[ntp:questions] lots of GPS modules and info at SparkFun

David J Taylor david-taylor at blueyonder.co.uk.invalid
Thu Feb 9 18:03:06 UTC 2012


> Hi David,
>
> I just finished reading your Sure board web page.  That's a really good 
> write up.  I now understand how you're getting the PPS signal.  Could 
> you possibly share the rev level of the board, since, if they change the 
> design, you patch instructions may not work any more?  Some boards don't 
> have a rev level.

I didn't make a note of the rev levels.  Just check that the inverter and 
TTL-RS232 gate are spare.

> As suggested by Brent Gordon's post, and confirmed in the manual for the 
> Trimble Copernicus II, I have switched my GPS to output only the GPZDA 
> sentence and changed the NMEA driver to respond to that.  I don't think 
> the GPZDA sentence has any position information, so it's length should 
> be very consistent.  Whatever the reason, the results are amazing. 
> Although I've only been running this way for 8 hours, my peak offsets 
> are now in the +/- 6 ms range.  Of course, we'll have to see if the 
> system continues this way, or if my GPS goes phycho again.  This is 
> twice the level of performance and accuracy than I had before.

Yes, this is excellent news.

> Now, I will probably try some PPS stuff, just for intellectual reasons 
> and just because it would be really cool to see that chart drop under 2 
> or 1 ms.  However, for my simple purpose of just keeping all my PC 
> clocks right to the second, if I can keep this thing under 10 ms of 
> error, I'm pretty happy with it.  And this is still USB only.
>
> Assuming it's possible to program the Sure board for GPZDA, it would be 
> interesting to see if doing that affects the performance you're seeing. 
> Of course, if you're using PPS, the specific content of the NMEA 
> sentence may not matter as much.
>
> Sincerely,
>
> Ron

>From the Sure board you would likely get best results with the PPS line 
tied to the DCD pin on a real serial port, and that's what I'm doing.

Cheers,
David 



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