siren circuit

Thread Starter


Joined Feb 8, 2012
wow. i just thought i could find help here. i guess i just found feeling smart people as in STUPID and boastful people.

Thread Starter


Joined Feb 8, 2012
well i'm sorry if i'm not as "intelligent" as you, to know what a feedback is and i'ts function.

you're not helping, you're humiliating.

Thread Starter


Joined Feb 8, 2012
it's ok. i guess i just have to find help with other people-- humble people. i hope you won't do that to other members in this site.


Joined Mar 24, 2008
I can't explain the circuit in totality my self, though I can explain parts of it. Many people won't jump in unless they can understand everything in a circuit.

I have a much older version of a siren that reminds me strongly of this one. If you want I can show you the schematic.

Many times the secret to full understanding is to break it up into smaller and smaller pieces until there is nothing left. My impression of the parts you are querying is they are a part of the frequency selection, the notes and tone of the siren.

I suspect R!f@@ is having a bad day, normally he has more tact.


Joined Dec 20, 2007
The resistor and capacitor apply the signal from the output transistor to the input of the first transistor of the oscillator creating positive feedback. Then a signal goes around and around between the two transistors and makes the oscillation sound.
The capacitor blocks the DC but passes the signal.

Ron H

Joined Apr 14, 2005
R!f@@, you seem to be violating the advice in your posted signature:
Do not get angry and do not be harsh because you will never regret being kind
I hope you went to get coffee, or whatever gets you going.:p


Joined Jan 10, 2012
Q2 and Q3 make an oscillator. That's what makes the 'sirene' sound. The resistor/capacitor, R7 &C3 are the positive feedback network. Together, they sustain oscillations and determine the frequency of the oscillator. The frequency is forther affected by the voltage across C2, which charges and discharges slowly, making the frequency slowly rise and fall. At least that's how I think it works.
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