[time-nuts] DS3231 drift over a year

Brooke Clarke brooke at pacific.net
Fri Jul 14 12:56:11 EDT 2017

Hi Pete:

AFAICR the DS3231 has a software fine tune.  Did  you set that before the test?

Have Fun,

Brooke Clarke

-------- Original Message --------
> Hi all,
> I use some DS3231 temperature-compensated real-time clocks with some
> Raspberry Pis, particularly those that might not always have internet
> access. About a year ago I wrote some code [1] to characterize the
> behavior of these particular chips using my Thunderbolt as a reference,
> using the Arduino/atmega328 as a glorified counter.
> As a somewhat longer-term test, I set the time on one of the DS3231s to
> the correct time using GPS-synced NTP on one of the Pis, then set the
> whole thing on the shelf for a bit over a year and forgot about it. If
> relevant, the only power source was the CR2032 battery.
> I checked it today, and the clock had drifted 16 seconds since June 6th
> of 2016 to now. That works out to around 0.5 ppm drift over that time.
> The chip is specced to +/- 2ppm. Not bad for a cheap module of
> potentially dubious provenance from eBay. For those who are curious, I'd
> be happy to provide a link to the specific item I purchased; contact me
> off-list for details.
> Cheers!
> -Pete
> [1] https://github.com/heypete/Frequency_Counter_32kHz

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