Hello Friends! Last week while trying out some odd experiments, I came across a task wherein I was required to do 4x4 keypad matrix interfacing with Arduino UNO microcontroller board.



4x4 numeric keypads are most widely used in numerous mini project which requires the user or the operator to give command to the system or to feed in some data into the embedded system.

In this post, I want to share with you the Arduino code which I made for 4x4 keypad interfacing. The program shared hereby is simple and easy to understand.

If you search more over the internet, then you may find some program involving keypad matrix interfacing using libraries, but problem with those codes are that, if you want to make some modifications in the code, then you are required to 'break in your head' to understand the complete code of the library file. Contrary to those codes, this program does not involve any library and is completely coded by me based on the conventional algorithm which is most commonly found in numerous books and internet sources.

In this program, the row pins are connected to A5, A4, A3, A2 and the column pins are connected to A1, A0, 10, 11. If you are changing the connections, then make sure that you update the changes in the first 8 lines of the the program

The code for 4x4 keypad interfacing with Arduino board is given below:

/*Program demonstrating 4x4 Numeric Keypad interfacing with Arduino UNO
Program Written by: Amit Biswal (Speaking Technology)
URL               : http://amitbiswal.blogspot.com       
*/
int r1=A5;
int r2=A4;
int r3=A3;
int r4=A2;

int c1=A1;
int c2=A0;
int c3=10;
int c4=11;

void setup()
{
  Serial.begin(9600);
  
  pinMode(r1,OUTPUT);
  pinMode(r2,OUTPUT);
  pinMode(r3,OUTPUT);
  pinMode(r4,OUTPUT);

  pinMode(c1,INPUT);
  pinMode(c2,INPUT);
  pinMode(c3,INPUT);
  pinMode(c4,INPUT);
  
}
void loop()
{
  int val;
  //setting the columns as high initially
  digitalWrite(c1,HIGH);
  digitalWrite(c2,HIGH);
  digitalWrite(c3,HIGH);
  digitalWrite(c4,HIGH);
  
  //checking everything one by one
  //case 1: col1 =0 while other col as 1
  digitalWrite(r1,LOW);
  digitalWrite(r2,HIGH);
  digitalWrite(r3,HIGH);
  digitalWrite(r4,HIGH);
  //checking each column for row1 one by one
  if(digitalRead(c1)==0)
  {
    Serial.println("key 1 pressed");
  }
  else if(digitalRead(c2)==0)
  {
    Serial.println("Key 2 pressed");
  }
  else if(digitalRead(c3)==0)
  {
    Serial.println("Key 3 pressed");
  }
  else if(digitalRead(c4)==0)
  {
    Serial.println("Key A pressed");
  }
  
  //case 2: col2 =0 while other col as 1
  digitalWrite(r1,HIGH);
  digitalWrite(r2,LOW);
  digitalWrite(r3,HIGH);
  digitalWrite(r4,HIGH);
  //checking each column for row1 one by one
  if(digitalRead(c1)==0)
  {
    Serial.println("key 4 pressed");
  }
  else if(digitalRead(c2)==0)
  {
    Serial.println("Key 5 pressed");
  }
  else if(digitalRead(c3)==0)
  {
    Serial.println("Key 6 pressed");
  }
  else if(digitalRead(c4)==0)
  {
    Serial.println("Key B pressed");
  }
  
  //case 3: col3 =0 while other col as 1
  digitalWrite(r1,HIGH);
  digitalWrite(r2,HIGH);
  digitalWrite(r3,LOW);
  digitalWrite(r4,HIGH);
  //checking each column for row1 one by one
  if(digitalRead(c1)==0)
  {
    Serial.println("key 7 pressed");
  }
  else if(digitalRead(c2)==0)
  {
    Serial.println("Key 8 pressed");
  }
  else if(digitalRead(c3)==0)
  {
    Serial.println("Key 9 pressed");
  }
  else if(digitalRead(c4)==0)
  {
    Serial.println("Key C pressed");
  }
  
  //case 1: col1 =0 while other col as 1
  digitalWrite(r1,HIGH);
  digitalWrite(r2,HIGH);
  digitalWrite(r3,HIGH);
  digitalWrite(r4,LOW);
  //checking each column for row1 one by one
  if(digitalRead(c1)==0)
  {
    Serial.println("key F pressed");
  }
  else if(digitalRead(c2)==0)
  {
    Serial.println("Key 0 pressed");
  }
  else if(digitalRead(c3)==0)
  {
    Serial.println("Key E pressed");
  }
  else if(digitalRead(c4)==0)
  {
    Serial.println("Key D pressed");
  }
  //giving delay between keypress
  delay(200);
  
}