Hope the video explains everything. The source code is linked below, feel free to use it, modify it, whatever. An automatic light calibration, plastic covers, and a Beagleboard are all that is left to make it a permanent installation. 

I think a nice addition would be to use Liquidware's touch screen for selecting the samples to be played on each step.

Here is the Arduino source code:

...and the processing source code:

Currently working on a little experiment combining a multi-touch screen showing an After Effects animation, taking a shot of each frame, then doing the same with the same scene lit with a softbox. Then combining and inverting the projected image in After Effects.

Kinda looks like a large animated e-ink display. More to come later.