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RS232 expander?

Discussion in 'Electronic Design' started by Abacus-Ri, Jun 15, 2004.

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  1. Abacus-Ri

    Abacus-Ri Guest

    Hi to all,
    I'm searching for help regards RS232 output multiplier. Unit should consist
    RS232 input (opto isolated) and minimum 12 outputs.
    Any help will be appreciated.

  2. scada

    scada Guest

    RS232 is not intended to communicate to more than one device at a time. You
    can convert the RS232 to RS485 which is designed to handle multiple
  3. James Meyer

    James Meyer Guest

    And what happens if I do exactly what "Abacus-Ri" wants to do? Do I get
    a late night visit from the RS-232 police?

  4. starfire

    starfire Guest

    That's not what he asked for...

    If you're trying to drive several RS232 receivers from a single RS232
    source, just receive the single RS232 with a MAX232 (convert it to TTL),
    optoisolate the signal, then send the TTL input to 12 separate MAX232
    drivers. Depending on the RS232 driver you choose, be careful to observe
    total input loading. If you need to, use a buffer after the optoisolation.
    Also make sure you observe polarity.


  5. dont know

    dont know Guest

    do you mean a unidirectional hub?
    one rs232 input feeds 12 rs232 outputs?
    you have to make one yourself!
  6. Abacus-Ri

    Abacus-Ri Guest

    Hi to all,
    Just to be clear, I plan to build RS232 repeater with just one source. I
    need it to connect navigation equipment to one gyro compass(3x radars, 2x
    communication antennas, 2x Inmarsat B, 2x Inmarsat A, 2 reference receivers
    and some spare)...


  7. CFoley1064

    CFoley1064 Guest

    Subject: Re: RS232 expander?
  8. Tim Shoppa

    Tim Shoppa Guest

    If the protocols are compatible (i.e. devices are uniquely addressable and
    always work as the slave in a master-slave arrangement) then it's just a
    matter of treating RS232 as a bus (which really it isn't, but a couple
    of diodes go a long way to getting there).

    If the protocols are not compatible or the devices talk whenever they feel
    like it then you want a "serial multiplexer"... type it into Google and
    look at what you get. If all your devices are
    NMEA (which they may be) then there are some off-the-shelf products
    that do this all with very little pain. If you have some that aren't
    NMEA then there are still solutions, but they will require some extra
    software on the single-RS232 side.

  9. Repzak

    Repzak Guest

    If the protocols are not compatible or the devices talk whenever they feel

    "standard" nmea signals are 0-5V ....

    if it is the case, then just use a TTL buffer....

    Or put a Max232 in the frontend and some TTL buffers on the output....

    if i remember right nmea uses open collector output, so 7407 could be a
    winner :)

  10. starfire

    starfire Guest

    The NMEA0183 interface from my Garmin E-Trex Vista is RS232.

    Depending on the installation, TTL NMEA0183 code may be available before
    going to the RS232 converter, though.

    I have no idea what the "standard" NMEA interface levels are.

    To the original question, though, if bi-directional serial interfaces are
    required, some sort of multiplexer will be needed or a very well controlled
    architecture to make sure the outputs don't walk on each other.

    This sounds like an interesting microcontroller project, though...

  11. Leon Heller

    Leon Heller Guest

    Where I used to work we designed a 'comms hub' that connected a number of
    RS-232/RS-422 devices to a PC. It used a mid-range PIC connnected to a
    number of Atmel AT90S2313s via SPI. It worked very well.

  12. I'm searching for help regards RS232 output multiplier. Unit should consist
    What's the problem? Use a fast optocoupler as isolation, 1489/1488 as
    level converters. For 12 outputs I would not bother with max232's,
    just get a +/- 10 Volt supply.

    Wouter van Ooijen

    -- ------------------------------------
    PICmicro chips, programmers, consulting
  13. Repzak

    Repzak Guest

    ..... NMEA is not bi-directional ....

    it uses one set of wire for rx and one for tx
  14. If it is RS-232 levels, it ain't NMEA-0183. (and I'm pretty certain
    that it is NMEA-0183)
    A TTL->RS-232 level converter inverts the signal, as well as changing
    levels. Since NMEA-0183 is the same "sense" as RS-232, you need an
    inverter _and_ an RS-232 converter to convert from NMEA to RS-232.
    Standard NMEA-0183 levels are 0 and +5 volts. RS-232 levels are -5
    (or more) and +5 (or more).

    Despite the difference in signal levels, most RS-232 serial ports will
    handle NMEA levels with no problems.
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