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Simple Lie Detector

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

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  1. audioguru

    audioguru Well-Known Member Most Helpful Member

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    You need a cheap 1mA analog meter movement, not an over-priced old multi-meter. I don't know if anybody sells a meter movement anymore.

    You need a linear 5k potentiometer, not an audio one.

    The circuit detects that a person is sweating, not lying. Some people lie all the time and do not sweat. Some people sweat when they are telling the truth.
     
  2. wmmullaney

    wmmullaney New Member

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    Aw, c'mon audio, why do you think? I'ts so cool, this is a great starter poject.

    (Are all Canadians like that?)
     
  3. audioguru

    audioguru Well-Known Member Most Helpful Member

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    The lie detector circuit doesn't detect lieing. It is just an ohm-meter that detects sweating and the amount of pressure on its probes.
    If you want to know if somebody is sweating then just look at them, you don't need an stupid simple ohm-meter.

    If you want to know if someone is lieing then look on Google at all the things that are needed for experts to guess (frequently wrong) if they are lieing.
     
  4. dave

    Dave New Member

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  5. Roff

    Roff Well-Known Member

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    It is a good idea to warn people that this is really not a lie detector, but it's still a magical little electronic thing that you can build yourself, play with, show your friends, and marvel at what you hath wrought.:eek:
    Hell, I started out with things as simple as putting a couple of small turns in a piece of copper wire, putting it across a flashlight battery, and wondering why the little coil was the place that glowed red.:D
     
  6. kozer

    kozer New Member

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    hi to everyone!!!this is my first post!!!in my school they tell us to make a simple circuit with orcad and i find lie detector a good simple project but i cant find in libraries where M1 and electrodes are...Can you help me by telling me the names of the parts plz...??????
     
  7. pradeep.durai

    pradeep.durai New Member

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    hi it looks cool and it works!!!!!!!!!1
     
  8. georgie

    georgie New Member

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    i've alrdy know about on this proj...the electrodes are the resistance coming from the tip of the finger...it neutralize how sweat is u'r skin...the more sweat, the more possibility means the person is not telling the truth...^^
     
  9. Willbe

    Willbe New Member

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    You also might look into false positives and false negatives, test sensitivity and specificity, and Paul Ekman's book on lying.

    Took a lie detector test once, and the tester lied to me about the results! I have observed that there is almost nothing that cannot be accomplished by lying.

    You can detect lies, but finding the truth is a bit more difficult.

    As to "other people", try this. . .
    http://www.mcafee.cc/Bin/sb.html
     
    Last edited: Aug 19, 2008
  10. Jerry.J.

    Jerry.J. New Member

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    Help with cad Electronic drawing program

    :(Hi from Jerry.J.(Cape Town) Good to be with you guy's!I am 61 years old and wish you all of the best! Been in Electronics and radio.HT,Pic 16f84 for long time.Go for it!You are our future.I am also a radio ham,ZS1JJM and need a electronic drawing progam in order to be able to send you some of my Ideas.Can anybody help with a "ZIP"? Best to u all Jerry.J.My Email:jerryjean@vodamail.co.za
     
    Last edited: Nov 9, 2008
  11. audioguru

    audioguru Well-Known Member Most Helpful Member

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    I make all my schematics with Microsoft Paint program.
     
  12. Roff

    Roff Well-Known Member

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    I use LTspice, which is a simulator, but has a pretty good schematic capture.
     
  13. Leftyretro

    Leftyretro New Member

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    Same here, started with a lamp. Then advanced to a small motor, but would piss off the parents because the brush noise would screw up their TV reception, we were in a fringe area. Then advanced to crystal radios with a long wire antenna. Heathkits were great.

    Lefty
     
  14. Willbe

    Willbe New Member

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  15. Willbe

    Willbe New Member

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    Even with high accuracy, this concept says you can still be lying, or not.
    Sensitivity and specificity - Wikipedia, the free encyclopedia
    It gets mathematical, with conditional probabilities.

    The way around it is to take several lie-detector/pregnancy/other-medical tests.

    I took a lie detector test once. The test-giver was lying to me about the results! (I didn't get the job, either. . .)
     
  16. Disco Elephant

    Disco Elephant New Member

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    I use this as well, and although it's a little clumsy to use, you get used to it. I like the simulator, but I did find it strange that I put in a circuit for an isolated SM power supply, and it didn't like the isolation, making me earth the input (which is naughty in SM power supplier).

    What's a good program for laying out PCBs? I used to use ezy tracks years ago, but haven't made one for many years.
     
  17. Roff

    Roff Well-Known Member

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    You can generally earth a floating input through a huge resistor, such as 1e12 ohms (1 million megohms).

     
  18. joelumuna

    joelumuna New Member

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    the meaning of electrode

    electrodes is any material that allows electron to flow
     
  19. Ussama

    Ussama New Member

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    It is really gr8......by tha way nice idea 4 tha next science fair....thnx
     
    Last edited: Nov 22, 2008
  20. diablo1

    diablo1 New Member

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    whats a 5K pot mean?? I know what a resistor is but whats a pot? The difference? Also do you need two 4.5V battery sources? What are those in the schematics?
     
  21. Roff

    Roff Well-Known Member

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    A pot (short for potentiometer) is a resistor with a 3rd terminal (wiper) that is a variable tap. If you connect the wiper to one end of the resistor, you have a variable resistor, also known as a rheostat.
    I posted an equivalent version of the original circuit that only uses one 9V battery on page 2 of this thread. I've attached it below.
    You can use almost any general purpose NPN, such as 2N3904, etc.
     

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    Last edited: Nov 22, 2008
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