// we will be using pin 3
int ledPin = 3;

void setup() {
  // setup pin 3
  pinMode(ledPin, OUTPUT);

}

void loop() {
  // put your main code here, to run repeatedly:
  // make a function that simulates the LED "breathing"
  breath(ledPin, 6); // we need pin number and delay
  delay(500); // delay 500 ms
}
void breath(int ledPin, int delayMs){
  for(int i = 0; i <= 255; i++){ // slowly lighting up
    analogWrite(ledPin, i); // analogWrite(pin, value) --> outputs PWM wave
    delay(delayMs); 
  }
  for(int i = 255; i >= 0; i--){ // slowly dimming down
    analogWrite(ledPin, i);
    delay(delayMs);
  }
}