RTC module: Alternatives to DS3231?

[amaruk]

Hi,
I got myself some DS3231 RTC modules recently. They work fine and I am very happy with them. However, I then came across some threads about the modules having a design flaw (ZS-042) or at least had that at some point in time as the threads are a bit old. The issue is that if you use a CR2032 battery (3V, lithium), which my modules came with, and connect Vcc to 5V the circuit is applying a high voltage across the battery terminals as in trying to charge it....! I have read that one fix is to remove a surface mount resistor on the module. I measured my modules (with battery taken out) and with a Vcc of 5V I get about 4.75V at the battery terminals. So my modules still suffer from the flaw. Thus, I can fix the modules I have or get another type of module that is designed properly. What are your thoughts on this?

[larryd]

Let's see what you did to the module.

[6v6gt]

If you are operating the module at 5 volts and are using a standard, that is a non rechargeable, CR2032 lithium cell, then remove the resistor from the charging circuit. The design was intended for a rechargeable battery of type LIR2032 .

[ShermanP]

I don't know if another type of DS3231 module is available.  But it's easy to remove either the diode or the resistor from the charging circuit:

https://www.youtube.com/watch?v=ND2shVqV9s4

[amaruk]

Thanks guys! Removing the resistor and or diode is what I will do then. I am just surprised that these sometimes sell with the CR2032 battery. I know that many don't include the battery with it but I thought that was simply due to shipping restrictions...

[6v6gt]

Thanks guys! Removing the resistor and or diode is what I will do then. I am just surprised that these sometimes sell with the CR2032 battery. I know that many don't include the battery with it but I thought that was simply due to shipping restrictions...

Look at the price difference between an LIR2032 and CR2032 and then you will not find it so surprising that some retailers put the cheaper, but less suitable, battery in.

[srnet]

I am just surprised that these sometimes sell with the CR2032 battery.

A single DS3231 IC from a standard electronics distributor, such as Farnell\Element14 will cost you about £5.
Yet you can buy a complete 'module' for around £1.50.
You do wonder if the DS3231s used in these modules are geniune, and if not is it any surprise that that a non-suitable battery is used as well ?

[aarg]

A single DS3231 IC from a standard electronics distributor, such as Farnell\Element14 will cost you about £5.
Yet you can buy a complete 'module' for around £1.50.
You do wonder if the DS3231s used in these modules are geniune, and if not is it any surprise that that a non-suitable battery is used as well ?

Generally, they're genuine. The low cost is undoubtedly due to huge quantity discounts and deals between the PCB and chip manufacturers. The battery charging issue goes away if you run it on 3.3V. I think nowhere, does it specify any particular supply voltage. But if you have a 5V processor, that isn't so easy. There are in fact, several alternative DS3231 modules that don't have this design problem. Just look around.

[amaruk]

I did un-solder the resistors on my modules. It took me about 5 seconds per resistor so no big deal at all. My Arduino circuits are up and running again - this time without charging the CR2032 batteries... Thanks again for the inputs!