[encoding them will take one common connection per switch, and four BCD bits for the lot of them]
-- sounds good so I'll only need one AT89S51 at 15 mA.

The switches are for setting the time controls.
All currently marketed clocks have this set by interfacing with the MCU in software -- a process that I can't stand; no matter how well it's designed you're going to forget how to do it if you don't do it frequently. This clock will be able to be set by anyone, even if they've never seen a digital chess clock before; I think of it as "The No-Brainer".

The extra switch is for use only with digital clocks, it's either:
Delay: the wait time before a clock starts decrementing, or
Bonus: the number of seconds each player gets added to his time (each move).

As of now I'm just going to build one model and forget about it. There's very little market for chess clocks as most serious players (those who use clocks) use the Internet. My idea, of using hardware to set the clocks, costs too much to be competitive.

Thanks,
Peter.