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Calculate the speed of an object

Discussion in 'Electronic Basics' started by Tom, Sep 20, 2006.

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  1. Tom

    Tom Guest

    I need to build a device to measure the speed of a pine wood derby car.
    One idea was to use two photo censors connected to a programmable logic
    controller with the output going to a simple display. Is there an easier
    way to accomplish this?
  2. Hi Tom,
    The Photo sensors are the way to go. I use an old laptop, printer port
    or com port for input and a simple basic program for timing. The
    display is already there.
  3. Ken Moffett

    Ken Moffett Guest

    Have you Googled "pinewood derby timer" ? 505 hits. 24600 hits if you
    leave off the quotes.

    Just asking.

  4. Phil Allison

    Phil Allison Guest


    ** Errr - a laser / radar gun ??

    Lots of other uses for one of them too.

    See them for under US$300 on line.

    ........ Phil
  5. Greg Hansen

    Greg Hansen Guest

    Depends on what you want to measure. What you described would measure
    average velocity. You might be interested in maximum velocity or
    velocity versus time or versus position, which would be different problems.

    Maybe you could dispense with the PLC if there's a good way to divide
    one analog signal by another, like using voltage-controlled resistors in
    an inverting amplifier (I'm not one of those electronics cognoscenti).
    Preset one voltage (or turn a pot) to represent the distance, and use an
    integrator to get a voltage representing time between the two photocells.
  6. Chris

    Chris Guest

    Yup. And the very first link shows project 14, "The Worlds Least
    Expensive Pinewood Derby Timer". That will work just fine, but I'd use
    a regulated +5V wall wart instead of the unregulated 6V supply shown in
    the link. I'm not comfortable about an unregulated +6V (which may peak
    as high as 9VDC) attached to a printer port input pin with a 10K
    resistor between.

    Use an old laptop, and amaze the kids.

    Good luck
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