Phone dial on an Arduino Uno

// Phone dial: an Uno reads the number dialed on an old telephone's rotary
// dial.
//
//   dial   GND -> GND   DIAL -> pin 2   PULSE -> pin 3   (INPUT_PULLUP on both)
//
// While the wheel runs back, the off-normal contacts hold DIAL low, and the
// pulse contacts open once a step: PULSE goes high once for 1 and ten times
// for 0, ten pulses a second. Counting the pulses while DIAL is low, and
// reading the count when DIAL goes high again, gives the digit. A real dial's
// contacts bounce, so the count only takes a pulse that has stayed high for
// a few milliseconds.
//
// Click the holes of the dial.

const int DIAL_PIN = 2;
const int PULSE_PIN = 3;

int pulses = 0;
bool wasDialing = false;
bool wasHigh = false;
unsigned long highSince = 0;
bool counted = false;
char number[17];
int length = 0;

void setup() {
  Serial.begin(9600);
  pinMode(DIAL_PIN, INPUT_PULLUP);
  pinMode(PULSE_PIN, INPUT_PULLUP);
  Serial.println("Phone dial ready");
}

void loop() {
  bool dialing = digitalRead(DIAL_PIN) == LOW;
  bool high = digitalRead(PULSE_PIN) == HIGH;
  if (dialing) {
    if (high && !wasHigh) {
      highSince = millis();
      counted = false;
    }
    if (high && !counted && millis() - highSince > 5) {
      pulses++;
      counted = true;
    }
  }
  wasHigh = high;
  if (wasDialing && !dialing) {
    int digit = pulses == 10 ? 0 : pulses;
    if (length < 16) {
      number[length++] = '0' + digit;
      number[length] = 0;
    }
    Serial.print("digit ");
    Serial.print(digit);
    Serial.print("  number ");
    Serial.println(number);
    pulses = 0;
  }
  wasDialing = dialing;
}