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

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Thu Feb 9 09:08:27 UTC 2012

OK, so I'm replying to my own message, what's strange about that?  8-)

VERY preliminary data, after running an hour with my USB GPS without PPS 
outputting only GPZDA sentences, I'm getting ~ +/- 5ms peak offsets of 
the computer clock vs GPS.  I'm liking it so far.  It initially looks 
more stable than when I was using GPGGA sentences.


On 2/9/2012 2:35 AM, Ron Frazier (NTP) wrote:
> 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:
> http://www.eecis.udel.edu/~mills/ntp/html/drivers/driver20.html
> 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.
> Sincerely,
> Ron
> 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.
I get about 300 emails per day from alternate energy mailing lists and
such.  I don't always see new messages very quickly.  If you need a
reply and have not heard from me in 1 - 2 weeks, send your message again.)

Ron Frazier
timekeepingdude AT c3energy.com

More information about the questions mailing list