Question about using RGB LEDs

Forum 2005-2010 (read only) Hardware Interfacing
1

Hello,

I have a question about using RGB LEDs combined with the Arduino Diecimilla.

Can I get a RGB LED up and running just by feeding it with 3 output pins and one ground?

(I am totally new to RGB LEDs)

Will this mean that you can only use 4 RGB LEDs at the same time?
(4 x 3 RGB pins = 12 output pins for 4 LEDs)

Thanks!

2

You should be able to do what you want, but remember two things:

  1. You won't be able to dim all 12 LEDs unless you write your own PWM.
  2. 200mA / 12 = 16mA per LED if you want all LEDs lit at the same time.
3

Can I get a RGB LED up and running just by feeding it with 3 output pins and one ground?

You need a resistor in line with each output. It depends on if you have a common anode or cathode.
The most common is the common anode, using this connect the anode to +5 and the RGB cathodes through a resistor to the arduino pin. Then a LOW will turn on that LED.

4

I have to admit, I am quite lost now. :-[
What is the best way to wire up as many RGB LEDs as possible, at the most efficient way as possible to the Arduino?

Like I said, I am a total RGB noob... (Never used a RGB LED before...) :-[

5

as many RGB LEDs as possible

You have to be more specific than that. How many LEDs? Do you want to use external hardware or just the Arduino? What current do you want them to run off? Do you have common anode or cathode LEDs?

Without answers to these questions it is impossible to answer your question.

6

You have to be more specific than that. How many LEDs? Do you want to use external hardware or just the Arduino? What current do you want them to run off? Do you have common anode or cathode LEDs?

Without answers to these questions it is impossible to answer your question.

I don't know how many LEDs I can use on the arduino without external hardware.
If it is possible I would like to start a project with 'undercar' lights.
For shows etc.
So I can switch colors on runtime under my car.

I am looking on Ebay for RGB LEDs, I think I will buy anode LEDs.
And about the current, I don't know exactly whats best.
My car produces 12 volts, unknown mA...

7

If it is possible I would like to start a project with 'undercar' lights.

Talk about making things difficult. If you want LEDs to illuminate under a car then these need to be high power LEDs. These are a lot more complex to drive and defiantly not something for a beginner. They require external hardware and good heat sinks. Also for under a car you have the additional difficulty of making everything water proof. These high power LEDs often take 350 to 750 mA each and require specialist drivers. Have a look at this thread and the links off it.
http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1234273497