#include <Keypad.h>

const byte ROWS = 4; //four rows
const byte COLS = 4; //three columns
char keys[ROWS][COLS] = {
        {'1','2','3','A'},
        {'4','5','6','B'},
        {'7','8','9','C'},
        {'*','0','#','D'}
        };
byte rowPins[ROWS] = {9, 8, 7, 6}; //connect to the row pinouts of the keypad
byte colPins[COLS] = {5, 4, 3, 2}; //connect to the column pinouts of the keypad

Keypad keypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );
byte heaterPin = 13;

boolean blink = false;

void setup(){
  Serial.begin(9600);
  pinMode(heaterPin, OUTPUT);      // sets the digital pin as output
  digitalWrite(heaterPin, HIGH);   // sets the LED on
  keypad.addEventListener(keypadEvent); //add an event listener for this keypad
}

void loop(){
  char key = keypad.getKey();

  if (key) {
    Serial.println(key);
  }
  if (blink){
    digitalWrite(heaterPin,!digitalRead(heaterPin));
    delay(100);
  }
}

//take care of some special events
void keypadEvent(KeypadEvent key){
  switch (keypad.getState()){
    case PRESSED:
      switch (key){
        case '#': digitalWrite(heaterPin,!digitalRead(heaterPin)); break;
        case '*':
          digitalWrite(heaterPin,!digitalRead(heaterPin));
        break;
      }
    break;
    case RELEASED:
      switch (key){
        case '*':
          digitalWrite(heaterPin,!digitalRead(heaterPin));
          blink = false;
        break;
      }
    break;
    case HOLD:
      switch (key){
        case '*': blink = true; break;
      }
    break;
  }
}