[sdiy] More Theremin - WHY??

[harrybissell]

My frequency is more like 1MHz. Maybe I should lower that some.  Using the
4013 as a detector is a little strange... but maybe that is my problem.  I have
no filter at all.

The 4013 is actually a phase discriminator (I figure :^)... it will output a
square
wave at the difference frequency by alternatly locking a high or low depending
on the status of D and Clock inputs.  It looks like it also had some
metastability
issues when the pulses are exactly equal... looks like some spurious triggers
at the nominal 1MHz clock rate.

I have what seems to be a 100mH choke in the circuit as antenna decoupling. Used
an aluminum
chassis to shield any RF entering the box.  Still I seem to be getting RF
rectification
in the audio output.  Oh well, like they say "Today is a good day to diy...."

H^) harry

Grant Richter wrote:

> 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