The Tricky Business of “Copylefting” Hardware

[Diesen Artikel gibt es auch auf Deutsch.]

It’s probably safe to say that the copyleft principle has been essential for the success of free software. Copyleft means that all versions of a software or document will remain free, preventing companies from creating “value-added” versions of free programs and selling them as proprietary, non-free software. The GNU General Public License (GPL)—the first and most well-known incorporation of the copyleft principle—is used for about 50–70% of all free programs, making it more popular than all other free software licenses together.

At first sight, the situation in the newly emerging field of free and open hardware might seem similar—here, copyleft licenses such as the GPL and the Creative Commons Attribution-ShareAlike License (BY-SA) are very popular too (see below for a more detailed analysis). But actually, the situation is very different for hardware design, since copyleft relies on copyright, and hardware is (in most cases) not protected by copyright law.

A Solution: Patents?

I know of only one license that is specifically targeted at open hardware and tries to work around this issue by relying not only on copyright, but also on a mutual patent immunity clause: the TAPR Open Hardware License, published in May 2007 (Version 1.0). The idea is that the licensor grants everybody who complies with the terms of the license the right to use any relevant patents they control. So if you don’t comply (e.g. by not publishing the “source” for physical products you build based on the licensed information), you might get sued by the licensor for patent violation, but if you comply you’re safe.

TAPR has published two versions of the license: the Open Hardware License (OHL), which emulates standard copyleft (like the GPL or CC BY-SA), and the TAPR Noncommercial Hardware License (NCL), which additionally prohibits commercial usage (like the CC BY-NC-SA).

Relying on patent law instead of copyright law for hardware makes sense, since patent law is made for hardware, while copyright law is made for information. But it’s also a problem, since getting a patent is a difficult and costly process, while getting copyright is free and automatic.

The TAPR licenses will only be really effective if the licensor possesses relevant patents, or at least if people can’t be entirely sure that (s)he doesn’t have any such patents. That’s a pretty bad limitation, since patents are difficult and expensive to get. Most peer projects will be unable or unwilling to apply for a patent, so the TAPR licenses will hardly be suitable for them.

Another unrelated problem of the TAPR licenses is that they require you to distribute the original designs you’ve received from others in addition to your own modified version—you must distribute both “before” and “after” versions of any files you’ve modified (§ 4.2 (b)). This might be extremely impractical for large version histories (think of hundreds or thousands of versions), and it makes the creation of printed versions of modified hardware documentation practically impossible. It’s also unclear what’s the point of this requirement.

Pragmatic Solutions: Just Use Standard Copyleft—Or No Copyleft Altogether

Most open hardware projects seem to care little about the specific issues of hardware licensing. Most projects aiming for copyleft just apply a standard license such as the GNU GPL or the Creative Commons BY-SA license, apparently either not knowing or not caring that is won’t apply to building hardware (see list of projects below).

Another solution is to forgo copyleft altogether and just use a permissive license such as the (modified) BSD license. This allows everybody to use the provided information in any way they like, without having to keep modifications or improvements open.

There even is a hardware-specific non-copyleft license, the Balloon Licence. The Balloon Licence is a simple MIT-style license. Since it does not try to apply any restrictions on the manufacturing of hardware (no copyleft or non-commercial clause), it doesn’t have the problems of other open hardware licenses. However, since this license is very similar to the commonly used MIT and (modified) BSD licenses and doesn’t address any new issues, there seems to be little reason to choose this special license instead of one of the standard ones.

What To Do?

As can be seen from the list below, there is a clear tendency of projects to use standard copyleft (the GPL or the CC BY-SA), protecting the design information itself but not any physical hardware built on their basis. Does this mean that projects are willing to live with a limited copyleft, or are they just unaware of the problem? I’m not so sure…

In any case, no convincing solutions seem to exist. The TAPR license, the only license that tries the address the problem of extending copyleft to the hardware itself, never became very popular—almost nobody outside the TAPR project seems to be using it. And indeed, its reliance on patent law makes the license very impractical to use for all but the biggest projects.

On the other hand, just using permissive licenses (like the Apache project and the BSD family do) doesn’t seem to be an attractive option for the majority of open hardware projects—most prefer to get at least the partial copyleft protection that standard licenses such as the GPL and CC BY-SA can give them.

But, as described above, their copyleft protection is very incomplete in case of hardware—hardware builders aren’t required to give back their improvements. In the case of the RONJA project, this difference between hardware builders not giving back but the project maintainers expecting them to do so, has already caused tensions that contributed to the downfall of the project. Whether similar problems will appear in other projects and weaken the open hardware community, remains to be seen…

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Appendix: Project Listing

The following projects use standard copyleft licenses:

Projects using a standard share-alike license that prohibits commercial usage (CC Attribution-Noncommercial-ShareAlike):

Projects supporting various Creative Commons license:

Projects using the TAPR Open Hardware License, a share-alike license designed specifically for hardware which relies on patent rather than copyright law:

  • TAPR, the community of radio amateurs which developed that license

Projects dual-licensing between TAPR License and standard copyleft:

  • Open Graphics Project, open source graphics cards; three license alternatives for its hardware descriptions (schematics and artwork): GPL, TAPR License, or a commercial proprietary license, cf. OGP FAQ and Announcement from 7 April 2009. Of course, dual/triple-licensing with TAPR as one of several options makes the special protections of the TAPR License void (users can just choose the GPL instead), so this multi-licensing model seems somewhat pointless.

Projects using a non-share-alike license specifically developed for hardware (the Balloon Licence):

  • Balloon Project, another circuit board (only parts of the design are free, some design files are kept proprietary)

Projects using a standard non-copyleft license (the BSD license):


  • OpenCores, develops computer components for CPUs, memory controllers, peripherals, motherboards etc.; uses a mix of GPL or (preferably) LGPL and modified BSD license, depending on the preferences of the contributors (OpenCores FAQ)

If I have forgotten important projects, add them in a comment and I’ll update the article. I didn’t try to cover projects that are small or in early development. Long lists of open hardware projects can be found in the Wikipedia article on open source hardware, the P2P Foundation’s Product Hacking page, the Open Innovation Projects site, the GOSH List of Open Hardware Projects and the GOSH List of Open Hardware Organizations.

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