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Gps module no fix status — Parallax Forums

Gps module no fix status

inubusinubus Posts: 8
edited 2012-03-15 17:46 in General Discussion
Hi

I am new to electronics doing a project with a gps module + pic18f2420+usb ( tracking device) my problem is that
my gps module is not getting a fix status the led is just flashing?

please help

Comments

  • FranklinFranklin Posts: 4,747
    edited 2012-03-12 15:19
    Let's start with some questions. Which GPS module and how is it connected? Are you trying it outside?
  • PublisonPublison Posts: 12,366
    edited 2012-03-12 17:00
    As Franklin said, most GPS unit have to be outside to get a lock. Some of the Parallax units I have will get a lock just by hanging them outside a window.
  • wasswass Posts: 151
    edited 2012-03-12 18:09
    I recently purchased a Parallax PMB-648 GPS module and I'm stunned by it's ability to lock on satellites virtually anywhere in my house. I get it to lock continuously when I'm 20 feet from a window in my partially underground basement through two floors and an antic above. This is by far the most sensitive GPS I've ever used. I've bought and tested several other GPSs (hand-held and car units, not modules) in exactly the same conditions they need to be right near a window. I haven't checked how many satellites it has a lock on but at least one, and that's all I need for my clock application.

    Was I just lucky in getting one that exceeds it's specs?
  • inubusinubus Posts: 8
    edited 2012-03-13 17:45
    Its a Parallax (PMB - 248) am using 3 wires from the GPS VIN, GND and TX1. is it possible to test the gps module on its own
    without hooking it to the rest of the circuit?
  • inubusinubus Posts: 8
    edited 2012-03-13 18:45
    Its a Parallax (PMB - 248) am using 3 wires from the GPS VIN, GND and TX1. is it possible to test the gps module on its own
    without hooking it to the rest of the circuit?
  • Mark_TMark_T Posts: 1,981
    edited 2012-03-13 20:37
    When a GPS receiver is first powered up it has to receive the almanac data from the satellites, this is transmitted at very low bandwidth so expect it to take several minutes and do this outside for fastest results - once the almanac data is stored it should re-establish a fix quickly.
  • sylvie369sylvie369 Posts: 1,622
    edited 2012-03-14 09:25
    Does the GPS module you're using have the little red LED that blinks when it's looking for a fix? It should turn solid when you have a good fix. You can test that part without any connections to the rest of your circuit by simply supplying the GPS module with power and ground.
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-03-14 10:00
    As others have mentioned, there can be a big difference between GPS units on how long it takes to get a lock.

    My older Parallax GPS takes a long time (several minutes) and needs to be outside to get a lock. I have another unit that will get a lock quickly while sitting at my desk.

    I've also found a switching power regulator can interfere with a GPS unit. If you're using a switching regulator, I'd suggest using a linear regular until you're sure you GPS unit is working correctly.
  • inubusinubus Posts: 8
    edited 2012-03-14 11:36
    It does have an led which just keeps on flashing indicating that there is no lock as per data sheet took it outside this morning
    Waited for 3minutes nothing, the led was just flashing. Could it be that the gps module is faulty?
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-03-14 11:42
    inubus wrote: »
    It does have an led which just keeps on flashing indicating that there is no lock as per data sheet took it outside this morning
    Waited for 3minutes nothing, the led was just flashing. Could it be that the gps module is faulty?

    The one I mentioned previously took longer than 3 minutes to get a lock. Try 10 or even 15 minutes.

    How are you powering it?
  • inubusinubus Posts: 8
    edited 2012-03-14 11:46
    Thank you very much took supplied power to the module, went outside for a good 10 minutes finally got LOCK the led was solid not flashing anymore will now proceed with my project, but I will be bothering you again if I get stuck thanks to everyone
  • sylvie369sylvie369 Posts: 1,622
    edited 2012-03-15 09:13
    Ten minutes is not unusual in my experience. I'm sure your module is working fine, and you just have to be patient.

    There are other, newer modules that get a lock much more quickly, but as someone has pointed out, that first time you will have to wait a surprisingly long time.
  • Mark_TMark_T Posts: 1,981
    edited 2012-03-15 17:46
    Ah, yes, just checked wikipedia, almanac takes 12.5 minutes to transmit - modern GPS units will have a recent copy preloaded I suspect (although it eventually gets out of date).
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