Pins for "DS3231 RTC Mini"

The only RS3231 available in store (without ordering on line) that I could find is a "mini" version, which has a different pin layout than the normal larger modules typically used in tutorials. I went ahead and purchased it as it was quite inexpensive. However I can't find documentation on how to use it, and now I am worried it might not work as per the normal module. The website suggests its compatible with Arduino and Pi devices.

The pin labels are partly obscured, they appear to be labeled:
+, D, C, NC, -

I wonder if anyone knows about this module or has seen documentation on it. (I've already spent 30 minutes googling for info and have not been able to stumble across search keywords that give me the correct information)

I'd suggest you look at the pinout of the chip as shown in the datasheet, then use your multimeter to see which pin is connected to which header pin. You should have Vcc, ground, SDA, SCL and the alarm pin. You might also check to see what the two 4.7K resistors are connected to - hopefully SDA and SCL.

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This could be the schematic:

The square solder pad is always pin 1. I think that is 3.3V or 5V (the DS3231 works both with 3.3V and 5V).

Pin 1 (square) = 5V or 3.3V "+"
Pin 2 = SDA "D" is data
Pin 3 = SCL "C" is clock
Pin 4 = not connected "NC" is Not Connected
Pin 5 = GND "-" is GND

Can you verify the GND ? If that is okay, than you can connect the module and run a I2C Scanner sketch to see if it is detected.

It should might be the same as its sister:

You could use the data sheet and take a look at where the traces go… long enough playing with this stuff you gonna have to know how to do that anyway. :expressionless:


Thanks everyone. You are always so helpful. I just discovered this previous forum post that asks the same question. Im reasonably confident that the description matches mine even though the ebay link expired.

Ill run with that (5v SDA, SCL NC GND) and post back results and a photo for the future reference of others.

“ I went ahead and purchased it as it was quite inexpensive. However I can't find documentation on how to use it,”

If there is no documentation, then don’t buy the product !

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I hear you, but amazon shipping to where I live is typically 6 weeks, If I pay $50USD to ship a $2 device, they will send it in 4 weeks :grinning:

So you buy a product and then have to get someone else to figure out how to get it to work for you

Makes a lot of sense.

I don't see what good it is if the alarm pin isn't brought out. Is there a module version that brings out the alarm but doesn't have all extra stuff found on the ZS-042 module?

I think with these pukka DS3231 RTC chips it's a matter of luck if you get a good one.
I'm running one, temperature compensated crystal, over a long period, say a year, and displaying the results on an LCD.
One thing I do notice is that now and again it does a jump on the seconds of maybe 5 seconds. I don't know if it's the LCD or the RTC.
I keep some MSF ("atomic clocks") running and they are remarkably consistent and accurate.
I use either these or the phone clock to check the DS3231 and I have to say, that it keeps really good time within seconds over many months.
Some of the worst RTCs are in things like programmable thermostats from people like Honeywell and they lose minutes in months.
GPS is a good source of accurate time.
I have a bog standard antenna outside on a roof and use an XBee radio to transmit the data stream to inside the house.
GPS or MSF/DCF can be used to correct the DS3231 on a regular basis.
For a real clock fanatic, look at Brett Oliver's website for what can be achieved with time pieces.
Udo Klein (Blinkenlights) is a DCF77 expert with a library or code for Arduinos

Like I said, I understand what you are saying. In an ideal world certainly this should be the approach.

I went to the store looking for a DS3231, that is apparently what people use for helping keep time. I went to the only shop in this city that sells a DS3231, and purchased it. I did not even know there were different types of these things. I could order a different one online, but the cost and time of doing this is prohibitive. I am not sure what you are suggesting I do differently? Are you suggesting that it would be better to spend $50 in shipping and wait 4 weeks?

Thanks for the tip. Im still learning how all of this works. My first project are some basic lighting controls, but I am sure I will find an excuse to get a GPS at some point. Im trying out bluetooth today. I was thinking of seeing if I can sending time synchronization data over bluetooth when the user does "light on" via bluetooth.

Let’s say you were in the market for memory upgrade for the Arduino.

You saw I2C memory at the store but there was no documentation, would you buy it ?

I hope not . . .

Did you have any success in getting the DS3231 PCB to work ?

Vcc, SDA, SCL, no connection, Ground

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There is a little documentation on that style RTC module if you search specifically for the Raspberry Pi, because that is what it is designed for. Be careful, the battery may not be a standard coin cell, but instead either a rechargeable battery or a high-capacity capacitor.

I've found a few schematics, with several having obvious errors such as the battery + terminal connecting to one of the I2C pullup resistors (not good when the I2C line goes low), or the two I2C pullups connected ONLY to the battery (presumably to charge the battery), but NOT connected to the I2C lines.

Nice link.

I have one of these RTCs. It's a standard coin cell, with no recharging circuit.

For anyone else reading this in the future. As far as I can tell, I can confirm this module (Green PCB marked "DS3231 For PI", with a small yellow battery holder) works as I would expect using the pin out discussed above and one of the standard Arduino libraries for interacting with SDA (D) and SCL (C).

Thanks for confirming that. It's just too bad pin 4 isn't connected to the DS3231 INT/SQW pin so you could use the alarm. Well I guess you could solder in a bodge wire. No pullup needed on that line.