float dutyCycle = 0.4;
float currentDutyCycle = 0;

boolean filterOpen = false;
boolean newWave = true;

int inputPin = 6;
int outputPin = 5;

int lastInputValue = 0;
int inputValue = 0;

unsigned long inputStartTime = 0;
unsigned long inputSwitchTime = 0;
unsigned long inputEndTime = 0;


void setup() {
  Serial.begin(9600);

  pinMode(inputPin, INPUT);
  pinMode(outputPin, OUTPUT);

  //Wait for first signal
  while ( digitalRead(inputPin) != HIGH ) {};

  Serial.println("Filter initializing!");
}


void loop() {
  inputValue = digitalRead(inputPin);

  //Check if the signal has changed
  if (inputValue != lastInputValue) {
    if (inputValue == 1) {
      //Signal is HIGH
      inputEndTime = millis();
      //Calculates the duty cycle
      currentDutyCycle = ( (float)inputSwitchTime - inputStartTime) / (inputEndTime - inputStartTime);
      inputStartTime = inputEndTime;
    } else {
      //Signal is low
      inputSwitchTime = millis();
    }
    lastInputValue = inputValue;
  }

  //Checks if filter is open or not
  if (currentDutyCycle >= dutyCycle) {
    filterOpen = true;
  } else {
    filterOpen = false;
  }

  //Determines output signal
  if (filterOpen) {
    digitalWrite(outputPin, inputValue);
  } else {
    digitalWrite(outputPin, LOW);
  }

}