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Every few Hours clock running fast rtc1307

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sajsaj220

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What may be the possible cause for RTC1307 Module(Purchased from Market) running fast approximately 1sec in 3hrs.

Let me elaborate what I have done,

My code is in xc8 and internal osc configured in 8mhz at mcu16f887.

Display is 7segments, data being extracted from RTC1307 (MODULE) with I2C, technique Multiplexed and two button is used for time setting in h/w side. All are going correctly, but

Once adjusting time with the actual, noticed that after (apprx) 3-4 hours 1-second running fast. Is it the problems of RTC1307 Module or others of my h/w or software.

As per my opinion that could be only for the cause of RTC module, if so then how do i get rid of that..


Than u.
 

KlausST

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Hi,

What do you expect from us?
* If you want us to validate the hardware --> you need to show us
* If you want us to validate the software --> you need to show us

Klaus
 

betwixt

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Do what Klaus suggests first.
If it is just the clock running fast, the problem is the crystal (or external clock if you are using one) is too high in frequency. That could be because of the crystal itself or the track layout around it. You have to follow the design guidelines in the 1307 data sheet if you want it to be accurate.

Brian.
 

FvM

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What does running fast for 1 sec actually mean? How much is the time advancing?
 

kripacharya

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Also what would be useful to know is - what clock are you using to compare this too ? Maybe your reference clock is actually running slow by 1 second per 3 hours !! 1 sec in 3 hours implies ~ 100ppm, which is not good. But then, DS1307 is not known for great accuracy or stability. Check out this writeup.
 

andre_teprom

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Most 32.768KHz crystals (you did not mention, but it is presumably the one you're using) have good acuracy, ranging from ±5/10ppm up to ±20ppm in the worst cases; however it is possible to find brands with poor specifications of ±50ppm and even of ±100ppm (e.g this), which apparently is the one you have been got; as you took it in the retail, you certainly do not have any reference to the model/manufacturer, and in that case the tip would be to acquire a different one from this one.
 

kripacharya

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It would seem that OP was using an inappropriate reference to check the accuracy. A common noob mistake.
 

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