const int ROWS = 4; // Number of rows in the keypad
const int COLS = 4; // Number of columns in the keypad

// Define the connections to rows and columns
int rowPins[ROWS] = {9, 8, 7, 6};    // R1, R2, R3, R4
int colPins[COLS] = {5, 4, 3, 2};    // C1, C2, C3, C4

// Define the key values as per the 4x4 keypad
char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};

void setup() {
  // Set column pins as outputs
  for (int i = 0; i < COLS; i++) {
    pinMode(colPins[i], OUTPUT);
    digitalWrite(colPins[i], HIGH); // Set columns to HIGH (not active)
  }

  // Set row pins as inputs with pull-up resistors
  for (int i = 0; i < ROWS; i++) {
    pinMode(rowPins[i], INPUT_PULLUP);
  }

  Serial.begin(9600); // Start the serial monitor
}

void loop() {
  // Scan each column
  for (int col = 0; col < COLS; col++) {
    // Set the current column LOW (active) and others HIGH (inactive)
    digitalWrite(colPins[col], LOW);

    // Check each row to see if a key is pressed
    for (int row = 0; row < ROWS; row++) {
      if (digitalRead(rowPins[row]) == LOW) {
        // Print the key corresponding to the row and column
        Serial.println(keys[row][col]);
        delay(300); // Simple debounce delay to avoid multiple readings
      }
    }

    // Set the current column back to HIGH (inactive)
    digitalWrite(colPins[col], HIGH);
  }
}