This circuit is from a June 1992 Radio Electronics. The circuit is for 4.5 MHz signals from old analog televisions or other similar applications.
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...