Alternative to large variable cap

[Raeden]

I am looking for an alternative to using a large value variable capacitor in a circuit, as I'm finding it very difficult to find one large enough (that won't cost me a lot of money). The project I am currently working on is a string of LEDs that has a variable fade in/out time. My original plan was to have the variable cap in parallel with the LEDs, but the values of the var caps I could find were too small.

Is the best option to amplify the cap using an op-amp?

*newb question* If that is the best option, would you put the cap in parallel with the op-amp? How would you accomplish that?

 

[Nigel Goodwin]

You don't need a large variable capacitor, that would be the completely wrong solution, and such large capacitors have probably never been made?.

To do such a thing you would use an opamp (or similar) with a fixed capacitor, and a variable resistor (which are easier and cheaper).

I suggest you post your circuit, or search for the many previously posted on here.

 

[Raeden]

Thanks for the quick reply.
Right now I'm currently hitting myself for not seeing the obvious answer of using a variable resistor instead. I understand sort of how it would work in theory, I just can't seem to grasp how to put it in properly. Would you connect the variable resistor and capacitor in series with the positive terminal of the opamp, then connect the output to a resistor and the LEDs?

I would post my circuit, but it is currently in shambles, since I'm still in the planning stages. And I am looking on the internet for something that is comparable to what I want to do, but I am yet to find anything.

 

[Nigel Goodwin]

A quick google finds a number of such projects