RGB LED: 256 colors via controlled voltage?

[Aetherys]

Hey guys.

I was hoping someone here (read: electrician ) might be able to shed a little light (no pun intended) on 256-color LEDs and how they're controlled. (XClio's 256-color cases, for example.)

With no real knowledge of how they're wired, it's my understanding that the 4-pin LED is fed current both on each individual pin, resulting in red, green, and blue light, and on a combination of those pins, achieving a mix which results in the 253 colors in between, the fourth pin being ground. Right?

If this is correct, I'd like to know how XClio's little board causes the LED to cycle through the spectrum. My guess is that it's a rather simple formula that starts with power to the red pole (please forgive (and correct) improper terminology) and gradually increases the voltage to the green pole until the first two are at full brightness, producing a change from red to orange to yellow. Then the voltage to the red pole is ramped down, creating a change from yellow to green. Needless to say, rinse & repeat with green & blue then blue & red and the LED makes its trip around the color wheel.

I could be way off here, but I doubt it. So I guess what I'm really asking is this: How difficult is it to create a circuit board that can produce these formulaic changes in voltage with a continuous rheostat (or is it a potentiometer)? This is possible, isn't it? Am I at least on the right track?

 

[Automata]

With three colors, all it has to do is change the intensity (voltage) of the individual colored LED to get a wide array of colors. Your explanation sounds correct.

You could use three rheostats to change the voltage to each color. If you want it automated, you are upping the complexity of this project by many magnitudes.

 

[Aetherys]

I didn't have any concrete proof, it just made sense that it would work that way. With my rudimentary understanding of electronics, I could set up a simple controller with rheostats for voltage on each pin, but I'd really like to have them all on one rheostat (is that what you meant by automated?) and the more I think about it, the more I figure I have no option but to etch a board and build a microcontroller.

 

[Automata]

If you had one rheostat, they would all be the same brightness. That wouldn't allow individual colors to be picked.

 

[Aetherys]

Sure, if they were all connected directly to that rheostat. What I was suggesting, though, is that I'm sure there is a way to do what I want by employing relatively simple components and wiring. Maybe I could just do it with a digital potentiometer or something. Like I said, I have no idea how, but I just know what I want can be done without going crazy. Too bad greenman100 is banned. I guess tomorrow I'll call an electrician.

 

[Evilsizer]

right some leds that have more then one color to them. they have the color changed based on voltage, the best way unless you want it manual. is to use a micro controller with a built in var-resistor to change the voltage. the manual way would be to just use a reo-stat or trimmer resistor.

 

[Aetherys]

I know I'm being vague because I don't know exactly the best way to ask, but I guess I was hoping there was a way to vary voltage on 3 different leads with only one potentiometer or rheostat. I've taught myself a lot of crap over the years but I can't say I was really looking forward to learning to build a micro controller.

/yawn

 

[Evilsizer]

well the other option for controlling the color would be using a 2-4 position switch... as each lead on the led would need different voltage, you could then use a fixed resistance on each output from the switch to the led/leg(s).

really it comes down to the LED your using on best how to do it. if automated though a micro-controller is going to be your only option really.

 

[Bobnova]

A single pot can't do three outputs, at least no pot i know of!

Microcontroller wise, check out Arduino.cc, it's a cheap ($30ish for the official board, as low as $12.50 for an Arduino compatible "Really Bare Bones Board" board.
It's more then capable of driving an RGB LED, or a stack of them as well!
The other really good setup is a JeeNode, it's the same little microcontroller brain but the pins are organized in a different way and it'd built to be easier to plug and play. (You can use either one just like the other with a bit of wiring, sharing the same brain makes it easy)

I just started playing with them a few months ago, great fun!