#include <LiquidCrystal_I2C.h>
#define I2C_ADDR    0x27
#define LCD_COLUMNS 20
#define LCD_LINES   4
LiquidCrystal_I2C lcd(I2C_ADDR, LCD_COLUMNS, LCD_LINES);
const int numRows = 4; 
const int numCols = 4; 
const int debounceTime = 20; 
const char keymap[numRows][numCols] = {
 { '1', '2', '3' ,'A'} ,

 { '4', '5', '6','B' } ,

 { '7', '8', '9','C' } ,

 { '*', '0', '#','D' }

};
const int rowPins[numRows] = {9,8, 7, 6}; 
const int colPins[numCols] = {5,4, 3, 2}; 
void setup()

{
  lcd.init();
  lcd.backlight();
  lcd.setCursor(3, 0);
  lcd.print("Using LCD");
 for (int row = 0; row < numRows; row++)

 {
 pinMode(rowPins[row],INPUT_PULLUP);
 }

 for (int column = 0; column < numCols; column++)
 {

 pinMode(colPins[column],OUTPUT); 

 digitalWrite(colPins[column],HIGH); 

 }

}

void loop()

{

 char key = getKey();

 if( key != 0) { 
 lcd.setCursor(3, 1);
 lcd.print("Got key ");
 lcd.print(key);
 }

}
char getKey()
{

 char key = 0; 
 for(int column = 0; column < numCols; column++)

 {

 digitalWrite(colPins[column],LOW); 
 for(int row = 0; row < numRows; row++) 

 {

 if(digitalRead(rowPins[row]) == LOW)

 {

 delay(debounceTime); // debounce
 while(digitalRead(rowPins[row]) == LOW)

 ;

 key = keymap[row][column];
 }

 }

 digitalWrite(colPins[column],HIGH);

 }

 return key; 
}