void setup() {

  Serial.begin(9600);

}

​

char rx_byte = 0;

​

void loop() {

  if (Serial.available() > 0) {    // is a character available?

    rx_byte = Serial.read();       // get the character

    // check if a number was received

    if ((rx_byte >= '0') && (rx_byte <= '9')) {

      Serial.print("Number received: ");

      Serial.println(rx_byte);

    }

    else if (rx_byte == '\n') {

      Serial.println("Newline");

    }

    else {

      Serial.println("Not a number.");

    }

  } // end: if (Serial.available() > 0)

}