Examples - Makuna/Rtc GitHub Wiki

// SDA = GPIO04 (D2)
// SCL = GPIO05 (D1)

#include <Wire.h>       //I2C Lib
#include <RtcDS3231.h>  //RTC Lib

RtcDS3231<TwoWire> rtcObject(Wire); // rtc object

void setup() {
  Serial.begin(115200);  // start serial
  rtcObject.Begin();     // start I2C
  
  /* set date and time */
  RtcDateTime currentTime = RtcDateTime(21, 07, 18, 10, 20, 0); //2021/7/18 10:20:0
  rtcObject.SetDateTime(currentTime); // save in RTC3231

}

void loop() {
  RtcDateTime currentTime = rtcObject.GetDateTime();  
  char str[20];

  sprintf(str, "%d/%d/%d %d:%d:%d",      
          currentTime.Year(), 
          currentTime.Month(), 
          currentTime.Day(),    
          currentTime.Hour(),  
          currentTime.Minute(),
          currentTime.Second() 
         );

  Serial.println(str); 

  delay(5000);
}