//Source code: https://lastminuteengineers.com/74hc595-shift-register-arduino-tutorial/
//Modified by Barbu Vulc! :))
int latchPin = 5; //Latch pin of 74HC595 is connected to Digital pin 5
int clockPin = 6; //Clock pin of 74HC595 is connected to Digital pin 6
int dataPin = 4;  //Data pin of 74HC595 is connected to Digital pin 4
byte leds = 0;    //Variable to hold the pattern of which LEDs are currently turned on or off

//We initialize the serial connection with the computer.
void setup(){
  //Set all the pins of 74HC595 as OUTPUT:
  pinMode(latchPin, OUTPUT);
  pinMode(dataPin, OUTPUT);  
  pinMode(clockPin, OUTPUT);
}

void loop(){
  leds = 0;    //Initially turns all the LEDs off, by giving the variable 'leds' the value 0.
  updateShiftRegister();
  delay(500);
  for(int i = 0; i < 8; i++){
    bitSet(leds, i);    //Set the bit that controls that LED in the variable 'leds'.
    updateShiftRegister();
    delay(500);
  }
}

/*„updateShiftRegister()” - This function sets the latchPin to low,
  then calls the Arduino function 'shiftOut' to shift out 
  contents of variable 'leds' in the shift register 
  before putting the 'latchPin' high again.*/
void updateShiftRegister(){
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, LSBFIRST, leds);
  digitalWrite(latchPin, HIGH);
}