const int LED_PINS[] = {9, 8, 7, 6, 5, 4, 3, 2};
const int POT_PIN = A0;

void setup() {
  Serial.begin(115200);
  for (int ledPin = 0; ledPin < 8; ledPin++)  {
    pinMode(LED_PINS[ledPin], OUTPUT);
  }
  Serial.println("Turn the knob!");
}

void loop() {
  int potValue = analogRead(POT_PIN);
  for (int step = 0; step < 8; step++)  {
    digitalWrite(LED_PINS[step], LOW);
    if (potValue > (128 * (step + 1)) - 64) digitalWrite(LED_PINS[step], HIGH);
  }
}