real time clock on MDBT42Q

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  • is there a real time clock on MDBT42Q bare module? If so, how accurate is it? If not, how can I add one?


  • Yes, there is! Someone asked this a week ago about the Puck (which has the same chip) so the answer there might help:­326756/#comment14462460

    In terms of accuracy it's about 20 parts per million I believe. Realistically most on-chip RTCs even with separate crystals end up around that as that's what a lot of the crystals are rated at.

    The DS3231 that you can add on is significantly better though at around 2ppm though.

  • Sorry, I don't understand what 20 parts per million means, is it like a few seconds a month?

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    20 (parts) per Hundred  (parts) = 20 per 100 = 20% = 0.20


    20 parts per Million (parts) = 20 per 1,000,000 = 0.000020. 

    Since an average month has 30 x 24 x 60 x 60 = 2,592,000 seconds, about 2,600,000 seconds = 2.6 M seconds , 20ppm means 20x2.6 = 52 seconds +- accuracy per month, about 1 Minute per Month or roughly 2 Seconds per Day.

  • I'm working on connecting a DS3231 to an MDBT. 4ppm, and battery backed up. Since it's i2c, should be pretty trivial to interface.

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real time clock on MDBT42Q

Posted by Avatar for barry_b_benson @barry_b_benson