siren circuit

Discussion in 'Homework Help' started by iamapril, Feb 12, 2012.

  1. iamapril

    Thread Starter New Member

    Feb 8, 2012
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    Good evening! need your help guys! what is the purpose of the 10nF capacitor in series with 22K resistor in this circuit?

    >circuit attached
     
  2. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    They are the feed back components
     
  3. iamapril

    Thread Starter New Member

    Feb 8, 2012
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    what are its functions? need more explanation please. thanks
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Umm hello.....Feedback......ring a bell.

    Don't tell me u do not understand feedback, now.
     
  5. iamapril

    Thread Starter New Member

    Feb 8, 2012
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    wow. i just thought i could find help here. i guess i just found feeling smart people as in STUPID and boastful people.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    Noooo! my dear it's not that...

    you are asking a silly question.

    Do you know what feed back is ?
     
  7. iamapril

    Thread Starter New Member

    Feb 8, 2012
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    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.
     
  8. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    I am sorry ..I did not mean to humiliate you....forgive me.

    I gtg ..will be back in a few minutes.
     
  9. iamapril

    Thread Starter New Member

    Feb 8, 2012
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    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.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    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.
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    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.
     
  12. Ron H

    AAC Fanatic!

    Apr 14, 2005
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    R!f@@, you seem to be violating the advice in your posted signature:
    I hope you went to get coffee, or whatever gets you going.:p
     
  13. Brownout

    Well-Known Member

    Jan 10, 2012
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    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.
     
    Last edited: Feb 12, 2012
  14. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    It was one of those days..:(
     
  15. Ron H

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    Apr 14, 2005
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    Yeah, I figgered as much.:D
     
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