Don, thanks for the info on your hall-effect board. So do you just place the coil near the rail, and a train located anywhere on that isolated block of track shows current anywhere along that track? If so, how do you isolate the block yet use a single power supply over multiple blocks? Or is it detecting the train passing past the coil? Dumb questions, I know! ;-)
If you don't want to connect all those relays directly to Arduino inputs, you can use a shift register. I use a product called Centipede Shield from Macetech (though I don't use it as a shield; I mount it adjacent to my Arduino): http://macetech.com/store/inde...o&products_id=23 Great product and great support from those guys.
Either way, don't forget that relay contacts "bounce" and will register as multiple closures if you poll them too frequently. Contacts can even "bounce" when released. It's easily addressed with a bit of code, though some people prefer to debounce using hardware. Just something to be aware of if your testing shows multiple entries into a block in a matter of a few milliseconds.
