Crazy (?) theoretical / technical ideas

"why do I keep looking for alternatives again?  Oh yeah: inductors have thermal stability, magnetic pickup, and bulk size issues; emissions are problematic; multi-sensor arrangements in close proximity to each other don't play nice; and mains hum is difficult to deal with in the FM domain." - Dewster

LOL ;-)

A list like that is enough to drive any sane designer away from this field - or cause them to tread this well worn path, seeking "the path less traveled on" - which turns out to be the path traveled on by everyone who isnt just copying established theremin designs and modifying them..

I dont think its hopeless though - probably futile, but not hopeless! ;-) .. Thermal stability can be reasonably simply corrected even without temperature sensing and feedback (and that's an available option for both analogue and digital) - Magnetic pickup can be greatly reduced by the way inductors are oriented (Ive been playing with the EW, replacing one of the 10mH inductors with two 5mH contra-aligned, and found reduction in magnetic coupling - perhaps not enough to make this worth doing, but IF I was to use the EW front-end (or anything with large inductance) I would probably use 4 inductors in a 'square' configuration to counter induced fields.

Bulk/size issues seem to be more of a selling feature than a disadvantage in this crazy pond - "Honking coils" give some perverse visual appeal it seems.. Then proximity problems can be overcome if one locks the frequencies as per my "upside down" topology or something similar...

Yeah - with effort, the LC topology can be made to work reasonably well - as proved by Lev in the 30's.. But I am not sure that any RC topology could be made to work.

Fred.

ps - glad you like Douglas Self's book.. I really enjoy reading it as well - unlike many technical books that one wouldnt want to read cover-cover, but just use as reference.

Have you come across "Analog Dialog" ?  There is a huge wealth of articles in these..

http://www.analog.com/library/analogdialogue/archives.html

"Have you come across "Analog Dialog" ?  - Sillyconica (FredM)

No I hadn't, thanks for that!  The electronics world would be a poorer place without app notes and the like.

Oh my! - Analogue Dialog is the classic! The archives go way back to when op-amps were cast in resin encapsulations and were made from discreet components (and cost £20+ each) .. I remember getting my first copies when I was 15, working at Hamrad (South Africa's equivalent of RS/Farnell back in the 60's/70's) in Cape Town as a component seller..

Back long before the internet, when the printed copy was treasured in an almost fetish way ;-) ... Brought back some strange memories trawling through those archives - at that time it was cheaper to make an audio amplifier using tubes than using transistors...

Fred.

"Yeah - with effort, the LC topology can be made to work reasonably well - as proved by Lev in the 30's.. But I am not sure that any RC topology could be made to work."  - FredM

After searching for and doing some reading re. very stable RC oscillators, it seems the sine types (Wien bridge, bridged-T) use two C's to form either BP or notch filter in some sort of feedback arrangement to boost Q (they're basically infinite Q BP filters).  Being only able to change one of the C's with hand capacitance means you're back to a square root of C frequency change (ala LC) but it does eliminate the inductor - as well as the high voltage unfortunately. 

Maybe generate a sine and feed it to an RC, and adjust the sine frequency for 45 degree delay.  Use multiplication rather than XOR to get a better "whole cycle best fit".

"ps - glad you like Douglas Self's book.. I really enjoy reading it as well - unlike many technical books that one wouldnt want to read cover-cover, but just use as reference."  - FredM

That man really knows noise!  And yes, the book is quite entertaining (as these things go).

Crazy Idea 8'b01101011 : FSK/MSK HV switched L oscillator

Minimum shift keying (MSK) is one way to FM modulate a binary signal.  Two frequencies are picked and their sine wave representations are used as output depending on whether a one or a zero is to be transmitted.  If we pick 100kHz for zero and 200kHz for one, then a zero might transmit as a complete cycle of 100kHz, a one might transmit as two complete cycles of 200kHz (in order to consume equal transmit time per bit).  Things are arranged so that the transition from one frequency to the other takes place at zero crossings, and going in the same direction, so as to minimize HF content.

The above (c) FSK is what I'm talking about.

If one were to somehow quickly change / switch the inductance value in an LC oscillator one could implement such an oscillator with high voltage output.  It might be possible to stimulate the oscillations themselves via the switching process, but amplitude would probably droop for long strings of 0's or 1's.  Integer multiples of frequency for the two waves wouldn't be necessary because we aren't transmitting real information - a LFSR XORed with its clock could provide the pseudo random data on demand as the oscillator needed it.

Such an oscillator would spread its energy over a broader bandwidth - and perhaps interact less with other similar oscillators nearby?

"If one were to somehow quickly change / switch the inductance value in an LC oscillator one could implement such an oscillator with high voltage output. " - Dewster

I dont know of a way to rapidly change inductor value without big losses - One can short a turn with an ideal switch, or switch tappings on the coil (probably the fastest if you can get a switch capable of the voltages - I used MOSFETs and IGBT's) - changing the saturation through a coupled winding is slow..

So lets say you had a tapped inductor and used this in a series resonant circuit (probably need a small trimming inductor on one tap) and switched the capacitor between these taps at the zero crossing - I can see that you could achieve the waveform shown in (c) or a continuous - but cannot see how you would get any other states (cannot see going from falling to zero and then rising without going through the -Ve 1/2 cycle)

oh - you could have series LC configured  Drive -> Cswitch -> L -> Cant .. If you change the Cswitch value at the antenna (say -Ve going) zero crossing, then with  a closed-loop oscillator you should be able to do FM digital coding - If Cswitch is >> Cant then Vant would not be greatly reduced...

Fred.

off topic -->

The ability to switch (change) inductance values quickly.. Hell - that brings back some memories! ;-) .. A lot of the "free energy" stuff seeks to do that - (or rapid switching of capacitance values) - The idea being that if one has energy stored, then somehow, by changing the storage 'capacity' of the 'container' you create "free energy" [oh - thats not what THEY say, its what I am saying ;-) They believe they are sucking free enery out of the vacuum between their ears! ;-) - "Hey, look, I had this capacitor charged to 10V, but by moving the plates further apart have created an extra 10V ! - Free energy! ... But it only works if I move the plates real fast and 'capture' this raised 'energy' quickly ".... LOL ;-)

More sophisticated versions of the above misguided thinking are propounded by "researchers" J Naudin in France and T Bearden in America - but I was paid for a year+ to build and evaluate the plausibility of these devices, and almost all were based on wishful thinking founded on dumb ideas - that and outright fraud! .. There were a few possible exceptions - I believe Floyd Sweet MIGHT have invented a magneto-resonant thermo-electric generator - a device which "sucked" thermal energy causing cooling, and changing this to electrical energy - But if he did, Tom Bearden managed to de-focus attention by calling it a "Vacuum Triode Amplifier" and postulating a completely absurd theory for its operation - and then probably saw to it that the device was destroyed and Floyd silenced.(I really dont like Tom - Spoke to him several times - I think hes working for the "other side" ;-)

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Dewster! - You may just have solved a big problem I am having...

If one switches the oscillator cycle-by-cycle between frequencies spaced a few kHz apart, one would then get a phase "marker" you could detect in the BPF / Phase comparator section (For others - I am referring to conversation on the digital thread)..

You would always know exactly what the deviation was, regardless of what the actual oscillator frequency was, provided the 'marker' frequencies were constant relative to each other..

The phase comparator would be a bit more complex but give twice the resolution (or n* the resolution if one had n "markers")..

Time to fix my simulator!

;-)

With 3 "markers" I could have one in the "near field" one in the "mid field" and on in the "far field" sections of the phase 'curve' and selectively combine these as they all move together due to sensed capacitance, to get linearization..

ok.. solves that "problem" - but trashes any idea of heterodyning the MO... Oh well... Thats way too big a price to pay -

Back to the drawing board..

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Update: See 5/30/2014 11:00:38 PM

http://www.thereminworld.com/Forums/T/28554/lets-design-and-build-a-mostly-digital-theremin?page=77

My thinking is that a newcomer starting with a 3 octave span might find playing easier - if they are able to increase the span as they become more competent, they wont need to upgrade.. With register switching, a 4 octave span will probably be well suited to most players - but if they have the ability to expand this field to 5, 6 or 7 octaves and choose to do this, its in their hands.

From a commercial angle a single build catering for all requirements is far saner than tying oneself to one set of specifications which may be unatractive to a fair percentage of the tiny potential market.

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I know you have been designing theremins for years now and have given up ever going commercial with one.

I'd love to see you put some of your designs out there for others to enjoy your genius.

Not being sarcastic, I am certain you have some great designs.

I bet you'd get maybe 4 or even maybe, just maybe, SIX people to build one and God bless anyone who thinks they could take your design and make a fortune off it.

You know they won't unless they can make big bucks selling 6 or 7 theremins.

LOL!

I'd love to see some of your ideas on a single sided board that one can etch at home and even would love to see some of your PSOC designs.

There is already one PSOC 4 design out there that I am certain is inferior to some you already have designed.

 My ideal design?

Good sounding (yeah, I want it ALL!), certainly 3-4 octaves and not 20 octaves, made from common parts even if it takes a few wound coils, on a single sided board.

Bells and whistles welcomed if not too costly or perhaps as addons as desired.

Hello Thereminworld :)

I am working on a project that takes the theremin/terpsitone concept and applies it to a large crowd.  I want to harvest static fields in a room and have feedback come through a subwoofer-speaker setup.  

I have had minimal success using layman's devices, but I realized I have to start learning engineering to build a prototype.  This device will be a speaker attached to a subwoofer, and will use either the floor or a series of rods to help conduct electric charge.  I've had really mild success with my home subwoofer and speakers but I am researching the theremin to improve the design.  

The gimmick of it is imagine going to your favourite dance concert, and you enter the room and a low bass noise begins to build as the room fills with excitement.  Then the act comes onstage and the static in the speakers goes up with the bass.  This bass noise is the "crowd energy" being caught by the set up, and the pitch and tone should change in such a way that it makes the concert goers (and the musicians) believe the crowd are telepathically singing along through the speakers.  In reality it's just EMI being amplified into sound.