I made a light theremin -- basically the same as in the Starter Kit tutorial book, but I've extended it so that it plays discrete tones (a common scale á la C, C#, D, D#, etc.).
Additionally, I wrote a simple HTML page and some JavaScript code, that changes the brightness of the computer's monitor, so that I can play music with the light theremin by "reading the song from the screen".
Check out my blog, that contains a video:
http://danbod.blogspot.se/2013/03/arduino-project-screens-brightness.htmlThe source code is on GitHub:
https://github.com/bodnerdan/js-arduino-theremin Very basic, but hopefully an inspiration for someone else!
