[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.
>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.
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