This circuit is based on the light comparison of two LDR sensors. We found it in a 90s Popular Electronics. The transistor must be according to the indicator or load being driven.
In the figure we have the way to make the three-phase control of a motor using opto-diacs. The circuit is...
This circuit for testing the voltage gain of a transistor was found in the March 1953 issue of...
This circuit was found in a PE Hobbyst Handbook from 1992. The second oscillator is a VFO. The...