// the external LED is attached to this pin.
    // onboard LED is attached to pin 13, 
    int ledPin = 13;

    // slider of potentiometer attached to this analog input 
    int analogInPin = 0;

    // On and off time in milliseconds for the light
    int delayTime = 300;
     
    void setup() {
      // configure ledPin to be a digital output
      pinMode(ledPin, OUTPUT);
    }
     
    void loop() {
      // read the voltage on the analog input and convert
      // into an integer value in the range [0, 1023]
      delayTime = analogRead(analogInPin);

      digitalWrite(ledPin, HIGH);
      delay(delayTime);

      digitalWrite(ledPin, LOW);
      delay(delayTime);
    }