#include <I2CKeyPad.h>
#define deltaTime(val) (millis()-val)

I2CKeyPad keyPad(0x38);
char keypad_layout[19] = "123A456B789C*0#DNF"; // N = NO_KEY, F = FAILED

// Just to avoid spamming
unsigned long lastKeyPress = 0;
unsigned long keyDelay = 200;

void setup() {
  Serial.begin(9600);
  
  if (!keyPad.begin()) {
    Serial.print("Cannot connect to I2C.\n");
    while(1);
  }

  keyPad.loadKeyMap(keypad_layout);
}

void loop() {
  if (keyPad.isPressed() && deltaTime(lastKeyPress) > keyDelay) {
    lastKeyPress = millis();
    char ch = keyPad.getChar();
    Serial.println("Pressed : " + String(ch));
  }

  // Makes the code run faster
  delay(10);
}