Real Time Clock reference material
From IOT-Guider:
From Amazon.ca: Wiring connection on an UNO:
+ : 3.3V-5V
D (SDA) : A4
C (SCL): A5
NC: Connect to GND according to DS3231.pdf
– : GND
Follow the instructions @ howtomechatronics titled: Arduino and DS3231 Real Time Clock Tutorial.
Use the script written by Henning Karlsen @ RinkyDinkElectronics.
+ : VCC
D : Blue – SDA – AREF+1
C : Orange – SCL – AREF+2
NC : No Connection
– : GND
Most of the ones I received have the DS3231M type chip; NOT the more standard DS3231SN type.Reviewed in Canada on July 15, 2019Verified PurchaseI ordered (and received in very good time) a total of 8 of these modules (2 lots of 4). Upon examining the laser markings on the board-mounted chips, I found that 7 of them had DS3231M chips, and only one had the more-well-known, standard DS3231SN chip.
I will state up front that both of these RTC chip types meet the specifications advertised on the Amazon product page. There is nothing wrong with with the “M” type chip, and it should perform as advertised for this product, but most purchasers probably expect that the board has the more standard “SN” type chip instead of the “M” type.
I did a web search of “DS3231M vs DS3231SN”, and the first item that came up was a blog (by someone whose pseudonym is “HeyPete”), and there ARE a few major differences of which I believe the buyer should be made aware, before purchasing this product. According to the blog and the chips’ data sheets:
* The DS3231M uses an internal “microelectromechanical system” (MEMS) resonator (of unspecified frequency) as its time-base, whereas the DS3231SN has the standard, internal, temperature-compensated 32,768 Hz quartz crystal oscillator as its time base.
* The DS3231M is accurate to 5 ppm over its full temperature range, whereas the DS3231SN is a bit more accurate (2 ppm) between 0 and 40 degrees C. (Note, however, that the 5 ppm spec. is as advertised on the Amazon product page). Both types of chips have temperature compensation to accurately derive the 1 Hz reference used for the RTC function, but the “M” type is slightly less accurate than the standard “SN” type. To be fair, the “SN” type’s accuracy degrades to 5 ppm when operating above 40 degrees C or below 0 degrees C (according to the spec sheet). Putting this in perspective, considering that there are approximately 31.5 million seconds in a year of 365.25 days, and assuming the devices are run at room temperature, the DS3231M could be out by as much as 2.5 minutes per year, whereas the DS3231SN (at room temperature) could be out by as much as 1 minute per year.
* The DS3231M 32 KHz output (chip pin 1) is NOT temperature compensated (the temperature compensation occurs at an internal stage AFTER the 32 KHz signal). The DS3231SN 32KHz output IS temperature compensated and, therefore, is much more accurate: so the DS3231SN can also be used as a 32 KHz TCXO (Thermally Compensated Crystal Oscillator), in addition to being a RTC chip (whereas the DS3231M cannot be used as a TCXO; but see Note below.)
* The DS3231M SQW output (chip pin 3) can only be programmed as either Int (alarm) or 1 Hz output. The DS3231SN can ALSO output 1.024 KHz, 4.096 KHz or 8.192 KHz (programmable). (But see the following note.)
Note that the last two points above are academic for these module boards, since these two chip pins (1 and 3) are NOT connected to any of the board’s five header pins. However, an easy modification to the board could connect either one of these pins to the “NC” pin on the board’s header, for use in the application circuit. So it is important to keep these differences in mind if you need the 32 KHz TCXO output, or one of the three lower frequency outputs that are not available in the DS3231M. (For example, “Step 3” of the “Instructable” entitled, “Clock-Calender Using DS3231+GLCD+Atmega32” [sic], shows how to modify these modules to access the SQW pin; the same could also be done for the 32KHz pin instead.)
I have not yet used any of these boards but I have downloaded the datasheets for both the DS3231M and DS3231SN. If I find other issues or differences, I will update this comment (or add a new one if I cannot update this).