makezine.com
In the Maker Shed: 64 Button Shield | Make:
The 64 Button Shield not only allows you to use up to 64 buttons with your next Arduino project, it also has a hidden "easter egg" that allows it to output MIDI. This video demonstrates MIDI functionality by using a 64 Button Shield, a Midivox, and an Arduino together for use as a physical interface for your favorite MIDI compatible music program.