This instructable will tell you how to make your own set of air drums using little more than an Arduino microcontroller and a few accelerometers.
Here's a video of the drums I based this design off of:
My drums feature a number of improvements over those shown in the video:
-Funtional Hi Hat Pedal: Looking at the original designer's code, I noticed he never got the photocell "hi-hat" to work. Instead, he programmed the cymbal drumstick to play a crash at high acceleration and a closed hi hat at lower accelerations.
-More responsive drumsticks and pedals