weed tech makes some nice interface modules, several of which I already support in XTension. Something I've been meaning to get ahold of is their analog output card so that I might make use of some of these old meters that I've collected. I broke down and bought myself the thing the other day ;) I had to revisit the code anyway to support serial connections over IP/serial adaptors and add support for their new analog input module anyway so I decided to add this to the list of maintenance being performed.
(letters from the future: I’m not sure that anybody other than me has found a use for this card, but I love to have the meters sitting around showing something vaguely useful. The support is included as part of the regular weeder plugin for XTension the demo version of which is included with the standard download as linked to above. The full weeder IO module support page is at the wiki site)