Many RGB LEDs

Other Hardware LEDs and Multiplexing
1

Hello, I'm new to Arduino and I need some help with powering and controlling LEDs though the Arduino. I want to string 8 RGB LEDs together and be able to control the brightness of each diode within them separately (so the red, green and blue) so that I can fade from blue straight through to red. But I have too many LEDs to just use the power from the Arduino so I need to connect them from a external power source. From what I've found is that I can use a transistor to turn them off or on with the Arduino, but I want to be able to control the brightness in order to reach every color from blue to red. I can't seem to find a way of allowing me to send PWM to LEDs that are linked to a external power source, but I know it is possible. Can somebody with experience point in the correct direction in terms of hardware and wiring? Thank you.

P.S. I plan on using the Uno R3, but that's just because that's the best documented and I'm new.

2

Look into WS2812B

Neopixed at http://www.adafruit.com/
or WS2803 from ebay (Niagara Falls seller) to control up to 6 RGB LEDs (common anode).

Separate 5V supply me be needed if you plan to have 24 LEDs all drawing 20mA at once (480mA).
www.dipmicro.com, 5V, 1A or 2A

WS2812.pdf (272 KB)

WS2803-preliminary-En.pdf (437 KB)

3

Thank you for the reply, but I'm not looking for the LEDs, I looking for a way to control them. I have too many LEDs to be powered by the Arduino's 5V so I need to connect an external power supply. I've found out that a transistor can be used to turn on and off LEDs when a external power source is wired in, but I want to be able to control the individual brightness (like with PWM) of each LED with a external power supply connected. I just don't know what chip to use or if there is a special way of wiring for this.

Fix: Never mind, I see what you are saying now. Thank you. Is this the only way, though, with 'smart LEDs', or is there a way to do it with normal RGB LEDs?

4

Could I use a Darlington transistor? Would this allow me to send PWM signals at a higher power?

5

You could use PWM with a transistor. The PWM output would just turn the transistor on and off rather than the LED directly, but the method would be identical; rapid switching on and off and varying duty cycles to control the brightness of the LED.

6

If you want the to spread them about then the Neopixel is the best. Otherwise you can use chips like the TLC5940, but for 24 LEDs you will need two chips. You can not use a Darlington because you do not have 24 PWM outputs on a Uno.
The other alternitave is to use three power shift registers and the shiftPWM software.

7

WS2803 controls regular, common anode RGB LEDs. Look at the datasheet.

Another way is WS2811, like a WS2812 but for controlling regular common anode RGB LEDs.

WS2811-preliminary.pdf (320 KB)