NE556 Police siren sound generator

NE556 Police siren sound generator

This is an extremely simple circuit that can produce a siren sound similar to that of an American police car, and the lights will flash synchronously while the siren sounds. This circuit can provide a load greater than 1A, and can drive several lights or a high-power amplifier. This circuit will produce considerable sound and light.

This circuit consists of two astable multivibrators. Here, NE556 is used 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 as astable multivibrator circuits.

First, the timer chip (as shown 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 control input terminal pin 3 of the second timer, so that it works in VCO (i.e. voltage controlled oscillator). The result is that the periodically generated square wave causes the loudspeaker to rise and fall, producing a realistic siren sound, just as you often hear in movies.

This circuit has only a few non-standard components, so you won't run into too much trouble when building the board.