GPS-time behind on DCF77?

by bartgrefte on Sun Nov 25, 2012 3:38 pm

Hi,

a little over 2 years a go I equipped my Ice Tube clock with a GPS. It has worked like a charm so far, but there's one thing that I am curious about.

When I compare the GPS-timesynch of my Ice Tube clock to my watch witch uses DCF77, the Ice Tube clock is 2 seconds behind. After putting Google to good use, I found out that clocks that use GPS/NMEA for timesynch are known to be a second behind.

Has anyone with the Ice Tube clock and GPS noticed the same thing?
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Re: GPS-time behind on DCF77?

by adafruit_support_rick on Sun Nov 25, 2012 5:00 pm

Don't forget that there is serial communication overhead between the GPS and the clock.
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Re: GPS-time behind on DCF77?

by bartgrefte on Thu Nov 29, 2012 3:46 am

Can something be done about that? Something to compensate the overhead?

Sorry for the late answer, was unable to reply yet again, captchas prevented me to. They kept failing to verify.
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Re: GPS-time behind on DCF77?

by adafruit_support_rick on Fri Nov 30, 2012 12:36 pm

Well, the overhead should be consistent. You could mod the code to subtract 2 seconds from the updates.
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Re: GPS-time behind on DCF77?

by bartgrefte on Sat Dec 01, 2012 4:49 am

Can this be done when you've only got the hex file?
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Re: GPS-time behind on DCF77?

by adafruit_support_rick on Sat Dec 01, 2012 12:34 pm

bartgrefte wrote:Can this be done when you've only got the hex file?

No, sorry. You'd have to mod the source and recompile.
The sources are available on the tutorial page.
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