Author Topic: Dr. Proxxi working! Thanks much to Munky for the cool idea!  (Read 2841 times)

Transmogrifox

Dr. Proxxi working! Thanks much to Munky for the cool idea!
« on: March 09, 2004, 12:31:59 AM »
Tonight, instead of being a good boy and doing my homework (again :wink: ), I built my proximity-controlled wah.  I am elated.  I was almost too excited to eat dinner (I know I have geek's disease to the worst degree)

Today I took my oscillator into the lab and tested it. PSPICE gave me a nice stable-amplitude sine wave at about 235 kHz....this circuit gave me a strangely compressed square wave, but at 230 kHz...which went to 240kHz when I lowered the supply voltage to 9V from 15V...so to say the least it's not the most "robust" and stable oscillator, but it's stable enough and good enough for this pedal...It did seem to be good for +/- 1kHz over about 5 min for sure when the supply voltage was held constant.

Anyway, I was thinking through the use of a phase-locked loop or RG's idea of a 1-shot multivibrator, but both are more sensitive to how the oscillator is tuned, so I figured out a simple RC low pass and precision rectifier were all it needed to work (geez I'm glad I didn't go dinking with the PLL).  

I happened to have a Dr. Quack built on my breadboard, so I took out the envelope follower and replaced it with the control output from my proximity detector.  With the sensitivity control, I can tuned it to pick up motion from very close to far away and it seems to be stable enough to not have to "re-bias" it every 5 minutes.  I didn't play for more than 5 min at a time, so I'm not sure what the drift is like, but it is truly something else to be waving my hand around a copper plate and hear my guitar wah around.  There's something that just puts a smile on a guy's face after smelling solder fumes 4 hours and you stick some audio jacks into a ratsnest of wires and electronic components, and your hair-brained idea actually works!

So here's some details in the event you should have need for a wah without mechanical parts:

1)  Don't use the Dr Quack wah. I really don't like it.  I have that shown in the schematic.  The 2 capacitors in the feedback loop that I have unmarked are 4.7 nF I think, but check the Dr. Quack schem if you want to build this one.

Instead, check out the Morley wahs.  They are LDR controlled, just build one of them and then use the proxxi control voltage to drive the LED instead.  The BIAS and SENSITIVITY controls in my schematic should allow you to tune the Morley wahs to proper operating range.

2)  2.5"x3.5" slice of un-etched copper-clad circuit board works well.

What I did is drill a hole through the middle of the board and soldered a wire to contact the copper, then sanded it down smooth for cosmetic purposes.  I cut a piece of Lexan (plexiglass) to the size of the copperclad plate, and drilled a 3/8" hole in the place where the wire coming out of the copper clad board fits when the Lexan and copper clad board line up flush.

I then lined them up so and used a small drill to make holes through the circuit board and plexiglass together, one at each corner, then used some small screws to fasten the board down to the plexiglass.

The final step is to super-glue some foil on the other side of the plexiglass, then drill another hole so that a wire can be secured by screw to the foil surface.  This wire is connected to ground for shielding.

The other wire from the copper board plugs into the oscillator

http://www.geocities.com/transmogrifox/ProxyOzzi.html

at the point "Antenna/Metal Plate" part that is modeled by the 14pF capacitor.

Then the output of the oscillator is connected to the Oscillator input of this circuit:

http://www.geocities.com/transmogrifox/DrP.html

This one also shows the modified Dr. Q wah circuit.  I only used this because I already had it built.  I do recommend a different LED/LDR controlled circuit, and just modulate the LED with the output of the Proxxi detector.

Enjoy DIY community!

I will have Pix when I get my next roll of film developed.
trans·mog·ri·fy
tr.v. trans·mog·ri·fied, trans·mog·ri·fy·ing, trans·mog·ri·fies To change into a different shape or form, especially one that is fantastic or bizarre.

Tim Escobedo

Dr. Proxxi working! Thanks much to Munky for the cool idea!
« Reply #1 on: March 09, 2004, 01:10:46 AM »
Sounds cool.

There was this guy in BC that was making PCBs for proximity detectors. His designs were simple using CMOS oscillators, and the intention was for people detectors, alarms, etc. Unfortunately, I can't find his site anymore.

Transmogrifox

Dr. Proxxi working! Thanks much to Munky for the cool idea!
« Reply #2 on: March 09, 2004, 01:20:14 AM »
Bummer...that probably would have been a simple "kit" solution.  

I think maybe an IR emitter/detector schem would be a better way to go about this.  I like this one because it's so reminiscient of the Theremin, and a fun project lending itself to much learning. Art's Theremin page has a schematic for the IR Theremin, and the proximity detector outputs a DC control voltage which he uses to control an VCO.

I suppose I could build a VCO and use this thing as a kind of a "mock Theremin"...add some synth sounds to my guitar signal path by producing pulses and filtering schemes....That's the nice thing about having a "DC" voltage control output instead of a varying inaudible frequency, is it can be used to control about anything from flangers to phasers to oscillators, to distortion parameters...volume control...zvex has only scratched the surface with his existing Probe series, but I don't put it past him to come up with some very cool stuff yet to be.
trans·mog·ri·fy
tr.v. trans·mog·ri·fied, trans·mog·ri·fy·ing, trans·mog·ri·fies To change into a different shape or form, especially one that is fantastic or bizarre.

Marcos - Munky

Dr. Proxxi working! Thanks much to Munky for the cool idea!
« Reply #3 on: March 09, 2004, 10:22:50 AM »
Cool. I didn't have time to try yet, but is great to heard that this goes right.

Transmogrifox

Dr. Proxxi working! Thanks much to Munky for the cool idea!
« Reply #4 on: March 09, 2004, 01:54:39 PM »
Yeah...now it can only improve.  It does drift around, so I can see myself needing to adjust the bias contol often, however it is exciting that it at least works.  If I use the right wah and set the sensitivity a little higher, the drift may not be a problem because I will be able to just "move past the rail" smoothly.  The diode makes it "pop" on with the Dr. Quack wah, but and LED/LDR assembly wah could just be biased at a minimum, then the proximity detector would increase it from there instead of just "popping" on.  The bias knob needs to be set "just so" to make a smooth transistion on the Dr. Quack wah filter.
trans·mog·ri·fy
tr.v. trans·mog·ri·fied, trans·mog·ri·fy·ing, trans·mog·ri·fies To change into a different shape or form, especially one that is fantastic or bizarre.

ExpAnonColin

Dr. Proxxi working! Thanks much to Munky for the cool idea!
« Reply #5 on: March 09, 2004, 07:04:46 PM »
Very cool, man.  I'm glad you figured this out!  I also know well the "Didn't to homework don't want to eat dinner" disease you have :)

Slightly OT, but does PSPICE really work for you?  I'm considering getting a mac version... how well does it do?  (It's basically supposed to let you draw a schematic and let you know how it would work, right?)

-Colin

Transmogrifox

Dr. Proxxi working! Thanks much to Munky for the cool idea!
« Reply #6 on: March 09, 2004, 10:08:10 PM »
yeah, PSPICE works well.  It has been a life-saver on a lot of filter designs and stuff.  As long as you have a good model for what components and such you are using, you can get things to look exactly like they do in the lab....however, if your models aren't as good, you can get some way wacked out stuff...

This oscillator is a good example of things not turning out exactly as they do on PSPICE.  If PSPICE was correct, then this oscillator would be very stable and have a 5 V peak to peak pure sine wave output.  as it is, it is not very stable and has a rail-to-rail square wave output.

For this pedal, that's fine with me.  I just keep tweaking with the sensitivity and bias controls every time I feel like I'm "losing the tone".

When you get this thing set right, you can get some of the most expressive wah sounds imaginable.

Actually, I have PSPICE designed and LDR controlled wah just tonight that moves toward a 4th order Chebychev response.

http://www.geocities.com/transmogrifox/wahfil.JPG

I haven't seen a chebychev wah yet, so I'm interested in seeing what this sounds like.  It obviously doesn't keep the cheby response over the whole range of travel, but it has that type of response on the low end, then on the high end....and it seems to "teeter-totter" the passband ripples as it moves up.  It looked cool in simulation...now to see what it's like in reality.

It should have a similar effect as having two wahs in series with one pedal travel lagging the other slightly
trans·mog·ri·fy
tr.v. trans·mog·ri·fied, trans·mog·ri·fy·ing, trans·mog·ri·fies To change into a different shape or form, especially one that is fantastic or bizarre.

Transmogrifox

Dr. Proxxi working! Thanks much to Munky for the cool idea!
« Reply #7 on: March 11, 2004, 04:09:29 PM »
For those who followed the link in the previous post:  I built the cheby-wah from the previous post, and it is an oscillator...I should have done a transient analysis on it.

Anyway, I came up with a pretty useable wah based on a state-variable filter.  It's nice to have the adjustable Q anyway.  Maybe some other day I'll re-design the cheby-wah so that it's stable.  It sounded like a police siren controlled by my proximity detector.  It was fun to play with anyway.
trans·mog·ri·fy
tr.v. trans·mog·ri·fied, trans·mog·ri·fy·ing, trans·mog·ri·fies To change into a different shape or form, especially one that is fantastic or bizarre.