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

unruh unruh at invalid.ca
Sat Mar 24 16:46:55 UTC 2012

On 2012-03-24, Ron Frazier (NTP) <timekeepingntplist at c3energy.com> wrote:
> 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, 

Peaked around zero in comparison with what? Remember that the serial to
usb of dcd and then the decoding of that interrupt is going to institute delays. It should always be later than "true time". 
> 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.

You can get 1us, not 1ms that way. But if a factor of 1000 is irrelevant
for you, then what you have is fine. 

> Sincerely,
> Ron

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