const int SN754410_12EN = 9;
const int SN754410_1A = 8;
const int SN754410_2A = 7;
int vitesse = 255;
int pingpong = 0;

void setup() {

        pinMode(SN754410_12EN,OUTPUT);
        pinMode(SN754410_1A,OUTPUT);
        pinMode(SN754410_2A,OUTPUT);
        Serial.begin(9600);
}

void loop () {
  
    if (pingpong ==0) {
     vitesse = vitesse-10;
      if (vitesse < 40){
       pingpong = 1; 
      }
    }
    else if (pingpong==1) {
    vitesse = vitesse +10;
      if(vitesse > 240){
      pingpong = 0;
      }
    }  
        analogWrite (SN754410_12EN,vitesse); // la vitesse varie en fonction du PWM (40 a 255) 
        digitalWrite(SN754410_1A,HIGH);   
        digitalWrite(SN754410_2A,LOW);
        delay(500); 
        Serial.println(vitesse);
}