Level meter on an Arduino Uno

// Level meter: a potentiometer on A0 and a ten-segment LED bar graph.
//
//   potentiometer   ends to 5 V and GND, wiper -> A0
//   bar graph       anodes A1..A10 -> pins 2 to 11, each through its own 220 ohm
//                   cathodes C1..C10 -> GND
//
// A bar graph is ten separate LEDs in one block, each with its own two legs,
// so it wants ten resistors exactly as ten LEDs would. Turn the knob and the
// bar follows; the top bar is dimmed with PWM in proportion to how far the
// reading is into it, so the meter moves smoothly rather than in tenths.

const uint8_t BAR_PINS[10] = {2, 3, 4, 5, 6, 7, 8, 9, 10, 11};

void setup() {
  for (uint8_t i = 0; i < 10; i++) pinMode(BAR_PINS[i], OUTPUT);
}

void loop() {
  // 0..1023 into 0..100: whole bars, and hundredths of the next one.
  long level = (long)analogRead(A0) * 100 / 1023;
  uint8_t whole = (uint8_t)(level / 10);
  uint8_t part = (uint8_t)(level % 10);
  for (uint8_t bar = 0; bar < 10; bar++) {
    uint8_t pin = BAR_PINS[bar];
    if (bar < whole) {
      digitalWrite(pin, HIGH);
    } else if (bar == whole && part > 0 && (pin == 3 || pin == 5 || pin == 6 || pin == 9 ||
                                           pin == 10 || pin == 11)) {
      analogWrite(pin, part * 25);  // the pins with PWM can show the fraction
    } else {
      digitalWrite(pin, LOW);
    }
  }
  delay(20);
}