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help needed for rs485 !!!!

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

  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.

    P.
     
  4. Jamie

    Jamie Guest

    we use bi-directional TVS diodes across and to ground (3)


    http://webpages.charter.net/jamie_5"
     
  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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