Built-in project · Arduino Uno R3

DS3231 real-time clock on I2C, on an Arduino Uno

A DS3231 clock module on A4 and A5 keeps the date and time; RTClib reads it once a second and prints the date, the time and the day of the week. The whole build, an Arduino Uno and 1 more part, runs here in your browser on the firmware below; open it in the editor to change the wiring or the code and run it again.

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DS3231 real-time clock on I2C · Arduino Uno R3live0.000 s 0.00x

Click to open it in the editor

The circuit itself, running here on the simulator. Press what can be pressed; click anything else to open it in the editor.

The code

The firmware exactly as the editor opens it. Change a line there and press Run: it compiles in the browser.

sketch.ino · Arduino Uno R3

// A DS3231 real-time clock: the date and time, kept by the module.
//
//   DS3231 SDA -> A4   SCL -> A5   VCC -> 5V   GND -> GND
//
// The DS3231 counts seconds on its own temperature-compensated crystal, and
// a coin cell on a real module keeps it counting with the board unplugged.
// RTClib asks it for the time over I2C.

#include <Wire.h>
#include <RTClib.h>

RTC_DS3231 rtc;
const char DAYS[7][4] = {"Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"};

void print2(int value) {
  if (value < 10) Serial.print('0');
  Serial.print(value);
}

void setup() {
  Serial.begin(9600);
  Serial.println("Mokxi Uno: DS3231 on A4 and A5");
  if (!rtc.begin()) {
    Serial.println("no clock found: check SDA and SCL");
    while (true) {
    }
  }
}

void loop() {
  DateTime now = rtc.now();
  Serial.print(now.year());
  Serial.print('/');
  print2(now.month());
  Serial.print('/');
  print2(now.day());
  Serial.print(' ');
  print2(now.hour());
  Serial.print(':');
  print2(now.minute());
  Serial.print(':');
  print2(now.second());
  Serial.print(' ');
  Serial.println(DAYS[now.dayOfTheWeek()]);
  delay(1000);
}