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 is from a 1995 publication. The components are all common and the number of LEDs may...
This circuit, found in a 1995 documentation, is intended for switching composite RGB video signals...
This circuit is from Motorola's Linear Interface ICs of 1993. The integrated circuit is not common...