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.
The gain of this amplifier is controlled by light shining on an LDR. The circuit is from a Radio...
This circuit produces a whistle sound when acting on switch S1. Aids is applied to a transformer that is...
This filter that rejects a frequency range determined by the double-T was found in the August 1993...