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.
This configuration found in GE documentation from the 90s, can also be seen elsewhere in this...
ST Microelectronics STSPIN32F060x Three Phase 600V Controller This STMicroelectronics component...
We found this circuit in the June 1992 issue of Radio Electronics magazine. The sensor is a common...