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Topic: Inaccurate DS1307 (Read 3 times) previous topic - next topic

Slugsie

OK, how do I find that out - without a datasheet for the crystal? I've tried to test it with my multi-meter, but it seems to show open circuit with the crystal unconnected to anything. Is there a way I can try and read the ESR?

jluciani

You would need the datasheet for the crystal.

This could be a half-baked idea -- if you set the DS1307 square wave
output to 32768Hz this should output the crystal frequency 1:1. You could
measure the frequency with an oscilloscope (or another Arduino). Any deviation
from 32768 would affect the time keeping accuracy.

(* jcl *)

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kg4wsv

Dallas also recommends a separate ground plane for the xtal and related IC pins.  Check the datasheet for details.

-j

Slugsie

@jluciani
Unfortunately I neither have access to an oscilloscope nor another Arduino, so testing the output would be hard. To be honest I'm not experienced enough at the moment to do that measurement with an Arduino anyway.

@kg4wsv
I'm very green with regards to electronics at the moment, so if grounding the body of the crystal isn't sufficient to achieve the 'ground plane' then can you point me at a resource so I can learn how to do this correctly.

Slugsie

I've just found a datasheet for the crystal, it has an ESR of 35kOhm, so it should be within tolerance.

http://www.farnell.com/datasheets/75563.pdf

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