It looks like there's a lot of confusion as to what open-source hardware is, so we made a godawful flowchart to help make it more clear what it means.
we probably should have put the vendor datasheets one earlier on, but at the moment we kinda feel like it's the hardest one.
if your device includes, for instance
- a camera
- an ARM SOC
- an FPGA
- a Wi-Fi transceiver
- a cellular modem
then it's often as good as impossible to find one with a datasheet available without NDA.
to make matters worse, there are some components, especially camera modules, whose datasheets are available, but complete garbage, with all the important parameters listed as "TBD" or "-", and many sections just missing completely
it's an open question as to whether devices using those components qualify as open-source hardware. they probably do in most cases, but it's always variable.
in our book, PCB layout and routing info, as well as component datasheets (and user manuals, where applicable) are actually dramatically more important than foss firmware. it's one thing if a device has a proprietary blob baked into the configuration memory of some component, but quite another - and much more immediately relevant to the owner-hacker of the device - if there's nothing available to tell where everything is on the board.
this maybe wasn't as important 30 years ago when every component had its value and part number printed on it, but now everything's SMT and extremely tiny, and finding out exactly what you're looking at is a huge task compared to what it used to be. this is why we need published schematics.
the main pitfalls we've seen self-proclaimed open-source hardware projects fall into are these:
- publishing abstract electrical schematics, but no PCB track layout information.
- not publishing any schematics at all, and only releasing firmware/driver source code.
- using parts which require proprietary firmware or programming tools, and/or which have no public datasheets.