Ideas for optical wah/expression-pedals?

[BN]

Last year I got the idea to build an optical controlled wah pedal. But though I couldn't figure out how to controll the lightflow from my LED I eventually ended up with a homemade mechanical wah-chassis anyway. That's something I won't do again for quite some time (now I understand the warnings on geofex.com)   

Does anyone have an idea of how to build a LED/ldr (or IR-LED/photodiode) "shutter" that could be used in an expression pedal? I've got access to a metal workshop even though it's not extremely well equipped.

[Paul Perry (Frostwave)]

You just have a kind of shark fin shape attached to the base of the moving pedal, so as the pedal moves more or less of the LDR is exposed to the nearby led.
Maybe a friendly music store will let you look inside a wah like this (I've looked inside plenty, tweaking ones where the led is knocked out of position & the wah is gone).
You need to experiment with the shape of the fin to get the wah taper right.

[B Tremblay]

I believe that it's actually much easier to use the wah pot to vary the brightness of the LED, rather than use the physical action of the pedal to move a shutter.  RG Keen spells it out here: http://geofex.com/circuits/ldrlfo.htm

I've been using that approach for an LED/LDR wah and it works very well.

[Paul Perry (Frostwave)]

Sure, it's easier, but it defeats the whole point, which is that 1. the sharks fin gives you total control of the taper, even two cycles or more per one press if you like (great idea for a trem) PLUS!! 2. it will never wear out. Ever. Noiseless.
And, anyway, the shark fin IS easier!! no gears.

[BN]

And, anyway, the shark fin IS easier!! no gears.

This is exactly why I wanted to build an optical pedal. The rack/pinion/gear-thingie got me quite frustrated last time, even though I came up with something that actually worked...    (many thanks to Paul that runs diyguitarist.com)

[Dave_B]

Another approach is the transparent plastic that moves between the LED and the LDR.  I've seen this on some of the all-in-one floorboards.  The plastic has a gradient that starts out transparent and ends up black.  If you can figure out the mechanics, the gradients can be created and tweaked in Photoshop, then printed on clear film.

[Processaurus]

Another approach is the transparent plastic that moves between the LED and the LDR.  I've seen this on some of the all-in-one floorboards.  The plastic has a gradient that starts out transparent and ends up black.  If you can figure out the mechanics, the gradients can be created and tweaked in Photoshop, then printed on clear film.

Very cool idea, using photoshop to draw the perfect taper.

Heres a couple pics of my Mu-tron Vol Wah it has an interesting optical mechanism, its a lot like the simple kind that use the shark fin with a V cut out for the light to shine through, but adds some lenses to focus the LEDs light I guess.  It has an two LDRs in one lense, and in the other lense it has an LED, and a third LDR, that is there for some kind of current regulation on the LED (it seems unnecessarily complex, but they must have been thinking something).





I'm sure if you have access to a shop, a crybaby shell could be modded to have a similar metal shade.  Maybe an IR LED so you don't have to worry about sealing the light out.  High brightness LEDs are much more directional than older LEDs, that could help with keeping light from leaking around your fin too.

I have a curious old Edwards "light beam" vol pedal too, that one is much simpler, it just has a light bulb hooked up to AC, and has a plastic thing with a V shape and some semi transparent film over the V, thats attached to the rocker and gets between the bulb and an LDR.

With an LDR, you can tweak the taper by putting fixed resistors (or trim pots) in series or parallel with it, to help get the response you want. 

We'd love to see a picture of your handmade pedal if you got one, I'm always impressed by that kind project.

[Paul Perry (Frostwave)]

With an infra-red LED, you have just as much (in fact more) trouble with light leaking, most of the light from incandescent bulbs & daylight is in the IR zone.
As for the double led/ldr system in the illustration, if one is left open, it could be that they are using a circuit I have seen where a voltage controlled amplifier is linearised, by using an identical control element in a feedback loop. Would have though it to be wild overkill for a guitar volume pedal, but maybe not!

[BN]

There might be some pictures of my wah in the future but right now I haven't got any digital camera and the pedal is borrowed to a friend who wanted to test it...

I have actually tried the toned plastic film approach. I played around a little in Paint Shop Pro (I never learned how to use photoshop) and printed the result on transparent film. Then I measured the LDRs resistance as I dragged the film between the LDR and the LED. The major problem with this solution is my poor skills when it comes to computer graphics... 

The idea with double LDRs sounds pretty good to me. If you hook them up to a differential amplifier ( http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampvar6.html ) an uses one of the LDR to measure the surrounding light you, at least theoretically, can get rid of the problem with interferring lightsources. But this calls for some voltage controlled resistance (a third LDR/LED maybe?  ) connected to the output of the OP.

[Roobin]

The idea with double LDRs sounds pretty good to me. If you hook them up to a differential amplifier ( http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/opampvar6.html ) an uses one of the LDR to measure the surrounding light you, at least theoretically, can get rid of the problem with interferring lightsources. But this calls for some voltage controlled resistance (a third LDR/LED maybe?  ) connected to the output of the OP.

Oh yeh, good idea! Using the difference between surrounding light.

I suppose building a light-proof enclosure would be very hard.

But, please explain why the VCR connected to the output?

[BN]

But, please explain why the VCR connected to the output?

Well, the output (as well as the inputs) of the OP has to be a voltage (or a current passed through a resistor, aka a voltage) and the idea is to use the whole thing instead of a pot, hence the VCR.

[mac]

Last year I got the idea to build an optical controlled wah pedal. But though I couldn't figure out how to controll the lightflow from my LED I eventually ended up with a homemade mechanical wah-chassis anyway. That's something I won't do again for quite some time (now I understand the warnings on geofex.com)   

Does anyone have an idea of how to build a LED/ldr (or IR-LED/photodiode) "shutter" that could be used in an expression pedal? I've got access to a metal workshop even though it's not extremely well equipped.

I found some useful parts at a hardware store and at my construction site. Basically it is a cylinder mounted on the pedal case, housing a spring and a piece of iron which I press with my foot. The other side has a black plastic that blocks the light of a small bulb going to the LDR. Similar to a pen that have a spring inside. The circuit is an idiot wah or photon filter.

Applying a gradient to a plastic with photoshop. Nice idea. I'm going to try it.

... Photoshop, the fuzz face equivalent in the world of PCs.


mac