int redPin = 9;    // Red LED connected to digital pin 9
int yellowPin = 10; // Yellow LED connected to digital pin 10

void setup()  { 
  // nothing happens in setup 
} 

void loop()  { 
  // fade in from min to max in increments of 5 points:
  for(int fadeValue = 0 ; fadeValue <= 255; fadeValue +=5) { 
    // sets the value (range from 0 to 255):
    analogWrite(redPin, fadeValue);
    analogWrite(yellowPin, (255 - fadeValue));   
    // wait for 30 milliseconds to see the dimming effect    
    delay(30);                            
  } 

  // fade out from max to min in increments of 5 points:
  for(int fadeValue = 255 ; fadeValue >= 0; fadeValue -=5) { 
    // sets the value (range from 0 to 255):
    analogWrite(redPin, fadeValue);
    analogWrite(yellowPin, (255 - fadeValue));    
    // wait for 30 milliseconds to see the dimming effect    
    delay(30);                            
  } 
}