Hello, as I've said these are quite new, cheap RTC modules. There is DS3231SN on them. Based on markings they were manufactured somewhere in 2008 but I've bought them recently.
I have two those modules. Both connected using I2C. First module is connected to Orange Pi sitting on my table. Pi is running NTP and is controlled by NEO-6M GPS module (not timing, I know butat this level accuracy of PPS signal should be enough). I measure in 10 seconds intervals difference between system time (which I consider stable in long term) and time reported by RTC chip as reported by adjtimex in compare mode. This is a little bit naive setup because timing from RTC is noisy but in long run (its running for 25 days now) it should give me reasonable results. I did modify offset register. Again using naive approach. I've let run unmodified module for one day and from that I did compute offset required. For second module I'm meassuring just now I don't care about time reported and meassure only interval between rising edge of its PPS pulses and PPS pulses from another GPS. Again for this measurement I consider GPS PPS signal as stable. This second one is a little bit worse (or may be wrongly calibrated) but I still get about 0.3PPM from my measurements. Petr Titera Dne 17. 2. 2019 v 19:00 Joe Hobart napsal(a): > Hello Petr, > > Your accuracy results are impressive. I have questions: > > What manufacture or brand DS3231 do you have? > > What do you use to communicate with the DS3231 and display time? > > How long has your DS3231 been running? > > Have you changed the crystal aging offset register(s) to compensate for > crystal aging? > > Thank you, > Joe > > > On 2/15/2019 12:51 PM, Petr Titěra wrote: >> Hello, >> >> sorry to reopen this old thread but it took me some time to measure. As >> I've said I have one RTC module sitting right on my desk in my room >> where temperatures can go anywhere between 3C and 20C. >> >> Using naive method of comparison of time difference between system time >> and RTC module I get time difference only about 4.487869e-02 seconds in >> 22 days. >> >> Petr Titera >> >> Dne 14. 1. 2019 v 16:11 Joe Hobart napsal(a): >>> Hello Petr, >>> >>> I have not found a low power RTC chip that will keep 1 second a month with >>> changes in temperature. This clock will be used to synchronize a portable >>> communications system. >>> >>> Thank you, >>> Joe >>> >>> >>> On 1/13/2019 2:23 PM, Petr Titěra wrote: >>>> I will probably sound dumb but did you consider cheap RTC chips? I have >>>> one based on DS3231 currently on my table and although its is specified >>>> to have precision +/-2PPM my seems to be in range about 0.5PPM right >>>> from package with possibility to do some corrections. >>>> >>>> Petr Titera >>>> >>>> Dne 11. 1. 2019 v 20:57 Joe Hobart napsal(a): >>>>> I need a relatively lightweight, self powered, portable clock accurate to >>>>> 1 >>>>> second per month. Temperatures may range from 10 to 35 C; altitude from >>>>> 1000 to >>>>> 7000 feet. Although expensive, some of the marine quartz chronometers >>>>> appear to >>>>> meet this requirement. ~0.3 PPM. >>>>> >>>>> Does anyone have any experience with these devices? >>>>> >>>>> If so, has anyone tried to detect the probably weak magnetic field >>>>> generated by >>>>> the clock mechanism for time comparison purposes? >>>>> >>>>> Thanks, >>>>> Joe, W7LUX >>>>> >>>>> --- >>>>> This email has been checked for viruses by AVG. >>>>> https://www.avg.com >>>>> >>>>> >>>>> _______________________________________________ >>>>> time-nuts mailing list -- [email protected] >>>>> To unsubscribe, go to >>>>> http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com >>>>> and follow the instructions there. >>>>> >>>> >> _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
