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Isolated RS-422 communication

  1. Nov 30, 2012 #1
    Hi!

    I'm currently using SN75179BP to convert RS-422 communication to UART, allowing communication from my Arduino to an RS-422 device.

    I need to isolate that device from my arduino+driver/receiver circuit.
    Does anyone know a good optocoupler solution for RS-422 lines?
    any already-isolated driver/receiver pair?


    Thank you,
    Liad.
     
  2. jcsd
  3. Nov 30, 2012 #2

    berkeman

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    Staff: Mentor

    Is it really RS-422, and not RS-232 or RS-485 comm?

    I did a Google search, and got some good hits. You might check out BlackBox Corporation -- they make lots of converters, including optoisolated ones:

    http://www.blackbox.com/Store/Results.aspx/Datacom/n-4294962623

    .
     
  4. Dec 1, 2012 #3

    MATLABdude

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    Science Advisor

    I've had some success with optoisolated RS232 to RS485 and RS422 modules from Serial Comm:
    http://www.serialcomm.com/

    However, instead of the full 57.6 kbps, I was only able to reliably get about 19.2 kbps. This was probably because I was using a COTS USB to RS232 converter--instead of the standard +/- 15V RS232 levels, they're usually only about +/- 5V, probably impacting both the energy harvesting (and hence, optoisolator rise/fall times) and the differential output. The caveat will probably also apply if you're using a MAX232.

    Since I needed faster speed and better reliability, I ended up rolling my own (galvanically isolated) high-speed USB to RS422/485 based around the Analog Devices' ADM2582E (16 Mbps) / ADM2587E (500 kbps) chip. It's a little pricey ($10 - 14 a pop at DigiKey) but does both signal and power isolation (meaning you don't need a power transformer / rectifier / converter). If you need to power other ICs, there's an even more expensive version that allows you to pull 50 mA or so.

    If you already have power available on the isolated side, you can get a slightly cheaper one that handles RS485 only (ADM2481E or ADM2483E) or RS422/485 (ADM2484E).

    Note that all of the above ICs only come in surface-mount format (but on the upside, there's standard 16 or 20-pin 0.050" spaced SOIC-W, 0.300" wide--easily-sourced breakout boards if you need something for prototyping).
     
  5. Dec 1, 2012 #4
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