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Thread: Mid$ not recognised39 days old

  1. #11
    Administrator John Drew's Avatar
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    Default Re: Mid$ not recognised

    @Charlie
    I think I make more compiles than the cricket team makes runs.

    @George
    I'm inclined to agree re the lock. In my rework of the GPS code for this latest project I detect the $GPGSA second item and decode that into 'No lock', '2D lock', '3D lock'.
    I wonder if during the 2D fix data gets a bit wobbly? Maybe that is what Charlie observed.
    In the meantime my software is now working nicely and the pins of the 16F628A and the socket survived. I only allow the LCD to display if there is a 3D fix.
    Now will the cricketers survive? I wish I received as much for my programming ($0) as the cricketers get ($lots)

    John

  2. #12
    Prolific Poster charliecoultas's Avatar
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    Default Re: Mid$ not recognised

    Found the answer: the GPS system has "leap seconds" added but some of the GPS receiver manufacturers apply it differently to others.
    To compensate for this the GPS system transmits a "leap second correction" every 12.5 minutes. Which is why my 2nd clock gets the correct time eventually.

    So the time you get on your start-up might be wrong by a few seconds but within 12.5 minutes it will be correct. It is to do with the difference between GPS time and UTC time.

    Charlie

    John: Would it be of interest for me to put my "GPS Clock (with Decatron seconds display)" on the Wiki?
    It has a very busy interrupt structure to keep several things all happening seamlessly.
    Last edited by charliecoultas; 20th March 2018 at 09:30.

  3. #13
    Administrator John Drew's Avatar
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    Default Re: Mid$ not recognised

    It certainly would be Charlie. I just polled but interrupt would be sweeter. There's a GPS section in Example code.
    What is the delay between the GPS calculating the time and the NMEA sentence arriving on the serial port? It must be another source of error.
    In the past I've found it necessary to add a second to more closely print the more accurate time.
    John

  4. #14
    Prolific Poster charliecoultas's Avatar
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    Default Re: Mid$ not recognised

    The one-pulse-per-second output from the GPS module is the sync signal to the time just given in the NMEA sentence. A bit like the speaking clock.

    Charlie

  5. #15
    Administrator John Drew's Avatar
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    Default Re: Mid$ not recognised

    Thanks, so just checking if I understand.
    1) read sentence
    2) do the sums
    3) wait for the pulse

    Cheers
    John

  6. #16
    Prolific Poster charliecoultas's Avatar
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    Default Re: Mid$ not recognised

    I reckon that's right John. I am currently inputting a WIKI article about my clock, the code for parsing the NMEA sentences is shown but I don't use the 1 second pulse.
    The one second pulse is a hardware output from the module.

    Charlie
    Last edited by charliecoultas; 21st March 2018 at 09:08.

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