Before I even start on this, I would just like to say that I realize that this isn't some poppin' fresh new idea that nobody's thought of before. I know this is the sort of instructable (like my hot glue instructable) that will draw a bunch of "Yeah, everyone knows that," type of comments. The point of this instructable is that I hadn't thought of it before, and maybe it'll be just the thing to inspire someone else who hasn't heard of this idea to do something really neat with it!
So, I came up with this when I was working on one of my previous instructables about diffusing your LEDs with hot glue. I had seen RGB LEDs on the internet, and they looked pretty neat, but I had just blown a bunch of money on parts for a set of nightvision goggles I was building, and I couldn't (at the time) think of a real reason to buy any except "I want some!" or "They look cool!"
Well, I was sitting around blobbing glue onto an LED, and this came to mind.
***UPDATE 5/3/10: If you make your own poor man's RGB LED and post some pictures (hopefully a little better than mine), I'll send you a patch!***
Step 1: Parts You'll Need
There are only six parts you'll need: 1 each red, green, and blue 3mm LEDs, and 3 resistors. You'll also need some hot glue (AGAIN!?!?) and solder, a soldering iron, and somewhere to test things. I used the breadboard on my radioshack electronics learning lab (absolutely the best thing I've ever found at goodwill).
I got the LEDs from some doodad or another that I picked up at the dollar store. I think it was a hand that you clapped and it lit up the LEDs. The resistors could be harvested from something else too, but I had a variety pack I got from radioshack.
Step 2: Select Your Resistors
This is actually a pretty tricky step, and one that I screwed up for the end product. Since I am an uncultured Philistine, I never make LED driver boards, I always run them directly from the battery. I intended to use this one with a 9 volt, so I stuck the LED's on my breadboard and hooked them up to the 9v power supply.
Next, I tested the LEDs with various resistors, trying to get them all to roughly the same brightness at 9 volts. I think I went wrong in 2 places here. I should have put the LEDs closer together, to better judge their relative brightness. I also should have realized that I had put 1.2 volt rechargeable batteries into the lab, not 1.5 volt alkalines, so I was testing them at 7.2 volts, not 9.
It doesn't look bad, but the red is definitely a lot stronger, and the green is too weak. The final resistance values I used were:
Red: 330 ohms
Green: 1000 ohms
Blue: 2200 ohms
Maybe I got it mixed up and should have had the red and green the other way around?
Step 3: Glue the LEDs
To put the LEDs together, you simply arrange them in a triangle with all of the negative leads pointing to the center, and put a dab of hot glue in the middle. After that hardens, fold the postitive leads a little away from the center, and twist the negatives together. I spread a little glue around the outside to make sure it would hold together. You now have an RGB led with 3 cathodes and a common anode!
You can stop at this point and call it done, or continue on to testing and adding the resistors.
Step 4: Testing and Adding Resistors
At this point, I plugged the LED back into my learning lab, and tested with the resistors I had selected before. I must have been tired, or else the 9v really made a difference when I attached that, but I didn't notice a problem at this point.
After I was satisfied with the brightness, I soldered the resistors in place, and it was done!
Step 5: The End!
While I realize it would be a million times simpler and less messy to just buy one of these, I didn't feel like I could justify blowing the money, and I also didn't want to wait for shipping, as I had come up with the idea for my next instructable (coming soon!) while I was thinking about how to do this.
I think it worked out pretty well, though if I do it again I'll be much more careful about the resistors!
Please take a moment to leave a rating or a comment! Let me know what you think, or if you have done this before (as I'm certain many have) show me what you've done with the final product. If this inspires you, post some pictures in the comments and I'll send you a patch!