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 amplifier with very high input impedance was suggested by Texas Instruments in a manual of...
This circuit is from a documentation from the 70s. The circuit uses logic gates of the time, which...
This 80's circuit uses a germanium transistor like the AC121. The circuit has an output...