[time-nuts] GPS Valid Fix Detector

[Ulrich Bangert]

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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