OpenTheremin MIDI implementation on V3

It's finally done! We have a true and clean MIDI implementation for the Open.Theremin! While the Open.Theremin has it's own sound generator and can be played as stand alone instrument the MIDI software allows you to connect your theremin to any MIDI device or various MIDI synthesizers installed on you computer. This largely extend the functionality and is just great fun to play.

The following MIDI implementation and instructions for Open.Theremin V3 were developed by Vincent Dhamelincourt. Vincent is an experienced electronics and firmware engineer from Lunel, France. He plays keyboards and theremin in a local band. *** A great thank you! ***


Download and install the arduino code from the following git repository and carefully read the instruction below. I recommend to first setup and test the theremin as described in the instruction that came with the theremin (using built in sound generator) and then move to MIDI.

To install:

  1. Download the Theremin MIDI code from

  2. Open up the Arduino IDE

  3. Open the File "Open_Theremin_V3.ino"

  4. In "Application.cpp", take care of selecting MIDI mode that corresponds to your situation (put "//" in front off inadequate line - MIDI through serial is selected by default here):
    Serial.begin(115200); // Baudrate for midi to serial. Use a serial to midi router

    //Serial.begin(31250); // Baudrate for real midi. Use din connection or HIDUINO

    I tested "Hiduino" and "MIDI to serial" modes, both are OK.

  5. Selecting the correct usb port on Tools -> Serial Port

  6. Select the correct arduino board from Tools -> Board

  7. Upload the code by clicking on the upload button.

MIDI synthesizer on the computer

OpenTheremin MIDI is sending at 115200 baud through USB serial.

Use a serial to MIDI router on your computer such as "hairless-midiserial" (
And to generate sound from the MIDI signal use a software MIDI synthesizer such as Gforce's Minimonsta (commercial), Minimogue VA or QSynth (free).

Real DIN MIDI interface

You can also use the OpenTheremin MIDI implemented to communicate with a real MIDI device.

To do so add a DIN connection. See here ( for the hardware required.
Set the baud rate to 31250 by changing Serial.begin(115200); to Serial.begin(31250); in the code (-> application.cpp -> midi_setup() )

USB-MIDI (HID) device

Through the code provided in the HIDUINO project the Open.Theremin MIDI implemented can be turned into a class-compliant USB-MIDI device. HIDUINO takes advantage of the ATmega (8u2/16u2) chip on the Arduino UNO. So you get a true USB-MIDI device for plug-and-play compatibility on Windows, OSX, and Linux - just like a commercial MIDI controller. Code and documentation can be found here (


The MIDI open theremin generates NOTE ON/OFF messages and Continuous Controler changes (MIDI CC) depending on settings and hands positions next to antennas.


In MIDI standard NOTE ON/OFF messages have a NOTE NUMBER and a VELOCITY.

Let's consider a Fade-in / Pitch Variation / Fade-out sequence (I use right handed convention):

  1. Fade-In
    When left hand moves away from VOLUME ANTENNA (LOOP) and volume crosses a settable threshold (Volume trigger), a NOTE ON is generated. VELOCITY depends on how fast left hand is moving. Right hand's position next to PITCH ANTENNA (ROD) determines the starting NOTE NUMBER.

  2. Pitch variation
    When right hand moves next to PITCH ANTENNA (ROD), PITCH BEND messages are generated (if activated) to reach exact pitch as long as pitch bend range will do. Beyond, a new NOTE ON followed by a NOTE OFF for the previous note are generated if legato mode is activated. Pitch bend range can be configured (1, 2, 7, 12 or 24 semitones) to align with synth's maximum capabilities.

  3. Fade-Out
    When left hand moves close to VOLUME ANTENNA (LOOP) and volume goes under Volume trigger threshold, a NOTE OFF is generated to mute the playing note.

MIDI Continuous Controllers (MIDI CCs):

It is possible to assign independent MIDI CCs to the PITCH ANTENNA (ROD) and to the VOLUME ANTENNA (LOOP).


There is two calibration mode. Best use a speaker connected to the theremin to verify calibration and timbre variation.

Normal calibration of antennas: turn REGISTER POT counter clockwise (all left) and press button for 3 seconds -> Runs normal calibration of antennas (yellow LED blinks until finished). Audio processing from antennas to output jack, including volume and pitch pots, LEDs and button functions, is exactly the same as in open theremin V3. You can play the Audio and the MIDI side by side.

MIDI configuration:


To change the settings, select a Parameter from the list below and move "Parameter's Value" to change corresponding setting:

  1. Register: 4 positions as in original Open Theremin V3
  2. Timbre: 8 positions as in original Open Theremin V3
  3. Channel: 16 positions (channel 1 to 16)
  4. Rod antenna mode: 4 positions (Legato off/Pitch Bend off, Legato off/Pitch Bend on, Legato on/Pitch Bend off, Legato on/Pitch Bend on)
  5. Pitch bend range: 5 positions (1, 2, 7, 12, 24 Semitones). For classical glissando and in order to have same note on audio and MIDI, use exactly same pitch bend range on your synth. Maximum setting possible is recomended.
  6. Volume trigger / Velocity sensitivity (how fast moves the volume loop's hand): 128 positions (0 to 127)
  7. Rod antenna MIDI CC: 5 positions (None, 8-Balance, 10-Pan, 16-Ribbon controler, 74-cutoff)
  8. Loop antenna MIDI CC: 8 positions (1-Modulation, 7-Volume, 11-Expression, 71-Resonnance, 74-Cutoff, 91-Reverb, 93-Chorus, 95-Phaser)

Default configuration is: Register = Lowest Register, Timbre = 1st Waveform, Channel = MIDI Channel 1, Rod antenna mode = Legato on/Pitch Bend on, Pitch bend range = 2 Semitones, Volume trigger = 0, Rod antenna MIDI CC = None, Loop antenna MIDI CC = 7-Volume.


Sends ALL NOTE OFF on selected channel and stay in mute until it is pushed again.

As long as you are inside pitch bend range you can play with the same linearity as with device's sound (same pitch is audible on stable notes without vibrato).
On 24 semitones wide pitch bend range capable monophonic SW synth (tested with Gforce's Minimonsta), the effect is rather good: We play on 4 octaves just like a normal theremin. 
12 semitones capable synth are also good but sometime note transition can be heard. 



What can I do to get a theremin like glissando?

Activate picth bend and set pitch bend range of the theremin with a high value (12 semitones or 24 semitones). Set pitch bend range of the synth with the same value.

If I do not trigger with the volume hand it also seems to trigger a new tone with the pitch antenna. Guess this is how MIDI works.

When legato mode is activated, if you trigger a note (with volume loop) and go in one direction (with pitch antenna) a new note will be triggered at the limit of pitch bend range.

Legato mode is used as a workaround for a limitation of MIDI (max 24 semitones pitch bend). Maybe some synth can perform pitch bend on more that 2 octaves but none of mine does...

Tweakable parameters (in application.cpp):

Changing this to your taste may require some test and trial.

"#define VELOCITY_SENS 9" -> How easy it is to reach highest velocity (127). Something betwen 5 and 12.

"#define PLAYER_ACCURACY 0.2" -> Pitch accuracy of player. Tolerance on note center for changing notes when playing legato. From 0 (very accurate players) to 0.5 (may generate note toggling).

Possible Human Machine Interface (HMI)

The picture at gives an example of possible HMI: on "Value" pot, red lines have 4 positions, grey lines have 5 positions and yellow lines have 8 positions. On "Parameter" pot you see coloured lines indicating which colour to follow for the "Value" pot.

Percussive Sounds

The volume trigger can be configured so as we have some volume at note attack on percussive sounds. The volume trigger setting is also used to set sensitivity for velocity (how fast left hand is moving when note is triggered). Volume trigger = 127 (Maximum) won't generate any NOTE ON. It can be used to generate MIDI CC only.

Manipulation of MIDI CCs

Manipulation of "Rod antenna MIDI CC" and "Loop antenna MIDI CC" is not error proof. MIDI newbies should be advised to change their value in MUTE mode.

Added and removed compare to Open Theremin V3.

Serial communication implemented for program monitoring purpose was removed (Particularly during calibration). If you need to monitor calibration for antenna problem fixing, please use original master branch from

Serial port is used to send MIDI messages now.


Original project written by Urs Gaudenz, GaudiLabs, 2016 GNU license. This Project inherits this 2016 GNU License. Check LICENSE file for more information All text above must be included in any redistribution

Calibration Diagnostics

The Open.Theremin V3 has a fully automatic calibration function integrated. The calibration tunes the antenna oscillators with your antennas. All you need to do is press the button on the board for 3 seconds and wait for the calibration to finish (as described in the instruction manual). If you want to check and diagnose your calibration you can use the following "Calibration Diagnostics":

To see the calibration data open the Arduino IDE (that you used to upload the code to the Arduino).

1. With the Open.Theremin connected via USB to your computer, hit the "Serial Monitor" button on the top right.
The Serial Monitor window should open. (If not, check the serial port settings)

2. Now set the communication speed to 115200 baud through the pull down menu.

3. Start the calibration of your theremin by pressing the FUNCTION button for two seconds.

You should now see the calibration data appear in the Serial Monitor window.

First the measured frequency of your Arduino is shown. Should be about 16'000 HZ

Then you see the pitch calibration data with the "Set Frequency" that and the "Tuning Range". Then you will see how the calibration routine adjusts the oscillators.

Then again the same procedure for the volume oscillators.

The calibration finishes with CALIBRATION COMPLETED.

If some of the values are 0 or out of range, check your antenna size and connections and restart.

Open.Theremin V3 Housings

The Open.Theremin V3 is designed in a way to be playable and look good without any case. Togheter with Artist and Designer Niklas Roy we created a functional circuit board with the electronic components on the back and a great user interface on the front. Still if you like you can design your own case around the Open.Theremin shield an make it a very special instrument. Below you find some open source case designs that fit the Open.Theremin V3. For more inspiration see also the Featured Builds.


The following case design, made from a combination of 3D printing and laser cutting, was generously contributed by Nikolai Demidenko. Nikolai Demidenko is a professional pianist and maker of big analog modular synth.

The design files can be found on Thingiverse here.

Thank you Nikolai Demidenko for sharing with the community.


Filigree 3D printable Case With Stand

Artist and Maker Kayne Dettmann (@alacrion) shared a beautiful, 3D printable "Filigree Case With Stand/Legs" with us on thingiverse. Thank you Kayne for adding such beautiful ornate design to the OpenTheremin.

Link to the design files:


LaserCut Open Theremin V3 Housing

Pablo from Spain made this nice laser cut housing and shared it with us on thingiverse, here.

3D printing Knobs and Frontpanel

Maker and Engineer Penguinmd from Kanada designed a 3D printable front panel and knobs for the OpenTheremin. The files are published under a Creative Commons - Attribution license on Thingiverse here:

Open Theremin v3 Top Panel Annotated

Knobs for Open Theremin controller

Thank you for this useful contribution, Penguinmd.





Special Edition White

Spring is here and I enjoy the sun and the beautiful flowers. To celebrate this I made a special edition of the newest Open.Theremin V3 in white and gold. The PCBs turned out amazing and the white theremin looks just beatiful. Now available in limited number in the small batch store.

Limited Edition Open Theremin V3 White.

The white and the black Open.Theremin V3.

The white Open.Theremin features:

  • Full digital auto-tuning (one button press)
  • Pitch and volume antenna with excellent linearity
  • Pitch and volume can be manually fine tuned during play
  • Sensitivity of the pitch antenna can be changed in 4 registers
  • 8 preprogrammed audio wave forms can be selected
  • Mute function
  • Waveform can be reprogrammed freely (stored in a look-up table)
  • Arduino compatible shield for easy re-programming and mollifications for own uses.
  • Completely open source hardware and software
  • USB powered, no extra power supply required, battery supply possible
  • 12bit digital audio converter
  • New Control Voltage (CV) option

Black and white theremin share the same functionality.

The white and gold PCBs with black silk printing, assembled and tested. Laser sharp and super precise.
Limited Edition, get it now.