REQUIRES A BASIC/GOOD KNOWLEGDE OF MIDI PROTOCOL.

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I built a MIDI controller prototype based on the Ondes Martenot, french instrument from around 1920. The instrument is rare as hell and costs a huge amount of money, so not an option. Same for the Ondomo and other similar devices. Instead, I decided to build a controller intended to be used with Soniccouture's Ondes Kontakt instrument. This is simply the best Ondes Martenot VST available out there.

MIDI is sent via USB, using Hairless MIDI/serial bridge and loopMIDI (a virtual MIDI input), or via standard MIDI plug. (just comment serial.begin and uncomment midi.begin in the setup part of the sketch).

So, I tried to replicate as much as possible the drawer of a real Ondes Martenot, with all the buttons and faders.

Basically, a few potentiometers and a button sending MIDI CCs. I used CCs that are by default unasigned, and then routed them to the different parameters shown in the Ondes VST. For more realism, use slide pots instead of regular pots. I'll probably go that way if I PCB this project, eventually.

The core of this project: a 10-turn 10k pot sending the pitchbend message. That's how you get the slide effect with the ring. That's what makes the Ondes Martenot a so unique instrument.

The volume pushbutton is actually an FSR, sending CC11 message. A NOTE ON(middle C + octaveshift) is triggered when pressed and NOTE OFF when released.

I added the 6 «trill buttons» you can find on a real Ondes Martenot. Each of them adds a certain amount of pitchbend to momentarily modulate the sound (quarter-tone up/down, semi-tone, tone, minor third and fifth up).

I also added octave shift buttons and MIDI channel buttons, and LEDs. I still got problems with these LEDs and idk why. When turned on, sometimes, the program sends notes on/off very fast or the sound gets weird when pitch shifted (high notes sounds a bit like a saw wave...). Coding mistake, I guess. I'm quite new to this... Anyways for now I disabled the LEDs so everything works fine, except a flickering pot. Probably due to a loose connection somewhere... I might just replace it.

A nice improvement would be to add a real keyboard to the controller. With a switch to switch between the ribbon control and the keyboard. On a real Ondes Martenot, the keyboard is «floating», allowing the player to do vibrato while holding a note. Quite a challenge to replicate on a DIY MIDI controller, but doable.

It could be convenient to add a switch to send MIDI wether via USB or 5-pin MIDI plug. So no need to open the sketch, modify, then reupload to the board... A switch to turn on/off the pitchbend ribbon could also be useful.

For more independance, a simple volume (CC7) slide pot could be added. Especially convenient if using CC11 with the FSR, wich I think is the best. If you use CC7 with the FSR, then no need for that.

For a quieter and smoother action with the ribbon, use only 2 pulleys instead of 4, and better quality ones...

EXPANDED TECHNICAL DETAILS

Micro-Tonal Musical HID Interface

This project recreates the ethereal sound and playing feel of the classic Ondes Martenot electronic instrument using modern MIDI technology and Arduino.

• Linear Potentiometer Ribbon Controller: Uses a high-quality linear potentiometer to mimic the "Ring" control of the original instrument, allowing for fluid glissandos and micro-tonal pitch shifts.
• Hairless MIDI-to-Serial Stream: The Arduino sends raw high-resolution data to the PC. The Hairless MIDI/Serial Bridge translates this into standard MIDI messages, which drive professional VST plugins like Kontakt Player.

Aesthetics

• Tactile Key Trigger Sensing: (Features) Includes a custom "Intensity Key" (pressure sensor) that allows the performer to control the volume and timbre of the notes with high-fidelity tactile feedback.