I seem to be on a bit of a roll at the moment, just got a prototype working of a PSoC based USB 5 to 1 switching unit, this is using relays salvaged from old ebay HP/Agilent 44471A relay cards.
It's very simple, really just the PSoC and a couple of ULN2003's ... initial testing looks good, so I just need to repurpose the USBTMC code from the Yaugi to provide a USBTMC or USBUART interface.
I've used the same approach as the HP modules ... so the quad pole relay is paralleled to act as a dual pole, presumably this was to reduce contact resistance, but also to cope with isolation limits with pin proximity.
The picture mostly hides the massive schoolboy error of not checking the footprint yet again and having too small holes for the relays, but luckily with a "just the right amount of flux" I managed to get them all soldered on ;-) ... clearly I'm not leaving school anytime soon!
I've just ordered an enclosure and front and rear (pcb) panels ... the intention is to have some led's and a couple of tactile switches on the front panel (for manual selection.) I was going to use Pomona binding posts, but that's £120 in posts which seems mad, so I'll just go for Cliff gold plated ones for now.
Slowly I'm getting to the point where I hope I can do something remotely metrologisty ... I now have three LTZ1000 references (in various states of completeness), a USB temp/pressure/humidity sensor (v2 coming soon), a USB switching unit, and a selection of USB GPIB interfaces .. all home made ... which goes a small way in offsetting how much I've spent on actual kit in the last year or so!