This post presents circuit which produces a long up and down variation of the sound that similar to police siren. Circuit is based on two 555 timers which operates in astable mode. In this mode a square wave output is generated.
|1.||Power supply (9V)||1|
|7.||10μF electrolytic capacitor||2|
|8.||100nf ceramic capacitor||2|
Circuit is designed on a breadboard.