tri color led working backwards

[JIMFUN71]

Hello fellas,
My name is Jim and I am an industrial electrician of 30 years. I have worked with everything from 30kv substations to 480v ac mcc's to 24v dc proxes. Now I have discovered programmable IC's like the Arduino and Raspberry Pi. I am currently working on a simple circuit. I just bought a tri color led...shack #276-0028. I am trying to make a 16MM color led 0-255 for red,green and blue. I followed several tutorials and each one said that the long pin on the led was the ground or collector and the other 3 pins were the colors or emitters. I worked this method for several hours to no result. Just before I gave completely up and took the led back to the shack , I (for giggles) hooked positive voltage to the ground and grounded the color legs out and it works. Is this not backwards? How can you control 3 different colors if you have a common source? You cant pwm the grounds can you? Has anyone ever heard of anything like this? Thanks for your help,
Jim

 

[Nigel Goodwin]

Such LED's can be either common anode or common cathode, you order the type you want - PWM can be done just as easily in either case, and in fact PWM (or even just switching) is easier in the ground side.

 

[MrAl]

Hi,

Yeah just switch the three 'cathodes' to ground to turn the respective LED on.

Good luck getting the colors to mix well though. All three dies are in different physical positions in one plane so the colors radiate out at slightly different angles. You'll need a good diffuser to get them to mix into one single color, and you'll still see color fringing on the edges. Also, good luck getting some colors to show up good. I got a good looking aqua color, in fact very good, while a good orange was almost impossible. Could be the LED i used but i never looked into it that much.
For a diffuser i've used foggy looking clear plastic, layers of tissue paper, heat moldable plastic, anything that is colored white and is partly transparent.

So by now you are getting the picture: It is partly a current distribution problem (vary average current to the three LEDs) and partly a diffusion problem (diffuse the light from the three LEDs so they appear to be producing only one mixed color).

 

[Nigel Goodwin]

As far as diffusers go, you might try stripping the ones out of an old LCD TV?.

 

[picbits]

Don't forget current limiting resistors whatever you do - it can be an expensive mistake to make.

 

[audioguru]

I looked in Google and found a few wrong Instructables written by little kids.
Then I went to Radio Shack online and downloaded the datasheet from Everlight (Radio Shack doesn't make the LED) that shows detailed spec's and the pins. It shows the long pin is the common anode.
Since it is Chinese then it says SUG for green, SUB for blue and SUR for red.

 

[JIMFUN71]

Hey guys,
Just wanna say thanks for all the input. I got something from every reply. Just wanna update you on my results. Using Arduino I was able to achieve 3 basic colors and pretty good 9 secondary colors, although I was not able to get good variations below secondary colors. For some reason the Arduino bleeds. All the R,G,B are always on to some small degree. I am switching to transistor and analog output from Arduino instead of PWM. Initial tests look much better than using pwm from Arduino. I also have toned down my unrealistic 16MM color to a 4K color expectation. I might even cook that down to something like 512 color. I see what you mean about blending an RGB LED. The colors come from different angles inside the led and once you get below a certain point of current you no longer get a blended color but two or three separate colors. Once again thanks for the input guys,
Jim