This video, via Conor Barry, demonstrates Teeter, a tangible music sequencing instrument.

Technical details:

This turntable based, free-time sequencer uses laser reflections to detect the distance of pegs as they pass by a camera and in turn trigger samples.

Programmed in Max/Msp, the PS3Eye camera calculates the distance of objects based on where the red dot reflection of the laser is on the y-axis of its lens. Up to 8 steps can be tracked reliably across the y-axis, with timing left completely free to the user to place pegs adhering to the visual grid or not.