String Read(){
  for(int i = 6; i <= 9; i++){   
    for(int k = 6; k <= 9; k++){ //set all pins to high
      digitalWrite(k, HIGH); 
    } 
    
    //set one of the pins to low
    digitalWrite(i, LOW);

    for(int j = 2; j <= 5; j++){ //check if any of the pins 2 - 5 are shorted with current "i" pin
      if(digitalRead(j) == LOW){
        while(digitalRead(j) == LOW){ delay(10); } //wait until button is released

        //convert two pin values into actual data from keyboard and return it
        if((i == 6) && (j == 2)){ return "1"; }
        if((i == 7) && (j == 2)){ return "2"; }
        if((i == 8) && (j == 2)){ return "3"; }
        if((i == 9) && (j == 2)){ return "A"; }

        if((i == 6) && (j == 3)){ return "4"; }
        if((i == 7) && (j == 3)){ return "5"; }
        if((i == 8) && (j == 3)){ return "6"; }
        if((i == 9) && (j == 3)){ return "B"; }

        if((i == 6) && (j == 4)){ return "7"; }
        if((i == 7) && (j == 4)){ return "8"; }
        if((i == 8) && (j == 4)){ return "9"; }
        if((i == 9) && (j == 4)){ return "C"; }

        if((i == 6) && (j == 5)){ return "*"; }
        if((i == 7) && (j == 5)){ return "0"; }
        if((i == 8) && (j == 5)){ return "#"; }
        if((i == 9) && (j == 5)){ return "D"; }
      }
    }
     delay(5); //a little delay, so our microcontroller wont go crazy
  }
  return ""; //if no button is pressed, return nothing
}

void setup() {
  for(int i = 2; i <= 9; i++){
    if((i >= 2) && (i <= 5)){
      pinMode(i, INPUT_PULLUP);
    } else {
      pinMode(i, OUTPUT);
    }
  }

  Serial.begin(115200);
  Serial.println("initialization");

}

void loop() {

  Serial.print(Read());
  delay(10);

}