This circuit was found in 80's telecom documentation. Its purpose is to control a microphone in the process of transmitting voice and Morse signals.
We found this circuit in November 1983 Radio Electronics magazine. The circuit drives an LED and...
This circuit was found in a documentation of the 80s, having didactic purpose. For R1 values...
This circuit was found in a 73 amateur radio magazine from the 90s. An LED extends the scale from 0...