Tilt hourglass on an Arduino Uno

// Tilt hourglass: six LEDs light one at a time as the time runs, and turning
// the hourglass over starts it again.
//
//   pins 2 to 7   the six LEDs, each through 220 ohm to GND
//   pin 8         the tilt switch: one leg to 5V, the other to pin 8 and
//                 through a 10k resistor to GND
//
// The sketch never stops to wait. It notes the time of the last LED with
// millis() and checks on every pass whether INTERVAL has gone by since, so
// it can keep watching the tilt switch the whole time. delay() would leave it
// deaf for the whole interval.
//
// INTERVAL is two seconds here so you can watch it run. Set it to 600000 for
// ten minutes a light, an hour for all six.

const unsigned long INTERVAL = 2000;
const int FIRST_LED = 2;
const int LED_COUNT = 6;
const int TILT = 8;

unsigned long lastTime = 0;
int lit = 0;
int lastTilt = -1;

void setup() {
  for (int i = 0; i < LED_COUNT; i++) pinMode(FIRST_LED + i, OUTPUT);
  pinMode(TILT, INPUT);
  Serial.begin(9600);
  Serial.println("Mokxi Uno: tilt hourglass");
}

void loop() {
  unsigned long now = millis();
  if (lit < LED_COUNT && now - lastTime >= INTERVAL) {
    lastTime = now;
    digitalWrite(FIRST_LED + lit, HIGH);
    lit++;
    Serial.print("lights on: ");
    Serial.println(lit);
    if (lit == LED_COUNT) Serial.println("time is up");
  }

  int tilt = digitalRead(TILT);
  if (lastTilt >= 0 && tilt != lastTilt) {
    for (int i = 0; i < LED_COUNT; i++) digitalWrite(FIRST_LED + i, LOW);
    lit = 0;
    lastTime = now;
    Serial.println("turned over: starting again");
  }
  lastTilt = tilt;
}