Nanode RF Expansion - RTC gains a minute a day

I've recently purchased and installed the Nanode RF Expansion to my EmonBase.

The expansion includes an SD Card socket, RTC chip, watch crystal etc.

I believe the RTC Chip to be a MCP7941x.

The problem I have is that the clock is gaining a minute a day.

I'm an absolute novice when it comes to the whole Arduino hardware environment (or any hardware environment for that matter). So any advice on how to get the RTC more accurate would be very greatly appreciated.

I did want to be able to upload to COSM as well as logging to the SD card, but so far it appears I'm running out of memory - I can each action separately, but when I try to do both in the same sketch the program doesn't run...I've tried changing INTs to BYTEs and moving static variables into FLASH memory, and reducing BUFFER sizes (at which point I get some response) to no avail.

Yes I know I can get the date/time in the reply from COSM, but if I can't upload to COSM and write to the SD Card at the same time, then I'd sooner just write to the SD card in which case I need the RTC date/time to be accurate.

imarioscy's picture

Re: Nanode RF Expansion - RTC gains a minute a day

i know it's late but i found this online! 

Note - after the production of the board, it was found that the MCP7941x requires 2x 22pF ceramic capacitors fitting. Without these, the RTC lost about a minute per day. To resolve this, fit a capacitor from each leg of the cystal to ground. I'll work out the best way to do this and add further instructions and photo(s) when I can. This is not required if you use a DS1307 IC instead of the MCP7941x.

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