Future Man , the percussionist for the jazz band Bela Fleck and the Flecktones , has a MIDI-based percussion controller, called the Synth-Axe Drumitar, that is worn like a guitar but uses finger-tap sensors for percussion. His version is completely one-of-a-kind, but there is also a commercial instrument, the Zendrum , that is similar in concept. I'd always thought the concept was fun, but since I didn't have the $1500 or so to buy a Zendrum, I thought I'd try to make my own version of the MIDI-drum-in-a-guitar package. The Electric Funkatron is the result.
This instrument has twelve velocity-sensitive percussion pads. When played, an Arduino MEGA converts the taps into MIDI note data which is sent to an external MIDI tone generator (I use a mid-90s Alesis QS7 keyboard synthesizer -- any synth that maps drum sounds to individual notes will work).
I built the instrument into a gutted Guitar Hero controller. The neck buttons are electrically-connected; currently the red button is used to cycle through all 16 MIDI channels and the orange button sends an "all notes off" command in case things get stuck. The others are not used, but could be by reprogramming the Arduino.
As a bonus, the whammy bar on the Guitar Hero controller is used to trigger a "turntable scratching" sound.
I originally built this from July to December 2010. This instructable is reconstructed from memory and my build notes .
Update 1/16/2012: Video added below