[ntp:questions] YEA! My Sure Electronics GPS just arrived.

David J Taylor david-taylor at blueyonder.co.uk.invalid
Sat Mar 24 11:05:13 UTC 2012

> I now have the PPS circuit working on the Sure board.  I have not 
> soldered it yet.  I just taped a jumper wire between the PPS test point 
> at the edge of the board and the DCD pin 1 on the RS-232 port.  The 
> serial data is coming in through the Trendnet TU-S9 serial - USB 
> converter, which is passing DCD.  I'm getting + .5 / - 1.5 ms offsets. 
> The PPS is nowhere to be seen on the statistics screen, but it is 
> obviously working.  I don't know why it's not more centered around zero, 
> and maybe that will change.  However, my total peak to peak range of 
> offset variance is 2 ms, and that's coming through USB.  If I can 
> maintain that level of accuracy, and it's consistent with UTC, then I'm 
> very happy.  That's plenty good for my purposes.  I still may try to run 
> it through a real serial port on another machine just for kicks.
> Sincerely,
> Ron


Yes, those were the sorts of figures I was seeing.


The jitter I saw was about 45 microseconds for the USB/PPS against 2.3 - 3 
microseconds for various serial-port/PPS.  All figures from Windows XP. 
If the graphs there are anything to go by it seems that the offset varied 
between -0.15 to +0.3 milliseconds (very approximately).


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