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 is from an old American documentation, from 1977, but it can be implemented with more...
This circuit was found in a 1970s American documentation. It can be applied to almost any...
This circuit generates an accurate 1 Hz signal controlled by a crystal. The circuit is from 1995...