Even though it is Faringdon, there are a lot of places out there which try to pretend the most "public domain" of circuitry can be described as "trade secrets".
+1 for this. Also, I've seen many misconceptions about copyright and patents, including on engineering forums. For example, an engineer may say a circuit design cannot be used here because it's still "copyrighted" (Marco Reps made this mistake in a video), or that the theory of operation of a circuit cannot be described or unknowable because it's "patented" (On another forum, I've seen an engineer who refused to explain the actual circuit in a Fluke voltage standard, and instead used a substitute instead. There are many valid reasons for refusing to explain it, but not because it's patented, you absolutely have the right to do this).
CopyrightCopyright only applies to the particular representation (e.g. drawing or writing) of a fact, not the fact itself. So a particular engineering drawing is copyrighted, and it's often a copyright violation to copy the original drawing. But it's underlying circuit netlist, topology, design, or even component values are not. Everyone else is free to replicate the same circuit independently. As long as the original drawing is not copied, copyright does not apply and is not violated. This is the entire legal basis of reverse engineering. And in some cases, even if the original drawing is copied exactly, it's still not a copyright violation due to
- Merger Doctrine - if the particular expression is the only possible way to express an underlying idea, this expression is essentially the idea itself, and one cannot claim its copyright. If I invented the common-emitter amplifier, I cannot claim I have the copyright of its drawing and stop others from drawing the same topology.
https://en.wikipedia.org/wiki/Idea%E2%80%93expression_distinction#Merger_doctrine- Fair Use (for example, if only a limited portion has been copied, and it's used for commentary or educational purposes, in such a way that the interests of the original copyright owner is largely unaffected - this is why you usually have the right to open a service manual, and making a video to explain how a particular subcircuit works).
https://en.wikipedia.org/wiki/Fair_use- Functional object. In some special cases, even a 100% copy is not necessarily a copyright violation. VLSI layout belongs to this category. Under standard US copyright laws, the circuit layout itself may be a copyrightable drawing, but the layout as it appears in a photomask of a chip is a functional object to create chips, not an artistic work of drawing, thus in some cases, it may be copied without violating copyright. It was exactly why the US semiconductor industry lobbied Congress back in the 1980s to create a special kind of "chip layout copyright" to cover this application, since "conventional" copyright is too weak. (P.S: Interestingly, following the same argument, it can be argued that PCB layouts, in many cases, can also be 100% copied without violating copyright, but nobody has lobbied Congress to create a similar kind of copyright, I suspect it was because the costs and stakes are high for chip makers, but are still too low for PCB makers so nobody in the industry bothered to do that).
https://en.wikipedia.org/wiki/Integrated_circuit_layout_design_protectionPatentsA patent is attached to abstract ideas, such as a circuit topology or design. By obtaining a patent, the patent owner gains exclusively rights to prevent others from replicating the same design without authorization, no matter whether copying is involved or not. But, at the same time, the design itself becomes public. While you're prohibited from replicating the device, you're allowed, and even encouraged to learn and discuss how the invention actually works (which is the very purpose of patent laws). And once all relevant patents have expired, the design enters the public domain and becomes free for all.
Trade SecretsAnd both are different from trade secrets. A trade secret, by its definition, is not patented. Making a design to be a trade secret instead of a patent is actually a rather risky decision, since once the trade secret has been rediscovered by a 3rd-party through legal means (such as reverse engineering a sample, or independent rediscovery), it automatically enters the public domain upon publication. But on the other hand, the benefits are: you can keep the design secret, you don't have to publish the design, and it doesn't have an expiration date. If the design is mysterious and arcane enough, it can last a really long time as a secret. For example, Tektronix's T-coil design equations for oscilloscope vertical amplifiers remained a secret for many decades.
https://www.electronicdesign.com/technologies/analog/article/21807815/whats-all-this-tcoil-stuff-anyhowConclusionIn conclusion, every hobbyist and engineer, including your competitor, has the right to understand and discuss how a circuit works, based on legally-obtained samples and information. Don't say one can't talk about a circuit because of "patent", and don't say one can't use a circuit because of "copyright"... And 90% of the circuit boards you see in everyday life have no secret.