theremins

[Grant Richter]

One trick I used successfully comes from a hobby magazine circuit (don't
remember which one).
Take a CD4046 PLL chip and tie the VCO control line to +V. Program the RC
values to give a fixed
oscillator in the range of 100kHz to 400KHz. Attaching an antenna to one
leg of the timing capacitor
will give a usable range of six inches or so from the antenna. Another 4046
can be used to turn the
varying oscillator frequency into a control voltage.

The problem is the coupling to the antenna. The theremin design uses large
inductors to decouple
the antenna from the oscillator and give a much smoother and longer control
range. As I recall
the output variation from the 4046 circuit running at 350kHz was about
25Khz from full contact
to about six inches away. The Big Briar Etherwave runs about 162?Khz and
changes about 2Khz
for twenty four inches of motion near the antenna.


Two 4046's can be used to make a direct conversion unit using the 
EXOR gate in one as the RF mixer. Nasty sounding square wave though,
and the same problem of excess range over too short of a distance.
It doesn't get much cheaper or simpler than a 4046 as a good place to
start experimenting with a home built proximity controller. The same
principle of
decoupling the antenna with large L values (60 millihenry?) would apply.
Even a 2Khz variation in RF oscillator output could be scaled with the 4046
circuit to give 0-10V over a usable range.

Electronotes issue #111 page 12 has an article by John Valente with two
designs
for Body Proximity controllers.

----------
> From: Arthur Harrison <theremin1 at worldnet.att.net>
> To: DIY <synth-diy at mailhost.bpa.nl>
> Subject: theremins
> Date: Thursday, December 10, 1998 7:48 AM
> 
> Travis wrote re: theremins:
> 
> >i'll hear your ramnblings quite gladly...i'll b up for making one of
these
> >beasts soon
> 
> I write:
> 
> Paul Perry and I were chatting about various theremin topologies,
> of which there are many, and many more to come, for certain.
> 
> For many synth DIYers, the objective is to use Leon Theremin's concept
> as a gestural controller for VCOs, VCFs, triggers, etc.  Of course,
> the instrument can also be relegated to its original form as a
stand-alone,
> voiced entity.  This topology is often referred to as a "heterodyne"
> theremin,
> where two RF oscillators, one fixed and the other varying per hand-
> capacitance, produce an audible beat frequency.  For those interested in
> such a basic implementation, I humbly refer you to my recent article at:
> http://home.att.net/~theremin1/SWTP.htm.
> 
> This is quite a nice little theremin which used the 1967 Louis Garner,
Jr.
> design
> as a starting point.  Since many of the folks on this list have hardware
> resources,
> perhaps some of you will try it.
> 
> The nice thing about this design is that it only uses less than 10mA from
a
> standard 9v  battery, and will thus run for hours, and is highly
portable.
> I am planning  another theremin for web publication soon, and it will be
> more
> signal-processing oriented, e.g., will employ a "double-synthetic"
topology
> whereby the voice is a VCO, not the actual heterodyned signal.  This one
> will
> be readily adaptable for CV applications, and have some goodies like a
> linearization circuit to even-out the pitch spatial relations.
> 
> In the meantime, I hope some of you will review the above mentioned, and
> give
> me some feedback!  If this theremin prompts enough response, I may make
> some blank PCBs for distribution.
> 
> Art in thereminland
> 
> 
> -----Original Message-----
> From: Travis Endersby <travis at it.net.au>
> To: Arthur Harrison <theremin1 at worldnet.att.net>
> Date: Wednesday, December 09, 1998 5:26 PM
> Subject: Re: theremin problems!
> 
> 
> >i'll hear your ramnblings quite gladly...i'll b up for making one of
these
> >beasts soon
> >
> >ta
> >trav
> >
> >On Wed, 9 Dec 1998, Arthur Harrison wrote:
> >
> >> Cool, Paul.
> >>
> >> (If anyone is interested in my theremin ramblings,
> >> just let me know, and I"ll CC my rants to the list.)
> >>
> >> -Art
> >>
> >>
> >> -----Original Message-----
> >> From: Paul Perry <pfperry at melbpc.org.au>
> >> To: Arthur Harrison <theremin1 at worldnet.att.net>
> >> Date: Tuesday, December 08, 1998 9:55 PM
> >> Subject: Re: theremin problems!
> >>
> >>
> >> >Thanks Art! I feel much less lonely now!
> >> >
> >> >If nothing gets done on this soon, I might go to a digital approach,
> >> >actually counting the pulses and working from that.. the figs seem to
> work,
> >> >just! (500KHz and a PIC)
> >> >
> >> >paul perry melb aust
> >> >
> >> >
> >> >
> >>
> >
> >