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Detecting a Thumb Touching a Finger on Same Hand?

  1. Jul 21, 2016 #1
    Would it be feasible to wear something on a wrist that could detect when the wearer's thumb is touching another finger on that same hand? Through changes in capacitance and/or resistance maybe – or something?
    If so, would it be able to tell which finger the thumb is touching?
    Where on the finger?

    If not something worn on the wrist, perhaps a ring worn on the thumb (or both – as long as they're not hard-wired together?
    Perhaps transmitting an RF signal and measuring the interference – kind of like the way a metal detector works?
    Something else (other than visual)?
  2. jcsd
  3. Jul 21, 2016 #2


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    If the user were wearing a special glove, it would make things a lot easier. Is that a possibility? Is this for a game input device?
  4. Jul 21, 2016 #3
    Not a game input device, necessarily, but an input device.
    No gloves or finger sensors. It has to be as unobtrusive as possible. Either a self-contained wrist device that could pass as a bracelet or watch, a self-contained ring that just looks like a ring, or both, connected wirelessly.

    Wouldn't touching a finger affect the electrical properties of your thumb in some measurable way?
  5. Jul 21, 2016 #4


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    Not that I can see with a quick glance. Perhaps others can see something I'm missing.
    You probably could detect the thumb touching a finger by mechanically sensing the movement of the proximal (near) end of the 4 finger metacarpal bones. If you feel just distal (out past the end) of your wrist bones where the metacarpal bones join the wrist, you can feel each finger's metatarsal bone lift slightly when you touch your thumb to that finger. It might take some experimenting to see how good the signal-to-noise ratio is, though. You could make a sort of bracelet that extends just distal past the wrist socket to sense the movement of the ends of the 4 finger metacarpals...

  6. Jul 21, 2016 #5
    What if the ring transmitted a signal, using the thumb as an antenna, and the bracelet were a receiver?
    Would touching a finger change the structure of the "antenna" and allow the bracelet pick up on the difference?
  7. Jul 21, 2016 #6
    ...for some reason I can't find the right keyword anymore, but a while ago I did some searching on some similar concept, and there's it seems to be some active research going on in this area right now.

    Some things that showed up right before:

    Body area networks: https://en.wikipedia.org/wiki/Body_area_network:
    Intra-Body Communication for Biomedical Sensor Networks,
    Comparison of Approaches to Intra-Body Communication

    The basic idea seems to be to use the body as a medium to transmit/receive a signal.


    Or with some kind of thimble? On the thumb that makes good contact to the skin underneath, and then measure the resistance/capacitance (or some other property, like frequency attenuation of an electrical signal or even acoustic/vibrational signal), when sent out through the hat, and receive again on the surface of the thimble... to discern between every of the 4 fingers. Or even those of the other hand?
    Last edited: Jul 21, 2016
  8. Jul 21, 2016 #7

    jim hardy

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    Last edited by a moderator: May 8, 2017
  9. Jul 21, 2016 #8
    A passive NFC tag embedded into the ring... Could touching the thumb to one of the fingers cause a slight shift in the effective length of the tag's loop antenna?
  10. Jul 22, 2016 #9
  11. Jul 22, 2016 #10


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  12. Jul 22, 2016 #11


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    Looks similar too and a very modern condensed version of this ?:smile:

  13. Jul 23, 2016 #12
  14. Jul 23, 2016 #13


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