Use of color-changing LED's in pedal projects

[slacker]

That's very neat, cheers for sharing it.

[dbp512]

I came up with this as 2nd gang of a gain pot for a fuzz I built for a friend and have used it a few more times:



It sweeps blue/purple to yellow/orange and while the gradation across the sweep is far from even it's pretty consistent from build to build; ie. magenta or pale purple "sound" about the same on different builds.  I hadn't seen this before on a commercial pedal or "in the wild." I guess I made this up . . . I am using 3-in-1 SMD LEDs like the ones that are used in rope lights.

Do you use LEDs that have separate anodes and cathodes? This looks really cool, but I realized it can't be done with diodes that share a leg, can it?

[ElectricDruid]

+1 Agree that proper control of bi-colour or RGB LEDs really needs a uP. That doesn't imply much cost necessarily, but it's more mucking about than most people want.
LEDs respond best to a PWM drive in my experience, and decent RGB control needs three PWM outputs - definitely a job for a little microprocessor.

That said, you can get more information out of less LEDs - colour can indicate one thing, brightness another. Or you can collapse the role of multiple LEDs (indicating waveform, perhaps) into one LED (red, yellow, green, blue, purple).

I don't see much advantage in pedal builds where mostly I seem to being trying to keep things as simple as possible and *not* add more parts!

Tom

[Rixen]

think there would be a market for an 8 pin microcontroller that runs as a LFO and has 3 outputs for RGB LED's ? of course it would need a 5v supply...

[ElectricDruid]

think there would be a market for an 8 pin microcontroller that runs as a LFO and has 3 outputs for RGB LED's ? of course it would need a 5v supply...

Dunno. 8-pin 5V LFO is on my list of things to do, but the 5V supply adds a few components, as I think you're suggesting.

Adding a RGB LED output to such a thing would be a nice touch, admittedly. Not sure what it'd do, but hey. People love pritty lights! I love pretty lights...oooh...pritty...lightss....

T.

[slacker]

Do you use LEDs that have separate anodes and cathodes? This looks really cool, but I realized it can't be done with diodes that share a leg, can it?

You should be able to change it slightly to work with a common anode RGB LED, swap the red LED and the 220Ohm resistor and replace the 1k5 resistor with a short, that makes it common anode. Then put resistors from the cathodes of the green and blue to either end of the 10k resistor. You might need to change some of the resistor values but you should be able to make it work in a similar way.

[samhay]

I don't know - haven't played with RGB LEDs. How do you get orange?

The proper mixture of green + red should give orange (using more red than green IIRC because equal amounts of R+G would be yellow so we dial the green back some to get orange). To get "RGB" colors we have to mix the individual LEDs at different brightness levels which results in less than satisfying results because the mixing doesn't work that well for certain combinations...

Thanks for the the explanation.
I concede that indeed there is rather a lot of supporting circuitry required to make these work in a desirable way.

[PEPPER!]

Do you use LEDs that have separate anodes and cathodes? This looks really cool, but I realized it can't be done with diodes that share a leg, can it?

You should be able to change it slightly to work with a common anode RGB LED, swap the red LED and the 220Ohm resistor and replace the 1k5 resistor with a short, that makes it common anode. Then put resistors from the cathodes of the green and blue to either end of the 10k resistor. You might need to change some of the resistor values but you should be able to make it work in a similar way.

Yep, these pieces are 3 separate LEDs that share a case and lens, the whole thing is 5mm square.  The shared lens creates the illusion of a solid color, and I also use a thin sheet of opaque plastic to diffuse the light further.  The different value resistors connected to anodes/cathodes are to make up for differences in perceived brightness for each color.  Lots of parts I guess but most are figured in to the circuit board or soldered on the pot.