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

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Thu Feb 9 07:35:36 UTC 2012

Hi Brent,

I spent a little while skimming over the 254 PAGE! pdf of the manual 
from the SparkFun website.  The device is certainly well documented.  I 
couldn't find where they specify the timing relationship you specify.  
That's very interesting if it's consistent.  I'm currently using a 
GlobalSat BU-353 USB only GPS, outputting only the GPGGA sentence only 
at 57600 baud.  I'm getting ~ +/- 15 ms peak offsets between the 
computer clock and the GPS polling every 8 seconds with jitter averaging 
around 3 ms.

Based on your note and some data in the Trimble manual, I've reset my 
GPS to output only the GPZDA sentence.  I looked at the link below to 
find the mode command to set NTPD to recognize this sentence:


It turns out mode 8 does the trick, plus the other bits I add to get to 
57600 baud, so it works out to mode 72.  So, the GPS part of my ntp.conf 
is thus:

server                prefer minpoll 3 maxpoll 3 mode 72
fudge time2 0.3550 refid GPS1

So, I'm going to let that run a while and see if it's more stable than 
the GPGGA setup.



On 2/8/2012 6:37 PM, Brent Gordon wrote:
> One cool thing about the Copernicus, beside the PPS, is that the 
> datasheet specifies the delay from the PPS to start for the ZDA 
> sentence.  This means you can use the serial data directly without 
> having to use the PPS.  On other GPS units I've looked at, the delay 
> from PPS to ZDA varies greatly (300 ms +/- 150 ms).
> Brent
> On 2/8/2012 3:23 PM, Ron Frazier (NTP) wrote:
>> Hello all,
>> While researching potential GPS modules to experiment with for PPS 
>> output, I discovered that SparkFun has quite a lot of modules, some 
>> of which have PPS and some of which don't.  You can't necessarily 
>> tell from the product page.  You have to check the data sheet.  You 
>> can go to their website and search for gps.  This link should also 
>> work.  Just thought I'd pass it along.
>> http://www.sparkfun.com/search/results?term=gps&what=products
>> Here is one unit which does have PPS but it's not obvious from the 
>> product page.  There are others as well.
>> 12 Channel Copernicus II GPS Receiver - from Trimble - 
>> http://www.sparkfun.com/products/10922


(PS - If you email me and don't get a quick response, don't be concerned.
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Ron Frazier
timekeepingdude AT c3energy.com

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