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combining RS232 messages

Discussion in 'Electronic Basics' started by Maddy, Apr 25, 2005.

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  1. Maddy

    Maddy Guest

    I have the following eqpt
    a.Gyro with RS232 or RS422 output (NMEA word $HEHDT ...)
    b.Log with RS232 output (NMEA word $GPRMC ...)
    c.Standard GPS NMEA output
    I want to give these to a single computer with only two serial ports.
    I want to combine all these signals and feed them to the computer as a
    single input.
    ps I live in India where nautical electronic hardware is hardly
    available. So would prefer a software or circuit diagram which can be
  2. BobG

    BobG Guest

    This sounds like a software problem. Call any US help desk to get a
    talented Indian software engineer on the phone.
  3. Andrew Holme

    Andrew Holme Guest

    Will they be transmitting data simultaneously?

    Do you need bi-directional links i.e. does the computer need to send data /
    commands to them?
  4. Maddy

    Maddy Guest

    Yes They will be transmitting data simultaneously. The computer does
    not need to send any data. Can any other pin apart from pin 2 of the 9
    pin serial port be used for receiving data?
  5. Afraid not. THis might be most easily dealt with by a dedicated controller
    with 4 serial ports: 3 inputs, one output, being smart enough to keep
    packets coming from the different inputs separate and passing them on to
    the main computer. Something pretty smart really.

    The simplest thing coming to mind is: let the computer sort it out but
    give it one serial port for each device. THere are inexpensive USB to
    serial converters that give you four serial ports for one USB connection.
    Then your software can sort out the different data streams.
  6. You need an NMEA multiplexer - there are several links on my GPS/NMEA
    site listed below, in the NMEA Programs area.

    Peter Bennett, VE7CEI
    peterbb4 (at)
    new newsgroup users info :
    GPS and NMEA info:
    Vancouver Power Squadron:
  7. Guest

    I saw the GPS multiplexer and it is exactly what I need. The problem is
    I dont think I can get it in India. Is any circuit diagram scematic
    available whic I can use for makin a simple 2 in 1 out multiplexer?
  8. I think most of the vendors listed on my site will ship naywhere.
    It isn't too simple.

    What you need is a microcontroller with one serial port for each
    source, and enough memory to hold at least one sentence from each
    port. The microcontroller will read and store incoming data then send
    it out when it gets a full sentence, providing it isn't already
    sending data from another input.
  9. Rich Webb

    Rich Webb Guest

    Or sufficient small microcontrollers, each with one UART and enough
    memory for a sentence, plus a supervisor (which could be one of them)
    that acts as a traffic controller. Request-to-send, clear-to-send, and
    an open collector buffer perhaps.
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