Vactrol Current Smoothing

[Unlikekurt]

I have a project I'm working on that uses a resistance to determine a certain setting.
Currently a switch selects between two resistance values to give two options.
It would be interesting for the effect if the transition between these settings was smooth, but didn't require the user to turn a potentiometer.
My thought was to utilize a vactrol and determine the current required to achieve an approximation of the designed resistances or perhaps paralleling the vactrol with a fixed resistor - same idea.
If we accept that the above is achievable, which it may not be, the question is actually:
Can an RC network be utilized to smoothly change between two current settings of the LED?
I've seen networks to fade an LED on or fade it off, but not both.  Would switching between a fade in and a fade out network on a switch achieve this?

[Fancy Lime]

Yepp, no problemo. Just use the switch to change between different current limiting resistors for the LED of the vactrol and put a large electrolyte cap (100u or so) across the LED. Will need extensive fiddling to get the resistances right, though, because the relationship between current limiting resistor and vactrol resistance is not trivial. May I ask why  you want that smooth switching? Seems a lot of extra parts for a rather silly gimmick, no? But I may just lack the imagination for why that would be awesome to have. I can imagine it would feel a bit more "professional", but is that worth the hassle?

Andy

[idy]

I can think of lots of nice apps for this. Hit the footswitch and something "morphs." Could be speed ramping. Could be gain/volume (switching two presets for both values.) I did a OD pedal with two volumes and two gains and a footswitch with vactrols so it almost felt like a cross-fade, very natural, not a click off/on. It's a very neat utility and not really that hard to "tinker" into a pleasing scenario.

[Unlikekurt]

Exactly!  LFO stuff.
My thinking is a fixed R in parallel with the vactrol resistor.
Then two current limiting resistors in series for the LED.  With a switch across one of them.  This would allow for two different current settings without ever turning the LED off entirely.  The CLRs would need to be selected so that the resulting vactrol resistances in parallel with he fixed R give me the values I need for the two speeds I want.  Definitely some tinkering BUT with the fixed R it might easier than trying to deal with the extremes of the vactrol dealing with cutoff etc.
And then dial in C accordingly.  That's my biggest concern actually, if the ramp up / ramp down will be usefully perceivable or not.
How did you employ the idea In your OD Idy?

[anotherjim]

I remember RG publishing something like this...
http://www.geofex.com/Article_Folders/lera/lera.htm

[Unlikekurt]

Wow!  Thanks!  That LERA hits the mark.  Thanks to RG as well.