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

unruh unruh at invalid.ca
Sat Feb 11 00:41:23 UTC 2012

On 2012-02-09, Ron Frazier (NTP) <timekeepingntplist at c3energy.com> wrote:
> On 2/9/2012 1:34 AM, David J Taylor 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
>>> Here are the parts of a pretty cool article referenced on the 
>>> SparkFun site regarding interfacing to these type of modules.  About 
>>> 70 pages of info not counting the data logger article.
>>> http://www.kronosrobotics.com/Projects/GPS.shtml
>>> http://www.kronosrobotics.com/Projects/GPS1.pdf
>>> http://www.kronosrobotics.com/Projects/GPS2.pdf
>>> http://www.kronosrobotics.com/Projects/GPS3.pdf
>>> http://www.kronosrobotics.com/Projects/GPS4.pdf
>>> http://www.kronosrobotics.com/Projects/GPSLogger.pdf
>>> Sincerely,
>>> Ron
>> Thanks for the posting.  Yes, those look good, Ron, although for the 
>> same money you can get a ready-made, full board with puck antenna 
>> which works nicely with NTP:
>>  http://www.sureelectronics.net/goods.php?id=99
>>  http://www.satsignal.eu/ntp/Sure-GPS.htm
>> Cheers,
>> David
> Hi David,
> I'm certainly considering that board.  It looks very attractive.  I'm 
> going to have to read over the documentation page you've put together.  
> It looks very comprehensive.
> Chris Albertson said to get a unit which had:
>       1) - a stationary mode, or possibly only a stationary mode
>       2) - self survey
>       3) - PPS
>       4) - serial output
>       5) - NTPD driver support

It depends on the accuracy you need. If you are using it to set the
clock on a computer, you cannot get better that us accuracy because of
all of the junk which delays the interrupt processing ( delays of the
order of a few us). If you want to use the board for ns accuracy, then 1
and 2 are desireable, but for us accuracy, they are complete overkill.
So, If you are timing the flight of neutrinos from Cern to Grand Sasso,
by all means worry about 1, 2. 
Note that serial output is not needed. usb output is fine as well. (the
nmea output is good to a few ms accrucy at best and for that usb and
serial are equally ok) The PPS output needs to go into some line that
can drive and interrupt line to the cpu. Serial DCD or parallel ACK ( on
an old fashioned motherboard, unsharable, edge triggered parallel port).

> Now I know the Sure board has 3) and 4).  And I presume you can do 5) 
> through the generic NMEA driver.  However, do you know if it can do 1) 
> and 2)?  Actually, does it have native PPS, or are you adding it by 
> using the LED output?

It has native pps, but yo udo  have to do a bit of soldering. For the
parallel port ACK, a line from the PPS pin ( well hole) on the board to
the ack pin on the parallel port is fine, and probably for serial DCd as
well. If you really want to make sure that the serial port gets a signal
that complies with the serial port standard, you can use the wiring on 
but most modern serial ports will be fine with taking the signal
directly from the PPS hole on the board, without the serial
conditioning. the extra problem is taht that conditioning adds probably
.5us delay to the pps signal. Not a problem for computer applications, a
disaster if you are doing neutrino timing. 

> Sincerely,
> Ron

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