I’ve mostly completed the “brain” for my air horn piano!
The hardware consists of a 12v fuse box, 12v USB sockets, Raspberry Pi, adjustable 12v to 5v step-down regulator, and 16-channel 5v relay board.
If you are reading and considering building your own, please be mindful of using correct wire gauges and fuses. Failing to do so could easily lead to a serious electrical fire.
The units software consists of Raspbian, my midi-to-gpio application (with thanks to rayanfer32) and the midi-to-gpio-web-interface which I’m in the process of building. This will allow control of the unit via a mobile device for the purpose of playing MIDI files or choosing MIDI input.
Here’s a few minutes of the relay board working, being triggered by MIDI playback on the Raspberry Pi. It also performs really well with my MIDI keyboard plugged in via USB.
Each of these 16 relays will have a 12v live running into the common terminal, every time the relay is on (lit up) then the 12v will flow through to a pneumatic solenoid – which will open, releasing air to an air horn. Each of the horns will be tuned chromatically, creating a 16 key horn piano.
Unfortunately I’m having issues with my test horn, however as soon as I’m able to get the horn diaphragm to actually vibrate, we’ll be very close indeed to playing songs on the air horn piano!
The song is Marc-André Hamelin‘s Circus Galop.