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Signals of a 5V encoder

Discussion in 'Electronic Basics' started by Haritztolete, Jan 27, 2006.

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  1. Haritztolete

    Haritztolete Guest

    Hi, I am going to use a 5V encoder of 600 pulses. The signal it gives
    me is a pulse train of 5V and it goes to a driver that is 25 metres far
    away from the encoder. The cable of the encoder goes close to some
    power cables and all the cables are shielded. I don't have any
    experience in such long distances and I would like to know if I could
    have problems with electric noise, and how to avoid it. Thanks a lot.
     
  2. Guest

    You will have trouble, use a RS232 line driver near the encoder to
    change the signal levels and a reciever at the other end to change them
    back.
     
  3. Chris

    Chris Guest

    Hi, Haritztolete. I hope you haven't purchased your encoder yet. If
    you haven't, look for one that gives you a line driver output. You can
    then set up a line receiver at the other end of the twisted pair line,
    and change the signal back into standard digital logic. A standard
    open collector output will be a noise nightmare at 25 meters, no matter
    what the pullup resistor.

    A line driver/line receiver setup will provide quite a bit of immunity
    from noise, because the noise is equally coupled into the both sides of
    the differential pair if you use twisted pair wire. The difference
    between the two voltages will still be the same, and that's what
    determines the logic level.

    However, you also have to worry about sufficient energy being
    inductively coupled into the signal lines to cause damage to the line
    driver or line receiver. You really should arrange for different
    routing of signal and power lines as a matter of course, shielded or
    not.

    Trust me on this one. There are few things more dispiriting, or more
    likely to evaporate your and others' trust in your electronics
    expertise, than creating solutions that kind of work or break down at
    random.

    Please post back if you have any questions.

    Good luck
    Chris
     
  4. Jasen Betts

    Jasen Betts Guest

    use twisted pair cable (eg one pair from a cat-5 cable) and put a
    optocoupler and suitable resistor on the far end.

    Bye.
    Jasen
     
  5. Eric R Snow

    Eric R Snow Guest

    Greetings,
    I am not an electronics expert by any means, just a rank beginner. But
    in the last year I have been using encoders for some custom
    applications and have learned quite a bit about them. Nearly all this
    knowledge came from US Digital. Their website is USDigital .com. I
    think. Anyway, they sell a device for connecting encoders to long wire
    runs. The prices are from $11 to $34 for these cable drivers. Here's
    the link: http://www.usdigital.com/products/ea/ . They will answer
    your questions and can tell you if their device will work with your
    encoder. They were able to help me connect a twenty year old encoder
    to one of their displays. Anyway, I'm just a satisfied customer. No
    connection to them other than that.
    Cheers,
    Eric R Snow,
    E T Precision Machine
     
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