I made this using a DIY electronics experiment I found online, which shows how to create a circuit attached to an arduino microprocessor. The circuit contains a Piezoelectric sensor (a cross between a contact microphone and a computer speaker) and a photodiode http://en.wikipedia.org/wik... which senses light. Basically, the resulting thing costs about five pounds on top of the arduino (which was a gift) and behaves like a theremin. The arduino is programmed to take the light input and turn it into the frequency of sound on the piezo, which I then played with with my hands and some LEDs. Hope you find interesting stuff in there!