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 English magazine from 1977, but it can be easily assembled since...
This circuit was originally suggested by Texas Instruments, as it is based on one of its...
This circuit was obtained in a 1998 publication, but it can be easily assembled. The circuit...