RBG Drive - Varience of whites when leds lit

[Dr. Willy]

So I am working on a led blinky animation of pulsing colors and when I do all white, not all the bottons are the same color white. I know white is made with red, green, and blue are all lite at the same time. Seems like some of the whites show to much of one of the 3 colors, making them just a little bit off. I have checked my connections on my led wiz and everything is good. Could it be perhaps that some colors are getting more power then others?

Any suggestions?

Thanks!

[SavannahLion]

I suppose you could check the tolerances of the resistors on each leg of each color with a multimeter makes sure the values are close to each other.

Other than variances in LED tolerances I can't say much else without knowing the wiring scheme.

[Dr. Willy]

wiring scheme is one of red, green, or blue into its own port on the led wiz, the I took all the power and soldered them together and stuck it in the 5 volt port on the ledwiz

[SavannahLion]

Did you install resistors on your LED's?

The LEDWiz manual should show resistors on all connections that's not the +5v line.

Each RGB resistor uses 3 resistors each with accommodation for their respective colors if necessary. I don't know the specs of the LED's you used, but Red, Green and Blue generally have a forward drop of 2, 2.2 and 3.3 respectively. So using the formula (V-fd)/0.02 where V is the 5v of your system we arrive at 150 ohms (give or take) for Red and Green and 100 ohms for Blue.

If you use resistors with a 20% rating that means you can have a variance of around plus or minus 30 ohms for 150 ohms. Meaning you can have a resistor that can be anywhere from 180 to 120 ohms. Same for the 100 ohms making a resistor range of 120 to 80 ohms.

That said, if you have worst case scenario where you have 180 ohms for the R and G channels but only 80 ohms for the blue, you might have a little too much blue. I'm just speculating really, I don't know how much a 20% difference worst case will have on the optics there.

One way you can defeat those variances is to over buy any resistors if you feel the resistor values are an issue and "bin" them. For instance, if I have 30 LED's, I'll buy 60 or 90 resistors. Then I'll take the time to measure them and sort them within say... 2% of each other. Once I reach the 30 I would need, I would use those resistors. It wouldn't matter if you the 30 is 150 ohms or 180 ohms as long as they're all the same.

That's a lot of work though, it might be faster to find resistors with guaranteed 5% or even 1% tolerances. You'll pay a little bit more, but you'll save time binning them.

The alternative is to tweak the "white" levels via software. I'm not certain if the LEDWiz is capable of that kind of granular control.

[Dr. Willy]

yeah the rgb drive has all the resistors built into it.

See here
http://groovygamegear.com/webstore/index.php?main_page=product_info&cPath=83&products_id=240

I have sent randy a pm asking his thoughts.

I appreciate your help in trying to solve this problem so far.

[SavannahLion]

yeah the rgb drive has all the resistors built into it.

See here
http://groovygamegear.com/webstore/index.php?main_page=product_info&cPath=83&products_id=240

I have sent randy a pm asking his thoughts.

I appreciate your help in trying to solve this problem so far.

No problem,   but for future reference, whenever you have a problem you can't solve, you should tell us as much as you can. It saves the person who responds a lot of effort and time not chasing down dead ends like that. No where in your previous posts did you mention using the RGB drive. Not everyone here uses complete package solutions like those offered by Randy (he's a great guy, I purchased from him before with zero problems) so it helps to know, what might seem to you, as unimportant details.

In any case, I'll step out. I don't use the LEDWiz in my own cab so I can't offer anything more.

[RandyT]

I guess the best way to start this is to say that if one is looking for a "pure" white light, the only real way to achieve this is to use a monochromatic LED, or to tweak the values of the R,G and B outputs to equalize the output of each color.  But even with tweaking, RGB LED's, by virtue of using three separate colors, will always be difficult to get perfect purity, as this relies on perfect diffusion of those three light sources into one.

Also, as SavannahLion stated, there are always going to be manufacturing tolerances which will cause slight variations between parts.  The other thing to consider with RGB lighting is that very often, just one color is being used more than the others.  While this isn't a big concern for newer parts, over time, the output from LED's will degrade.  So, for example, if you have two RGB buttons which are on all the time, one red and one blue, over time, the red and blue components will not be at the same level as the other two components which are not used as often, making those two buttons slightly different from one another when all three colors are enabled.  This isn't an issue with something like a large LED video display, where the colors are always changing, allowing the three chips in a pixel to degrade evenly.

All of that being said, the LED-Wiz will allow you to "tune" the white color to make it uniform between units.  Most will just find it not worth the trouble, as absolute purity isn't terribly important to most in a control panel application.