Patents are a problem when designing a theremin?

Hello all,
I plan to design, as many here, a theremin.
My idea is to work around standard ideas (heterodyning for pitch, measure resonance for volume), but trying to bring those good ideas to current technology.
My question is: how much of my effort would violate existing patents? What should I be aware of?
Thanks a lot.
Regards

At first I would try to get the original Theremin patent files in order to see, what exactly has been copyrighted more than 70 years ago.

It was first patented in Germany on December 8th 1924, and in the USA on December 5th 1925.

There is a transcript of the US patent here: http://www.sagebrush.com/therpat.htm

Interesting that Theremin does not refer to the pitch rod and volume loop as antennas but as electrodes. The only use of the word is to note that they do not operate as antennas.

Hmmm... my English, you know... but if I understood well, every Theremin and -like circuit, be it built by Dr. Robert Moog, George Pavlov, Art Harrison, Anthony Henk, Jake Rothmans, Fred Mundell etc. makes use of this patented technology.

May it be that the patent has in the meantime expired?

Thank you Gordon.
I'm also surprised that the original ideas are patented. Would other manufacturers/designer have a permission?
Because if *that* is patentable, I'm sure someone else has a patent that is in force.

According to Wikipedia (so don't quote it in a court of law as a reliable source!)

"a patent provides the right to exclude others from making, using, selling, offering for sale, or importing the patented invention for the term of the patent, which is usually 20 years from the filing date"

I think the term on the theremin patent probably expired some time ago.

First thing.. If you make less than about 10, dont worry about the LEGALITY regarding any patent, design right, or copyright.. no one will bother you! - So following comments really only apply if you plan to go into production..

All the original patents for Theremin technology expired many years ago..
But beware - there are newer patents which cover improvements to capacitance sensing, and if one deviates at all from the original heterodyning ideas, you could fall foul of these.
One of the surest ways to be safe is to file a patent application on what you are doing, and proceed with this appication up to the search stage.. this is not cheap (cost me £300 for one dud idea) but it does return everything relevant, and one gets the advice of the patent inspector thrown in 'free' (or, at least this applies in the U.K. - dont know about elsewhere)..
One can also undertake a patent search yourself - but you need to know exactly what areas to look at.. If you go through your patent office, they are looking (or SHOULD be) for causes NOT to grant a patent.

Having said all the above, I think it really does depend a bit on 'luck' and on how strict your patent inspector is.. I have seen patents go through the whole process and be granted, when there was a clear 'prior art' making the patent unworthy of the paper it was written on.. This is failure on the part of the inspector - but one has no legal recourse.. I examined one patent presented to a client by an elderly inventor who had spent his lifes savings obtaining it - The patent was worthless (in fact, it infringed an existing valid patent)
Also, remember.. Even if you do find an active patent which would stop you, do not assume that just because this patent has been granted it is REALLY valid.. I have been told by an international patent agent I had the good fortune to meet, that about 10% of all patents granted can be thrown out as they are invalid - and that certain countries have a record of granting a even larger number of invalid patents.. The U.K. France and Germany are among the strictest, but because of the differences in procedures in different American States, quite a high percentage of American patents are weak.

There is only one real danger - Some 'borderline' ideas are patented by companies who have no intention of ever producing product.. They sit back and watch for similar patents being granted, bide their time, then when the 'victim' is in full production they make their move, demanding huge royalties retrospectively.. There are moves to outlaw this practice, but it is difficult - a bit like cyber-squatting.. these 'squatters' usually have strong legal resources and can squeeze the life out of a victim. There are now legal companies who make their living by taking on the 'squatters'.....

Thank you everyone for the comments, and thank you Fred for your extensive experience sharing, I appreciate it.

I would strongly suggest you go build a "standard" hetrodyne theremin before going off to re-invent the world. It is quite the exercise in humility and you will see what things affect other things.

Many think the theremin design screams for improvement, but come to find out there are non-obvious reasons for the way some things are put together.

Probably the best thing is to buy a kit from PAIA, assemble it and tune it exactly as they recommend, then tinker with the finished unit to learn more about theremin operation. That will get you to where you want to be faster. I don't think there's much to argue about that design vs another design for gaining a basic understanding, and in the near and short term you will end up spending less money than starting from scratch.

One thing you will stumble on almost immediately if you start from scratch is "ok, is it seems to be doing something, but what SHOULD it be doing" . Another is trying to understand what parameters to design to. At the onset it seems simple enough ... 2 RF oscillators beating against each other at some mid-AM band frequency, peak detector and filter to sort out the modulation (i.e. audio frequency occurring from the difference of the 2 oscillator frequencies). But it's those non-obvious things that you learn that are either not specified, or are not easily specifiable as design criteria.

That's my take on it.

Don

Thank you Don!
I did build an EM Theremin/Etherwave from scratch, and is working just fine. And you're absolutely right, I only understood it after fixing all the problems that emerged.
I do believe a theremin IS an hetherodyne. I won't attempt anything different in this respect. Not because I think it's the only way to make an instrument to sound by moving hands, but because it's what I want to do. Hetherodyne is where the whole idea comes from, rather than a solution devised to a purpose; my feeling is that it's a key concept.
I don't think the "clasic" theremin needs a lot of improvement. To my liking, the etherwave is a beautiful design. However, I think it's too constained by 1) cost; 2) 90's technology.
And today we have a many professional players who generally would like more stability, linearity and range. Personally I'd like to have the tone quality of original theremis (and yes, whithout any "digital" cheating! :)
Cheers