Blue Pill crystal does not start

Generic boards that are not Maple or Maple mini clones, and don't contain the additional USB reset hardware
asmallri
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Joined: Fri Oct 06, 2017 12:37 am

Re: Blue Pill crystal does not start

Post by asmallri » Thu Dec 07, 2017 3:23 pm

This is the same behaviour I am seeing. If I do not use the alarm function the RTC keeps accurate both when the system is continually powered up and when the system is shutdown for hours or days. However if I put the processor into a deepsleep and wake-up every 2 minutes then the RTC will lose several minutes per day.

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RogerClark
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Location: Melbourne, Australia
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Re: Blue Pill crystal does not start

Post by RogerClark » Thu Dec 07, 2017 7:59 pm

are you sure this is the same problem

It potentially sounds like a software issue related to waking and sleeping

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ahull
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Re: Blue Pill crystal does not start

Post by ahull » Fri Dec 08, 2017 11:38 am

It sounds to me like you are setting the wrong clock source for the RTC (or the wrong source is set by some other code within the libs you are using), when entering your sleep mode. You need to ensure the 37768 Hz crystal remains the clock source for the RTC, otherwise you may end up loosing accuracy, or stopping the RTC completely.

https://electronics.stackexchange.com/q ... ock-source
- Andy Hull -

ag123
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Joined: Thu Jul 21, 2016 4:24 pm

Re: Blue Pill crystal does not start

Post by ag123 » Sat Dec 09, 2017 6:27 am

more recently i've somewhat improved on my 32k crystal soldering, a recent attempt here
viewtopic.php?f=3&t=2602&p=38423#p38423
oh yes, on another note, i keep vbat powered on a coin cell battery (cr2032), rather often i simply unplug usb, cutting off power, leaving rtc running on the coin cell. reconnect, and time is kept, no issues, i didn't meddle with alarm or sleep though. i'm not too sure if on MM, BP if 3v3 is connected to VBAT
i think i read somewhere it is recommended if you do not power vbat separately

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