rubyArduino.ino

#define LED 13

// Using http://slides.justen.eng.br/python-e-arduino as refference

void setup() {
    pinMode(LED, OUTPUT);
    Serial.begin(9600);
}

void loop() {
    if (Serial.available()) {
        char serialListener = Serial.read();
        if (serialListener == 'H') {
            digitalWrite(LED, HIGH);
        }
        else if (serialListener == 'L') {
            digitalWrite(LED, LOW);
        }
    }
}

RubyArduino.rb

require "serialport"

@serial_port = SerialPort.new "/dev/tty.usbmodem1421"

def onOff()
21puts "Type something..: (on/ off / bye )"
	command = gets.chomp
	if command=="on"
		puts "The LED is on..."
		sleep 1
		@serial_port.write "H"
		onOff()
	elsif command=="off"
		puts "The LED is off..."
		sleep 1
		@serial_port.write "L"
		onOff()
	elsif command=="bye"
		puts "See you!..."
		sleep 1
		@serial_port.close
	else
		puts "Sorry..type another thing..!"
		onOff()
	end
end

sleep 2

onOff()