Suitable for clandestine listening and in SMD assembly, this circuit was found in the Radio Eletronics magazine of August 1988. The listening is in headphones and the amplifier is electret.
This circuit was published in an article in Radio Electronics magazine in October 1988. It uses...
This 3-component circuit uses an analog indicator. We found it in an old publication....
This simple circuit can be used to power a simple communication system using ordinary telephones....