You show an LED connected directly to the arduino pins with no current limiting resistor.
The first version of this tutorial was written for the tutorial series of an Indian start up called Ardubotics (learn.ardubotics.com
), the workshops that they organize use the Freeduino USB board (http://probots.co.in/index.php?main_page=product_info&cPath=55_56&products_id=395
) which has a current limiting resistor attached on pin 13.
Also, in the blog post I pointed that most Arduinos have a led connected to pin 13 and adding the LED was optional.
However, I will update the post.