Looking for a simple proximity detecter with good range

Hi folks,
While not specifically about theremins, I thought someone here may be able to help.

Im looking for a relatively simple proximity detector circuit, with a range of at least a 2-3 feet. It's for an interactive sculpture that Im working on. I just need a pulse high (or low) when a viewer passes through the field, so a digital circuit is fine. I want to keep it pretty inconspicuous, and dont want to have to use externally mounted sensors, like ultrasonic, pir,etc.
So far Ive tried this:http://electronicdesign.com/article/analog-and-mixed-signal/Capacitive-Proximity-Sensor-Provides-Accuracy-And-Speed.aspx

For five components, this works ok, with a modest range of about 6" But I definitely need more "oomph." Was thinking about using the volume circuit from an etherwave/em modded for a positive cv out. I think that range-wise this will be good but maybe overkill.
You guys have any suggestions? I'd like to keep it pretty simple and avoid surface mount stuff as much as possible. Anyone build any of the simple digital theremins schematics out there? Any of them have a decent range?

Thanks

Hello Chobbs,

I respect you as an excellent builder, so if you don’t get a response from others to your request that you're happy with over the next few days I will share with you some of my info which I will gather together. My prerequisite is that you know how to use a PDF printout to iron-on or make your own circuit board and are willing to spend about $50 in components from Mouser.

My circuit board design uses stable Hartley Osc heterodyning and a remote tuning Pot (mount the Pot up to several feet away) which will give you excellent sensitivity. This board layout can be an ideal stand alone theremin volume control 10" shading, a 9 volt proximity Schmitt triggered square wave output or an adjustable line level output for a pleasant sine wave pitch only theremin, plus other interesting possibilities.

I don't have time to make a proper webpage for everyone else or answer multiple public emails as most of my construction time is already helping other people with some interesting theremin technical approaches.

Chobbs, so you’re a sculptor, I wish we were in the same neighborhood, I just got a quote from a local sculptor from San Diego State University to turn an old oak log into an object of art to contain one of my theremin projects but he wanted $5000, he is very good. I could help a lot of people with that amount money so I will hold out and see what the next bid or commission might be.

If you are “Lazy Dreamer” I have your email address.

Christopher

Hi Christopher,
Thanks,
Would you please email info on your circuit...yes, Im "lazy dreamer" though I havent updated that site in a while.
charbot at gmail.com

BTW- Im going to have a sculpture in a San Diego gallery (a robotic 'ghost' that roams the gallery space)...I think it opens Oct 18. If you're interested, check it out. Not sure of the address right now. I still have to ship my work, so Ill post an update when I sure of where it is going.

Hello All,

I threw a party for Chobbs but he never showed up?

Maybe his email rejected me, hope he is OK, he is a brilliant young man.

In case anyone was wondering....
I went ahead and used the volume circuit from an EM/EW- and it works great! I can get about 4-5 feet easy, maybe 6-7 when its all tuned just right and not sitting on my junk cluttered bench.

I just took the volume part of the circuit (Q 6-8, 2nd half of IC 1 and associated components,

reversed the response and converted to a 0-12v CV output (as described in the "Hot Rodding" manual.

I have the Cv out going to a voltage divider pot( to fine tune) which triggers a transistor to drive a 12vdc motor.

Really works great. the response is not linear..... good for on/off type of detection.
exactly what I needed.

As with all my other EM theremins, I hand wound the variable inductor with good results. I bought a bunch of cheap NOS surplus variables a few years back. I just cut off the original windings and use the form.

Ill try tp post a photo soon.
Charlie