[sdiy] More Theremin - WHY??

[Grant Richter]

There was a design in some magazine that used two 4046s to make a Theremin.
One formed the fixed oscillator. One was used as the variable oscillator and
the XOR gate was used to generate the audio difference tone from the low RF
sources.

The antenna connects directly to one of the cap pins on the 4046 oscillator
through a 60 milli Henry choke. I've tried frequencies from 100 kHz to 500
kHz. Some where between 200 kHz and 350 kHz seemed to work best.

Adding another 4046 locked to the audio side tone produces a control voltage
from 0 to 10 volts. A single pole low pass filters out the high band from
the XOR gate. The XOR output is a square wave which feeds the final 4046
nicely.

> From: harrybissell <harrybissell at prodigy.net>
> Date: Sun, 22 Aug 2004 18:28:32 -0700
> To: synth-diy at dropmix.xs4all.nl
> Subject: [sdiy] More Theremin - WHY??
> 
> Howdy all...
> 
> I'm playing with the U. Glasgow 'digital theremin'.
> 
> I added an RF choke at the suggestion of Grant Richter... it helps quite
> 
> a bit. Put the thing in a metal box... that makes it a lot more stable.
> 
> For a detector, I'm using a 4013 a'la "thereminvision.com"   The range
> of
> this thing is in the very high audio / ultrasonic. I plan to get a CV
> from it
> (eventually).
> 
> Listening to the audio output, there is MASSIVE noise at very low
> frequencies...
> its possible that it is getting some FM interference. As I move my hand
> closer
> the noise (jitter) decreases.   But WHY ???
> 
> Here's a good idea (from the Etherwave)... make the oscillator without
> the antenna
> the variable one... this way you can tweak the pot without screwing up
> the variable
> osc.
> 
> In a finished product, I think you would need a remote variable
> resistance... tough
> trick at 20pF   :^P
> 
> Trying to make a multi-axis theremin controller by using multiplexed
> detectors... might
> be pretty hard.   ThereminVision uses the LMC555 which might be more
> stable than the
> CD4093 I'm using... but 4093 is in stock :^P
> 
> H^) harry