This is another cool design that took me a loooong time to post, since i had some "minor" problems with my motherboard. Chris from pyroelectro sent me this link. Chris made a simple (yet working) theremin which can play the base notes from one octave to another (C4 to C5). The IR proximity sensor detects how far the hand (or an object) is and the instrument produces a specific pitch for that distance. The circuit is based on the PIC 18F452 microcontroller. Watch the following video, and visit this link for a detailed documentation. Thanks [Chris]!