ExtBat to set Real Time Clock (RTC)

Discussion in 'UDOO QUAD' started by rswamy, Sep 20, 2017.

  1. rswamy

    rswamy New Member

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    I'd like to add an external battery for the real time clock, but not sure if it will be drained quickly if it's powering other things on the board.

    What are the specs of the ExtBat and what is it used to power?
     
  2. sirrab

    sirrab UDOOer

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    If you internet access, why not use that to update the time?
     
  3. rswamy

    rswamy New Member

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    I don't have internet access in my application which is why I'm looking at the extbat, thanks for the tip though!
     
  4. fetcher

    fetcher Member

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    The 3V battery connects directly to VDD_SNVS_IN on the i.MX6 CPU, which runs only the RTC and a few registers. Either a lithium coin cell (CR2032, etc.) or 2*AA's in a holder will work. I've measured the current draw and found it negligible, but can't remember the exact value.

    Unfortunately, there appears to be something wrong with the RTC on Udoo Quad boards, possibly in how the 32kHz watch crystal is connected or bypassed. I've found it to be wildly inaccurate across multiple boards, running far too fast when main system power is on, but too slow when power (except the battery) is removed. Here's an old post I made about that over two years ago, which never saw any follow-up:

    https://www.udoo.org/forum/threads/real-time-clock-i-mx6-rtc-snvs-is-very-inaccurate.2171/

    I'm still using old 3.0.35 kernels on my Udoo's, and it's possible this was a software setup issue with the RTC's driver that got fixed in a subsequent release, so it'd be worth trying to see how yours performs, but be sure to test RTC accuracy before relying on it!

    My systems usually have Internet access for NTP synchronization, so for me this is more an annoyance than a show-stopper (leaving the battery connected is still useful for getting a correct date, if not time, in initial boot logs before the network's available).
     
    rswamy and waltervl like this.

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