DS1307 RTC battery problem

Thread Starter

Saeedk9574

Joined Jan 1, 2024
9

Thread Starter

Saeedk9574

Joined Jan 1, 2024
9
A new CR2032 battery produces 3V for a long time when its current is only 0.2mA.
Maybe your CR3032 is a used or an old one.
Actually, the battery is 3v, but after 510k resistance we have 1.5v on ds1307. If this 510k is big for this battery then why they have designed this circuit for module?
 

Ian0

Joined Aug 7, 2020
9,842
Hi everybody,
DS1307 RTC Works well when I connect it to power, but it does not work with its back up battery which is CR2032. Minimum required voltage for this ic is 2V, and battery provide 1.5v to ds1307.
By the way I used the circuit from its module and I did not design circuit by myself.
Here the is the circuit schematic diagram:
https://circuitdigest.com/sites/default/files/inlineimages/u4/DS1307-RTC-Module-Schematic.png
That's a scary circuit. Where did you find it? Are they trying to make the battery explode? Lithium primary cells really don't like being charged. And what is the R2/R1 potential divider for?
@ericgibbs has the right circuit. It's the one out of the datasheet, recommended by the manufacturer. It's the one I use. Why use a dubious circuit off the internet, when the manufacturer gives you a perfectly good circuit in the datasheet?
 

Thread Starter

Saeedk9574

Joined Jan 1, 2024
9
That's a scary circuit. Where did you find it? Are they trying to make the battery explode? Lithium primary cells really don't like being charged. And what is the R2/R1 potential divider for?
@ericgibbs has the right circuit. It's the one out of the datasheet, recommended by the manufacturer. It's the one I use. Why use a dubious circuit off the internet, when the manufacturer gives you a perfectly good circuit in the datasheet?
Actually, as the schematic is for a module that is being sold in all around the world I supposed it was reliable. This is the picture of module that is in the market. I wander why they have made such mistakes in their design?
https://circuitdigest.com/sites/default/files/inlineimages/u4/DS1307-Pinout.jpg
https://nikushop.com/20080-large_default/ds1307-module.jpg
 

JohnInTX

Joined Jun 26, 2012
4,787
The attached 'tinyrtc' PDF implies that the original circuit used a rechargeable Li cell. That would explain the diode to Vcc for charging current and voltage divider to keep VBAT in the recommended range when charging from 5V. The battery number specified does not appear to be correct but some Reddit users speculate that the P/N is a typo and offer some alternatives. It is interesting that the photos of the board show a non-rechargable CR2032. As @Ian0 points out, that isn't good. The circuit as shown would be more suitable for a super cap instead of the battery.

Actually, as the schematic is for a module that is being sold in all around the world I supposed it was reliable. This is the picture of module that is in the market. I wander why they have made such mistakes in their design?
Keep in mind that lots of this stuff is copied by pirates that don't really understand the original design of the circuit. Parts are frequently counterfeit copies. It would not surprise me to learn that the DS1307 is pulling more VBAT current than the original causing the lower voltage at the pin. Just thinking out loud...

I would pull D1, R1, R2 and jumper R2 to connect the CR2032 battery to the VBAT of the DS1307 and get on with it.

Good luck!

EDIT: the component designators here refer to the schematic in post #1, not those in the attached datasheet. Post #12 has the correct ones for the datasheet. H/T to @jiggermole for catching that.
 

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jiggermole

Joined Jul 29, 2016
161
I must not be looking at the same diagram as you have linked JohnInTX.
I would pull R4, R5 and D1 and jumper over R6. From what I see R2 and R3 are your pullups for I2C so you don't want to jump either of those. Correct me if I'm wrong please.
 

JohnInTX

Joined Jun 26, 2012
4,787
I must not be looking at the same diagram as you have linked JohnInTX.
I would pull R4, R5 and D1 and jumper over R6. From what I see R2 and R3 are your pullups for I2C so you don't want to jump either of those. Correct me if I'm wrong please.
I was referring to the schematic in post #1 (for no particular reason) but you are correct, the schematic in the ‘tinyrtc..’ manual I attached in #11 has the same components labeled differently.

Thanks for pointing out the confusion.
 
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