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.
This circuit is from the 1994 Linear Applications Handbook. The operational circuit can be...
This circuit is suggested by National Semiconductor (now Texas) in an old manual. The circuit...
With this circuit, found in a 80s Popular Electronics, it is possible to use two ordinary phones in a...