrESS COM December 2012 Issue 269 www circuitcella
53. which if allowed to exceed this temperature will most likely ruin the thermoelectric device The differential temperature AT is the difference between T the tempera ture measured at the device s hot side and Toop the temperature measured at the devices cold side The cooler the cold side can be kept the greater AT will be and the more energy can be extracted The trick is to get as much heat as possible from the hot side to the cold side In Figure 2 you can see that as the heat transfer is increased going up the graph lower left side the current increases in the graph s lower section and the voltage also increases in the graph s upper sec tion The currents and voltages are also proportional to AT along the graph s bottom The graph shows the energy input needed to create a temperature difference between a thermo electric device s two sides when it s used for cooling or heating The same relationships are in force when used to transform heat into electricity MAXIMUM POWER In my article Charging with PV Cells Circuit Cellar 265 2012 I talked about maximum power point MPP when using solar arrays A Peltier device has similar qualities in that its MPP will vary with conditions so the load must be varied for maxi mum efficiency I used an STMicroelectronics SPV1040 battery charger to obtain MPP from a varying solar cell array With a 5 5 V maximum input voltage the SPV1040 isn t as powerful as the CP85
54. 0 otherwise Start over if totalBits 64 if we didn t ever find one State STATE_START_OVER bail break goto INT_DONE case STATE_COLLECT_BITS cardBits if cardBits 5 After 4 we skip parity break www circuitcellar com CIRCUIT CELLAR Here is where I take advantage of the clock output This clock is 64 pulses per bit so there are 32 pulses before the transition and 32 pulses after the transi tion I start counting clocks when the data line becomes active After 16 clocks I should be in the middle of the left hand side of the bit LHB After 32 more clocks i e 48 total I should be at the right hand side of a bit RHB After 64 clocks the bit is over see Figure 6 If after 48 clock cycles I test the LHB value and find it s the same as the RHB value I must conclude that there is no transi tion and I am out of phase by 32 clock cycles I set the clock counter to 16 and start over because I was already at 48 counts Once I establish that I am in the correct phase I continue checking for 64 total bits in a row to verify that the LHB doesn t match the RHB every time This encompasses the entire card s bitstream Once I verify the entire bitstream is in phase I can start hunting for the nine 1s that make up the preamble The simplicity of this is that the LHB is the actual bit value I want To further validate the datastream the nibbles s parity bits can be teste
55. 0 2004 www analog com static imported files data_sheets AD630 pdf R Lacoste Radio Frequency Mixers Circuit Cellar 263 2012 Stanford Research Systems Inc About Lock In Ampli fiers Application Note 3 www thinksrs com downloads PDFs ApplicationNotes AboutLIAs pdf D Wenn Microchip Technology Inc AN1115 Imple menting Digital Lock In Amplifiers Using the dsPIC DSC 2007 www microchip com stellent idcplg IdcService SS _GET_PAGE8nodeld 18248appnote en532447 SOURCES AD360 Balanced modulator demodulator Analog Devices Inc www analog com dsPIC33FJ256GP710 Microcontroller Microchip Technology Inc www microchip com SR830 Lock in amplifier Stanford Research Systems Inc www thinksrs com products SR810830 htm CIRCUIT CELLAR www circuitcellar com CIRCUIT CELLAR ADUGG4S 1 MICFOCOT From Microcontroller Th Jesign Manual eory to Design Projects ADuC841 Microcontroller Design Manual Buy it today December 2012 Issue 269 UT 0 EMBEDDED IN THIN SLICES by Bob Japenga USA Concurrency in Embedded Systems Part 4 Introducing Linux and Concurrency This is the fourth article in a multi part series about concurrency in embedded systems Here you learn how embedded Linux provides the mechanisms to design robust systems with concurrency y previous articles examined common pitfalls in systems with concurrency and discussed in gene
56. 1 The ATmega328P SPI bus is used to interface to the SD memory card socket and the digital potentiometer IC6 which controls the LCD contrast based on the current temper ature Note the heartbeat LED on GPIO pin PBO is also the SPI slave select SS signal for the digital potentiometer s SPI bus So whenever SPI based accesses are happening to the digital potentiometer or the SD card the heartbeat LED must first be turned off The temperature is obtained from a Maxim Integrated Products 1 Wire device IC5 from another GPIO pin PC5 GPIO pin PC4 monitors the power fail input from a reset supervisor device IC3 using pin change interrupts for early power down notification The scaled battery voltage is monitored on one of the ATmega328P s ADC channels ADC1 The scaled voltage from R1 and R2 seen by the processor is approximately V _ 20 which enables a battery voltage of up to 66 V to be monitored An external high side low ohm shunt resistor RS is used to sense the electric drive motor current It is then amplified and www circuitcellar com CIRCUIT CELLAR scaled by IC2 and filtered by R4 C3 and C5 before it is moni tored on the ATmega328P s ADC 0 channel With a 2 5 mQ external shunt resistor the current s voltage seen by the processor is approximately 2 5 mQ x motor current x 20 gt x This enables a motor current up to about 33 A to be monitored Jeff Bachiochi wrote about using the MAX4081T IC2
57. 2 4 Pt lagi ty 5 Gi Propert lapieem IEO Le mamcp 11 i ua E GRAPE CREF karate Se a FILI Peet aig em i Emi t ha Lp eS Fi Baan 7 pies 6 x bmi rasa k O FP AtarTETTPFJ i vend Gseriiain veid pa i i initialize tack if Ethernetir OSC TAGA remi 4 2 OSthangeFrio Mata FaTO i Enabi s stslUpda ta S ATLHETTF J s pried el Bac arie 33 pg 3 7774 73 iprintt Belle BetBarner Horid in jy white i I OSTLnsD ly 25 7 j m j gaj ja a S Preteens 2 Tasks gt t a fhukd HelloletkurwWocd Netfiurner IF Search Connect ma 2 Hifind Micontg H NANO54415 Core Module 32 bit 250 MHz processor 64MB DDR2 RAM 8MB flash 10 100 Mbps Ethernet 30 general purpose 1 O Eight UARTs Four I2C Two CAN 3 SPI 1 Wire SSI MicroSD flash card ready 6 analog to digital converters ADC Two digital to analog converters DAC ceecceccece EF FELA Fiti Tt Lt sari Bacty seinen g Fred 7078 bytes of 2044384 avaiiabie z Connpchor Setting Mendes Settings iflasa 4 89 Seed 6413609 bytes of BIRIGA availabic ram 7 476 Pert Mot w _ butte compiere for project E release tag verni nik l 2 5 2 Information and Sales sales netburner com Web www netburner com Telephone 1 800 695 6828 Y etBurner Networking in One Day Lee ETA ari INO see Khe oss Ha PEESI T WA lihri pee 5 fe
58. 2AGX95DF25C6N XC6SLX75 2FGG484C HET FAR RoHS compliant AB a etter esa XC6SLX100 2FGG484C HMM Credit card size 86 x 54 mm XC6SLX150 2FGG484C RoHS compliant Compact size 43 x 54 mm ALTERA PLCC68 Series RoHS compliant Ss Cyclone III PLCC68 FPGA Module AP68 04 Virtex 5 FFG676 FPGA board ait UUBE s TET Cyclone M je D Cyclone M Cyclonel V GX F484 FPGA board EP3C25U256C8N XCM 01 1 series ACM gt CM 0 24 series Virtex 5 if ERAM Ji SDRAM Ak 3 3V single power supply operation Cyclone IV GX DDR2 SIF40 PY On board oscillator 50MHz XC5VLX30 1FFG676C 0 O O jp p Ka EP4CGX50CF23C8N XC5VLX50 1FEG676C RoHS compliant skoki 1 XC5VLX85 1FFG676C FR nee XC5VLX110 1FFG676C Re O a Credit card size 86x54 mm Fillies Cyclone III PLCC68 FPGA Module redit Card size X mm ini RoHS compliant akk 03 RoHS compliant EP3C10U256C8N Virtex 5 LXT FFG665 FPGA board AE wo User S XCM 017 series One User Switch Slide Cyclone IV E F484 FPGA board Virtex 5 SDRAM CYA CSIF40 RoHS compliant ACM 107 series XC5VLX30T 1FFG665C fF XC5VLX50T 1FFG665C 225 a fi ZOZ 7 MAX V PLCC68 CPLD Module Credit card size 86 x 54 mm Cyclone IVE MRAM EP4CE55F23C8N AP68 02 EP4CE75F23C8N RoHS compliant PRNNNNNNNANNO IN 3 MAX V EP4CE115F23C8N Compact size 43 x 54 mm SM570ZF256CSN External Clock inputs RoHS compliant On board Voltage regulator RoHS complia
59. 5 bit 36 row parity nibble 10 bit 37 bit 38 bit 39 bit 40 row parity some point the level will change so I will take advantage parity column parity Table 2 Here is a breakdown of all 64 bits in the RFID card s bitstream The bits are received left to right top to bottom interrupt to occur with each clock cycle and sample the data line The interrupt will be set back to the data line at the end If the data was corrupted the process starts over However the clock runs at approximately 125 kHz as long as the module is enabled There are 64 clock cycles per bit streamed from the reader The data encoded in proximity cards is 64 bits in total which are encoded as five 8 bit bytes with nine 1 bits of preamble and a collection of even parity bits tossed in for good measure Each parity bit appears after 4 data bits so 10 bits are used to represent 1 data byte Finally there is a nibble that contains the parity Figure 4a This is a sample of a Manchester encoded datastream b This is a clock stream not to scale Figure 5 Here is a stream of all 1s Or is it all 0s Figure 6 The bit can be thought of as a left hand bit and a right hand bit each one divided into 32 clock cycles The longer pulse in the center does not have a transition and is therefore a bit boundary W 0 column parity column parity column parity 0 bits for the previous nibbl
60. 7 Jameco Electronics awa tas Gee eae wi 11 Jeffrey Kerr LLC 9 0 a nae aan SA rec 78 JK microsystems Inc 00 eee 12 Labcenter Electronics 4 4441111 3 MaxBotix INC aaa 79 Not a supporting company yet Contact Peter Wostrel peter smmarketing us Phone 978 281 7708 Fax 978 281 7706 to reserve your own space for the next issue of our member s magazine Head Office Circuit Cellar Inc 4 Park Street Vernon CT 06066 Phone 860 875 2199 Copyright Notice Entire contents copyright 2012 by Circuit Cellar Inc All rights reserved Circuit Cellar is a registered trademark of Circuit Cellar Inc Reproduction of this publication in whole or in part without written consent from Circuit Cellar Inc is prohibited Disclaimer Circuit Cellar makes no warranties and assumes no responsibility or liability of any kind for errors in these programs or schematics or for the consequences of any such errors Furthermore because of possible variation in the quality and condition of materials and workmanship of reader assembled projects Circuit Cellar disclaims any responsibility for the safe and proper function of reader assembled projects based upon or from plans descriptions or information published by Circuit Cellar The information provided by Circuit Cellar is for educational purposes Circuit Cellar makes no claims or warrants that readers have a right to build things based upon these ideas under patent or
61. 9 Solar Data Logger Part 2 Data Points Circuit Cellar 227 2009 SOURCES Arduino MEGA Arduino Pro Mini and Arduino UNO Arduino http arduino cc en Main ArduinoBoardMega2560 http arduino cc en Main ArduinoBoardProMini http arduino cc en Main ArduinoBoardUno ATmegai6U3 ATmegai6U3 and ATmega328 Microcontrollers Atmel Corp www atmel com MIC5205 regulator Micrel Inc www micrel com page do page product info products mic5205 shtml NCP1117 Regulator ON Semiconductor www onsemi com PowerSolutions product do id NCP1117 CIRCUIT CELLAR www circuitcellar com CUWIN5500 gt CUWINS200 Windows CE 6 0 Touch Controller IN CL The CUWIN is a series of Windows CE touch controllers that are more cost effective than a PC but with more features than an HMI touch screen Create sophisticated applications with C or any Net language 533MHz ARM CPU 128MB SDRAM amp Flash SD Card Support Ethernet RS 232 485 USB Audio Out Windows Embedded CE 6 0 The CUPC is a series of industrial touch panels with all the features of a modern PC for the most feature rich user experience ATOM N270 1 6GHz CPU 2GB RAM 320GB HDD SD Card Support Color Display 1024 x 768 RS 232 Ethernet USB Audio Out Windows XPe XP Pro CUPC gt CUPC P200 COMFILE kn Industrial Touch Panel PC with ATOM Processor C Programmable Modular Industrial Controller B
62. ASIC with LADDER LOGIC CONTROLLER Po gh Integrated CUBLOC Controller and I O Board CB210 The CB210 is an inexpensive integrated CUBLOC controller and I O board programmable in both BASIC and Ladder Logic 1 0 Ports x20 10 bit A D x6 PWM x3 RS 232 x1 80KB Program Memory 3K Data Memory pom P CUPC P220 1175 Chess Dr Suite F FOSTER CITY CA 94404 call 1 888 9CUBLOC toll free 1 888 928 2562 TECHNOLOGY email sales comfiletech com MOACOIN The MOACON is a modular C programmable ARM based automation controller designed for industrial environments Choose from a diverse feature rich selection of modules including Digital 1 0 Analog 1 0 RS 232 485 Motor Control Ethernet High speed Counter amp PWM The CUSB is a series of compact CUBLOC integrated industrial 1 0 boards programmable in both BASIC and Ladder Logic CUBLOC CB280 Core Module 80KB Program Memory 3KB Data Memory DC 24V Inputs x9 16 A D Inputs x2 6 Relay Outputs x6 16 PWM x2 6 High speed Counters x0 2 RS 232 485 x1r 2 December 2012 Issue 269 Ul HE DARKER SIDE Locked In by Robert Lacoste France Synchronous Detection Explained At some point in your electronics engineering career you ll need to extract a signal in a noisy environment When the time comes consider a lock in amplifier You ll find the information in this article about lock in amps and synchronous detection in
63. Any time you use multitasking you must know how the ker nel performs scheduling The kernel does not make a distinction between processes and threads with regard to scheduling In Linux a single thread process is treated the same as all other threads Linux gives the designer significant flexibility by enabling a number of options for the scheduling type when a process is created Out of the box the default scheduling algo rithm used for a process is round robin time slicing SCHED_OTHER In round robin time slicing every task gets an equal real time slice Each task either runs for its allotted time or until it relinquishes control Although there are priorities they are more like suggestions to the kernel i e telling children to play nice Appropriately these are called nice values In addition there is Round Robin with real priorities SCHED RR First In First Out SCHED FIFO which eliminates the time slice i e each task runs until it blocks or terminates Batch Mode scheduling SCHED_BATCH which tells the kernel this process is not nice and gives it less favor when scheduling and Idle mode SCHED_IDLE which is the same as SCHED_OTHER but with a nice value so low it never has to run In addition Linux now provides the ability to create a group of processes that uses what is called real time extensions Each group can be assigned a specific amount of time it can run with in a given time period An
64. DUCED BY Si Gece Genius attracts Feel the pull DAO 4IMSID LV AILSIDJA VAVAIN SVDSASWI EL0Z TT AYVANVI AYAIN 8 AAYNNYI AVGSINL REGISTER NOW December 2012 Issue 269 LP Sallen Key filter SUI dsPIC33FJ256GP710 Amplifier LP Filter Figure 8 This example extracted from a Microchip Technology application note shows the simplicity of a digital lock in amplifier s hardware Here four GPIOs are used as a DAC and generate a wheatstone bridge s sine excitation signal thanks to the firmware The detected signal is fed back the on chip ADC and the microcontroller takes care of the multiplication and low pass filtering stages You must know this is possible It will be easier to directly use the excitation signal IMPLEMENTATIONS At this stage you may want to try implementing a lock in amplifier in your next project but how would you start First decide if you prefer an analog or a digital approach Both are possible for a lock in amplifier which existed years before the first digital signal processor was invented The analog solution is simply built around an analog signal mul tiplier or mixer and a low pass filter Analog Devices has several chips that will work e g the AD630 balanced mod ulator demodulator Figure 7 which is extracted from the AD630 s datasheet shows an example of an analog lock in amplifier Analog lock in amplifiers are great and are still used today i
65. Energy challenge og Bee a For people who are passionate about hardware and software design embedded development and computer applications Awesome projects tutorials industry news y Se Ae AN MY Ey je aS verte 4 ee je LY O a ee ga 4 LE wia z design challenges and more Follow us on Twitter Like us on Facebook i A ZDIIEN m Ee Pa ee et BM Beer rts pit CircuitCellar SEE ae editor_cc SS circuitcellarmagazine gt 1Ha a i BOARDS BOOKS DVDs AND MORE AT WWW ELEKTOR COM SHOP Elektor Shop The world of electronics at your fingertips Han Nabben The world s 1 book with NFC technology integrated B NF hotspots inside lektor The world s first book with NFC technology integrated inside Catch the Sun The oldest known contactless connectivity technology dates back 2000 years to the Han dynasty in China In that era the Kongming lantern was invented a small hot air balloon used primarily for transmitting military signals The Kongming balloons have today been replaced by chips Near Field Communication or NFC provides wireless connectivity over short distances based on semiconductor technology This book links both technologies together Catch the Sun is the world s first book with NFC semiconductor technology integrated inside while the content of this high tech book is about the beautiful magic of low tech ballooning The book has mult
66. I L A N D S c Blr r r r P H _ O I H al vi IN S O I K lal T A N c 1 r IR DIiAlRILItINiG tlo N s N lal lo ic I G Ic 1 WIA FIE R M T L N pir ElL E c TIRI1I ciclolRIE K r D T IH E RIMO PILIA S TII C Y December 2012 Issue 269 gt RIORITY NIERRUPI by Steve Ciarcia Founder and Editorial Director A Onward and Upward t the end of our conversations longtime Circuit Cellar columnist Ed Nisley always says Onward and upward To this day I m not quite sure what that means but it seems like a useful exit line Of course leaving a conversation and leaving a career are two completely different things Both involve some strategy With a conversation one expects you ll talk later and not everything has to be resolved by the conversation s end With a career there is more finality You want to know you have accomplished some goals left the world a better place and placed your legacy in the hands of people who will properly transition it These days I m not sure whether to laugh or cringe when I get an e mail or meet a Circuit Cellar reader who starts a conversation by saying they have been reading my stuff and following me since BYTE magazine Certainly I take it as a compliment but it also means we are both over the proverbial hill True the BYTE days and the seeds that generated Circuit Cellar magazine began 35 yea
67. I built a fire to test the circuitry which I mounted behind a thin wall of foam insulation I covered that with a thin aluminum sheet hoping it would reflect the heat back toward the fire The only thing exposed through the insulation was a number of thin aluminum fins I wedged into a ball grid array BGA heatsink I used as a heat collector The Peltier device was mounted between the BGA heatsink and the fan heatsink which stuck out from the back of the insulation just above the circuitry When the circuitry was powered up the LCD displayed ambient A D Interrupt Read present A D channel and store result Increment channel number Read registers from the SPV1020 using SPI Calculate volts and display on LCD Figure 5 Most of the work to con stantly display data is done within the main loop The SPV1020 provides voltage and current information while the TD5A tempera ture sensors read the Peltier device s hot and cold sides Temperature data is continually avail able thanks to the A D interrupt Warnings are audi ble via a piezoelec tic transducer XX MR Calculate current and display on LCD XX X lie Calculate temp T1 and display on LCD Timer1 interrupt Decrement tick if not already zero Hot xxxC Calculate temp T2 and display on LCD ColdxxxC Turn the fan ON if T1 OWIZESSSE Turn the warning ON imito 61 C CIRCUIT CELLAR www circuitcellar com Photo 2 The pr
68. N Tell us about your cur rent occupation STUART I have been an engineering manager but made the switch back to engineering a few years ago I have found over the years that while outside projects aren t always directly applicable to my work the principles in firmware hardware and analog design are applicable R N microcontrollers NAN You ve written 19 articles for Circuit Cellar since 1995 Several of them focus on Atmel AVR architec ture or devices What is your fascina tion with AVR STUART I tend to write about what interests me something I want to do or sometimes something that I will find useful myself I have liked the AVR I tend to stick with things that work as long as they fit the application Some years ago I introduced DSPs to the engineering organization At that time I was using Analog Devices s parts but I was using them as very fast architecture ever since I started using it In some ways Microchip Technolo gy s architecture has advantages espe cially in the area of the timer counter blocks But the AVR has a very orthog onal architecture and lends itself well to instead of as DSP blocks I designed a lot of hardware using those parts some of which they are still using now after 15 years Engineering Innovation Experimentation 8 Explanation An Interview with Stuart Ball Beginning with his early fascination with electronics Stuart Ball has always nurtured
69. OS S PIJOM SUL 4V1140 LINOHIO 697 ON 39 3 peppoquwy 103 921n Huy SOIU0 UOIREW IOJUT Huadu 91901 ATAVWWVHDOUd ZTOZ H48W3031Q PROJECT Proximity Card Access Control INSIGHT Determine a Design s Failure Rate INNOVATE Power Up with Heat LOCATION United States LOCATION Canada LOCATION United States PAGE 34 PAGE 64 PAGE 68 GIRCUIT CELLAR THE WORLD S SOURCE FOR EMBEDDED ELECTRONICS ENGINEERING INFORMATION DECEMBER 2012 MCU Based Bike Computer Inside Arduino s T Power Supply Linux amp Concurrency po e se ees Synchronous Detection Explained a Electrically Actuated Sound Effects A PLUS Green Energy Design Ai CoN Innovative RL78 Based Projects Jl Electrostatic Cleaning Robot Jl Solar Powered Water Heater l Portable Power Quality Meter a 9 00US 10 00CAN 0 74470 JI 0 www circuitcellar com 12 gt MOD54415 Core Module 32 bit 250 MHz processor 64MB DDR2 RAM 10 100 Mbps Ethernet Eight UARTs Two CAN 3 SPI 1 Wire 5 pulse width modulators PWM SSI MicroSD flash card 8 anal tal to analog converters DAC y Hetkurar Haptic Barat WY od imac Mafci ne ID Brine 22 stents titan Soe ten Peet tae BY 0 0 0 i verter za ZBanE dr e G Zd Mkia roe ee ory 3 goa TRZE os Nnkan
70. about _ 65 C 40 C 50 C W 500 mW Knowing the DC supply voltage at the regulator which you can measure at the Vin pin and the regulator power dissipation its easy to find the maximum regulator current P _ 500mW E Vy 5V Ivax For a 12 V supply that works out to about 70 mA If that seems oddly low you re right In round numbers the ATmega328 microcontroller will draw 10 mA when running at 16 MHz with a 5 V supply the ATmega16U2 USB interface draws another 15 mA and the other circuitry and LEDs add up to 10 mA or so for a total of 30 to 40 mA Under my restrictive thermal rule the regulator can supply barely enough current for the Arduino UNO board itself without any power for your circuitry from a 12 V wall wart Homework plug a 12 V supply into an Arduino and run the Blink sketch If the regulator becomes surprisingly warm then the numbers I used aren t far from the truth It won t hit 65 C because those numbers are pessimistic R 0 Bonus attach a thermocouple bead to the central tab on the NCP1117 package and record the actual temperature Vary the load current plot temperature vs power dissipation and derive the thermal coefficient The Arduino UNO is the most recent addition to a family of microcontroller boards ranging from the tiny Pro Mini in Photo 4 to the much larger MEGA board in Photo 5 Each Arduino PCB has a different DC regulator copper foil layout and thermal behavior so
71. achine FSM to debounce the push button signals and determine The EBikeMeter configuration and nonvolatile statistics data loaded from the processor s EEPROM at start up include speedometer wheel size LCD backlight timeout LCD subscreen timeout LCD backlight brightness correction minimum which event action should be taken Three types of push button events are recognized single button pressed dual button pressed and single button hold The temperature is periodically read and a digital potentiometer is used to adjust the LCD contrast based on this value The accumulated statistics data is continuously logged to the SD memory card s log file but only if the bicycle is moving All logging is suspended when the bicycle stops Another periodic activ ity is determining if the throttle limiting control needs to be changed based on the current speed motor current or battery voltage value and the associated config ured limits Finally the serial interface is checked to determine if any commands have been received for processing These commands are used for the various EBikeMeter configuration settings and basic SD card file management Additional firmware detail informa tion including application programming interfaces APIs device driver access and source file organization can be found in section 8 of the EBikeMeter Ref erence Manual with the manual and the full source code which are available on Circuit Cell
72. ading more than 100 tags per second The MAGIC PCB identifi cation system features a high reading accuracy with a wide reading angle and a low number of manual operations The system does not require optical contact It reads through enclosures and packaging Additional user memory e g for software version maintenance information etc is also available Contact Beta LAYOUT for pricing Beta LAYOUT www beta layout com NEW PRODUCT NEWS ja CIRCUIT CELLAR www circuitcellar com It s gt a great ta w a AF JJ if can pula NYSE e A wild collection of maker designed electronics projects All projects packaged as step by step kits available for sale e Kit designers earn a commission on every sale e Request a project and help influence the design process e DIY inspiration EEE ae a Dust off that workbench fire up the soldering iron and get back in the garage Visit www ClubJameco com Fireup to join the fun December 2012 Issue 269 TWO WAY WIRELESS M BUS METER READING MODULE The RC1700HP MBUS4 is a 169 MHz wireless M Bus module for long range automatic meter reading AMR The mod ule is capable of secure two way communication between a meter and a concentrator It contains the Wireless M Bus stack supporting all physical layers MAC layers and frame formats transport and security layers The module handles all critical timing for two way communication along with very low
73. am mable logic chips e g dynamic reconfiguration memory and HDLS Robotics Projects about robot systems devices capable of repeating motion sequences and MCU based motor control designs e g mobile robots motor drives proximity sensing power control navigation and accelerometers Signal Processing Projects and technology related to the real time processing of signals e g DSP chips signal conditioning ADCs DACs filters and compar isons of RISC DSP VLIW etc Wireless Communications Technology and methods for going wireless e g radio modems Wi Fi IEEE 802 11x Bluetooth ZigBee IEEE 802 15 4 cellular infrared IrDA and MCU based wireless security applications FEATURES Build a Function Generator by Larry Cicchinelli MCU Based Model Helicopter Controller by Akshay Dhawan and Sergio Biagioni Open Source Hardware Development by John Vaughn Tomas Carvalho e Silva and Josh Davis Control Center Software Design by Scott Weber COLUMNS Web Based Tools for Home Energy Efficiency by Jeff Bachiochi Failure Mode and Criticality Analysis by George Novacek Embedded Authentication by Patrick Schaumont Fa r Se ee umi am z pa er 7 qe ZJ a TU JRE z 1 ia La oe x a in r A J m mg j 1 R i 4 a gt i s m LJ ee A CELE i WITH PROTEUS PCB DESIGN Our completely new manual router makes placing tracks quick
74. ar s FTP site FILE SYSTEM SELECTION MODIFICATION The EBikeMeter firmware file system needs to support a PC compatible FAT based file format I found several FAT type file system firmware packages online but most were too large to fit in the available flash memory space along with the rest of the application code Some firmware packages were too large to fit even without any application code I found a Roland Riegel MMC SD SDHC card library that was small enough to do the job but it had one drawback it only supported FAT 16 for SD cards from 32 MB to 2 GB I had a sur plus of FAT 12 based 8 and 16 MB SD cards I preferred to use in this application After studying the Roland Riegel MMC SD SDHC card library code I found I could add FAT 12 support to it for these smaller SD cards and it would still fit into the available flash memory barely with the appli cation code CIRCUIT CELLAR www circuitcellar com ON OFF OO s D O Speed sensor NE Closed when card partially inserted Open when card fully inserted and card locked Panasonic SD Card socket Detect closed when card fully inserted I wee ee ee ee ee ee ee ee A A A A ee ee tbe ess ccscscscsssss I I Mini DIN ee p gt A RZE Serial TTL lt gt RS 232 Figure 5 This detailed wiring diagram shows the connectors speed sensor voltage supply current shunt associated protective fuses and throttle control modifications I a
75. areful with external supplies Two older Arduino Duemilanove boards in my collection have capacitors rated at 25 V and 35 V both in packages of about the same size Photo 2 shows the power section of an EKit sZone UNO a competitive board loosely based on the Arduino schematic with through hole 100 uF electrolytic capacitors rated at 25 V All those capacitors will operate comfortably at the board s 20 V maximum voltage specification As always pay attention to both the formal specifications and the actual hardware in hand any mismatches will rarely be in your favor THE LIMITS OF POWER The Arduino UNO has an ON Semiconductor NCP1117 5 V regulator in a SOT 223 Photo 3 The Arduino UNO PCB layout shows many thermal vias around the NCP1117 linear regulator The total copper area remains fairly small and the regulator runs hot for seemingly small load currents www circuitcellar com CIRCUIT CELLAR Photo 2 An EKitszone UNO board uses 100 uF 25 V through hole capaci tors in the power supply section The small copper pour around the 5 V regulator lacks the thermal vias appearing in Photos 1 and 3 surface mount package shown just above the DC power jack in Photo 1 The regulator datasheet specifies a 20 V absolute max imum input which certainly accounts for that bullet item in the Arduino feature list as you just saw the input capacitor may also restrict the maximum voltage The regulator dropout voltage runs
76. award for Best Sound Design for the 2010 2011 season The main point though is how much easier it was to use a microcontroller and an integrated motor driver to design and program this circuit than it would have been with one or more 555s or 556s and a bunch of discrete parts All the hardware design required was simply hooking the 16F505 to the L293 Everything else could be done by tweaking firmware No matter how much we love the smell of solder in the morning burning a new version of some firmware is a whole lot easier il Author s note I thank the Las Cruces Community Theatre and Les Boyse for giving me the opportunity to work on this project Joseph J Pfeiffer Jr earned a BS in Computer Science and Physics in 1979 and a PhD in Computer Science in 1986 both from the University of Washington in Seattle He is an Emeri tus Professor having retired from the New Mexico State Uni versity Department of Computer Science in 2010 Some of his interests include all aspects of theatre embedded design and programming old cars dog obedience training model rock etry and shooting Joe is currently constructing a shop oven which will be capable of solder reflow for surface mount com ponents and more general heating such as the type required for powder coating small parts AF AS Gigabit Tecno gey ARM based System on a Chip e Gigabit Ethernet e Small Cheap Fast f Pi yeaa 7407 Both QFP and BGA Podee
77. being totally iso lated for extended periods The BioLite website touts 2 W 5 V i e 200 mA and while the heat ener gy can be as high as 5 kW thats less than 0 1 efficiency This brings to mind a project for the future a dynamic load that can be used to measure power pro ducing devices outputs My present cir cuit wastes more than half its precious power using a linear regulator for 3 3 and 5 V i e system power I need to change to switchers for better efficiency So many cool toys so little time i Jeff Bachiochi pronounced BAH key AH key has been writing for Circuit Cellar since 1988 His background includes product design and manufacturing You can reach him at jeff bachiochi imaginethatnow com or at www imaginethatnow com RESOURCES J Bachiochi Charging with PV Cells Circuit Cellar 265 2012 BioLite www biolitestove com CUI Inc Series CP85 Description 8 5 A Peltier Module 2012 www cui com Product Resource PDF CP85 pdf Omega Engineering Inc Reference Temperatures www omega com temperature Z pdf z021 032 pdf STMicroelectronics SPV1020 Interleaved DC DC Boost Converter with Built In MPPT Algorithm 2012 www st com internet com TECHNICAL_RESOURCES TECHNICAL_LITERATURE DATASHEET CD00275733 pdf Tellurex Corp Frequently Asked Questions About Our Power Generation Technology 2010 www tellurex com pdf seebeck faq pdf SOURCES CP85438 8 5 A Peltier mo
78. bility and know how to make smart decisions about components based on failure rate data ast month I discussed calculating product failure rate A This month I ll continue to see how those numbers affect your design Reliability should always be kept in mind from the moment you begin the preliminary design You should keep updating it concurrently with the design progress Your obvious concern is whether or not you can meet the customers required mean time between failures MTBF but there is a lot more to it than that To begin you should plot the failure rates of all individual components see Figure 1 Notice that the ordinate uses logarithmic scale and therefore each gridline represents one order Figure 1 This graph shows individual components failure rates Q R of magnitude or difference A B C and so forth plotted on the abscissa represent individual com ponents of the same type under the same stress For example RLR 0 25 W resistors with 50 der ating i e operating at no more than 50 of their maximum rating are represented by category A 0 1 uF 50 V capacitors exposed to no more than 12 VDC are represented by B and so forth ANALYZING FAILURE Depending on your design you may decide components with A below say 1 x 10 have no sig nificant impact on the overall failure rate and can be ignored This reduces the number of components to plot and analyze leaving you with only components E thro
79. blanket that keeps the heat away from the plastic parts As any camper knows collecting small dry tinder and kindling is the most important part of starting a wood fire If you dont spend enough time gathering the right essential elements the only thing you ll ever light is a match Ifits a damp or rainy day look for some Birch bark from a fallen tree as this can be lit even when it s wet Because the firebox is deep and narrow the hardest part about using this stove is getting the tin der started Don t try and light a bit of tinder in the bottom of the firebox instead fill it to the top with small dry Photo 5 Here you can see the Peltier device I ve pulled from inside the BioLite CampStove s orange plastic housing The device has a finned heatsink attached to the cold side that dissipates heat assisted by an electric fan On the device s hot side is a heat spreader plate with a 0 5 cop per rod used to transfer the heat from inside the firebox Note the sheet of insulation material to prevent any flames from escaping the firebox tinder If you pile the tinder to one side at the top you can use a match to light the tinder closest to top Once a few pieces have become inflamed you can press the BioLite CampStove s On button to start the fan providing a constant oxygen flow to the spreading flames The 3 diameter firebox limits the wood size you can stoke which means the fuel will need constant replenishment
80. chip com L293D Push pull four channel drivers with diodes STMicroelectronics www st com BUILD A 23RD CENTURY MEDICAL DEVICE WANT TO MANGE THE WORLD JOIN Us December 2012 Issue 269 N 78 Green Energy Challenge szen Winners Announcement The RL78 Green Energy Challenge set forth to revolutionize the way engineers approach new designs in a world where low power consumption high efficiency and renewable resources ANALOG are integral parts of daily life Participants from over 67 countries were invited to showcase their skills in developing green energy designs for applications such as energy harvesting 5 metering low power and control systems using Renesas s RL78 microcontrollers and a GainSpan robust software environment powered by Renesas and its alliance partners Thank you for everyone s participation and congratulations to the winners First Prize Electrostatic Cleaning Robot Solar tracking mirrors called heliostats are an integral part of Concentrating Solar Power CSP plants They must be kept clean to help maximize the production of steam which generates power Using an RL78 the innovative Electrostatic Cleaning Robot provides a reliable cleaning solution that s powered entirely by photovoltaic cells The robot traverses the surface of the mirror and uses a high voltage AC electric field to sweep away dust and debris CMX Y ron Poria
81. com B Oik Subscriptions Circuit Cellar P O Box 462256 Escondido CA 92046 E mail circuitcellar pcspublink com Phone 800 269 6301 Internet www circuitcellar com Address Changes Problems circuitcellar Q pcspublink com Postmaster Send address changes to Circuit Cellar P O Box 462256 Escondido CA 92046 Ken Davidson David Tweed Hugo Van haecke Shannon Barraclough KC Prescott Jeff Yanco Debbie Lavoie Kim Hopkins CIRCUIT CELLAR THE WORLD S SOURCE FOR EMBEDDED ELECTRONICS ENGINEERING INFORMATION ektor VOICE tf COIL India Sunil D Malekar 91 9833168815 ts elektor in Russia Nataliya Melnikova 8 10 7 965 395 33 36 nataliya m larionovaQyandex ru Turkey Zeynep K ksal 90 532 277 48 26 zkoksal beti com tr South Africa Johan Dijk 27 78 2330 694 316 109 31 926 J Dijk elektor com China Cees Baay 86 0 21 6445 2811 CeesBaay gmail com PHBE H US Advertising Strategic Media Marketing Inc 2 Main Street Gloucester MA 01930 USA Phone 978 281 7708 Fax 978 281 7706 E mail peter smmarketing us Internet www circuitcellar com Advertising rates and terms available on request New Products New Products Circuit Cellar 4 Park Street Vernon CT 06066 E mail newproducts circuitcellar com We now have 2013 International CES All Electronics Corp 4a4a44411 Sign up at www circuitcellar com members In
82. d Sensor D5 D3 X 1N4148 1N4148 D6 D4 4 4 R13 1N4148 1N4148 3 3V O Temperature PC6 RESET ADC5 SCL PC5 ADC4 SDA PC4 ADC3 PC3 ADC2 PC2 ADC1 PC1 ADCO PCO PD7 AIN1 PD6 AINO PD5 T1 PD4 XCK TO PD3 INT1 PD2 INTO PD1 TXD PDO RXD DS1820 SCK PB5 MISO PB4 MOSI OC2 PB3 SS OC1B PB2 OC1A PB1 ICP1 PBO PB7 XTAL2 OSC2 PB6 XTAL1 OSC1 GND 4x 20 1N4001 De VM1 Vin Vcc Vin GND Remote On Off 9 EM DAT2 1 TMR4811 EE D C MD C17 C18 47a 0 1 C9 j C10 GND Ciil C12 WB T LM2950 a T 10u O1p 100u O 1p Figure 2 The complete EBikeMeter schematic depicts the off board interfaces to the push button switches an SD card a speed sensor a battery a motor controller a throttle and a serial console bootloader interface pcan SD Card December 2012 Issue 269 Screens Driver Display Partition FAT SD Raw PWM nl G AE voc mo PCINT1 INTO UART T2 Pin Ext Ti OWI High OWI Bit EEPROM EEPROM Digital a L amp R Pwr 0 Figure 3 The EBikeMeter includes many firmware and hardware layers CIRCUIT CELLAR www circuitcellar com Broadest Family of High Performance 8 bit MCUs Bp z a mimE a a i ta oko EZ 21350 0 pt mi 5 a MICROCHIP PIC18F45K22 n The PIC18 K series is the broadest portfolio of high performance low power 8 bi
83. d as well as the column parity bits see Table 2 How ever I have not implemented this in the code that is available on Circuit Cellar s FTP site Figure 3 shows the basic state diagram Listing 1 shows the code for both state machines which contains the ISR for both the proximity card and the UART To verify this process by hand I use my oscilloscope to make a video record ing of the bitstream and play it back pausing frequently to hand draw the waveform Photo 4 shows a single screen capture The entire movie is available on Circuit Cellars FTP site I then manually decode the pattern and compute the bytes They match exactly the values shown on the card see Photo 2b Within the programs main loop a test is performed to determine if a card has been accurately read exactly like the test for a UARTs message If a clean read has occurred the card bytes are compared to the values stored in the EEPROM to verify access permis sion The command protocol enables me to update the card byte values in EEPROM so I can add or change cards at will December 2012 Issue 269 UJ December 2012 Issue 269 Listing 1 Continued from p 39 if goto IN if cardBits 10 4 cardBits 0 break if 1hb Is it one reader cardBytej 0x80 gt gt bits bits Next bit if bits 8 after 8 we skip parity bits 0 and start over at cardbyte
84. d a USB isolator The circuit described in Elektor s October 2012 edition offers an optimal electrical isolation of both the data lines as well as the supply lines between the PC and the USB device Populated and tested Board Art 120291 91 101 40 Embedded Linux Made Easy Today Linux can be found running on all sorts of devices even coffee machines Many electronics enthusiasts will be keen to use Linux as the basis of anew microcontroller project but the appa rent complexity of the operating system and the high price of development boards has been a hurdle Here Elektor solves both these problems with a beginners course accompanied by a compact and inexpensive populated and tested circuit board This board includes everything ne cessary for a modern embedded project a USB interface an SD card connection and various other expansion options It is also easy to hook the board up to an Ethernet network Populated and tested Elektor Linux Board Art 120026 91 93 30 N p SE a December 2012 Issue 269 1 00E 01 1 00E 00 1 00E 01 1 00E 02 1 00E 03 1 00E 04 JE CONSUMMATE ENGINEER m ceorse novace canada Product Reliability Part 2 The Meaning of Failure Rate Now that you know various calculations for determining a product s failure rate it s time to investigate how the numbers figure into your design A successful product designer must understand the concept of relia
85. d signal down to 0 Hz and enables the use of a low pass filter for better noise rejection The signal is now 10 times higher than the noise which enables the measurement of its amplitude www circuitcellar com CIRCUIT CELLAR December 2012 Issue 269 Ul December 2012 Issue 269 AC Power Transmitter source High loss medium Known phrase shift gt Phrase shift Receiver Synchronous detector Preamplifier Multiplier Low pass filter Measurement 1 Hz Figure 4 A manual phase shifter could be added in the reference path to compensate and measure the phase shift between the excitation and the receiver fl f2 and f1 f2 Here f1 f2 100 kHz so the two output frequencies are 0 Hz and 200 kHz the latter of which is later cancelled by the low pass filter Some formulas may make it more clear Assuming the received signal has an ampli tude B and a phase shift noted Dph then Excitation A x cos 2nft received B x cos 2nft Dph and multiplied A x cos 2pift xB x cos 2pift Dph Or remember 2 x cos a x cos b cos a b cos a b which provides AxB Multiplied cos Dph 2E cos 4mft Dph The low pass filter selects only the first term providing Detected Ma cos Dph If the delay due to the light transmission and the preamplifier is small compared to the excitation signal frequency then the phase shift will be zero wh
86. dule CUI Inc www cui com SPV1040 Battery charger STEVAL ISV009 demonstration board and SPV1020 Boost converter STMicroelectronics www st com Create complex electronic systems in minutes using Flowcode 5 FL FLOWLODES WCODES Design gt Simulate gt Download 5 www circuitcellar com Flowcode is one of the World s most advanced graphical programming languages for micro controllers PIC AVR ARM and dsPIC PIC24 The great advantage of Flowcode is that it allows those with little experience to create complex elec tronic systems in minutes Flowcode s graphical development interface allows users to construct a complete electronic system on screen develop a program based on standard flow charts simulate the system and then produce hex code for PIG AVR ARM and dsPIC PIC24 microcontrollers CIRCUIT CELLAR Convince yourself Demo version further information and ordering at www elektor com flowcode i ti Fat 1 December 2012 Issue 269 U UT December 2012 Issue 269 Ac 1 10 12 14 16 18 19 k i ND zk co Sz A ross According to Ed Nisley in his Circuit Cellar 265 2012 article this type of tester characterizes a transistor s behavior by computing the drain resistance at each combination of measured voltage and current Type of force on a charged particle caused by electromagnetic fields Tests your engineeri
87. dy for Delivery From 16MB to 128MB Available Call 530 297 6073 Sales jkmicro com www jkmicro com microsystems Inc International Orders Welcome i 100 Low Cost Controllers with ADC DAC UARTs 300 I Os solenoid relays CompactFlash LCD Ethernet USB motion control Custom board design Save time and money VISA MasterCard owak mom NO alee December 2012 Issue 269 gt 7 December 2012 Issue 269 Electronic and Electro mechanical Devices Parts and Supplies Wall Transformers Alarms Fuses Relays Opto Electronics Knobs Video Accessories Sirens Solder Accessories Motors Heat Sinks Terminal Strips L E D S Displays Fans Solar Cells Buzzers Batteries Magnets Cameras Panel Meters Switches Speakers Peltier Devices and much more www allelectronics com Free 96 page catalog 1 800 826 5432 PIC SERVO MOTION CONTROL MOTION CONTROLLERS F BRUSH BRUSHLESS AND STEPPER MOTORS e controller chips e controller boards www picser JEFFREY KERR LLC Propeller Debugger ViewPort brings powerful tools to the Parallax Propeller Step line by line breakpoint Performance profiler 80 MSps analysis of IO pins 7 Realtime graphs Change values with custom interfaces _ Rewind time and zoom in out Win OSX Linux C BASIC SPIN IDE hannoware comviewpor PDQ
88. e amp iPod Touch Available on the i App Store CIRCUIT CELLAR www circuitcellar com www circuitcellar com LISTEN TO YOUR MACHINES Ethernet PLCs for OEMs FMD88 10 and FMDl l6 I0 Integrated Features ETHERNET Modbus TCP IP 16 or 32 digital I Os 10 analog I Os RS232 and RS485 LCD Display Port I O Expansion Port Ladder BASIC Programming 229 and 295 before OEM Qty Discount tel 1 877 TRI PLCS web www tri plc com cci htm 5 TRIANGLE TR RESEARCH INTERNATIONAL Across 2 FLOWCODE Columnist Jeff Bachiochi taught readers how to use this graphical programming language in his recent article about flowcharting Circuit Cellar 266 2012 7 LAPLACE This type of transform is similar to Fourier but expresses functions into moments as opposed of vibration 11 RACEWAY Channel to hold wires cables and so forth 12 SENSORS Circuit Cellars 250 issue 2011 focused on Measurement and this other topic 13 LANDS A metallic contact area 14 BITTI Interviewee Circuit Cellar 253 2011 who designed the Witness Camera a self recording surveillance camera 17 DARLINGTON This type of pair can be pro duced using individual transistors or purchased as a single device as in a 2N6301 18 WAFER A slice of semiconductor material upon which monolithic ICs are produced 19 DIELECTRICCORE The insulating material that makes up the center of the cable th
89. e data for analysis Andr Barbosa Brazil diybrasil gmail com Portable Power Quality Meter www circuitcellar com RenesasRL 8Challenge RE7R December 2012 Issue 269 qe S SA cu z by Scott Weber USA Controlling Access with a Proximity Card Open the Door to Manchester Encoding A radio frequency proximity card and reader can be used to control access to many things This article explains how the data is Manchester encoded on the card how to find the bitstream s beginning and how you can use the data and clock lines to bit bang the waveforms into a microcontroller reviously I wrote about the RS 485 network I wired through my home I interconnected exterior light controllers and a device that broadcasts time which it extracts from a GPS receiv er MCU Based Light Control Longer Serial Communication on Differential Wires Circuit Cellar 265 2012 I thought if I can design a unit that controls and monitors my exterior lights why not design units that can do the same thing with my garage doors And if I can do that I can probably put in some nifty access as well So I went looking for something nifty I used a 125 kHz radio fre quency RF proximity card and reader The reader triggers the door to open or close by closing a relay for a second I used a MikroElektronika RFid reader board and a credit card sized access card The card reader outputs a clock signal and a Manchester
90. e of one winding alone U two at a time and keep count If you hook them up out of phase the inductance will cancel out and you ll while x be left with the resistance of the wire and a lot of parasitic interwinding remove the lowest set bit from x this Capacitance DOE the start of a string of ones Answer 2 With the two windings connected in phase and in parallel the AR amp X inductance will be exactly the same as the single winding case But the result i ing inductor will be able to handle twice the current as long as the core itself remove the next set bit from x this doesn t saturate A the end of that string of ones X amp X 8 X Answer 3 Here s a solution that iterates over the number of strings rather than the number of bits in the word return result ine strings umsigned Tong int x int result 0 Answer 4 The term process in this case refers to the manufacturing process at the plant where the FPGA is made It s a measure of the statistical convert x into a word that has a 1 for every variability of the physical characteristics from chip to chip as they come off the transition from 0 to 1 or 1 to 0 in the original line This includes everything from mask alignment to etching times to doping i r levels These things affect electrical parameters e g sheet and contact resist 00 15 ance actual transistor gains and thresholds and parasitic capacitances These kinds of variations are
91. eally be experts in all of them So when my first book was in process the senior editor called me and said an assistant editor took the manuscript to read through it and then came back very excited and said I understood this NAN Are you currently working on or planning any microprocessor based projects STUART Many years ago I used to hand wire computers My first comput ers were Z80 based systems running CP M 80 and wired on perfboard In fact my first magazine articles were written on those systems I later built my first IBM PC clone the same way I ve toyed with the idea of building a Z80 computer using modern parts to see if the entire thing can be shrunk to a single 6 x 8 perfboard But right now it s just an idea and I don t even know if I ll do it I m not sure I want to prove this con cept badly enough to write and debug another CP M BIOS Other than that I don t have any specific projects planned I tend to write about whatever has intrigued me enough to actually build it I definitely have less time for this than I used to I do tend to lean more toward simpler projects now rather than the very complex projects I used to build But most of that is just due to time limitations NAN Last question Let s say you had a full year and a nice budget to work on any embedded design proj ect you wanted Call it your dream project What would it be STUART I ve done a lot of t
92. ed The response message buffer is simply built by swapping the source and destination addresses and placing a sen tinel value in the fourth position After the incoming message is acted upon if a response is needed the fourth byte is examined to see if it contains an outgo ing message rather than the sentinel value If so the RS 485 driver is switched to Transmit mode and the mes Sage is fed to the UART The UART is then monitored for a busy status and when the last byte is sent the RS 485 driver is switched back to receive PROXIMITY CARD READER The RFid proximity card reader board is based on an EM Microelectronic EM4095 RFID reader chip with a built in antenna and the interface broken out in a nice header In addition to a proximity card all I needed to get data pouring out of it was five pins V Gnd Enable Data and Clock The data signal is typi cally low and goes high when a card is brought close to the antenna This is used to trigger an interrupt However once the data line is active I switch the goes into a loop waiting for an indi none Commands the device to open the door if it is not already open cation that a card read has occurred none Commands the device to close the door if it is not already closed or a message was received from the RS 485 network The interrupt service routine W 0 5 byte card ID Adds a new proximity card number to the EEPROM Table 1 Th
93. ed reasonable to further reduce the parts count using an L293 dual H bridge in place of the output transistor The transistor would have required an input resistor and a snub ber diode to protect it from its highly inductive load while the L293 could be driven directly from the microcontroller and has internal snubber diodes Using a single output transistor also only produces a 12 V signal to drive the transformer while the L293 can reverse the output s polarity and provide 24 V This ends up providing a stronger signal to the bell I needed a single user input and three outputs to control the L293 one for the chip enable and one for each of the two H bridge halves to analyze the necessary control signals A fourth pin was also used for a blinkenlight for debugging and status reporting Using a PIC and enabling in circuit pro gramming also required pins for power and ground and three pins for programming with a Microchip PICkit 2 programmer A 14 pin PIC could accomplish all this with pins to spare so I used a PIC16F505 see Figure 1 The bell is scavenged from an old telephone see Photo 1 The power supply runs from a 12 V source Since several of the other effects e g the alarm bells and car horn required a 12 V supply it seemed reasonable to use a 12 V standard for all the electrically actuated effects The PIC16F505 micro controller generates all the timing signals Half an L293 is used to drive a 12 6 V filament tra
94. either hardware or software compensation The Seebeck voltage or uV C isn t linear with temperature and look up tables are often used to ensure accuracy Now let s switch gears a bit My PC does not use any extraordinary means to get rid of CPU generated heat unless you consider a heatsink mounted fan extraordinary Initially no cooling devices were used on the CPU although the power supply had a built in fan Circuitry requires more power while a signal is transitioning through its linear region The more tran sitions the more heat is generated While this can be reduced by running the core at lower voltages it s just about reached its limit and must therefore deal with the extra heat It s standard operating procedure to use CPU fans to help keep the CPU from overheating Some manufacturers go to extremes to cool CPUs You may have seen liquid cooled CPUs or even thermoelectric cooling The liquid cooling method uses a liquid to absorb heat and carry it away from the processor where it can be more eas ily radiated Thermoelectric cooling uses electricity to produce a heat absorbing surface In 1834 Jean Peltier discovered the inverse of the Seebeck effect now known as the Peltier effect Applying a voltage to a thermocouple creates a temperature differen tial between two dissimilar metals This results in an effective but extremely inefficient heat pump PELTIER A Peltier device is actually a solid state cooler
95. eonardo the Zumo Chassis becomes a low profile Arduino controlled tracked robot that is less than 10 cm on each side i e small enough to qualify for Mini Sumo competitions The Zumo Shield works with a variety of micro metal gear motors enabling a customizable combina tion of torque and speed An optional stain less steel Zumo Blade can be used for applications involving pushing other objects Arduino libraries and sample sketches are available to help quickly get a Zumo robot up and running A Zumo Robot Kit for Arduino which includes a Zumo Shield a Zumo Chassis Kit and a Zumo Blade costs 42 95 With typical motor selection the combination costs 74 95 Sold separately to those with a Zumo Chassis the shield costs 24 95 Pololu Corp www pololu com RFID PCB IDENTIFICATION SYSTEM The MAGIC PCB is an RFID PCB identification system that can be used to embed RFID chips into a PCB The chips are embedded during the initial production steps to enable identification and traceability The RFID chips function within the UHF frequency bands 860 to 960 MHz and can be globally operated The MAGIC PCB consumes less space on the PCB than barcodes or dot matrix codes RFID chips can be embedded in PCBs or surface mounted Because it doesn t require an antenna the system doesn t take up space on the PCB s front or rear The MAGIC PCB performs fast data acquisition i e a very short read time and is capable of simultaneously re
96. es If you ve been counting that adds up to 64 bits Table 2 provides a breakdown of all 64 bits read from the card Data is out put serially from the reader in 4 bit groups followed by a parity bit Because the pattern includes an even parity bit after 4 regular bits it is impossible to get five 1 bits in a row unless it is the preamble This means once you can detect the nine 1s you are certain to have found the preamble Sounds easy doesn t it Not so fast MANCHESTER UNTIED Robert Lacoste provides a good expla nation of Manchester encoding in his article Line Coding Tech niques Circuit Cellar 255 2011 but I will provide a brief description here Manchester encoding uses an NRZ that relies on a transition in the middle of each bit Figure 4a shows a sim ple bitstream with a datastream Figure 4b shows its a not to scale clock There are two com mon encoding schemes The first is referred to as G E Thomas encoding in which a low to high transition is encoded as a 0 and a high to low transition is encod ed as a 1 The other encoding is IEEE 802 3 which is exactly the opposite It took some investi gation but I was able to deter mine that the proximity cards used G E Thomas encoding Take a look at Figure 5 If I asked whether this was a string of 1s or Os which would be the cor rect answer The only way of of that Remember because of the parity bit there wi
97. ese are some additional communication messages understood by the garage controller CIRCUIT CELLAR www circuitcellar com HOLTEK iULULU holtek com 1 5V Battery MCU Highly Integrated Flash MCU Solutions Low operating voltage 0 9V 1 8V 16 bit multiple function Timer Module Integrated comparator 0 Integrated accurate high and low speed oscillators Integrated power IC and microcontroller High noise ESD immunity ma One Battery One Chip Holtek s new generation 1 5V Flash microcontrollers the HT66F01xL and HT68F01xL series contain fully integrated power IC features allowing the implementation of single cell battery applications in a single chip This allows for simplified external circuits permitting minimum circuit board areas as well as a reduced component count and reduced battery requirements to meet present demands for green products This series includes the A D type HT66F01xL and I O type HT68F01xL device series offering a variety of flexible functional selections all with small packages and diversified functions These devices can be applied for use in a wide range of low voltage consumer products such as electric toothbrushes electric shavers remote controllers massagers and other consumer products which operate with a single cell power source 32kHz CTM 16 bit x 1 HT66FOI6L 8MHz 09V 18V EE 1IKx16 64x8 64x8 13 12bitx4 CIM IB EX 1 16DIP NSOP SSOP HT66FO17L 8MHz I ao
98. every 5 min or so Once sufficient heat is Fascinated by technology s impact on the future Check out Tech the Future Computing power and global interconnectivity are pushing tech innovation into overdrive Pioneering technologies and creative workarounds affect even the couch potato 24 7 Tech the Future reports on technology strides that shape the future yours included www techthefuture com Follow Tech the Future Gf OR N R nana Cra zazna Sad On s 9 aight ba mals ky a D anaki hasa poaki iraina s et waginy p L is wan oi 1 E ze A e e Qa fhis gt Oech Temas on Testes PONI Hoyw si hacked Packe tt tha i Let SOPA bami si CIRCUIT CELLAR www circuitcellar com being transferred via the copper rod exposed to the flames generated current charges the internal battery While fully charged the BioLite CampStove can recharge any external device via a power only USB connector mounted on the front A green LED signals its readi ness to recharge your device AIN T NO SUNSHINE While the BioLite CampStove can be used to cook meals using wood fuel and keep devices charged it is heavier and less efficient than a small solar panel On the other hand the BioLite CampStove can be used on days when there is no sun and it replaces the liquid fuel stoves so many backpackers are used to so it might catch on with those needing to remain connected while
99. g a Phone Bell Integrating modern technology and old school equipment can lead to exciting results This article details the development of microcontroller based circuitry and firmware that s used to ring a retro telephone bell during a theatrical production have been interested in live theatre for many years I act I direct I work backstage I serve on the Board of Directors of the Las Cruces Community Theatre LCCT as vice president for membership and I wrote the computer program LCCT uses to play sound cues during per formances Like most live theatres LCCT s sound effects are ordinarily produced by playing recorded sound Samples Most theatres use a CD play er and some use commercial computer programs LCCT uses a program I wrote that runs on a computer in the theatre s light and sound booth When an LCCT patron hears the sounds of a thunderclap a doorbell a telephone or someone falling down a staircase what they re really hearing is a record ing played by a computer running my software In fall 2010 the theatre took on a new challenge recreating a 1940s radio show live on stage The play was Vin tage Hitchcock written by Joe Landry and directed by Les Boyse For this pro duction most of the sound effects needed to be produced on stage using technology that at least looked like it was from the 1940s Les asked me to design the sound effects for the produc tion build the hardware for the effects and act
100. gs SD card interfacing and FAT file systems are no longer mysterious Unfortunately the biggest hurdle with this project was the lack of the AVR s available code space It is completely full This prevented me from making the code as robust as I would have liked as many error conditions are not handled as well as they could be I started with the ATmega168 16 KB flash memory and quickly moved to the ATmega328P 32 KB flash memory once I realized how much code a FAT file system uses I could have easily used a non existent larger drop in replacement AVR part e g ATmega648 with 64 KB flash memory For those interested the source code available on Circuit Cellars FTP site contains additional development and debugging commands from the serial interface These can be used by turning some of the commands on and turning some of the other functionality off to fit into flash memory SD card support and temperature support are two ideal candidates from the defines h header file Additional information about this project is available on my EBikeMeter website i Dan Karmann dlkengQmsn com is a semi retired embed ded systems developer He spent 27 years at AT amp T Bell Labs American Bell AT amp T Information Systems Lucent Technologies Bell Labs Avaya Labs Prior to that Dan worked as a CB radio repair technician while earning a BSEET magna cum laude from the University of Nebraska Omaha Dan spent six years as an Electronic Warfare tech
101. hat deal with computer networking human to human interaction human to computer interaction and electronic information sharing e g speech recognition data transmission Ethernet USB I C and SPI Data Acquisition Projects technologies and algorithms for real world data gathering and monitoring e g peripheral interfaces sensors sensor net works signal conditioning ADCs DACs data analysis and post processing Embedded Applications Projects that feature embedded controllers and MCU based system design e g automotive applications test equipment simulators consumer electronics real time control and low power techniques Embedded Development Tools and techniques used to develop new hard ware or software e g prototyping and simulation emulators development tools programming languages HDL RTOSes debugging tools and useful tips Embedded Programming The software used in embedded applications e g programming languages RTOSes file systems protocols embedded Linux and algorithms Internet amp Connectivity Applications that deal with connectivity and Internet enabled systems e g networking chips protocol stacks device servers and physical layer interfaces Measurement 8 Sensors Projects and technologies that deal with sensors interfaces and actuators e g one wire sensors MEMS sensors and sensor interface techniques Programmable Logic Projects that utilize FPGAs PLDs and other progr
102. he things I want to do and I m budgeting my time differently now than I used to But if I was going to spend my days working on something like this if I was going to quit my job and spend eight hours a day on it then I might work on things that let the next gener ation of engineers experiment with electronics so they can get into the field in a practical way For example when I wrote Analog Interfacing to Embedded Microproces sor Systems I created a demonstrator for control systems that used a tiny light bulb coupled to a phototransistor It enabled me to demonstrate various control techniques without a lot of complicated hardware and in a way that was easy to understand and explain The light bulb introduces delay because the filament has to heat up before producing light it demonstrates all kinds of properties of real loads in real control systems It was controlled from a PC using an off the shelf USB module the plots were done in Excel and the software was done in Python It was really cheap and easy to set up Developing that sort of thing interests me provided that I see a path where it can actually be used Doing things just to do them doesn t interest me as much as it used to al December 2012 Issue 269 R w December 2012 Issue 269 R R FA BOVE THE GROUND PLANE Power Supply by Ed Nisley USA Arduino Survival Guide Arduino boards appear in many projects that call f
103. his N type material Note Copper a good conductor has one valence electron and could be considered an N type material Likewise when silicon is doped with a material that has three valence electrons i e indium there is an elec tron missing in the stable crystalline structure and electrons are constantly being borrowed by neighboring atoms to fill in the hole In this case the hole becomes the charge carrier mov ing in opposition to the current in this P type material Similar to the way a magnetic field can force electrons i e charge carriers to flow in a copper wire heat conduction will affect the flow of electrons This process in a copper wire i e N type material moves electrons i e charge carriers from the hotter end toward the cooler end Note In a P type material holes i e charge carriers move from the hotter end toward the cooler end You can t measure this in a material unless you com plete the circuit path When you can measure it the currents through the two similar materials cancel You need to use two dissimilar materials so the heat flow to current capabilities are different In fact N and P type material is optimal As I previ ously mentioned while heat flow and charge carriers move in the same direction current flow moves toward electrons but away from holes A voltage will be produced across an N and a P type material when the junction of the two materials is heated Multiple pairs in
104. his is absolutely critical Processes are the way to go in that case End of discussion I have experienced few problems in systems caused by errant pointers that need the kind of memory protection processes provide The data sharing threads permit when rightly designed is more efficient in the kind of systems we design What do you do when a thread crashes Unlike a server or even a desktop use of Linux our embedded systems usually cannot tolerate any task failing On a desktop if your browser locks up you just restart the browser What you don t want is for the browser failure to bring down the whole system In an embedded system if one task were to crash should the rest of the system keep working Would you want to design the sys tem to restart just the failed process or thread My opinion which we have implemented wherever possible is to force a restart of the entire system in the case of a single thread fail ure Recently some code we wrote got passed off to a customer who modified it in an attempt to restart a failed thread This was done in the watchdog logic We immediately jumped all over the unsuspecting code maintainer nicely of course about the risks of doing this In our case all processes were talking over queues that did not recover well from a restarted process But more importantly when something unexpected happens that causes a process or thread to crash why risk restarting the processes when the system is in an u
105. hours the amp hours the average trip speed the maximum trip speed and the j O odometer readings to a removable on board SD memory card The EBikeMe ter s system also controls the LCD moni tors user push buttons for the user inter face and provides a control output for speed current voltage controlled throttle override Additionally a serial interface is provided for system configuration and firmware upgrades Figure 1 shows a block diagram of the EBikeMeter An Atmel ATmega328P microcontroller is at the heart of the sys tem To measure speed and distance traveled it receives pulse inputs from Photo 1 The EBikeMeter is mounted on an electric assisted recumbent bicycle s handlebar the speed sensor which is mounted on the bicycle s front fork The ADC inputs to the ATmega328P are used to monitor the battery voltage and motor current The system s user interface is via a back lit 4 x 20 LCD with temperature com pensated contrast and two push buttons A standard SD memory card socket is connected to the ATmega328P s serial peripheral interface SPI bus The throt tle override signal is an ATmega328P PWM output The system is powered from the 48 V battery associated with the electric motor and motor controller I used a 5 V only LCD and a 3 V only SD card Therefore I used a 48 to 5 V con verter along with a 3 3 V regulator to provide the required voltages I used a reset supervisor to receive early
106. ich will provide AxB Detected The detected signal is then simply proportional to the excita tion voltage A and the received signal voltage B The beauty of this method is that the band pass filter was replaced by a low pass filter and designing a low pass filter with a cut off frequency as low as desired doesn t cause any problem Why not use a 1 Hz low pass filter This wont be a problem as AC Power Transmitter source High loss medium Known phrase shift Amplitude V I Q long as the wheel rotation is slower than a turn accom plished in a couple of seconds As in the previous example the noise will be reduced by the square root of the noise bandwidth 1 MHz divided by filter width here 1 Hz which provides 1 000 The noise will be reduced down to 1 mV i e 1 V 1 000 Then the signal which is still 10 mV can be easily detected and measured as the remaining noise is 10 times lower If the noise is still too large you could reduce the low pass filters bandwidth down to 0 1 Hz or even lower The noise will be reduced accordingly at the expense of a longer measure ment time which may not be a problem if you are looking at Slow phenomena Mathematically this detector works because we know the signal to be detected is a sine wave at a precise frequency and phase All other signals and noise are nullified when multiplied by a sine signal and low pass filtered i e integrated over enough time A caution
107. ided by I Efficient isn t it What else can be improved As dis cussed one last difficulty with synchro nous detectors either simple or IQ is that they require access to the excitation Signal This is not a problem in my exam ple but may be more problematic if the transmitter is on the moon and the receiver is on earth the wire will be long Can you still use a synchronous detector The answer is yes but in that case you will need to locally regenerate a signal with the exact the same frequency and phase as the excitation signal This is how a phase locked loop PLL works see Figure 6 In fact this last diagram is more or less the full block diagram of nearly all commercial lock in amplifiers However the PLL approach s disadvan tage is that the signal strength must be high enough for the PLL to lock which reduces the overall performance com pared to an external excitation signal PEJPE ZNEM NAN VAN AN AN a atin AN AN MODULATED SIGNAL A ROR UNATTENUATED ROPY CMY CREE TATY RW ORD ETI hl ks ha Bi tt gu ke and ATTENUATED SIGNAL PLUS NOISE B alte VAVAVAVAVA i inde Low pass Filter Figure 7 This is an example of an analog lock in amplifier extracted from Analog Devices s AD630 synchronous demodulator datasheet The chip which is used as an analog multiplier enables a signal recovery even after 100 dB of attenuation Ul R CIRCUIT CELLAR www circuitcellar com PRO
108. ineers From Around Th DODODOPODODODODEE i Z ze BERR RRR REE EEEN OCORRE EEEE TO amazon com amazon co uk MaxSonar Ultrasonic Ranging is EZ LV ProxSonar EZ People sensing made easy Proximity Sensor MSRP 29 95 HRXL MaxSonar WR 1P67 1 mm resolution Industrial packaging Weather resistant MSRP 109 95 I2CXL MaxSonar EZ Great for UAVs High noise immunity 2C interface Starting at 39 95 I2CXL MaxSonar WRC m 2C interface a Compact packaging i Weather resistant MSRP 109 95 www maxbotix com Real Time Data Access Without Halting MCU 4 AS se w IDE Comp ilers nEk version 4 129 or better www ccsinfo com ccide Togga e Eliminate a diagnostic serial port and save money b oa data through the ICSP inte Set serial s and calibration values in production e Review log data in the field PS salesaccsinfo com Sas Wd ui 262 522 6500 ext 35 PIC MCU dsPIC and MPLAB are registered tradmarks of Microchip Technology Inc R L olwicio plE lol lv U I E y T N LIA PILIAJCIE 1 O E D c tc T N L M K o lal lo HL r IT P E u in rR Rlalcielwialy E Y I G N IL G S N S O R S R D E T
109. iple NFC chips inside that allow the book to connect to the internet simply by touching an NFC hotspot in the book with your NFC enabled smartphone or tablet 128 pages ISBN 978 9 07545 861 9 57 50 Prices and item descriptions subject to change E amp O E p 2 2 m onl Mastering Surface Mount Technology LabWorX 2 Straight from the Lab to your Brain Mastering Surface Mount Technology This book takes you on a crash course in techni ques tips and knowhow to successfully introduce Surface Mount Technology in your workflow Be sides explaining methodology and equipment at tention is given to parts technology and soldering technique Several projects introduce you step by step to handling surface mounted parts and the required technique to successfully build SMT as semblies Many practical tips and tricks are dis closed that bring surface mounted technology into everyone s reach without breaking the bank 282 pages ISBN 978 1 907920 12 7 47 60 Elementary Goorse BASCOM AVR gt G A Free Software CD ROM included Elementary Course BASCOM AVR The Atmel AVR family of microcontrollers are extremely versatile and widely used Elektor magazine already produced a wealth of special applications and circuit boards based on ATmega and ATtiny controllers The majority of these projects perform a particular function In this book however the programming of these controllers is the forem
110. irectly below the red alarm bell blinkenlight somewhere The ability to turn on a light to tell you the firmware has reached some point in the code is unbelievably help ful The PIC instruction set also makes it easy to use a single instruction to turn the LED on or off so insert ing the debugging code has minimal impact on the firmware In this case when the circuit was first assembled I turned the LED on immediately after startup so I knew whether or not the microcontroller was running Later when the bell wasn t ringing as planned I turned the LED on at the same time as the L293 chip enable The problem turned out to be a poor solder joint to one of the bell wires Once the debugging was complete it was programmed to flash five times per second whenever the input pin was grounded This was useful to isolate and quickly resolve problems with the power supply and signal inputs while the effects were being installed on stage The power LED indi cated the circuit was live while the software controlled LED indicated the input was active While an oscilloscope or a volt meter could have been used for this purpose the flashing light was a valuable self diagnostic aid The cadence was adjusted by modifying program constants and reprogramming the microcontroller If this had been designed as a commercial product some other way of config uring the cadence would have been needed There are a number of ways to accomplish this bu
111. is driven by a simple 2N2222 transistor with a base resistor intended to keep the microcontrollers drive current less than 1 mA The relay coil has a Zener diode across it to keep spikes out of the power supply rails Finally J5 is used to accommodate the in circuit programmer used to program the controller s flash memory I mounted two of the circuit boards in an industrial enclo sure and placed it on the wall between my two garage doors Photo 3 shows the final unit The RS 485 bus terminates on the barrier strip at the rear and includes the termination resis tor at this end The magnetic and relay contacts plug directly into the header on the boards which enables the units to determine the door s state and trigger the garage door to open or close December 2012 Issue 269 W 5 December 2012 Issue 269 Message processed Not our address SCH Arrived Any UART error Buffer filled up Read address Our address ETX Arrived Message arrived flag Figure 2 The ISRS state machine reads incoming messages from the RS 485 network CODE I used the demo version of Microchip s MPLAB C18 C compiler The compiler integrates perfectly with Microchip s MPLAB integrated development environ ment IDE and is well equipped with libraries that enable use of the devices EEPROM UART interrupts timers and other features I didn t need The project uses only two source code files One han dles the mainli
112. ised to 150 C the TDR will measure 3 128 Q Now the drop across the TDR will N be 2 012 V which converts to a 625 count A change in 150 causes a change of 132 counts By reducing this by a factor of 2 I can remain within the 16 bit arithmetic result ing in this formula count 493 x 75 132 x 75 Temperature 66 66 150 I plan to use the old CPU heatsink fan assembly to cool the Peltier device s cold side The fan blows ambient air into the top of the heatsink fins drawing heat from the sink as it passes through the fins and out its sides This one is rated at about 1 2 C W approximately given some standard air flow rate in linear feet per minute LFM This means for every watt it throws off its temperature will rise 1 2 C above the ambient temperature Without forced air flow the thermal performance will be more than 10 times less efficient So it is important to run the fan anytime the tem perature exceeds some normal ambient temperature I ll use 33 C i e 90 F Any time either of the temperature sensors registers above 33 C I ll turn on the fan It will remain on until both sensors fall below 33 C As a precau tion I m adding a piezoelectric transducer that can beep if either temperature sensor exceeds 80 C i e 176 F That s the hot sides maximum rated temperature with the solder melting point approximately 138 C IT S ON FIRE
113. ithout coming close to it or using a physical rotation sensor One solution is using a light beam which will be alternatively cut by the wheel depending on its position Figure 1 shows an example of your first attempt which is simple You hook up a light transmitter to a continuous 10 V source at one side and a light detector at the other side You design a preamplifier to multiply the detected voltage by a factor of 100 and you display it on a voltmeter Unfortunately you soon discov er that it doesn t work as expected The output voltage stays around 1 V whatever the wheel s Receiver Preamplifier Measurement Signal 0 1 mV Signal 10 mV Noise 10 mV Noise 1 V Figure 1 You can use a constant light beam to detect a wheel s rotation Unfortunately in this example the ambient light causes a noise 100 times higher than the useful signal CIRCUIT CELLAR www circuitcellar com Transmitter AC Power source GH 2 High loss medium 1 Attenuation 100 000 added noise 10 mV noise DC to 1 MHz Receiver Preamplifier Band pass filter Measurement 100 kHz Q 100 1 kHz cP mO Signal 0 1 mV Noise 10 mV Signal 10 mV Noise 1 V Signal 10 mV Noise 32 mV Figure 2 Using a modulated light source drastically improves the signal over noise ratio thanks to a band pass filter on the receiver side However here the noise is still far too high due to the filter s limited quality factor position Of course y
114. le speed the user can still pedal faster to increase the speed without electric motor assistance If there is a motor cur rent control override the motor current draw should be limited to extend the batterys operating range forcing the user to run slower or pedal harder If there is a battery voltage override the electric motor assist operation should be limited if the battery voltage is too low This condition can cause battery failure The processors UART is con nected to an external serial inter face to facilitate upgrading firmware and configuring the EBikeMeter configuration settings To initiate the processor s on board bootloader for firmware upgrades the serial DTR signal is used to reset the processor The EBikeMeter s serial interface s elec trical interface is 3 3 V TTL level signals To connect to a PC COM port an external TTL to RS 232 converter is required e g a MAX3232 style converter device If its needed the 3 3 V power line is also supplied on the serial connector to power the external TTL to RS 232 converter The required RS 232 signals needed are TxD RxD Gnd and DTR DTR is only needed for firmware upgrades via a MCS Electronics BootLoader which I used because I first started programming AVRs using the BASCOM AVR BASIC environment which included the MCS BootLoader capability I use the same firmware bootloader even in the WinAVR C develop ment environment using a stand alone host boot
115. ll never be more than four 1 bits in a row However there can be more than four 0 bits In fact a proximity card with noth ing on it can have 55 0 bits in a row Although I can be certain there is a tran sition in the middle of every bit there may not be a transition from one bit to another I know when the bit changes from a 1 to 0 or the other way around there is no transition at the bit boundary because the next bit has to transition in the other direction If this isn t clear go back and take another look at Figure 4 In the middle of the image the bit changes from a 0 to a 1 Results in the level do not change at the boundary So if I can locate where there is no transi tion I have found the bit boundary ile Edit View Window Help 000050 Io BSGGE Photo 4 I recorded a segment of the waveform coming from the card reader The entire video is available at Circuit Cellar s FTP site CIRCUIT CELLAR www circuitcellar com Listing 1 This is the entire ISR that handles bytes from the UART and interrupts from the card reader The top portion initially responds to a change in the data line by switching to interrupting on the clock line The codes lower portion collects UART bytes into an incoming message Both segments set a flag so the main loop knows something arrived Note Listing continued on p 40 DATA LINE ON INT 0 CLOCK LINE ON INT 1 pragma interrupt ProcessInterrupt void ProcessInterr
116. lloon is the carrier section A glider the payload of the balloon is the return section A ground base section is used for communica tion and display telemetry data not part of the contest project Using the REFLEX flight simula tor for testing the glider has its own micro GPS receiver sensors and low power MCU unit It can take off climb to pre pro grammed altitude and return to a given coordinate Jens Altenburg Germany iens altenburg t online de Honorable Mention Wireless Remote Solar Powered Meteo Sensor You can easily measure me teorological parameters with the Meteo Sensor The RL78 MCU based design takes cyclical measurements of temperature humidity atmospheric pressure and supply voltage and shares them using digital radio trans ceivers Receivers are configured for listening of incoming data on the same radio channel It simplifies the way weather data is gathered and eases construc tion of local measurement networks while being optimized for low energy usage and long battery life Grzegorz Kaczmarek Poland ky3orr gmail com Wireless Remote Solar Powered Meteo Sensor Honorable Mention Portable Power Quality Meter Monitoring electrical usage is becoming increasingly popular in modern homes The Portable Power Quality Meter uses an RL78 MCU to read power factor total harmonic distortion line frequency voltage and electrical consumption information and stores th
117. lly necessary in our culture to designate achievement Too little business was not an issue The too much business event happened right after the introduction of the IBM PC Circuit Cellar was the third company in the country to market an IBM PC clone I thought it was a good idea Everybody who couldn t get a real IBM PC started banging on our door for an MPX 16 We got 1 million in orders in just a few weeks What was I supposed to do Certainly not what 99 of you would have done I stopped taking orders Remember I didn t want to work for anybody and I dont like doing reports Delivering thousands of PCs might have made us into another Apple but it also meant using lots of outside money no more BYTE magazine and no more fun monthly projects It really meant venture capitalists and lawyers ugh Was it the right decision You decide Circuit Cellar is still here and every early PC clone maker from back then is gone In 1988 we started Circuit Cellar magazine While our money came from manufacturing projects and kits we knew the real product was Circuit Cellar itself It was time to launch the magazine as a unique product Back in 1988 it typically cost about 2 million for a big publisher to start a magazine like Circuit Cellar We pulled that off without any other sources Finally there comes the toughest decision for any entrepreneur when to hang it up I have to admit I wasn t quite sure about this one Its not because I pla
118. loader application Although the motor controller cannot increase the bicycle speed the user can still pedal faster to increase the speed without electric motor assistance If there is a motor current control override the motor current draw should be limited to extend the battery s operating range forcing the user to run slower or pedal harder Additional schematic detail information can be found in section 7 2 of the EBikeMeter Reference Manual which is available on Circuit Cellars FTP site THE FIRMWARE The EBikeMeter firmware development was done in C using the Atmel AVR Studio 4 development environment with the WinAVR C compiler The EBikeMeter firmware periodically monitors an elec tric bicycles battery voltage motor cur rent ambient temperature and bicycle speed Various measured and calculated statistics from this monitored data are displayed on a 4 x 20 backlit LCD and some of the monitored data items are maintained in EEPROM The LCD is organized as five screens selectable with two momentary push buttons For night time operation a push button can be used to enable the displays LED back light When the bicycle is moving vari ous measured and calculated statistics are continuously logged on an SD card using a PC compatible file system Addi tionally based on user configured set tings the EBikeMeter firmware can limit the electric motor controllers throttle input to limit bicycle speed motor c
119. lso included a schematic of the Panasonic SD card connections and cables used for the serial interface adapter EBIKEMETER ASSEMBLY The EBikeMeter circuitry was assembled on a modified Pro tostack PB MC AVR28 28 pin AVR full size development board which was sandwiched with the LCD board This was placed in a small project box with the push buttons mounted on the left and right sides The box had a custom cutout and window on its front for the LCD and featured a machined alu minum rear plate where the SD card socket and I O connec tions for power speedometer serial port and mounting brackets for the bicycle handlebar cross member were made I used the FreePCB open source PCB editor to help optimize the component layout for the point to point wiring This tool was also used to design a couple of proposed layouts for PCBs one for the LCD mounted on the PCB s component side and one for the LCD mounted on the PCB s noncomponent side but neither have been fabricated into an actual board More details e g photos of this assembly and layout are available at my DLK Engineering website http dlkeng cwahi net EBikeMeter htm INSTALLATION CONFIGURATION 8 OPERATION Figure 5 shows how the EBikeMeter is wired with the bicy cle s electric assist motor controller battery throttle and the speedometer sensor The EBikeMeter was mounted on the www circuitcellar com CIRCUIT CELLAR handlebar cross brace and the speedometer sensor was
120. lutions Inc MIL HDBK 217F What is MIL HDBK 217F http quanterion com Publications MIL HDBK 217 index asp The Reliability Information Analysis Center RIAC 217Plus RIAC s Reliability Prediction Methodology www theriac org productsandservices products 217plus SoHakR Inc Free MTBF Calculator www sohar com reliability software free_mtbf html P Tobias and D Trindade Applied Reliability Third Edition Chapman and Hall CRC 2011 CIRCUIT CELLAR www circuitcellar com NSS SWB ENN ty ESSENTIAL Circuit Cellar s first book Assembly Language Essentials is a matter of fact guide to Assembly that will introduce you to the most fundamental programming language of a processor ore Author Larry Cicchinelli provides readers with e An introduction to Assembly language amp its functionality e Essential terminology pertaining to higher level programming languages amp computer architecture e Important algorithms that may be built into high level languages multiplication division and polynomial evaluation e Overview of Interrupt Service Routines e Free downloadable Assembler program and more On Sale NOW 47 50 CIRCUIT CELLAR WWW C R C U ITC E LLA R C OM VAPYAWYJ 2 C C W E B S H P K C OM THE WORLD S SOURCE FOR EMBEDDED ELECTRONICS ENGINEERING INFORMATION December 2012 Issue 269
121. more securely Even better solder 22 or 24 AWG stranded wire to a header pin reinforce the joint with heat shrink tubing and get a much more reliable con nection with flexible wire that won t break in normal use Never poke stranded hookup wire into the header sockets even if you ve sol dered the loose ends together because tuning fork contacts simply can t grip an irregular surface covered with flux residue Much worse a single errant strand can thats pronounced will touch other pins or components and instantly destroy the microcontroller A few minutes devoted to preparing good wire terminations will pay off in more reliable prototypes and a much longer life for your Arduino board CONTACT RELEASE I don t have an Arduino UNO board in hand so I m relying on the specifications and illustrations on their website the actual hardware may be somewhat differ ent As always verify what you read in product descriptions against the chip man ufacturer s datasheets then apply good engineering judgment to your designs i Poughkeepsie NY Contact him at ed nisleyQieee org with Circuit Cellar in the subject to avoid spam filters RESOURCES Arduino products from Sparkfun www sparkfun com Electronic Kits Zone www ekitszone com also available at eBay www ebay com sch ekitszone E Nisley Solar Data Logger Part 1 PCB Layout Inductor Saturation and Other Troubles Circuit Cellar 225 200
122. n numerous applications but you may prefer trying a digital amplifier The key advantage of the ones and zeros solution is the implementation s stability and the digital low pass filter s flexibility You can easily build a configurable digital filter with a cut off frequency ranging from tens or hundreds of kilohertz down to millihertz or even less This would enable the opti mization of the detection performances either for fast systems or for slow but highly noisy ones Depending on the required performances you can build a digital lock in amplifier using anything ranging from a high end digital signal processor or FPGA down to a low cost 8 bit microcontroller As an example Microchip Technology s Darren Wenn published AN1115 Implementing Digital Lock In Amplifiers Using the dsPIC DS which explains how to build a lock in based weight scale measurement device around a dsPIC33F microcontroller All that s needed is a 4 bit homemade DAC and some operational amplifiers see Figure 8 Lastly you may want to use a lab class lock in amplifier for your scientific applications There are several products on the market such as the impressive devices built by Stanford Research Systems As an example its DSP based SR830 pro vides more than 100 dB of dynamic reserve and works from 1 mHz to more than 100 kHz see Photo 1 This type of device can be configured either as the excitation signal s gen erator or can lock on an externally su
123. n the product is finished and released for production Its risky to wait until the end of the design to calculate the failure rate but this is often done to meet contract requirements You may get lucky and meet the specified requirements without design modifications or obtain ing a waiver but you probably won t have a robust design MTBF MTTR amp MTTF MTBF is the reciprocal of the failure rate A It is a convenient easy to understand reliability measurement You may also encounter a percentage of failures per million hours failures per cycles or a unit called FITS which is equivalent to one failure per billion hours These units are conventions often specific to differ ent industries and can easily be converted from one to another Fundamentally MTBF is meant for repairable products expressing the expected time between two successive failures 4 NU THE ORIGINAL SINCE 1994 WBU Beta LAYOUT EAGLE a me pcb pool com download button KS on your first order z a VE igure ie www pcb poolcom a www circuitcellar com CIRCUIT CELLAR while the product is repaired after each of those It can be determined by a test where Mir Oe Number of failures 1 The total operating time should include the repair time The mean time to repair MTTR must be established by a test that measures how long it takes to fix the various failures Then MTBF mean time to failure MTTF MTTR and the system
124. nd connect it to a magnetic door striker This would enable keyless entry to the house When I started this project my goal was to design an external reader I could use to open my garage doors This goal required finding an effective way to decode the Manchester bitstream which I have described here I hope you found it insightful i After working in software development for 20 years Scott Weber scotty42 csweber com is tired of the direction the PC software world is taking He is now striving to complete his Electrical Engineering degree at the University of Texas Arlington PROJECT FILES To download the code go to ftp ftp circuitcellar com pub Circuit_Cellar 2012 269 REFERENCE 1 Wikipedia Manchester Code 2012 http en wikipedia org wiki Manchester_code RESOURCES R Lacoste Line Coding Tech niques Circuit Cellar 255 2011 S Weber MCU Based Light Control Longer Serial Communication on Differential Wires Circuit Cellar 255 2012 SOURCES EM4095 RFID Reader chip EM Microelectronic www emmicro electronic com PIC18F2221 Microcontroller MPLAB C18 C compiler and MPLAB IDE Microchip Technology Inc www microchip com RFid Reader board MikroElektronika www mikroe com CIRCUIT CELLAR www circuitcellarcom Microprocessor Design Using Verilog KDL With the right tools such as this new book designing a microprocessor can be easy Okay ma
125. nd its associated resistors and capaci tors With a microcontroller I could also use a single compo nent to manage all the timings i e ring cadence as well as the ring itself Cadence adjustment could be accomplished entirely in software without adjusting any external compo nents With this in mind I started designing a microcon troller based ringer circuit I ve used Microchip Technology PIC processors in similar projects Low pin count PICs are well suited to this sort of thing since they have simple and flexible power require ments and can generate their required clocks without exter nal components They can also configure their input pins to have internal weak pull up resistors further reducing the parts count They are capable of easy in circuit programming by simply putting a male header on the board Finally their instruction set is well optimized to control the input and out put pins with the capability of reading from or writing to a single pin in a single instruction There are literally hundreds www circuitcellar com CIRCUIT CELLAR of PICs available in different configurations and with different capabilities all at a low cost In a lot of ways the PIC can be regarded as a general purpose IC that can be made to do whatever you want as long as a microsecond response time is acceptable That was certainly the case with this project While it would have been possible to replace the 555s with a PIC it also seem
126. ne code the other handles any of the interrupt routines from the UART or the card reader The code is available on Circuit Cellar s FTP site The source file main c contains the startup code The peripherals are disabled and port A2 is configured as an input to monitor the garage door s condition The Microchip C18 library provides the func tions to configure the UART Following the setup the microcontroller reset cause is determined and recorded into EEPROM I used this technique in my other project It enables the reset reasons to be later investigated to determine the units stabil ity This is primarily to track watchdog resets to help determine the pro gram s solidity Finally the inter rupts are enabled and the mainline Command ISR is where the program determines what external event occurred and what to do about it All the code is con tained in the interrupt c file The ISR first determines the reason for the interrupt then branches to the code that decides what to do about each one In the case of the UART the handling is shown in a state diagram see Figure 2 In the case of an interrupt from port B the cause would be from the proximity card reader which is shown in another state diagram and will be described later see Figure 3 When the interrupt is from the UART the incoming character is examined for an SOH value If the character isnt SOH the ISR returns Once found the second character received
127. ng know how in every issue of Circuit Cellar In last months Task Manager Circuit Cellar Editor in Chief C J Abate mentioned this was one of the hottest topics in the magazines earliest issues two words In his article in this issue Bob Japenga defines this as an instance of a software program that utilizes CPU resources to accomplish some purpose Swiss computer scientist who designed the Pascal programming language An LED s purpose Enables a lower level software layer to request a higher level defined subroutine German physicist Georg Ohm 1789 1854 first introduced this concept two words NJ Down 2 Cryptographer known as the father of information theory 3 Does not rely on human interaction two words 4 Represents a system gain and phase as a frequency function two words Commonly used for PCB design A device that can determine RPM These types of projects utilize FPGAs PLDs and other chips two words 11 Type of cooling that relies on the Peltier effect to alter heat between two types of materials 13 Used to measure magnetic fields strength and intensity 15 Focus of Renesass 2012 design challenge two words 17 Available for a limited time R The answers are posted at www circuitcellar com crossword and will be available in the next issue CIRCUIT CELLAR www circuitcellar com DEA BOX THE DIRECTORY OF PRODUCTS AND SERVICES AD FORMAT Advertisers
128. nknown state Which to choose For these reasons I find that a design with a few processes and many threads is better than a design with many single threaded processes We use a sophisticated watch dog mechanism to force a complete reboot rather than restart ing an individual process I use processes when development needs e g software updates or number of project designers make them easier to use DESIGNING CONCURRENT SYSTEMS Embedded Linux provides system designers with an arsenal of weapons to design a system with concurrency The mature kernel and tasking model gives most designers more than they need Next month I ll examine additional tools to make your tasks play nice Bob Japenga has been designing embedded systems since 1973 In 1988 along with his best friend he started MicroTools which spe cializes in creating a variety of real time embedded systems With a combined embedded systems experience base of more than 200 years they love to tackle impossible problems together Bob has been awarded 11 patents in many areas of embedded systems and motion control You can reach him at rjapengaQmicrotoolsinc com RESOURCE M Kerisk The Linux Programming Intertace A Linux and UNIX System Programming Handbook No Starch Press 2010 CIRCUIT CELLAR www circuitcellar com SE S o e 0 0 0 0 0 0 0 0 0 0 00 0 0 0 0 010 0 OG ONONENO j e CONNECT oa ALTO a pengsan A
129. nnected my circuit and applied the heat The circuit was powered up from the heat The 12 V fan was still connected to the 12 V battery and not from the 3 3 V generated from the heat but at least I hadn t struck out I ve got to look into Peltier devices made to withstand hotter temperatures which also means J Taaka 7 e Photo 3 The LCD shows a rise in hot side temperature The fan kicked in and is keeping the cold side close to ambient temperature measuring temperatures using thermo couples What goes around comes around RECHARGING This summer I received two backlogged items I d ordered a Raspberry Pi which I cant wait to play with and a BioLite CampStove This couldnt have come at a more opportune moment since the Bio Lite CampStove is wood fueled with a built in Peltier device that produces a charging current for electronic devices e g cell phones Photo 4 shows the Get PUBLISHED Get NOTICED Get PAID Circuit Cellar feature articles are contributed by professional engineers academics and students from around the globe Each month the editorial staff reviews dozens of article proposals and submissions Only the best make it into the pages of this internationally respected magazine Do you have what it takes Contact C J Abate Editor in Chief today to discuss the embedded design projects and programming applications youve been working on and your article could be featured in an upcoming iss
130. nned to hang in until the bitter end It was because I didn t immediately see any company that would appreci ate Circuit Cellar enough to properly continue it Over the years the four major U S technical trade publishers had sniffed around Circuit Cellar with acquisition in mind I never got a good feeling about them and I m sure they knew I wasn t going to be a happy indentured servant in any deal they proposed Why it takes a European publisher to appreciate an American magazine and its readers I ll never know From day one I felt Elektor would treat Circuit Cellar properly It s been three years since that transition and I feel I made the correct decision The collective benefits of being part of a larger publishing company will prolong Circuit Cellar s existence and enable it to expand into new markets I was too complacent to tackle The loyal Circuit Cellar employees deserve a career path beyond my short term ambitions and now they have it As for me I plan on spending time stringing more wires for my HCS and I m ecstatic about having zero responsibilities anymore I m around if needed but plan on taking a four wheel drive out to the beach to find me So until then I ll just close with onward and upward and see where that takes me Re steve ciarciaQcircuitcellar com CIRCUIT CELLAR www circuitcellar com www ftdichio com mum ENFANCED USB PERFORMANCE Streamlined USB Bridge Solutions X CHIP
131. no board Fortunately there s a another more practical approach that directly reduces the chip temperature Most of my projects require power sup plies for the analog circuitry often includ ing a 12 V supply that would produce far too much dissipation in the Arduino s regulator Rather than drive the Arduino board directly from that supply I insert another regulator that produces a lower voltage at the Arduino s DC input I use a simple linear regulator attached to a heatsink because an efficient step down switching supply doesn t make sense for the projects you see here Photo 6 shows one of the power supply terminal blocks on the MOSFET tester I presented in my June August and Octo ber 2012 columns An external switching supply provides 12 V for the op amps and 5 V for the logic with an LM7808 regulator on the heatsink reducing the 12 V supply to 8 V at the Arduino board s Vin pin That LM7808 regulator has the advan tage of being easy to use but it was the last one in my parts heap A less expensive LM317 adjustable regulator with two resis tors would produce 7 V to keep the Arduino regulator even cooler Depending on the circuit load you can set the pre reg ulator voltage even lower The regulator s dropout voltage makes no difference here because there s plenty of margin Hint When the power supply becomes more expensive and intricate than the www circuitcellar com CIRCUIT CELLAR Photo 6
132. nsformer which is wired backward to produce the bell s required voltage A 20 Q resis tor limits current to the L293 s 600 mA maximum Finally two LEDs not visible to the audience provide status for debug ging One LED is directly connected to the power supply and shows that power is being provided to the circuit The other is controlled by the microcontroller A standard programming header for use with the PICkit 2 programmer was also on the board The circuit was laid out on a small piece of Veroboard and encased in a metal utility case The ringer circuit and the phone bell itself were attached to a piece of plywood so the unit could be easily installed on the set This same basic circuit could be used in a variety of proj ects requiring control of a relatively low current load There are enough pins leftover on the PIC to wire up both halves of the L293 and it could be used as the brain for a mobile robot with bumpers to detect collisions Using a PIC with ana log inputs also enables you to use the circuit for a line follow ing robot I made several design decisions based on obtaining parts in a short time frame An eight pin PIC e g a PIC12F508 would also have been suitable if I d wanted to share pins between the in circuit programming and my I O but the PIC16F505 is a December 2012 Issue 269 N N December 2012 Issue 269 part I keep on hand for that matter I have no doubt that other micr
133. nt HuMANDATA LTD See all our products A D D A conversion board WWW hdi CO F CC boards with USB chip from FTDI and accessories at Ej Gi 7 p December 2012 Issue 269 MEMBER PROFILE Dev Gualtieri Member Name Dev Gualtieri was inexpensive and a great way to show family photos Location Northern New Jersey Current Projects Dev used a Microchip Technology PIC microcon troller to build a Morse code flasher in a baby bottle for his newborn grand son It does an LED light show and flashes the alphabet and numbers in gt Morse code he explained I m work Member Status He has been a sub ing on a steampunk style digital clock scriber since the first day and I ve breadboarded an inexpensive digital balance that could be used by students in their school science Technical Interests Dev enjoys analog and embedded projects he added design He writes a science and technology blog www tikalon com blog blog php and he published two science fiction novels Thoughts on the Future of Embedded Technology Education BS in Physics and a PhD in Solid State Science and Technology Occupation Embedded Firmware Engineer which are available from Amazon and other sources Dev said he thinks electronics have become inexpensive but designers need development systems that make their Most Recent Embedded Tech Related Purchase Dev jobs easier Things such as the Raspberry Pi which bo
134. o control the ring cadence and the blinkenlight s flash rate On each processor reset caused by either powering up the circuit or a WDT interrupt the input pin is sampled If the button isn t being pressed the H bridge is disabled its control inputs are set to a known state and all the counters are initialized to known values If the button is being pressed the state variables and counters are checked to deter mine what action if any should be taken whether or not the ringers state should be changed and whether or not the blinkenlight s state should be changed A counter is used to control the ring cadence While the cadence actually used in North America is 2 s on and 4 s off this seemed very slow when on stage The times used in this project are closer to 2 s on followed by 2 s off When the but ton is first pressed the counter is initialized and it is decre mented on each WDT interrupt When it reaches zero the motor driver is disabled and the counter is used to count down the off time A second counter determines when the blinkenlight LED s state should be changed Im a firm believer that any embed ded microcontroller project requires a software controlled N GO Photo 2 A performance of Vintage Hitchcock was captured from a video taken by Patrick McKinley The sound bench is on the right The wall of electrically actuated effects is below the On Air and Applause signs The phone bell ringer is d
135. ocontroller fami lies would have worked just as well as a PIC Likewise the careful reader will note the circuit calls for a 20 Q 5 W resistor but the actual prototype used two 10 0 10 W resistors that s what the electronics store had in stock that day Finally and most importantly designing a custom PCB would have provided a much nicer result than any prototyping sys tem I designed my circuit using tools from the open source gEDA electronics design suite under Linux FIRMWARE STATE VARIABLE 8 COUNTERS The firmware is also quite simple The input pin is config ured to be internally tied to a weak pull up so grounding the pin with a switch on the control panel is used to signal a ring all the other electrical effects used are also actuated by grounding an input The microcontroller s unused pins were configured as outputs so I wouldn t need to worry about pull ups or pull downs on those pins The PIC s internal watchdog timer WDT has an 18 ms nominal period which I used for my time base The motor driver output is reversed on every watchdog interrupt resulting in an approximately 28 Hz output frequency A 20 Hz output frequency would have been ideal but this was well within the bell s tolerance A state variable is used to track whether or not the button is currently being pressed If the button is being pressed the state variable also tracks whether or not the bell is currently ringing Counters are used t
136. ocontroller to reduce your overall Sole ee project risk and accelerate time to market Current TS Ja email Serie 0002 rE ENB SOCKET products include 75mm 2 953 in WOO WHypeppaqua mM uw WO ae CH Si z E ue uw TS 4200 Atmel ARM9 with super low power TS 4300 600MHz ARM9 and 25K LUT FPGA TS 4500 Cavium ARM9 at very low cost TS 4700 800MHz Marvell ARM with video TS 4800 800MHz Freescale iIMX515 with video Dual 100 pin connectors Secure connection w mounting holes Common pin out interface Several COTS baseboards for evaluation amp development Low profile w 6mm spacing ai Over 25 years in business m Custom configurations and designs w a Open Source Vision excellent pricing and turn around time ma Never discontinued a product A Most products stocked and available A Engineers on Tech Support for next day shipping Design your solution with one of our engineers 480 837 5200 New Products Touch Panel Computers 800MHz with Video Acceleration Resistive touchscreen LED backlit display Gasketed construction Tough powder coated finish Fanless operation from 20 C to 70 C 800MHz ARM CPU 256MB RAM 256MB SLC XNAND Drive AERO sel Fully enclosed TPC BO kj dei j one 5K LUT programmable FPGA available Q3 Dual Ethernet USB ports CAN RS 232 ports RS 485 Mono speaker on PCE stereo audio jack SPI DIO Industrial Controllers AA Technolog 5 8820 Powerful Rugged Affordable Systems
137. oject circuitry is mounted behind the insulated surface which will keep the fire s radiation from cooking the components The heat collection sink is facing the fire I ve built in a portable fire pit temperature for the Peltier device s hot and cold sides With the fire roaring I faced the heat collector toward the fire just a few feet away from the flames see Photo 2 I felt the surrounding air already getting warmer if that s possible Back behind the insula tion the LCD showed a rise in hot side temperature and the fan suddenly turned on see Photo 3 However the volts and current both showed zero I added more fuel to the fire and after a few more min utes the piezoelectric transducer began beeping This meant the temperature was approaching 80 C so I moved the fixture away from the fire With the circuitry pulled from the Peltier device I connected a volt meter to its leads When I brought the fixture back to the fire and watched the temperatures and the voltmeter the output rose to about 1 V with a 25 C differential temperature which seemed like about 4 V for every 100 C I couldn t heat it high enough to achieve the SPV1020 s 6 5 V mini mum without exceeding the solder melting temperature I went back to my project boxes and pulled out the SPV1040 from my MPP project This device begins operating with about 0 5 V After attaching the Peltier device and setting the SPV1040 s output for 3 3 V I co
138. oject within the actual limits The Arduino headers include three power outputs e Vin raw DC e 5V regulated e 3 3V regulated The Vin header socket connects directly to input of the 5 V regulator that feeds the 5V header socket and the rest of the Arduino as I ll describe below The USB interface chip which is an Atmel ATmega16U2 on the UNO board and an FTDI FT232RL on earlier versions includes a small 3 3 V regulator Because Vin connects downstream of the reverse polarity protection diode at the coaxial DC jack reversing the GND and Vin connec tions will destroy the Arduino board All of the circuit ground pins in the jacks and headers connect to the same copper areas on the PCB although the PCB rout ing introduces some serpentine traces with many vias The UNO board provides much better grounding than earlier Arduino boards and can produce fewer problems with low level analog circuitry although as we ll see later you must always treat the ground connections with care The rightmost 47 uF electrolytic capacitor in the lower cen ter of the board provides bulk energy storage for power arriv ing through the DC jack Although the UNO specifications in Figure 1 list the maximum power input as 20 V the capacitor case shows a 16 V limit Electrolytic capacitors tend to fail cata strophically when pushed beyond their specifi cations and the output of unregulated DC wall warts can exceed their nominal rating at low currents so be c
139. or a microcontroller because they re easy to use and program In this column Ed explores the often overlooked Arduino power supply shows why Arduino projects sometimes exhibit difficult to debug problems and describes how to keep your Arduino project running smoothly rduino microcontroller boards make a great deal of sense for small projects that need a dash of intelligence a short pro gram twiddling a few I O pins Unfortunately the casual jam LEDs in the headers clip on a battery download a sketch and watch it blink approach tends to produce baffling problems that have little to do with software errors and everything to do with hardware problems It s so easy to get a simple project running that newcomers generally believe more complex cir cuits should Just Work You ve seen Arduino microcontrollers in this column since early 2009 where I ve often used them for analog data collection and linear con trol While they re not an ideal platform for ana log hardware designs they re cheap readily available and perform well enough for the job Along the way Ive figured out how to avoid some of the quirks and gotchas that can afflict projects ranging from LED blinkers to low level analog sensors In this column TIl explore the Arduino board s built in power supply arguably the least appreciated and most important part of the circuitry and explain how to keep it happy In fact when confronted with a misbehaving
140. ost concern Using lots of practical examples we show how using BASCOM you can quickly get your own design ideas up and running in silicon 224 pages ISBN 978 1 907920 11 0 56 40 DIDVD ROM ectronics Modem Valve Eh LI fa Eh E na 3a F a 4 m BR Ar Presented by Menno van der Veen DVD Masterclass Modern Valve Electronics This filmed seminar 165 mins video and more starts with a short discussion of the classic approach using valve load line graphs follo wed by current sources and current foldback techniques Next the negative effect of cathode electrolytics is covered as well as reducing supply voltage interference With the help of state of the art measurement techniques the in correctness of feedback is proven while also clarifying what s happen ing deep within the core of the output trans former ISBN 978 1 907920 10 3 40 20 Circuits ideas tips and tricks from Elektor CD 1001 Circuits This CD ROM contains more than 1000 circuits ideas tips and tricks from the Summer Circuits issues 2001 2010 of Elektor supplemented with various other small projects including all circuit diagrams descriptions component lists and full sized layouts The articles are grouped alpha betically in nine different sections audio amp video computer amp microcontroller hobby amp modelling home amp garden high frequency power supply robotics test amp measurement and of cour
141. other relevant intellectual property law in their jurisdiction or that readers have a right to construct or operate any of the devices described herein under the relevant patent or other intellectual property law of the readers jurisdiction The reader assumes any risk of infringement liability for constructing or operating such devices Circuit Cellar 2012 Printed in the United States Embedded Systems High End Performance TS 7800 with Embedded Ruggedness 500MHz ARM9 Unbrickable Low power 4W 5V 2 2 9 ty 100 128MB DDR RAM WY _512MB high speed 269 17MB sec onboard Flash qty 1 a sa 12K LUT customizable FPGA shown NEW 4 4 a gt Se Internal PCI Bus PC 104 connector ka h og 2 host USB 2 0 480 Mbps j a Gigabit ethernet 2SD sockets 3x faster Ss ts gt Sal 10 serial ports 110 GPIO i ee lt a 5 ADC 10 bit 2 SATA ports compatible with TS 72xx i hi Sleep mode uses 200 microamps Boots Linux 2 6 in 0 7 seconds Linux 2 6 and Debian by default Series starts at TS SOCKET Macrocontrollers 92 Jump Start Your Embedded System Design SPE PPP eter iS A B Dasid 00GP S1 wyga qty 100 139 TS SOCKET Macrocontrollers are CPU core modules that securely connect to a baseboard using the TS SOCKET connector standard COTS baseboards are available or design a baseboard for a custom solution with drastically reduced design time and complexity Start your embedded system around a TS SOCKET Macr
142. ou suspect this is due to the noise i e the ambient light Nighttime testing shows the design is work ing The received signal is close to zero as expected when the beam is cut but increases to only 10 mV when the light shines through So you deduce the light transmission s attenuation in terms of equivalent voltage and take into account the pre amplifier gain of 100 is 10 V mv 100 That means before preamplification the received signal was 0 1 mV whereas the noise was 10 mV providing 10 mV of sig nal and 1 V of noise after amplification respectively Normally that doesn t work The signal is deeply hidden in the noise at least during the day What should you do except explain to your customer that your design only works at night and maybe dur ing a total eclipse FILTERING OPTIONS One option is to replace the continuous light with a modulated light source see Figure 2 On the transmitter side the continu ous source is replaced by an AC source with the same 10 V level e g a 100 kHz sine source As the source peak voltage is unchanged the useful signal and the ambient noise are still the same on the receiver side if you use the same preamplifier i e 1 V noise plus 10 mV of useful signal But this time the signal is a 100 kHz fast carrier modulated by the wheel s slow rotation This modulation provides an efficient way to improve the signal over noise ratio You can add a simple band pass fil
143. pplied signal as explained By the way this company s website features some interesting publications about lock in amplifiers UT 0 Photo 1 SRS s SR830 is an example of a lab grade lock in amplifier WRAPPING UP I can t guarantee lock in amplifiers will be adequate for all your projects but this technique should be included in every electronic designer s bags of tricks You will most likely need it at some point Lock in amplifiers are invaluable each time you must measure a small and noisy signal s amplitude and or phase and especially if you can control the excitation source The examples are numerous e g small signal captors such as weight scales or force sensors optoelectronic devices scientif ic instruments ultrasound etc I hope this article helps you to think of using them Robert Lacoste lives near Paris France He has 24 years of experience working on embedded systems analog designs and wireless telecommunications He has won prizes in more than 15 international design contests In 2003 Robert started a consulting company ALCIOM to share his passion for innovative mixed signal designs You can reach him at rlacoste alciom com Dont forget to write Darker Side in the subject line to bypass his spam filters REFERENCE 1 Wikipedia Lock in Amplifier http en wikipedia org wiki Lock in_amplifier RESOURCES Analog Devices Inc Balanced Modulator Demodulator AD63
144. r based designs Analog Interfacing to Embedded Microprocessor Systems Embedded Microprocessor Systems Real World Design and Debugging Embedded Microprocessor Systems You also collaborated with other authors to write Test and Measurement Know www circuitcellar com CIRCUIT CELLAR My first computers were Z80 based systems running CP M 80 and wired on perfboard I later built my first IBM PC clone the same way I ve toyed with the idea of building a Z80 computer using modern parts to see if the entire thing can be shrunk to a single 6 x 8 perfboard It All What do you enjoy most about writing and explaining microproces sor design Do you plan to write any future books STUART I don t have any actual plans to write additional books although I ve thought about a couple of concepts With the move to surface mount tech nology SMT parts it is hard for future electrical engineers to do anything hands on for experimenting So I ve considered a book of projects that would be designed around some simple off the shelf parts that are still readily available do something useful and demonstrate important electronics con cepts Projects you can do without 2 000 in SMT assembly tools I think I can summarize what I enjoy about writing this way Book editors at technical companies tend to be more editorial than technical They usually have to edit books for more than one technical field so they cant r
145. r com CIRCUIT CELLAR j Ul December 2012 Issue 269 by Dan Karmann USA Build an MCU Based Bicycle Computer The EBikeMeter is a microcontroller based bicycle computer that displays a variety of data The design continuously stores the data on an on board SD memory card and features a firmware file system that supports a PC compatible FAT based file format friend of mine recently upgraded his home built recumbent bicycle with an electric assist hub motor to ease his work com mute He asked me if I could design a monitoring logging system and bicycle computer to display and help character ize the bicycle s operation The result is the EBikeMeter an Atmel ATmega328P based bicycle computer see Photo 1 This article provides a system overview and high level descriptions of the hard ware and the operating firmware It also includes information about choosing and modifying the SD card file system assembling the EBikeMeter mount ing the computer on a bicycle and configuring and operating the unit SYSTEM OVERVIEW The EBikeMeter s system require ments include displaying and moni toring the real time speed trip dura tion elapsed trip mileage tempera ture motor current draw battery voltage and power consumption on a backlit four line by 20 character LCD The system continuously logs all those items as well as the mini mum battery voltage the maxi mum current draw the maximum wattage the watt
146. r display can be indefinite ly displayed all the other screens have a timeout after which the display reverts back to the Main screen The throttle over ride configuration control values limit the throttle for the maximum speed the maximum motor current draw and the minimum battery voltage The EBikeMeter operation is fairly simple When it is pow ered on a sign on screen is shown for a few seconds then the Main screen appears As shown in Figure 6 the right user push button is primarily used to navigate to other sub screens see Photo 2 The Main screen is the primary screen needed as a bicycle computer but pressing the right push N A button will select the next screen in the sequence Main Power Speed Distance Throttle Override and optionally Recent Log Files List When on the Main screen the Throttle Override screen or the Recent Log Files List screen the left user push button toggles the LCD backlight s state When on the Power screen the Speed Distance screen or the Throt tle Override screen the left and right user push buttons con trol clearing power statistics clearing the trip statistics and modifying the throttle override settings Additional configuration and operating information can be found in the EBikeMeter User s Manual and the EBikeMeter Reference Manual which are available on Circuit Cellar s FTP site TIME TO RIDE This has been an interesting project and I have learned some new thin
147. r dissi pation in the 5 V regulator KEEPING IT COOL I epoxied the finned DIP style heatsink to the regulator on the MEGA board in Photo 5 to reduce its case temperature Even with the thermal vias visible on either side of the heatsink the regulator still ran too warm for my thumb Adding a heatsink to Photo 5 A heatsink epoxied atop the linear regulator on this Arduino MEGA board helped reduce the operating temperature to a comfortable level This is certainly not recommended engineering practice but its an acceptable hack CIRCUIT CELLAR wwwi circuitcellar com the epoxy case isn t the best practice but it was the only practical way to retrofit slightly more cooling into the existing board design The thermal coefficient from the regu lator chip junctions through the case to my heat sink isn t specified for good rea son the epoxy case makes an excellent insulator compared to the metal leads and tabs soldered to the PCB That heatsink will cool the case but it s not an effective way to control the junction tem perature and isn t recommended in any datasheet you ll ever read Similarly although I could add a dis crete heatsink on the bottom of the board the limited number of thermal vias and Small copper foil area severely restricts the thermal transfer from the chip I ve seen PCBs with active cooling applied below chips with extremely high power dissipation a technique that doesn t apply to an Ardui
148. ral terms how to deal with these pitfalls The next several articles will discuss the embedded Linux features available to implement a well designed system with concurrency Hardware and software concurrency issues were considered in previous articles This and upcoming articles will strictly examine software This article discusses the mechanisms to create concurrency in your software through processes and threads Upcoming articles will show how semaphores pipes mutexes first in first outs FIFOs sockets shared memory and message queues can be used with these concurrent threads and processes Keep in mind we are taking this in thin slices To learn more a great resource is Michael Kerrisks The Linux Programming Interface I ll introduce the features and you can dig deeper with this and other books PROCESSES 8 THREADS The first concurrent operating system OS I used was Digital Equipment Corporation s RSX 11 You might be interested to know that the second instantiation of Windows NT is a descendent of RSX 11 In RSX 11 concurrent operations were called tasks Later when I wrote my own real time multitasking OSes thank goodness those days are over we always used the word tasks to describe the separately executable programs that concurrently ran When I first started using Linux actually QNX was my first exposure to a Unix Linux like architecture I needed to learn a new set of terms processes and threads For
149. rough which the conductors are run two words 20 THERMOPLASTIC A synthetic flexible mix ture of rosins used as an insulting material CIRCUIT CELLAR Tels JWASREAREH jejejajajeja Available From JJAMECO ELECTRONICS space in Circuit Cellar and CC Strategic Media Marketing 978 281 7708 peter smmarketing us www smmarketing us Down 1 ROUNDKEYS In his article Hardware Accelerated Encryption Circuit Cellar 266 2012 Patrick Schaumont said AES encryption s real secrecy comes from the periodic additions of these 3 OILCAN A type of planar tube similar to the lighthouse tube which has cooling fins 4 VECTORGRAPHICS In the 1970s Circuit Cellar founder Steve Ciarcia wrote his first article for BYTE about this topic 5 VOLTAGECONTROLLED An oscillator con trolled by voltage input there are usually two types harmonic and relaxation two words 6 TEMPEST Describes compromising emanations 8 ACQUISITIONTIME In a communications system the time interval required to attain synchronism two words 9 INTEL Company credited with making the first single chip microprocessor 10 HANDSHAKING How one device communicates with one or more other devices at a predeter mined speed 15 VARACTOR Used as a capacitor to control voltage 16 SALLENKEY Active filer two pole two words b BusBoard Prototype Systems Reserve advertising News Notes today Connect With Design Eng
150. rs ago Thats a long time for any of us When you read the 25 Anniversary issue you ll find my article describing the history of how this all started I d like to say I had a grand plan from the very beginning but my career path had a far simpler strategy To create a product that would be in demand for a long time to stay under the radar away from lawyers and competitive vultures and find good people with similar beliefs who would help me accomplish these goals I d like to say I intuitively knew what to do as a boss but remember I was trained as an engineer not an MBA A wise person once told me there were two ways to learn things in life through trial and error or through someone telling you I just took to heart a business article I read in college and religiously applied it to my career path It said the majority of small businesses fail for one of four reasons Too little business too much business insufficient capital or no plan for succession Since I wasn t having much fun in corporate America back then five jobs in five years succeeding in business had more of a do or die imperative than the average job Let me warn any budding entrepreneurs that these four events test your gambling tactics more than your business acumen In my case Ciarcia s Circuit Cellar was the product 30 years ago along with the supporting manufacturing company It grew quickly and afforded certain luxuries e g Porsches BMWs Ferraris etc typica
151. s the mechanisms to create concurrently in your software through processes and threads On page 64 George Novacek presents the second article in his series Product Reliability He explains the importance of failure rate data and how to use the information Jeff Bachiochi wraps up the issue with a article about using heat to power up electronic devices p 68 Fire and a Peltier device can save the day when you need to charge a cell phone Lastly be sure to set aside time to carefully study the prize winning projects from the Reneas RL78 Green Energy Challenge p 30 Among the noteworthy designs are an electrostatic cleaning robot and a solar energy harvesting system C Ll cj circuitcellarcom N THE WORLD S SOURCE FOR EMBEDDED ELECTRONICS ENGINEERING INFORMATION THEME Embedded Applications Wireless Communications Robotics Embedded Programming Measurement 8 Sensors Communications Internet 8 Connectivity Embedded Development Data Acquisition Signal Processing 280 November Analog Techniques 281 December Programmable Logic Analog Techniques Projects and components dealing with analog signal acquisition and generation e g EMI RF reduction high speed signal integrity signal conditioning A D and D A converters and analog programmable logic ISSUE 270 January 271 February 272 March 273 April 274 May 275 June 276 July 277 August 278 September 279 October Communications Projects t
152. s a voltage and current measuring device the project can tap into and display along with the temperatures Fan operation is based on either sensor s temperature CHART THE COURSE Once you know where you are and where you want to go its a simple matter of connecting the dots right Not always but its a good place to start Figure 5 shows the flowchart I used to connect my dots The SPV1020 s internal registers can be inter rogated via a SPI to gather status information I ve chosen to display both the voltage and current readings on the first of two LCD screens I used 16 bit integer arithmetic to calculate the voltage and current from the register values using the following formulas i Volts register x 1 25 RI RZ 1 023 R2 and Gmi eT 495 1 023 which Ive simplified to Volts register x 10 54 and register Current mA T Temperature sensor monitoring is done via an interrupt rou tine that saves the present channels 10 bit sample conversion count and increments the A D channel before beginning the next conversion After a short delay for the first LCD screen each temperature count must be translated into a correspon ding temperature The count is based on the fact that at 0 C the TDR will measure 1 854 Using a 2 000 Q series resistor across 3 3 V that translates into a 1 587 V drop across the TDR Reading the TDR with a 10 bit A D will result in a 493 count i e approximately 0 003 mV bit When ra
153. se a section miscellaneous for everything that didn t fit in one of the other sections Texts and component lists may be searched with the search function of Adobe Reader ISBN 978 1 907920 06 6 55 70 More than 75 000 components CD Elektor s Components Database 7 This CD ROM gives you easy access to design data for over 11 100 ICs 37 000 transistors FETs thyristors and triacs 25 100 diodes and 2 000 optocouplers The program package consists of eight databanks covering ICs tran sistors diodes and optocouplers A further eleven applications cover the calculation of for example zener diode series resistors voltage regulators voltage dividers and AMV s A colour band decoder is included for determining resistor and inductor values All databank applications are fully interactive allowing the user to add edit and complete component data This CD ROM is a must have for all electronics enthusiasts ISBN 978 90 5381 298 3 40 20 Elektor is more than just your favorite electronics magazine It s your one stop shop for Elektor Books CDs DVDs Kits amp Modules and much more www elektor com shop SJektor Elektor USA 4 Park Street Vernon CT 06066 USA Phone 860 875 2199 Fax 860 871 0411 E mail order elektor com USB Isolator If your USB device ever suffers from noise caused by an earth loop or if you want to protect your PC against external voltages then you nee
154. st partition is opened and checked for supported par tition type and the file allocation table FAT system is opened and checked for Supported FAT type Because of the ATmega328Ps limited code space the EBikeMeter s file system is restricted to a FAT 12 or FAT 16 file system Newer FAT 32 and SDHC card file systems are not supported Due to the limited amount of files that can be stored in a FAT based file system s root directory all EBikeMeter log files are stored in the LOGS subdirectory There are five available screens see Photo 2 Each time through the main loop the LCD screen timer is checked to see if the currently displayed screen needs updating using customized BIG numbers for speed on the Main screen if the Main screen needs to be redis played and if the rotating items on the Main screen need to be changed More information about using BIG numbers can be found at the Arduino Forum see the Resources section The speedometer input value is checked and the bicycle speed trip duration maximum speed and average speed are calculated Also voltage and current values are accumu lated and watts watt hours and amp hours are calculated The power fail input and user push buttons are checked and acted upon If a power fail event occurs all nonvolatile items stored in EEPROM are updated and further processing stops until power is restored User push button inputs are run through a finite state m
155. sue 269 R N December 2012 Issue 269 WORLD S SMALLEST world s smallest MSO ht This DIP sized 200KHz e ch scope includes a spectrum analyzer and Arbitrary Waveform Gen Measures only 1 x 1 6 inches in size XPROTOLAB 49 IPHONE SCOPE SMHz mixed signal am scope adapter for the iPhone iPad and iPod Touch The FREE iMSO 104 app is available for download from the Apple App Store IMSO 104 297 99 ZOMHZ SCOPE _ Remarkable low iT cost 30MHz 2 ch 250MS s sample rate oscilloscope ee 8 in color TFT LCD and AutoScale function Includes FREE carry case and 3 year warranty SDS5032E 299 a GOMHZ SCOPE oe 6OMHz 2 ch scope i cee with 500MSa s rate ki and huge 10MSa memory 8 color TFT LCD and FREE carry case SDS6062 349 100MHZ SCOPE High end 100MHz 2 ch p 1GSa s benchscope ae J W ALIT U NS with IMSa memory and USBport FREE sa SCOpe Carry case New super low price DS1102E 399 _ gt __100MHZ MSO 2 ch 100MSa s Gi Cx ese scope 8 ch logic analyzer USB 2 0 and 4M samples storage per channel with advanced triggering amp math functions CS328A 1359 HANDHELD 20MHZ Fast amp accurate handheld 20MHZz 1 ch oscilloscope 100 M S sample rate 3 5 in color TFT LCD 6 hour battery life FREE rugged impact resistant case HDS1021M 269 95 WWW SAELIG COM Z amp U ee 44 LET
156. t MCUs This family offers easy migration with code and pin compatibility as well as extremely low power in Active and Sleep modes Visit www microchip com 8bit for eXtreme Low Power 1 More than 280 8 bit MCUs As low as 20 nA in Sleep Mode widely available Down to 75 wA MHz in Run Mode 2 Datasheets and application notes to help with your designs Broad Family with High Performance 20 80 pin packages 8 128 KB Flash Up to 16 MIPS with C compiler optimized architecture 3 Low cost tools and demo boards Flexible Peripherals for Optimal Integration mTouch capacitive touch sensing Multiple PWMs and communication channels Include options with segmented LCD display drivers full speed USB CAN or 12 bit ADC PIC18 Explorer Development Board DM183032 MICROCHIP Microcontrollers Digital Signal Controllers Analog Memory Wireless The Microchip name and logo the Microchip logo dsPIC MPLAB and PIC are registered trademarks of Microchip Technology Incorporated in the U S A and other countries All other trademarks are the property of their registered owners 2012 Microchip Technology Inc All rights reserved 03 12 December 2012 Issue 269 motor controller The typical control signal from the throttle control is a 1 to 4 V analog volt age with the highest voltage indicating full throttle The circuitry that implements the throttle override signal is a PWM GPIO output from the processor to diode D2 via Q2 R10
157. t they all need more capable PICs than the one used in this project If I d used a PIC with an analog input I could have used potentiometers to set the times Alternatively if I d used a PIC with on board EEPROM it would have been possible to capture button presses from a user which could be used to configure the cadence The latter probably would have been the better option Since I was designing the circuit writing the firmware and designing the sound simply modifying the constant was the easiest approach The firmware was written and programmed into the PIC using tools from Linux s open source gputils tool suite SHOWTIME Photo 2 shows the set for Vintage Hitchcock which ran for nine performances over three weekends in October 2010 I operated the effects with assistance from Karen Buerdsell and everything worked flawlessly After one of the performances I was approached by Ron Szatkowski who would be directing Its a Wonderful Life another live radio show written by Joe Landry for the El Paso Playhouse during the 2010 holiday season He asked if I d be willing to loan his production some of the equipment Id built Of course I agreed and I also made several trips to El Paso to help with the installation Their production was also CIRCUIT CELLAR www circuitcellarcom successful and the effects equipment performed well It was especially gratifying to learn after the end of their season that they had given me their
158. ted with optical approaches but decided the magnetic approach was the most usable from a DIY perspective I dont use the joystick anymore although I do still have it Most modern PCs don t have game port inputs for joysticks they use USBs And I really don t play video games either on the computer or on anything else Honestly they bore me silly NAN In Connect with USBLab Circuit Cellar 178 2005 you describe your Atmel ATmega8515 microprocessor based solution to using a parallel printer port Tell us how you developed the USBLab and how the ATmega8515 factors into the project design STUART This was actually a larger proj ect that was too specific for a magazine article So I built a more general pur pose scaled down version of the project specifically for the article I no longer use the original project although I have used the same AVR USB interface numerous times for specialized things NAN Tell us what inspired you to write Voltage Solutions Harness the Power of Voltage Converters Circuit Cellar 198 2007 Was it a specific design requiring high voltage STUART This was a collection of cir cuit ideas more than a specific project At the time I was looking at some high voltage generation ideas for a commercial project I dug into the var ious ways of generating those voltages and I have since used those techniques a few times NAN You ve written several books about microprocesso
159. ter centered at the carrier frequency i e 100 kHz Since an ideal band pass filter doesn t exist you will need to design a sharp filter to remove as much noise as possible If you design an analog band pass fil ter then achieving a 100 quality factor is already challenging This means the band pass will be 0 01 of the center frequency AC Power Transmitter Receiver source High loss medium 1 Attenuation 100 000 added noise 10 mV noise DC to 1 MHz gt Signal 0 1 mV Noise 10 mV here 1 kHz i e 100 kHz 100 Assume the noise was a white noise spreading in an uniform way from DC to maybe 1 MHz The band pass filter will not significantly attenuate the useful signal but it will damper out the noise except in a small 1 kHz window The associated noise reduction is proportional to the filter band width s square root Therefore the noise will be reduced by a fac tor of the square root of 1 000 i e 1 MHz 1 kHz which pro vides around 32 So the noise voltage after preamplification is reduced from 1 V down to 31 mV i e 1 V 32 Thats a great achievement and it explains why nearly all light beam systems use modulated carriers For example the ubiquitous infrared RC4 remote controls are using a 38 kHz modulated infrared stream However in the example the noise is 31 mV This is still higher than the 10 mV useful signal making a precise measurement dif ficult if not impossible
160. the amount of heat drawn away and the differential temperature between the Peltier device s two sides gt 0 D o gt 3 Q 6 8A Heat pumped W AN ELL EBE ALLELE IE ANOLE BUTE BOWL z se LL m ad op 50 40 30 AT Th Te C E KELI AEAN L PV Cell string l I PGND O VIN_SNS_M A D l l l l l l l l l l Converter l l l l l A D l Converter A D l Converter l i SPI DATA IN O SPI_CLK o OSC IN Figure 3 This block diagram of a STMicroelectronics SPV1020 shows one of the four phases that are combined to dynamically change the load presented to the input device to maximize the power collected from it Its output is regulated to a set point determined by the output resistor divider J CIRCUIT CELLAR www circuitcellar com camping Even though using technology while camping defeats the whole purpose having a cell phone for personal safety can not be overemphasized TEMPERATURE IS A KILLER My heat source is a campfire which could be made from char coal or wood Temperatures are often hundreds of degrees Fahrenheit around the fire The temperature depends on the wood type and its moisture content Standing dead wood is often best as it is drier than wood that has been on the ground A wood fire is difficult to cook on as its temperature is quite hot and dif ficult to control
161. the hot and cold side temperatures Using a simple voltage divider these have a fairly linear tempera ture versus resistance characteristic in the 40 C to 150 C range I used two A D inputs to read the resulting voltages I had a small two line by eight character LCD laying around that displays temperatures voltage and currents It happens to be a 3 3 V model which means I ll be running the microcon troller on 3 3 V as well I used other parts including a 12 V fan and associated heatsink from a discarded I mean recycled PC Had I purchased this stuff new I would have used a 5 V fan and LCD which would have made things simpler FlashPro430 FlashPro CC ss FlashPro2000 L GangPro430 GangPro CC Gi WIT 5 instrun Ten its MC Us MSP430 Chipcon CCxx C2000 DSPs Fee y BE 5 Reliable and the fastest programmer on the mark Perfect for production usage can assii g n unique serial n umber de got pt ne up to eight p ogrammers can be connected to one PC and program 1 target devices simultaneously Programmers JTAG SEW_ s s mi z Ze a One PC and 8 programmers DE use Fpa s amp Incorporated www elprotronic com December 2012 Issue 269 N 7 December 2012 Issue 269 Figure 4 This project s circuit will monitor temperatures on the hot and cold side of the Peltier device under test The SPV1020 serves a
162. ual phase shifter in the reference path The measurement will be exact if this phase shift compensates the system phase shift and will be lower in all other cases due to the cosine term The man ual phase shifter must be gently increased until it produces a maximum measured value You will have canceled out the measurement channels phase Clipped Band limited White Noise 100 dB Attenuation Modulated 400 Hz Carrier Carrier Reference shift Moreover you can measure this phase shift if the manual phase shifter is calibrated However a variable and precise phase shifter is not easy to design so the actual lock in amplifiers prefer to use a so called IQ synchronous demod ulator see Figure 5 The idea is to implement two synchronous detectors one using the reference and one using the reference shifted by a fixed 90 These two channels enable you to measure the signal s in phase I and the quadrature Q components If the phase shift is zero then I will be the signal amplitude and Q will be zero It will be the opposite if the phase shift is 90 but all other values will provide some signal on both outputs A simple vector calculation enables the deduction of both the signal amplitude and phase shift The amplitude is the magnitude of the resulting vector which is the square root of I squared plus Q squared thanks to the Pythagorean theorem Similarly the phase can be calculated as the inverse tangent of Q div
163. ue of Circuit Cellar magazine editor circuitcellar com CIRCUIT CELLAR www circuitcellar com CIRCUIT CELLAR gi p gasit wi December 2012 Issue 269 gt W December 2012 Issue 269 Photo 4 BioLite CampStove is a wood fired personal camping stove that can be used to not only prepare meals but also to recharge any electronic device i e cell phone plugged into its USB power only port Here I have a stoked unit powering a USB LED lamp I ve plugged in stainless steel firebox stocked with wood with a plastic housing hanging off the side A second perforated stainless outer shield maintains a 0 5 air space around the firebox to provide some insulation The housing contains a small circuit board a lithium polymer battery fan and a Peltier device The fan serves two purposes It blows air over the heatsink s cold side and it directs the air through a connector into the bottom of the firebox This is like constantly blowing on the fire to give it extra oxygen and enable the fuel to burn clean and hot As always I dissected my new toy before I operated it The orange housing is stored inside the firebox as the two halves simply detach The protruding 0 5 copper rod is an integral part of the hot side plate used to transfer heat to the Peltier device Photo 5 shows the Peltier device sandwiched between the hot side heat pipe and the cold side finned heatsink Note the insulating
164. ugh K plus M Those are the components on which you want to concentrate If the total failure rate is too high to satisfy the specification they are the first to review But even if the target failure rate is not a problem you should examine the components with high A and see if they are optimally used because they are the most likely to fail You may be able to reduce their A e g increase their derating cool them with a heatsink etc Or you may want to choose a different component Even if their A is Satisfactory you should also review com plex and expensive components There may be better less expensive alterna tives In other words analyzing compo nents selection will help you balance CIRCUIT CELLAR www circuitcellar com your designs cost performance ratio In the same way as is shown in Figure 1 you should analyze the entire design where A B C and so forth stand for func tional blocks Your reliability may suffer because you have too many unnecessary components with otherwise low A Or one functional block may exhibit a large failure rate and be designed such that the time to repair or replace it may be unacceptably long thus reducing the system availability Then you may want to modify the architecture and spread the fail ures among several blocks This is an iterative process If there is a design change the analyses must be updated and reviewed Your reliability predic tion only becomes final whe
165. ught a color Nook book reader and hacked it into an packs Linux into an inexpensive PC board with loads of Android tablet computer which he said was much easier than peripheral connections will accelerate development of it sounds The touch screen is resistive not capacitive he some powerful embedded projects Dev said I think the explained so it s not as responsive as other tablets but it days of Assembly language programming are over ki Keep in touch and interact 2 2 2 0 2 with the Circuit Cellar editorial department microcontroller circuitt embedded FPGA tech volts ADC Hanalog DSP WiFi rok HRFIDHcodekfschematicHlogicHPWM electro RE TEE AAE RTOS ohm byte sensor engineering P plaj ae mea witn valuable RAM servo CPLD Hencoder duct anno ements be 1 S m4 Tv 3 Ji al ui T JE kos ae CUJI oce gt ZAKA OWAK Twitter p T i y a i L E lll T j r r Sof NAKE t 5 F F F Al EE es 7 ANM T 5 m F ae _ i F ym a Y R CIRCUIT CELLAR www circuitcellar com Test dod CIRCUIT CELLAR Edited by David Tweed ANSWERS for Issue 208 Answer 1 Assuming you connect the windings in phase you ll have double every pair of ones in the new word represents the number of turns so the resulting inductance will be about four times the K a string of ones in the original word Remove inductanc
166. upt if PIRI bDItS REIF 4 goto SERVICE_UART When the data line INT 0 goes HIGH it s maybe a START if CINTCON amp 0x12 0x12 Shut down the data line and start the clock INT1 INTCONDits INTOIF 0 INTCONDits INTOIE INTCON3bits INTIF INTCON3bits INTIE clockCount 0 totalBits 0 preamble 0 state STATE_FIND_PHASE And start at state 0 return J CLOCK INTERRUPT Used to sample the PORTB input if CINTCON3 amp 0x09 0x09 4 INTCONSbits INTIF 0 Clear the interrupt clockCount Increment the count if clockCount 16 4 lhb PORTBbits RBO Get the left side goto INT_DONE i if clockCount 48 rhb PORTBbits RBO get the right side if lhb rhb if they match then is not clockCount 16 the correct phase so we try again goto INT_DONE if clockCount 64 goto INT_DONE Now we are ready to examine the bit clockCount 0 Switch state What are we doing with this bit we found case STATE_FIND PHASE totalBits if totalBits 64 if we found 64 good ones we are in phase totalBits 0 state STATE_FIND_PREAMBLE goto INT_DONE case STATE_FIND_PREAMBLE totalBits if 1hb preamble if preamble 9 4 pe lt TES Stiers SA state STATE_COLLECT_BITS cardBits 0 cardByte 4 bits 0 readerLcardByte 0 goto INT_DONE preamble
167. ur rent draw and or minimum operating battery voltage An external serial inter face is also provided for firmware upgrades and EBikeMeter configuration Layered hardware firmware architecture is used to structure the EBikeMeter firmware as a classic small embedded system with a foreground main loop and background interrupt processing see Figure 3 After reset the various processor I O modules are initialized the configura tion items are loaded from EEPROM interrupts are enabled and the main CIRCUIT CELLAR wwwi circuitcellar com ie ese sc Agilent Technologies Ea p f ETT q A CY ag FH ANALOG IAR ly A 4 Lali DEVICES I 2 X m NT a i gg e 6 gt ie 1 z S LEA A Honeywell Sensing and Control P 4 Littelfuse d molex IE Tektronix Bg KiJ TEXAS is INSTRUMENTS 9a oo gill ify I s oP VIPI i VISHAY E ENGINEERING SOLUTIONS Start here At Newark element14 all your engineering needs come together in one source vast product range from world class brands The Navigation and fast online search seamless purchasing ordering Process are tools resources and services one on one Easy to work Thanks support and a community of experts Here you ll find simpler smarter and faster ways Richard Newark element14 customer to do business BUS elementiy HOW MAY WE HELP YOU TODAY COMMUNITY element1 4 com WEBSITE ne
168. ut the advantages quickly disappear if you design separate processes that require a lot of shared memory Even with all the isolation processes provide you can still declare certain memory as a shared resource across processes If your concur rent task design requires a lot of shared memory you should use threads We recently profiled one of our designs that used a lot of shared memory between processes and found that on an ARM AM3517 running at 600 MHz each Shared variable access cost 50 us Advantage Processes unless you need shared memory Context switching times Any time the kernel switches from one task to another we call that a context switch This can happen when a task s allotted time runs out when the task releases control to the kernel or when a higher priority task preempts another When the kernel s scheduler switches from one thread to another within the same process the virtual memory space remains the same During the context switch between processes all virtual memory must be switched out An additional cost that is more difficult to measure but can be significant is that a context switch for processes affects the CPU s caching mechanism When a context switch happens the cache s memory addresses are no longer useful This adds an indeterminate amount of time to the context switch Pub lished benchmarks on this are sketchy and not helpful Some provide a 10 to 15 advantage to threads If context switch
169. v iev faj 2Kx16 128x8 i 64x8 18 12 bitx4 GT IBEX 1 16DIP NSOP SSOP HT68FOI6L 8MHz 09V 18V JZ 1Kx16 64x8 64x8 18 Wa 1 16DIP NSOP SSOP HT68FO17L 8MHz 0 9V 18V taj 2Kx16 96x8 64x8 413 A 1 16DIP NSOP SSOP Touch Flash MCU RETTE STD 8051 Flash MCU USB STD Flash MCU 32bit MCU Enhanced OTP MCU TinyPower MCU UART MCU Phone MCU EEPROM WLED Backlight Holtek Semiconductor USA Inc HOLTEK SEMICONDUCTOR INC 46729 Fremont Blvd Fremont CA 94538 Tel 510 252 9880 Fax 510 252 9885 E mail sales holtek com http www holtek com December 2012 Issue 269 Nine Preamble 1s 1 1 1 1 1 knowing is to determine the nibble 1 bit 1 bit 2 bit 3 bit 4 row parity location of the bit boundaries to nibble 2 bit 5 bit 6 bit 7 bit 8 row parity the bits and I conveniently left nibble 3 bit 9 bit 10 bit 11 bit 12 row parity them off the diagram So there nibble 4 bit 13 bit 14 bit 15 bit 16 row parity is no way to determine if a bit nibble 5 bit 17 bit 18 bit 19 bit 20 row parity stream like this is all 1s or all Os nibble 6 bit 21 bit 22 bit 23 bit 24 row parity Of course if the bitstream was nibble 7 bit 25 bit 26 bit 27 bit 28 row parity only 1s or Os and never nibble 8 bit 29 bit 30 bit 31 bit 32 row parity changed there wouldn t be much value in it anyway At nibble 9 bit 33 bit 34 bit 3
170. valuable when you need to measure a small and noisy signal s amplitude or phase elcome back to the Darker Side column Fifteen years ago I attended a training session on the first 3G wireless stan dards As an ice breaker the trainer asked every participant to try speaking in English to someone at the other end of the room at the same time Of course the noise level escalated and nobody could understand anything said We were instructed to continue while two people spoke in French still from one side of the room to the other Magically they were able to understand each other without any problem even with the high noise level This exercise was meant to illustrate code division mul tiple access CDMA In a nutshell knowing the type of signal you are expecting helps you filter out the noise This month I present a more simple but power ful way to extract a signal from the noise synchro nous detection This technique is the key building block of so called lock in amplifiers which DC Power Transmitter High loss medium source Attenuation 100 000 1 added noise 10 mV noise DC to 1 MHz according to Wikipedia were invented by Prince ton physicist Robert H Dicke in 1962 A lock in amplifier enables precise signal measurement even if it is a thousand times lower than the noise I ll start with the basics HOUSTON WE HAVE A PROBLEM Imagine you need to detect a slowly rotating wheel s position w
171. wark com PHONE 1 800 463 9275 LEARN MORE newark com together December 2012 Issue 269 Photo 2 The EBikeMeter s LCD screens in sequence are Main a Power b Speed Distance c Throttle Override d and Recent Log Files List e loop is entered as shown in Figure 4 Interrupts are used to monitor the speedometer input power fail input user push button input general timer based event timing UART transmit and receive operation and ADC voltage and current input monitoring The EBikeMeter configuration and non volatile statistics data loaded from the processors EEPROM at start up include speedometer wheel size LCD back light timeout LCD subscreen time out LCD backlight brightness LCD contrast correction minimum tem perature and digital potentiometer adjustment speed throttle override speed motor current throttle over ride current and minimum battery throttle override voltage The non volatile statistics items include minimum operating voltage peak motor current amp hours peak watts watt hours maximum trip speed trip distance trip duration and odometer mileage The current log file number is also retrieved N N LCD contrast temperature and digital potentiometer adjustment speed throttle override speed motor current throttle override current and minimum battery throttle override voltage from EEPROM When initializing the on board file sys tem the SD card s fir
172. ww mcselec com index php option com_contentatask view amp id 159 amp Itemid 57 Roland Riegel MMC SD SDHC Card Library www roland riegel de sd reader index html SourceForge WinAVR http sourceforge net projects winavr SOURCES ATmega328P Microcontroller Atmel Corp www atmel com OAR 3 Open air sense resistors IRC www irctt com DS18S20 1 Wire digital thermometer and MAX4080 MAX4081 amplifiers Maxim Integrated Products Inc www maxim ic com BootLoader Windows application MCS Electronics www mcselec com MCP414x 416x 424x 426x 7 8 Bit single dual SPI digital potentiometer Microchip Technology Inc www microchip com MC34064 Undervoltage sensing circuit ON Semiconductor www onsemi com PB MC AVR28 28 Pin AVR development board Protostack www protostack com TMR 4811 DC DC Converters TRACO ELECTRONIC www tracopower com www circuitcellar com CIRCUIT CELLAR Get a little pushy Small enough for Mini Sumo flexible enough to make it your own general purpose I O for sensor modules dual motor driver 3 axis accelerometer and compass Put your Arduino on the right tracks with the new Zumo chassis and Arduino shield biPololu Robotics amp Electronics Learn more at www pololu com zumo December 2012 Issue 269 N Ul December 2012 Issue 269 Z S SA cu z by Joe Pfeiffer USA Electrically Actuated Sound Effects A Circuit and Firmware to Rin
173. y time not allocated to the real time group will be allocated to the other processes in the standard round robin fashion After the kernel is built to support this the software can dynamically set the scheduling period and a global limit as to how much time real time scheduling it can use Virtual address space Program and static libraries thread process www circuitcellar com CIRCUIT CELLAR Argv and environment variables Stack for starting p Stack for Thread 3 Stack for Thread 2 Stack for Thread 1 Dynamic shared libraries m EEE Heap dynamic memory Uninitialized data Initialized data Main process Figure 1 Memory allocation is a multiple Remember this is in thin slices there is much more I could say about this If there is interest I can write a future article about my company s experience using real time extensions A lot of work is being done in Linux in this area in particular for real time embedded systems so you need to know what is supported by your particular version of Linux main process can grow PROCESSES VS THREADS For the software system s designer the question arises as to when to use processes and when to use threads This choice depends on the differences between the two and the associated advantages and disadvantages Data isolation One cannot speak highly enough about the advantages of eliminating shared data space in creating robust sys tems B
174. ybe not easy but certainly less complicated Monte Dalrymple has taken his years of experience designing embedded architecture and microprocessors and compiled his knowledge into one comprehensive guide to processor design in the real world Monte demonstrates how Verilog hardware description language HDL enables you to and SO you can Microprocessor Design Using Verilog HDL will provide you with information about e Verilog HDL Review e Verilog Coding Style e Design Work e Microarchitecture e Writing in Verilog e Debugging Verification and Testing e Post Simulation and more www cc webshop com Yours for just 45 00 Microprocessor Design oar iV 7 1 DJK jas z J Verlog LL ARE t 4 a ZE by Monte Davie e NH NK KI U NU i oo S M JA Nie IRCUIT ester CREAR December 2012 Issue 269 QUESTIONS ANSWERS NAN Where are you located STUART I live in Longmont CO NAN How did you become interested in electronics STUART I knew I would do something in the sciences ever since grade school I was always drawn to things related to science At about age 12 I read a copy of Wal ter Tompkin s book SOS at Midnight and knew I wanted to work in electronics I tin kered with electronics all through high school and earned a BSEE from the Uni versity of Missouri Columbia I also have an MBA from Regis University NA
175. year new projects are just around the corner Sooner or later you ll regain your energy and find yourself back in action Plus we re here to give you a boost This issue is packed with projects that are sure to inspire your next flurry of innovation Turn to page 16 to learn how Dan Karmann built the EBikeMeter MCU based bicycle computer He details the hard ware and firmware as well as the assembly process Another interesting project is Joe Pfeiffer s bell ringer system p 26 Although the design is intended for generating sound effects in a theater you can build a similar system for any num ber of other uses You probably dont have to be coerced into getting excited about a home control project Most engineers love them Check out Scott Weber s garage door control system p 34 He built it around a PIC18F2221 and a 125 kHz proximity card and reader Once considered a hobby part Arduino is now implemented in countless innovative ways by professional engineers like Ed Nisley Read Ed s article before you start your next Arduino relat ed project p 44 He covers the essential but often overlooked topic of the Arduino s built in power supply Need to extract a signal in a noisy environment Consider a lock in amplifier On page 50 Robert Lacoste describes synchro nous detection which is a useful way to extract a signal This month Bob Japenga continues his series Concurrency in Embedded Systems p 58 He cover

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