int ledG = 3, ledH = 4;

void setup() {
  pinMode(ledG, OUTPUT);
  pinMode(ledH, OUTPUT);
  digitalWrite(ledG, LOW);
  digitalWrite(ledH, LOW);
  Serial.begin(9600);
}

void loop() {
  if (!Serial.available()) return;
  switch (Serial.read()) {
    case '0':
      digitalWrite(ledH, LOW);
      break;
    case '1':
      digitalWrite(ledH, HIGH);
      break;
  }
}