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 is the receiver circuit for the previous remote control published in the same Radio...
This circuit, for signals up to 1 MHz, is based on an RCA operational amplifier. The circuit was...
This frequency shift modulation circuit was found in the November 1994 issue of Electronics Now...