[time-nuts] GPS Valid Fix Detector

Robert Darlington rdarlington at gmail.com
Mon Nov 24 15:48:03 UTC 2008


I worked wtih a GPS module that would spit out all zeros for lat/long if
there was no fix, and another that would spit out the coordinates for the
manufacturer's office.  It'll probably be hard to weed out every special
case, but with the code, any of us can easily just modify it for our own
needs.  Thank you for taking the time to at least get *me* started :)  You
saved me a lot of trouble.

-Bob

On Mon, Nov 24, 2008 at 3:00 AM, Ulrich Bangert <df6jb at ulrich-bangert.de>wrote:

> Peter,
>
> in general NMEA decoding involves
>
> 1) Message type detection
>
> 2) End of message detection
>
> 4) Checksum test
>
> 5) Looking for what is to be found between comma N and comma N+1, having
> in mind that there may also be NOTHING.
>
> Best regards
> Ulrich Bangert
>
> > -----Ursprungliche Nachricht-----
> > Von: time-nuts-bounces at febo.com
> > [mailto:time-nuts-bounces at febo.com] Im Auftrag von Yuri Ostry
> > Gesendet: Montag, 24. November 2008 04:21
> > An: Peter Putnam; Discussion of precise time and frequency measurement
> > Betreff: Re: [time-nuts] GPS Valid Fix Detector
> >
> >
> > Hello,
> >
> > Monday, November 24, 2008, 1:08:45, Peter Putnam wrote:
> >
> > P> Greetings,
> >
> > P> For those interested in a very simple means of determining if the
> > P> NMEA data stream from a GPS receiver contains valid fix
> > data, I offer
> > P> design details for a "Valid Fix" detector that runs in a Microchip
> > P> 12F629, an 8-pin DIP device.
> >
> > P> No other components are required if the GPS receiver provides CMOS
> > P> output levels:
> >
> > P> http://www.ni6e.com/time/GPS_Valid_Fix.html
> >
> > P> Regards,
> > P> Peter
> >
> >
> > Looks like your firmware will need some correction, as there
> > is a lot of NMEA variations...
> >
> > Below is examples of GPRMC sentences from several different
> > GPS receivers. You'll need to pick character after second
> > comma, not by particular offset, to be compatible.
> >
> >
> > uBlox LEA4A (firmware 4):
> > $GPRMC,214541.00,A,5558.55936,N,03709.54595,E,1.116,104.33,120
> > 107,,,A*6A
> >
> > Trimble Pathfinder Pro XR
> > $GPRMC,050945.00,A,3504.227794,N,13545.810149,E,000.0,57.1,140
> > 302,6.5,W,A*12
> >
> > Garmin GPS III Plus
> > $GPRMC,031655,A,3404.456,N,13531.788,E,000.0,360.0,110101,006.8,W*6D
> >
> > Garmin GPSMAP 76S
> > $GPRMC,040014,A,4242.0410,N,14134.2795,E,1.4,51.0,010802,8.0,W,A*35
> >
> > Blue Logger GPS (Something from Japan)
> > $GPRMC,021803.751,A,3501.5666,N,13546.9457,E,0.00,212.31,110604,,*07
> >
> > uBlox SBR-LS (firmware 3.01)
> > $GPRMC,051250.00,A,5558.55523,N,03709.54211,E,1.177,229.34,080
> > 705,,,A*6E
> >
> > GlobalSat BT-338 (SiRF)
> > $GPRMC,100643.000,A,5522.9036,N,03710.1282,E,0.16,119.11,200507,,*0D
> >
> >
> >
> >
> >
> > --
> > Best regards,
> >  Yuri                          mailto:yuri at ostry.ru
> >
> >
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> >
>
>
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