Police Siren Alarm: Electronics Mini Project

Hi friends, in this series of mini projects today we are going to make one simple mini project of police siren alarm using IC 555 (timer IC). This mini project generates a sound like police siren using astable multivibrator circuit of NE555 timer IC. You can make this project as your first or second year engineering mini project. This is one of the simple but useful mini projects and all components used in the circuit are easily available.

Components required

• Two NE555 timer ICs


• Resistors and Capacitors as shown in circuit diagram of police siren alarm


• Speaker (64 ohms, 560mW)


• 12 V DC power supply

Circuit Diagram

[caption id="" align="aligncenter" width="300"] Police Siren Alarm using 555[/caption]

Working of Police Siren Alarm Circuit

As discussed earlier this circuit uses two NE555 timer ICs which are connected as an astable multivibrator. This circuit can be operated on the 12V dc power supply (you can also use 9V battery). To generate a siren sound we have used a speaker having specification as 64 ohms and 560 mW.

In this circuit, IC1 is used as slow astable multivibrator which works at 20Hz and having duty cycle as 50%. IC2 is fast astable multivibrator and having high frequency than IC1 nearly equal to 600Hz. These frequencies of IC1 and IC2 depend on values of resistors and capacitors used in the circuit.

Because of two different frequencies of IC555 and output of first is connected to the second it produces sound like a police siren.

See also: Rain detector with alarm - mini project.

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