//Acionamento de led na saída

const uint8_t LED = 2;
const uint8_t BTN = 4;

void setup() {
  pinMode(LED, OUTPUT);
  pinMode(BTN, INPUT_PULLUP);     // botão entre BTN e GND
}

void loop() {

  bool pressed = (digitalRead(BTN) == LOW);  
  digitalWrite(LED, pressed ? HIGH : LOW);
}