The open-source nature of the project also means that you can modify and expand upon the design to suit your requirements. “TheMIDInator is a MIDI controller based on an Arduino MEGA 2560.

When looking through existing Arduino drum kit projects, [joekutz] noticed that most of them just used the microcontroller as an input for an existing MIDI device. That’s fine if you’re… ...

YouTuber Alex Coover, aka Glacial Geyser, has build an awesome Arduino-powered MIDI controller to help with his budding music career. Here's a demo.

For instance, Adafruit has provided the files needed for the ESP8266, which recently received the Arduino treatment.

Is it a keyboard? Is it a guitar? It's the ARKeytar, an Arduino-based MIDI controller shaped as a maple wood keytar.

Thorin Klosowski DIY musical instruments are their own thing entirely, but if you're looking for a place to start, Adafruit has a guide to building your own MIDI controller using an Arduino.