We found this circuit in a publication by General Electric in the 1980s. The transistors and the PUT are from that time. The control is done by a tachometer based on an optical coupler.
This circuit is from Radio Electronics. The magazine no more exists, but the circuit can be...
Found in a 1990s US publication, this alarm circuit detects when a light beam is interrupted. Optical...
This telephone circuit was found on a 90's EDN. It keeps a flashing LED to indicate that there was a...