// Source: https://desertbot.io/blog/d1-mini-blink

void setup() {
  pinMode(LED_BUILTIN, OUTPUT);
}

void loop() {
  digitalWrite(LED_BUILTIN, HIGH);   // Arduino: turn the LED on (HIGH)
                                     // D1 Mini: turns the LED *off*
  delay(1000);                       // wait for a second
  digitalWrite(LED_BUILTIN, LOW);    // Arduino: turn the LED off (LOW)
                                     // D1 Mini: turns the LED *on*
  delay(1000);                       // wait for a second
}