Rhythm Ring percussion sequencer

http://people.ece.cornell.edu/....land/courses/ece4760
The Rhythm Ring provides a tangible method of arranging a musical rhythm. In our design, the user can arrange beats and modify them in real time by moving steel ball bearings between holes—a physical representation of notes on a musical staff. The Rhythm Ring continuously loops up to three tracks, each with its own voice. A central ring of LEDs provide the user with live feedback for current "playhead" position, and bright LEDs pulse when a note is played due to a detected bearing. The three tracks allow the playback of three different percussion sounds: snare, hi-hat, and bass drum. See also
http://www.youtube.com/watch?v=hLHauwG_SJ8