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Audible sensor?

Discussion in 'Sensors and Actuators' started by heathen, Dec 21, 2012.

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  1. heathen

    heathen

    2
    0
    Dec 21, 2012
    Hello all,

    I am very sorry if this is a stupid question or in the wrong forum (i was going to post in the parts forum, but this is for a circuit i want to build as a little project)

    i am looking to see if there is such a component that will act as a switch when audio above a certain threshold is picked up... and could be used on a 9v battery circuit.. basically to power one or two LED's as an alert.. however i also want the LED's to remain on for one minute after the component has been triggered... so i also need to know what kind of component i would need for this?

    Would i need a capacitor to store up enough power to power it for one minute? or would i just need to have the audio sensor act as a relay switch to power on some kind of component switch that auto shuts off after one minute?

    As you can probably tell by now i am a newbie to this so im sorry if im talking complete nonsense

    Thanks
    H
     
  2. davenn

    davenn Moderator

    13,721
    1,913
    Sep 5, 2009
    hi there
    welcome to the forums :)

    yes it is possible, just not with only 1 component
    its a reasonably involved circuit with several stages to it

    1) -- a microphone to pick up the sound
    2) -- a preamplifier to boost the tinly signal level from the mic
    3) -- a level detection circuitry ( probably based around an Op-Amp)
    4) -- whose output will drive/trigger a timer circuit, based around a 555 timer chip
    5) -- whose output will drive the LED's

    now knowing those basic requirements ... what are your electronics skills like to build something like that ? :)

    Dave
     
  3. kong

    kong

    122
    2
    Sep 26, 2010
    I have worked with this type of circuit before, and I happen to have found one searching the web that works well. It's relatively simple, depending on your experience. I will post the link. It might be a little too involved but I'll post it anyway and hopefully it will be of use to you. http://lucidscience.com/pro-sound activated camera-2.aspx
     
  4. kong

    kong

    122
    2
    Sep 26, 2010
    I see you also would like it to remain on for one minute, this circuit won't do that, but it's a good starting point anyway. There are several simple solutions to that problem, probably a 555 monostable circuit would be simplest. Here is a good site that is very informative and has a schematic of one. You will need to calculate the values of R and C to get required time delay. The 555 is accurate up to about 10min. http://www.kpsec.freeuk.com/555timer.htm
     
  5. davenn

    davenn Moderator

    13,721
    1,913
    Sep 5, 2009
    interesting little circuit :)

    I suspect you would have problems extending the delay out to a minute or greater considering the values already used just to get a 1 sec delay

    hence why I suggested the 555 timer .... so replace the 74121 with a timer cct and keep the front end components

    Dave
     
  6. kong

    kong

    122
    2
    Sep 26, 2010
    You would have to substitute the 74121 for the correctly calibrated 555 timer. The 555 can source up to 200mA out of pin 3, so no transistor is needed to drive relay. Remember to use a protection diode in reverse on the relay coil. If any of this is unclear to you, do not fret, the second link is very good for beginners and is very informative. It covers most everything you need to know. Come back and ask if you get stuck, though.
     
  7. kong

    kong

    122
    2
    Sep 26, 2010
    Yep, you'll want to replace the 74121 with a 555. I hope that helps! Good luck to you!
     
  8. heathen

    heathen

    2
    0
    Dec 21, 2012
    Wow thanks for the help guys!! you have given me a great base to start on my quest for knowledge...

    My previous experience is novice but capable, i worked for a repair depot many years ago and would often be tasked with replacing resistors and such from faulty boards, however these were with specific fault report cards so i knew exactly what components needed to be replaced, i wouldn't have been experienced enough to actually diagnose the fault..

    I am very grateful for the warm welcome to the site and thanks for giving me a starting point..

    Cheers
    H
     
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