Hello,

Im not sure if its even possible but I have been trying to mix colors using a single Tricolor RGB LED. For example I would like to have Red and Blue to make Purple etc. I do not have an Arduino, only an Electronics Learning Lab.

I believe I have the Common Anode, 4 prong type. I am able to make each individual color so I know the LED is in working condition however I cant figure out how to mix the color.

Im hooked up to 3v and am using a single 1kΩ resistor. Anode is wired to the resistor and then to 3v. I can jump each color prong to ground individually to emit a single color but when I jump two colors to ground I only get one color. Also I tried jumping from red to blue then from blue to ground but only get red (if that makes sense).

Any help would be great if its even possible.

Thanks

 

The 1k resistor is too high; that's only 3mA. I don't know what's the right amperage for your RGB LED, but for a regular one is about 20mA; which would require a 150 Ω resistor. Now, consider that when you feed 2 colors those 3mA would be divided between both. The solution would be to use 2 resistance of a lower value; one for each color.

 

Wow very cool, that worked great. I was able to get bright Purple and Amber-ish using 2x 100ohm Resistors. Thank you. The Learning Lab I have has me using 10k - 100k ohm resistors for the LEDs so I had no idea.

So Im curious if there is some kind of a formula or table or something along those lines that would help me get a desired color using specific amounts of Ohms? Or is it just guess and check?

 

Lucky you, it tried the same experiment just a couple of days ago and my dual color LEDs are so bad I could only see one color no matter which side I feed.

Well, I'm a bit color blind, so I guess that influenced a lot.

The Learning Lab I have has me using 10k - 100k ohm resistors for the LEDs so I had no idea.

Then you should continue to use those resistors for the LEDs that come with the lab.

So Im curious if there is some kind of a formula or table or something along those lines that would help me get a desired color using specific amounts of Ohms? Or is it just guess and check?

I don't think there is; but you can probably calculate it yourself if you know which combinations of RGB makes which colors; you could use different currents for each color value from 0mA to 20mA.

To calculate the current you use this formula:

R = V / I
​

Where R is the resistor you should use for each color, V the 3 volts, and I the intensity of the color from 0 to 0.02 A (which are the maximum 20mA).

 

I suppose I could do that... Ill play around with it some more now that I know about using smaller Resistors. Thanks again, man.

 

You're welcome.

You can google for an RGB table and you would get an idea of the colors you would get.