Arduino Digital Clock using 7 segment display

In this post we are going to learn how to construct 16 digit – 7 segment display digital clock using Arduino. The clock will display date, time and temperature. The clock can be powered with any 5V supply and requires very little power. The brightness can also be adjusted with only a simple change in code. For driving the display units I will be using MAX7219. You may read my blog on how to use MAX7219 with arduino here.

Arduino digital clock final look by
Arduino digital clock final look

RTC Module

In this project I will be using Chronodot 2.0 module. It has a DS3231 chip in a circular breakout board. Read more about using chronodot with arduino here.

digital electronics circuits lab schematic
Chronodot 2.0

The RTC module has a battery holder to power the chip when the clock and microcontroller is off. It will keep the date and time until you remove this coin cell from the module.

Circuit Diagram

Arduino digital clock circuit diagram by
Arduino digital clock circuit diagram

You may download the pdf of schematic also.

The circuit is very very straightforward. Since one MAX7219 can display only 8 digits, so I have used two MAX7219 chips to display 16 digits. The two MAX7219 ICs can be daisy chained to work together.

Arduino digital clock circuit by digitaleclab
Arduino digital clock circuit (front)
Arduino digital clock circuit by
Arduino digital clock circuit (back)

If yo are interested in reading about using atmega328 in your project, you may read this article.

Arduino Code

Download the code here:

You can copy the code here.

//////////////// Code by Digital Electronics Circuits Lab //////////////////////////////

/*This code required adafruit RTC library to work with DS3231
 * Please subscribe to my Youtube channel "Digital Electronics Circuits Lab"
 * This is version 0.1 of the projects and has many scope for improvement.
 * Using this code for any commercial purpose or advertisement is strictly prohibited and may led to copyright claims.
 * The project is just a demonstration and can be used only for development purpose.
 * Visit my website for more projects and tutorials.

#include <RTClib.h>

RTC_DS3231 rtc;
#define MAX7219_DIN 12
#define MAX7219_CS 11
#define MAX7219_SCK 10
#define DISPLAY_MODE 0x0F
#define SDN_MODE 0x0C
#define DECODE_MODE 0x09
#define INTENSITY 0x0A
#define SCAN_LIMIT 0x0B

int tempC;
int my_str [16];
int digit_code = 0;

void setup() {
  if (rtc.lostPower()){
  rtc.adjust(DateTime(F(__DATE__), F(__TIME__))); //to set current date and time from PC
  //rtc.adjust(DateTime(YYYY, MM, DD, hh, mm, ss)) //use this line to set time and date manually.

void initialise() {
  digitalWrite(MAX7219_CS, HIGH);
  pinMode(MAX7219_DIN, OUTPUT);
  pinMode(MAX7219_CS, OUTPUT);
  pinMode(MAX7219_SCK, OUTPUT);
  out(DISPLAY_MODE, 0x00, DISPLAY_MODE, 0x00);
  out(SDN_MODE, 0x01, SDN_MODE, 0x01);
  out(DECODE_MODE, 0xff, DECODE_MODE, 0xff);
  out(INTENSITY, 0x0f, INTENSITY, 0x0f); //change the hex values to adjust brightness. 0x00 is minimum and 0x0f is maximum.
  out(SCAN_LIMIT, 0x07, SCAN_LIMIT, 0x07);

void out(byte address1, byte data1, byte address2, byte data2) {
  digitalWrite(MAX7219_CS, LOW);
  shiftOut(MAX7219_DIN, MAX7219_SCK, MSBFIRST, address1); //send address
  shiftOut(MAX7219_DIN, MAX7219_SCK, MSBFIRST, data1); //send data
  shiftOut(MAX7219_DIN, MAX7219_SCK, MSBFIRST, address2); //send address
  shiftOut(MAX7219_DIN, MAX7219_SCK, MSBFIRST, data2); //send data
  digitalWrite(MAX7219_CS, HIGH);

void loop() {
    DateTime now =;
  if (now.hour() < 10) {
    my_str[0] = 0;
    my_str[1] = now.hour();
  } else {
    my_str[0] = now.hour() / 10;
    my_str[1] = now.hour() % 10;
  if (now.minute() < 10) {
    my_str[2] = 0;
    my_str[3] = now.minute();
  } else {
    my_str[2] = now.minute() / 10;
    my_str[3] = now.minute() % 10;

  if (now.second() < 10) {
    my_str[4] = 0;
    my_str[5] = now.second();
  } else {
    my_str[4] = now.second() / 10;
    my_str[5] = now.second() % 10;

  if ( < 10) {
    my_str[6] = 0;
    my_str[7] =;
  } else {
    my_str[6] = / 10;
    my_str[7] = % 10;
  if (now.month() < 10) {
    my_str[8] = 0;
    my_str[9] = now.month();
  } else {
    my_str[8] = now.month() / 10;
    my_str[9] = now.month() % 10;
  my_str [10] = now.year() / 1000;
  my_str [11] = (now.year() / 100) % 10;
  my_str [12] = (now.year() / 10) % 10;
  my_str [13] = now.year() % 10;

  tempC = rtc.getTemperature();
  my_str [14] = tempC / 10;
  my_str [15] = tempC % 10;
  out(0x01, digits(my_str[8]), 0x01, digits(my_str[0]));
  out(0x02, digits(my_str[9]), 0x02, digits(my_str[1]));
  out(0x03, digits(my_str[10]), 0x03, digits(my_str[2]));
  out(0x04, digits(my_str[11]), 0x04, digits(my_str[3]));
  out(0x05, digits(my_str[12]), 0x05, digits(my_str[4]));
  out(0x06, digits(my_str[13]), 0x06, digits(my_str[5]));
  out(0x07, digits(my_str[14]), 0x07, digits(my_str[6]));
  out(0x08, digits(my_str[15]), 0x08, digits(my_str[7]));


int digits(int x)
  switch (x)
    case 0:
      digit_code = 0x00;
    case 1:
      digit_code = 0x01;
    case 2:
      digit_code = 0x02;
    case 3:
      digit_code = 0x03;
    case 4:
      digit_code = 0x04;
    case 5:
      digit_code = 0x05;
    case 6:
      digit_code = 0x06;
    case 7:
      digit_code = 0x07;
    case 8:
      digit_code = 0x08;
    case 9:
      digit_code = 0x09;
  return digit_code;

Connect FTDI with the board and upload the code.

Arduino digital clock circuit with FTDI by
Arduino digital clock circuit with FTDI
Arduino digital clock circuit with FTDI
Arduino digital clock circuit with FTDI

Video on My YouTube Channel

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