@Thierry:
That has to pay back, I have four little daughters to feed. Thus I simply cannot give it away for free.
It's making enough money to support a big family? Wow, I'd figured that it was the niche of all niche markets and you'd be lucky to sell ten or so in as many years.
That's also why I'm not too happy with dewster's early publishing of something which might appear as something similar at a first glance, at least in the eyes of a so called "noob".
I use the term endearingly. Like RS Theremin says, no one builds anything anymore, they're too busy texting. I have books that show you how to grind and lap your own telescope mirror! Once upon a time there were multiple people per block grinding and lapping away in their basements once they saw their neighbor's great newtonian in their backyard. Before the great distraction set in.
Perhaps if you demonstrated your mastery of Theremin engineering by revealing your circuit and explaining what it does, how it does it, and how it's a one-size-fits-all solution to the EWS woes, that would help your prestige in the field and boost sales. Anyone that was going to buy one almost certainly still will, and some who weren't going to buy one might change their minds. At the moment it's just a black box to me, that's mainly why I wasn't interested in buying it (well, that and I'm unemployed).
If one is building anything that makes decent money one will develop competitors, and they will likely reverse engineer what you make, so the only people who don't know how well you design and build your stuff is your customers - which is a crazy situation! Industrial secrecy is at best pointless IMO.