char val;
int times = 3;
#define LED 25

// the setup function runs once when you press reset or power the board
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED, OUTPUT);
  Serial.begin(9600); //initiate serial communication at 9600 baud/sec
}

void loop(){
      if (Serial.available() >0) {                         
      val = Serial.read(); //create 'character' datatype variable 'val' 
                            
       if (val == 'b'){ //if 'b' received over serial
       BlinkLED();
       } 
       else if (val == '0'){
        digitalWrite(LED,LOW); //turn LED OFF
       }
      }
  }

  void BlinkLED(){
    while(times--)
    {
      digitalWrite(LED,HIGH); //turn LED ON
      delay(200);
      digitalWrite(LED,LOW); //turn LED OFF
      delay(200);
    }
    times = 3;
  }