LM339 RGB LED fade effect

Try a ring oscillator for the signal you need

1) A three segment Astable Multivibrator will give a nice color organ effect. It'll be a pattern something like R, R+G, G, G+B, B, B+R... the only thing I wouldn't like about it, is that each color will fade on, but they'll turn off quickly. With this setup, it'll be hard to get them to fade off, but it's super easy to build. 2) You could use two op amps (741s maybe?) to create a sawtooth signal. Then use #1, #2, & #3 of the 339 to turn on each LED at different points on the sawtooth. Basically use the sawtooth as an input on each one, then setup a voltage divider on each one as a Vref. Methinks that would just turn each color on and off, not fade them. To be honest I haven't put a ton of thought into it, but it might be worth looking into.

Or you can build an arduino uno clone for less that $10. ;)

I posted an example of what I had in mind.