Here's the basic idea - to place a row of LDRs (light dependent resistors) in a row, then place the whole lot inside a box. The inside of the box stays darks, and a small pin-hole is placed in the lid. Each LDR can now receive just a little bit of ambient light, but only from a specific direction. By moving your hand around above the hole, each LDR should be affected but only when your hand covers a narrow region above the box.
By doing this, we should be able to map when the user has placed their hand to a specific sound-trigger. I think this is how the pinhole light harp works. We're working on creating a digital trigger device to begin with, then we'll add an ultrasonic range-finder to calculate how high the player's hand is above the instrument (perhaps to increase volume or play different notes).
