#define LED1 1
#define LED2 5

void setup() {
  Serial1.begin(115200);
  Serial1.println("Hello, world!");
  pinMode(LED_BUILTIN, OUTPUT);
  digitalWrite(LED_BUILTIN, HIGH);
  pinMode(LED1, OUTPUT);
  pinMode(LED2, OUTPUT); 
}

void loop() {
  digitalWrite(LED1, HIGH);
  digitalWrite(LED2, LOW);
  delay(500);
  digitalWrite(LED1, LOW);
  digitalWrite(LED2, HIGH);
  delay(500);
}