NE555 Police Siren Circuit

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.

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M 3482 Alarm Water Sensor Circuit

This is an easy musical alarm circuit that produces a musical tone when water or some conducting liquid comes in contact with the two sensor wires provided. The circuit is based on four transistors and one melody generator IC (M 3482).

When water comes in contact with the sensors wires A & B, the base of Q1 gets connected with the negative and it conducts. This makes Q2 and Q3 ON. When Q3 is ON the power is available for the music generator circuit and it starts producing 12 totally different melodies one after another. The music continues as long as there's water between the sensor wires. The POT R12 can be used as a volume controller.

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