ABSTRACT
The photoresistor changes resistance in response to changes in light level. This change is harnessed in resistance to control the pitch, volume, and filtering of an oscillator. The photoresistor can also be used as a gate or volume control to pass, block, fade, or pan any audio source (such as a music file or an electric guitar) and can substitute for some switches in toys, keyboards, and other circuits. By adding a second photoresistor and some more connectors and audio devices, one can expand the gate into a light-controlled panner or mixer. The basic panner/mixer circuit can be expanded with more photoresistors, inputs, and/or outputs to make four-channel panners, multi-channel mixers, etc. Modulating the pitch of a photoresistor-controlled audio oscillator with an LED blinking at a genre-appropriate beats-per-minute yields a pleasingly disco-tinged “Syn-Drum” swoop. Sometimes, if the on-resistance is low enough, a photoresistor can be substituted for a low-current switch.
