This old voice circuit suitable for telephones of the time was found in a Radio Electronics from September 1973. The circuit is powered by a voltage of 7 V.
This circuit can function as a light alarm by changing the sound when light falls on the sensor....
Based on a unijunction transistor, this circuit was found in the January 1994 issue of Electronics Now...
Although it is a common configuration today, these circuits were taken from an old publication. The...