This circuit was originally designed to be used in the car. When talking, the sound of the voice automatically lowers the volume of the radio or car sound. The circuit can be implemented with BC548 and BC558 transistors. The small lamp must be mounted in a tube in contact with an LDR, as it is its light that, through the LDR, controls the volume of the sound. The microphone must be piezoelectric, or crystal and the circuit is adapted to the volume of the car sound, which must be of the analog type.
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