motor

int pos = 155;
int M = 255;
int m = 155;
int dir = 1;

void setup(){
   pinMode(9,OUTPUT); 
   
   Serial.begin(9600);
}

void loop(){
  
  //if(pos%10==0)
   analogWrite(9,pos);    

  delay(20);

  pos += 1 * dir;

  if(pos>=M)
    dir = -1;
   else if(pos <= m)
     dir = 1;
     
    Serial.println(pos);
}