// -------- GLOBAL VARIABLES --------
int pin2 = 0; // D0
int pin3 = 1; // D1
int pin4 = 2; // D2
int pin5 = 3; // D3

int timedelay = 1000;

// -------- SETUP --------
void setup() {
  pinMode(pin2, OUTPUT);
  pinMode(pin3, OUTPUT);
  pinMode(pin4, OUTPUT);
  pinMode(pin5, OUTPUT);
}

// -------- LOOP --------
void loop() {
  for (int count = 0; count < 16; count++) {
    // bitRead extracts the value (0 or 1) of a specific bit in the 'count' variable
    digitalWrite(pin2, bitRead(count, 0)); // LSB
    digitalWrite(pin3, bitRead(count, 1));
    digitalWrite(pin4, bitRead(count, 2));
    digitalWrite(pin5, bitRead(count, 3)); // MSB
    
    delay(timedelay);
  }
}