Extending Antenna's Hand Distance detection

Jestern,

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The distance you need cannot be done with the theremin principle.

In my early research I did something like you want using Ultrasonics. My interest was volume control but it was a bit to sluggish. Pitch is normally a slower process.

I could see Ultrasonics working in your application, can you solder?

There is a spot on the PCB below where the voltage rises and falls due to the distance of an object. Use this variation to control a generated pitch. Stick an antenna on top to make it look theremin like, no one will know.

Schematic PDF          Product

This might be a better approach for a kids theremin in a museum, I will call it the Altermen. (Alternative Theremin)

Hi jestern,

You would be dealing with extremely tiny capacitance changes in an electrically and magnetically noisy environment.  You might be able to make something you can play from ~1m away, but only with larger plate antennas, very stable oscillators, hum filtering, and lots of averaging / low pass filtering - the last of which would probably make the gestural response very sluggish.  You could probably tailor the filtering based on the hand distance to make it response degradation less intrusive / more playable in the normal range, but >1m is definitely in the diminishing returns zone of hand & finger position data acquisition.

The useful maximum playing distance also depends on how you intend to play.  My prototype seems to respond to my pinky finger opening and closing at ~1m, but if I "play" by waving my arm around the response distance is obviously somewhat larger.  Moving my body around gives several meters of response.

[EDIT] And, as Christopher points out, at these larger distances you should probably be looking into alternative technologies to LC capacitance sensing.

Hi Oldtemecula, thanks for your reply, yes I can solder. I can try this. Is it reliable for 22 feet? I can use the input to control other parameters if it is stable... and reaches 22 feet actually.

Dewster I want to use it with dancers so body is more important than pinky.. it seems that your protutype could be interesting for us. Are you willing to tell me how you modify the original design or share your design? Or at least what modification you added?

Thanks for the answer guys :)

jestern, my main stuff is described (ad nauseam) over on my digital Theremin thread.  It's been going for years, and it's kind of all over the place.  Even with large plate antennas, I'm thinking maybe capacitance sensing isn't the best way to go for longer distances. Sonar, modulated LED reflection, or one of those X-Box IR spots + camera (Kinect) interfaces might be more what you're looking for.

An interesting concept.  Are you hoping to sense the bodies of multiple dancers or just one at a time?

Other pitch control techniques might be preferable.  For example, reflected light (infrared or visable) from the dancers could be used for a voltage controlled oscillator.

Multiple plate antennas below the floor of the stage might be used for traditional theremin design. The distance from the antenna of the feet of the dancers would fall into the range of detection.

Others here might have additional ideas.

edit: I see dewster beat me to the answer. Great ideas.  I like sonar. Easy to build and cheap, especially with 40kHz transducers.

jestern said:  Hi Oldtemecula, thanks for your reply, yes I can solder. I can try this. Is it reliable for 22 feet? I can use the input to control other parameters if it is stable... and reaches 22 feet actually.

You keep moving the goal post, you first said 3 or 4 meters and now we are up to 6m or 7m. If you want to monitor dance then I would have ultrasonics pointed down from overhead. Not knowing what  the response triggers or what kind of dance I would also place cameras on the bottom side or underneath looking up.

Christopher