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Tilt/movement switch question

Discussion in 'Electronic Basics' started by Bob, Apr 17, 2004.

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  1. Bob

    Bob Guest

    Looking for a small switch that will detect if the device it's mounted on
    is tumbled. Not really a tilt, because the orientation after tumbling is
    not anything I can count on, so if it's normally open, I need it to open
    again after a momentary close (bouncing is ok). I'm thinking of some kind
    of metal film connected as common that can bend back and forth between two
    possible contacts.

    The other requirement, it's gotta be cheap, hopefully under $2 even as a
    onesy twosey.

    Thanks.
     
  2. Art

    Art Guest

    Most I've seen are non-reset used to sense if an LCD or Plasma unit has been
    subjected to a non-upright position is shipping. These devices respond to a
    specific angle beyond horizontally plumb. The only thing that I could
    invision sensing that effect and resetting would be some type of liquid
    switch or maybe a microswtch with a "loaded" trigger arm attached to it. One
    that will react to gravity vs position. May want to search Google or Yahoo.
     
  3. Nemo

    Nemo Guest

    There are various tilt switches that may work. The old ones used a blob
    of mercury. Modern ones use a ball bearing inside. Just look for "tilt
    switches" in your favourite electronics supply catalogue...
     
  4. SB

    SB Guest

    Accelerometers are popular with microcontroller crowds...but definately not
    cheaper than $2!

    Analog devices is one company

    Do a google for MEMSIC
     
  5. I just bought some piezo-gyros from a guy on Ebay. They were $20 apiece, but
    they might fit the bill. Any rotational acceleration along their main axis
    will perturb a voltage output, one way it goes down, the other way it goes
    up. I got a set of three for $60.

    If you hook up a couple of comparators as a window detection circuit, and
    it'll trigger if you tumble faster than a certain speed. You need three to
    get an accurate picture of three dimensional rotation, of course.

    They are used in camcorders, I believe, for stabilization.

    There are also accelerometer chips, which may not tell you when the rotation
    is occuring, but which can detect the direction of gravity when the system
    is motionless. I was just looking at a two axis one from analog for around
    $20 ( from digikey. ) Type 'accelerometer' into the digikey search page.

    Regards,
    Bob Monsen
     
  6. SB

    SB Guest

    The accelerometer chips indicate movement with respect to gravity.
    The ADXL210 from Analog Devices outputs a 50% duty cycle square wave when
    it's sitting still (at 1G). As it moves in either direction, the ducty
    cycle changes (lessens for one direction and increases in the other). Their
    devices max out for each model (the 210 is good up to 10G's).

    I have one mounted on a radar dish and through mistakes of my own I didn't
    get it square on the PCB or in the box or on the mounting strut! So I have
    a constant offset from it's 50% duty cycle. Not a big deal to fix with
    microprocessors!

    You can get a measuring cycle of 1mS which is good for vibrations. You
    could code your microprocessor to give velocity as well....since you are
    moving at a constant speed, the accelerometer will show a likewise
    deflection depending on your speed (faster you go...the more the
    deflection).

    Check out Basic Stamps for a really easy microprocessor to use!
    www.parallax.com

    sb
     
  7. Soeren

    Soeren Guest

    Hi Bob,

    Use a spring from an used up ball point pen or something similar.

    Solder (or better bolt) one end to a PCB and put a small nut in the free
    end to make it more sensitive to motion.

    A metalcylinder or -ring of sorts, eg. a piece of brass tubing or some
    tinned copper wire should encircle the nut with some free play.


    | PCB
    |
    |
    |\
    _|-------------_---
    |_| |_| Nut
    Bolt |_|/////(((((((|_|(() Spring
    |_| |_|
    |-----------------
    |/
    | \
    | Solder the tube

    Remember to isolate the tube from the spring :)

    To increase sensitivity, stretch the spring (a bit at a time, don't
    overdo it).

    Price: Some rubbish from the junkbox.
     
  8. Si Ballenger

    Si Ballenger Guest

    I got a couple of blinking LED toys (a ball and a dice) at the
    DollarTree store that have the spring type of shock sensors in
    them for $1 each. Spring type of sensors work more on shock than
    tilt situations.
     
  9. For years pinball machines used a heavy plumb bob on the end of a long metal
    rod; encircling that rod was a metal collar. During normal play the metal
    rod would not touch the collar that surrounded it. But if somebody tilted
    the machine, the rod would touch the collar, and the TILT circuit would
    close.
     
  10. Soeren

    Soeren Guest

    Hi,

    shb*NO*SPAM*@comporium.net (Si Ballenger) wrote in
    Yes, they can be used that way too, it is all a matter of selecting the
    right spring and weight.
    I have med sensors so sensitive that you would trigger it by just thinking
    about moving the pieces of equipment they are in :)

    (That would be highly impractical in your ball and dice, so there it is
    made much less sensitive of course).
     
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