This optical theremin was found in a 90s Hands-On Electronics. The basic frequency is given by C1 and the output is made in a speaker through a small output transformer.
This simple CMOS metronome circuit can be mounted in a small box, providing both sound and light...
Although indicated in the original publication of the 1980s as a capacitance switch, the circuit...
In the figure below we have a simple way to do chroming, silvering or another type of...