THEREMIN REACHES OUT AND KILLS NOTEBOOK TOUCH PAD

Ok, so that title was a bit dramatic. Here's a really weird thing I've discovered.

I've just brought home a brand new bouncing baby Samsung Chromebook with the latest OS. I intend to use it as an accompaniment playback device for traveling gigs because it's cheap enough It won't be so bad if it gets nicked on a gig.

Right. Here's the weird thing I've discoverd. It's not something common to my other notebooks which are older by at least 4 years, and they use what's known as resistive touch pads. My new Chromebook uses the newer capacitive touch pad. I've observed that when my theremin is on, and even within 10 feet of the notebook, the touch pad goes out. You then have to fallback to an external mouse or trackerball in order to use the notebook. When I switch off the theremin, the touch pad comes back to life, and behaves normally. This was experimented with while the notebook was both on, and off the AC mains.

At first I thought it was the AC mains adaptor causing this strange problem because it would happen when the mains adaptor was plugged in, also with the theremin on.

There is one other possible aspect to this problem. The Chromebook uses wi-fi which has to be connected in order for the web based Chrome OS to work fully for accessing your cloud storage, and other functions.

Oh, yeh, the Etherwave Standard was, and still is in the room. I'll have to try the other theremins to see if they affect the Samsung touch pad.

UPDATE: All full (pitch / vol) theremins have been tried that I have here. Only the Etherwave Standard seemed to have the most impact on the Samsung Chromebook. The lesser impacts were noticed from the Wavefront Travel Case, and Etherwave Pro. Neither Burns, nor Lost Volts had impacts on the touch pad.

Ok FredM, or whomever else is qualified,  the floor is yours. 

"Ok FredM, or whomever else is qualified,  the floor is yours. " - Thomas

LOL ;-) once again I jump in as "qualified" LOL ... But in this case I might just be a bit more "qualified" than most, even if my knowledge of the subject is far less than most subjects where I have no "qualification" .. (I am a certified Cypress consultant - I underwent the most rigourous exam [back in 2005] I have ever been subjected to in order to get certified - Capacitive sensing was one major "topic" - But I really dont have a clue about the later more sophisticated CapSense and its use in things like notepads - the studies I undertook may well be what led me to theremins - and to making the huge mistakes I did - But most capacitance sensing I have really worked on has not used Cypress CapSense)

It is a little strange to me that the effect is so dramatic - I have used PSoC (Cypress) CapSense with theremins without problem (in fact, I have been looking at implementing CapSense for the controls of my latest theremin)..

I suspect that perhaps the Synaptics (a competitor to Cypress, and I have no inside knowledge of their hardware or software)  capacitance sensing used in the Samsung Chromebook is working to a much higher resolution than what I have been playing with - I have played with simple capacitive "buttons" and "sliders" and use a lot of digital filtering - each sensor effectively only requires an "off" state and an "on" state, and the thresholds are quite wide apart, and dynamic calibration looks for noise and adjusts the thresholds to compensate for backgound stuff.. Only quick changes (like turning a theremin on) can upset it momentarily..

But with touch screens where one is looking for "analogue" data on multiple dimensions over a small surface, and require fast recognition of gestural actions, I suspect that the sensitivity to signals which could be "seen as" capacitive influences, will be FAR higher.. One does not have the luxury of wide (or any) "thresholds" -

And I suspect that if a clean signal is not obtainable from the capacitive sensors, the software will disable the sensors - Better to have no capacitance sensing than to have the pointer randomly selecting  objects and activating them or doing other nasties.

Nonetheless, the severity of the problem does surprise me.. As for a "fix" this will depend on the causitive mechanism / path.

If the player is well grounded, then I imagine capacitive coupling from the theremin to the notepad is likely to be via direct coupling.. So it may be worth playing with putting the notepad into a grounded enclosure which obscures the pad from the theremin on a line-of-sight path.. Something like a grounded aluminium book-end between the theremin and the notepad might be enough.

Otherwise you might just need to wait for me or someone else to produce shielded directional antenna theremins.. This tale makes me quite pleased that I opted for directional antennas which supress all radiation except for the focus field.. One of the main motivations for this was the notion that one wants to keep signals confined to the playing area so that they dont upset other theremins or other electronic equipment.. And this technology also shields the theremin from reception of interference from all sources not in the playing focus field.

But waiting for me - well - it might be a long wait.. Kind of sad really, because I now have all the technology independently tested, quite a lot has been put together in trial systems - but its still only a load of prototype boards and prototype antennas and gigs of design files and simulations.. All there - But all an expensive and difficult distance from production.

Fred.

Oh, I dont know much about WiFi - But it would REALLY surprise me if this was in any way related to the problem.

@FredM: Yeh, I'll likely have to try that simple shielding test you mentioned with a bit of bent metal plate connected to ground, and parked between the theremin, and Chromebook.

@FredM: Your theory has been verified. I just tried changing the angle of the Chromebook on the yaw axis, and noticed changes in the level of interference with the touch pad. Most noticeable when the Chromebook faced the theremin. Nearly none at all when the Chrome book face away from the theremin. Also, noticed changes in interference when the screen was tilted at different angles on the pitch (tilt) axis. I suspect the metalic structures within, such as the screen, chasis, electronic boards, battery, ect, contribute to shielding in some way, as well as the screen possibly acting as an antenna.

Yeh, I agree, regarding wi-fi. It's on a totally different frequency. But, still, had to ponder it.

i know it is a different thing, but when i play my theremin, keep my right hand on the volume loop to silence it ~ then reach for my laptop mouse pad, it works erratically! and if I lift my hand from the volume loop, then it works again!

Hi Amethyste, Yeh, I think what's going on, is you're changing your capacitence by touching the theremin's volume loop. So, your touchpad is not getting te same capacitence it normally would, and, this might be that you're extending the field to the touch pad, causing the same effect as mentioned above. FredM? Your take?

"FredM? Your take?"

LOL ;-)

This all comes I think down to the fact that we are, as some Star Trek alien once said, "ugly bags of mostly water" (I may have got it, or even the source wrong, but whoever / whatever it was - I think it was some crystal life-form -  it was right! We are bags of water with minerals and iron desolved into it, making us reasonably good conductors and a good capacitave 'bulk')

Our 'bulk' couples to a good ground reasonably well, so when playing the theremin, the capacitive coupling to the theremin antenna/s is predominantly a "loading" function - We do not tend to "re-radiate" the HF signals much, because the predominant potential on us has a good coupling to ground.

However.. If any part of our body is really close to or touching the theremin, or if our "bulk" coupling to ground is inadequate, our bodies potential (the voltage / waveforms "on" us with respect to ground or other appliances) will be higher than if we are well grounded or the antenna coupling to us is more distant..

In this state, we will radiate the theremins signals.. In fact, we will always radiate some of the signals we are exposed to, but usually because of our ground coupling the signals "on" us are low.. These signals, if they get strong enough (for the reasons I have described above) will radiate from our fingers ..

And I suspect it is this which is messing up mouse-pad operation.

Tie a ground connection to your ancle, or get a broad metalic belt and connect ground to this, or make a grounding mat, or any of the schemes described in the "Battery supply for EW" thread, and it may fix this problem.

Fred.

Actually, all this has got me thinking.. Perhaps one could use these cap sense appliances to determine if you have good ground coupling! As if you are well grounded, there should be less problems - But if poorly grounded, you might be able to "kill" your mouse pad or whatever just by pointing at it!

Not exactly scientific ;-) .. but this posting isnt exactly "scientific" so please dont quote my "loading" and "re-radiating".. These ideas need a lot more depth to be quotable!

Now if I could kill my garden weeds like that, I'd be all over it!

Hi FredM, Yeh, you got that episode spot on. :) The things we discover with the theremin. Eh?

@Amethyste: Yeh, LOL, if you could figure that one out, you'd be winning the Nobel prize. :)