Theremin-Controlled Voltage

[John Egerton]

Hey guys...

Anyone have any stupidly simple schematics for a theremin based voltage controller?  

Thanks in advance..

John

[bioroids]

That would be very nice, but I dont think the circuit would be so simple...

Luck

Miguel

[John Egerton]

I was only joking  

I'm basically lookign for something with few parts, kinda like 1 or 2 IC's

Thanks

John

[strungout]

This is OT but I like your signature Always thought it would be a good compromise: we get to keep eating meat and the animals are saved!

[John Egerton]

Basically what I need is to be able to get an LED to gradually go from off to full brightness...

Reason I need this is I would like to make a sort of theremin-type expression pedal...

Think of it...

As well as your existing pots on your pedals, you wire in parrallel  simple 1/4" jack socket on each pedal. This way, the socket, on eah pedal is in parrallel with the pot that controlled a cetain thing you want to us with the expression pedal.

Then i simply make a theremin expression pedal with multiple sockets and DPDTs and voila! I manipulate certain effects on their own, or all of the pedals in my rig at once.

I want a theremin on rather than a rocker pedal for that 'coolness' effect.  

As long as I can get a circuit that can vary the brightness of a superbright LED it should be plain sailing!

Ta...

John

[toneman]

check out the Thermax by paia
(www.paia.com)
their schematic is on their site.
the Thermax output a voltage proportional to
the distance to the antenna.
Basically, full-wave-rectify the tunable oscillator.
Then U have a voltage proportional to frequency.
If U just want a "touch switch" also see the
touch-switch articla at www.paia.com.
can U tell i'm a BIG Paia Phan??
staytuned
tone

[bioroids]

I can see the use of it, very cool idea.

In the theremins I know, your hand and the antena make a tiny capacitor, whose capacitance varies as you move the hand. That's used to change the frequency of an oscillator. The difference in frequency is the sound you hear, basically (it needs another fixed oscillator as a reference).

If someone knows how to turn this into a control voltage, that's a very interesting circuit I'd like to see

Luck

Miguel

[mlabbee]

Check out this page:

http://www.seanet.com/~tpaddock/c2cv.html

There's a chip that pretty much gives you everything you need for a one degree of freedom controller.  I've looked up the data sheet for the chip and it looks like the circuit would be pretty simple.  It's pretty far down on my list of projects, but if you wind up building something, I'd love to see the schematic.

I've assumed that Zvex uses a theremin for his "probe" units - a very cool idea. No more scratchy pots.

[John Egerton]

Thats a rather complex schematic for me toneman!

Anything simpler?

Thanks for answering though... I really appreciate it....

Thanks again..

John

[John Egerton]

WOW!

Will this single chip do exactly what I need?

http://www.qprox.com/products/qt300_301.php

Thanks mlabbee!

[John Egerton]

In fact... This company makes ICs for everything I've ever wanted to build!

I've bee searching on farnell for things such as 'proximity controll' and 'resistor strip' (past posting, some of you may know).

These guy make the IC's to do just that, plus you can buy demo boards!

NICE ONE!

[toneman]

the "proximity" chips are escentially "Thermin-in-a-box".
They originated(IMO) from an article in RadioElectronics
on a proximity sensor/alarm.  The article acknowledged
that the "capacitance sensing" idea came from Thermin.
This chip also has EEPROM and other gizmos.
Prices range from $20ea & up.
I alway go "descrete".
I don't like "special" ICs.
But, if it will simplify your design task, well.......
afn
staytuned
tone

[mlabbee]

Actually, the chips are under $4 a pop at digikey.

Re discrete designs - that's still an option.  Keep in mind the Paia Theremax does a lot more than what you're looking for. It has a tone generator and 2 sensing axes.  A one axis theremin capacitance sensor with nothing but a cv output will be just a small portion of that Paia schematic.  I have never built one, so I don't know for sure, but it's my understanding that the sensor circuit of a theremin is pretty simple.

[toneman]

i just pointed to the Thermax cause the schemo was online.
Sure, U don't need *all" of it, but the "proximity" thingie is there.
AWA the voltage output.
The chip i check @ digikey was $20, but i only check one number.
$4 sounds like a deal!!
since sound is not important, U could do it (*) with digital gates.
create stable osc with, say, the famous 4049s.
then creat stray capacitance antenna to vary osc.
put output into freqency window comparator.
above freq--ON
below freq-OFF
is there anything those 4049s *can't* do???
afn
tone

[niftydog]

you said stupidly simple?

http://www.geocities.com/SunsetStrip/Studio/2987/theremin.html

[austin]

I built voltage control theremin for my final project in school.  We stumbled onto the technique accidently when prototyping Wien bridge oscillators.  Leaving off the amplitude stabilizing part of the circuit allowed for the amplitude to change with frequency.  So the output was rectified and then amplified before going into a VCO.  I don't have the circuit anymore, but it was not very complicated.  It was, however, very difficult to adjust the sensitivity.

[John Egerton]

Thanks for all your help guys...

I think I'm gonna stick with the IC that mlabbee found as it does exactly what I need.

The IC's datasheet even tells me how to wire it up with a control plate to do exactly what I need!

On their website they said that they made these chips specifically for the utilization of them in the musical intrument market and also the construction industry (sort of monitoring the proximity of a certain substance with another).

What a nice company  

[mlabbee]

Hey John - I'd love to see the schematic of what you wind up with.  Let us know how it goes.

Mike

[ExpAnonColin]

Obviously very late on this one, but our forumite friend Transmografix made a similiar device by taking a normal theremin circuit and setting a lowpass filter to it.

-Colin

[chumpito]

There are also some pretty simple ones and some tech. info here:
http://www-personal.engin.umich.edu/~jglettle/class/phys489.html
The optical one might be of use.
Look at the pdf.

I know there is one that is super simple with one 555 timer and only a couple of resistors and caps, but I can't find that article anywhere :evil: .  It was extremely simple though and wouldn't have taken much to convert the freq to voltage.