There was a thread posted in 2010 in this sub-forum about using an Arduino for Atari 8 bit computer communication. I found this thread when I started researching for a project. Basically, it was suggested that the FTDI chip be wired into, to hook up to the Atari.
I wanted to actually use the Arduino. I purchased one and began to program. Although it did not take too long to get it operational, it took me forever to post the information. That thread is too old to reply to now. I thought in case anyone ever did a search, they could see another way to do it, actually using the Arduino itself. I finally put up a site with the information.
I thought this way was way more fun. http://diskwiz.wordpress.com/sio2microsd