#include <ShiftRegister74HC595.h>
const int kbdRows = 4;
const int kbdCols = 4;

int serialDataPin = 4; // DS
int clockPin = 2; // SHCP
int latchPin = 3; // STCP
unsigned long time_now = 0;

ShiftRegister74HC595<1> sr(serialDataPin, clockPin, latchPin);

//                   C5 C4 C3 C2
//const int pinCols[4]={9,8,7,6};
//                    R1 R2 R3 R4
const int pinRows[4]={13,12,11,10};     //pins of the differents rows


char act = "", ant = "";
int trueCols;
int trueRows;

char keys[4][4]={                  //correspondence with the keys of the keypad
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};

void setup() {
  Serial.begin(9600);
  for(int i=0;i<4;i++){               //defining the output and input pins
    //pinMode(pinCols[i], OUTPUT); 
    pinMode(pinRows[i],  INPUT);
    //digitalWrite(pinCols[i], HIGH);
    }
  sr.set(0, HIGH);
  sr.set(1, HIGH);
  sr.set(2, HIGH);
  sr.set(3, HIGH);
}

void loop() {
  time_now = millis();
  readKey(); 
  /*while(millis() < time_now + 100){
  }
  */
  /*
  if (act != ant){ 
    lastDebounceTime = millis();
  }
  else{
    ant = act; //3
  }
  */
  //delay(100);
}

void readKey(){
  for(int i=0; i<4;i++){
    if(digitalRead(pinRows[i])==HIGH){      //reading if a row is active
      trueRows=i;                           //so the right row is the one how is high
      for(int x=0; x<4; x++){
        sr.set(0, LOW);      //putting all the cols low
        sr.set(1, LOW);
        sr.set(2, LOW);
        sr.set(3, LOW);
        sr.set(x, HIGH); //except the one we want to test
        if(digitalRead(pinRows[trueRows])==HIGH){ //if now the row is high when a special column is high, we know the button how is pressed
          while(digitalRead(pinRows[trueRows])==HIGH){
            digitalRead(pinRows[trueRows]);
          }
          trueCols=x;
          act = keys[trueRows][trueCols];
          Serial.println(act); //we display the right symbol
                
          }
        }
      }
  }
  sr.set(0, HIGH);  //re-putting the cols to high position to be ready for an upcoming reading 
  sr.set(1, HIGH);
  sr.set(2, HIGH);
  sr.set(3, HIGH);
}