[time-nuts] DS3231 drift over a year

Pete Stephenson pete at heypete.com
Fri Jul 14 20:27:22 EDT 2017

Hi Brooke,

No. I did not perform any software fine-tuning. My earlier tests using
my Arduino/Thunderbolt-based testing setup indicated its short-term
drift was <1ppm, so it didn't think it'd be worthwhile. After over a
year of testing, I'm even more impressed.

In addition, I forgot to mention that the DS3231 in question was in an
indoor environment but not one with particularly stable temperatures: in
winter, indoor temperatures dropped to around 15C, while in summer it'd
get up to 30C, with direct sunlight from the window shining directly on
the Raspberry Pi enclosure holding the device for several hours each


Pete Stephenson

On Fri, Jul 14, 2017, at 06:56 PM, Brooke Clarke wrote:
> Hi Pete:
> AFAICR the DS3231 has a software fine tune.  Did  you set that before the
> test?
> -- 
> Have Fun,
> Brooke Clarke
> http://www.PRC68.com
> http://www.end2partygovernment.com/2012Issues.html
> -------- 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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