This circuit detects when an audio signal exceeds a certain level or even occurs due to an object falling, a door slamming or other. The circuit is from a Radio Electronics from January 1980.
This circuit has the transistor chosen according to the maximum current desired at the output. Unlike...
We found this configuration with CMOS-compatible output in the 1994 National Semiconductor Linear...
This very low frequency amplifier has a gain of 1,000 and was found in a 1967 documentation. The circuit is...