Few questions regarding RGB LEDs

Forum 2005-2010 (read only) Hardware Interfacing
1

I need to interface 120 RGB Led independently. This is pretty much the biggest project I have ever undertaken, and I want to see if its even possible under my budget.

So here are the questions:
1)Which RGB led should I buy? Common Cathode or Common Anode?
2)Which led drivers would be the best for me? What is the max amount of drivers I can hook up?

I've seen two products I can afford:
http://www.sureelectronics.net/goods.php?id=311 - common cathode LED (also comes as common anode)
http://www.sureelectronics.net/goods.php?id=313 - fast flash RGB LED

4)What is a fast flash led? how do you change from one color to another?
I really need 6 different colours (the shade does not matter as long as you can distinguish between them).

I have 6 combinations with just turning certain colours on and off: {255,0,0} {0,255,0} {0,0,255} {255,255,0} {255,0,255} {0, 255, 255}

  1. Do I need PWM if this is the case? Is the price difference between PWm chips and non PWM chips huge?

  2. How much power would I need to run something like this? Would 5V, 2.5 Amp be sufficient?

Tons of questions huh! Sorry about the barrage of them. Any help would be appreciated

2

Common cathode or common anode will tweak your required driver circuit, but otherwise is not very different.

The fast-flash LED only has two pins, you just tell it "light up and do your blinky thing" or "shut off." You don't control the blinky thing it chooses to do.

You have 7 combinations, don't forget {255,255,255}. I'll forgive you for ignoring the 8th: {0,0,0}.

I'd suggest you look at all the "matrix" projects on this board, such as those with 74HC595 techniques, even if you don't actually arrange your LEDs in a matrix shape. Learn a bit from those.

3

Never missing an opportunity to shamelessly promote my own stuff look at :-
http://www.thebox.myzen.co.uk/Hardware/Mini_Monome.html

For an example of an RGB matrix.

4

A lot of people uses MAX7221 chips, but those don't come cheap...
You'll need at least 6 chips to control the 120 leds...

5

Yeah I looked at the MAX7221 chips but I was hoping to find a cheaper alternative. Was hoping to spend 40 CAD. 6 chips from digikey is going to cost me almost 100 bux after shipping and tax.

This blows. Don't think this project will be within my budget after all

6

Might want to see these if you haven't already

http://www.wayoda.org/arduino/ledcontrol/index.html
http://www.arduino.cc/playground/Learning/TLC5940

7

After some digging, I think I might have found a cheaper solution to the Max7221 chips.

Check this out:

It seems to be pin for pin compatible. And at approx 4.50 CAD, its way more affordable

8

Yeah, austriamicrosystems seems to make a business out of cloning other companies' products, they have a cheaper clone of the TLC5940 too. However they still aren't cheap. If you buy them from their website, single quantities for the MAX7219 are about $9 plus a $30 shipping charge. If you buy 1000 then you get a good price.

9

hmm... true...

avnet sells it for about 3.55 each but they have a 39 dollar shipping fee as well.

I just ordered a few samples to see if I can get it to work. If they are exactly pin compatible with the MAX7221 and work with the same code, I wouldn't mind buying 200-500 of them and selling them to people on this forum for no profit. Im sure everybody would be happier using these instead of dropping 10 dollars on the max7221 + paying the heavy shipping fees.

10

Well, the actual 7219 gets down to $4.34 if you order 500, too.