Police siren using NE555

  
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A lot of electronic circuits using NE555 timer IC are already published here and this is just another one. Here is the circuit diagram of a police siren based on NE55 timer IC. The circuit uses two NE555 timers ICs and each of them are wired as astable multivibrators. The circuit can be powered from anything between 6 to 15V DC and is fairly loud. By
Police siren using NE555 - schematic

connecting an additional power amplifier at the output you can further increase the loudness. IC1 is wired as a slow astable multivibrator operating at around 20Hz @ 50% duty cycle and IC2 is wired as fast 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 simple words, the output frequency of IC2 is controlled by the output of IC1. For all of you who do not have a clear understanding of the working and basics of the NE555IC, we have provided an online book store for you. Here 3 books are reviewed in detail with links to buy the books online itself. Get your copy now by clicking here:- 3 Great Books to Learn 555 Timer Circuits and Projects



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