The guys over at Nerd Kits have made a cool Human Theremin project that uses Infrared Light. IR light from an infrared LED is bounced off someones hand and some of the light is reflected back onto an infrared transistor. The closer the hands are the more IR light is reflected back onto the IR transistor. The output of the IR circuit is fed into a Nerd Kit microcontroller and sounds are created based on the analog values. As Humberto demonstrates this makes for a cool wearable project that allows for cool interactions. The same IR technique was used in the Nerf Gun Hack when an IR LED and IR transistor were used to make an invisible beam which fired the gun when crossed.
“This project recreates the properties of a musical instrument called the theremin. A theremin is played without the performer having physical contact with the instrument. A “normal” theremin uses two antennas and changing electric fields to sense the position of the players hands (not unlike our previous Capacitive Proximity Sensor from last Halloween); one hand controls the pitch of the note, and the other hand controls the volume or amplitude of the note.”