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 figure shows how to measure current with a 3 ½ digit 7107 meter described in Electronics Now...
I found this electronic organ in magazine published in 1976 from my vast collection of foreign...
The presented circuit uses the National Semiconductor's LM3909, an oscillator that operates with...