These optical relays, which can act as a shield, were found in an American documentation from the 1980s. The circuit has a LDR sensor. It can be adapted for other types of sensors.
We find this circuit in a 1974 Motorola PUTs (Unijunction Programmable Transistors) documentation. The circuit...
This electronic roulette has several draw options depending on the position of the selector...
This simple circuit for experimental LED sequencing is based on a multivibrator with transistors....