I have never used a library for my RTC but it looks like I might need to re-think this as I intend to use SQW to control my loop. The sample code I have uses RTClib but does not incorporate the wire and i2c libraries. Is this because the necessary is included in RTClib?

Checking the source code for Adafruit RTClib shows that it incorporates another of Adafruit's libraries, which resumably includes Wire and perhaps others. #ifndef _RTCLIB_H_ #define _RTCLIB_H_ #include <Adafruit_I2CDevice.h> I tend to avoid Adafruit libraries because they try to hide details from…

Thanks. I now recall previous comment to that effect. I will look elsewhere!

Hi @Nick_Pyner , [image] Nick_Pyner: I have never used a library for my RTC but it looks like I might need to re-think this as I intend to use SQW to control my loop. The sample code I have uses RTClib but does not incorporate the wire and i2c libraries. Is this because the necessary is include…

[image] Nick_Pyner: I have never used a library for my RTC but it looks like I might need to re-think this as I intend to use SQW to control my loop What is it about controlling the SQW output that prevents you from writing your own code? Seems like just a slightly different series of comman…

[image] david_2018: What is it about controlling the SQW output that prevents you from writing your own code? Seems like just a slightly different series of commands to set the proper bits in a control register. +1 I use the DS3231, but generally avoid RTC libraries. It seems there are at l…

Do you want to use it for square waves or as an interrupt?

I want SQW for the interrupt and a countdown in seconds. I wasn't clear enough about this and I now realise that I don't actually need a library for that. I guess though that I might as well use a library for stuff I don't normally do, like auto update and setting up for future events. The order of…

You may want to look at my Garagerator project. It uses a DS3231RTC to time data logging intervals. It is a bit dated now but the idea is usable. Ignore the majority of the code. The parts of interest are rtcISR() to handle the timer interrupt, setNextSampleTime() to update the alarm Time, setup() e…

[image] oldcurmudgeon: parts of interest are rtcISR() to handle the timer interrupt, setNextSampleTime() to update the alarm Time, setup() external interrupt setup, Rtc setup and the timerInterupt handling in loop(). Thank you. I'm coming to the conclusion that I don't actually need an RTC at…

If you just need a square wave, an alternative would be to get a GPS module with a PPS output pin. It will give you exactly 1Hz that you will never need to sync. But the downside would be the current draw. GPS can be greedy.

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Nick_Pyner August 9, 2025, 5:54am 17

Simply the lack of expertise, which has now been acquired - after considerable internet trawling.

ZS-042 DS3231 RTC module? post#9

It’s been amazing how difficult this has been to sort out, and/or how little attention the SQW pin gets.

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