This circuit is from American documentation from the 70s. The circuit makes use of the operating system of the time, but it can be implemented with more modern equivalents.
This is yet another version of the light-controlled oscillator that can be found on this website. This...
Originally created to feed the filaments of a 12AX7 as an audio preamplifier to eliminate the...
The incidence of light in the LDR causes this circuit to start operating, emitting a sound whose...