How To Use a 4-Digit 7-Segment Display in Arduino Project

A seven-segment display is one of the simplest and cheapest electronic display units. It is used to display numerical output that has few place values or decimal places. 7-segment indicators exist in different forms. Some of the common types are one-digit, 2-digits, 3-digits, and 4-digits display units. Of those that have more than one place value, there are those that have decimal points and colons. The seven-segment display units with decimal points are ideal for displaying numerical output with few decimal places while those that have colons are mostly used to display time.

Though simple in design, a 7-segment display unit can be difficult to interface with a microcontroller, especially because of the many connection pins. It is even more difficult to interface multiple-digit units because they have more pins. In this article, I will teach you how to interface a 4-digit seven-segment indicator with Arduino microcontroller. We will then use it to display the temperature measured from the LM35 sensor.

Parts

  • 4-digit seven-segment display unit
  • LM35 temperature sensor
  • Arduino
  • Wire jumpers
  • Breadboard

Circuit diagram

wiring-diagram-for-seven-segment-and-arduino-interface
Circuit Diagram for Arduino – 7-segment display interface

Code

/**
 * Author      : Julioceaseless
 * Date        : September 2019
 * Description : Display temperature from LM35 temperature sensor 
 *               and display it on a 4-Digit Seven Segment Display
 * Website     : https://nandgeek.com
**/
 
// Pin 2-8 is connected to the 7 segments of the display.
#define ADCPIN 0

int pinA = 2;
int pinB = 3;
int pinC = 4;
int pinD = 5;
int pinE = 6;
int pinF = 7;
int pinG = 8;
//common pins
int D1 = 9;
int D2 = 10;
int D3 = 11;
int D4 = 12;
//decimal pin
int Dot = 13;

double Temperature = 0;
int temp = 0;
int placeValuesofTemp[4];

int period = 1000;
unsigned long time_now = 0;
// the setup routine runs once when you press reset:
void setup() {
  analogReference(INTERNAL); 
                
  // initialize the digital pins as outputs.
  pinMode(pinA, OUTPUT);     
  pinMode(pinB, OUTPUT);     
  pinMode(pinC, OUTPUT);     
  pinMode(pinD, OUTPUT);     
  pinMode(pinE, OUTPUT);     
  pinMode(pinF, OUTPUT);     
  pinMode(pinG, OUTPUT);   
  pinMode(D1, OUTPUT);  
  pinMode(D2, OUTPUT);  
  pinMode(D3, OUTPUT);  
  pinMode(D4, OUTPUT);  
  pinMode(Dot, OUTPUT); 
  Serial.begin(9600);
}

// the loop routine runs over and over again forever:
void loop() {
  
// read temperature every second
if(millis() > time_now + period ){
  time_now = millis();
  Temperature = analogRead(ADCPIN);
  //Temp = Temperature/10;
  //Vin = ADCresult*Vref/(2^10)
  //Temp (C) = Vin/10 = ADCresult(mV)*Vref(mV)/((2^10)*10)
  Temperature = Temperature*1100/(1024*10);

  temp = Temperature*100;

  placeValuesofTemp[3] = ((temp)/1)%10;
  placeValuesofTemp[2] = ((temp)/10)%10;
  placeValuesofTemp[1] = ((temp)/100)%10;
  placeValuesofTemp[0] = ((temp)/1000)%10;
  /**Serial.print(Temperature);
  Serial.print(" Degrees >>");
  Serial.print(placeValuesofTemp[3]);
  Serial.print(placeValuesofTemp[2]);
  Serial.print(placeValuesofTemp[1]);
  Serial.print(placeValuesofTemp[0]);
  Serial.println();
  **/
} //end millis() if statement
  //
  int number [10][7] = {
    {1, 1, 1, 1, 1, 1, 0},//0
    {0, 0, 0, 0, 1, 1, 0},//1
    {1, 1, 0, 1, 1, 0, 1},//2
    {1, 1, 1, 1, 0, 0, 1},//3
    {0, 1, 1, 0, 0, 1, 1},//4
    {1, 0, 1, 1, 0, 1, 1},//5
    {1, 0, 1, 1, 1, 1, 1},//6
    {1, 1, 1, 0, 0, 0, 0},//7
    {1, 1, 1, 1, 1, 1, 1},//8
    {1, 1, 1, 0, 0, 1, 1},//9
        
    };
  int commonPin [5][4]= {
    {0, 1, 1, 1},//enable digit 1
    {1, 0, 1, 1},//enable digit 2
    {1, 1, 0, 1},//enable digit 3
    {1, 1, 1, 0},//enable digit 4
    {0, 0, 0, 0},//enable all
    };
    for (int n = 0; n<4; n++){
      for (int x = 0; x < 4; x++ ){
        digitalWrite(x+9, commonPin[n][x]);
         (n==1)?digitalWrite(Dot, 1):digitalWrite(Dot, 0);//display decimal after second digit
          /**
          //debug multiplexing
            Serial.print("digitalWrite(");
            Serial.print(x+9);
            Serial.print(", ");
            Serial.print(commonPin[n][x]);
            Serial.println(");"); 
          **/
           }//end for loop for x
          //write digits
          for (int j = 0; j < 7; j++){//loop seven segments
            digitalWrite(j+2,number[placeValuesofTemp[n]][j] );  
            
            /**     
          //debug digits display                      
            Serial.print("digitalWrite(");
            Serial.print(j+2);
            Serial.print(", ");
            Serial.print(number[placeValuesofTemp[n]][j]);
            Serial.print(")");
            Serial.println();
            **/
          }
          delay(5);
      }//end n for loop
}
  
  

Video Demo of 7-Segment Display Unit in Arduino Project

Video demo for interfacing seven-segment display unit with arduino uno