In this circuit the LED lights up when the voltage drops below the value set in the trimpot. The transistors can be the BC548. The circuit is from a 1999 American publication.
The circuit shown is from the 1994 National Semiconductor Linear Applications Handbook. The...
This precision circuit, which also functions as a bridge, was found in a February 1967 Popular...
This circuit was obtained from a Hands On-Electronics, an American magazine from January 1987. This...