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Simple Lie Detector

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

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  1. arun babu

    arun babu New Member

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    sir,
    why don't i get the selected thing.i am a student of 15years .give me simple low cost electronic project.
     
  2. colin55

    colin55 Well-Known Member

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    You can get ECG electrodes from a hospital that stick on your skin to create a more-reliable connection. You can then measure the internal resistance of your body.
    Most of the resistance of your body is in the small distance between the outside of your skin and the inside of the skin.
    If you press harder on an electrode, the resistance decreases enormously.
    This effect is much larger than the change in resistance due to sweating.
    That's why lie detectors are so inaccurate.
    I have a circuit for a "super-sensitive" lie detector for those with dry skin.
    A person with dry skin does not activate a simple lie detector AT ALL.
     
  3. Sceadwian

    Sceadwian Banned

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    Actually lie detectors are inaccurate because a knowledgeable tester can manipulate the subject and a knowledgeable subject can manipulate the test. Last time I checked lie detector tests were inadmissible as evidence in US court because the test is so easily manipulated.
     
  4. dave

    Dave New Member

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  5. Leftyretro

    Leftyretro New Member

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    And even at best the interpretation of test results are very subjective.

    I recall some decades ago the show 60 mins did a report/expose on lie detectors and the agencies that contract out their services. It was a setup where they pretended to be a small company that was having some office thefts and that while they suspected a specific employee who they did identify to the testers, they had no proof so wished to have all the office employees tested. The results from three different agencies were all the same and that was that the suspected employee was lying and only he was lying. Of course the suspected employee was an actor (as were all the 'employees') and was told not to lie. Funny that results equaled expectations! Of course all three agencies denied subjectivity (or worst, fraud) and said the tests were flawed because all the actors were not under real life stress. Also turns out that the lie detector association is a very profitable organization that 'sells' certifications for their 'member' agencies and help keep out independent and 'non licenced' and 'unqualified' testers.

    As practiced, at least in that N.Y. city area, it is or was at least then a scam and just a way for some people to make a rather sleazy living.

    Lefty
     
    Last edited: Apr 9, 2009
  6. Sceadwian

    Sceadwian Banned

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  7. Leftyretro

    Leftyretro New Member

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    Interesting read. Did you notice all the exemptions from this law, nearly all government and military are not restricted in anyway from using polygraph testing. :rolleyes:

    Always strange how a goverment for and by the people can often pass laws that apply to normal people but exempt themselves.

    Lefty
     
    Last edited: Apr 10, 2009
  8. Zach

    Zach New Member

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    And for the person looking for the M1 mA reader to make the schematic in pPsice... Just draw a short circuit and put your current probes on that node and have it output that to a graph. I'd take a digital multi meter and measure your skin, and use that as a load across where the electrodes would go. Then graph that current. Then you could increase and decrease the load resistance a little be and see how this effects the current. i.e. you would be modeling it after how a person's skin resistance could increase or decrease and the effect it would have on the current that you are motoring.
     
  9. Zach

    Zach New Member

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    Hey guys I have a question was hoping could be answered. I'm an EE undergraduate student so I have been exposed to many type of transistor circuits.

    Can you tell me what role the capacitor plays in this circuit? I do not understand why there needs to be a capacitor connected in between the two electrodes.

    Thanks
     
  10. Roff

    Roff Well-Known Member

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    The cap is probably not necessary. Human bodies will generally have a lot of common-mode mains-related voltage (primarily 50 or 60Hz, depending on where you live), but this is relative to earth ground. I don't think there will be enough differential-mode noise to drive the transistor into saturation on the peaks, which would screw up the bridge. The cap is probably cheap insurance though, just in case.:)
     
  11. parthibank72

    parthibank72 New Member

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    can any one explain how it will work?
     
  12. colin55

    colin55 Well-Known Member

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    How WHAT? will work.
     
  13. joseflor

    joseflor New Member

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    Any comments if it really works fine? It seams to simple to really work well detecting lies, but it could be possible if the lier is a big one and the person is very nervous.
    Kind regards
     
  14. Nigel Goodwin

    Nigel Goodwin Super Moderator Most Helpful Member

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    Of course it doesn't really work, it's a skin resistance meter, that's all - it will only detect is the person sweats when he lies.
     
  15. joseflor

    joseflor New Member

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    OK Nigel, thanks
    It is for my nethew. Actually he lies a lot and it will be funny to get him.
    Regards
    Jose Flor
     
  16. audioguru

    audioguru Well-Known Member Most Helpful Member

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    People who lie a lot are calm and do not sweat when telling lies. But maybe they get nervous and sweat when telling the truth.

    An expert uses a skin resistance test plus heart rate plus breathing rate plus tremmors in the voice and still are not always correct to determine a lie.
     
    Last edited: Sep 5, 2009
  17. mneary

    mneary New Member

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    You can tell some one is lying when he claims to have a simple design for a lie detector.
     
  18. prashantsingh

    prashantsingh New Member

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    Ultrasonic Vision

    Nice Project sir ,If u hav some projects on ultra sonic vision please mail me............





     
  19. HiTech

    HiTech Well-Known Member

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    OMG!!! The last two pages of this thread are simply hillarious to read! I think Audio Guru has posted more replies here than in any other thread! Hey buddy, you're preaching to a choir that apparently has the collective intelligence of a door knob. I also think we have a troll lurking about since many of the replies are 1-2 post wonders.
    As for the pleading by some of the boneheads to so desparately want to build this basic circuit, by all means go ahead, have at it. In the end you will have accomplished the task of building a basic electronic circuit. However, it's not up to performing the job or specification of it's mis-represented name. You built a circuit, go have fun with it, but don't base your spouse or girlfriend's alleged infidelity on it.

    And to think that some of these nations have peaceful and tactical nuclear capabilites!!!:eek::(
     
  20. pratham7674

    pratham7674 New Member

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    Helpp

    Hey dude ,can i use bc147 npn transister ..will it work ?? Reply me fastt plzzz
     
  21. Techie7

    Techie7 Member

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    dude, you can use 2n4401 or bc547. you should use high gain types for reliability. is my reply fast enough?? ;)
     
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