[time-nuts] TruePosition on the Arduino
holrum at hotmail.com
Tue Jun 6 22:39:15 EDT 2017
If you run it on a system with an accurately set clock, Lady Heather can measure the offset (and standard deviation and ADEVs) between the time in the receiver time code message and when the last byte of the time code message comes in. It also calculates a histogram of the message offsets. Since Heather does not use a 1PPS interrupt, it uses the message offset to adjust the receiver time code time to the displayed time (the on-screen clocks are updated when the last byte of the time code message comes in).
Most receivers are surprisingly well behaved in their message timing... a few are not. Only a few receivers (like the Z38xx and RFTG-m) output the time code message before the 1PPS. Most receivers have a message offset of around +200 milliseconds. The Jupiter receiver time codes are off by around 1200 milliseconds!
I just added some code to Heather for doing an audible "tick" clock that ticks the second and beeps the minute (you can change that with your own sound files). The tick clock uses the end-of-message offset time to make sure the ticks are closely aligned to the PPS time.
> Calibrating your GPS pulse ambiguity is one of the all time great reasons to get a
WWVB based wall clock !!!
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