int potPin = A5;
int potReading = 0;

int ledPin = D2;
int ledBrightness = 0;

int buttonPin = D5;

void setup(){

  pinMode(ledPin, OUTPUT);
  pinMode( buttonPin , INPUT_PULLUP); 
  Spark.variable("pot", potReading );
}

void loop() {
    int buttonState = digitalRead( buttonPin );
    if( buttonState == LOW )
  {
    // digitalWrite( ledPin, HIGH);
     potReading = analogRead(potPin);
     ledBrightness = map(potReading, 0, 4095, 0, 255);
     analogWrite(ledPin, ledBrightness);
     delay(100);
    
  }else{
    digitalWrite( ledPin, LOW);
}
}