This circuit is from a Popular Electronics from the 90s, consisting of a repeater relay for remote control of TV, which today can be done by Wi-Fi or other simpler resources.
This well-known siren configuration using complementary transistors is from a 1980s documentation. The...
This circuit was found in an old American magazine and could make use of more modern components...
This circuit is from the Philips integrated circuits manual of 1990. It is intended for magnetic...