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How to sense motion

  1. Sep 27, 2008 #1
    Hello, I would like sense motion (speed) only in one direction. I dont need it to be accurate, I just want it to be a cheap solution (homemade).
    I googled something about piezoelectric sensing with the help of a normal crystal (or piezo buzzer?).

    Does anyone have more details on that?
    Can I sense speed with it?
    Thanx for hints,
    Meereck
     
  2. jcsd
  3. Sep 27, 2008 #2

    dlgoff

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  4. Sep 27, 2008 #3
    hello, thanks for the links.
    It measures acceleration not speed, right. So If I move it at a constant speed, it will not work? Am I right?
    Furthermore, I reckon it is quite expensive, isnt it?
    cheers
     
  5. Sep 27, 2008 #4

    f95toli

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    No, it is impossible to sense that you are moving if the motion is uniform (this is one of the basic principles of physics) UNLESS you somehow use information from the environment, the most obvious example being a GPS.
    However, if you have an accelorometer you can always tell when/how much your has speed changed and by integrating you get the speed.

    Accelerometers are not very expensive nowadays, an accelerometer chip is only a few dollars. However, if you need a complete module it will obviously be more expensive.
     
  6. Sep 27, 2008 #5

    brewnog

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    Get a length of string, and a bell. Tie the string to whatever you want to sense the movement of, and tie the bell to the other. When the bell rings, your subject has moved. If your subject moves in the other direction, the string goes slack and the bell won't ring.
     
  7. Sep 27, 2008 #6
    f95toli : thnx
    brewnog : that is the cheapest solution. Pretty cool!:)
     
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