This circuit with the 555, was obtained in a 90s American documentation. The signal must be applied to a good amplifier. The sound is similar to that of a police siren.
This switched power supply was found in a 70s documentation. The basic components are from that...
s. In it, a set of batteries or battery provides the reference voltage for the output. The...
Found in American documentation from the 90's, this circuit activates a 12 V sensitive relay. The...