I hope some of the electricians in the house stop by here. This post to control 120v through a LV relay looks really nifty. I'm wondering if it's code legal once the LV and HV portions are put in separate boxes?

I would not put all the LV stuff in the bottom of the box as this guy has. I'd put the LV stuff in its own HandyBox or 3d print a case for it and screw it to the stud next to the mains voltage box.

I'd post it as a question, but I don't want to rewrite the article to make it link-only proof.