Multiplexing RGB LEDs but not for cube

Hey there, So I'm new to electronics but I'm a decent enough programmer. I'm building this RGB LED setup for a band. Basically it involves 9 spheres that I light from within with a couple RGB LEDs each. Eventually I'll build some software that lets me control them precisely, etc. but right now I just want to get the basic setup working so that I can individually control each sphere's lights. The lights inside a single sphere will do the same thing, so I'm assuming it's logically like having one LED in there, I just connect 'em. Yeah? My main problem is the multiplexing, I find it complicated. I'm also told it would be impossible to 'plex this many LEDs (27 I guess) even with charlieplexing. What can I do?

Do you want to dim the LEDs as well as turn them on an off. If so you need a driver chip like the TLC5940. As an RGB LED has a common lead (anode or cathode) you can't Charley them.

http://arduino.cc/playground/Learning/TLC5940

Ah, yes, thank you! So I would only need one of these to power 9 units? Each unit being 2 RGB LEDs (inside each unit the LEDs do the same thing, but each separate unit does something different).

So I would only need one of these to power 9 units?

Well if each unit has 2 RGB LEDs that is 6 LEDs per unit. My maths says 16 / 6 = 2 units per TLC5940.

How far away from each other are these going to be? These chips use high speed signals and these don't travel well. Alternitavly you could use something like a shift bright to power each unit.

http://macetech.com/store/index.php?main_page=product_info&products_id=1

Each unit would be doing the same thing though, so I think it would just be 3 LEDs per unit really. They are going to be far apart, so maybe it won't work. At least 5 feet.

At least 5 feet

You might just get away with that.

I would not use an Arduino but 9 Tinys for that. Attiny processors are very cheap. With such a setup you would need only 3 outputs per processor which is easily available for a tiny. Then you could interface each cube over serial or whatever interface you desire. The advantage of this would be that the cubes could be build indepentently. Especially it would be possible to add more cubes if you interface design is accordingly.

Very interesting. What sort of wire can use serial? I've only had experience using the Arduino UNO USB as a serial interface.

Also, since I'll be wiring each unit to some central computer, I'll have to carry R, G, B, and GND signals to each. Is there some vocabulary for simple electronics cable that comes pre braided and maybe in a shield, with 4 wires?

I'll have to carry R, G, B, and GND signals to each

No that information is transferred by the data on the serial line.

Is there some vocabulary for simple electronics cable that comes pre braided

Twisted pair.

with 4 wires?

CAT 5

To communicate "on the serial" line is still confusing to me. I've used it before, but as I said it was via USB. I guess I'm curious what exactly serial communication is w/ an Arduino. Can it be done with a single wire?

No you need three wires, TX, RX and ground. Connect pin 0 of one arduino to pin 1 of the other, likewise cross pins 1 and 2. Send messages with Serial.print and recieve them one byte at a time with Serial.read.

I've been checking out the ATtiny chip and it appears to only have two PWM outputs. Is that true? If so, how can I fade 3 separate colors with it?

Use a software PWM technique or a hardware PWM chip.

What do you mean by hardware PWM chip?

A chip that controls LED brightness by using PWM, there are lots of them about. The TLC5940 is but one example.

For a project like this i think i would go for the shiftbrite "intelligent" RGB led:

http://macetech.com/blog/node/54