Found in a 90s Popular Electronics, this circuit checks if a remote-control transmitter is emitting signals. The sensor is a general-purpose type found in many electronic devices.
This circuit is from an August 1984 Radio Electronics magazine. It monitors the state of a RAM...
Analog Devices suggests this circuit in documentation from the 1990s. The circuit is for 75-ohm...
This circuit, which can be built with several CMOS gates, was found in the March 1996 issue of...