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Hot!using OSCULP32K as time keeping purpose

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XYXD
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2020/01/16 16:09:27 (permalink)
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using OSCULP32K as time keeping purpose

Hi, has anyone used internal 32kHz ULP OSC for calendar time keeping ? I'd like to use it if possible, but the frequency shifts as Vdd and temperature. I did worst case calculation and find it can end up off by many days after 1 year. 
I intend to use it as time keeping for environmental sensor, but if it is off by days it won't be useful. But I may overestimate the error, just want to see if anyone has experience on this.
Thanks.
 

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    NKurzman
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    Re: using OSCULP32K as time keeping purpose 2020/01/16 17:20:34 (permalink)
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    First you did not specify a chip, or even a chip family.  And you did not post in a forum for your Chip.
     
    BUT, In general internal oscillators are not good for time keeping. And the 32KHz are usually the worst.  How many hours per year are you looking for.  Note for General time keeping Standard CPU Crystals are also not good.
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    XYXD
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    Re: using OSCULP32K as time keeping purpose 2020/01/17 07:52:26 (permalink)
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    Thank you. I am testing with ATTiny1614, but there can be other 8-bit choices. Maybe I need separate RTC. My application is battery powered environmental sensor that also log calendar time. The supply voltage can vary between 3~1.8V and I think the temperature might vary between -40C~60C. I wish to have accuracy of a couple minutes for a year. Is it possible ?
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    Aussie Susan
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    Re: using OSCULP32K as time keeping purpose 2020/01/19 18:56:02 (permalink)
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    Many crystals have 10ppm accuracy which equates to 10E-5 error. Given there are about 31,557,600 seconds in a year that is 316 seconds a year or a little over 5 minutes.
    I think you may also get variation with temperature but you will need to look at the crystal data sheet for exactly how much.
    Susan
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    NKurzman
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    Re: using OSCULP32K as time keeping purpose 2020/01/19 23:30:27 (permalink)
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    Many pics will run a 32KHz watch crystal on a secondary ocillator. That is also an option.
    #5
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