Electronic dice on an Arduino Uno

// Electronic dice: press the button, watch it tumble, read the number.
//
//   segment a b c d e f g  ->  pins 2 3 4 5 6 7 8
//   the common cathode     ->  220 ohm to GND
//   pin 9                  ->  the roll button, to GND, internal pull-up
//
// The display is common cathode, so a segment lights when its pin goes HIGH
// and all the return current leaves through the one resistor on the common
// pin. That is the cheap way to wire one: the more segments are lit the less
// current each gets, so an 8 is dimmer than a 1. Seven resistors, one per
// segment, is the right way.
//
// SEGMENTS[] is the usual seven-segment font, one bit per segment, bit 0 = a.
// The tumble is just the roll repeated with a delay that grows each step, which
// reads as the die slowing down and settling.

const int SEG_PINS[] = {2, 3, 4, 5, 6, 7, 8};
const int BUTTON = 9;

// bit 0 a, 1 b, 2 c, 3 d, 4 e, 5 f, 6 g
const uint8_t DIGITS[] = {
    0x3F,  // 0
    0x06,  // 1
    0x5B,  // 2
    0x4F,  // 3
    0x66,  // 4
    0x6D,  // 5
    0x7D,  // 6
};

static void show(uint8_t mask) {
  for (int i = 0; i < 7; i++) {
    digitalWrite(SEG_PINS[i], (mask >> i) & 1 ? HIGH : LOW);
  }
}

static bool pressed() { return digitalRead(BUTTON) == LOW; }

void setup() {
  for (int i = 0; i < 7; i++) {
    pinMode(SEG_PINS[i], OUTPUT);
  }
  pinMode(BUTTON, INPUT_PULLUP);
  Serial.begin(115200);
  Serial.println("Mokxi Arduino Uno: press the button to roll");
  show(DIGITS[6]);
}

void loop() {
  if (!pressed()) {
    delay(10);
    return;
  }

  int face = 1;
  unsigned long step = 40;
  for (int i = 0; i < 14; i++) {
    face = (int)random(1, 7);
    show(DIGITS[face]);
    delay(step);
    step += step / 4 + 5;
  }

  Serial.print("rolled ");
  Serial.println(face);

  while (pressed()) {
    delay(10);
  }
}