Apple 2e - building a simple expansion card and calling it from BASIC (or assembly)?

Has anyone built their own Apple 2 expansion card and programmed it to do something?

If it wouldn't be ridiculously hard, I would like to try etching a circuit board to plug into one of the expansion slots on my 2e. The board would contain a single relay, which could be opened or closed from BASIC code (or if it is not possible from BASIC, from 6502 assembly).

I'd also like to have the board contain 2 leads that the computer could tell when they are connected together.

Maybe later I would expand the # of relays or leads, or build an additional card or two with these same components, for more "inputs" and "outputs".

Any information would be appreciated...

Thanks