串口收发的简单栗子

String str = "";

void setup() {
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for native USB port only
  }
}

void loop() {
  while (Serial.available() > 0)
  {
    str += char(Serial.read());
    delay(2);
  }

  if (str.length() > 0)
  {
    delay(200);
    str="R:"+str;
    Serial.println(str);
  }
  
  delay(10);
  str = "";
}

参考资料：
https://www.lxx1.com/3905