Hey guys!

I'm new to the DIY electronics game, but am taking an opportunity to get into it now with a small project to improve the looks on my PC. I recently purchased a cool kit to put RGB LED strips into my PC (found here https://www.amazon.com/ATTAV-Magnet...485989684&sr=8-3&keywords=magnetic+RGB+strips). I also decided to upgrade the RGB controller to a 44 key model to give me a few more options (found here http://www.ebay.com/itm/171597936994?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT). Everything right now works great! The only thing is, I have a relatively obnoxious red LED that is wired into my PC case that I'd like to replace with an RGB LED wired into the same system as the strips so that it lights up and changes colors alongside the case LEDs. I did a little research and found that what I'm looking for is a simple RGB LED with a common anode, similar to the strips (I'm looking at these here http://www.ebay.com/itm/141199404224). I also would need a splitter for the RGB controller (looking at this one right now http://www.ebay.com/itm/RGB-4-pin-2...ash=item33a191d945:g:dAQAAOxy4YdTWXcQ&vxp=mtr). I also realize I would need a resistor for the common power on the single LED, which is what I'm here to ask about!

All of the websites I've found on calculating resistors for LEDs seem to be for single color LEDs or common cathode RGB LEDs. I'm unsure if I'm supposed to add all of the minimum voltages on the common anode LED to give me a baseline power draw for the calculator, and do the same for the current, or if I should just go with the largest value of the 3. With this common anode setup, what kind of resistor will I need?

Original LED kit (showing the power adapter and LED strips that are going to be used, not the controller itself) - https://www.amazon.com/ATTAV-Magnet...485989684&sr=8-3&keywords=magnetic+RGB+strips

LEDs in question - http://www.ebay.com/itm/141199404224

Controller I'm using (running off a 12v molex adapter included in the original kit) - http://www.ebay.com/itm/171597936994?_trksid=p2057872.m2749.l2649&ssPageName=STRK:MEBIDX:IT

Y Splitter for controller (not sure if this matters) - http://www.ebay.com/itm/RGB-4-pin-2...ash=item33a191d945:g:dAQAAOxy4YdTWXcQ&vxp=mtr

Ideally I will most likely purchase a cable with a compatible 4-pin RGB connector, strip the wires, then wire each terminal on the LED to it's corresponding wire for the pins (with the resistor in line with the common power). If you guys see any flaws in any of this, please let me know! Again this is one of my first projects, so any criticism is appreciated.

 

You need to calculate the correct resistor value for each color separately: R,G,B all have different forward voltages.
Typically, G and B are almost the same, but R always has the lowest Vf of the three.

Look up the Vf from the data sheet for the LED in question - or measure it using a 9V battery with a 1K resistor in series as a simple test setup.
Get the LED to light up, then measure the voltage across it with a meter, this will get you close enough.

 

Thanks for the reply!

That was my understanding for common cathode RGB LED, but wouldn't a common anode RGB LED only have a resistor on the common positive input? Or would I use the same resistors that would be used for a common cathode RGB LED on the individual RGB negative channels?

Just curious, this had me stumped earlier!