This quarter, Brie Bunge and I built a new musical instrument in the form of a giant musical kaleidoscope for Music 250A: Physical Interaction Design for Music. It consisted of a triangle of mirrors with two spinning bicycle wheels at one end, where one wheel controls the melody and the other the harmony. We filled the spokes of the wheels with colored gel slides.
The musical component came from an Arduino hooked up to a laptop, with magnets on the spokes providing the input via Hall effect sensors. The laptop generated notes each time a magnet passed a sensor, based on a probabilistic model. We also learned how to weld in the process! (And sanded a tremendous amount of grease off of steel pipes...) See the full writeup for more pictures, or check out the instrument in action: