Theremin Thermal Drift will be an issue on a project like this.

DC 12V 4 Channel Voltage Comparator Stable LM393 Comparator Module

This one is a 4 channel versions. $12 At Ebay, Amazon and Banggood, I ordered one to try out, I can see the potential here driving this off my 12 volt dc controlled ramp theremin output voltage. 

From the first Post I thought you wanted theremin control over external peripherals switching on higher voltages, like driving a lamp-On facing towards Tower Art or photos, On/Off at a predetermined hand distance adding a RF theremin oscillator board. 

Christopher

I don't think I follow you...

that looks like it takes a voltage input...  I'm looking for a schematic, where I can create a control voltage output, generated from human interaction with an antenna... hence looking for a theremin schematic that gives me control voltage output instead of audio out.

I just need to get a control voltage output... once I have that output... I'm already golden from there... the circuitry and computer programs have all been written to work with the control voltage.

I just need to generate the control voltage output... ideally without having to build an entire etherwave or theremax circuit...
looking for a circuit that does not generate audio output or have various waveform, brightness, or velocity controls.

[EDIT] Take the volume side of a Theremin, which almost always generates a voltage somewhere to feed to a VCA.  This is usually an LC oscillator driving a second LC resonant circuit (passive or active), then detected (clip, 1/2 wave rectify, or full wave rectify) and low pass filtered.

If you have a way to precisely adjust the drive frequency, the absolute simplest method is to feed an LC tank & antenna with a fixed frequency (square wave will do fine) and then detect and low pass filter the result.  An FPGA NCO is the obvious choice for drive, but a PWM processor peripheral might work too.

If your system can use a serial data stream in place of the analog voltage, you might try livio's Theremino boards: http://www.theremino.com/en/, specifically the CapSensorHQ: http://www.theremino.com/wp-content/uploads/2012/02/Slave_CapSensor_Datasheet_ENG.pdf

I wonder if the Bob Moog archives still have a circuit diagram for his CV only theremin controller.

http://www.thereminworld.com/Article/15193/flashback-big-briar-model-500-theremin-controller

oldtemecula: Where you live is similar to Elsa in Frozen

Xoadc - I am looking for a circuit design for a CV output only theremin. 

oldtemecula: The most practical and compact way to meet your need is to hire Thierry to draw the schematic, RF Osc to CV out, then route it and output Gerber files for you. This should be less than a day’s effort. If you go commercial boards a two sided should work fine and cheap. If you were etching your own boards I would do a one sided PCB as the layout is not complicated.

oldtemecula:When etching your own boards what method are you using? You might be creating a monster.

oldtemecula: With Arduino and Theremino boards there should be something on YouTube to demonstrate your concept?

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oldtemecula: 

I have a few questions, my not being a musician or engineer can anyone answer these below

What is a practical minimum distance of the hand to the antenna/sensor for the positive CV voltage to start increasing? As seen in the youtube video below the distance is limited.

Does Control Voltage = 0 to 5 volts at 0 to 5 khz with a positive tip on a 3.5mm mono TS plug?

What is needed on the Xoadc project, some CV can be 0 – 10 volts

What happens when 0-10v CV is used accidentally on a 0-5v CV input? 

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         Xoadc your video is restricted from view in the USA

http://en.daily.vice.com/videos/the-spooky-stories-behind-canadas-maritime-shortwave-radio-towers

Christopher

David Young in this video below used a Theremaniacs Pitch Only Theremin in his early designs, he may still.