Software

int ledPin = 9;      // LED connected to digital pin 9

int brightness = 0;         // variable to store the read value


boolean stringStart =  false;  // whether the string is start
char delimiter_start = 's';
char delimiter_end = 'e';
String inputString = "";         // a string to hold incoming data
boolean stringComplete = false;  // whether the string is complete

// *************************************************************************************
// ********************           Serial Event            ******************************
// *************************************************************************************

void serialEvent() {
  while (Serial.available()) {
    // get the new byte:
    char inChar = (char)Serial.read();
  //start messege
    if (!stringStart && inChar == delimiter_start) {
      stringStart = true;
      continue;
    } 
    if (stringStart)
    {      
      //echo
      //Serial.print(inChar);     
      // add it to the inputString:
      inputString += inChar;
      // end messege
      if (inChar == delimiter_end) {
        stringComplete = true;
        stringStart = false;
      }
    //check accumulated lengh of the massege
      if(inputString.length() > 11) {
        inputString =  "";
        stringStart = false;
      }
    }
  }
}

// *************************************************************************************
// *************************************************************************************
// *************************************************************************************  


void setup()

{

  pinMode(ledPin, OUTPUT);   // sets the pin as output
 analogWrite(ledPin, 0);  // analogRead values go from 0 to 1023, analogWrite values from 0 to 255
 Serial.begin(9600);
 inputString.reserve(10);
}



void loop()

{

  if (stringComplete)
  {
    String command = inputString;   //Serial.readString();
    inputString = "";
    stringComplete = false;

    if (command[1] == delimiter_end)
                {
                  brightness = (int(command[0]) - 48);
                }
                else if (command[2] == delimiter_end)
                {
                  brightness = ((int(command[0]) - 48) * 10) + (int(command[1]) - 48);
                }
                else
                {
                  brightness = ((int(command[0]) - 48) * 100) + ((int(command[1]) - 48) * 10) + (int(command[2]) - 48);
                  if (brightness > 255) brightness = 255;
                }
    //brightness = Serial.read();
    Serial.print(String(delimiter_start) + String(brightness) + String(delimiter_end));
    // set the brightness of the LED:
    analogWrite(ledPin, brightness);
  }
  

}