Simple RBG led question , newbie

hey all, ive ordered my arduino deciemelia :) and now im starting to look into how i can build my project ,

ive been researching for hours now , and im slowly starting to understand it all, basically i need to controll around 50 RBG LED's , using the arduino ,

from my research i have found that the arduino has no where near 50 outputs, and that i would need to daisy chain the led's or multiplex them or charlieplex them , although i dont thibk that charlieplexing is what i need,

somehow i need to chain the led's , i would like to be able to controll the pwm values of the led's ,. either all at once , or have it fade accross the group ,

this needs to be an interactive project, so i spose using a potentiometer, that could be turned to change the colour of the group

, i can spend time working that out later , what i am most interested in learning now ( i have 8 months to build this , so i will start small to try it all and get used ot it ) , is learnign how to link the led's and make use of them

, i have learnt that normal leds have 2 leads and rgb led's have 4 , red anode , green anode , and blue anode , and a common cathode , i think ( correct me if im wrong ) , the cathode is the ground , and the 3 other leads take a signal? which then produces the colour .

if any one can help me in my quest for knowledge id be very greatful, i also understand that the arduino could not power that many rgb led's alone , so couls i just use a power adaptor , if so how would i do this ? thanks. i know im asking allot .

rgb led’s have 4 , red anode , green anode , and blue anode , and a common cathode ,

Or red cathode, green cathode, blue cathode and common anode.

Could you maybe slip some paragraph breaks and some capitals into your post using “modify”? It’s very hard to read as it is.

Hi, first of all you need to know how many leds you want to control individually. If you want to control all 50x3 leds, you need to be able to control 150 leds for example using the MAX7219.

Most ICs control the leds by multiplexing, so it's very hard to dim them individually. because they "scan" row after row very quickly, so you need to program the dimming your self.

there also exist programmable potentiometers, which you could use. if you want to use a 2nd external power supply, you also need a LDO power regulator: which you use to source the MAX7219 - but only if the power isn't too high.

also have a look at the peggy project from evilmadscientist:

or at mine :-)

hope this helps, regards, toby

What is it with the need to control 50 LEDs this is about the seventh such project over the last month. 50 is not a very "computer number", these tend to go in powers of two as that is what is "natural" to control both in software and hardware.


The max6954 will allow you to control 128 LEDs and dim them in groups of 16. It uses the charilplexing technique look for application note AN1880 on line.

Note that common anode LEDs are most common and most chips are designed to use these so don't buy the common cathode type.

arduino could not power that many rgb led's alone , so couls i just use a power adaptor

You will need not only a power adaptor but some way of switching the LEDs like a transistor or FET or driver chips like those that have been recommended. However try one RGB LED first, many beginners are disappointed by the quality of the colours you can get from them.

The max6594 will allow you to control 128 LEDs and dim them in groups of 16.

but the max6594 is a common cathode driver - can you easily invert the direction ? (i have a similar problem controlling 8 14-segment displays)

btw: i think you mean the MAX6954

thanks for the replies guys , has anyone ever used shiftbrites? they look perfect for what im doing , and easy to use too! it hink i may of found what i need

i think you mean the MAX6954

Indeed I did thanks.

has anyone ever used shiftbrites

Not used them but one of our members is the guy who makes them. They look good and just the sort of thing that is right for you.

It's easier and cheaper to switch the low side of apower supply than the high side, so you will almost certainly want to use common anode LEDs.

A TLC5940 will do PWM control of up to 5 RGB LEDs. I'm pretty sure there have been forum postings from one or more members who have done it.

Also, see my recent posting about things to watch out for when shopping for RGB LEDs.