This circuit cuts out ads between songs, based on the fact that the speech signal has small interruptions that can be detected. The circuit is from a Radio Electronics from April 1987.
This version of a mixer with a transistor appears elsewhere in this section and on this website. The...
This circuit, from a 1995 publication, powers incandescent lamps according to the power grid. The...
This circuit is intended for underwater communications. Of course, the critical point is the...