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.
Found in a PE Hobbyst Handbook of 1991, this circuit was originally proposed to time photographic...
This TTL circuit was found in an American documentation from the 80s. The components are common in the...
Versions of this circuit have appeared several times on this site and even in this section. This...