This circuit is based on the light comparison of two LDR sensors. We found it in a 90s Popular Electronics. The transistor must be according to the indicator or load being driven.
The circuit shown in the figure is suggested by ON Semiconductor (www.onsemi.com), based on its...
September 2016 - can be found at Mouser Electronics the new amplifiers with digital variable gain...
This simple 1-transistor audio preamplifier appeared in the June 1968 Radio Electronics magazine. The...