ZVex: Proximity plates theramin style

[NaBo]

Robbie:  it has to be a pot wired as a variable resistor using an LDR... fortunately, plenty of the coolest things to have dynamic control over use these types of controls...  Opto-based wahs, delay time, chorus, phaser, trem depth and speed...  Basically anything with an optoisolator already in it involved in some type of control, and pretty much anything LFO-based.  That's plenty of stuff to be varying with a wave of the foot  

Colin: True... it has come up a lot... I suppose I'm guilty of carrying a rather large stick with which to pummel it deeper still, and always chiming in on the subject too .  Proximity controls are such a cool concept, I spose people cant help get excited and curious about it.  There isn't really any in-depth build reports or resources that deal with it specifically, so natch, there's gonna be frequent postings here.  I hope to get a bit of experimenting done this summer, maybe with the qt301 too (seems worth a try)... Hopefully i can compile a little bit of info about what worked with what and how well... and quell the ravenous hordes of curious apes :wink:


*cough* *cough* *cough* ... had to  :lol:

[ExpAnonColin]

Not to be pissed off, ornery, and pessimistic, like many of us on this forum are these days (whoops just did it), but even after there are detailed how-to tutorials there will still be threads asking how it's done.

OK, enough of that attitude.

-Colin

[robbiemcm]

So, if we learn how to do it, then at least we'll be able to use it. We'll just have maybe an increase of people wondering why it doesn't work (I bet I'll fall in to that category).

Anyway, if we do find a way of doing it, don't the ones at ZVex have the ability, through a trimpot, for your to set how far away your foot needs to be when you start to enter the field it creates around the plate?

[Paul Perry (Frostwave)]

Searching google for: capacitive distance sensor DIY
gives a number of useful leads, including
www.media.mit.edu/resenv/pubs/papers/2002-05-02_Hasan_final.pdf
which has a handy list of references.

Trust me, capacitive sensing has been done to death & in fact (if money is no object) there are any number of industrial modules doing just that (usefully, water or anything containg water - like us - has a very high dielectric constant, tailor made for capacitive sensing).

[Zero the hero]

I've tried for a month to build something that works like a "xyz probe", but I had no success so far. I've never seen how those pedals look like, so I have no hints about them.
If someone can get this workin', let me know... I've wasted a lot of time with this application note...

http://www.maxim-ic.com/appnotes.cfm/appnote_number/235

Cool idea, maybe it need to be tweaked a bit.
I'll try a different approach, since I've found another way to use capacitive probes in audio circuits

[Kilby]

Just chipping in from the sidelines on this.

How about a long range sensor just to out wierd Mr Z

I was reading some app notes on a single chip radar solution a couple of years ago, the chip was intended for measurement of levels in silos etc.

I think I have the url at home (should be back there in a couple of weeks) though googling it will I'm sure give the usual useful results.

Kilby...

[Paul Perry (Frostwave)]

Thanks for that app note, Zero!
I can see some trouble trying to decide what frequency to use, though...
maybe 60 or 50Hz (depending where you live) to stop mains interference.
Or would that be far too low??

[toneman]

check out the "Electric Field Proximity Sensor" article
in the July 1997 issue of Nuts & Volts...!!
i think, this is where/how the "one chip solution" eventually was made/came from.
easy 2 build, includes pcb layout.  no exotic parts.  
staysensed
tone

[NaBo]

That IS a very nice app note, zero... very very nice!  I like how figure 2 illustrates the basic requirements for C->V conversion... definitely helps me understand what everything is doing in that circuit.

What are you having problems with in yours?  Are you getting any change in voltage at the test points?  Could be that it's just not enough to trigger the LED.  Which leads me to my next point:
If you haven't, I think you can and should just do away with everything after TP2 if you intend to make LED brightness proportionate to the distance from the plate.  The second half of IC2 and the tranny let NO DC through to the LED, until the threshold is broken, then it's lit to full brightness as long as said thing stays within the threshold... basically, it's like having an SPST switch instead of a pot.  Cool for other purposes, but not useful for a variable control.  So if you light the LED from where TP2 is, you should be able to get a smooth control over the brightness.  That's just what I (an uneducated moron) gathers from their description anyway.

I think I'm gonna try to build this one first... (when my samples get here... FIRST ones i've ever ordered from anywhere, and it IS for prototyping and educational purposes which Maxim says is cool... so don't think im bad, if you're that type!  :wink:).  Transmogrifox complained of a bit of drift with his design, so maybe this one won't have much of a problem with that... "Passing the XOR inputs through nearly identical comparators largely nullifies the effect of offset voltage, drift, and propagation delay through the comparators."  Not sure exactly what they mean, but it sounds good...  

In the meantime, I think i'll add an isolated mono switching jack before every variable-resistor pot that I think i'd wanna use the proximity control in its place.  I'll have everything but the optoisolator in a separate enclosure and use a 1/4" patch to connect V-out to the LED side of the customized opto in the pedal, switching the pot out.  I realize I'll have to make an opto for EVERY pedal, but I think this way I avoid a potential ground loop (ie: proximity control and pedal running off same supply, LED grounded through jack at chassis) and minimize the length of wire the stompbox circuit's signal travels through (the patch carries DC into the LED side of the opto instead of carrying the signal out of the pedal to the LDR in the proximity contol).  Not to mention the ability to tweak the opto to work best with the specific pedal, while using the same control.  Come to think of it, I could also screw the jack switching and use a toggle/stomp... to kick in the proxi mid-song and switch back to a stationary setting with the pot.  Hmmm...

Sound like a good idea?  Any suggestions or things I should watch for? ... Aside from some moronic bandmate plugging the proximity control's DC output to some poor stompbox's input or something?   :roll:

Actually getting back to the one-of-the-coolest-guys-ever who inspired these types of threads in the first place, I soemtimes wonder why Zach doesn't have the probe series set up something like this... or maybe have it as an option.  A single proximity control unit that can plug into the wah, trem, or fuzz circuit... or all three at once with a switch to choose which one to control.  That'd save a lot of pedalboard space, but I guess you couldnt use them at the same time... well you probly could, but it would all vary at the same rate... but you only have one free foot so you cant control more than one at the same time, differently, very easily... hmm...  these thoughts are probly just degenerating into senseless ramblings at this point, (it's 6AM  :shock:... i should get to bed) there's probably some pragmatic reason against this, whether electronically or economically based...  I'm no EE, and I don't own a business  :wink:

*Phewf*... probly my longest post ever.  And nowhere near as intelligent as something a few other long-posters would write  :wink:

[NaBo]

One more thing  :oops:... that circle with a squiggle in the left part of the schem...  That's what you'd call a 1MHz crystal clock oscillator, right?  Something like the MXO45?

If so, does it connect like this:


K, i'll go sleep for a while so someone else can say something before I say something else...  that sentence hurts my brain