PowerPoint Presentation
Tori ChitwoodTori QuallsArduino Theremin
Invented in 1919 by Russian Physicist Lev Termen (Leon Theremin)
Brought instrument to US in 1920, but was taken back to Soviet
Union by force in 1938Different Rock bands have used it in the 60s
and 70s including Led Zeppelin
History
Musical Instrument that operates off of hand capacitance in
relation to the antennae (talk more about this later)One antenna
controls sound pitch and one antenna controls volume levelTalk
about different ranges pitch in picture
Nowadays, costs range from $99-$450The lower end is for single
antenna theremin; for pitch and volume control, at least $170
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Schematic for Leons Theremin
How a real theremin works There are multiple oscillators (a
couple for pitch and one for volume) that generate the tone of the
instrument and control the volume.Tone works by multiplying the
outputs of the variable pitch and fixed pitch oscillators, when
waves multiplied and low pass filtered, the frequency of the output
is the difference of the frequencies of the variable and fixed When
playing, the goals is to alter very slightly the frequency of the
variable pitch oscillator so that the overall difference in
frequency changesThis is done by utilizing the capacitive effect
that the players hand has on the antenna. Hand acts as ground plate
and varies the antenna capacitance by different amounts depending
on how close or far it is away. Change in capacitance then causes a
change in current. With inductors, change in current causes a
change in voltage across the inductor and change in frequency of
oscillator.Volume works in similar way but converts the frequency
to a DC voltage which controls then is used in conjunction with the
difference in frequency gained from the pitch antenna circuit to
produce a sound
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Takes a single measurement at a time and translates it into a
value through code before outputting a tonePitch controlVolume
controlArduino sends data to speakerHow Ours is Different
Required to use Arduino or labviewWe also had two antennae: one
for pitch and one for volume Other used oscillators to generate
different sounds by comparing an output from a reference oscillator
to an oscillator affected by hand movement4
Arduino Code
Here is our Arduino code. It is divided into six main
sections
** Capacitive sensign for pitch and volume, reset code, digitpot
initialization, data mapping, tone
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Arduino Code
Here is our Arduino code. It is divided into six main
sections
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Capacitive Sensing
Pitch Control
Tone
Have separate Capacitive sensing circuits for pitch and
volumeDownloaded Capacitive Sensing Library from Arduino website;
heres how it worksCapsenseArdunio changes send pin state eventually
changes the state of the receive pin.Time delay between send and
receive pin is determined by RC with C being the sum of the Cpin
and CsensedCpin used to stabilizeCsensed is what we control** The
capacitiveSensor Function argument (where it says 30) represent the
number of samples in one sensing cycle and the capacitive sensing
library has a built in low pass filter to smooth noiseToneInput
value received from capacitive sensing code into map() functionTake
mapped value and use tone() function to generate sound7
Volume Control
Capacitive SensingUsed same capacitive sensing library as the
pitch control to get a valueInstead of directly using the map
value, we first constrained the values to ensure we didnt try to
tap into a digipot state that didnt exist (7 bit digipot with 128
different resistance states)Constrained values were mapped and then
rounded and sent to digipot
DigipotNo simple Arduino method the way there was for pitchFound
someone who used a digipot to control light intensityThe digipot
has 7 bits and 128 states but the lower the state number, the
greater the volume, so in our code we constrained the state values
to 1-20 to keep the volume audibleArduino has a few different
libraries that can be used to communicate with digipotWe used SPI
library because it better fit our purposeThe first block code is
how it is initialized, ss is the chip number if have multiple
chips, reg is the wipper blade number (some are duel
potentiometers), and level is the state number
1P is chip select for if you have more than one potentiometer in
your device (we have one)2P clock which is used to keep track
whether it is SDI or SDO3P is SDI/SDO which is the interpreted and
mapped data from our sensing plate4P is ground5P is unused6P is the
wiper and leads to the speaker7P is our tone/pitch input (so the
wiper only affects the amplitude of our sound wave but the
frequency of the sound wave is still included and regulated by the
pitch sensing plate)8P is power (5V)
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Circuit Schematic for PCB
**Our circuit design (for reference):Sensitivity (#of
resistors), stability (extra 100 pF capacitors), linearity (mapping
of capsense values to freq range), resolution (mapping, bit range,
changed mapping to narrow range of freq outputted), SNR (MAF)
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PCB design and Soldered Board
Picture with PCB schematic and soldered boardWorked, but didnt
seem to work as well Unknown cause, potentially soldering error and
we didnt have time to redo it
**Values were all over the place like what happened initially,
so possibly charge build up10
Noise and Data RegulationChallenges
MAF to increase SNR and smooth spikes outAdjusted window width
to get best response timeToo big = must hold hand a long time to
changeToo small = didnt get rid spikes
Changed mapping to play within certain range of frequenciesDidnt
want to go all way to human hearing range because it was unpleasant
and unmusical
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Capacitor values increase randomly
Sensitivity
Challenges
Reset codeIf the cap values for pitch went too high, it reset
the Arduino without having to press the button and the values go
back downOnly applied to pitch because the volume values were more
stable and less likely to randomly jump up**Charge build up might
be cause of increasing values
Resistor values More resistors mean slower because you are
increasing the time constant (R*C)But increased sensitivity because
now smaller changes in capacitance change the time constant12
Video: pitch
Video: volume
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Referenceshttps://www.arduino.cc/en/Tutorial/Smoothinghttps://www.youtube.com/watch?v=pp36Q5i08HEhttps://www.arduino.cc/en/Reference/SPIhttp://playground.arduino.cc/Main/CapacitiveSensor?from=Main.CapSensehttp://www.thereminworld.com/Article/14232/what-s-a-theremin-http://www.theremin.info/index.php?module=-&type=file&func=get&tid=15&fid=image&pid=54
