Arcade lever on an Arduino Uno

// Arcade lever: a Sanwa JLF style lever on four pins, read the way a fight
// stick board reads it, and printed in numpad notation.
//
//   lever   GND -> GND   UP -> 5   DOWN -> 4   LEFT -> 3   RIGHT -> 2
//   LED     the board's own, on pin 13: lit while the lever is off center
//
// A lever is four microswitches around the foot of the shaft, one leg of each
// on the common. With INPUT_PULLUP on, a pin reads LOW while its direction is
// held, and a corner holds two of them.
//
// Fighting game players write directions as the keys of a numpad: 5 is
// neutral, 8 up, 2 down, 4 left, 6 right, and the corners are 7, 9, 1 and 3.
// That is what this prints, every time the lever moves.
//
// # Debounce without a delay
//
// A microswitch chatters for a millisecond or two as it closes. A stick board
// cannot afford to wait that long on every press, so it takes the new reading
// at once and then ignores that switch for a few milliseconds. Turn on the
// lever's bounce property and watch: one line per move, not three.
//
// Drag the ball on the lever, or use the arrow keys or W A S D. Change the
// gate to 4way and the corners are gone.

const uint8_t PINS[4] = {5, 4, 3, 2};  // UP, DOWN, LEFT, RIGHT
const unsigned long LOCK_MS = 5;

bool held[4];
unsigned long changedAt[4];
uint8_t shown = 5;

const char *const NAMES[10] = {"", "down-left", "down", "down-right", "left",
                               "neutral", "right", "up-left", "up", "up-right"};

// The numpad direction for the four switches. A lever cannot hold opposite
// directions, but four separate buttons can, and then the two cancel.
uint8_t numpad() {
  int x = (held[3] ? 1 : 0) - (held[2] ? 1 : 0);
  int y = (held[0] ? 1 : 0) - (held[1] ? 1 : 0);
  return 5 + x + 3 * y;
}

void setup() {
  Serial.begin(9600);
  for (uint8_t i = 0; i < 4; i++) pinMode(PINS[i], INPUT_PULLUP);
  pinMode(LED_BUILTIN, OUTPUT);
  Serial.println("Arcade lever ready: 5 is neutral");
}

void loop() {
  unsigned long now = millis();
  for (uint8_t i = 0; i < 4; i++) {
    if (now - changedAt[i] < LOCK_MS) continue;  // still settling
    bool down = digitalRead(PINS[i]) == LOW;
    if (down != held[i]) {
      held[i] = down;
      changedAt[i] = now;
    }
  }
  uint8_t direction = numpad();
  if (direction != shown) {
    shown = direction;
    Serial.print(direction);
    Serial.print(" ");
    Serial.println(NAMES[direction]);
    digitalWrite(LED_BUILTIN, direction == 5 ? LOW : HIGH);
  }
}