This telegraph monitor was found in an American documentation for radio amateurs from the 1970s. The indicator is a common 1 mA full-scale milliammeter.
This version of the circuit is from 2000, using a source of negative voltage that allows to obtain...
This somewhat complex circuit was found in the May 1984 issue of Radio Electronics magazine. The...
This basic circuit is from an old documentation. The relay must be 50 mA maximum and must have a...