This circuit makes use of a low impedance microphone. The relay is according to the supply voltage which can be between 9 and 15 V. The operational gain is approximately 100.
This Intersil circuit was found in a 1980s documentation. Operational are of the time, but current...
New Low-Power PIC24 “GA7” Microcontroller Family Now Available CHANDLER, Ariz., Dec. 12, 2016 — The...
This circuit was found in a 1976 NASA manual, making use of components of the time. The transistor...