Ne556 Police Siren Sound Generator Circuit

By Author: Jennie
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This is an extremely simple circuit that can produce a siren sound similar to that of an American police car. The alarm lights will flash simultaneously when the alarm sounds. This circuit can provide a load greater than 1A, can drive several lights or high-power loudspeakers, this circuit will produce considerable sound and light.

This circuit consists of two astable multivibrators. NE556 is used here instead of the commonly used 555. You can also use two separate 555s, if you think this is more suitable for you. Both timer chips are set up as non-steady-state multi-resonant circuits.

First, the timer chip (as shown in the figure below) generates a 2Hz square wave signal at pin 9 by setting the parameter values ​​of R1, R2 and C2, and controls the on and off of the power transistor T1 to control the on and off of the warning light La1. Secondly, the timer chip (as shown in Figure 1) sets the values ​​of R4, R5 and C4, and generates a square wave at pin 5 to drive the loudspeaker LS1. The switching voltage generated by the first timer pin 9 periodically charges and discharges the electrolytic capacitor ...
... C3 through R3, and C3 is connected to the second timer control input pin 3 to make it work on the VCO (voltage controlled oscillator). The result is a periodic square wave that causes the loudspeaker to rise and fall, producing a realistic police siren sound, as you often hear in movies.
More information:
https://www.utmel.com/components/ne556-dual-timer-ic-circuit-pinout-and-datasheet?id=156