Interface 16 switches to arduino uno using only 5 digital pins (HEF4067BP)

Under certain situations, we will have to interface many switches to our arduino uno. Simplest method to interface switches to arduino uno is to connect the switch directly to any one of the digital pin or analog pin of arduino uno. But, if we have to interface many switches to arduino uno, previous mentioned method is not advisable because, only 14 digital pins and 6 analog pins are available in arduino uno. If we connect switches to all these pins, we could not use this arduino uno board for any other purposes. Then, we have to go for some other methods which use minimum pins of arduino to interface maximum number of switches.

Circuit given below shows a simple method to interface 16 switches to arduino uno using only 5 digital pins. A HEF4067BP multiplexer/demultiplexer IC should be connected in between switches and arduino uno as shown in the diagram.

After completing the circuit, upload the following program to your arduino board.

int val = 0;         // variable to store the read value

int A_zero = 8;       
int A_one = 9;
int A_two = 10;
int A_three = 11;

int z = 12;

void setup()
{
  
  pinMode(z, INPUT);      // sets the digital pin "z" as input

  pinMode(A_zero, OUTPUT);      // sets the digital pin "A_zero" as output
  pinMode(A_one, OUTPUT);       // sets the digital pin "A_one" as output
  pinMode(A_two, OUTPUT);       // sets the digital pin "A_two" as output
  pinMode(A_three, OUTPUT);     // sets the digital pin "A_three" as output
  
  Serial.begin(9600);

}

void loop()
{
  // Select address 0000  
  digitalWrite(A_zero, LOW);    
  digitalWrite(A_one, LOW);     
  digitalWrite(A_two, LOW);     
  digitalWrite(A_three, LOW);   
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 1");  
    delay(50);
  }

  // Select address 0001  
  digitalWrite(A_zero, HIGH);   
  digitalWrite(A_one, LOW);     
  digitalWrite(A_two, LOW);     
  digitalWrite(A_three, LOW);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 2");  
    delay(50);
  }

  // Select address 0010  
  digitalWrite(A_zero, LOW);   
  digitalWrite(A_one, HIGH);     
  digitalWrite(A_two, LOW);     
  digitalWrite(A_three, LOW);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 3");
    delay(50);  
  }

  // Select address 0011  
  digitalWrite(A_zero, HIGH);   
  digitalWrite(A_one, HIGH);     
  digitalWrite(A_two, LOW);     
  digitalWrite(A_three, LOW);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 4");
    delay(50);  
  }

  // Select address 0100  
  digitalWrite(A_zero, LOW);   
  digitalWrite(A_one, LOW);     
  digitalWrite(A_two, HIGH);     
  digitalWrite(A_three, LOW);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 5");
    delay(50);  
  }  

  // Select address 0101  
  digitalWrite(A_zero, HIGH);   
  digitalWrite(A_one, LOW);     
  digitalWrite(A_two, HIGH);     
  digitalWrite(A_three, LOW);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 6");
    delay(50);  
  }  

  // Select address 0110  
  digitalWrite(A_zero, LOW);   
  digitalWrite(A_one, HIGH);     
  digitalWrite(A_two, HIGH);     
  digitalWrite(A_three, LOW);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 7");
    delay(50);  
  }  

  // Select address 0111  
  digitalWrite(A_zero, HIGH);   
  digitalWrite(A_one, HIGH);     
  digitalWrite(A_two, HIGH);     
  digitalWrite(A_three, LOW);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 8");
    delay(50);  
  }  

  // Select address 1000  
  digitalWrite(A_zero, LOW);   
  digitalWrite(A_one, LOW);     
  digitalWrite(A_two, LOW);     
  digitalWrite(A_three, HIGH);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 9");
    delay(50);  
  }  

  // Select address 1001  
  digitalWrite(A_zero, HIGH);   
  digitalWrite(A_one, LOW);     
  digitalWrite(A_two, LOW);     
  digitalWrite(A_three, HIGH);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 10");
    delay(50);  
  }

  // Select address 1010  
  digitalWrite(A_zero, LOW);   
  digitalWrite(A_one, HIGH);     
  digitalWrite(A_two, LOW);     
  digitalWrite(A_three, HIGH);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 11");
    delay(50);  
  }

  // Select address 1011  
  digitalWrite(A_zero, HIGH);   
  digitalWrite(A_one, HIGH);     
  digitalWrite(A_two, LOW);     
  digitalWrite(A_three, HIGH);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 12");
    delay(50);  
  }

  // Select address 1100  
  digitalWrite(A_zero, LOW);   
  digitalWrite(A_one, LOW);     
  digitalWrite(A_two, HIGH);     
  digitalWrite(A_three, HIGH);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 13");
    delay(50);  
  }

  // Select address 1101  
  digitalWrite(A_zero, HIGH);   
  digitalWrite(A_one, LOW);     
  digitalWrite(A_two, HIGH);     
  digitalWrite(A_three, HIGH);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 14");
    delay(50);  
  }

  // Select address 1110  
  digitalWrite(A_zero, LOW);   
  digitalWrite(A_one, HIGH);     
  digitalWrite(A_two, HIGH);     
  digitalWrite(A_three, HIGH);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 15");
    delay(50);  
  }

  // Select address 1111  
  digitalWrite(A_zero, HIGH);   
  digitalWrite(A_one, HIGH);     
  digitalWrite(A_two, HIGH);     
  digitalWrite(A_three, HIGH);  
  if(digitalRead(z)==1)
  {         
    Serial.println("Switch pressed is 16");
    delay(50);  
  }
}