Assessing how open something is ...

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  • chris_j_hunter
    Automated Home Legend
    • Dec 2007
    • 1713

    Assessing how open something is ...

    looking for a way to measure just how open or closed a window or curtain or door or draw is .... one way might be to adapt a retractable pull-cord device - the sort of thing used for badges & passes ... eg:



    one with a centre that rotates as the cord is pulled or released would be good - have Googled, but none of the dozens available seem to have this feature ...

    had hoped there'd be a small tape-measure device with digital read-out (stretch the tape, read it later - more accurate than laser, easier than trying to read the markings on the tape) which could tap into, but no such thing seems to exist ... so having a rotating centre seemed the next-best thing (could maybe add some marks & read them with a photo-cell & count the pulses) ...

    the approach might work in many situations, but maybe there's a better way ??
    Our self-build - going further with HA...
  • JonS
    Automated Home Guru
    • Dec 2007
    • 202

    #2
    Hi Chris - why do you want this ability?
    To tell if the window was fully closed, open a bit or wide open you could use a couple of carefully placed reed switches one registering fully closed the other wide open. You could implement this with a 4 core cable to the window the first reed switch fitted close to the opening edge of the window and the second closer to the hinge.
    Would this give you the information you need?
    2p
    Jon
    JonS

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    • toscal
      Moderator
      • Oct 2005
      • 2061

      #3
      Something I did when at university was a project to know the location of a spindle.
      I came up with several ideas. The cheapest and quickest option was to use a potentiometer connected to the spindle and just read off the resistance. A certain resistance meant a certain position. Not 100% accurate.
      Second idea was to a optical encoder disk. This uses something called gray code. The position was then read using an optical sensor this gave a binary code which could then be used to give a position. This required more electronics and time to build but depending on the number of binary digits used you could get a very accurate position.
      This link explains the gray code wheel http://engknowledge.com/shaft_absolu...gray_code.aspx and here for an explanation of the gray code system http://en.wikipedia.org/wiki/Gray_code
      This could also be adapted to your tape measuring idea.

      something else may be to use normal door/window alarm sensors. these are just magnetic switches. place a set of the switches along the path and then when the magnet passes a sensor it triggers the switch. This may be possible for curtains or similar. But not for windows.
      Some form of ultrasonic system may also work.

      There is also the things from Add A Motor

      Whether you desire security, temperature control, or automation of window treatments and pet doors our products can meet all your needs. Find out more!
      Last edited by toscal; 25 April 2009, 07:48 PM.
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      • chris_j_hunter
        Automated Home Legend
        • Dec 2007
        • 1713

        #4
        several reasons -

        good idea generally to measure anything that moves, especially with something smart like Idratek around ...

        reed switches are fine, but they are binary & can be a problem due to warping (of what they're mounted on) & exactness of closure, etc, especially on things like doors & windows ...

        could be useful to know, too, that something's swinging with the wind, and if the door has been moved slightly by someone / something passing-through ...

        ditto drawers & curtains, bed (motorised inclinations), garage door, car end-stop, clothes-airer, etc ... and many other things that might move or be moved, to which a cord might be attached ...

        was looking at force sensors, but found nothing to suit ... and also at potentiometers & optical discs on a spindle, about which a sprung cord could be wrapped, somewhere between its ends - but slippage issues were a worry, and it seemed much better to have the disc actually at the tied & sprung end ...


        would enable a number of things - eg: feedback to enable control of curtains & blinds to intermediate positions, ditto reclining beds & chairs to personal positions (as some cars have, these days), etc, etc ... plus things like switching according to position ...

        various sensors are available :



        string pots, yo-yo pots, LVDTs ... various manufacturers, for industrial use ... but so far have not found anything (sufficiently) low-cost yet !

        key point here, besides sensing position, sufficiently accurately, is affordability & ease of incorporation & aesthetics - what's envisaged would (hopefully) be easy to add to doors & draws & curtains & whatever, in many situations, pretty inconspicuously !
        Last edited by chris_j_hunter; 26 April 2009, 05:41 PM.
        Our self-build - going further with HA...

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