const byte knobPin = A0;
const byte ledPin = 9;
unsigned long reportedAt = 0;

void setup() {
  pinMode(ledPin, OUTPUT);
  Serial.begin(9600);
}

void loop() {
  const int reading = analogRead(knobPin);
  const int duty = reading / 4;
  analogWrite(ledPin, duty);
  const unsigned long now = millis();
  if (now - reportedAt >= 200) {
    reportedAt = now;
    Serial.print("ADC="); Serial.print(reading);
    Serial.print(" PWM="); Serial.println(duty);
  }
}