[time-nuts] GPS Valid Fix Detector
Ulrich Bangert
df6jb at ulrich-bangert.de
Mon Nov 24 10:00:45 UTC 2008
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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