/*
 * Interfacing Arduino with common anode 7-segment display
 * 4-Digit counter example.
 * This is a free software with NO WARRANTY.
 * http://simple-circuit.com/
 */
 
// counter button definition
#define button A0
 
// segment pin definitions
#define SegA   12
#define SegB   11
#define SegC   10
#define SegD    9
#define SegE    8
#define SegF    7
#define SegG    6
// common pins of the four digits definitions
#define Dig1    5
#define Dig2    4
#define Dig3    3
#define Dig4    2
 
// variable declarations
byte current_digit;
int  count = 0;
 
void setup()
{
  pinMode(button, INPUT_PULLUP);
  pinMode(SegA, OUTPUT);
  pinMode(SegB, OUTPUT);
  pinMode(SegC, OUTPUT);
  pinMode(SegD, OUTPUT);
  pinMode(SegE, OUTPUT);
  pinMode(SegF, OUTPUT);
  pinMode(SegG, OUTPUT);
  pinMode(Dig1, OUTPUT);
  pinMode(Dig2, OUTPUT);
  pinMode(Dig3, OUTPUT);
  pinMode(Dig4, OUTPUT);
 
  disp_off();  // turn off the display
 
  // Timer1 module overflow interrupt configuration
  TCCR1A = 0;
  TCCR1B = 1;  // enable Timer1 with prescaler = 1 ( 16 ticks each 1 µs)
  TCNT1  = 0;  // set Timer1 preload value to 0 (reset)
  TIMSK1 = 1;  // enable Timer1 overflow interrupt
 
}
 
ISR(TIMER1_OVF_vect)   // Timer1 interrupt service routine (ISR)
{
  disp_off();  // turn off the display
 
  switch (current_digit)
  {
    case 1:
      disp(count / 1000);   // prepare to display digit 1 (most left)
      digitalWrite(Dig1, LOW);  // turn on digit 1
      break;
 
    case 2:
      disp( (count / 100) % 10);   // prepare to display digit 2
      digitalWrite(Dig2, LOW);     // turn on digit 2
      break;
 
    case 3:
      disp( (count / 10) % 10);   // prepare to display digit 3
      digitalWrite(Dig3, LOW);    // turn on digit 3
      break;
 
    case 4:
      disp(count % 10);   // prepare to display digit 4 (most right)
      digitalWrite(Dig4, LOW);  // turn on digit 4
  }
 
  current_digit = (current_digit % 4) + 1;
}
 
// main loop
void loop()
{
  if(digitalRead(button) == 0)
  {
    count++;  // increment 'count' by 1
    if(count &gt: 9999)
      count = 0;
    delay(200);  // wait 200 milliseconds
  }
}
 
void disp(byte number)
{
  switch (number)
  {
    case 0:  // print 0
      digitalWrite(SegA, LOW);
      digitalWrite(SegB, LOW);
      digitalWrite(SegC, LOW);
      digitalWrite(SegD, LOW);
      digitalWrite(SegE, LOW);
      digitalWrite(SegF, LOW);
      digitalWrite(SegG, HIGH);
      break;
 
    case 1:  // print 1
      digitalWrite(SegA, HIGH);
      digitalWrite(SegB, LOW);
      digitalWrite(SegC, LOW);
      digitalWrite(SegD, HIGH);
      digitalWrite(SegE, HIGH);
      digitalWrite(SegF, HIGH);
      digitalWrite(SegG, HIGH);
      break;
 
    case 2:  // print 2
      digitalWrite(SegA, LOW);
      digitalWrite(SegB, LOW);
      digitalWrite(SegC, HIGH);
      digitalWrite(SegD, LOW);
      digitalWrite(SegE, LOW);
      digitalWrite(SegF, HIGH);
      digitalWrite(SegG, LOW);
      break;
 
    case 3:  // print 3
      digitalWrite(SegA, LOW);
      digitalWrite(SegB, LOW);
      digitalWrite(SegC, LOW);
      digitalWrite(SegD, LOW);
      digitalWrite(SegE, HIGH);
      digitalWrite(SegF, HIGH);
      digitalWrite(SegG, LOW);
      break;
 
    case 4:  // print 4
      digitalWrite(SegA, HIGH);
      digitalWrite(SegB, LOW);
      digitalWrite(SegC, LOW);
      digitalWrite(SegD, HIGH);
      digitalWrite(SegE, HIGH);
      digitalWrite(SegF, LOW);
      digitalWrite(SegG, LOW);
      break;
 
    case 5:  // print 5
      digitalWrite(SegA, LOW);
      digitalWrite(SegB, HIGH);
      digitalWrite(SegC, LOW);
      digitalWrite(SegD, LOW);
      digitalWrite(SegE, HIGH);
      digitalWrite(SegF, LOW);
      digitalWrite(SegG, LOW);
      break;
 
    case 6:  // print 6
      digitalWrite(SegA, LOW);
      digitalWrite(SegB, HIGH);
      digitalWrite(SegC, LOW);
      digitalWrite(SegD, LOW);
      digitalWrite(SegE, LOW);
      digitalWrite(SegF, LOW);
      digitalWrite(SegG, LOW);
      break;
    
    case 7:  // print 7
      digitalWrite(SegA, LOW);
      digitalWrite(SegB, LOW);
      digitalWrite(SegC, LOW);
      digitalWrite(SegD, HIGH);
      digitalWrite(SegE, HIGH);
      digitalWrite(SegF, HIGH);
      digitalWrite(SegG, HIGH);
      break;
 
    case 8:  // print 8
      digitalWrite(SegA, LOW);
      digitalWrite(SegB, LOW);
      digitalWrite(SegC, LOW);
      digitalWrite(SegD, LOW);
      digitalWrite(SegE, LOW);
      digitalWrite(SegF, LOW);
      digitalWrite(SegG, LOW);
      break;
 
    case 9:  // print 9
      digitalWrite(SegA, LOW);
      digitalWrite(SegB, LOW);
      digitalWrite(SegC, LOW);
      digitalWrite(SegD, LOW);
      digitalWrite(SegE, HIGH);
      digitalWrite(SegF, LOW);
      digitalWrite(SegG, LOW);
  }
}
 
void disp_off()
{
   digitalWrite(Dig1, HIGH);
   digitalWrite(Dig2, HIGH);
   digitalWrite(Dig3, HIGH);
   digitalWrite(Dig4, HIGH);
}