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.
The idea of this circuit from a 1960 publication is simple: we can switch the transistor being...
Using a small speaker as a microphone, this 10-LED circuit was found in the March 1992 issue of...
We found this circuit in a 1977 documentation. The National Semiconductor's LM380 is no longer...