Arduino DS1307 Clock

1) Introduction and Images

Hello friends, today I am going to build a Digital Clock using Arduino UNO and famous DS1307 Real Time Clock IC.

Before we begin, here are some images of the completed project. You can find the YouTube video at the bottom of the page

2) DS1307 RTC IC

DS1307 is a low power serial real time clock with full binary coded decimal (BCD) clock/calendar plus 56 bytes of NV SRAM.

The RTC provides year, month, date, hour, minute and second information. The end date of months is automatically adjusted for months fewer than 31 days including leap year compensation up to year 2100. It can operate either in 24-hour format or 12-hour format with AM/PM indicator. Below are the key features of this IC. [1]

Arduino DS1307 Clock

  • Real-Time Clock (RTC) Counts Seconds, Minutes, Hours, Date of the Month, Month, Day of the week, and Year with Leap-Year Compensation Valid Up to 2100
  • 56-Byte, Battery-Backed, General-Purpose RAM with Unlimited Writes
  • I²C Serial Interface
  • Programmable Square-Wave Output Signal
  • Automatic Power-Fail Detect and Switch Circuitry
  • Consumes Less than 500nA in Battery-Backup Mode with Oscillator Running
  • Optional Industrial Temperature Range: -40°C to +85°C
  • Available in 8-Pin Plastic DIP or SO [2]

The DS1307 IC uses I²C protocol to transfer data to the Microcontroller.

3) What is I²C Protocol?

I²C (Inter-Integrated Circuit), pronounced I-squared-C, is a multi-master, multi-slave, single-ended, serial computer bus invented by Philips Semiconductor, known today as NXP Semiconductors, used for attaching low-speed peripherals to computer motherboards and embedded systems. Alternatively I²C is spelled I2C (pronounced I-two-C) or IIC (pronounced I-I-C). [3]

4) DS1307 Circuit

Before we begin, you have to build a small circuit with some components. Other than the DS1307 IC, you need following components to build this small circuit. This circuit is also available as a completed board. You can search on eBay and other famous electronic shopping web sites for more information.

  • 10k Resistors – 2 [pull up resistors]
  • 32.768 KHz Crystal Oscillator
  • 3V coin cell battery [to provide backup power]

Please use the following schematic to build the DS1307 circuit [4].

5) Let’s connect DS1307 circuit to your Arduino UNO

After you completed the above circuit, it is time to connect this circuit to Your Arduino UNO.

Please use the following configurations table to connect your DS1307 circuit to Arduino UNO

Following schematic will help you to further understand the pin configurations

6) The RTClib.h

We are going to use a special library called the RTClib and in it there’s an example sketch which sets the time on the DS1307 IC. Upon the first power up, the DS1307 will start counting from 1/1/2000 0:00 which is not right, so we need to set it up to the correct date and time. We’ll only need to do this once as long as the coin cell battery is not removed. [4]

7) Source Code for the Step 1

As I mentioned in the introduction of this tutorial, first we are going to test our real time clock using the Serial Monitor window of the Arduino IDE. Later we will connect our circuit to a LCD screen.

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


void setup () {

  if (! RTC.isrunning()) {
    Serial.println("RTC is NOT running!");
    RTC.adjust(DateTime(F(__DATE__), F(__TIME__)));

void loop () {
    DateTime now =;
	Serial.print(now.year(), DEC);
	Serial.print(now.month(), DEC);
	Serial.print(, DEC);
    	Serial.print(' ');
    	Serial.print(now.hour(), DEC);
    	Serial.print(now.minute(), DEC);
    	Serial.print(now.second(), DEC); 

Arduino DS1307 Clock Schematic What this code does is basically sets the time and date according to when the sketch is compiled. Of course there will be a slight delay from the time the code compiles and it is fully uploaded to the Arduino. I think it’s less of a problem on the newer Arduinos that are using the Atmel 8U2 and 16U2 as the upload times are significantly faster.

8) Connecting 16×2 LCD Screen to the Project

If you are succeed with the above experiment, now it is time to build a fully working Digital Clock using a LCD screen. You can use the same circuit you built earlier in the first step. Only difference is, instead of using the serial monitor, this time we are going to use a LCD screen to display the time.

Please use the following schematic to connect 16×2 HD44780 compatible LCD screens to your Arduino UNO board.

For more detail: Arduino DS1307 Clock


About The Author

Ibrar Ayyub

I am an experienced technical writer with a Master's degree in computer science from BZU Multan University. I have written for various industries, mainly home automation, and engineering. I have a clear and simple writing style and am skilled in using infographics and diagrams. I am a great researcher and is able to present information in a well-organized and logical manner.

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