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help needed for rs485 !!!!

Discussion in 'Electronic Basics' started by michael nikolaou, Apr 5, 2009.

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  1. Hi to newsgroup

    I want to implement an RS485 interface to an microcontroller with the
    purpose of creating a network of 10 controllers
    located about 200 mt from a pc . Although everything is clear regarding the
    interface what is obscure is the protection
    needed. I've seen schemes using a 100 ohm resistor between grounds and a 2
    zeners series connected clamping at 13 volts
    between each data line and ground . Other suggestions are zenistors and
    varistors , other suggest optical isolation . Does anybody have experience
    to suggest a simple solution (it is a cost sensitive application) to protect
    the devices and data lines from surges ??? . I know you can't protect from
    all surges but a usual protection is ok.
  2. Jasen Betts

    Jasen Betts Guest

    couple the device directly to the rs485 and isolate all the other I/O ?
  3. P.

    P. Guest

    At such long distances it is much better to use a small dc/dc
    converter and optocouplers to isolate the RS485 from your device. And
    use a good RS485 driver, there are several.

    Whatever clamping you use, you will always have ground loops with
    problems if you don't.

  4. Jamie

    Jamie Guest

    we use bi-directional TVS diodes across and to ground (3)"
  5. Guys

    mt stands for meters, thats 0.2 (km or kilometers)
  6. Fred Abse

    Fred Abse Guest

    The usual abbreviation is just "m".
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