Want to build a theremin - question about antenna placement

I'm working on an oddball project: I want to construct a science-fictiony hand-held scanner device that will have me scanning people and objects with a theremin antenna.

I want to have a box hanging near my waist that would house the electronic components. I want to have a hand-held device that looks like a satellite dish with a theremin antenna protruding from it. And I want the box and satellite dish to connect via flexible tubing.

I have never constructed a theremin (I am leaning towards Minimum Theremin Kit 101 at HarrisonInstruments.com (http://harrisoninstruments.com/101/101_description.html)) and I'm not all that electrically knowledgeable.

Does this sound possible? Looking at the assembly instructions (http://harrisoninstruments.com/101/101_assembly_instructions.html) for the kit I am considering I get the impression that the antenna needs to be connected to the PCB with a wire 8" or shorter. I was hoping to use a wire that is two or three feet in length. If this doesn't sound doable, are there any kits that would make it doable or are there any finished products I could disassemble and reassemble my way?

Scanning people via a Theremin and with the antenna being hand-held might work, there are some disadvantages. A nice solution might be an optical Theremin with the 555 Timer IC as the heart piece. It works with a photoresistive element (LDR). It is an easy build with just a few parts. The "antenna" could be a thin tube, where the LDR is being placed in. This of course will react on light intensity (and so color) changes only. In any case, the audience will have an imagination caused by your acting with the antenna and the audible result. You also could override the LDR by a hidden potentiometer.. this might be worth a try for your pupose, i don´t know..

I would second that opinion about using an optical method rather than RF. The RF method is a bit to finicky for your project. And I gather you are more interested in making "spooky noises" than music, right?

Another thing you might want to try is to use an infrared photocell. That would respond to different temperatures. So a person's belt buckle, for instance, might be colder than say their face or hands. Maybe even an IR photocell and a temperature sensor (thermistor for example).

Temperature sensors are usually a bit slower responding than IR photocells, so it might make for an interesting effect. The IR starts at one frequency and the thermistor kicks in slightly delayed ... indicating a "deeper probe" maybe?

Don

Where would I find things like you both have described? And more importantly, will the be buildable by a guy with novice skills?

Smirnov Theremin Sensors (http://asmir.theremin.ru/tsensors_sch.htm) gives schematics for having a Theremin 'sensor' remote from the mixer / audio output.. This would get 'round the problem of long antenna lead..

The actual 'antenna' could be a metal disk or whatever. I agree with the others in this thread, that 'Theremin' (capacitive) sensing may not be best for this application - but you have a problem with all the technologies if you are not able to work out the required circuit (and perhaps more importantly, do the debugging) yourself.

Getting noise of some kind from a Theremin type circuit as you approach the victims body parts, should not be too difficult ;) .. you could actually do this probably easiest with a 'Glasgow Digital Theremin' circuit.. this could be built on a small board in the 'hand-held' part of the 'scanner'. I will paste links here when I find them -

see last 3 postings on this thread: here (http://www.thereminworld.com/forum.asp?cmd=p&T=3906&F=1&p=3)

Have just drawn up a quick schematic based on the Glasgow front-end..
startrek.gif (http://www.therasynth.com/assets/images/startrek.gif)

Temperature sensors ...

Here's the datasheet from National Semiconductor for a simple device:

http://www.national.com/ds/LM/LM35.pdf

Try building some of there application circuits with it to get a feel for how this part works.

They discuss a bit about how to make a remote probe. So you can build your sensor part first, set it up to output a useful range of voltage vs temperature, then build a voltage-controlled oscillator circuit to turn that temperature change into frequency change.

That might be all you need for your application.

Good luck!
Don

Here's another idea..
small audio amplifier (IC or module - cheap modules and kits for this sort of thing are available).. small directional piezo microphone on the input, speaker arranged so that when microphone / speaker are close to an object, audio feedback occurs due to reflected sound.