A lot of electronic circuits using NE555 timer IC Here is the circuit diagram of a police siren based on NE55 timer IC. The circuit uses two NE555 timers ICs and every of them are wired as astable multivibrators. The circuit will be powered from something between 6 to 15V DC and is fairly loud. By connecting an extra power amplifier at the output you can further increase the loudness.IC1 is wired as a slow astable multivibrator operating at around 20Hz @ 500th duty cycle and IC2 is wired as quick astable multivibrator operating at around 600Hz. The output of first astable mutivibrator is connected to the control voltage input (pin5) of IC2. This makes the output of IC2 modulated by the output frequency of IC1, giving a siren effect. In easy words, the output frequency of IC2 is controlled by the output of IC1.
