It's the common one that you find, when you search eBay for DS1307.
It came with a Coin Cell battery, of type Lithium-Ion.
A few years ago when I read about Coin Cell batteries,
I remember that it was explained that they come in both Non-Rechargeable, and Rechargeable types.
The Non-Rechargeable materials are:
Lithium
Alkaline
and Rechargeable materials are:
Lithium-Ion
Note that "Lithium" (without "-Ion") is under Non-Rechargeable..
Only the Lithium-Ion ones are Rechargeable.
And now my question..
I had a look at the Datasheets of both DS1302 and DS1307.
The DS1302 is described as performing "trickle-charge".
On the other hand, the DS1307 doesn't mention any kind of charging.
So i am curious,
why was my DS1307 module supplied with a Lithium-Ion (which is Rechargeable) battery?
Maybe the module does something that the DS1307 chip doesn't?
Or maybe the DS1307 does charge, despite not finding anything about it in the datasheet?
BTW,
I took a multimeter and measured the battery's voltage,
and it's a completely clean 0v..
Even If I set the multimeter to mV measurement, it's still 0v,
not even a slight deviation from that.
Does this mean, that even if the module has a charging circuit, that the battery is dead?
From what I remember, Li-Ion batteries should not go below a certain minimal threshold,
or else the battery dies.
(this minimal threshold is usually 70% of the battery's fully-charged voltage)
Am I correct or there's a chance to get anything from this battery (assuming there is a charging circuit..)
Li-Ion batteries should not go below a certain minimal threshold, or else the battery dies.
Correct. Did you take the battery out of the holder to make that measurement?
If so, it is probably useless. A standard CR2032 cell will last years anyway.
The module probably does have charge circuitry and it is likely to be similar to that found on many of the DS3231 modules (I would bet money that "D1" is part of it).
jremington:
Correct. Did you take the battery out of the holder to make that measurement?
Yes..
jremington:
If so, it is probably useless. A standard CR2032 cell will last years anyway.
OK then, luckily I have a few regular ones.
jremington:
The module probably does have charge circuitry and it is likely to be similar to that found on many of the DS3231 modules (I would bet money that "D1" is part of it).
Without a schematic, its going to be very difficult to be sure.
There are adverts for that board, with a CR2032 (3V non-rechargeable) and an option to use a LIR2032, but no mentioned modifications.
The implication is that there is a charge circuit on board, so the CR2032 might well be receiving a charge current too. Datasheets for CR2032s suggest a small amount of charge current is 'permitted'.
I would say, easy way to check for (trickle) charge. Just remove the battery, connect the module to Vcc, measure Vbat. Is there any significant voltage?
OK I decided to throw away the Li-Ion coin battery, since it seems to be dead.
septillion:
I would say, easy way to check for (trickle) charge.
Just remove the battery, connect the module to Vcc, measure Vbat. Is there any significant voltage?
I did it now, and between Vbat and Gnd I am getting 3.5v.
(the module was supplied with 5v from a USB Powerbank)
So seems that it is indeed trying to charge.
srnet:
The implication is that there is a charge circuit on board, so the CR2032 might well be receiving a charge current too.
Datasheets for CR2032s suggest a small amount of charge current is 'permitted'.
I see, so it should be OK to put a regular (Lithium, or Alkaline) CR2032.
OK, I have some available.
BTW, there is the small "DS3231 for Pi" RTC module, which of course is good also for Arduino,
Is that module better in this case?
(by better I mean not in terms of accuracy, which obviously it is better than the DS1307,
but in terms of not having a charging circuit)
It is so small, that I think it doesn't have any charging circuit..
From what I see in its images, the components it has are:
card5:
BTW, there is the small "DS3231 for Pi" RTC module, which of course is good also for Arduino,
Is that module better in this case?
(by better I mean not in terms of accuracy, which obviously it is better than the DS1307,
but in terms of not having a charging circuit)
What do you think?
That module is just fine. Make sure you do get one with a battery. Many of the sellers sell it without the battery because of implications of shipping lithium-batteries.
The DS3231 does not charge the battery.
Also the cell is not "welded" - It's a cell that's supplied with solder tabs that is in turn spot welded to the cell case. You cannot solder to a lithium-cell, it will explode.
The board you started out with is a terrible design. Some enterprising person designed it to trickle charge the cell via the onboard zener diode and resistor, problem is 99% of sellers sell the module with a CR2032 (primary cell) in the socket, and sooner or later you will have a leaking or exploding cell. the best thing you can do is remove the diode and put in a CR2032 and the module works fine. The capacity of the LIR2032 is very small, so i'd rather have a CR2032 that lasts 10 years, instead of a LIR2032 that's dead in a few months.
Must I disable the charge circuit?
I don't want to mess with SMD components..
If you wish to use a CR2032 battery in the module that has a charge circuit, yes. But it is really easy to do -- just use a hot solder pencil tip to "swipe off" the diode.
raschemmel:
RTCs don't have coin cell charging circuits. I don't know where you got that idea but they don't.
If they did , why would you need to change the battery every year ?
Zapro:
The best thing you can do is remove the diode and put in a CR2032 and the module works fine.
The capacity of the LIR2032 is very small, so i'd rather have a CR2032 that lasts 10 years, instead of a LIR2032 that's dead in a few months.
jremington:
If you wish to use a CR2032 battery in the module that has a charge circuit, yes.
But it is really easy to do -- just use a hot solder pencil tip to "swipe off" the diode.
I see.
OK I will swipte the diode off then..
And also buy the small RPi RTC module that barely has a circuit on it.
(I wonder what the 2 resistors + 1 capacitor there do, I will try to find its diagram)
raschemmel:
RTCs don't have coin cell charging circuits. I don't know where you got that idea but they don't.
If they did , why would you need to change the battery every year ?
raschemmel, from your answer, it seems that you did not bother to read the existing posts in this thread.
That's too bad, because If you did, you would see that indeed they have..
Either built-in the chip, like in the DS1302 for example,
or as a small charging circuit, contained in the module.
I find it difficult to understand people who enter a thread with several posts, and don't read the existing posts - completely ignoring them, and just write something that they wanted to write..
Which then turns out to be completely off-context.
This is not the first time I stumble upon this phenomenon..
It's not rare in forums
Someone who just saw the title of the thread, and replied.
(in worse cases, they don't even read the OP's original post even.. just the title is enough for them)
Zapro:
The resistors are I2C pullups and the cap is the decoupling cap for the chips VCC supply.
Thanks!
wow, that's quite minimal.
The DS3231 is a fantastic chip, really no need for a module when using it.
But for me, I would buy it as a module, since it's not a Thru-Hole chip, but an SMD one.
I prefer Thru-Hole chips, since they are breadboard friendly,
and also since when I solder components, I don't really do SMD, as mentioned before..
From what I remember, we need the 2 pull-up resistors once, for the whole I2C bus,
and not for each component/module on the bus..
So I wonder why they include the 2 I2C pull-ups in many modules.
They assume that the user does not know about the need for pull-ups on the bus?
(and that their module is the only one on the bus?)
What happens when you connect several modules, to the same I2C bus,
and each of them has the 2 pull-ups..
Is that problematic, or because the pull-up resistance is high, then we should not worry?
I2C is usually recommended with 4.7KΩ for its pull-ups,
so If you connect 4 modules that each has it's own 4.7KΩ resistors, you then get close to 1KΩ..
card5:
From what I remember, we need the 2 pull-up resistors per the whole I2C bus, and not for each component on the bus,
so I wonder why they include it in many modules.
They assume that the user does not know about the need for pull-ups on the bus?
(and that their module is the only one on the bus?)
Exactly
What happens when you connect several modules, to the same I2C bus,
and each of them has the 2 pull-ups.. Is the problematic, or because the resistance is usually high, then we should not worry?
Usually it will work fine. I2C pullups have a good middle ground at arund 4k7 - I2C specs state anything between 1 and 10K will work. So you will have to have many modules before running into problems.
Remember, these modules are made for amateurs. More advanced users will know about this and they will probably remove the extra pullups if they find it vital.
