const byte font[] = { 0x3F, 0x06, 0x5B, 0x4F, 0x66, 0x6D, 0x7D, 0x07, 0x7F, 0x6F, 0 };

#define CK1 11
#define CK2 12
#define CK3 13

int count = 0;

void out7seg(byte data) {
  digitalWrite(4,  0b00000001&data); // a
  digitalWrite(5,  0b00000010&data); // b
  digitalWrite(6,  0b00000100&data); // c
  digitalWrite(7,  0b00001000&data); // d
  digitalWrite(8,  0b00010000&data); // e
  digitalWrite(9,  0b00100000&data); // f
  digitalWrite(10, 0b01000000&data); // g
}

void scan7Segment(int x) {
  while(x-=4) {
    for (int i=0;i<3;i++) {
      int n = count/(int)pow(10, i)%10;
      out7seg(font[n]);
      digitalWrite(CK1+i, 0);
      delay(1);
      digitalWrite(CK1+i, 1);
    }
  }
}

void setup() {
  pinMode(4, OUTPUT);
  pinMode(5, OUTPUT);
  pinMode(6, OUTPUT);
  pinMode(7, OUTPUT);
  pinMode(8, OUTPUT);
  pinMode(9, OUTPUT);
  pinMode(10, OUTPUT);
  pinMode(11, OUTPUT);
  pinMode(12, OUTPUT);
  pinMode(13, OUTPUT);

  digitalWrite(CK1, 1);
  digitalWrite(CK2, 1);
  digitalWrite(CK3, 1);
}

void loop() {
  scan7Segment(1000);
  count++;
}