gps module connection problems

Discussion in 'Embedded Systems and Microcontrollers' started by bassplayer142, Aug 25, 2010.

  1. bassplayer142

    Thread Starter Active Member

    Jan 2, 2007
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    0
    I ordered a gps module online called SiRFstarIIeLP with a simple uart connection. It says that the default is 9600 baud, but the data collected from a terminal roughly every second looks like it could be something at 9600 or 4800 baud.

    I'm aware that this module can be communicated with using NMEA and sirf binary protocol, but the data I get seems corrupt as I can't even find any start or stop delimiters or anything for either protocol at any baud. Below is some data taken at 4800 then 9600 baud respectively in ascii characters.

    4800 baud
    ›.%‰é9óææ¦L™fM̙3šæææfÍææææ͖šææææfÍææææM—šæÍææM™fÍæÍfÍæM–šfÍæM–šfÍæÍæææfM™2y=›.%Éé9Ó9Óæ͚ššššššššššš™fÍæM™fÍæM™fÍfͦ¦Ïϛ.e¥K9óææ¦L™fM̙3š*šæææfÍææææ͖šææææfÍææææM—šššæ¦¦æfæ͚5gdy=

    9600 baud - anything in the squiggly brackets is hex
    {00}ž{18}~øf{06}†à†þ†˜øxþxæxþxžxþàx˜˜àx†˜x~æøxþxþxþx{1E}æøxþxþxþx~æxxø˜øxþxþxþxþx{1E}æøxþxþxþx~æ˜~ø˜øx~æøxþx~昆øx{1E}æøx~æøx{1E}æøx~æ˜xø˜øx{1E}æøx~æ˜xø˜øx{1E}æøx~æøxþxþxþxžæ{18}†{18}xfþxþøž{18}~øf{06}†x†þ†˜˜†˜˜x~æø˜ø˜ø˜ø˜ø˜ø˜ø˜ø˜ø˜ø˜ø˜ø˜˜†øx{1E}æøx~昆øx{1E}æøx~昆øx{1E}æøxžæøxfxfþxþøž{18}~øfžffž{18}†˜øxþxæxþxžxþàx˜˜àx†˜x~æxfø˜øxþxþxþx{1E}æøxþxþxþx~æxxø˜øxþxþxþxþx{1E}æøxþxþxþx~æ˜~ø˜ø˜ø˜˜xþxæxæxþxžx~æø˜xæ˜xžxfþxþ{00}

    I currently have the device on my window ledge and part of me thinks it may be not communicating with the satellite. But in that case the module should be sending messages out in the correct protocol anyway.

    Also, I attached a text that was emailed to me from the supplier (ebay), that is obviously written by someone foreign. It may shed light If I could understand half of it. I have found from it that the module has a battery that charges up when power is connected and that is working properly along with a red lit led on the module.

    Long post I know, but thanks to anyone who can help.
     
  2. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    How do you connect the GPS usart output signal to the PC?

    Are the GPS module output already at RS232 level or you have an adaptor cable?
     
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  3. bassplayer142

    Thread Starter Active Member

    Jan 2, 2007
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    Yes, I am using a level converter and bringing the information into a terminal program called Hercules which I have used many times before. There is a tx, rx, ground, and 5v supply connection and that is it.
     
  4. davebee

    Well-Known Member

    Oct 22, 2008
    539
    46
    Could the serial signal be inverted? I've heard of some devices that send serial data that's logically inverted, so you need to use an inverter logic chip or an inverting transistor to be able to feed the data to a standard serial receiver.
     
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  5. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Could you be getting sirf binary protocol messages outputs?

    You would need to capture some data in HEX format as according to this link, sirf message always starts with A0 A2 and ends with B0 B3.
     
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  6. bassplayer142

    Thread Starter Active Member

    Jan 2, 2007
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    I was not able to find any start or stop delimiters in either protocol (NMEA and sirf). Here below is the posted same response's in hex values.

    4800 baud
    {22}{91}{33}{5A}{AD}{A1}{45}{A4}{6A}{AE}{AD}{B5}{AD}{AD}{2A}{5A}{AD}{AD}{BB}{AD}{4D}{6B}{B5}{AD}{42}{45}{B5}{B5}{B5}{6B}{55}{B5}{6B}{B5}{B5}{2D}{AD}{AB}{6D}{BB}{37}{9C}{CC}{BE}{52}{6A}{6A}{6A}{6A}{6A}{6A}{42}{B5}{B5}{5A}{BB}{42}{45}{BD}{A1}{7B}{22}{71}{85}{52}{52}{5A}{D5}{AB}{ED}{6B}{AE}{AD}{BA}{BD}{2A}{F6}{AD}{46}{6D}{DA}{AD}{A9}{52}{BB}{A4}{AD}{DA}{AD}{AD}{B7}{AD}{B5}{99}{AD}{5D}{B5}{AD}{AD}{22}{AA}{52}{A9}{AD}{9A}{7A}{A5}{2C}{00}

    9600 baud
    {78}{98}{F8}{78}{7E}{E6}{98}{78}{F8}{98}{F8}{78}{1E}{E6}{F8}{78}{7E}{E6}{98}{78}{F8}{98}{F8}{78}{1E}{E6}{F8}{78}{7E}{E6}{F8}{78}{FE}{78}{FE}{78}{FE}{78}{9E}{E6}{18}{86}{98}{86}{98}{F8}{78}{FE}{F8}{9E}{18}{7E}{F8}{66}{06}{86}{78}{86}{FE}{86}{98}{98}{86}{98}{98}{78}{7E}{E6}{F8}{98}{F8}{98}{F8}{98}{F8}{98}{F8}{98}{F8}{98}{F8}{98}{F8}{98}{F8}{98}{F8}{98}{F8}{98}{F8}{98}{98}{86}{F8}{78}{1E}{E6}{F8}{78}{7E}{E6}{98}{86}{F8}{78}{1E}{E6}{F8}{78}{7E}{E6}{98}{86}{F8}{78}{1E}{E6}{F8}{78}{9E}{E6}{F8}{78}{66}{78}{66}{FE}{78}{FE}{F8}{9E}{18}{7E}{F8}{66}{9E}{66}{66}{9E}{18}{86}{98}{F8}{78}{FE}{78}{FE}{78}{E6}{78}{9E}{78}{66}{78}{1E}{E6}{98}{E0}{98}{E0}{98}{86}{F8}{98}{78}{66}{F8}{98}{F8}{78}{FE}{78}{FE}{78}{FE}{78}{1E}{E6}{F8}{78}{FE}{78}{FE}{78}{FE}{78}{7E}{E6}{78}{78}{F8}{98}{F8}{78}{FE}{78}{FE}{78}{FE}{78}{FE}{78}{1E}{E6}{F8}{78}{FE}{78}{FE}{78}{FE}{78}{7E}{E6}{98}{7E}{F8}{98}{F8}{98}{F8}{98}{98}{78}{FE}{78}{E6}{78}{E6}{78}{FE}{78}{9E}{78}{7E}{E6}{F8}{98}{78}{E6}{98}{78}{7E}{78}{66}{FE}{78}{FE}{00}

    I should also point out that sometimes the data is different lengths and different, but I still can't find any data that can be deciphered at all. The company even gave me a terminal program that is supposed to display all the information but it doesn't even display anything as received. That program is below if interested.

    Also, Inverting the hex above with a simple not command in win 7 programmers calculator isn't giving anything reliable either.
     
  7. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    Your captured data doesn't look random to me. The value {78} and {98} both occur 158 times.

    The buyer's program don't output anything as it is also looking for the start of messages which of course there isn't any to be seen.

    If the messages are spilling out roughly every second, chances are the GPS MCU is working.

    What's left is the physical adapter cable signal level(5V or 3.3V to RS232) and the comm protocol settings like baudrate, start bits, stop bits and parity bits. Have you tried changing any of these yet?

    What is the logic level at the output of the GPS uart pins? 5V or 3.3V?

    If you can somehow prove that the cabling side to the PC works, then it must be the GPS module at fault and you can return it to seller.
     
    Last edited: Aug 27, 2010
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  8. t06afre

    AAC Fanatic!

    May 11, 2009
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    Do you have any info about this device like a manual. Have you tested it on another PC?
     
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  9. bassplayer142

    Thread Starter Active Member

    Jan 2, 2007
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    I have attached the full zip that was given to me. There is no real datasheet for the module which leads me to believe that it was taken out of some other working unit and sold on the side (for cheap might I add). I've done just about every possible combination for baud rate, stop bits, parity, and message length with no avail. The output from the unit is most likely 5V but I don't have access to a scope right now. The conversion is a simple max232 chip, but I suppose a 3.3v output would not satisfy that chip. I haven't tested this on another computer but I have with different terminal programs. I have used this particular max232 conversion board for microcontroller to computer communication with no problems either.

    Thanks all
     
  10. eblc1388

    Senior Member

    Nov 28, 2008
    1,542
    102
    I'm 99% sure that your GPS is from this seller in eBay.

    If that is the case, then the seller of the GPS has remarked in the eBay ad that the GPS will output RS232 signal level, meaning that you don't need an adapter cable for level changes and can directly connect the GPS uart signal to a PC serial port.

    The default factory baudrate is 4800,8,n,1 and the output format will be NMEA.

    [​IMG]
     
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  11. bassplayer142

    Thread Starter Active Member

    Jan 2, 2007
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    At this point I'm game to try anything and that sounds sensible. I can't find the ebay log of it anymore as it was deleted. Man, I really need to get my hands on a scope. It would save me great deal of time on everything if I could have checked that a long time ago...
     
  12. t06afre

    AAC Fanatic!

    May 11, 2009
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    A scope is not nice to have it is need to have;) At least if you want to keep on as a hobbyist. If you are on a budget get a used analog one.
     
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  13. bassplayer142

    Thread Starter Active Member

    Jan 2, 2007
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    Ahh, it didn't load the picture last time for some reason but that is definately the same module! Thanks a ton, unfortunately I'm busy today and I need a serial converter. I will post back in a few days with hopefully good news haha. I can't believe I didn't see that when I bought it...

    Thanks to everyone for all the help!
     
  14. bassplayer142

    Thread Starter Active Member

    Jan 2, 2007
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    The data looks good now. I don't have time to decipher it but I was too excited to wait and bent some wires around the pins haha. Thank you everyone for the help.
     
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