Wireless GPS Project

Discussion in 'The Projects Forum' started by tornado151, Apr 15, 2010.

  1. tornado151

    Thread Starter Member

    Apr 15, 2010
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    Hi,
    I am trying send gps data from a gps module to a serial port on my computer.

    So far I have the following items:

    • 10khz (115200 baud) GPS Module Link
    • TM50-1 RF Transmitter Link
    • RM1SGS RF Receiver Link
    • TTL RS232 to USB Link
    I have connected them as shown below:

    [​IMG]

    But it does not work, I just get a load of junk on the screen:

    [​IMG]

    If I connect the GPS module straight to the TTL RS232 to USB converter it works.

    I think I have set up the wireless circuit wrong somehow? Someone suggested I buy 2 MAX232 chips a place it between the transmitter and the GPS module and one between the receiver and TTL RS232 to usb converter, is this correct?

    Any help would be really appreciated,
    Thanks,
    Alex
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,645
    2,344
    Hello,

    There is a missmatch in the datarates of the rs232.
    The GPS module is 115200 Baud
    The transmitter is 9600 Baud max.
    The reciever is 2400 Baud

    Bertus
     
  3. tornado151

    Thread Starter Member

    Apr 15, 2010
    34
    0
    Hi,
    Thanks for your help.

    Should this circuit work if I buy the correct transmitter & receiver?

    Thanks
     
    Last edited: Apr 15, 2010
  4. retched

    AAC Fanatic!

    Dec 5, 2009
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    You should see if you can adjust the baud rates to match.. You may not have to buy new components.. But if you had components with matching data rates, it should work fine.

    [ed]
    OK, just checked the GPS device... That requires a 115200 uC or Tx device. so you will need a faster Tx and Rx device.
    [/ed]
     
    Last edited: Apr 15, 2010
  5. tornado151

    Thread Starter Member

    Apr 15, 2010
    34
    0
    Hi,
    Thanks for your help.

    Do you know where I can get a 10khz (115200 baud) transmitter & receiver from?

    Or is there circuit which can slow down the data rate?

    Thanks
     
  6. retched

    AAC Fanatic!

    Dec 5, 2009
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    not exactly.. You COULD use a uC to take the data and save it in memory then transmit it at a slower rate... like a buffer.. But the amount of memory you would need would cost you more than a new kit. And it would not be real-time.

    lemme see if I can find something with that fast of a data rate.
     
  7. tornado151

    Thread Starter Member

    Apr 15, 2010
    34
    0
    Thanks for your help.

    I found an RF chip that I think supports the rate (Link) but it only transmits up to 100 meters, ideally I want at least 1km or more. There dont seem to be many others around, well at least on ebay.

    Any ideas?
     
  8. retched

    AAC Fanatic!

    Dec 5, 2009
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    Yeah.. I cant find any that fast that have a more than 100m.. Maybe someone will come along that has some info..

    Why would you need to transmit the gps info so far?
     
  9. tornado151

    Thread Starter Member

    Apr 15, 2010
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    0
    I found this site: http://www.lprs.co.uk/, looks interesting.

    I found this module (Link) which can transmit up to 1km at 15k bps. As it is a higher rate than the gps device would this work? or does it have to be the same rate?
     
    Last edited: Apr 15, 2010
  10. retched

    AAC Fanatic!

    Dec 5, 2009
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    The fastest data rates I can find on their equipment is 76,800bps and that is for short range 250m.

    Long range stuff has 4800bps limits. @ 800m line of sight.

    nothing for 1km or more
     
  11. tornado151

    Thread Starter Member

    Apr 15, 2010
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    I think its possible to send a command to the gps module to change its baud rate. Will look into this.
     
  12. retched

    AAC Fanatic!

    Dec 5, 2009
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    Ok. You may be able to shut off a few options so less data needs to be sent. Then you may be able to reduce the baud rate.
     
  13. tornado151

    Thread Starter Member

    Apr 15, 2010
    34
    0
    Hi,
    I found I can change the data rate of the gps module by sending the following commands to it:
    Code ( (Unknown Language)):
    1.  
    2. $PMTK251,4800*14<CR><LF> to setup output baudrate as 4800 bps
    3. $PMTK251,9600*17<CR><LF> to setup output baudrate as 9600 bps
    4. $PMTK251,19200*22<CR><LF> to setup output baudrate as 19200 bps
    5. $PMTK251,38400*27<CR><LF> to setup output baudrate as 38400 bps
    6. $PMTK251,57600*2C<CR><LF> to setup output baudrate as 57600 bps
    7. $PMTK251,115200*1F<CR><LF> to setup output baudrate as 115200 bps
    The transmitter and receiver will still mismatch though, so I am not sure what will happen.
     
  14. retched

    AAC Fanatic!

    Dec 5, 2009
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    The problem now is that your reciever cant be faster than 2400bps.. You need a receiver that can handle 4800bps
     
  15. tornado151

    Thread Starter Member

    Apr 15, 2010
    34
    0
    The gps module seems to ignore the command to change the baud rate, even though its connected up. It responds to other commands.

    I need to get some sleep now, will look again tomorrow at this.

    Thanks for all your help :)
     
  16. tornado151

    Thread Starter Member

    Apr 15, 2010
    34
    0
    Hi,
    I have bought new modules with a longer range and set the gps module to use a lower baud rate.

    Thanks for all your help.
     
  17. retched

    AAC Fanatic!

    Dec 5, 2009
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    No problem and good luck.
     
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