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Topic: DS1307 backup not running (Read 745 times) previous topic - next topic

joe jefferies

Hi

I have a Nano with a DS1307 RTC daughter board attached. The clock is working Ok but for one thing - the backup oscillator does not run when I disconnect the power. The Nano is (for the present) getting power from the USB (checks out as 4.8 volts) , the lithium battery voltage checks out at 3.7V and the RAM registers are held for when I re-power the circuit.

any ideas please

Joe

Erdin

Perhaps the crystal has problems.
If you search this and other forums, you will find a lot of problems with the DS1307 with cheap components.

The 3.7V should be enough, even with a cheap crystal. Are you sure it is connected as it should ? Would an extra 100nF on the power supply help to reduce a power glitch ?

joe jefferies

Hi
Thanks for your reply.

I am sure the components on the daughter board are very cheap as the while thing cost much less than the individual components would and you get what you pay for.

As to whether it is connected correctly, I just connected scl and sda and power to the board and it does function.

Are you implying that a cheap crystal would oscillate at 5V but not at 3.7? - I don't know about these things.

I will try your suggestion of the 100nF capacitor on the power supply when I lay my hands on one.

Joe

afremont

The maximum Vbat is 3.5V, maybe that's a problem.  You could try draining the battery some with a resistor until the voltage gets down below 3.5V.
Experience, it's what you get when you were expecting something else.

joe jefferies

Hi
Thanks for that.
Actually this afternoon when I was looking for something else I found a brand new 2032 lithium battery and swapped in for the one in the clock and hey presto it works fine now. So cheap and nasty battery was the problem.

Thanks again
Joe

afremont

Out of curiosity, what is the voltage on the "new" battery?  Is it less than 3.5V?  I've noticed before that those CR2032 batteries are pretty high on their initial voltage.
Experience, it's what you get when you were expecting something else.

joe jefferies


afremont


Hi
Its about 3.5V
Joe



So the 3.7V would seem to be the source of the problem.  Thanks for replying.
Experience, it's what you get when you were expecting something else.

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