one pot, two resistances?

[caress]

i'm not going to be able to get to my breadboard for a few days so i just wanted to ask...

one pot controlling 2 equal resistances - essentially a single pot being used in place of a dual pot.

using the one pot as a simple voltage control:  9v+ on one side, ground on the other, wiper to X.  X being 2 jfets?  2 led/ldr combos?
would that work?

[earthtonesaudio]

If you want two resistors to both change in the same way (increase or decrease) at the same time, there are dual vactrols  you can buy.  One LED and two photoresistors in one package.  More current through the LED makes both resistors decrease.  The trick is the resistor values are fairly linear over a small range of currents, but highly nonlinear over a small range of voltage.  So you'd want a current limiting resistor in series with the pot's wiper, at least.  You could do two LEDs and two LDRs, but it's harder to get two LEDs to match than it is to adjust parallel/series resistance of the LDRs, so that's why I suggested one LED with two LDRs.

On the other hand if you want one resistor to increase while the other decreases, one LED/two LDRs is not enough.  You could do two LEDs but you run into the same problem of them being mismatched.  In fact any two active devices are going to be difficult to match, including JFETs.  When you want to do something this complex with any degree of linearity I think switched-capacitor or switched-resistor techniques start to become more attractive in spite of their increased complexity.  For just voltage control you can make resistor PWM pretty simply.  A 555, two diodes, one cap and a pot gives you variable duty cycle output, which you can then use to control a CD4053 or CD4066. 

[caress]

If you want two resistors to both change in the same way (increase or decrease) at the same time, there are dual vactrols  you can buy.  One LED and two photoresistors in one package.  More current through the LED makes both resistors decrease.  The trick is the resistor values are fairly linear over a small range of currents, but highly nonlinear over a small range of voltage.  So you'd want a current limiting resistor in series with the pot's wiper, at least.  You could do two LEDs and two LDRs, but it's harder to get two LEDs to match than it is to adjust parallel/series resistance of the LDRs, so that's why I suggested one LED with two LDRs.

On the other hand if you want one resistor to increase while the other decreases, one LED/two LDRs is not enough.  You could do two LEDs but you run into the same problem of them being mismatched.  In fact any two active devices are going to be difficult to match, including JFETs.  When you want to do something this complex with any degree of linearity I think switched-capacitor or switched-resistor techniques start to become more attractive in spite of their increased complexity.  For just voltage control you can make resistor PWM pretty simply.  A 555, two diodes, one cap and a pot gives you variable duty cycle output, which you can then use to control a CD4053 or CD4066. 

ok i'll give it a try with one LED, two LDRs as both resistances would be increasing or decreasing together.

[Processaurus]

Wait, why wouldn't you use a dual pot?

[caress]

Wait, why wouldn't you use a dual pot?

i don't have any on hand.
also, just curious as to other methods...