To send MIDI to the drummer from your computer's USB port, you'll need a MIDI-capable music application such as Garageband, Reaper, or Ableton Live. You can use a MIDI keyboard with your music app to control the the drums, but it's more fun to compose sequences and play them back over MIDI. Fast, complex sequences actually sound pretty impressive on this little kit.

Here's my kit playing a sequence from Ableton Live …

MIDI Map

The code responds to MIDI note on messages for the following note/pitch numbers: 

• 24 (C1) = port 2
• 25 (C♯1) = port 3
• 26 (D1) = port 4
• 27 (D♯1) = port 1

Solenoids will be triggered by these notes on any MIDI channel.

Limitations

Because the drummer code needs to pause and wait for a very short amount of time while each solenoid is powered on, it is only able to process one note at a time.  This means that when 2 different drum notes are received in fast succession, only one will be played.