Help please

Discussion in 'General Electronics Chat' started by asdff1818, Dec 9, 2009.

  1. asdff1818

    Thread Starter Member

    Dec 7, 2009
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  2. SgtWookie

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    Jul 17, 2007
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    Gee, your subject of "Help please" does nothing to explain what you need help with.

    The fact that you posted is an obvious indication that you want help.

    I already told you how the lie detector works, and how an Ohmmeter would give a more accurate indication.

    We are not medical people here, and have no qualifications to assess skin resistance vs lying.

    Stop posting this question here, as you will not receive a good answer.

    I'm going to request that this topic be closed.
     
  3. Audioguru

    New Member

    Dec 20, 2007
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    You can use an ohm meter if you want but it won't make the horrible square-wave buzzing variable frequency sounds.

    Even an expert has difficulty determining if somebody is lying. They measure the skin resistance like here, measure the heart beat rate, measure the breathing rate and measure the fluctuations in the suspect's voice frequencies. But some people still fool the experts.
     
  4. asdff1818

    Thread Starter Member

    Dec 7, 2009
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    There is a reason why I put that as a subject. Furthermore, this is a different question which what is the benefit of not using the ohm meter an vise versa. This question has nothing to do with medical stuff, only electronics. And why do it with the frequency sound if it is easier and more accurate to do it with the ohm meter. And why do so many people use complicated electronics to measure skin perspirattion which you can do directly with the ohm meter? What is the benefit, that is my question.


    Thank you both!
     
  5. asdff1818

    Thread Starter Member

    Dec 7, 2009
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    And why will you request this to be closed?
     
  6. SgtWookie

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    Jul 17, 2007
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    I'm requesting that it be closed because skin resistance is not a completely accurate indicator of whether or not a person is telling the truth.

    This topic could waste a lot of experienced peoples' time, instead of helping people who have problems or questions that can be easily solved.

    There is no "solution" to your question. It is merely an academic question that could be argued in finitum, wasting a great deal of time and resources.

    You will not get a definitive answer to your question on this forum, nor anywhere else.

    Closing this thread would be the best answer that you will get.
     
  7. asdff1818

    Thread Starter Member

    Dec 7, 2009
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    I still don't think you understand my question, I am not asking if skin resistance detects lies, but I am asking the best way to build something that measures skin resistance and why and then I will build it.

    Thank you!!!!
     
  8. beenthere

    Retired Moderator

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  9. t06afre

    AAC Fanatic!

    May 11, 2009
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    The setup you should build is a skin conductance meter. Measuring the skin conductance in Siemens, or more correct micro Siemens.
    You should read this
    http://www.sprweb.org/articles/Fowles81.pdf
    http://www.uniklinik-freiburg.de/iuk/live/forschung/publikationen/EDA_JP_2000.pdf
    Also I see no reason in closing this thread. Using skin conductance measurement as lie detector for a party trick or just for fun is well within the scope of this forum. But be aware that it is not a very precise indicator
     
  10. t06afre

    AAC Fanatic!

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    Also if you use Labview I can point you to a very cool project
     
  11. asdff1818

    Thread Starter Member

    Dec 7, 2009
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    Thanks!

    Thank You both for your responses! I think that this is little bit too complex. Is there something a little bit less, but not too easy.
    Sorry I'm still asking this question, but would using just an meter directly work?

    Thank You!!!!
     
  12. t06afre

    AAC Fanatic!

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    No you can not use just your meter. If you read this link, you will understand http://www.bem.fi/book/ Go to section 27 The Electrodermal Response
     
  13. asdff1818

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    Dec 7, 2009
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    I still don't understand why, this is my thought, please tell where I am wrong,

    the when the skin sweats, it becomes a better conductor, and with the ohm meter, you can measure the resistance of something, conductors have less and insulators have more, so when someone sweats it will be less ohms.

    Which part was wrong?

    Thank You!!!!
     
  14. asdff1818

    Thread Starter Member

    Dec 7, 2009
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    Thank You, that was very helpful! So, if I video taped the ohm meter during the questions, would that work? Because I would be listening to the person, and at the same look at the ohm meter, and that would be recorded, so that I could rewind and etc. Would that work?

    Thank You!!!!
     
  15. t06afre

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    What are you trying to do? Your plan is quite futile if you ask me. Also in order to make proper skin conductance measurements, you need medical grade electrodes. Not some aluminium foil coiled around your finger. It seams to me that you jumping into a project, without proper knowledge. It would have helped if you told us more about your project. I have designed and build several medical grade skin conductance measurement system. So I actually do know something about this topic. And I can tell you have much to learn.
    In the picture I have a sample of a skin conductance measurement done with proper equipment and electrodes. As you can see the changes are quite small. And by using dry electrodes you will hardly see a thing.
     
  16. BMorse

    Senior Member

    Sep 26, 2009
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    the op is trying to put together a Lie Detector.... which will be highly unreliable with the way he is doing things.....

    Even sophisticated Lie Detection system results can not be used in the courts of law because they are unreliable... the technology for detecting Lies has not been proven to work...
     
  17. t06afre

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    In this link http://www.sprweb.org/articles/Fowles81.pdf That I have given the OP. It is a very simple circuit what will measure skin conductance. It will give a output voltage that is proportional with the skin condutance. It use DC which I am not very fond of using, as I prefer a low Hz AC. But it is a proper circuit. It will perhaps need a differential amplifier. The OP may try to connect a volt meter in low range to read the output. The OP should at least start with that circuit. Not the one he has now. By the way the circuit I pointed to use a LM113T. This is an old circuit hard to get. Replace it with LM385
     
    Last edited: Dec 13, 2009
  18. asdff1818

    Thread Starter Member

    Dec 7, 2009
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    I`m trying to make a device that measures skin conductance, but not too complicated/complex (not university level or if it is, very basic university, because I am only in grade 8, but I understand things more easily than most people my age, so pretend you are talking to someone older, but not as old as university at the mostly as old as grade 12, but please do take in consideration my age if I don't understand things right away).

    Why?
    What exactly are these?

    I'm Just trying to understand the electronics, not the medical stuff, but, I admit that I don't have much knowledge in this subject, but I do know some about it.

    I am making a science fair project, the purpose of it is to figure out if skin perspiration changes when one lies, and I will be measuring the skin conductance of several people when they are asked questions, and I have to see if it changes when the people lie. If you have ideas for control variables, it would be helpful even though that is not my question. Sorry, I didn't realize I had so little information about my project.

    :) It seems like you are the right person to help me.

    I completely agree. That is why I am seeking for help.

    How can I make a device that can output something like this? I will tell you if it is too complex for me.

    Thank You!!!!
     
  19. t06afre

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    Can you use that building blocks like operational amplifiers (opamps)?
     
  20. asdff1818

    Thread Starter Member

    Dec 7, 2009
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    What do you mean?
     
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