#include <LiquidCrystal_I2C.h>

#define I2C_ADDR    0x27
#define LCD_COLUMNS 16
#define LCD_LINES   2

LiquidCrystal_I2C lcd(I2C_ADDR, LCD_COLUMNS, LCD_LINES);

char buttons[16] = {
  '1','2','3','A',
  '4','5','6','B',
  '7','8','9','C',
  '*','0','#','D'
};

void setup() {
  pinMode(2, OUTPUT);
  pinMode(3, OUTPUT);
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);

  pinMode(6, INPUT_PULLUP);
  pinMode(7, INPUT_PULLUP);
  pinMode(8, INPUT_PULLUP);
  pinMode(9, INPUT_PULLUP);

  pinMode(13,OUTPUT);
  lcd.init();
}

void ResetAll(){
  for(int i=2;i<=5;i++){
    digitalWrite(i, HIGH);
  }
}
bool ReadPulseIO(int output,int input){
  ResetAll();
  digitalWrite(output, LOW);
  return digitalRead(input)==LOW;
}
int ReadNumpadKey(){
  for(int i=0;i<4;i++){
    for(int j=0;j<4;j++){
      if(ReadPulseIO(5-i,9-j)) 
        return i+j*4;
    }
  }
  return -1;
}
bool IsNumpadKeyPressed(int key){
  return ReadNumpadKey()==key;
}
bool waiting = true;
void loop() {
  // put your main code here, to run repeatedly:
 if(ReadNumpadKey()!=-1 ) {
    if(waiting) {
     lcd.print(buttons[ReadNumpadKey()]);
      waiting = false;
    }}
  else 
  waiting = true;
 
}