Simple Clock Using Arduino UNO

MakeMindz ⏱ Intermediate Project

Arduino Project · Intermediate Series

Simple Digital Clock
with RTC & LCD

Build a real-time digital clock using Arduino UNO, a DS3231/DS1307 RTC module, and a 16×2 I2C LCD display. Time stays accurate even after power loss.

🔵 Intermediate Level ⏱ 45–60 min build 📡 I2C Protocol 🔋 Battery Backed RTC

📺 Live Preview — What your LCD will display

Time: 00:00:00 Date: 07/04/2026

This mirrors exactly what scrolls on your 16×2 LCD screen in real time.

1Components Required

🧠

Arduino UNO

× 1

🕐

DS3231 or DS1307 RTC

× 1 (DS3231 preferred)

📟

16×2 I2C LCD Display

× 1

🔌

I2C Module for LCD

× 1 (optional, recommended)

🔋

CR2032 Coin Cell

× 1 (backup battery)

🟫

Breadboard

× 1

🔁

Jumper Wires

Male-to-Male

🔗

USB Cable

For programming

2Working Principle

⏰

1. Time Keeping (RTC)

The DS3231 has an internal crystal oscillator that tracks hours, minutes, seconds, day, month, and year. A CR2032 coin cell keeps time even when Arduino is off.

📡

2. I2C Communication

Arduino communicates with both the RTC module and LCD over the I2C bus using SDA (A4) and SCL (A5). Both devices share the same two wires.

📺

3. Display Update

Every second, Arduino reads time data from the RTC, formats it, and pushes it to the 16×2 LCD — Row 1 shows HH:MM:SS, Row 2 shows DD/MM/YYYY.

3Circuit Diagram

💡 Both the RTC module and LCD share the same SDA/SCL lines — that's the power of the I2C bus.

4Wiring Connections

RTC Module (DS3231 / DS1307)

RTC Pin	Connect To (Arduino)	Wire Color
VCC	5V	🔴 Red
GND	GND	⚫ Black
SDA	A4	🟡 Yellow
SCL	A5	🟠 Orange

16×2 I2C LCD Display

LCD Pin	Connect To (Arduino)	Wire Color
VCC	5V	🔴 Red
GND	GND	⚫ Black
SDA	A4	🟡 Yellow
SCL	A5	🟠 Orange

ℹ️

Both the RTC and LCD use the same I2C bus (SDA and SCL lines). They have different I2C addresses so they don't conflict. The LCD I2C backpack's address is usually 0x27 or 0x3F — check with an I2C scanner sketch if unsure.

5Step-by-Step Instructions

1

Install required libraries

In Arduino IDE, go to Sketch → Include Library → Manage Libraries. Search and install: RTClib by Adafruit, LiquidCrystal I2C by Frank de Brabander, and ensure Wire.h is available (it's built-in).

💡 RTClib works with both DS3231 and DS1307. Just change the object type in code.

2

Insert CR2032 battery into RTC module

Before wiring, slide the CR2032 coin cell into the battery holder on the back of the RTC board. This ensures your time is retained even when Arduino is unplugged.

3

Set up breadboard power rails

Connect Arduino's 5V to the breadboard's red (+) rail and GND to the blue (−) rail. Both the RTC and LCD will draw power from here.

4

Wire the DS3231 RTC module

Connect RTC VCC → 5V rail, GND → GND rail, SDA → Arduino A4, SCL → Arduino A5.

5

Wire the 16×2 I2C LCD

Connect LCD VCC → 5V rail, GND → GND rail, SDA → Arduino A4, SCL → Arduino A5. Both devices share these same two data wires — that's I2C in action!

6

Find your LCD's I2C address

Upload the I2C Scanner sketch (available in Arduino examples) to find the LCD's address. It's usually 0x27 or 0x3F.

💡 Update the address in the code: LiquidCrystal_I2C lcd(0x27, 16, 2);

7

Upload the code & set the time

The first upload automatically sets the RTC time to your computer's compile time. After uploading once, comment out the rtc.adjust() line and upload again to prevent time reset on every restart.

8

Test & verify the display

The LCD should show the current time on Row 1 (HH:MM:SS) and the date on Row 2 (DD/MM/YYYY), updating every second. Adjust the LCD contrast using the potentiometer on the I2C backpack if text is invisible.

6Arduino Code

simple_clock.ino

// Simple Digital Clock using Arduino UNO
// Components: DS3231 RTC + 16x2 I2C LCD
// MakeMindz.com | Intermediate Series

#include <Wire.h>
#include <RTClib.h>
#include <LiquidCrystal_I2C.h>

// LCD address is usually 0x27 or 0x3F
// Change if your LCD does not display text
LiquidCrystal_I2C lcd(0x27, 16, 2);

RTC_DS3231 rtc;
// For DS1307, replace above with: RTC_DS1307 rtc;

void setup() {
  lcd.init();
  lcd.backlight();

  if (!rtc.begin()) {
    lcd.print("RTC not found!");
    while (1);
  }

  // Set RTC to compile time (run once, then comment out)
  rtc.adjust(DateTime(F(__DATE__), F(__TIME__)));
  // After first upload, comment above and re-upload
}

void loop() {
  DateTime now = rtc.now();

  // Row 1: Time — HH:MM:SS
  lcd.setCursor(0, 0);
  lcd.print("Time: ");
  printTwoDigits(now.hour());
  lcd.print(":");
  printTwoDigits(now.minute());
  lcd.print(":");
  printTwoDigits(now.second());

  // Row 2: Date — DD/MM/YYYY
  lcd.setCursor(0, 1);
  lcd.print("Date: ");
  printTwoDigits(now.day());
  lcd.print("/");
  printTwoDigits(now.month());
  lcd.print("/");
  lcd.print(now.year());

  delay(1000); // Update every 1 second
}

// Helper: print leading zero for single digits
void printTwoDigits(int num) {
  if (num < 10) lcd.print("0");
  lcd.print(num);
}

8Try the Simulation

🎮 Try it Without Hardware

Run the full clock simulation in Tinkercad — watch the LCD display tick in real time right in your browser.

▶ Open Tinkercad Sim ⬇ Download Code

9Features

✅ Real-time hours, minutes, seconds

✅ Day, month, and year display

✅ Time saved after power loss

✅ Clear 16×2 LCD readout

✅ I2C reduces wiring complexity

✅ Beginner and classroom friendly

10Possible Upgrades

🔔 Add alarm function with a piezo buzzer

🌡️ Display temperature (DS3231 has a built-in sensor)

📶 Bluetooth time synchronization via HC-05

🌐 IoT clock with NTP auto time-sync (ESP8266/ESP32)

🔘 Add push buttons to manually set/adjust time

💾 Data logging with an SD card module

11Learning Outcomes

📡 I2C communication protocol

🕐 RTC module interfacing

🔢 Time formatting and display logic

📟 16×2 LCD interfacing

⏱ Embedded timing concepts

🔋 Battery-backed hardware design

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