NXT-G and GPS - closer than ever?

Saturday, September 15th, 2007

I’ve been working on the issue of BT GPS connection for the past few days, ever since Antonio’s NXC code demonstrated that this is a possibility. In the LabView diagram above (click here for full resolution image) I show a preliminary step toward this goal. I’ve made VIs (i.e. the LabView term for blocks) that read an ASCII stream, and some prelimiary string parsing VIs. Since I have no BT GPS, I had my PC connect as the slave device, and wrote another LabView code that sends the NMEA-0183 formated string:
$GPGGA,023346.028,3604.1654,N,08655.7973,W,0,00,50.0,198.2,M,-31.6,M,0.0,0000*76\r\n
at specified intervals (e.g. each 1000 milisecond).
The resulting file stored on the NXT contains a long list of this message:
GPGGA,023346.028,3604.1654,N,08655.7973,W,0,00,50.0,198.2,M,-31.6,M,0.0,0000
GPGGA,023346.028,3604.1654,N,08655.7973,W,0,00,50.0,198.2,M,-31.6,M,0.0,0000
GPGGA,023346.028,3604.1654,N,08655.7973,W,0,00,50.0,198.2,M,-31.6,M,0.0,0000
GPGGA,023346.028,3604.1654,N,08655.7973,W,0,00,50.0,198.2,M,-31.6,M,0.0,0000
.
.
.
without any errors so far. From another test is seems that as I suspected the NXT ‘catch’ the GPS data correctly every 2-3 cycles of my “GPS” data stream.
What’s next? Parsing the GPGGA data, and making the NXT-G block around all this… Keep watching for it!

In the meantime, Antonio posted me an improved version of the code. He claims this code loses only 20% of the messages (compared to ~60% in mine, and his old code). You can download the new code here. I still need to figure out what makes the difference, and see how I can implement it in LabView…

Questions/comments - use this forum topic.

Guy Ziv

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