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Infrared reflective sensor

Discussion in 'Electronic Basics' started by Jen, Apr 28, 2006.

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  1. Jen

    Jen Guest

    Hi All,
    I'm looking for a part which provides an output signal when a reflective
    surface is placed in front of it. I'm designing a circiut for my kids in
    which an LED should go on everytime their hamster makes one revolution in
    it's spinning wheel.
    Thanks in advance for your help!
  2. Christopher

    Christopher Guest

    Hello Jen,

    Here is one effective and interesting approach if you can get the
    pieces to build it.

    Someone in the group brought this to my attention a little while back,
    I thought of mounting one on my backyard miniature 7' windmill.

    * * *

    Temecula CA.USA
  3. Phil Allison

    Phil Allison Guest


    ** Try attaching a small magnet to the wheel and have it activate a reed
    switch each revolution.

    Then it's just battery, reed switch and LED - plus maybe a resistor.

    Reed switch = tiny, glass encapsulated, magnetically *closed* switch used
    in burglar alarms to detect open doors and windows.

    ........ Phil
  4. Jen

    Jen Guest

    That's a neat idea, if I can get it to work. It also would demonstrate to
    the kids how mechanical energy can be turned into electrical energy.
  5. Jen

    Jen Guest

    Thanks for the idea! If the first solution posted here doesn't work, than I
    have a backup.
  6. Tim Auton

    Tim Auton Guest

    I've been using Hanamatsu P5587 photoreflectors, which are designed
    for exactly this purpose. They include LED and sensor in a single
    5-pin package and have a schmidt-trigger and amp built in, so they
    provide a clean 0-5V signal you can generally use without further
    conditioning. They're popular with robotics enthusiasts for making
    wheel encoders, which is what I use them for. I've found them to be
    pretty sensitive to the distance between sensor and target though, and
    need to be within a few mm with a fairly true wheel to work reliably.
    That's using laser a laser printed patter with stripes 3-4mm wide
    though, larger stripes and reflective material eases the positioning
    requirements quite a bit. Even so, a hamster wheel may be a bit too
    wobbly for them. If you want to try them, they're available in small
    quantities from robotics enthusiast stores, has them
    for example. A search on the part name and 'robot' will find plenty of
    examples and advice.

    If you're not dead-set on an optical sensor, I think I prefer Phil
    Allison's magnet and reed switch idea. Much less sensitive to
    positioning and it won't stop working when the hamster flicks a bit of
    sawdust on the sensor. Bicycle computers work this way, with a magnet
    on the wheel and a reed switch on the frame.

  7. redbelly

    redbelly Guest

    One could probably just buy a bicycle speedometer and use it directly.
    They should have calibration instructions, and you could probably
    calibrate it so that 1 revolution gives a reading of 0.1 or 0.01 miles,
    making it easy to figure the number of revs from the odometer reading.

  8. Jasen Betts

    Jasen Betts Guest

    a maget's going to unbalance the wheel (easily cured) but also cause a
    non-uniform drag and a cogging action when it passes near the steel axle
    supports, dunno if that'll trip the hamster up or not.

    a piece of retro-reflective tape would probably work well if cleaned

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