[time-nuts] DS3231 drift over a year

[Pete Stephenson]

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

-- 
Pete Stephenson