Police Horn Breadboard Circuit -Reverse Engineering

Thread Starter

Temp_connor

Joined Mar 13, 2020
2
I came across a police-style horn circuit a few months ago. Its sound is basically spot-on and I'd love to make it. The problem? No circuit diagram. When contacted, the author has been unresponsive. In the few responses he has given, he seems unwilling to provide the circuit diagram. Hence, the need to reverse engineer it.

The video is:
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Any help would be appreciated. Based on the resistor color codes I should be able to find out the resistance of the resistors, and I can guess-and-check the capacitors. Does anyone know how to make the colors in a frame more vibrant? The lighting isn't very good in the video.

Any thoughts would be appreciated.
 

SamR

Joined Mar 19, 2019
2,131
Welcome to AAC! Simply Google for siren circuit and you will find many applicable 555 timers used as such.
 

Thread Starter

Temp_connor

Joined Mar 13, 2020
2
Welcome to AAC! Simply Google for siren circuit and you will find many applicable 555 timers used as such.
Thanks for the advice! Will do.

I noticed that his circuit uses two 555 timers, whereas other circuits I've found online (most, actually) use 1. I have a hunch that the second 555 timer is what gives it the better sound, but I'm likely wrong.

Thanks again for the advice!
 

Dodgydave

Joined Jun 22, 2012
9,169
Looks like this circuit, R1, R2 ,C1 set the sweep speed, R3, R4, C2 set the frequency, try 10uF for C1, and 10nF for C2,...
R1, R3 1K,, and R2 220K sweep speed is approx 0.5 to 2Hz, try R4 47K frequency is probably 3.5Khz centred .

20200514_124613.jpg
 
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SamR

Joined Mar 19, 2019
2,131
Read the PDF for the 555. Pin 5 is a bit of a "special case" when using the 555 and has some very interesting application results.
http://www.ti.com/lit/ds/symlink/ne555.pdf?HQS=TI-null-null-dscatalog-df-pf-null-wwe&ts=1589460147773

Then look at feeding the output into an LM386 amplifier chip to make it LOUD! With a bit of playing around with the circuit, you can make some dastardly evil noise.
http://www.ti.com/lit/ds/symlink/lm386.pdf?HQS=TI-null-null-dscatalog-df-pf-null-wwe&ts=1589460877414
 
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