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Advice on a "stretch" sensor

Discussion in 'Electronic Basics' started by Thot, May 19, 2005.

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  1. Thot

    Thot Guest

    I am planning to make a breathing sensor (to check for breathing movements)
    by strapping an elastic band around the chest and attaching a "stretch
    sensor" to it that varies its characteruistics, such as resistence,
    according to how much it is stretched and then recoils when the patient
    exhales . I think somethig like that must exist as it should be something
    like a modified potentiometer. But I don't know its name or where to find
    one with the characteristics I need.

    Can somebody point me in the right direction?

    Thanks

    Luca
     
  2. There is such a thing as a string potentiometer (a rotary
    potentiometer, turned by an unwinding string, and the string under
    tension from a rewind spring).

    http://www.corsa-inst.com/sensorsez/sp10ez.html
    http://www.spaceagecontrol.com/

    But, in this case, the range is so small that I think you could use a
    linear potentiometer with a spring preload. You might be able to
    adapt a slide pot used in audio balance controls.
    http://www.abra-electronics.com/catalog/potentiometers/p1k_sl_pc.html

    The precision ones made for long term motion are kind of expensive:
    http://www.etisystems.com/linearselect.asp

    Maybe you can come up with something based on variable overlap of two
    insulated plates to form a capacitor that varies as the wearer breaths.
     
  3. Another idea:

    Use black antistatic foam, the kind chips are pushed into to keep the
    legs at the same potential.

    Put a few such foam pads between two metal plates, the plates can be
    unetched clean copper pcb material.

    When this sensor is pressed together the resistance through the foam
    will decrease.

    Tie a rope around the chest of the person under test, put the sensor
    between the rope and the chest.

    When air is drawn in the chest is getting bigger, pressing the sensor
    harder together, the resistance between the plates is decreasing.

    Such foam can be used for many other sensor tasks, like put it under a
    mat to indicate when people walk on it.
     
  4. John Smith

    John Smith Guest

    "Rope around their chest". I thought the Spanish Inquisition had ended?

    Anyway... my idea is a strain guage.
     
  5. Z80

    Z80 Guest

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