int pwm = 9;                   // This is the pin that we will use
 
void setup() {
    pinMode(pwm, OUTPUT);       // declare the pin to be an output
}
 
void loop() {
    delay(1000);  
  //blue                    // wait for a second
   for(int i=0; i<256; i++) // Increase brightness from 0 to 255
  {
    analogWrite(pwm, i); // Set the duty cycle to i
    delay(10); // Wait for 10ms
  }
  
  for(int i=255; i>=0; i--) // Decrease brightness from 255 to 0
  {
    analogWrite(pwm, i); // Set the duty cycle to i
    delay(10); // Wait for 10ms
  }
  
}