We are going make a Police Siren Circuit using two 555 timer IC. The circuit will produce an up-down wailing sound from the speaker. In this circuit there are two 555 timer ic is used.
Both 555 ic is connected as astable multivibrator/oscillator. In an Astable mode, it delivers a continuous sequence of pulses on its output Pin No. 3, the capacitor C1 charges and discharges continuously .
The first 555 is wired as a low frequency astable oscillator. IC2 is wired as Fast astable Oscillator and output of first ic from pin 3 is connected to shift the signal with control voltage pin 5 of the second 555. Whose frequency is modulated depending on the varying voltage from the IC U1. The voltage shift on pin 5 makes the frequency of the second oscillator to rise and fall.
The frequency range of the siren can vary with the changing the value of R2 and R4 resistor with potentiometer variable resistor.
The circuit can be made with one NE556 ic at the place of two separate 555. 556 has dual 555 timer. Output sound can Amplified for high pitch by using any audio amplifier to make loud sound.
This circuit can be assembled on any general purpose pcb/vero board
555 timer IC – 2
68K Resistor – 1
1K Resistor – 1
10K Resistor – 3
10uf Capacitor – 2
o.1u (104)capacitor – 2
Speaker – 1