ArduinoSerialWaitTest

int incomingByte = 0;

void setup(){
Serial.begin(9600);

  while (Serial.available() <= 0) {//keep sending until we get some bytes from the pc
    Serial.write(42);   // just a constant
    delay(100);
  }
  while(Serial.available()>0) Serial.read(); //immediately after we get something from the PC clear the input buffer by reading from it until it's empty
}

void loop(){

  if (Serial.available()>0) {
    incomingByte=Serial.read();
      delay(incomingByte*50); //simulate waiting for a physical event
      Serial.write(incomingByte);//echo the input byte
  }
}