DS1307 backup not running


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


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 ?

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.


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.

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

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.

Hi Its about 3.5V Joe

[quote author=joe jefferies link=topic=156347.msg1174556#msg1174556 date=1364399276] Hi Its about 3.5V Joe


So the 3.7V would seem to be the source of the problem. Thanks for replying.