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 circuit is from 1950, from the time when some still called the crystal triode transistor. The circuit is...
In the circuit shown in the figure, when the input voltage rises to 27 V, the TL431 triggers the...
This circuit was found in a Popular Electronics from the 90s. The power source must be symmetrical...