This Arduino program interfaces with a 4x4 numeric keypad to detect button presses. It uses 8 digital pins to control the 4 rows and 4 columns, setting each row low while reading the columns to detect which button is pressed. When a button is pressed, the corresponding key value (e.g. "1", "2", etc.) is printed to the serial monitor. It loops through each row, setting one low at a time while reading the columns, to continuously monitor the keypad for input.

1. /*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);

2. 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)
{

3. Serial.println("Key D pressed");
}
//giving delay between keypress
delay(200);
}