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 was obtained in an Electronic Engineering of the 90s. The operational amplifiers and...
The two amplifiers are practically the same, except for the gain. They have the following...
Found in Popular Electronics from the 90s, this circuit reaches a few tens of megahertz. L1, C1...