Ok, since this post has gotten so many replies and gone off on more
tangents than i thought possible I'll give the concept I'm working on.  And
maybe clear up some of the confusion that has arisin from my analogy.

    The real project is designing "smart" building-blocks.  Around the size
of Duplo blocks or other large "Lego" like blocks.  The goal is to create a
set of blocks that can do math when connected in a correct order.  There
will be number blocks, addition, subtraction, multiplication, and division
blocks.  All of them are like the cars in the train.  The Equals block works
like the engine to gather the order and type of block conected to it and
computer the equation.  With such a small size, electrical contacts seem the
most inexpensive way to go.  My buget is as low as I can make it.  The lower
the better.  I went for a PIC that would just meet my needs (at $.90
wholesale) and plastic and phone jack connectors for my contacts.  The block
is being desiged by another group memeber but we are looking at cents each.
The blocks cannot be plugged in backwards, they have a front and back.

Dan Larson made a nice picture to illustrate this


-----     -----     -----     -----     -----
|   |---->|   |---->|   |---->|   |---->|   |
| 7 |     | = |     | 5 |     | + |     | 2 |
|   |<----|   |<----|   |<----|   |<----|   |
-----     -----     -----     -----     -----

Speed is pretty much not an issue, under a second is fine. In reality it
should do it in a fraction of that.

The Equals block is going to be an impresive bit of code, we have a lot more
blocks than just numbers and simple math.  Since all the others are just
slaves with an ID code, it all lies in there.

If anyone has any input still,  I'm still open.  This is the second try at
this project, now with a PIC chip and i hope i can acomplish my goal.

-Stu