Electronic Potentiometer

[prprog]

Hi
Which electronic circuit can be used to substitute a potentiometer? I have found so far circuits that used digital IC's to substitute one side of a pot. What I am looking is a circuit that substitute the 2 sides of a potentiometer, therefore it will have 3 connections to control.

I took a look at a AD5220 , it is what I intended to do....but I don't have such IC. Can it be done with a LED + LDR (optoisolator) . I have plenty of those which I used for audio analog control. I was thinking of using 2 optoisolators, but need to make the led in one light up "more" and the other to light "less" with the same control signal. Any suggestions?

Thanks,
PRPROG

 

[Diver300]

Optoisolators are not linear, so it would be difficult to use them to replace a potentiometer.

I think that you should say more about what the rest of the circuit does, before anyone will be able to help.

 

[ronsimpson]

I have used cadmium sulfide photo cells to control audio. They are very linear.
**broken link removed**

 

[prprog]

I have used cadmium sulfide photo cells to control audio. They are very linear.
**broken link removed**

Thanks Ron.

What I intent to do is to substitute a potentiometer on a guitar pedal effect . I have used LED + LDR (optoisolator) with audio with excellent results. But this is a 2 connection device. I guest that I have to couple 2 LED + LDR (optoisolator) in "some way" and make one LED to increase glow and the other LED to decrease at the same time....but how do I do that? Again I can control the intensity of one LED; how do I "invert" the other LED to do the opposite.
Thanks,
PRPROG

 

[alec_t]

You could perhaps do it mechanically by having the pedal move a shutter so that one LDR gets more light as a second LDR gets less.

 

[prprog]

On the following circuit I can control audio source volume depending on the sounds capture by the electret. I used it as a breath controller. (there are other components on the audio in/audio out path but in essence this is the complete circuit). The Led glow more or less depending on the electret capture sounds/breath.

Requirement : What I need is to add another LED + LDR (optoisolator) and make it behave the opposite as the first LED + LDR. Which means that the second LED will be lighted all the time and will reduce its intensity once the electret capture sounds. I will wire the two cadmium sulfide photo cells in series, which will give me 3 contact points, which I believe can substitute a potentiometer. How can this be done?

Thanks,
PRPROG

 

[MrAl]

Hello,

If you run a constant current through two LED's in series they both light up about the same brightness.
If you shunt some current around one of the LED's that LED will grow dimmer while the other grows brighter.
Perhaps you can use that as the mechanism to change the resistance of two photo cells.
The current shunting might be done with a transistor or a third (single) photocell and LED.pair.

 

[dougy83]

On the following circuit I can control audio source volume depending on the sounds capture by the electret.

If you're happy with the circuit you've given for one LED, then simple duplicate it and either change the amplifier configuration to non-inverting, or connect the LED and resistor between 5V and the opamp output.