This circuit makes use of a low impedance microphone. The relay is according to the supply voltage which can be between 9 and 15 V. The operational gain is approximately 100.
This sensitive circuit detects the live pole of a power grid or outlet. The circuit makes use of a high...
This FET stage circuit was obtained from old American documentation but can be applied to any FET....
Found in old American documentation, this circuit can use crystals between 27.5 and 33 MHz...