int led1 = 2;
int led2 = 4;
int led3 = 16;
int led4 = 17;

void setup() {
  Serial.begin(115200);

  pinMode(led1, OUTPUT);
  pinMode(led2, OUTPUT);
  pinMode(led3, OUTPUT);
  pinMode(led4, OUTPUT);

  Serial.println("Android Home Automation Ready");
  Serial.println("Send commands: A/a B/b C/c D/d");
}

void loop() {
  if (Serial.available()) {
    char cmd = Serial.read();

    if (cmd == 'A') digitalWrite(led1, HIGH);
    if (cmd == 'a') digitalWrite(led1, LOW);

    if (cmd == 'B') digitalWrite(led2, HIGH);
    if (cmd == 'b') digitalWrite(led2, LOW);

    if (cmd == 'C') digitalWrite(led3, HIGH);
    if (cmd == 'c') digitalWrite(led3, LOW);

    if (cmd == 'D') digitalWrite(led4, HIGH);
    if (cmd == 'd') digitalWrite(led4, LOW);
  }
}