Listens to MIDI messages on one pin and triggers drums on the other pins (4 or 5 pins for ATtiny85).
I needed this when making analogue drums loosely following this schematics from Delptronics. I did not want to make a hardware sequencer, so opted to making a simple MIDI input instead.
The code is for ATtiny85, but should work on any Arduino. (For ATtiny85 you can use "Digispark (8mhz - no USB)" board in the Arduino IDE.)
This one is for ATtiny85 but should be easy to apply to any Arduino.