Stopwatch: four-digit display, digits on 10 to 13, on an Arduino Uno

// A stopwatch on a four-digit display: minutes and seconds.
//
//   segments a, b, c, d, e, f, g, dp -> 220 ohm each -> pins 2 to 9
//   digit 1 -> pin 10   digit 2 -> pin 11   digit 3 -> pin 12   digit 4 -> pin 13
//
// The four digits share their segment lines, so only one digit can show at a
// time. The sketch lights digit 1, then 2, then 3, then 4, a few milliseconds
// each, over and over: too fast to see, so all four look lit. It is a common
// cathode display, so a digit pin LOW turns its digit on.

const int SEGMENTS[8] = {2, 3, 4, 5, 6, 7, 8, 9};
const int DIGIT_PINS[4] = {10, 11, 12, 13};

const byte PATTERNS[10] = {
  0b00111111, 0b00000110, 0b01011011, 0b01001111, 0b01100110,
  0b01101101, 0b01111101, 0b00000111, 0b01111111, 0b01101111,
};

void showDigit(int position, int value, bool dot) {
  byte bits = PATTERNS[value] | (dot ? 0b10000000 : 0);
  for (int s = 0; s < 8; s++) digitalWrite(SEGMENTS[s], (bits >> s) & 1);
  digitalWrite(DIGIT_PINS[position], LOW);
  delay(3);
  digitalWrite(DIGIT_PINS[position], HIGH);
}

void setup() {
  for (int s = 0; s < 8; s++) pinMode(SEGMENTS[s], OUTPUT);
  for (int d = 0; d < 4; d++) {
    pinMode(DIGIT_PINS[d], OUTPUT);
    digitalWrite(DIGIT_PINS[d], HIGH);
  }
  Serial.begin(9600);
  Serial.println("Mokxi Uno: stopwatch, minutes and seconds");
}

void loop() {
  unsigned long seconds = millis() / 1000;
  int minutes = (seconds / 60) % 100;
  int secs = seconds % 60;
  showDigit(0, minutes / 10, false);
  showDigit(1, minutes % 10, true);
  showDigit(2, secs / 10, false);
  showDigit(3, secs % 10, false);
}