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 a 1979 publication. The sensor consists of plates or screens that, when...
The circuit is from a Radio Electronics from August 1989. The cells used at that time did not have...
The automatic modulated siren circuit shown in the figure really produces an interesting sound...