Optical ThereminChallenger II

The Challenger II is a an optical theremin named after the Space Shuttle Challenger. I built the Challenger II in 2008 along with the Challenger I, which was a similar optical theremin. Challenger I was given away to a local musician shortly after being built.

Challenger II Front PanelChallenger II Front Panel

The Challenger II uses a 555 IC oscillator circuit. Pitch is determined by the amount of light that reaches the photoresistor mounted to the circuit board.

Photoresistor and circuit

There is a small plastic guard that protects the circuit board and acts as a filter for the photoresistor.

Photoresistor behind the plastic panelPhotoresistor behind the plastic panel

The “OSC” LED is tied to the oscillators output, and blinks along with the frequency of the square wave output.

OSC indicatorOSC indicator

The only control aside from the photoresistor is the ON/OFF switch mounted at the top of the face of the unit. There is no volume control; the speaker is hard-wired into the output of the 555 IC.

ON/OFF switchON/OFF switch