#define LED_BUILTIN 18

void setup() {
  // put your setup code here, to run once:
  Serial.begin(115200); // define baudrate

  pinMode(LED_BUILTIN, OUTPUT); // set the digital pin as output:

  Serial.write(45);     // write a byte with the value 45 => '-' character
  Serial.write('\n');   // write a newline character
  Serial.println("Hello, ESP32");

  // check buffer size 
  int wlen = Serial.availableForWrite();
  // prints the received data
  Serial.print("TX buffer size: "); 
  Serial.println(wlen);

}

void loop() {
  // put your main code here, to run repeatedly:

  // listen serial data from PC
  if(Serial.available()) {
 
    // READ SERIAL DATA ONE BY ONE 
    // int incomingByte = Serial.read();
    // // Serial.println(incomingByte); // real data get from pc (int)
    // Serial.print("I received: ");
    // Serial.println((char)incomingByte);

    // READ DATA UNTIL SENDER PRESS ENTER
    String command = Serial.readStringUntil('\n'); // read string until newline character

    if (command == "ON") {
      digitalWrite(LED_BUILTIN, HIGH); // turn on LED
      Serial.println("Turn LED ON");
    } else if (command == "OFF") {
      digitalWrite(LED_BUILTIN, LOW);  // turn off LED
      Serial.println("Turn LED OFF");
    }

  }
  delay(10); // this speeds up the simulation
}