Photoresistor Arduino Midi Theremin




Introduction: Photoresistor Arduino Midi Theremin

I call it the C041D-2020

I made this during the second COVID lockdown in UK, from ideas borrowed from about 5 other projects I found here on Instructables and also on Youtube. As you can see from the video it makes acidy noises by covering the photo resistors, or adding lighter to the photo resistors. The Arduino code is also borrowed from other projects here in Instructables.

The noises are produced by the software (Ableton Live/ Lite), using a Plugin called TAL-NoiseMaker, the potentiometers are MIDI-mapped to effects.



1) Just about any Arduino board, I used an 'Uno'

2) Some Photoresistors, I used 4, it also worked with just one

3) Some potentiometers, I used 5 potentiometers and a slider, - IMPORTANT - they need to be 10k (linear), they are called 'B10K'

4) A resistor, I used 300ohm, I have seen instructions to use a 10k

5) Make some kind of box or enclosure with a top panel or 3D print one

6) Some knobs for the potentiometers


1) Hairless MIDI to Serial Bridge

2) Ableton Live or Lite (you can get a free version here)

3) TAL-NoiseMaker (free VST Plugin)

4) Arduino IDE

Step 1: Make Some Kind of Box

Make some kind of box or enclosure with a top panel, or 3D print one. I used some scrap wood, and 1mm aluminum sheet, drilled hols for the potentiometers, and photoresistors. My dad milled a slot for the slider. I used duct tape to cover the sides of the box, made some rubber feet from an old car tyre innertube. Decorated the box (see pdf logo), and used clear Gorilla tape to stick on the cutout paper. Add knobs to your potentiometers. I designed and 3D printed some stuff for this project, they may work with yours, you can download



Step 2: Wire Up the Device!

Just use the guide in the image gallery, to join all the parts together - I'm pretty sure this is correct (I drew up the schematic diagram from memory, a few days after I finished the project and closed up the box).
When I first made this, I didn't use the photoresistors, it was just controlled by the knobs, then added the photoresistors later.

Step 3: Add the Code to Your Arduino

If this is your first time using Arduino, have a search on google or youtube for a guide on how to setup your board for the first time using Arduino IDE

Then add the code to your board:

int val = 0; //Our initial pot values. We need one for the first value and a second to test if there has been a change made. This needs to be done for all 3 pots.
int lastVal = 0;

int val2 = 0; int lastVal2 = 0;

int val3 = 0; int lastVal3 = 0;

int val4 = 0; int lastVal4 = 0;

int val5 = 0; int lastVal5 = 0;

int val6 = 0; int lastVal6 = 0;

void setup() { Serial.begin(9600); // Set the speed of the midi port to the same as we will be using in the Hairless Midi software }

void loop() { val = analogRead(0)/8; // Divide by 8 to get range of 0-127 for midi if (val != lastVal) // If the value does not = the last value the following command is made. This is because the pot has been turned. Otherwise the pot remains the same and no midi message is output. { MIDImessage(176,1,val);} // 176 = CC command (channel 1 control change), 1 = Which Control, val = value read from Potentionmeter 1 NOTE THIS SAYS VAL not VA1 (lowercase of course) lastVal = val;

val2 = analogRead(1)/8; // Divide by 8 to get range of 0-127 for midi if (val2 != lastVal2) { MIDImessage(176,2,val2);} // 176 = CC command, 2 = Which Control, val = value read from Potentionmeter 2 lastVal2 = val2; val3 = analogRead(2)/8; // Divide by 8 to get range of 0-127 for midi if (val3 != lastVal3) { MIDImessage(176,3,val3);} // 176 = CC command, 3 = Which Control, val = value read from Potentionmeter 3 lastVal3 = val3;

val4 = analogRead(3)/8; // Divide by 8 to get range of 0-127 for midi if (val4 != lastVal4) { MIDImessage(176,4,val4);} // 176 = CC command, 3 = Which Control, val = value read from Potentionmeter 4 lastVal4 = val4;

val5 = analogRead(4)/8; // Divide by 8 to get range of 0-127 for midi if (val5 != lastVal5) { MIDImessage(176,5,val5);} // 176 = CC command, 3 = Which Control, val = value read from Potentionmeter 5 lastVal5 = val5;

val6 = analogRead(5)/8; // Divide by 8 to get range of 0-127 for midi if (val6 != lastVal6) { MIDImessage(176,6,val6);} // 176 = CC command, 3 = Which Control, val = value read from Potentionmeter 6 lastVal6 = val6;

delay(10); //here we add a short delay to help prevent slight fluctuations, knocks on the pots etc. Adding this helped to prevent my pots from jumpin up or down a value when slightly touched or knocked. }

void MIDImessage(byte command, byte data1, byte data2) //pass values out through standard Midi Command { Serial.write(command); Serial.write(data1); Serial.write(data2); }

Step 4: Install the Apps to Make Music and Test


1) Hairless MIDI to Serial Bridge (this turns the serial data from the Arduino into midi code)

2) Ableton Live or Lite

3) TAL-NoiseMaker (free VST Plugin, that runs within Ableton)


Plug your board into your PC USB port - (I have an Apple Mac)
Run the Hairless MIDI app, make sure you have flashing lights on the app and you can see the serial data running - IMPORTANT - don't have the Arduino IDE app running or open in the background, or the Hairless MIDI app won't pick up the serial code to send to Ableton.

Keep the Hairless MIDI app running and open up Ableton, and go to your preferences, and set up your device in your MIDI settings.

Step 5: Make Some Noises!

If you have not used Ableton before, there are plenty of tutorials on Youtube to show you how to get started. Then make a midi track, and use the TAL-NoiseMaker plugin, there is a preset called 'LD Acid Saw TAL', I used this setting, and configured a bunch of the filters to be MIDI-Mapped to the pots on the device.

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    Question 12 months ago

    looks very nice...
    what's the device on the right, the one with the LEDs?


    Question 12 months ago on Step 5

    Hi! That's so nice!
    Don't know nothing about couding, and only know a few things about electric 😩😁 but i wold love to be able to do something similar to that to make soundtracks for my future content (I'm an artisan...), Staying home due to the pandemic... I'm making some clip's of the things I make.
    Do I need the pad/midi thing that you have, our it's possible to do only with the computer and the Photoresistor connected to the PC?
    Thank you!


    Answer 12 months ago

    A photoresistor is an analog device. It changes resistance based on the amount of light it is exposed to. A regular PC has only one "analog input" - the microphone jack. While you could, with a lot of experimenting, make a circuit that would connect a photoresistor to the microphone input, it runs the risk of breaking your computer if you get it wrong.

    The pad/midi thing is not needed. The Arduino plugs directly into the computer. The Arduino is basically acting as an Analog to Digital converter, which reads the positions of the knobs and fader, and converts them into MIDI messages. It does the same for the photoresistors - sensing their resistance and sending a corresponding MIDI message when they change (I'm guessing here - not associated with the OP).

    Coding can be easy and fun to learn. There are many free courses and tutorials on line. If you can afford something like an ESP32 development board, or a Seeeduino Xiao, they are great, cheap ways to get started. The Arduino Uno can be a little more expensive - and not that much easier to work with. If you can afford a little more, the Circuit Playground boards from Adafruit are awesome - lots of sensors and RGB LED's to practice your programming!


    Reply 12 months ago

    Hi, the other device in theh video is called a Launchpad, the launchpad was just used to start off the samplese, you dont need the launchpad.


    Tip 12 months ago

    Awesome work! I admit I'm biased, as I love MIDI projects. Nice layout and neat wiring job, too. Here's an idea for an upgraded version - a ranging sensor that wouldn't need external light.

    Penolopy Bulnick
    Penolopy Bulnick

    1 year ago

    Nice job! Thanks for sharing :)


    Reply 1 year ago

    You're welcome! And thank you!