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 circuit was found in a 1998 documentation and its purpose is to automate controls by timing its...
This circuit is from a 1977 Radio Shack documentation. It produces a modulated sound of good...
This second-order filter was found in old American documentation and can be applied to other...