This photoelectric sensor that triggers a relay was found in an English book from 1989. The transistor is a general-purpose type, and the integrated circuit consists of an operational amplifier.
This voltage inverter circuit is from a Radio Eklectronics from October 1965. It was used in...
Today we have more compact solutions. This is from a Radio Electronics magazine from October 1990....
The circuit presented was found in a 1988 documentation. It consists of an alarm siren that it...