//Create an arduino circuit that will take 5 seconds to go from off 
//to fully on back to off gradually using analog output. (2.5 seconds 
//to get to fully on, 2.5 seconds to get to fully off)
int pin3 = 3;
void setup() {
  // put your setup code here, to run once:
}
void loop() {
  // put your main code here, to run repeatedly:
  for (int i = 0; i <= 255; i+=5) {
    analogWrite(pin3, i);
    delay(50);
  }
  for (int i = 255; i >= 0; i-=5) {
    analogWrite(pin3, i);
    delay(50);
  }
}