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

Ron Frazier (NTP) timekeepingntplist at c3energy.com
Sun Mar 25 21:06:21 UTC 2012

On 3/24/2012 12:46 PM, unruh wrote:
> 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".

I just meant that the offsets were shifted more toward the positive on 
the graph rather than being centered around zero.  They seem to be 
centered around zero now.

>> 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.

I don't have to have 1 us.  I just want the computer's clocks to be 
right and to be doing better than I can with internet servers.  In that 
regard, any offsets better than 50 ms are good.  I plan to test this GPS 
for a while and and make sure it's stable.  Then, I want to set up every 
computer so it can use the GPS if it's attached.  Then, I'll try the 
real serial thing on the PC that has a port.  Eventually, I want to make 
probably that one a server for all the rest.  I'll probably have to give 
the server a fixed IP address in my router since those can change when 
DHCP assigns them.

>> Sincerely,
>> Ron


(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
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Ron Frazier
timekeepingdude AT c3energy.com

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