int led = 8;
int button = 7;
int change = 0;
int countDown = 50;
String serialCommand = "vazio";
String on = "liga";
String off = "desliga";

void setup() {
  pinMode(led, OUTPUT);
  pinMode(button, INPUT_PULLUP);
  Serial.begin(9600);
}

void loop() {
  if (Serial.available()) {
    serialCommand = Serial.readStringUntil('\n');
    if (serialCommand == on) digitalWrite(led, HIGH);
    if (serialCommand == off) digitalWrite(led, LOW);
  }
  if (digitalRead(button) == LOW && countDown == 0) {
    Serial.print((!change) ? "liga" : "desliga");
    change = !change;
    countDown = 50;
  }
  countDown = (countDown == 0) ? 0 : countDown - 1;
  delay(10);
}