volatile signed char temps;
volatile signed char direction;

void setup() {
  Serial.begin(9600);
  temps = 0;
  direction = 0;
  DDRD = 0b11111111;
  PORTD = 0b11110000;
  TCCR1A = 0;           // Init Timer1A
  TCCR1B = 0;           // Init Timer1B
  TCCR1B |= 0b00000100;  // Prescaler = 256
  TCNT1 = 3035;        // Timer Preloading
  TIMSK1 |= 0b00000001;  // Enable Timer Overflow Interrupt
}


ISR(TIMER1_OVF_vect)
{
  TCNT1 = 3035; // Timer Preloading
  if (direction == 0) {
    temps++;
    if (temps > 15) {
      direction = 1;
      temps = 14;
    }
  }
  else {
    temps--;
    if (temps < 0) {
      direction = 0;
      temps = 0;
    }
  }
}

void loop() {
  Effacer();
  Afficher(temps);
  Serial.print("Temps : ");
  Serial.println(temps);
}

void Afficher(unsigned char valeur) {
  if (valeur > 7) {
    digitalWrite(7, HIGH);
    valeur -= 8;
  }
  if (valeur > 3) {
    digitalWrite(6, HIGH);
    valeur -= 4;
  }
  if (valeur > 1) {
    digitalWrite(5, HIGH);
    valeur -= 2;
  }
  if (valeur > 0) {
    digitalWrite(4, HIGH);
  }
}

void Effacer(void) {
  digitalWrite(7, LOW);
  digitalWrite(6, LOW);
  digitalWrite(5, LOW);
  digitalWrite(4, LOW);
}