CERN-OHL (CERN Open Hardware Licence)

The CERN Open Hardware Licence (CERN-OHL) is a legal tool developed by CERN, the European particle-physics laboratory, to promote collaboration among hardware designers and protect the freedom to use, study, modify, share, and distribute hardware designs and the products built from them. Software licenses such as the GPL were drafted for source code, and they map awkwardly onto physical objects; CERN-OHL is purpose-built for the "source" of hardware: schematics, PCB layouts, mechanical drawings, HDL, bills of materials, and the documentation needed to fabricate a working thing. First released in 2011 out of CERN's Open Hardware Repository, it was substantially rewritten as version 2 in 2020, and the v2 texts are OSI-approved.

The three variants of version 2

CERN-OHL v2 comes in three options that deliberately mirror the software licensing spectrum, so designers can choose their reciprocity level without inventing bespoke terms:

• CERN-OHL-P (Permissive) imposes minimal obligations, essentially attribution and notice preservation, and allows the design to be used in closed products. It is the hardware analogue of a permissive license like MIT.
• CERN-OHL-W (Weakly Reciprocal) requires that modifications to the licensed design itself be shared, but allows the design to be combined with separately developed components kept under other terms, comparable in spirit to the LGPL. This suits designs meant to be embedded as modules inside larger, possibly proprietary, products.
• CERN-OHL-S (Strongly Reciprocal) is the most protective: any product or derivative that incorporates the design must make its complete design source available under the same license, the hardware equivalent of GPL-style copyleft. Improvements cannot be taken private.

What makes hardware licensing different

Copyright covers the design files, not the physical object built from them, so a hardware license has to work through the artifacts it can reach: the sources, the documentation, and the act of conveying products. CERN-OHL v2 handles this with careful definitions, "Source," "Complete Source," "Product," and a notice mechanism that travels with fabricated items, and it addresses patents with an implicit license from contributors, one of the sharper risks in hardware that software-era licenses handled poorly. The practical upshot for a builder: if you sell a board derived from a CERN-OHL-S design, you owe your customers the complete, buildable design source, not a marketing schematic.

Why it matters for open mining hardware

Open mining hardware is one of the healthiest corners of the open-hardware movement, and CERN-OHL is common currency there. Bitaxe-class single-chip miners, open controller and carrier boards, and PSU breakout designs circulate as published design sources that anyone can fabricate, audit, and improve, and reciprocal licensing is what keeps that flywheel turning: a shop that improves a community board design must publish the improvement, so the commons compounds instead of leaking into proprietary forks. D-Central builds on this tradition deliberately, our DCENT_axe stands on the shoulders of the open miner designs that came before it, because auditable hardware is the physical-layer half of "don't trust, verify." When choosing a variant, designers weigh the same trade-off seen in software: maximum adoption under permissive terms, or guaranteed downstream openness under reciprocal ones. For hardware whose trustworthiness is the product, the reciprocal variants make a strong argument.

Compliance, in practice, is about keeping the design source attached to the thing. A builder distributing CERN-OHL hardware ships or links the complete source files, preserves the license text and copyright notices within them, marks modified versions as modified, and, for the reciprocal variants, publishes changes under the same terms. The license even anticipates the realities of fabrication, allowing notice on the product itself or its documentation when silkscreen space runs out. None of this is onerous, and that is the point: the license was written by people who actually build instruments, for people who actually build boards.