4chord MIDI

4 Chord USB MIDI Keyboard

4chord MIDI board

4chord MIDI is a USB MIDI keyboard to simply play the four chords of the I-V-vi-IV progression. Why? Because The Axis of Awesome made it clear, all it takes to make a hit pop song is those four chords.

4chord MIDI functions like a regular USB MIDI controller just like any other MIDI keyboard, except it has only four playback buttons - and of course additional buttons and a LCD as user interface to adjust the playback. Playing just the chords as triads is a bit limiting after all.


4chord MIDI is under active development and therefore new features will come. As of right now, the following features are already implemented:

  • I-V-vi-IV chord progression in any key
  • Chord, arpeggio and mixed playback modes
  • Arpeggio playback in any tempo from 30bpm to 240bpm
  • User interface to selected key, mode and tempo


4chord MIDI is built around an ATmega328 microcontroller with custom firmware using V-USB. A Nokia 3310 LCD and three buttons serve as user interface. The PCB is credit card sized, uses SMD components and is directly powered from USB, so no extra power supply needed.

See the Technical Details page for further information on hardware and firmware.


4chord MIDI is fully open. The hardware is licensed under the CERN Open Hardware License v.1.2 and the software is released under the GNU General Public License version 2.