I am going to attempt to create an electronic drum kit with an Arduino and some coffee cans!  Based on the Knock Sensor circuit and the code for Drum Kit Kit I think I’ll be able to do it…  I will post updates as they happen.

http://www.spikenzielabs.com/SpikenzieLabs/Serial_MIDI.html – info and links for the software portion that runs on your Mac

http://todbot.com/blog/2006/10/29/spooky-arduino-projects-4-and-musical-arduino/ – shows diagram of circuit with resistor and xener diode so you don’t blow out your Arduino

http://www.spikenzielabs.com/SpikenzieLabs/DrumKitKit.html – shows construction of pads and everything, with links to Serial Midi software, and most importantly an Arduino Sketch