void setup() {

    Serial.begin(9600);
    Serial.println("Type your Instruction here..");

  for (int thisPin = 2; thisPin < 6; thisPin++) {

    pinMode(thisPin,OUTPUT);

  }
}

void loop() {

  // read the sensor:

  if (Serial.available() > 0) {

    int inByte = Serial.read();

        switch (inByte) {

      case 'a':

        digitalWrite(5, HIGH);
        delay(1500);

        break;

      case 'b':

        digitalWrite(3, HIGH);
         delay(1500);

        break;

      case 'c':

        digitalWrite(6, HIGH);
         delay(1500);

        break;

      case 'd':

        digitalWrite(7, HIGH);
        delay(1500);

        break;

      case 'e':

        digitalWrite(8, HIGH);
        delay(1500);

        break;

      default:

        for (int thisPin = 2; thisPin < 9; thisPin++) {

          digitalWrite(thisPin, LOW);

        }

    }

  }
}