Build Your Own Clone Message Board

I'm wondering what kind of photo resistor I would need to use in order to control the fixed wah setting on the envelope filter. I'm assuming that I would replace the potentiometer with a photo resistor, but I don't know what value or where the lugs would go.

while you wait for an expert answer (I haven't built this particular BYOC circuit), I would theorize that you should be able to keep the pot, and add a DPDT switch so you could have either Pot OR Photo Resistor operation with the flip of a switch, if you are so inclined.

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Need more information. What do you want the photo resistor to do?

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What I want (I saw this done on youtube) is to be able to control the fixed wah filter by covering or uncovering a photo resistor with my foot. Basically I need to know where the lugs of the photo resistor would need to be wired to in order to make it so that when I cover the PR with my foot, it's as if I'm rocking forward on a real wah pedal, and when I uncover it and allow light to hit it, it's as if I'm rocking back on a real wah pedal. I also need to know what value PR I would need to use. Thanks for the help!

Here's the video of what I want. https://www.youtube.com/watch?v=IyX9zVhq1P8

It's kinda hit and miss with optos. The amount of light available will vary, they react at different speeds etc. If the manual pot is 100k, as long as the opto sweeps through that range you should get something. Most of the one's I've had range from a few hundred ohms to a few of Meg, but they can take a while to get there.
Here's one way to hook it up:



In that diagram it is replacing the pot completely, but I'd be inclined to try it with it added across lugs 1 and 3 of the manual pot too. You'll be able to add parallel resistance which will give you some adjustability for different light levels and opto specs.
Put it on a switch to break one of the connections if you don't want it on all the time.

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"Spud knows tone"

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Why do you have to use a stereo jack? why not just send wires from board to dpdt switch?

If you don't want the expression pedal option you could indeed just wire the switch to the board.
It's not an ordinary stereo jack, it's a switched jack. When an expression pedal plug is inserted it disconnects the components on the switch, so, unplugged, that's exactly what's going on anyway.
I just reposted someone else's picture, it's from another thread.

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"Spud knows tone"

codtone.com

Thanks mate, I saw the video with that opto on a byoc envelope filter and I just didn't see reason why to do it. Its an auto, so let it do its thing and if I wanted a real wah I'd one instead. But its an interesting option