DIY footcontroller for a Digitech RP unit?

[darwin_deathcat]

Hi all,

   After a long romance with analog, I recently had a change of heart when I heard the new Digitech RP255 that my friend had. I had to have one myself, but being a devote DIY'er, after a bit of initial research, I bought the Digitech RP155 unit rather than the 255. The price difference was about $50 between the two, and the only real difference is that the 255 has a built in (built on?) foot controller to modulate the Wah models or to act as a volume pedal. The 155, on the other hand only has has an input for an external control. What kind of controller is it? Well, they recommend usign an Ernie Ball VP Jr. volume pedal. You apparently just use a mono TRS lead and connect the output jack of the volume pedal to the "control in" jack of the RP155.

So here's my question: Can anyone point me to a reliable scheme for that Earnie ball pedal. I believe it's just a 250k audio pot wired as a standard VC (input to lug one, output on lug 2, and lug 3 to ground),a nd then hooked up via a gear system to the pedal mechanism. If this is true, then the "control in" jack expects to see a pot wired as a "reverse" VC, no? It must just send a signal up the hot lead, and expect to read it back on the negative lead after being modulated by the resistance of the pot along it's travel?

As for build considerations: I have one of those cool old metal sewing machine footpedals that I want to build this in. The mechanics of the pedal motion are slightly different than those in a standard Wah or Volume pedal, but there seem to be two options for transferring the pedal motion to the pot. One is to use a gear or belt system to turn a standard turn pot. The other would be to use a slide pot, and just keep all t he motions linear. Can anyone point me to a good DIY writeup or something? I've had little success finding anything good via a google search....

Thanks in advance,

DDC

[handwire]

grab an ldr and a trs 1/4 plug.

Wire one end the ldr to the ring and sleeve and the other to the tip, and boila, i did this many moons ago for my zoom 505

[darwin_deathcat]

That's an interesting idea. How do I control it? Use the shadow of my foot, or something? Or do I also need to wire up an LED, and make some kind of mechanical way to block the light of the LED hitting the LDR? ie. just a slip of black plastic or something, attached to the end of the footpedal so I can move it up and down provideing more or less light to the LDR...


Eventually, I found this link http://www.electrongate.com/projects/index.html which seems like an easy and ultimately very effective DIY solution. I'll probably go that way since it's truly passive (ie. needs no batteries)...