#define NO_KEY 0

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

uint8_t RowPin[4] = { 6, 7, 8, 9 }; // Pins connected to C1, C2, C3, C4
uint8_t ColPin[4] = { 2, 3, 4, 5 }; // Pins connected to R1, R2, R3, R4

void setup() {
  int i;
  Serial.begin(9600);
  for(i=0;i<4;i++){
    pinMode(RowPin[i], OUTPUT);
    digitalWrite(RowPin[i], HIGH);
    pinMode(ColPin[i], INPUT_PULLUP);
  }
}

char GetKey(){
  int col,row,last;
  char kch=0;
  last=3;
  for(row=0;row<4;row++){
    digitalWrite(RowPin[last], HIGH);
    digitalWrite(RowPin[row], LOW);
    last=row;
    for(col=0;col<4;col++){
      if(digitalRead(ColPin[col])==LOW){
        kch=KeyCh[col][row];
        delay(2);
      }
    }
  }
  return kch;
}
void loop() {
  char key = GetKey();
  if (key != NO_KEY) {
    Serial.println(key);
    while(GetKey());

  }
}