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USB 'breakout'??

Discussion in 'Electronic Basics' started by Steve, Nov 16, 2003.

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  1. Steve

    Steve Guest

    I have a laptop with and have my GPS connected to the USB port using NMEA
    183 4800 baud .. The navigation software finds this input without a problem.
    However I need to have the software communicate with my Autopilot for course
    correction.. This is signal is sent out in the NMEA 183 data sentence as
    well but the software has no provision for me to direct it to a different
    serial port.

    Since the software insists on sending it data communication out on the same
    USB port that is is receiving the NMEA 183 input, I need to be able to tap
    the data out line from that USB port.

    Is there a USB break-out box available that I can plug into the USB port
    and then plug the GPS into, while leaving a connector strip that give me
    access to the other lines??

    I can't get any support from the software vendor because I haven't been

    Thanks for any help.

    s/v Good Intentions
  2. Does the GPS connect directly to the USB port, or does it connect
    through an RS-232<->USB adaptor?

    If the GPS connects directly to USB, I think you're stuck.

    If it really outputs serial data, and you use an RS-232<->USB adaptor
    between it and the PC, you just have to do your splitting on the
    RS-232 side of the adaptor.
  3. Steve

    Steve Guest

    The GPS is one of those modules, about a third the size of a pack of
    cigarettes. Gets it's power from the USB port. It has a molded cable and USB
    connector. No place to tap into the data out line..

    Since the GPS is a talker only and the autopilot is a listener only, I
    figure that neither wouldn't care if I tapped into the Data Out from the
    Laptop. I need the cross track error portion of the NMEA sentence for the

    This wouldn't be a big deal if I had purchase the Serial Port model of the
    GPS, but that required a connection to the keyboard connector or something
    to get the power for the module (seemed kinda hokie to me).

    If the software were using a standard serial port, I could pick the NMEA
    sentence off the DB9 connector data out pin.

    I suppose that could be done if I opened the molded USB connector but I
    thought I would look for something like a breakout box for USB..

    Thanks again Peter

    s/v Good Intentions
  4. the Wiz

    the Wiz Guest

    The connection is using NMEA protocol but I doubt that it's at 4800 baud - USB
    doesn't run at that speed. If your device uses the standard 4 wire USB cable,
    "baud" is a meaningless term.
    NO. USB is NOT like serial. It's a high speed 4 wire (2 power, 2 signal)
    connection that does NOT provide the equivalent of a serial connection.
    That "hokie" connection to the keyboard provides the power to the serial version
    because the serial port is designed for communications, not for powering
    devices. The USB port provides both power and communications, but it's a
    totally different animal.

    More about me:
    VB3/VB6/NSBasic Palm/C/PowerBasic source code:
    Drivers for Pablo graphics tablet and JamCam cameras:
    johnecarter [email protected] mindspring com. Fix the obvious to reply by email.
  5. Although USB does use serial data transmission, it is quite unlike
    RS-232/NMEA-0183. USB uses a complex protocol, and uses differential
    bi-directional communications. That is, there are not separate
    transmit and receive wires in the cable - there is one pair of wires,
    that carry data in different directions at different times.

    It is possible that you may be able to find some serial transmit data
    on the GPS side of the USB<->GPS interface chip, if the USB interface
    function isn't integrated into the GPS processor.

    Are you sure that your navigation program can't send the autopilot
    commands out a second serial port? (either a "real" serial port, or a
    USB<->serial adaptor port). My nav program (Ozi Explorer) allows me
    to set the GPS i/o and autopilot output ports independently.
  6. Steve

    Steve Guest

    Ok, I think I understand what your telling me about the USB. The USB version
    of this GPS module is most likely not using a serial communication since it
    is independent of the NMEA 183 buss.

    I guess that leaves me with the prospect of obtaining a serial GPS module or
    trying to get Nautical Technologies to support my Ver 6.1 of The Cap'n

    I'll try this question of seperate data output from The Capn on some of the
    other boating forums.. I don't hold much hope for the Nautical Tech. forum.
    Very crappy attitude there if your not using the latest version. Same with
    their tech support..

    s/v Good Intentions
  7. Jim Large

    Jim Large Guest

    The O.P. said that the same GPS module is available
    in either USB or RS-232 configurations. I'd bet
    money that the the USB version has a built-in
    USB <-> RS232 adapter. It's probably a single chip
    in an SMT package that's no bigger than your pinkie
    nail. The same companies that sell the chips will
    even customize their driver software so that it
    looks like a custom driver for your product rather
    than a generic USB serial port driver.

    There probably really *IS* async serial data
    flowing at 4800 BPS. There's just no easy way to
    break it out.

    -- Jim L.
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