This circuit from a Popular Electronics from the 90s uses a common optocoupler and a general-purpose transistor to control a sensitive relay that can be from 6 to 12 V.
This circuit is from 1990 documentation. When we press D1 the lamp remains on for a time interval that...
Some old multimeters have a high resistance scale that has an internal circuit powered by a 22.5 V...
This circuit, from a 2001 documentation, appears elsewhere on this site. Its purpose is to obtain a...