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Simple Lie Detector

Discussion in 'Electronic Projects' started by ElectroMaster, Jul 19, 2002.

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  1. haka

    haka New Member

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    cos i still not sure for it circuit.. so any1 can helping me?
     
  2. akg

    akg New Member

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    it just measures/ shows the variation in the skin resistance(aka galvanic skin resistance) .when we lie , biological changes occur in our causes perspiration , so that the skin resistance goes low .
     
  3. Elektrohead

    Elektrohead New Member

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    Hi all, Noob here, just wondering if you can tell me what size wire I need to use?
    I have some 30awg solid, will this work? Thanks
     
  4. dave

    Dave New Member

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  5. Roff

    Roff Well-Known Member

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    Yes. It needs to be insulated except where connections are made.
     
  6. Elektrohead

    Elektrohead New Member

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    Cool, thnx Ron.
    I'll post a pic once I am done and get it working. :)
     
  7. kambliarup

    kambliarup New Member

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    Impressive Post
     
  8. rishirajarora

    rishirajarora New Member

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    hi.i hav made this project but i hav used power transistor BD115 instead of 2N3565.Can u tell me whether it is ok or not and if not please tell me the transistor as 2N3565 is not available in the market

    with regards
    Rishi Arora
     
  9. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    I wouldn't have thought it suitable? - you just need a general purpose small NPN transistor - NOT a power transistor, it will have too low a gain.

    Try a BC109, which should be ideal!.
     
  10. muki55

    muki55 Member

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    Cool!!!!!!! Thanks for the great idea.
     
  11. muki55

    muki55 Member

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    Its better to use analog meter w/ needle in the center
     
  12. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The electrodes are the parts of the circuit that touches your skin for the circuit to measure the resistance.
    Electrodes are usually made from rotting dead fish, aren't they?:D
     
  13. sahil_maratha

    sahil_maratha New Member

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    Thanks for giving this valuable and simpe circuit. But I am unable to get this transistor . Can u think this will work with any other transistor like BC 548 or simply tell me about the equivalent. Thanks again...
     
  14. audioguru

    audioguru Well-Known Member Most Helpful Member

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    This simple circuit will work with any little NPN transistor.
     
  15. weegee

    weegee New Member

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    what mods would i need to do, to measure this as a voltage on my sillyscope??

    Is it just a case of putting a load resistor in place of the meter, and probing either side with the scope?
     
  16. Tarsil

    Tarsil New Member

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    Made the circuit ...it's quite a nice gadget :lol.I used something like 0.5X2.5 inches strips of metal (Al) with tape as electrods. I used a 2n4401 transistor.
    I already cought my girlfriend lying :lol.
     
  17. HiTech

    HiTech Well-Known Member

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    Yeah, it's always wise and best to thwart future problems by dumping her now. And to think you have a 1-transistor circuit to owe it all to.
     
  18. LeeMorgan

    LeeMorgan New Member

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    Lie Detector Question

    Hi everyone -

    Just wanted to know why exactly there are two power supplies in the lie detector circuit as opposed to one - what is the function in relation to how this circuit works?

    Thanks!
    LM
     
  19. Roff

    Roff Well-Known Member

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    I posted a single-supply version on page 2 of this thread that is identical in function. Here it is again.
    The circuit is a Wheatstone bridge.
     

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  20. LeeMorgan

    LeeMorgan New Member

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    Hmm...

    Thanks for the reply, Ron - I like your schematic alot. My class will be building these and your version will allow us to have smaller groups working on this since we will now have more power supplies to work with. I see how your particular circuit can be re-drawn to essentially be a wheatstone bridge circuit. However, I am still a bit stuck on how the original circuit can be represented this way with those two power supplies. Why did the designer feel that two power supplies were needed in this circuit?
     
  21. audioguru

    audioguru Well-Known Member Most Helpful Member

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    Your class doesn't need any power supplies. An ordinary little 9V battery can be used.
     
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