Idiot Wah - inverting LDR control?

[NaBo]

Hey everyone... I made an idiot wah using an LDR as the VR, and its excellent... however, i was wondering if there was any simple way of making the control behave like a regular wah, foot down = high freq., foot up = low. its more of an "aww" pedal at the moment.  can a "unity gain op amp inverter" be used after the LDR, or am i just talking out of my ass  :?

I'm surprised i didnt find any posts about this with a search!  maybe im just the only fool who can't seem to turn my comfy world of wah upside down

[Paul Perry (Frostwave)]

I'm not sure what you mean, do you have a shutter system across the LDR? Because you can cut the edge of the shutter to go either way.
Or if you have a pot somewhere, you could reverse the pot?

[NaBo]

nope, no shutters or pots... i'm just waving my foot up and down over the LDR.

I see how it can be done mechanically, with a pedal/shutter of some sort... but then it would lose the charm of being a completely touchless control!  i gotta impress my "normal" guitar-playing friends who don't realize how simple this stuff can sometimes be :wink:

I'm just wondering if there is any way to reverse how the LDR behaves, so that full light will result in a high resistance, and darkness will result in low resistance?  I've actually gotten kind of used to the "backwardsness"... actually i kind of like it for some purposes.  but if this can be done easily enough, i'd certainly jump at the chance to add it in and use a toggle to switch between the two control modes.

[Paul Perry (Frostwave)]

OK NaBo, I'm with you now!
Sometimes in a wah (or more often an autowah) you see the variable resistor replaced by a transistor, wiht the transistor's base being modulated by a voltage to change teh apparent resistance of the transistor.
SO in your case, you could replace LDR by a transistor, and use the LDR as one of the two bias resistors. A bit of arsing around to make it work, but I'm sure it could be done. (a two pole switch would let you switch the LDR and other resistor around, with opposite effects).

[NaBo]

Thanks Paul!!!  I'll have to try that out!

The Tone God's post over in my QT301 thread gave another way of achieving the same result with an op-amp and optoisolator.  I think i'll try breadboarding both ways, and possibly building another idiot wah altogether...

I've always wanted to screw with two wahs at the same time...  in series, in parallel, with same-direction sweeps, with opposite sweeps...  hopefully they'll do more than just sit there and oscillate, but that'd be cool too.  lol, i just imagined a row of 8 or so of these, with all different ranges... it's almost like a manual zvex seekwah!  :twisted:

[The Tone God]

Actually that might be an interesting way to do things. Use the opamp idea and simply drive two optos with each opamp in either inverting or non-inverting modes. Maybe another way would be use a asymetrical drive circuit with a NPN and PNP transistors like the 3-pole "Rock N' Control" circuit.

Andrew

[David]

Actually that might be an interesting way to do things. Use the opamp idea and simply drive two optos with each opamp in either inverting or non-inverting modes. Maybe another way would be use a asymetrical drive circuit with a NPN and PNP transistors like the 3-pole "Rock N' Control" circuit.

Andrew

While we're on the subject, Andrew, do you know of a way that the same pot could simultaneously drive your 3-pole RNC and a volume circuit to make a volume/wah?

[Paul Perry (Frostwave)]

Andrew, do you know of a way that the same pot could simultaneously drive your 3-pole RNC and a volume circuit to make a volume/wah?

If you really want to use a wah and vol at the same time locked together, you could use a two gang pot!
(You can even lock 2 hotpotz together wiht mecchano type gears, if you are Heath Robinson!)

[David]

Andrew, do you know of a way that the same pot could simultaneously drive your 3-pole RNC and a volume circuit to make a volume/wah?

If you really want to use a wah and vol at the same time locked together, you could use a two gang pot!
(You can even lock 2 hotpotz together wiht mecchano type gears, if you are Heath Robinson!)

I just want to have to rock one pedal.  I doubted that I had the electronics savvy to switch the pot into either the wah circuit or the volume circuit.  Also, I wanted to explicitly avoid the dual-gang pot.  That's two pots to get scratchy, not just one.

[The Tone God]

While we're on the subject, Andrew, do you know of a way that the same pot could simultaneously drive your 3-pole RNC and a volume circuit to make a volume/wah?

You might be able to drive two RNCs at once. Never really tried it. There maybe a need for a buffer between the two RNC and the pot. Also each circuit might need different calibrations which maybe furthur necessitate the need for a buffer.

Sometime I'm going to update that article, along with everything else on that site, with some opamp RNC versions. I did the basic transistor setup just for cost, simplicity, and for people who fear opamps. I think the opamp versions will be alot more consistant and DIY friendly.

Andrew

[NaBo]

WAIT A SECOND!!!

I just realized something!  I think another circuit on Tim's page might be exactly what I was looking for... the Photon Filter!  it uses an LED as a variable resistor to ground, with an LDR controlling the voltage it receives.  sweet!  im gonna put the photon filter and idiot wah in a 1590B together with a toggle to switch between the two... mmmyeeees, my Wah-Aww pedal shall live soon, soooooooooooooooooooooooooooooon  :twisted:

[David]

Hey everyone... I made an idiot wah using an LDR as the VR, and its excellent... however, i was wondering if there was any simple way of making the control behave like a regular wah, foot down = high freq., foot up = low. its more of an "aww" pedal at the moment.  can a "unity gain op amp inverter" be used after the LDR, or am i just talking out of my ass  :?

I'm surprised i didnt find any posts about this with a search!  maybe im just the only fool who can't seem to turn my comfy world of wah upside down

Questions:

R.G.'s article on wah technology includes Anderton's de-scratch mod which implements a LED/LDR combo.  Did you happen to try this?  If you did, it might be interesting to connect 9V to pin 2 of the pot and pin 3 to the "output" so that the resistance decreases and the LED brightens as you move the pot clockwise.  I intend to try this myself (if I ever finish my backlog).

At least, that's what I think would happen...   :oops:

[Transmogrifox]

I believe the allure of a touchless wah is more than just scratchy pots.  I had a crybaby for about 7 years that never scratched--then I modded it and sold it.

For DIY purposes, I like it because it doesn't require me to buy expensive hot potz, I don't have to fool with the mechanical rocker pedal (another potentially expensive DIY build), and it can all be done with parts readily on hand.

The simple touchless wah is like NaBo has ---just an LDR exposed to the outside light and you block the light with your foot.

The more involved build is like Zvex proximity FX that use a high frequency oscillator and a circuit to demodulate the change in capacitance on a metallic plate.

One could also play on some stud-finder technology to do this, in fact, you could probably buy an old capacitive stud find on eBay for cheap and modify the output to control your wah.   You just need to test it on your foot.  If you're a enough of a stud, you can control your wah with it.