Found in an EDN from the 1980s, this circuit uses a double 555. The circuit activates a relay that controls a horn or siren. Next to the diagram we have the timings.
I found this circuit in a 1980 documentation, but it can be easily assembled with BC548...
This circuit is from the Audio Handbook of the National Semiconductor of 1977. Its purpose is to...
We found this circuit that warns when the gate of a house is opened in an old documentation,...