https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&c...
or stack in HP 12c calculator
I have a number of ideas for the minimum I/O set to support initially. Of course, this could easily be enhanced through expansion ports.
I am trying hard to limit the scope of the project. It's far too easy to complicate the heck out of it.