#include <Keypad.h>

const byte ROWS = 4; // Number of rows
const byte COLS = 4; // Number of columns

// Keypad layout
char keys[ROWS][COLS] = {
  {'1', '2', '3', 'A'},
  {'4', '5', '6', 'B'},
  {'7', '8', '9', 'C'},
  {'*', '0', '#', 'D'}
};

// Pin assignments for the CD74HC4067
const int S0 = 2;
const int S1 = 4;
const int S2 = 7;
const int S3 = 8;
const int SIG = A0; // Signal pin connected to multiplexer

void setup() {
  Serial.begin(9600);

  // Set multiplexer control pins as outputs
  pinMode(S0, OUTPUT);
  pinMode(S1, OUTPUT);
  pinMode(S2, OUTPUT);
  pinMode(S3, OUTPUT);

  // Set multiplexer signal pin as input
  pinMode(SIG, INPUT);
}

// Function to select a multiplexer channel
void selectChannel(int channel) {
  digitalWrite(S0, channel & 0x01);
  digitalWrite(S1, (channel >> 1) & 0x01);
  digitalWrite(S2, (channel >> 2) & 0x01);
  digitalWrite(S3, (channel >> 3) & 0x01);
}

void loop() {
  for (int row = 0; row < 4; row++) {
    // Select the row
    selectChannel(row);

    // Check all columns for a pressed key
    for (int col = 0; col < 4; col++) {
      selectChannel(col + 4);

      // If the signal pin reads HIGH, a key is pressed
      if (digitalRead(SIG) == HIGH) {
        Serial.println(keys[row][col]); // Print the pressed key
        delay(300); // Debounce delay
        return; // Exit after detecting one key
      }
    }
  }
}