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Homework Help: Determining the direction of rotation of a wheel

  1. Sep 26, 2010 #1
    1. The problem statement, all variables and given/known data

    Hello All.
    I am trying to design a system to determine the direction of rotation of a wheel.
    I do not have access to a flywheel but only the wheels inner face.
    Can anyone please recommend a sesnor or soultion to help me?
    Many thanks

    2. Relevant equations

    3. The attempt at a solution

    I have found a few hall effect sesnors with a quadrature output, which I should be able to use but unfortunatley they all seem to require like an encoder wheel or flywheel teeth. There are some ICs that do this but nothing that is roust enough for my application.
  2. jcsd
  3. Sep 28, 2010 #2


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    There is a possible way of doing this easily. I haven't tried it (I just thought of it), but it seems like it would work.

    Make a S-R flip flop and put a LED on the Q output of it.

    Glue a strong magnet to the wheel.

    Have two Hall switches near each other and near the magnet when it passes. Only one Hall switch should turn on at a time.

    Connect one Hall switch to the SET input and one to the RESET input of the S-R flipflop.

    Whenever the magnet passes the SET Hall switch, the LED lights up. When it passes the RESET Hall switch, the light goes out.

    Now, if you turn the wheel one way, the light will turn on and the wheel will rotate nearly all the way around before it goes out. If you turn it the other way, the light will come on briefly but only stay on for a short time until the magnet reaches the RESET Hall switch and this turns the LED off.
    So, the lamp will be almost fully lit in one direction of the motor and almost fully off in the other direction.
  4. Sep 28, 2010 #3
    Hello vk6kro, and many thanks for you reply!

    You are right in what you are saying.
    I am using a PIC on the back end of this so I think if i had the 2 quadrature outouts from the sensor then I can interpret them ok.
    Its just that this sensor is primarily a speed sensor based on a flywheel, and I am not sure it will suit just having access to a metallic stud or magnet

    Please see link for closest switch I could find
    BY using the lead/lag of these 2 waveforms I shoud be able to determine rotation.
  5. Sep 28, 2010 #4


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    I'm not sure how that would work. What would the sensor be sensing?

    I had another idea. An optical mouse can tell if it is being moved up or down on a surface. So what if the surface was moving and the mouse was stationary?
    The mouse would give outputs as if it was moving.
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