gistfile1.txt

int digitToDisplay = 1234;

int latchPin = 1;
int clockPin = 3;
int dataPin = 0;

int digits[4][2] = {
  { B11111110, B01011111 },
  { B11110111, B01011111 },
  { B11110110, B11011111 },
  { B11110110, B01111111 }
};

int top[2] = { B11111011, B11111111 };
int topright[2] =  { B11111111, B10111111 };
int bottomright[2] = { B11111111, B11110111 };
int bottom[2] = { B11111111, B11111101 };
int bottomleft[2] = { B11111111, B11111110 };
int topleft[2] = { B11111101, B11111111 };
int middle[2] = { B11111111, B11101111 };
int dp[2] = { B11111111, B11111011 };
int nil[2] = { B11111111, B11111111 };

int digitSegments[10][8] = {
  { top, topleft, topright, bottomleft, bottomright, bottom, nil, nil },
  { topright, bottomright, nil, nil, nil, nil, nil, nil },
  { top, topright, middle, bottomleft, bottom, nil, nil, nil },
  { top, topright, middle, bottomright, bottom, nil, nil, nil },
  { topleft, topright, middle, bottomright, nil, nil, nil, nil },
  { top, topleft, middle, bottomright, bottom, nil, nil, nil },
  { top, topleft, middle, bottomleft, bottomright, bottom, nil, nil },
  { top, topright, bottomright, nil, nil, nil, nil, nil },
  { top, topleft, topright, middle, bottomleft, bottomright, bottom, nil },
  { top, topleft, topright, middle, bottomright, nil, nil, nil }
};

void setup() {
  pinMode(latchPin, OUTPUT);
  pinMode(clockPin, OUTPUT);
  pinMode(dataPin, OUTPUT);

//  attachInterrupt(2, incrementDigit, RISING);
  MCUCR |= B00000011;    //watch for rising edge
  GIMSK |= B01000000;    //enable external interrupt
  SREG |= B10000000;     //global interrupt enable
}

void displaySegment(int digit[], int segment[]) {
  digitalWrite(latchPin, LOW);
  shiftOut(dataPin, clockPin, MSBFIRST, digit[0] & segment[0]); 
  shiftOut(dataPin, clockPin, MSBFIRST, digit[1] & segment[1]);
  digitalWrite(latchPin, HIGH);
  delayMicroseconds(10);
}

void loop() {
   int displayDigits[] = { 0, 0, 0, 0 };
   int x = digitToDisplay;
   int i = 3;
   while (x > 0) {
      displayDigits[i] = x % 10;
      x = x / 10;
      i = i - 1;
   }
   
  for (int i = 3; i >= 0; i--) {
    for (int j = 0; j < sizeof(digitSegments[displayDigits[i]])/sizeof(digitSegments[displayDigits[i]][0]); j++) {
      displaySegment(digits[i], digitSegments[displayDigits[i]][j]);
    }   
  }
}

ISR(INT0_vect) {
  digitToDisplay++;
}