A bare bones Arduino ATmega32U4 MIDI implementation with one button.
This is great if you just want some simple MIDI controller foundation code, or if you only need one button. I built this as a PTT button for SDR-Console for QO-100.
For this to work you need to use an Arduino with the atmega32u4 chip as it supports running the arduino as a native MIDI device. Simply wire a switch between pin 8 and GND, power it up and you'll have a MIDI device that sends a noteOn and noteOff with each keypress.