Controlling a Resistor-to-Ground Wah With an Expression Pedal

[David]

For space and utility, I need kind of a "Swiss Army Knife" input processor.  I was thinking about a noninverting buffer, a sustainer (probably a Flatline, maybe an OS since I already have the PCB), a volume control and a wah in one enclosure.  The wah would either be inductorless like a Coloursound, or perhaps an inductor wah.  Doesn't matter.  The former should be easy and the latter I already have.  I'd like to do the resistor-to-ground thing with an LED/LDR combo thing (recall the Anderton retrofit in the wah article on GEO)  being driven by the expression function of a DOD FX-17.  I would power the FX-17 from the "Swiss Army Knife".  Its expression pedal function supposedly implements a voltage divider over a stereo plug.  I believe the tip is the wiper of the "pot".  At least, this is what I recall from the FX-17 schematic on Paul Marossy's site.

What I found troubling was the output "ordering" of the pedal, if you will.  I believe Paul indicated that the expression pedal output is 0 volts with the pedal toe-down, and +5 with the pedal toe-up.  This is not quite what I expected, I guess.

1)  Does a resistor-to-ground wah go trebly as resistance to ground increases or decreases?
2)  Could an LED be driven properly in this application with only 5 volts?  Am I safe in assuming I would have to change the current-limiting resistor (probably to what you use for driving an LED from a PIC)?

3)  Which DIY autowah circuit has a simple envelope detector that could be "unbundled" from the autowah circuit and also used to drive the LED in the resistor-to-ground component to create an autowah function?  I looked at a few and couldn't see how to "unbundle" them.

I'll stop there for now.  Thanks, all!

[David]

Well, I was wrong about one thing.  The FX-17 only has 2 outputs from the expression pedal, so that means it's not a voltage divider.  It's a rheostat.  That would tell me that I'd just have to connect an LED with the appropriate resistor across its terminals and shine that at the LDR.  Voila!