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NEEDED: Touch sensitive material (to electronically record linear touch locatio — Parallax Forums

NEEDED: Touch sensitive material (to electronically record linear touch locatio

eeleel Posts: 2
edited 2005-12-07 07:55 in General Discussion
Hi everyone, I used to post a lot on the yahoo board·but just got back to it and·realized it's innactive.·shocked.gif
I'm doing an experiment where someone has to use a finger to touch their·arm at different locations. I want to electronically record the location of the persons touch on the arm. I only need to record how far along the arm the touch occured, I don't need to record how far to the side of the arm.·I was thinking of either a rigid transparent touchscreen (the person would touch the screen layed on top of their arm), or a flexible touch sensitive material that I could tape onto the arm itself. I'm having trouble finding either on google, anyone have any suggestions?· Thanks!· smile.gif

-Lee
P.S. I guess a video system would work too, but I don't want to spend a lot of time or money on a program that would automatically identify the finger and its location along the arm.

Comments

  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-12-06 21:52
    I don't think you need to go as elaborate as a touch screen. The most straightforward method would be to have a carbon strip along the length of the arm and a electrode on the finger of the other hand. Determining position is as simple as measuring the resistance of the loop.

    If you want to get more complicated you can use the natural conductance of the human body, where a finger of the arm to be measured has a electrode that is in contact with the finger. You would then send a low voltage modulated signal (a sine wave should be sufficient) through that electrode. Again you would have another electrode on the finger of the other hand (not in contact with the finger), and when the second electrode comes in contact with the arm (it would have to be bare skin) you measure the attenuation of the signal to determine how far away the two electrodes are. The second method is more difficult because of the following factors:

    skin conduction varies from person to person, requiring a calibration step for each new user.

    skin conduction can vary in real time, this is called the galvanic skin response.

    the amount of pressure used to touch the arm will alter the contact resistance and hence the measured resistance.

    And most important, use low voltages and never use it on a person with a pacemaker installed. Also the frequency of the signal should not approximate any of the biological signals going through a human body, both to increase the reliability of the system and to reduce interference with biological processes·(ie it should not be close to a heartbeat; low voltage, high frequency (in the kHz) is the safest).

    When dealing with running currents through a human body, it is always best to research or hire a professional in the biomedical instrumentation field to advise, at the very least you should use yourself as the guinea pig.


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    Post Edited (Paul Baker) : 12/6/2005 9:56:21 PM GMT
  • eeleel Posts: 2
    edited 2005-12-06 22:15
    Thanks for the advice, the carbon strip idea makes sense, but where can I buy carbon tape from?
    However, I forgot to mention that I'm thinking of training a monkey to do the same task in the future, so I probably can't have anything that requires an electrode on the finger (the monkey would gnaw it off or gnaw on the electrode wire).

    -Lee
    P.S. if anyone else is interested I found a website that seems to have cheap clear touch screens, although I'm still looking for cheaper ways of doing this.
    http://www.ezscreen.com/index.html?target=dept_7.html
  • Paul BakerPaul Baker Posts: 6,351
    edited 2005-12-06 22:33
    A monkey-proof system? You have me stumped, a monkey wouldn't mess with a touch screen strapped to thier arm?

    Here's a site that has all sorts of graphite products: http://www.hpmsgraphite.com/

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    ·1+1=10

    Post Edited (Paul Baker) : 12/6/2005 10:36:44 PM GMT
  • Kevin WoodKevin Wood Posts: 1,266
    edited 2005-12-07 04:43
    eel said...
    However, I forgot to mention that I'm thinking of training a monkey to do the same task in the future

    I think this adds a whole new dimension to outsourcing...icon6.gif
  • kelvin jameskelvin james Posts: 531
    edited 2005-12-07 06:51
    You could look at one of these at this link, will work for touch as well as slide.
    www.qprox.com/products/qslide_qt401.php

    kelvin
  • kjennejohnkjennejohn Posts: 171
    edited 2005-12-07 07:02
    Couldn't you use a jacket with horizontal and vertical stripes every inch? Sort of like wearable graph paper. I've seen monkeys wear clothing, so you could probably get the monkey to wear it. Of course, by monkey I figure you're talking about a chipanzee. If it isn't, all bets are off.
    Any ways, if it would wear a coat (shirt?) like this, you could do short photographic stretches of multiple shots, which most digital cameras do now adays. Use a coordinate system based on the "graph coat" to record his touch point with these photos.

    kenjj
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2005-12-07 07:55
    Regarding a 'carbon strip'....
    You might use the foam stuff that Parallax and others use to ship static sensitive devices.
    It is available in larger sheets which can be cut into strips and is impregnated with carbon.

    I am not sure, but it may be pressure sensitive to so degree [noparse][[/noparse]in close proximity to the actual connection wire].
    So, you may have to protect the areas around your connections with some kind of a 'hard shell'.

    Alternatively, you could easily make a strip of pads.

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    "When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

    ······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan
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