fkeel:
would a hall effect sensor work?otherwise one of those IR-slit sensors?
I'm going to have to get a good linear HE in the shop tomorrow to see if the process would be repeatable in any solid way. For everyone's reference, we're talking about gold here, so that's a little tougher to catch with normal metal detector style circuits and gets a little picky on the coil/frequency.
PERHAPS on that IR option. Are you just referring to my original post, or are you thinking about a specific thing you've seen?
I have a solid collection of very high quality opto endstops, but I'm guessing that busting one in half wouldn't likely work. I think they're pretty needy on who much light gets through, and I can't count on the ring to reflect THAT much.