I did one a few months ago with a different micron controller. One thng I would recomment is to use some opto isolators so that there is no physical connection between the fox and the inputs.
I used a 2n3904 as the transistor and an IN404 (or something) as the diode. They are both bog standard and I have a hundred of each for all sorts of things (I stuck one of the diodes in a knackered electric fence machine the other day and it works great now. No idea what the original spec was. I got both lots off ebay. check the avr io on www.olimex.com. They have some great schematics. The io is great for you as it shows the step up from 5 volt to 12 volt, so there are two circuts. Regards Diarmuid check out my blog where I show how to do cool stuff with the Meraki and soon the fox. http://designbuildtestrepeat.wordpress.com
