My advice is to stay away from "FOSS" unless you're GPL, and "open source" unless you're an OSI-certified license. It's not that I don't think those terms apply to anything other than that, but using those terms invites debate about licensing and attempts to control language instead of discussion of your project.
"Source available" is a term that usually no one gets mad at.
The thread title as of this moment (subject to moderator edit) says "source available" which seems reasonable. So I don't think you made a mistake. "With published design" might also work.
I've got my own little GitHub page with projects that I share. They usually involve both hardware and code. I'm also not an engineer, but a scientist and electronics hobbyist, both of which have cultures of open design that predate the software industry. What I do with my projects is attach a MIT license, attribute the sources of any code or ideas that I borrow from elsewhere, and wish you good luck. ;-)
I'm very new to posting on this platform.