On Wed, 13 Jun 2018 21:42:39 +0100, Simple Simon wrote:

> I use a Raspberry PI to run the WeeWX Weather Staion software.
> The weather staion it is connected to is a Vantage Pro2.
>
> The Pi as we all know does not have a real time clock and gets its time
> from the network.
>
> WeeWX sets the clock on the Vantage at startup.
>
> WeeWX starts up before the network is up and if there has been a power
> outage it sets the time wrong. The Pi then picks up the corrects time
> and there is a conflict of times.
>
> I could have written a delay into WeeWX but thought I would have go at
> adding a RTC.
>
> https://www.adafruit.com/product/3386
>
> Is the one I got. Very simple to set up and get running.
>
> When the RTC is installed, as per instructions, I wated till the correct
> time had been picked up from the network and then I used
>   sudo hwclock -w
> to set the correct time on the RTC. I then uninstalled the Fake Hardware
> Clock.
>
> Now the questions!
>
> 1) Is there anyway to check the battery level on one of theses (I
> suspect not)
>
> 2) I assume that the RTC will not be updated with the network time
> automatically. If this is correct I will need to correct the drift. Is
> there a way to check for drift or should I just used crontab to do a
> regular sudo hwclock -w if so how often? Hourly, daily, weekly or
> monthly!
>
> Thanks



You should be able to set the rtc when the pi gets an update from ntp.
Adafruit also has a couple of 'learn' articles about working with rtc on
the pi.

It's always been my experience that rtc's on computers - even expensive
ones - don't keep time as well as a $5 watch.

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