Ask your current employer. Or at least ask about a picture, or something -- much less harm in that than a physical prototype. If you're afraid to ask... there's probably a reason why...
Personally, I tend to bring
this around. I made it back in, like, 2007 or something like that, so it's not especially representative of my current state of knowledge. But I'm pretty happy with how it turned out:
- It's hand made. Signs: I'm not afraid to get my hands dirty. Hand printed, hand drilled, hand soldered. And, all those hand made steps were done with care (of course, this neglects the other boards I made that didn't turn out so well for various reasons..).
- It looks nice. Shiny, reasonable layout, easy to see where everything is and what's going on.
- It sucks. So, I can talk about things I did wrong, and "what I would do differently" now.
If you don't have any examples like this, make your own. There's no harm in bringing a pad and pen and drawing something up. Maybe you can't illustrate so directly and exactly as a physical sample does, but you can still discuss in general terms.
You wouldn't want to get so specific as to indicate what chips and pinouts and routing and everything you did... and such information is hardly relevant to the interviewer, anyway. But I don't see any harm in a vague description. Example: microcontroller here, FPGA there; assorted digital logic; line drivers; etc. There's a million projects that have those sorts of requirements, so the generality is relevant to almost anything.
Routing technique would be better described than drawn, i.e., draw an ugly bunch of lines and describe it as 'dozens' (e.g.) of traces, spaced evenly, give or take the design rules, or other constraints (e.g., 6/6 mil minimum trace thickness / spacing; maybe up to 8-16 mil for impedance controlled lines; whatever).
If you are asked about some of these things in more depth, again, don't go into very specific detail (or indicate that you don't think you should talk about it -- that's fine, they'll understand), but if you can, do be honest. If you made an informed choice, talk about the reasons; if you didn't, say you didn't know about it -- yet another thing to put on your mental list of "things I don't know but should learn about some day". There's always a learning opportunity in something!
Tim