The frequency of the tone produced by this oscillator depends on the amount of light falling onto the sensor. The sensor is a common LDR and frequency range can be adjusted by P1. The circuit is powered from cells or battery sourcing voltages in the range between 3 and 12 V. For 9 to 12 V supplies Q2 is a BD136 mounted on a small hetasink. For 3 to 6 V sources the transistor Q2 is a BC558.
Photo Oscillator
