Moog Theremini Theremin

New Technology - Capacitance sensing redundant in the future?

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Posted: 1/29/2013 6:27:11 PM
FredM
From: Eastleigh, Hampshire, U.K.
Joined: 12/7/2007

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This is probably more for those interested in technology more than those interested in theremins..

Plessey have been involved in biometric monitoring for years - but it seems that the trchnology has now advanced well beyond the ability to detect biological signals through clothing etc.. It seems they can detect changes to electrical fields over long distance, and are applying this technology to gestural control interfaces.

A brief overview of Epic Gestural control (or imPart) can be found here -

>> Plessey’s Director of Business Development, Steve Cliffe, explains why he thinks CES 2013 is the right place to debut imPart: “CES is the perfect showcase for this stunning new technology. People are amazed at how sensitive it can be at picking up very small signals even at a distance of up to 100 cm without physical contact.” <<

Ok, I suspect it will be many years before this Epic Technology becomes common - but apparently they have now managed to produce their sensors "cheaply" - what exactly they mean by "cheaply" I do not know - their early sensors were far from cheap - but were for a market which could afford it.

It certainly (to me) looks like a technology which could be used for musical applications, and possibly replace capacitive sensing for theremin type instruments of the future.. Probably long after I am pushing up daisies though..

Difficult to find / link to the relevant sections on the site - so I paste some info below:

Security

Because of EPIC's mode of operation, it can be used to detect any disturbance in the local electric field at distances of up to several tens of meters. The human body, because it acts as a large container of conducting/polarizable material, causes a large perturbation in the electric field and so presents an easily detectable target for the sensor. Sitting a few meters away from the sensor, one has only to raise the sole of one's foot to create a strong signal. Arrays of sensors can be used to provide spatial resolution and therefore the location of a target. Such arrays can also distinguish between humans and quadrupeds because the time signature of the response is a direct function of cadence. Such a system of sensors could perhaps be used for border security in remote areas.

Man-machine interface

The ability of EPIC to resolve signals unique to various muscles or groups of muscles presents opportunities for improved man-machine interaction. For example, a quadriplegic who currently depends on either a unicorn stick or a suck/blow tube to issue commands to equipment within his or her local environment could achieve a faster and more efficient interaction using EPIC for eye tracking and detection of activity in any muscle groups still under voluntary control. Alternatively, because EPIC can assign a unique signature to the use of certain muscle groups, it opens up many possibilities for interfacing with and controlling prosthetic limbs.

 

Posted: 1/29/2013 8:14:23 PM
dewster
From: Northern NJ, USA
Joined: 2/17/2012

threads posts

Funny, a week or so ago I was thinking guard band techniques might possibly be useful to reduce stray capacitance at the Theremin's pitch antenna.  Any reduction in capacitance here translates directly into increased sensitivity / SNR.

Posted: 1/29/2013 9:09:25 PM
FredM
From: Eastleigh, Hampshire, U.K.
Joined: 12/7/2007

threads posts

Hi Dewster -

Not only does it reduce stray capacitance, it also allows one to have a directional antenna.. One can shield the antenna from people standing close in front of it, for example..

And its quite simple (particularly if low voltage is on the antenna) - the shield just needs to have a low-Z duplicate of whatever potential is on the antenna..

Right back in my earliest days at TW I was bragging about this technology! LOL ;-) .. It is great - but getting high speed voltage followers to track a 60VRMS on the antenna is a little more challenging than doing this for a 10V triangle wave - so as soon as I moved to LC, the simplicity decreased..

But its still far from impossible.. And a directional antenna is a real boon.

- but I am a wee bit curious.. What link is there regarding shielding with reference to the Epic sensors ?

Fred.

ps - I use active shielding on my volume / position antennas - its a lot easier because these are fixed frequency.

Posted: 1/30/2013 12:05:03 AM
dewster
From: Northern NJ, USA
Joined: 2/17/2012

threads posts

"- but I am a wee bit curious.. What link is there regarding shielding with reference to the Epic sensors ?"  - FredM

Go here:  http://www.plesseysemiconductors.com/epic-plessey-semiconductors.php

and click on the tab "Technical Information" | "What is EPIC?"

They actually get kind of technical.  Operates from ~30MHz to 200MHz.  Guarding to reduce capacitance, bootstrapping to increase input impedance.  I wonder how they keep static from killing it?

As a kid I wired a FET in a resistive balanced bridge with a meter and battery.  It would easily track Earth's vertical DC voltage gradient, kind of spooky.

Weird that you thought of guarding for Theremins too!  (Then again maybe not, because you are always several steps ahead of me!)  With some controlled directivity in the vertical direction one might be able to improve linearity.  But, yes, with LC voltages & frequencies it's not a simple matter of using an op amp or something.

Posted: 1/30/2013 12:52:25 AM
FredM
From: Eastleigh, Hampshire, U.K.
Joined: 12/7/2007

threads posts

"Weird that you thought of guarding for Theremins too!  (Then again maybe not, because you are always several steps ahead of me!)  With some controlled directivity in the vertical direction one might be able to improve linearity.  But, yes, with LC voltages & frequencies it's not a simple matter of using an op amp or something." - Dewster

Not weird at all - I think it is almost impossible to have a truly "new" idea - I remember years ago, before I had got into capacitive sensing (or as I was just starting) coming up with the idea of shielding to reduce background capacitance.. It was one of those "moments" I frequently have, where I think "this is a big one" - but, from expierience, I know to think "So why hasnt anyone done it before"...

I then go and check to see if anyone has done it before - And with capacitive shielding, I found that NASA had been granted patents on the idea three years previously..

And if I find no-one has done it before, it usually (almost always) means that there is some flaw in the idea which I only discover later.

Being "the first" to think of something would be nice - but thinking of something "new" without knowing its been thought of before has its own satisfaction - not the kind of satisfaction which brings money or esteem, but satisfaction nonetheless..

So the "because you are always several steps ahead of me!" is irrelevant - NASA was several years ahead of both of us, LOL ;-) .. Neither of us work for a large corporation who could facilitate us getting patents filed on anything, and even if we did, what we got would ammount to theft anyway -

So we have both sculked off into our corners to play with our theremins ;-)

Strange ol life!

Fred.

ps - thanks for guiding me to that article.. I hadnt actually realised how these sensors worked - I knew they were effectively similar to Fets with an exposed gate substrate . We used some early Plessey (or I think they were Plessey - may be wrong) sensors back in the mid 80's which worked on this principle (electrometry) for measuring bio sample interactions - But these look a lot more advanced.

pps - Capacitive shielding is top of my mind right now, as I have just developed a couple of sensors for a client (one monitoring compression of silicon rubber sheet, the other is a capacitive position decoder for an extremely weird UFO type motor) which rely heavily on active shielding - Prototypes will be tested in a couple of weeks, and I only get fully paid if they pass proof-of-concept.. So its kind of on my mind, LOL ;-)

"As a kid I wired a FET in a resistive balanced bridge with a meter and battery.  It would easily track Earth's vertical DC voltage gradient, kind of spooky."

We did similar things as kids! - Kind of sad that today they arent interested - The Game Boy and similar have a lot to answer for.. And they make science so damn boring for kids these days! Science without science, if you know what I mean - No risk, no adventure.. No phosphorus setting fire to the classroom, or mercury to mess about with... :-(

Posted: 1/30/2013 3:36:24 PM
dewster
From: Northern NJ, USA
Joined: 2/17/2012

threads posts

I know exactly what you mean by eureka moments either not panning out or not being original.  Nothing new under the sun, I suppose, but as you say they can be personally rewarding.  Even this sensor seems to be applying known techniques in order to improve sensitivity.  The first time I saw guarding IIRC was on the schematic for a pH meter - it looked pretty weird at the time!  The first time I saw bootstrapping IIRC was in some otherwise lame TAB opamp book and it looked crazy too. 

Speaking of applying known techniques, Walter Jung's "IC Op-Amp Cookbook" introduced me to the use of a transformers in microphone preamps, where they are simultaneously impedance matching and voltage gain elements.  That's what makes me want to use a transformer as the Theremin tank inductor, for impedance matching between the outside world (high impedance) and the series tank (low impedance) - it's just one more winding on the tube so it's almost free.  Though it feels like baby steps in terms of development.

Kids are distracted, but it's hard to blame them - they are fascinated with very early versions of what will likely replace us all!  It's kind of too bad that computing isn't more accessible to the average person at the lowest level, PCs weren't the most ideal platform to push overall computing forward IMO.

Posted: 1/31/2013 8:07:13 AM
FredM
From: Eastleigh, Hampshire, U.K.
Joined: 12/7/2007

threads posts

"they are fascinated with very early versions of what will likely replace us all! " - Dewster

OT - NOT THEREMIN RELATED!

LOL - now theres a cheery thought if I ever heard one ;-) ... Perhaps thats why "the matrix" was so popular, and, for that matter, Terminator... Preparation for fighting the machines which now keep them amused..

But it does break my heart sometimes - My youngest daughter arrived home in floods of tears yesterday - she had been working her way through a complex game, and just defeated a "boss" she had beaten after days of effort - In the car she plugged the charger in, and the program crashed.. she lost the lot.

And im thinking - Why should she be going through this at six? (I find the level of violence and psychological entrapment embedded in these games appalling anyway - the kids would never have these games if my wife didnt spoon feed this sh*t to them behind my back) - But to go through the trauma of losing your "work" as a result of software failure, well - age 16 is soon enough IMO.

Really frightens me how real these created worlds are to them - It different from what I had - I created my own worlds - todays kids are programmed IMO by adults with often bad agendas..

I remember in the early days of computing - working in a hospital, and getting a job offer from the senior psychiatry consultant .. He had a kid he was studying (in patient) and needed a programmer to devise tests etc - this kid played games all day, all being monitored.

I thought the whole process was dubious - particularly when I found where the funding was coming from.. The Ministry of Defence !  (I declined the job and made the matter public - but no one was interested.. nearly lost my job over it - but got offered a job in R+D in the medical school which turned out to be the most exciting move I ever made.. this was back in the early '80s).

Fred.

Posted: 1/31/2013 3:29:43 PM
dewster
From: Northern NJ, USA
Joined: 2/17/2012

threads posts

I've played many combat flight sims and more FPS than I care to admit.  I think they're like most entertainment in that they offer maximum drama: books do it, music definitely does it, movies do it like nobody's business.  Every SF / Action / Thriller lately has a ticking time bomb and fist fight at the end (even if it makes no sense) - I think "Aliens" originated this plot construct but I could be wrong.

Humans like drama for some reason, I suppose it goes with the whole emotional social thing.  And there's no drama like the possibility of dying in a fire fight! 

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