[time-nuts] Re: RTC DS3231: how well can it be regulated?

[ASSI]

On Sonntag, 18. Juli 2021 04:06:56 CEST Tim S wrote:
> I did want to pose the question, are you aware of the existence
> of DS1341/DS1342 RTCs? These parts have a 1pps (or power-line 50/60Hzr
> following built-in.

On these chips the PPS alignment is done by selecting an edge from a 128Hz 
division of the XTAL input, which is always completely free-running.  This 
results in a skew window of almost 8ms on the PPS pulse and large deviations 
in holdover.  So while I can see them working very well for a different 
application, that's not what I was looking for.

The DS3231M can be tuned from the datasheet value of ±5ppm or about half a 
second per day to around 15ms/day holdover.  I have one module lying around 
that I set up a year ago and then disconnected to let it run on battery.  
Based on the experience with the active one over that same year (which you've 
seen the plots of) I think it should still be within 30s when I eventually 
connect it again, which would be absolutely amazing considering the price of 
these modules.
 

Regards,
Achim.
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