How to Set Up a Real-Time Clock (RTC) with ESP32 and DS3231 Using NTP Time Synchronization

Introduction

Accurate timekeeping is crucial for electronics and IoT projects. A Real-Time Clock (RTC) is essential for maintaining precise time, especially during power outages. However, more than relying solely on the RTC module might be required for long-term projects due to drift over time. This is where Network Time Protocol (NTP) comes in. By synchronizing the RTC with an internet time server, you can ensure that your system stays perfectly in sync, regardless of how long it runs.

In this guide, we’ll show you how to set up a Real-Time Clock using ESP32 and an RTC DS3231 module, with the added benefit of NTP synchronization. Whether you’re new to electronics or an experienced developer, this tutorial will help you create a system that maintains precise and reliable time in all conditions.

Components Required

ESP32 (Main microcontroller)
DS3231 RTC Module (Accurate real-time clock)
20×4 I2C LCD Display (To display time)
Jumper wires
Breadboard (optional)

Circuit Description

In this setup, the DS3231 RTC and the I2C LCD share the I2C communication protocol, using the same SDA (data line) and SCL (clock line) pins on the ESP32. This reduces the number of GPIO pins required and simplifies the wiring.

Checkout the article on How to interface RTC module with Arduino and ESP Board

Figure 1: Real-Time Clock (RTC) with ESP32 and DS3231 Using NTP Time Synchronization

The ESP32 communicates with the RTC to retrieve the time and display it on the LCD. Additionally, the ESP32 synchronizes with an NTP server over Wi-Fi to keep the time accurate.

Circuit Connections

Below is the wiring guide for connecting the ESP32, DS3231, and I2C LCD.

Component	Pin	ESP32 Pin
DS3231	SDA	GPIO 21
DS3231	SCL	GPIO 22
DS3231	VCC	VIN or 3.3V
DS3231	GND	GND
I2C LCD	SDA	GPIO 21
I2C LCD	SCL	GPIO 22
I2C LCD	VCC	VIN
I2C LCD	GND	GND

Code Walkthrough

Libraries Used

Wire.h: Enables I2C communication.
LiquidCrystal_I2C.h: Controls the I2C LCD display.
WiFi.h: Manages the Wi-Fi connection.
NTPClient.h: Synchronizes time with an NTP server.
RTClib.h: Interacts with the DS3231 RTC.

#include <Wire.h>
#include <LiquidCrystal_I2C.h>  // For LCD
#include <WiFi.h>               // For Wi-Fi connection
#include <NTPClient.h>          // For NTP sync
#include <WiFiUdp.h>            // For NTP communication
#include "RTClib.h"             // For DS3231 RTC

// Wi-Fi credentials
const char *ssid = "amitsherstha221_2";
const char *password = "CLB2AA4F79";

// Time server details
const char *ntpServer = "pool.ntp.org";
const long gmtOffset_sec = 20700; // Nepal Time (GMT +5:45 in seconds)
const int daylightOffset_sec = 0; // No DST in Nepal

RTC_DS3231 rtc;  // Create RTC object
WiFiUDP ntpUDP;  // UDP instance for NTP
NTPClient timeClient(ntpUDP, ntpServer, gmtOffset_sec, 60000); // Sync every minute

LiquidCrystal_I2C lcd(0x27, 20, 4); // LCD address 0x27, 20 columns, 4 rows

String scrollMessage = "Best EngineeringProject ";
int scrollPosition = 0;

void setup() {
  // Start serial and I2C communication
  Serial.begin(115200);
  Wire.begin();

  // Initialize the LCD
  lcd.init();
  lcd.backlight();

  // Initialize DS3231 RTC
  if (!rtc.begin()) {
    Serial.println("Couldn't find RTC");
    while (1);
  }

  if (rtc.lostPower()) {
    Serial.println("RTC lost power, setting time!");
    rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));  // Set the time to compile time as fallback
  }

  // Display initial message on LCD
  lcd.clear();
  lcd.setCursor(0, 0);
  lcd.print("WiFi Connecting");

  // Connect to Wi-Fi
  connectToWiFi();

  // Initialize NTP
  timeClient.begin();
}

void loop() {
  // Sync with NTP server if connected to the internet
  if (WiFi.status() == WL_CONNECTED) {
    timeClient.update();
    unsigned long epochTime = timeClient.getEpochTime();
    DateTime ntpTime = DateTime(epochTime); // Convert epoch to DateTime format
    rtc.adjust(ntpTime);                    // Update RTC with NTP time
  }

  // Get current time from RTC
  DateTime now = rtc.now();
  
  // Display scrolling message in the first row
  scrollMessageOnLCD();

  // Display Wi-Fi status in the second row
  displayWiFiStatus();

  // Display date in the third row
  displayDate(now);

  // Display time in the fourth row
  displayTime(now);

  delay(1000); // Adjust as needed
}

void displayWiFiStatus() {
  lcd.setCursor(0, 1);  // Set cursor to the second row
  if (WiFi.status() == WL_CONNECTED) {
    lcd.print("Wi-Fi Connected");
  } else {
    lcd.print("WiFi Not Connected");
  }
}

void displayDate(DateTime now) {
  lcd.setCursor(0, 2);  // Set cursor to the third row

  // Add leading zero for month and day if they are less than 10
  String month = (now.month() < 10) ? "0" + String(now.month()) : String(now.month());
  String day = (now.day() < 10) ? "0" + String(now.day()) : String(now.day());

  // Display the formatted date
  lcd.print(now.year());
  lcd.print("-");
  lcd.print(month);
  lcd.print("-");
  lcd.print(day);
}

void displayTime(DateTime now) {
  lcd.setCursor(0, 3);  // Set cursor to the fourth row

  // Add leading zero for hour, minute, and second if they are less than 10
  String hour = (now.hour() < 10) ? "0" + String(now.hour()) : String(now.hour());
  String minute = (now.minute() < 10) ? "0" + String(now.minute()) : String(now.minute());
  String second = (now.second() < 10) ? "0" + String(now.second()) : String(now.second());

  // Display the formatted time
  lcd.print(hour);
  lcd.print(":");
  lcd.print(minute);
  lcd.print(":");
  lcd.print(second);
}


void scrollMessageOnLCD() {
  lcd.setCursor(0, 0);  // Set cursor to the first row
  
  // Display part of the scrolling message
  String displayPart = scrollMessage.substring(scrollPosition, scrollPosition + 20);  // Display 20 characters
  lcd.print(displayPart);

  // Update scrolling position
  scrollPosition++;
  if (scrollPosition > scrollMessage.length() - 20) {
    scrollPosition = 0; // Reset to the beginning
  }
}

void connectToWiFi() {
  Serial.println("Connecting to Wi-Fi...");
  WiFi.begin(ssid, password);

  unsigned long startAttemptTime = millis();  // Record the start time

  // Loop until Wi-Fi is connected or 30 seconds have passed
  while (WiFi.status() != WL_CONNECTED && millis() - startAttemptTime < 30000) {
    delay(500);  // Small delay to avoid flooding output

    // Display a connecting animation on LCD (dots) on second row
    lcd.setCursor(0, 1);
    lcd.print("WiFi Connecting...");
  }

  // Check if connected after the timeout
  if (WiFi.status() == WL_CONNECTED) {
    Serial.println("\nWi-Fi connected.");
    lcd.clear();
    lcd.setCursor(0, 1);
    lcd.print("Wi-Fi Connected");
  } else {
    Serial.println("\nFailed to connect to Wi-Fi within 30 seconds.");
    lcd.clear();
    lcd.setCursor(0, 1);
    lcd.print("WiFi Not Connected");
  }

  delay(2000);  // Display the connection result for 2 seconds
}

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#include <Wire.h>

#include <LiquidCrystal_I2C.h> // For LCD

#include <WiFi.h> // For Wi-Fi connection

#include <NTPClient.h> // For NTP sync

#include <WiFiUdp.h> // For NTP communication

#include "RTClib.h" // For DS3231 RTC

// Wi-Fi credentials

const char *ssid = "amitsherstha221_2";

const char *password = "CLB2AA4F79";

// Time server details

const char *ntpServer = "pool.ntp.org";

const long gmtOffset_sec = 20700; // Nepal Time (GMT +5:45 in seconds)

const int daylightOffset_sec = 0; // No DST in Nepal

RTC_DS3231 rtc; // Create RTC object

WiFiUDP ntpUDP; // UDP instance for NTP

NTPClient timeClient(ntpUDP, ntpServer, gmtOffset_sec, 60000); // Sync every minute

LiquidCrystal_I2C lcd(0x27, 20, 4); // LCD address 0x27, 20 columns, 4 rows

String scrollMessage = "Best EngineeringProject ";

int scrollPosition = 0;

void setup() {

// Start serial and I2C communication

Serial.begin(115200);

Wire.begin();

// Initialize the LCD

lcd.init();

lcd.backlight();

// Initialize DS3231 RTC

if (!rtc.begin()) {

Serial.println("Couldn't find RTC");

while (1);

}

if (rtc.lostPower()) {

Serial.println("RTC lost power, setting time!");

rtc.adjust(DateTime(F(__DATE__), F(__TIME__))); // Set the time to compile time as fallback

}

// Display initial message on LCD

lcd.clear();

lcd.setCursor(0, 0);

lcd.print("WiFi Connecting");

// Connect to Wi-Fi

connectToWiFi();

// Initialize NTP

timeClient.begin();

}

void loop() {

// Sync with NTP server if connected to the internet

if (WiFi.status() == WL_CONNECTED) {

timeClient.update();

unsigned long epochTime = timeClient.getEpochTime();

DateTime ntpTime = DateTime(epochTime); // Convert epoch to DateTime format

rtc.adjust(ntpTime); // Update RTC with NTP time

}

// Get current time from RTC

DateTime now = rtc.now();

// Display scrolling message in the first row

scrollMessageOnLCD();

// Display Wi-Fi status in the second row

displayWiFiStatus();

// Display date in the third row

displayDate(now);

// Display time in the fourth row

displayTime(now);

delay(1000); // Adjust as needed

}

void displayWiFiStatus() {

lcd.setCursor(0, 1); // Set cursor to the second row

if (WiFi.status() == WL_CONNECTED) {

lcd.print("Wi-Fi Connected");

} else {

lcd.print("WiFi Not Connected");

}

void displayDate(DateTime now) {

lcd.setCursor(0, 2); // Set cursor to the third row

// Add leading zero for month and day if they are less than 10

String month = (now.month() < 10) ? "0" + String(now.month()) : String(now.month());

String day = (now.day() < 10) ? "0" + String(now.day()) : String(now.day());

// Display the formatted date

lcd.print(now.year());

lcd.print("-");

lcd.print(month);

lcd.print("-");

lcd.print(day);

}

void displayTime(DateTime now) {

lcd.setCursor(0, 3); // Set cursor to the fourth row

// Add leading zero for hour, minute, and second if they are less than 10

String hour = (now.hour() < 10) ? "0" + String(now.hour()) : String(now.hour());

String minute = (now.minute() < 10) ? "0" + String(now.minute()) : String(now.minute());

String second = (now.second() < 10) ? "0" + String(now.second()) : String(now.second());

// Display the formatted time

lcd.print(hour);

lcd.print(":");

lcd.print(minute);

lcd.print(":");

lcd.print(second);

}

void scrollMessageOnLCD() {

lcd.setCursor(0, 0); // Set cursor to the first row

// Display part of the scrolling message

String displayPart = scrollMessage.substring(scrollPosition, scrollPosition + 20); // Display 20 characters

lcd.print(displayPart);

// Update scrolling position

scrollPosition++;

if (scrollPosition > scrollMessage.length() - 20) {

scrollPosition = 0; // Reset to the beginning

}

void connectToWiFi() {

Serial.println("Connecting to Wi-Fi...");

WiFi.begin(ssid, password);

unsigned long startAttemptTime = millis(); // Record the start time

// Loop until Wi-Fi is connected or 30 seconds have passed

while (WiFi.status() != WL_CONNECTED && millis() - startAttemptTime < 30000) {

delay(500); // Small delay to avoid flooding output

// Display a connecting animation on LCD (dots) on second row

lcd.setCursor(0, 1);

lcd.print("WiFi Connecting...");

}

// Check if connected after the timeout

if (WiFi.status() == WL_CONNECTED) {

Serial.println("\nWi-Fi connected.");

lcd.clear();

lcd.setCursor(0, 1);

lcd.print("Wi-Fi Connected");

} else {

Serial.println("\nFailed to connect to Wi-Fi within 30 seconds.");

lcd.clear();

lcd.setCursor(0, 1);

lcd.print("WiFi Not Connected");

}

delay(2000); // Display the connection result for 2 seconds

}

setup()

In the setup() function, we initialize the RTC, ESP32 Wi-Fi, and NTP synchronization. This function also establishes communication with the 20×4 LCD.

loop()

The loop() checks the Wi-Fi status, updates the time via NTP, and retrieves the current time from the DS3231 RTC if the connection is successful. It then displays the time and a scrolling message on the LCD.

Displaying Time on the LCD

You can display the time in the format HH:MM:SS and scroll to a custom message in the top row.

Setting Up NTP Synchronization

Network Time Protocol (NTP) ensures that the time on your device stays accurate over the long term. In this section, you’ll learn how to set up NTP with the ESP32 and synchronize it with a reliable time server.

Conclusion

Setting up an RTC with ESP32 and NTP synchronization ensures that your project maintains accurate timekeeping, even during power outages. This setup is essential for many IoT and smart systems where precision timing is crucial.

By following this guide, you’ve learned how to:

Wire the DS3231 RTC and I2C LCD to the ESP32.
Set up NTP synchronization for accurate time.
Display the current time on an LCD screen.

Figure 2: Wi-Fi Connecting

Figure 3: Time when Wi-Fi is not connected

4 Thoughts to “How to Set Up a Real-Time Clock (RTC) with ESP32 and DS3231 Using NTP Time Synchronization”

Henry Doan

September 29, 2024 at 2:04 am

I have been retired a little over four years. It is great to see your logo again. I had followed your Engineering Projects Posts for a long time. The contents in this project are much clearer. Thank you for all your dedicated work that help a lot people like me.

1. Engineeering Projects
  
  September 29, 2024 at 9:33 am
  
  Thank you so much for your kind words and long-time support! It’s wonderful to hear that you’ve been following the Engineering Projects for so long, and I’m glad you found the content in this project clearer and helpful. Your appreciation means a lot, and it’s feedback like yours that keeps me motivated to continue creating valuable resources. Enjoy your retirement, and feel free to reach out anytime!
  
Za

October 5, 2024 at 6:55 pm

Hi,
Works fine!
How can I modify the sketch, to start up with the time, date, etc. with battery in the RTC.
With no internet (Wi-Fi) connection on switch on, there is no display.
If the Wi-Fi fails when the unit is running, the time continues to move on.
How can I display the time/ date from either the Wi-Fi connection or the RTC on startup?

Zahir

October 5, 2024 at 6:56 pm

Hi,
Works fine!
How can I modify the sketch, to start up with the time, date, etc. with battery in the RTC.
With no internet (Wi-Fi) connection on switch on, there is no display.
If the Wi-Fi fails when the unit is running, the time continues to move on.
How can I display the time/ date from either the Wi-Fi connection or the RTC on startup?

Introduction

Components Required

Circuit Description

Circuit Connections

Code Walkthrough

Libraries Used

setup()

loop()

Displaying Time on the LCD

Setting Up NTP Synchronization

Conclusion

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