Police siren circuit given here is a circuit based on NE 555 timer IC. This circuit uses two NE 555 ICs (IC1 and IC2) and which are the core working parts of this circuit. Here two timer ICs are wired to work as astable multivibrators. But these two timer ICs are working at different frequencies. IC1 is slow astable multivibrator operating at a frequency of 20Hz and a duty cycle of 50% whereas IC2 works at 600Hz as fast astable multivibrator. The output of IC1 is fed to the control pin (pin5) of IC2. By this connection, the output frequency of IC2 will be modulated with the output frequency of IC1.
The circuit can be powered from a DC supply voltage ranging between 6V and 15V. Power supply used here is 12V DC supply. The loudness of output can be further increased by inserting a power amplifier circuit at the output stage of this circuit.
- Use a Perf board to assemble this circuit.
- The output frequency of IC2 is controlled by the output of IC1.
- One NE 556 IC can be used instead of two NE 555 ICs.
Use speaker with rating 64 ohm, 500mW.