My cousin's kids have a toy (ingenously designed, I feel) that consists
of something that looks not unlike a Speak-n-Say, only instead of
pulling a string (that breaks on day 2 of ownership), the child places
an object in a hole.  The toy then announces the name of that
object in the language du jour (different cartridges available), and
either makes excited happy noises if it was the right object or
repeats the name of the one it wanted.

It broke, and I was (of course) tasked with fixing it.  The really
neat thing is how it works (aha! The point arrives!).

Each cartridge contains a small processor and a card-edge connector.
Each object contains a resistor.  The main unit is only a speaker, an
amplifier, and batteries/power regulation.  When a toy is placed in
the hole, it is guided to its proper resting place by, well, being stuck
in a hole.  There's a metal plate in the bottom of the toy which
pulls a magnet up against its underside, closing a switch, which lets
the processor know that a new object has arrived.  On the bottom
of the object are also two little metal contacts, which touch a pair
of concentric metal rings.  Those serve as the contact points for,
you guessed it, a precision resistor.

My point here is that this toy is CERTAINLY treated far rougher
by my 2 and 4 year old cousins than an electric chess board, and
the resistor trick works quite well for it.  Rather than seating the
pieces in a hole, have a little plug on the bottom that fits into
a hole on the board.  The magnet beneath not only serves to
close the switch and notify the processor of a change, but
also to pull the piece down tight.

For anyone who made it this far and still cares, the toy is called
a "Little Linguist."

Mike H.

>If you think you can make reliable contact between the chesspieces and
>at least two contacts on each square of the board, I think I'd feel a
>lot better about some sort of digitial signal (dallas one-wire PROMS?)
>than analog.  Getting reliable low contact resistance, as you'd need
>for different resistors to identify the pieces, is tricky.  I think.)
>(so how many unique identifiers do you need anyway?  One for each piece
>of each color?  Or as few as one per each type of piece of either
>color?)  (I really like the idea of an IR-transparent chessboard...)
>
>BillW

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