This circuit was found in a Popular Electronics from the 90's. The operating curve is given next to the diagram. The power transistor must have a heat sink.
This circuit was found in old American documentation. Transistor is general purpose and relay is...
This simple alarm with latching uses a relay as the main element. The circuit is from a Radio...
This circuit is from an Italian publication called Fare Elettronica from 1987. What we have is an...