[time-nuts] DS3231 drift over a year
craigk46 at comcast.net
Fri Jul 14 12:36:43 EDT 2017
I set a DS3231 to correct time of WWVB in January 2017 and it has not gained or lost one second in over six months!
The clock chip is part of a project board that I have running on power during the day and powered off overnight meaning that for about half the day the DS3231 is keeping time using just the watch cell backup battery. Temperatures have varied in the range of 60F to about 85F.
This performance is impressive for an Integrated circuit chip costing under ten dollars.
I bought a second DS3231 and I'm thinking of a simple experiment project to compare two of the chips and how they drift relative to each other just for fun.
On Jul 14, 2017, at 2:55 AM, Pete Stephenson <pete at heypete.com> wrote:
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  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.
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