Can you change a theremin from capacitance control to inductance?

I have a music class project to create a new instrument and I picked making a new electrophone. I have been looking at simple instruments based with electricity, and obviously the Theremin ranks up at the top.

In order to make a new instrument, I was wondering if I could change a Theremin to use variable inductance to control the pitch rather than variable capacitance. In this way, I'd create an instrument where moving a coil along another coil would control the notes being played rather than using the body to make music.

Is this even a feasible idea, or should I go back to the drawing board? I am fairly good at soldering and circuit building, but don't have much theoretical electrical knowledge. I am sure I could build it if I can figure out how the circuit operates, but I don't know how to modify the circuit to allow inductance control instead of capacitance control.

Any help or alternate ideas would be appreciated.

It sounds like you're looking at building something along the lines of a tannerin, or an ondes martinot. Mabe even a theremi cello, or persephone.

There are several great folks here who can really hep out with the technical side of these instruments, but basically, the above instruments are what you would be looking at for your project.

Welcome aboard, and good luck.

I have actually found a much simpler design that controls the pitch using variable resistance instead. I am planning on linking 3 together such that I can get some harmonics going. The link if anyone else finds this post useful is http://www.paia.com/bckit1/getitfrompaia.asp

It's very simple and oh so cheap to experiment with.

There are lots of ways to build an oscillator. Theremins of the heterodyne type use inductors and capacitors in a Hartley, Colpitts or similar circuit. The antenna allows you to affect the oscillation frequency of one of the oscillators. The audio part is obtained from the interaction of a fixed oscillator and the variable oscillator ... do a web search on heterdyne and you can learn all about it.

If you want something controlled by resistance change, you can just build an audio oscillator with a pot used to change the frequency ... of course you could just go buy an audio oscillator that already does just this, but where's the fun in that?

The "digital" theremins -- called that because they used CMOS digital parts are not so musical, but you can definitely change the frequency with a pot. You might look into circuits that use the Intersil 8038 chip. This link has a circuit using one: http://www.mitedu.freeserve.co.uk/Circuits/Testgear/funcgen.htm

With a function generator chip you can choose between waveshapes -- sinewave, triangle, squarewave. The difference in sound based on waveshape would make a nice project for you.

Don

"In order to make a new instrument, I was wondering if I could change a Theremin to use variable inductance to control the pitch rather than variable capacitance. In this way, I'd create an instrument where moving a coil along another coil would control the notes being played rather than using the body to make music."
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If you take a conventional LC oscillator as found in a Theremin, and vary either the L or the C (or both), the frequency will change.

If you took a Theremin, disconnect the antenna, fit a capacitor (about 20pF?) fron the antenna connection to ground, and then find a way to change the inductance of the pitch coil manually, you should be able to "play" the instrument...

BUT - Why waste a Theremin? .. Get a simple "Metal Detector" circuit.. the ones which change pitch as you approach a metal object.. these are effectively acting by the change the metal makes to the inductance and/or coupling on the sensing coils..

Put some iron rings on your fingers, and you might be able to play this!

(PS.. I have not done the above - so have no idea how plausible it is!)

I visited a sonic installation by Ray Lee (http://ah.brookes.ac.uk/staff/details/lee/) last year. (Ray Lee works with theremins, related devices and rotating sound sources) One of the artworks was a metal detector mounted on a rotor that emitted a variable pitch as it passed near some metal objects placed around it.

"a rotor that emitted a variable pitch as it passed near some metal objects placed around it."

Sounds like a great idea.. one could even expand on this, have 2 detectors on the rotor, one for pitch, one for volume - hey, how bout a 3rd for harmonics.... then one could have a musical sequence 'programmed' by the placement of metal objects... If the rotor was in the centre of a table, and there were (perhaps skittle shaped) objects (perhaps color coded for pitch, volume, harmonics) with the placement of the metal on the correct vertical plane to interact with the apropriate sensor.. one could then have people moving the skittles and collaboratively creating music.....

I have seen a fancy table top synthesiser with virtual objects people can move, and a display in the table (Extremely hi-tech and no doubt astronomically expensive) - But the skittle idea could probably be put together quite cheaply..

Want a new musical instrument based on inductance? This one would probably be a worthy first year university project..

Theremin Harmonograph (http://www.metacafe.com/watch/1089563/build_a_harmonograph/)!