ZVex: Proximity plates theramin style

[robbiemcm]

I've been trying to find out how to make something like this, and I've seen other people on the board trying to find answers, everyone seems to never quite get to the bottom of it.

Your a master of implementing such a technology into your pedals, is this a trade secret that you would rather not reveal, or something you'll openly share with us? No hard feelings if you don't want to tell us, I can understand that.

One question I would like to ask you, whether you decide to reveal the secret or not is... do you have to, by trial and error, position the LED perfectly to get it to work properly with the light sensitive resistor?

Thanks for all help you're able to contribute,
Robbie

[Paul Perry (Frostwave)]

I think there is some confusion here, because the use of the word 'plate' implies to me some kind of capacative detecting approach (changign the capacitance of the plate by moving close to it, thus either changing the frequency of an oscillator like in a traditional RF theremin, or generating a voltage in a bridge circuit like those elevator buttons that are touch-sensitive) whereas the mention of a LED makes me think of the approach where you vary the light falling on a light dependant resistor, either by directly obscuring it, or by changing the amount of light reflected to it (as in my SpaceBeam infrared optical theremin).
I havn't any idea about the Zvex device, as such.

[shawn]

I figured out how the zvex "plates" work but I have slept since then. Maybe I'll dig through and find my notes unless zvex wants to answer this one.

[Dragonfly]

...though im not sure how Zach does his "plates", you might do a search on "Hall effect" .....

[NaBo]

Transmogrifox made a schematic for a proximity control circuit, but the links for the "phase-locked-loop" stage which follows it, aka the part that actually makes it a control, have gone dead.  But I suppose you already saw me complain about that in one of the other threads...  

Personally, I don't think zvex should divulge (or be expected to (not that you were expecting)) every bit of info we need...  The proximity controls he's implemented have clearly had a lot of work put into them and I'm sure they're a big part of the coolness-factor associated with his products.  If he dumbed it down enough and tossed it out there for all us nubs to copy (not to mention the many many hacks that would jump at the chance) and start probing with every pedal we make, that would be silly.  I'm sure it's no easy task to come up with a proximity control design that A) works,  B) works well, and C) fits a reasonably sized enclosure.  So let's not bug Mr. Vex for this one

We did have a rather awesome forumite Transmogrifox take the time and effort and use his knowledge which oh-so-magnificently dwarfs mine to come up with a proximity controlled oscillator circuit, and he was quite willing to share his experience and findings here.  Which is extremely cool.  But it just teases me cuz it's still beyond my understanding how to make that thing act like a pot or variable resistor.

I think I'll ask my favourite question just one more time... can anyone toss a bone and link to some material that would help figure out what needs to come after the Ossi's output?  Preferably in terms more specific than "a phase-locked-loop", but preferably not too specific... I really don't want to paint by numbers on this one cuz I want to feel somewhat proud and/or wicked after finally figuring it out.  :wink:

[robbiemcm]

I didn't think the circuit was too complicated, I though people just didn't know how to do it. Maybe I was wrong.

From www.zvex.com

How it works - The probe circuit generates a small (one or two inches high) "bubble" of RF energy at about a million cycles per second above the copper plate. As your foot or hand (or any wet or metallic object, for that matter) approaches the copper plate, the RF field is disturbed and the circuit reacts by increasing the brightness of an LED, which drives a photoresistive cell and controls the Z. Vex wah circuit. The wah circuit is actually the Seek-Wah sound circuit without the sequencer control. It's also the same wah circuit as the one in The Drip guitar that I make. The only difference is the boost circuit in this Wah Probe model.

Hopefully we'll be able to crack this one, it would be extremely useful. But considering it lights up an LED as you get closer, shouldn't we be able to use the light sensitive resistors (I don't know the proper name for them) and use all the values in which they come in? So it's not really acting like a variable resistor, it is one isn't it. Unless I have everything wrong once again, which is quite common.

[Gladmarr]

I have a wah probe, and I'm pretty sure the LED he's talking about is actually inside the optoisolator that runs the wah circuit.  There is an LED on the case, but I think it runs parallel (or series) to the optoisolator.  I wish I could tell you more, but Mr. Vex had the foresight to sand down his chips.   :wink:

I too think this is a great idea.  It's not an original idea at all (theremin), but it's a great use of that control method and makes for extra cool factor on Zvex pedals.

[NaBo]

You know what, I just found Tranmogrifox's original post... 'again, for the first time'...

And um... HOLY F$*#%$& SH#*!!!!!!!!!!  It appears he didn't end up using a PLL at all (that would explain why they're no longer on-line!!!)...  and everything except the bottom right of the schem he gives for his Dr. Quack (never even looked at that part before) looks like what he uses to get a control voltage from the oscillator... which can then be used to drive an LED in an optoisolator!  oooooo baby.  hot diggity.  I'm rather excited to try this out.  It's amazing the things you find out when you go back and read stuff with a little more knowledge in your noggin.

THANKS FOR WAKING UP MY BRAIN robbie.  I was going down the entirely wrong path scouring the net for PLL implementations and whatnot.  well, not the "wrong" path, but the decidedly more difficult one.  :wink:  I suppose you are somewhat limited to replacing pots wired as VRs, but hey, that's plenty good for me.  I think I'm gonna work on this and whip up a layout for it as soon as I'm done exams.

Speaking of exams, I have another half of a 2nd year stats course to learn in 5 hours... BYE!!!

p.s.  the light sensitive resistors are called LDR's, Light Depending Resistors, also known as "Photocells" at ratshack.  Cadmium Sulphide (CdS) reacts best to green light wavelengths, Cadmium Selenide (CdSe) reacts best to red light wavelengths.

p.p.s  Thanks for finally making me search and find what I was looking for!!!

p.p.p.s. oh, and huge thanks to Transmogrifox  

[The Tone God]

You seem to be mixing up technologies. The Probes use a plate to sense presence. The circuit in turn drives an optocoupler which is used to interface to the audio circuitry. Nothing to do with light directly.

I made the suggestion awhile ago about using a LDR directly as a "gheto theremin". Never really did anything with it since it seems so easy to impliment.

As for theremin-style circuit control I've played with it awhile ago and came up with several solutions but I'm keeping them in the vault for now. Its not as hard as people like to make it. Just sit down, do some research, and experiment.

Just as a minor assist here is a tidbit. In the PLL idea it shouldn't be too hard to interface the proxi circuit to the PLL. Set up the internal oscilator to run at the same frequency as the driver. When you approach the antena the frequency of the driver should change causing the output of the PLL reflect that change. IMHO, from personal experience, I think the proxi circuit linked to above is alittle overkill in terms of complexity. About the only thing I could say about it is that it may have alittle less clock noise then other circuits.

Andrew

[mlabbee]

Google qprox

[The Tone God]

Google qprox

No thanks.

http://www.diystompboxes.com/sboxforum/viewtopic.php?t=27065

Andrew

[NaBo]

Google qprox

http://www.diystompboxes.com/sboxforum/viewtopic.php?t=28615&highlight=proximity  :wink:

Edit:  LOL Tone God  

[The Tone God]

Edit:  LOL Tone God  

LOL. :lol: You beat me to that thread also.

Andrew

[Johnny G]

i thought that everyone had come to the descision that it was a theremin control most likelly using a 4049 CMOS Not Gate chip as an oscillator?

[troubledtom]

Z's circuit is a great ,low parts count idea to say the least. but when i wanted to use this type of stuff for my pedal line , he was very cool but made it clear to me that he wouldn't like it.
    Z got me out of a few binds for yr's and i would never take that for granted so i backed off. Z has been very kind to me so i just settled for
photocells.
    funny , my clients have not complained yet........... except J.R. from
 DREAMTHEATER.NET hell he's friends w/ bob moog. he'll want for nothing.
               peace,
                      -tt

[Johnny G]

Z's circuit is a great ,low parts count idea to say the least. but when i wanted to use this type of stuff for my pedal line , he was very cool but made it clear to me that he wouldn't like it.

sounds fair enough to me. for coming up with one of the most inovative ideas for a while i think he's well within his moral rights to keep the credit lol

[Dan N]

Here is something interesting not too far from the topic:

http://i3.photobucket.com/albums/y64/earthstandstill/touchcontrol.gif

(touch it and the led turns on)

[Paul Perry (Frostwave)]

If I was starting from scratch & wanted "remote leg control", I'd be searching the DIY robot groups (hint: ranging, distance sensing). Because those guys do it all the time. Robotology is the closest mainstream thing to waht we do (well, it's mainstream compared to stompboxes!)

[robbiemcm]

Ahh crap... I just noticed the problem. How do you make a photocell act like a pot, lol. How do you actually do it. Without knowing the resistance of all the circuits that come after the one you're using (impedance?), I guess you could use a pot for calibration?

[ExpAnonColin]

Man, this topic is beat into the ground... but this thread is missing the Qprox theremin link directly...

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

This could be VERY EASILY converted to an LED's brightness, then to a photocell.

-Colin