Tilt dice on an 8x8 matrix, on an Arduino Uno

// Electronic dice: shake the tilt switch, watch the die roll and stop.
//
//   tilt switch -> pin 2 and GND (INPUT_PULLUP)
//   MAX7219 DIN -> pin 13    CLK -> pin 7    CS -> pin 8
//   RGB LED red -> pin 9, green -> pin 6, blue -> pin 5, each through 220 ohm
//
// A tilt switch is a ball in a tube. Shaken, the ball bounces on the contacts
// and the pin flickers between HIGH and LOW. An interrupt on pin 2 counts
// every flicker without the sketch having to watch for it. While flickers keep
// coming the die keeps rolling; when they stop, it slows down and settles on
// a number, and the RGB LED turns green.
//
// Click the tilt switch a few times to shake it.

#include <LedControl.h>

const int TILT = 2;
const int RED_PIN = 9;
const int GREEN_PIN = 6;
const int BLUE_PIN = 5;

LedControl lc = LedControl(13, 7, 8, 1);  // DIN, CLK, CS, modules

// One face per number, eight rows each.
const byte FACES[6][8] = {
    {0x00, 0x00, 0x00, 0x18, 0x18, 0x00, 0x00, 0x00},
    {0x00, 0x06, 0x06, 0x00, 0x00, 0x60, 0x60, 0x00},
    {0xC0, 0xC0, 0x00, 0x18, 0x18, 0x00, 0x03, 0x03},
    {0x00, 0x66, 0x66, 0x00, 0x00, 0x66, 0x66, 0x00},
    {0xC3, 0xC3, 0x00, 0x18, 0x18, 0x00, 0xC3, 0xC3},
    {0x66, 0x66, 0x00, 0x66, 0x66, 0x00, 0x66, 0x66},
};

volatile unsigned int shakes = 0;
unsigned int seen = 0;

void onShake() {
  shakes++;
}

void showFace(int n) {
  for (int row = 0; row < 8; row++) lc.setRow(0, row, FACES[n - 1][row]);
}

void color(int r, int g, int b) {
  analogWrite(RED_PIN, r);
  analogWrite(GREEN_PIN, g);
  analogWrite(BLUE_PIN, b);
}

void roll() {
  color(0, 0, 160);
  int n = 1;
  int wait = 40;
  while (wait < 300) {
    n = random(1, 7);
    showFace(n);
    delay(wait);
    if (shakes != seen) {
      seen = shakes;
      wait = 40;  // still shaking: keep rolling fast
    } else {
      wait += 30;
    }
  }
  color(0, 160, 0);
  Serial.print("rolled a ");
  Serial.println(n);
}

void setup() {
  pinMode(TILT, INPUT_PULLUP);
  pinMode(RED_PIN, OUTPUT);
  pinMode(GREEN_PIN, OUTPUT);
  pinMode(BLUE_PIN, OUTPUT);
  lc.shutdown(0, false);
  lc.setIntensity(0, 6);
  lc.clearDisplay(0);
  attachInterrupt(digitalPinToInterrupt(TILT), onShake, CHANGE);
  randomSeed(analogRead(A5));
  Serial.begin(9600);
  Serial.println("Mokxi Uno: tilt dice. Shake the tilt switch.");
  roll();
}

void loop() {
  if (shakes != seen) {
    seen = shakes;
    roll();
  }
}