Spreadsheet for Theremin inductance capacitance etc

Fred Nachbaur did an extremely useful article "On Theremin Sensitivity" Link (http://www.dogstar.dantimax.dk/theremin/thersens.htm) and I have used the data from this to give a slightly expanded version of what he produced.. You can enter Frequency you require, and tank capacitance, and return inductance.. or you can enter L and C and get frequency.. it also gives Fred Nachbaur's extremely sensible sensitivity value (kHz/pF) for your entered parameters.

The .xls can be downloaded from Theremin Developers Group (http://www.element-14.com/community/groups/theremin-development?view=overview) by anyone.. But it would be real nice if some engineers and developers joined this group.. (I would really like a slide-rule wielding mathematician there.. ;-)

I plan to only post stuff which is really too technical for TW at this group.. I think (despite trying to restrain myself ;-) that I sometimes go too technical for most people here. I will also use this group when I need to place files for download - I have real problems doing this from other sites.

Posted: 10/15/2009 2:30:20 AM 2

From: Colmar, France

Joined: 12/31/2007

This article and the formulas are fine - for unlinearized theremins. The computations for this are rather simple. But if a linearization coil comes in, things become more complex, especially if the resonant frequencies of the oscillator's tank circuit and the series tank circuit formed by the linearization coil and the antenna's capacitance are close together. This can multiply the effect of capacitance variance by a factor > 1000. And this factor becomes frequency depending, which just allows linearization. I found a formula to describe the phenomenon but I didn't yet find a simple algebraic solution of it and am working with recursive iterations...

Posted: 10/15/2009 9:37:06 AM 3

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as WaveCrafter.com . ...................................

Joined: 12/7/2007

Hi Thierry,

I have tried to include the basic linearization elements within my spreadsheet.. I realise that the real sensitivity (dF/dC) for the combined tank LC and equalizing coil + antenna LC is more complex.. but I cannot do any better than this.

The spreadsheet now allows one to calculate aproximate L+C values for the oscillator, and if one has an idea about the antenna + antenna circuit capacitance, to calculate an aproximate required inductance for the equalization coil.

Please feel free to edit this spreadsheet and change it so that it works better... I have used this spreadsheet and it has worked well enough for me - I suspect that the dF/dC results from it (when used with the equalizing circuit) are wrong or innacurate - but they at least give an indication of values which increase / decrease sensitivity... The values I entered show the Moog EW components, and the results look, to me, to be quite close to reality.

Posted: 10/15/2009 1:41:03 PM 4

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as WaveCrafter.com . ...................................

Joined: 12/7/2007

I have updated the spreadsheet to compute aproximate inductor values for tank (oscillator) and equalisation (antenna).

This does not give any indication of linearity, and the dF/dC is probably not accurate ..

ThereminLCF2.xls is at Theremin Development (http://www.element-14.com/community/groups/theremin-development?view=documents).

Thierry - Thanks for joining, and for posting that great .pdf .... Only hope it doesnt encourage people to build more "Glasgow" Theremins! ;-)

Posted: 10/15/2009 1:45:44 PM 5

From: Colmar, France

Joined: 12/31/2007

Fred, I think that we should continue the discussion on the other playground. In my eyes the dF/dC is not a reasonable characteristic of a theremin because it tells nothing about musical linearity...

Posted: 10/15/2009 3:06:22 PM 6

djpb_designs

From: Escondido, CA

Joined: 2/6/2008

Ok, I joined the other playground with you guys. :)

Interesting site!

Don

Posted: 10/15/2009 3:08:51 PM 7

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as WaveCrafter.com . ...................................

Joined: 12/7/2007

I agree completely -
The "Theremin sensitivity" article does not address linearity at all - and all I have done with the spreadsheet is to crudely simplify (I hope) the process of selecting 'ball park' values for oscillator and equalizing inductor values.. The dF/dC computations are probably nearly useless.

Alas, when it comes to the maths for anything more complex, I am completely and utterly out of my depth - I can comprehend and partially visualise the process, but thats as far as it goes.. and where the breadboarding begins.

If you are able to illuminate this area and present something comprehensible for the likes of me, I (and I am sure many other people) would be extremely grateful to you.. It is not lazyness which prevents me from "getting it" - I have spent years trying to 'master' maths.. Sometimes I feel like I am getting somewhere - but a week later, when I try to apply what I think I "got" I find myself back at square one.

I envy you!

Posted: 10/15/2009 4:27:07 PM 8

From: Colmar, France

Joined: 12/31/2007

The playground contains now something new to think about...

Posted: 10/17/2009 6:04:45 PM 9

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as WaveCrafter.com . ...................................

Joined: 12/7/2007

Some people have emailed me saying they have had problems joining this group..

Here is how you do it:

HOW TO JOIN:

1.) At top of page, next to "Welcome, Guest" You will see Login and Register.. Click Register.

2.) Go through simple registration procedure

3.) You will then be returned to the page you registered from.. If this is not the "Theremin Development" home page, you need to go to it.

4.) On the right, you should see a "Join this group" button.

5.) Click this button

6.) in a few moments you should then be a member of this group.

I think the problem occurs if one goes through the registration process and dont realise that this process merely gives one full access to the Element14 site - it does not sign you up to any groups.. you must do this for any group you wish to join by visiting the groups home page and selecting "Join this group".

If you have registered, you need to log in to Element14 before you can join a group.

If you still have problems, email me.. There are 3 people who have said they wanted to join, but were not able to.. none of you have yet appeared in our "playground" !

Posted: 10/18/2009 9:49:42 AM 10

From: Colmar, France

Joined: 12/31/2007