Schematic Volt

Both ic 555 respectively build the astable multivibrator circuit and generate output signals with different frequencies. It is intended to be used as one of the high frequency generator or a screeching sound and the other as a regulator of the swing from last shrill voice. If we observe the working principle of this circuit is very similar to a series of modulation fm. Where the shrill sound signal likened to a high frequency signal from the oscillator circuit and control signal swing is the wail of the information signal or input signals that will transmit. This is consistent with the shape of the output signal associated with the loudspeaker, which has an output signal frequency changes in the form of regular meetings wave tenuous.

Actually a series of sirens could be simpler than if you use a 556 IC which is a dual multivibrator or equal to two pieces of IC 555. IC 556 has two multivibrator circuit menfaatkan so you can meet the workflow of this siren sound-producing circuit. Or you can also make it by using a combination of multiple transistors. And it could be you do remember the oscillator circuit can be easily made with transistors.

Appropriate image above then:

R1, R2, and C1 is a determinant of the frequency of the signal generated by IC1

R3, R4 and C3 is a determinant of the signal frequency whine

Signals generated by IC1 IC2 pin 5 connected to the control signals intended for the resulting shrieks

Screeching sound signal will swing to follow the control of the output signal IC1

You can do experiments in order to gain more understanding of police sirens this circuit by changing the value of some critical components such as the frequency of R1, R2, R3, R4, C1 and C3.