Electronic – Which resistor to use for this LED

You should use 3 different resistors, one for each color, although the blue and green have the same specs.

At 150mA the forward voltage for the red is 2.2v, green is 3.5v and blue is 3.5v. So you should use a 22ohm 1watt resistor for the red, and 10ohm .5watt resistor for the green and blue. You have a bit of wiggle room on these figures, and if you don't have a resistors that can handle that wattage you can use more than one in parallel just make sure you calculate the correct resistance between them.

Also I doubt your microcontroller can provide 150mA (it's probably more like 20mA,) so you will probably need to use a transistor on each color so that they can pull enough power. Take a look at this image for how to hook up the transistor to your system. Although ignore the 12v and multiple LEDs.

You may also want to have each color driven by a PWM pin, so that you can alter the brightness of each color to change the overall color at will.

The problem ended up being a PWM issue. (It was solved in the comments, however I've posted the following to help future readers of this.)

First switch the Red or Blue with the Green. This will determine where the problem lies. If the Red or Blue still doesn't work then the problem is with the LED (very unlikely) or somewhere in the connection. Otherwise it is a software problem, like incorrect use of PWM.

Helpful links:

• Basics of PWM with an Arduino
• PWM with Arduino Video
• A much more advanced app note from Atmel about PWM