#include <Keypad.h>
const int numRows = 4;
const int numCols = 4;
const int debounceTime = 20;

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() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  for(int row = 0; row < numRows; row++)
  {
    pinMode(rowPins[row], INPUT_PULLUP);
  }
  for(int column = 0; column < numRows; column++)
  {
    pinMode(colPins[column], OUTPUT);
    digitalWrite(colPins[column], HIGH);
  }
}

void loop() {
  // put your main code here, to run repeatedly:
  char key = getKey();

  if(key != 0)
  {
    Serial.print("Got key ");
    Serial.println(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);
        while(digitalRead(rowPins[row]) == LOW);
        key = keymap[row][column];
      }
    }
    digitalWrite(colPins[column],HIGH);
  }
  return key;
}