Description

Digital wall Clocks are getting more popular now days and they are better than analog clock as it provides accurate time in hours, minutes and seconds and its easy to read the values. Some digital clocks also have many facilities like displaying temperature, humidity, setting multiple alarms etc. Most of the digital clocks use seven segment display.

We previously built many digital clocks circuits either using 7 segment displays or using 16x2 LCD. Here you can the complete PCB designs of AVR based Digital clock. This tutorial is about making a Digital clock by multiplexing four- 7 segment displays using Arduino UNO and displaying the time in HH:MM format.

Components Required

• 4-Digit 7 Segment Display
• 74HC595 IC
• DS3231 RTC Module
• Arduino UNO
• Breadboard
• Connecting wires

4-Digit 7 Segment Display

4-digit 7 Segment display has four seven segment display joined together or we can say multiplexed together. They are used to display numerical values and also some alphabets with decimals and colon. The display can be used in both direction. Four digits are useful for making digital clocks or like counting numbers from 0 to 9999. Below is the internal diagram for 4-Digit 7 Segment display.

Each segment has one LED with individual LED control. There are two types of seven segment displays such as Common Anode and Common Cathode. The above image shows the common anode type 7 segment display.

Common Anode

In Common Anode, all the positive terminals (Anodes) of all the 8 LEDs are connected together, named as COM. And all the negative terminals are left alone or connected to the microcontroller pins. By using microcontroller, if logic LOW is set to illuminate the particular LED segment and set logic High to turn OFF LED.

Common Cathode

In Common Cathode, all the Negative terminals (cathode) of all the 8 LEDs are connected together, named as COM. And all the positive terminals are left alone or connected to the microcontroller pins. By using microcontroller, if set logic HIGH to illuminate the LED and set LOW to turn OFF LED.

Learn more about 7 segment displays here and check how it can be interfaced with other microcontrollers

74HC595 Shift Register IC

The IC 74HC595 also known as 8-Bit Serial IN – Parallel OUT Shift Register. This IC can receive data input in serial and can control 8 output pins in parallel. This is useful in reducing pins used from microcontroller. You can find all the 74HC595 shift register related projects here.

Working of 74HC595 IC: 

This IC uses three pins such as Clock, Data & Latch with the microcontroller to control the 8 output pins of the IC. The clock is used to provide continuously pulses from microcontroller and data pin is used to send the data like which output needs to be turned ON or OFF at the respective clock time.

Pinout:

Pin Number

Pin Name

Description

1,2,3,4,5,6,7

Output Pins (Q1 to Q7)

The 74HC595 has 8 output pins out of which 7 are these pins. They can be controlled serially

8

Ground

Connected to the Ground of microcontroller

9

(Q7) Serial Output

This pin is used to connect more than one 74HC595 as cascading

10

(MR) Master Reset

Resets all outputs as low. Must be held high for normal operation

11

(SH_CP) Clock

This is the clock pin to which the clock signal has to be provided from MCU/MPU

12

(ST_CP) Latch

The Latch pin is used to update the data to the output pins. It is active high

13

(OE) Output Enable

The Output Enable is used to turn off the outputs. Must be held low for normal operation

14

(DS) Serial Data

This is the pin to which data is sent, based on which the 8 outputs are controlled

15

(Q0) Output

The first output pin.

16

Vcc

This pin powers the IC, typically +5V is used.

DS3231 RTC Module

DS3231 is an RTC module. RTC stands for Real Time Clock. This module is used to remember the time and date even when the circuit is not powered. It has a battery backup CR2032 to run the module in absence of external power. This module also includes a temperature sensor. The module can be used in embedded projects such as making digital clock with temperature indicator etc. Here are some useful projects using it

steady time can be seen.

Note that to access the RTC module, the I2C bus voltage has to be maintained. In order to give any suggestion or if you have any doubt then please comment below.

Code

//Four-Digit 7 Segments Multiplexing using Arduino: Display time in HH:MM

//CIRCUIT DIGEST

#include <Wire.h> //Library for SPI communication

#include <DS3231.h> //Library for RTC module 

#define latchPin 5                       

#define clockPin 6

#define dataPin 4

#define dot 2

DS3231 RTC; //Declare object RTC for class DS3231

int h; //Variable declared for hour

int m; //Variable declared for minute

int thousands;     

int hundreds;

int tens;

int unit;

bool h24;

bool PM;

void setup () 

{

    Wire.begin();    

    pinMode(9,OUTPUT);

    pinMode(10,OUTPUT);

    pinMode(11,OUTPUT);

    pinMode(12,OUTPUT);

    pinMode(latchPin, OUTPUT);

    pinMode(clockPin, OUTPUT);

    pinMode(dataPin, OUTPUT);

    pinMode(dot,OUTPUT);

}

void loop () 

{

    digitalWrite(dot,HIGH);

    int h= RTC.getHour(h24, PM); //To get the Hour

    int m = RTC.getMinute(); //TO get the minute

    int number = h*100+m; //Converts hour and minute in 4-digit

    int thousands = number/1000%10; //Getting thousands digit from the 4 digit

    int hundreds = number/100%10; //Getting hundreds digit from 4 digit

    int tens = number/10%10; //Getting tens digit from 4-digit

    int unit = number%10; //Getting last digit from 4-digit

    int t= unit;

    int u= tens;

    int v= hundreds;

    int w= thousands;

//Converting the individual digits into corresponding number for passing it through the shift register so LEDs are turned ON or OFF in seven segment

switch (t)

{

  case 0:

  unit = 63;

  break;

  case 1:

  unit = 06;

  break;

  case 2:

  unit =91;

  break;

  case 3:

  unit=79;

  break;

  case 4:

  unit=102;

  break;

  case 5:

  unit = 109;

  break;

  case 6:

  unit =125;

  case 7:

  unit = 07;

  break;

  case 8:

  unit = 127;

  break;

  case 9:

  unit =103;

  break;  

  }

switch (u)

{

  case 0:

  tens = 63;

  break;

  case 1:

  tens = 06;

  break;

  case 2:

  tens =91;

  break;

  case 3:

  tens=79;

  break;

  case 4:

  tens=102;

  break;

  case 5:

  tens= 109;

  break;

  case 6:

  tens =125;

  case 7:

  tens = 07;

  break;

  case 8:

  tens = 127;

  break;

  case 9:

  tens =103;

  break;  

  }

  switch (v)

  {

  case 0:

  hundreds = 63;

  break;

  case 1:

  hundreds = 06;

  break;

  case 2:

  hundreds =91;

  break;

  case 3:

  hundreds=79;

  break;

  case 4:

  hundreds=102;

  break;

  case 5:

  hundreds = 109;

  break;

  case 6:

  hundreds =125;

  case 7:

  hundreds = 07;

  break;

  case 8:

  hundreds = 127;

  break;

  case 9:

  hundreds =103;

  break;  

  }

  switch (w)

  {

  case 0:

  thousands = 63;

  break;

  case 1:

  thousands = 06;

  break;

  case 2:

  thousands =91;

  break;

  case 3:

  thousands=79;

  break;

  case 4:

  thousands=102;

  break;

  case 5:

  thousands = 109;

  break;

  case 6:

  thousands =125;

  case 7:

  thousands = 07;

  break;

  case 8:

  thousands= 127;

  break;

  case 9:

  thousands =103;

  break;  

  }

    digitalWrite(9, LOW);

    digitalWrite(latchPin, LOW);

    shiftOut(dataPin, clockPin, MSBFIRST,thousands); // The thousand digit is sent

    digitalWrite(latchPin, HIGH); // Set latch pin HIGH to store the inputs 

    digitalWrite(9, HIGH); // Turinig on that thousands digit

    delay(5); // delay for multiplexing 

    digitalWrite(10, LOW);

    digitalWrite(latchPin, LOW);

    shiftOut(dataPin, clockPin, MSBFIRST,hundreds ); // The hundered digit is sent

    digitalWrite(latchPin, HIGH);

    digitalWrite(10, HIGH);

    delay(5);                                 

    digitalWrite(11, LOW);

    digitalWrite(latchPin, LOW);

    shiftOut(dataPin, clockPin, MSBFIRST,tens); // The tens digit is sent

    digitalWrite(latchPin, HIGH);

    digitalWrite(11, HIGH);

    delay(5);

    digitalWrite(12, LOW);

    digitalWrite(latchPin, LOW);

    shiftOut(dataPin, clockPin, MSBFIRST,unit); // The last digit is sent

    digitalWrite(latchPin, HIGH);

    digitalWrite(12, HIGH);

    delay(5);

}