Arduino RS232 Interface

This is an Add-On.  On this site, add-ons are things that are relatively cheap and it wouldn’t make sense to pay for shipping. My original idea was, if you buy something for $10 or more and pay for shipping - you earned the right to purchase as many add-ons as you want with no additional shipping cost. However, that was really hard to fit into the underlying assumptions of the web hosting company. So, the new version is: Buy something and the shipping cost is flat rate $6.50. Each additional item adds $0.10 to shipping.