The NovaDrone - Casper Electronics
Contents
1. 8 I Mix average Figure 4 Phase controlled amplitude This phenomenon of phase controlled amplitude is something many musicians use without even realizing it This is the vary trick one uses when tuning a guitar You tune one string to the other until the beating effect slows and eventually disappears SECTION 2 NOVADRONE OSCILLATORS 2 1 Thecircuit The NovaDrone contains 6 oscillators Each oscillator outputs a square wave and a triangle wave The circuit which generates the oscillators is clean simple and robust They are generated using a remarkable device called an op amp If you are interested in building synthesizers and don t know where to start read up on op amps They are the key elements of most oscillators filters envelope generators mixers and amps Schematic Each channel of the R NovaDrone Red green ra and blue has 2 oscillators T 336 i These are shown in fig 5 279 x and fig 6 They are very XA similar to one another but have been calibrated for different purposes Osc 1 is an audio frequency oscillator It has a coarse and fine tune adjustment and only operates at audible frequencies 20Hz 20kHz Osc 2 is calibrated as a low frequency oscillator LFO with cycles as long as 2 minutes It has a range switch and a single adjustment knob2. Figure 5 Osc 1 audio oscillator Feedback loops The oscillator circuit is a feedback loop between two op amps that are configured as a schmitt trigger and an inverting integrator Basically an integrator turns square waves into triangle waves A Schmitt trigger is a kind of comparator that turns modulating signals like triangle waves into square waves Figure 6 Osc 2 LFO The key elements of the relationship between these two circuits is that they form a loop Schmitt gt integrator gt Schmitt gt integrator gt etc and that the integrator is also an inverter This creates a continuous cycle of modulation 1 Schmitt output goes HI 2 Integrator inverts Schmitt signal and outputs slope going down LOW 3 When slope is near zero volts Schmitt trigger is thrown and its output goes LOW 4 Integrator inverts and generates upward slope HI 5 When integrator slope reaches peak Schmitt trigger is thrown and output goes 6 etc This is an overly simplified explanation but enough for our purposes Do more research on these valuable circuits once you are familiar with some of the basics of op amps RC time constant In both oscillators fig 5 and 6 the element which defines frequency is the RC time constant This relationship is a core component of most oscillators and is worth reading up on The RC time constant is a period of time defined by the relationship between a resistor
3. FL B 2 1 t 4Q4 4 Pt 42 d 1 ELR rp 4 Osc 1 input 1 Osc 2 input 2 PWM output Figure 9 Pulse width modulation detail Mixer The audio signals from each of the three channels of the NovaDrone are mixed using M the circuit in fig 10 This mixer is nice and simple and uses just one op amp and a few Ta gt other components This circuit is configured 4 hi as an inverting mixer with an amplitude t H controlled by the feedback resistor and input resistors The amplitude is calculated as RF RI In this case RF 10 000 and RI 100 000 That means the output signal is Figure 10 simple mixer 1 10 the amplitude of the input signal LED drivers 3 2N3904 NPN transistors are used to make 3 LED drivers A driver is a simple but important circuit which isolates elements which use lots of current like LEDs from sensitive circuits like the oscillators in the NovaDrone Failure to use a driver can result in 4 something called a loading effect which basically means that the device being driven will affect the behavior of the rest of the Figure 11 LED driver circuit in bad ways like the pitch changing when the lights turn on The LED in the NovaDrone uses a lot of current relative to the rest of the circuit S0mA vs around 30mA for the rest of the circuit therefore a driver is necessary The key component of a drive
4. of identical amplitude and frequency The green oscillator is the mix or average of the red and blue oscillators Phase is measured in degrees with 360 degrees being one complete cycle 180 degrees is exactly 1 2 of a cycle In fig 3 the phase of the blue oscillator is offset at 45 degree increments from the red oscillator from left to right With each step you ll notice that the waves get farther apart and that the amplitude of the green average oscillator decreases This may seem confusing at first but it s really quite simple The green oscillator is the average of the red and blue oscillators Let s say the red and blue oscillators sweep from 5 to 5VDC 10Vp p Now look at the right most illustration of the 2 waves out of phase by 180 degrees When the blue wave is at its positive peak 90 degrees of 5 volts the red wave is at it s negative peak 270 degrees of 5 volts What is the average of 5 and 5 Zero They are always going to be the opposites of each other so the average will always be zero Now look at the 90 degree image When Blue is at 5 volts 90 degrees red is at 0 volts zero degrees The average of 5 and zero is 2 5 volts The important thing to take away from the info above is that the amplitude of an oscillator created by mixing two similar oscillators is relative to the difference in phase of the two source waves In fig 3 the oscillators have identical frequencies This means that the phase relationship once
5. speaker the voltage charges a coil in the speaker which pushes the cone of the speaker back and forth This action pushes air which travels to our ears and is perceived as sound as our ear drums are excited into vibration The sounds we hear around us are all incredibly complex patterns of air pressure modulation Most electronic oscillators including those used in the NovaDrone are precise and easily controllable There are three basic factors that make up all oscillators frequency amplitude and wave shape In musical terms we would call these pitch volume and timbre will also talk a fair amount about phase which is relevant when working with multiple oscillators and plays an important role in creating drones The red line in fig 1 represents a voltage which goes up and down over a period of time This is an oscillator Frequency One complete sweep up and down is called a cycle The number of cycles per second is your Frequency or Pitch Frequency is commonly measured in Hertz which is the number of cycles per second Pitch is another term for frequency which is used only when referring to the frequency of an audio signal The image to the left shows a triangle wave with a cycle length of 5 seconds The frequency of this wave would freq in Hertz cycles second be determined by seeing how amplitude difference between peaks many cycles will occur in 1 second In this case there are 2 complete cycles in 1 second That
6. THE MO Y ADPONE www casperelectronics com novadrone FEEOQUENMCY ciToo RED CHANNEL GERLUM DEREN 1 IX AD OSCILLATOR i AM ED AMPLITUOL RUL AJL TANT PULS ut fH 8 HODULATOR curo 4 QUENCY T FEE Ga BED 50 2 OUT HIM LL RED OSCILLATOR 2 ED Tel 2 Out f T OH COMOSE FINE GREEN CHANNEL OW LN 3 1 OUT GACEN 1 NCW TRE GW EN a allt AOJUS TRENT TALEN ALSC HIDTH HODULATOR LED Beha TRI 2 OUT BLUE CHANNEL BLUE OSCILLATOR 1 OSTEN PUN IN BLUE APEX 0 1 IN ACLS TRENT BLUE AARSE HOTH x PLATS XO E FEX QUENCY a rato 3 2 HH FD LOU LED ORLA AUDIO MIXER u GREEN CHANNEL hot R14 M pe d mne d CHO BLUE ase 2 Se Tore 4 of 2 Ou 1 i i E E D 5 M BI 2 QUT bI q x AMA svc saa ume BREECH LED DRIER a Hie BLUE CHANNEL NOVA DRONE U1 3 CASPERELECTRONICS 2612 SS ee Throughout this guide will attempt to give you some insight into the circuit theory and scientific principles at
7. The more you open the spigot reduce resistance the more water electrical current will flow and the faster the cup will fill capacitor will charge The oscillator circuit is configured in a special way which causes the capacitor to continuously charge and discharge It is looking for two states from the cap fully charged or fully discharged When the cap reaches either of these states the whole circuit reverses polarity and the capacitors charge status begins moving toward the opposite state The amount of time it takes to charge and discharge is your RC time constant gt 2 2 pulse width modulation pwm PWM is exciting stuff really It is essentially a 1 bit digital representation of an analog wave form Digital wave forms only have 2 states high and low High is a voltage at or very close to the positive supply voltage Low is a voltage ator very close to the negative supply voltage It is basically just a square wave Analog on the other hand is infinitely variable Think about it like the difference between a light switch digital and a light dimmer analog PWM is a wave form that bridges the gap between these two formats It can be used to make sound control the brightness of an LED control the speed of high torque motors and speak to microprocessors It is also the language that a microprocessor will use to speak with the analog world Pulse Width PW refers to the relative durations of high and low voltage in a single cyc
8. and a capacitor The equation for this is simply Time R C This equation defines the length of time it takes for one stage of your cycle to complete for instance the rise time of your triangle wave The wave created by this circuit is symmetrical which means it s rise and fall times are identical therefore the duration of one complete cycle can be defined by 2 RC In Oscillator 2 the R is a 500k potentiometer in series with a 4 7k resistor between pins 8 and 13 of the two op amps The C is one of the three capacitors between pins 13 and 14 of the rightmost op amp One of these caps is selected using a three way switch on the NovaDrone circuit board This controls the frequency range of the LFO Let s say the pot is all the way up full resistance and the middle cap has been selected The equations for RC and subsequently the frequency is R 504 700 Ohms C 000022 Farads RC time constant R C 504 700 000022 11 1 seconds cycle 2 RC 22 1 seconds Frequency in Hz 1 2 RC 045 Hz How it works Resistors limit the flow of current and capacitors store current Current flows through the resistor and is stored in the capacitor The resistor controls how much current flows into the capacitor per second Therefore the size of capacitor and the amount of resistance will determine how long it takes to fill the capacitor A common analogy is to think about current flow as water the resistor as a spigot and the capacitor as a cup
9. established will remain the same and the resulting averaged amplitude of the two waves will also remain the same Q What will happen if the frequencies of your two waves are NOT identical We established above that the amplitude of the averaged waveform is relative to the phase difference of the two wave forms therefore as the phase difference of two waves increases and decreases so too will the averaged waveforms amplitude What we have here is phase controlled amplitude modulation and the rate of phase modulation is controlled by the frequency difference between your two oscillators In fig 4 the blue oscillator has a frequency of 10 Hz the red is 11Hz That means that it takes the red wave 1 10 of a second longer to complete a cycle than the blue wave You can see that with each cycle the red wave lags a little bit further behind the blue wave which increases the phase difference between the two As a result the amplitude of the averaged wave green decreases as the phase offset approaches 180 degrees and then increases as it continues past 180 to 360 degrees WR T ARE N GT EET EEE OCIO XEM TO ES Sa IG Ru 503 1 T RA RW TIO eur CU ECT WIE Ut I CL EY mi Ss nl LU EE o OLUCT UY a 2 vlt CITOCTOC IY R C I VEIT SE Ee IUE OUT UCET AM POET ee Re Rene Ee eee 2 CC
10. le of a square wave e wb es es db ep em em eo bw ep em dp wb Gm m dbwb Co em em em died em em em dp cm am dp db eo e e em dp wb Gm em do em dp Ae e do wb es em em dp wm dp em em dp wb cm em QU bw eo m dp wb Cm em e em em lb b Cu e dp wb em em dp wb cm em db wb em em dp wb em ee dub de ee do wj em a ona db wb ae un up p n p ux ee ek un n an un n un Dp es Ap up cuf up enu pun UD pen up p cut diu oun en up on peur an d oun en UD uou up cran db pu en p on up up uf oen an up n ke en UD p ex up up pur en up pu an D pu en ul js Figure 7 Pulse width Fig 7 shows three square wave oscillators of the same amplitude and frequency but with differing pulse width The red oscillator has a 1096 pulse width That means the wave goes high for 10 96 of the duration of one cycle The green wave is 5096 and the purple wave is 90 What is important to note is that pulse width has nothing to do with frequency and only refers to the relationship between the high and low swing of the wave The Comparator The job of a compa
11. means the wave has a frequency of 2 Hertz This is well below the hearing range Humans can hear oscillators between 20Hz and 20 000 Hz Amplitude Amplitude refers to the magnitude of voltage change across one cycle of an oscillation This in turn impacts the volume of the signal if it is sent to a speaker The image above shows a triangle wave with a positive peak of 5 volts and a negative peak of 5 volts The amplitude is determined by figuring the absolute difference between these peaks In this case that difference is 10 volts This is commonly referred to as 10 Vpk pk 10 volts peak to peak There are many different ways to measure amplitude pk pk RMS Vp etc but we ll just be talking about Vpk pk Waveshape The wave shape is the pattern of amplitude modulation over the course of a cycle The waveforms in fig 2 are Sine ramp triangle and square oine triangle and square are the most common and are all symmetrical waves That means the positive and negative portions of each cycle are of the same duration Many musical synthesizers offer other wave forms which are asymmetrical versions of these common waves such as ramp saw and pulse waves The importance and impact of wave shape depends on its application Many audio effects such as tremolo or phaser use low frequency oscillators LFOs to modulate certain parameters of the sound It is commonly more desirable to use a sine or triangle wave for many of these effec
12. play in the NovaDrone The user manual is the HOW guide to the NovaDrone This document is the WHY That said will be giving little more than an intro to each topic and strongly encourage you to do further reading on topics you find interesting Before reading this guide suggest you read or at least skim through the users manual in order to become familiar with the general layout of the NovaDrone This is a beta version of the NovaDrone Technical Guide expect to make revisions over time and eagerly encourage readers to send me feedback questions suggestions and especially corrections Comments should be addressed to pete casperelectronics com TABLE OF CONTENTS section 1 Oscillator Primer 1 1 Frequency amplitude amp waveshape Frequency Amplitude Waveshape Review 1 2 Phase Phase controlled amplitude modulation section 2 NovaDrone Oscillators 2 1 The Circuit Feedback loops Schematic RC time constant How it works 2 2 Pulse Width Modulation The comparator 2 3 The Mixer section 3 Light incomplete 3 1 Sound and light 3 2 LED driver 3 3 Video patterns SECTION 1 OSCILLATOR PRIMER gt 1 1 Frequency amplitude and wave shape The NovaDrone is basically a bunch of oscillators so it s important to understand what an oscillator is An oscillator is simply a pattern which repeats indefinitely All of the electrically produced sound we hear is a repeating pattern of fluctuating voltage When this is applied to a
13. r is the transistor This is another topic worth reading a lot about
14. rator is simple Two signals are fed into the and inputs labeled 10 and 9 in fig 8 respectively If the voltage at the input is higher than the input the output of the comparator goes high If the Figure 8 Comparator PWM input drops below the input the output goes low In the NovaDrone the triangle output of Osc 1 and Osc 2 combine through a simple comparator fig 8 to make a single square wave with a modulating pulse width In this way the comparator also functions as a pulse width modulation processor Fig 9 below shows how two triangle waves are transformed through the comparator into a square wave with a modulating pulse width The blue triangle wave in fig 9 is oscillator 1 The red triangle is osc 2 The green line is the combined PWM output Any time the blue line osc 1 is above the red line osc 2 the green line pwm goes high As the red line rises the percentage of each cycle that the blue line is above the red line decreases This changing percentage is what makes our modulating pulse width effect oe ee eee ee LL rrr 4 4 4 4 4 4 4 4 4 1 4 4 7 4 d d b Rcp B 4 4 4 p ti4 4 H 2 t T bR d d rBp 4
15. ts such as the tremolo which fades the volume in and out Using a square wave for this would create dramatic shifts in volume which can be unpleasant Many natural sounds are synthesized using overlapping wave forms like those shown above For instance a flute can be synthesized using several octaves of a sine wave A horn on the other hand will use more square waves and maybe a triangle or saw wave More advanced wave and synthesis theory sites the sine wave as the basis of all wave forms It is shown how even square waves can be created by combining several sine Waves Figure 2 Wave shapes Review The basic components of an oscillator are Frequency The number of oscillation cycles that occur in one second Measured in Hz Amplitude Magnitude of voltage sweep in one cycle of an oscillator Measured in Volts or Vpk pk volts peak to peak Wave shape Sine triangle square 1 2Phase Phase is a bit more complicated than the other terms but plays an important role in audio circuitry and especially in making drones Phase refers to a particular position in a single cycle of a wave such as the positive or negative peak and is measured in degrees It is most commonly used to describe the relationship between multiple waves 180 degrees out of phase 135 degrees 45 degrees 90 degrees out of phase out of phase out of phase Osc 2 out of phase E Figure 3 Phase Fig 3 shows two sine waves red amp blue
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