int ones_bit_pin = 2;
int twos_bit_pin = 3;
int fours_bit_pin = 4;
int eights_bit_pin = 5;

int waitTime = 2000;

void setup() {
  // put your setup code here, to run once:
  pinMode(ones_bit_pin, OUTPUT);
  pinMode(twos_bit_pin, OUTPUT);
  pinMode(fours_bit_pin, OUTPUT);
  pinMode(eights_bit_pin, OUTPUT);
}

void loop() {
  // put your main code here, to run repeatedly:

  // Represent the number 0 (0000)
  digitalWrite(ones_bit_pin, LOW);
  digitalWrite(twos_bit_pin, LOW);
  digitalWrite(fours_bit_pin, LOW);
  digitalWrite(eights_bit_pin, LOW);
  delay(waitTime);

  // Represent the number 1 (0001)
  digitalWrite(ones_bit_pin, HIGH);
  digitalWrite(twos_bit_pin, LOW);
  digitalWrite(fours_bit_pin, LOW);
  digitalWrite(eights_bit_pin, LOW);
  delay(waitTime);

  // Represent the number 2 (0010)
  digitalWrite(ones_bit_pin, LOW);
  digitalWrite(twos_bit_pin, HIGH);
  digitalWrite(fours_bit_pin, LOW);
  digitalWrite(eights_bit_pin, LOW);
  delay(waitTime);

  // Represent the number 3 (0011)
  digitalWrite(ones_bit_pin, HIGH);
  digitalWrite(twos_bit_pin, HIGH);
  digitalWrite(fours_bit_pin, LOW);
  digitalWrite(eights_bit_pin, LOW);
  delay(waitTime);

  // Represent the number 4 (0100)
  digitalWrite(ones_bit_pin, LOW);
  digitalWrite(twos_bit_pin, LOW);
  digitalWrite(fours_bit_pin, HIGH);
  digitalWrite(eights_bit_pin, LOW);
  delay(waitTime);

  // Represent the number 5 (0101)
  digitalWrite(ones_bit_pin, HIGH);
  digitalWrite(twos_bit_pin, LOW);
  digitalWrite(fours_bit_pin, HIGH);
  digitalWrite(eights_bit_pin, LOW);
  delay(waitTime);

  // Represent the number 6 (0110)
  digitalWrite(ones_bit_pin, LOW);
  digitalWrite(twos_bit_pin, HIGH);
  digitalWrite(fours_bit_pin, HIGH);
  digitalWrite(eights_bit_pin, LOW);
  delay(waitTime);

  // Represent the number 7 (0111)
  digitalWrite(ones_bit_pin, HIGH);
  digitalWrite(twos_bit_pin, HIGH);
  digitalWrite(fours_bit_pin, HIGH);
  digitalWrite(eights_bit_pin, LOW);
  delay(waitTime);

  // Represent the number 8 (1000)
  digitalWrite(ones_bit_pin, LOW);
  digitalWrite(twos_bit_pin, LOW);
  digitalWrite(fours_bit_pin, LOW);
  digitalWrite(eights_bit_pin, HIGH);
  delay(waitTime);
}