Is it possible to make a photoresistor, preferably passive, powered expression pedal?

[GrooveChampion]

I am trying to build a mini expression pedal and so far I couldnt come up with a mechanism that would fit a 1590B style box. Is the photoresistor idea possible?

[Travis]

Yes you could have a photoresistor externally mounted so that the amount of light it "sees" controls the "expression. You could fit it in a 1590LB or any tiny enclosure really.

It's obviously not going to be an equivalent to a normal expression pedal

[Zanius]

I don't recall what pedal it was, but someone had mounted an ldr on a angled jack and used it by foot successfully...
Not sure how practical that is, as lighting isn't always the same wherever you play. Good idea though!

[Zanius]

Not the one I had seen, but apparently people have done it.

[GrooveChampion]

OK so how can I put it to use in a closed box?

How do I wire the LDR to the stereo jack?

Are there LDRs of different values like pots?

Should I just make it active by adding an LED?

[nocentelli]

What expression pedal are you hoping to emulate, or what effect parameter are you hoping to control? Most exp pedals are a potentiometer with the wiper wired to tip, hot (lug3) to ring and cold (Lug1) to shield. They are usually 10k-100kB. A single photoresistor/LDR can often act as an expression device if you only need to vary a single resistance, but you will need some active circuitry to either invert the response (so lowering your foot over the LDR replicates the action of lowering your toe over a rocker pedal) or to have a single LDR accurately replicate the action of a voltage divider (i.e. two resistances that shift in opposite directions and three connections, of which one is common).

Andrew "thetonegod" has written a good article on exactly this subject:

http://tech.thetonegod.com/rockncontrol/rock.html

[GrooveChampion]

Typical 10k expressions. But I wanted to use it in the same manner as the AMT mini volume. As in the LED and LDR are within the enclosure and theres a piece of metal attached to the trradle that gradually blocks the LED.

[nocentelli]

The amount of engineering required to get a shutter to mechanically move over two LDRs doesn't seem much different to building a mechanism that would drive a pot....

[GrooveChampion]

Well if that the case, maybe I should go with a simpler mechanism.

[Travis]

IMO it would make more sense to have a treadle controlling a pot which is controlling the brightness of the LED rather than add more mechanical parts

The simple way to do this photocell exp pedal is to have the photocell externally mounted and use your foot to control the amount of ambient light that the photocell sees. The purpose of this is it's compact size and simplicity, it is functionally not as good as a regular expression pedal

Is this a great idea? No, that's why nobody is really doing it.

Is the version with the LED a great idea? Well it is an active circuit so that's drawback number one. You will need to find a pot and LED/LDR combo that have the performance that you're looking for. Since that's way more complicated than just choosing a pot value, that's obviously drawback number two. Basically the only advantage is that you wouldn't have to worry about a scratchy pot if you use it as a volume pedal.

In just about every way it makes more sense to build a regular exp pedal. It's possible to use a photocell but it arbitrarily reinvents the wheel

[GrooveChampion]

OK so about the mechanism, originally I was going to fit an actual rack and gear on a pot, but due to the height of the box the rack wouldnt travel enough to turn the pot all the way. Hence why I thought about other solutions.

The idea is to mass produce these expression pedals at an afordable price cos expression pedals here cost a fortune and importing them is pointless. Please note: This was intended to be a TINY expression pedal, fitting inside a 1590B box.

Maybe I should just go with the Ernie Ball method?

[Travis]

Have you checked out Daier enclosures? I think the treadle enclosures are $20 each

[GrooveChampion]

Yeah but I wanted it to be smaller than a standard wah.

[Travis]

If you can figure out a way to turn 1590Bs into treadle pedals and create an attractive product that you can sustainably profit from at less than the price of a moog or other common expression pedal, then you're already way ahead of us here.

At any rate, this is not a DIY project, and I know that I won't be doing any work developing this idea for free. Keep in mind this is currently a 100% undeveloped business idea and you're basically asking random people on the internet to develop a product that you wish to profit from. If I were to do that work, I would be a fool to hand it over to you and not take the profit myself

[rocket88]

there's a guy that did that on DIYSB if i remember correctly. he used the base plate from another enclosure as the treadle had to "weld" on mounting tabs to the enclosure and the new treadle.