This circuit was found in a documentation for radio amateurs from the year 70. Its purpose is to produce a tone on a transducer when transmitting messages in SSB telegraphy.
This circuit, found in a 1986 documentation, uses an optical sensor to count pulses and, in its...
This different alarm system, found in an old publication, uses the starter chain to protect the...
This circuit was obtained from an American publication of the 80's. The integrated circuit is of the...