many decades ago I played with the idea of using magnets on the bottom of the chess pieces and reed switches under the squares. i designed a discrete TTL circuit to scan the squares looking for a change in the state of a reed switch. now i would do it with a micro-controller. anyways, i couldn't find good magnets back then and dropped the project. there was also the problem of the magnets wanting to "get together" with neighboring pieces.
the new commercial designs are nice but very pricey. it would be great to find a DIY solution that wouldn't take more time/effort/cost than one of the commercial boards.
finding the right kind of sensor is the key, me thinks.
"An Engine's strength flows from the Search. But beware, pruning, extensions, reductions; the dark side of the Search are they. Once you start down the dark path, it will dominate and consume you, as it has to so many developers before.” -- Yoda