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Rotary encoder

Discussion in 'Electronic Design' started by Pete, Dec 19, 2005.

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  1. Pete

    Pete Guest

    Hi,

    I need to make a rotary encoder which fits onto a motor shaft from
    which I will read the amount of movement in both directions.

    The way I want to do this is by using a mechanism similar to that found
    in a ball mouse where a slotted wheel interrupts the light to a pair of
    sensors.

    I've taken apart a couple of mice but can't find any markings on these
    devices (phototransistors). If anyone could point me in the right
    direction for a manufacturer, I would be very grateful.

    Many thanks,

    Pete
     
  2. Tim Wescott

    Tim Wescott Guest

    Digi-key carries phototransistors from a number of manufacturers. The
    last time I disemboweled a mouse the phototransistors were pretty
    standard looking parts. Look in the Digi-Key catalog.

    You can also get LED-phototransistor pairs that are already mounted in
    handy little holders -- this is a good thing if you are making your own
    mechanical assembly, because it saves you having to make the mounts.
     
  3. Robert Scott

    Robert Scott Guest

    Before you re-invent the rotary encoder, look around for an
    off-the-shelf solution. There are many many forms of rotary encoder
    packages. They come in a wide range of resolutions. Most of them
    have their own shaft which you would have to couple to your motor
    shaft. However there are also the "hollow shaft" type that can be
    fitted onto an existing shaft. In searching, use the term
    "incremental encoder".


    -Robert Scott
    Ypsilanti, Michigan
     
  4. John Fields

    John Fields Guest

     
  5. Guest

    The HP incremental encoders - HEDS-9100 and up - in the Farnell
    catalogue all come with either two or three channels - the two channels
    are two incremental outputs in quadrature, from which any competent
    enigneer can get directional information, and the third channel - when
    provided - is an index output.

    In fact most of the incremental encoders in the Farnell catalogue
    explicitly offer quadrature outputs, and I suspect the rest do too,
    even if Farnell's copy-writers haven't bothered to mention it

    Perhaps you might like to reprogram the relevant bit of your brain? You
    seem to have posted one of those bits of information "that ain't so".
     
  6. Guest

    You're assuming it's flash.
     
  7. Tim Wescott

    Tim Wescott Guest

    Eh? Quadrature incremental encoders give direction information, and
    have for decades.
     
  8. Jamie

    Jamie Guest

     
  9. Jamie

    Jamie Guest

    an A,B,Z incremental type will do it.
     
  10. Jamie

    Jamie Guest

    John, incremental encoders come in Quadrature A,B,Z or Just A,Z or just
    A output.
    Maybe your thinking of absolute types generating the gray/nat binary ?
     
  11. Guest

    I've seen John Field's brain in action here before. There's nothing
    flash about it.
     
  12. I recall a time long ago when a Boston University graduate student put
    up an avertisement for someone to figure out how to calculate the
    rotational velocity of a disk for $50.00US using photodiodes. I was an
    undergrad and had never heard of quadrature, but I remember riding in
    his car several times from Boston to his home 40 miles out in the
    suburbs to work on the thing in his basement. During the trip, he
    would drive while I listened to a professor explaining how it works on
    tapes that he secretly recorded in the professor's office. I was very
    intrigued, but after three weeks, and having not received any money, I
    demanded to be paid, at which point he reluctantly gave me a check from
    Discover Card, which he promplty warned me just two hours after would
    bounce. Enraged, I burned my (his) notebook, including the design for
    a proportional-integral-derivative (PID) controller that I had just
    begun. A fight ensued where he threatened me with lawsuit, and I did
    my own investigation (since he and his wife were suspiciously
    overstressed) and discovered that I was doing his master's thesis, and
    I called the professor at Boston University (turned out to be his
    advisor) and he called the university police and started a campaign to
    get me expelled. What's odd is that he eventually graduated with
    hardly and reprimand while I was placed under investigation for 2
    months by a university detective and the office for academic
    discipline.

    -Le Chaud Lapin-
     
  13. Google AS5040

    Enough said.

    jg
     
  14. Pete

    Pete Guest

    Thanks for all your help,

    The type of sensor I'm looking for is specifically the type found in a
    ball mouse. Mainly, the (probable)price and size of the components make
    this method desirable. The type of rotational detector often found in a
    mouse consists of an led facing a small device containing 2
    phototransistors situated in such a way that you can decode the
    direction and speed of rotation with a bit of simple programming by
    looking at the state of "sensor 1" and then looking whether "sensor 2"
    goes from light to dark or dark to light. I've tried the HEDS type
    complete package which is fine although expensive in the long run.

    If anyone knows specifically the sensor I'm still looking for (which,
    if you look inside a mouse, you might see something like LD1 for the
    LED and LQ1 for the sensor marked on the PCB silkscreen) I'd be
    grateful for a part number or manufacturer to get me started.

    Many thanks,

    Pete
     
  15. John Fields

    John Fields Guest

     
  16. John Fields

    John Fields Guest

     
  17. John Fields

    John Fields Guest

     
  18. Robert Scott

    Robert Scott Guest

    What we have been trying to tell you is that a standard incremental
    encoder has that type of sensor integrated with a wheel with lines on
    it. You are not going to easily make the equivalent of an incremental
    encoder starting with just two optical sensors. It is not easy to
    align the sensors to the proper 90 degree offset. Perhaps the mouse
    ball is the only example you have seen of an incremental encoder, but
    it is not the best example to couple to a motor. Why not take the
    easy way out and just buy an incremental encoder instead of trying to
    build one from scratch?


    -Robert Scott
    Ypsilanti, Michigan
     
  19. Nah, it's just Bill Sloman. ;-)

    I think everybody pretty much knows your style - you do dynamite
    electronics, yet can get a little bit cynical from time to time. :)

    I'd like to think of you as an "informed optomist." :)

    Cheers!
    Rich
     
  20. Pete

    Pete Guest

    Thanks,

    You're probably right. There is a fairly small incorporated assembly
    for under 5 pounds from Agilent. It's important for me to get the
    component cost right down which doesn't always give the easy solution.

    Thanks again,

    Pete
     
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