void setup() {
  pinMode(A0, INPUT);
  pinMode(11, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  int val = analogRead(A0);
  int led_val = map(val, 0, 1023, 0, 255);  //0-1023 to 0-255
  analogWrite(11, led_val);
  Serial.print("val ");
  Serial.print(val);
  Serial.print(" led val ");
  Serial.println(led_val);
  delay(100);
}