binary_led_arduino.ino

const int numLEDS = 4;
const int LEDs[numLEDS] = {5, 6, 3, 9};

int binaryVariable = 0;

void setup() {
  // put your setup code here, to run once:
  for (int k = 0; k < numLEDS; k++) {
    pinMode(LEDs[k], OUTPUT);
    analogWrite(LEDs[k], 0);
  }

}

void loop() {
  int sequenceSpeed = 100;
  int brightness = min(255, binaryVariable * 10);
  for (int k = 0; k < numLEDS; k++) {
    int mask =  1 << k;
    int maskedbinaryVariable = binaryVariable & mask;
    bool isBitActive = maskedbinaryVariable >> k;
    analogWrite(LEDs[k], isBitActive ? brightness : 0 );
  }

  delay(sequenceSpeed);
  binaryVariable = (binaryVariable + 1) % int(pow(2, numLEDS));
}