Sound activated alarm

Discussion in 'The Projects Forum' started by abey007, May 18, 2011.

  1. abey007

    Thread Starter New Member

    May 18, 2011
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    Hello here. Am new in this site and i am a beginer in electronics. I am trying to build a sound activated alarm system, with 9v battery as the power supply. I have been able to build the amplifier with the use of lm386 and 741, on which i used electrect mic. I'v built two diffferent oscillators for the alarm.
    My troubles have being swithching the oscillator with the signal from the amplifier.
    I want a transistor latch switching system, such that when the mic signal is fed to the switch via the amplifier, the transistor will switch the oscillator on untill the rest button is pressed. I have atrnsistor bc141 and 2n2222.
    I will be happy for assistance from anyone in the house.
    thank you.
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
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  3. abey007

    Thread Starter New Member

    May 18, 2011
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    thanks for the responds. I'll try to post the schematic 2morow.
     
  4. abey007

    Thread Starter New Member

    May 18, 2011
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    The schematic diagram is in the attachment. I need some help on the switching part of the circuit. someone please help.
     
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  5. abey007

    Thread Starter New Member

    May 18, 2011
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    Some please help me wi the schematic.
     
  6. CDRIVE

    Senior Member

    Jul 1, 2008
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    It's possible that the reason that you haven't received any replies is your schematic. Because of its orientation, it would have to be saved and re-opened in Fax Viewer or other program to rotate it. This equates to unnecessary work on the part of the member helping you.
     
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  7. abey007

    Thread Starter New Member

    May 18, 2011
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    Ok. I'll change the orientation o the shematic.
    Thank u.
     
  8. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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  9. CDRIVE

    Senior Member

    Jul 1, 2008
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    Thanks Kermit2. Obviously, you're not as lazy as me. ;)

    Anyway, take a look at this link. Q1 & Q2 form the basis for a a basic SCR latch.
    http://forum.allaboutcircuits.com/showpost.php?p=315058&postcount=6
    BTW, I think a Piezo would be be more appropriate than an 8Ω speaker. Also, what's the purpose of the .47Ω/5W resistor? Is that used for some attempt at latching? I would loose it!
     
  10. Kingsparks

    Member

    May 17, 2011
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    What is the purpose of the 15n/250V capacitor at the top of the uA741CN? Between pins 6 and 2 except it shows shorted the way your schematic is drawn. :confused:
     
  11. abey007

    Thread Starter New Member

    May 18, 2011
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    Sory i didn't cm here 4 a while.
    Has anyone tried any alteration to the circuit to achieve the aim. Pls help me out on this or any alternative circuit u know can work in there.
     
  12. Kingsparks

    Member

    May 17, 2011
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    First, I am new to this board so you can take my answer at face value. Having said that there are two points I will state then the rest is up to you.

    1) It is obvious you have not even reviewed the response already posted to your request. There are two legitimate answers, either of which would work as latches.

    2) There are two questions, again both legitimate, you have completely ignored.

    Why? I have found in the short time I have been here people will go out of their way to help. If you don't even respond to the post why bother?

    I doubt you will get any further response until you correct this, at least answer the questions and indicate you have explored the solutions suggested.
     
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  13. CDRIVE

    Senior Member

    Jul 1, 2008
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    In your control panel you should have your settings set to receive emails when a reply is posted. Then, as KingsPark astutely noted, you must read the replies.
     
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  14. abey007

    Thread Starter New Member

    May 18, 2011
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    Am sory i didn't respond to most of the questions. This is due to some reasons, ranging frm inadequate experience, lack of internet facilities and inavailability of components in my current location.
    All my attempts to the suggested solutions were extinguished by inavailability of components-expecially transistor and ics.
     
  15. CDRIVE

    Senior Member

    Jul 1, 2008
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    Where did you find the schematic that you posted? It has a few oddities, besides the fact that there's nothing there that will latch. For one thing, the flip-flop drives a TIP42C power transistor, which drives the speaker. Nothing odd about that, except for the fact that the TIP42C, the flip-flop and the speaker gets its current supply from a small signal transistor (BC141)! There isn't much point in having a high power transistor, like a TIP42C, if it gets its supply current from another transistor that's rated at < 1/10th its power and current rating. On the up side, the 1K resistor in series with the speaker won't pass enough current to deliver any real power anyway.
     
  16. abey007

    Thread Starter New Member

    May 18, 2011
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    One of my old friends once worked on this project but he gave it to someone to build. He gave me the schematic to try it out. But the schematic was without the oscillator part, as they used alarm from a toy for the oscillator. I drew the schematic that i posted here, with the schematic that the guy gave me as the amp and latch through the bc141 but the oscillator part is from an old article on biastable multivibrator circuit.
    I testet the oscillor separately and it worked.
     
  17. Kingsparks

    Member

    May 17, 2011
    118
    5
    abey007

    You tried to ask help with another thread and were told to use the one already open. So you must still be interested. Don't be discouraged, no one wants that and understanding your problem with lack of Internet access we will be patient. It was not knowing these things that resulted in no answers to your post.

    Your circuit is workable with a few modifications but you will have to try to meet anyone at least half way, no one is going to just hand you a circuit. That's not what this forum is about.

    Come on back and if there is something someone posted you don't understand, ASK about it. You will be surprised at the response and now that we know you don't have fast access to the Internet we will be patient. I have your post flagged and will be notified any time is is active. So come on in, the waters fine. :D
     
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