float brightness = 0; // our main variable for setting the brightness of the LED
const int ledPin = 9; // we use pin 9 for PWM
const int sensorPin = 4; // we use pin D4 for the button

int buttonState = 0;
float counter = 0;
// the ratio between counter increment and fade should be tweaked
float counter_inc = 1.0; 
float counter_fade = 0.99;
int counter_threshold = 90;


void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);
  pinMode(ledPin, OUTPUT);
  pinMode(sensorPin, INPUT);

}

void loop() {
  buttonState = !digitalRead(sensorPin);
  // digitalWrite(ledPin,buttonState); // don't do this
  
  Serial.println(counter);

  // fading pattern that requires 'effort'
  if (buttonState == HIGH) {
    
    counter += counter_inc;
  } 
  
  counter = counter*counter_fade;
 
  if (counter > counter_threshold){
    brightness ++;
    // here you could also switchCase(myCase)
    }
   else {
    brightness = brightness * 0.99;
   }

  brightness = constrain(brightness, 0, 255);
  
  analogWrite(ledPin, brightness);
  
  delay(5);
}