Organik Tech

Those who know me know LED art is among my top obsessions. It is a relatively new art form, that has been growing exponentially, particularly since the viable production of multi-color (RGB) LEDs have hit the market.

For those who aren't as hip to it, an RGB LED or RGB LED cluster is actually a red, a green and blue LED either stamped in the same package or as separate diodes soldered in close proximity. By dynamically varying (dimming) each color element, one can produce ANY color in the rainbow (hypothetically).

Any Colour You Like:

But (of course) dimming LEDs isn't as straight forward as dimming a normal incandescent light bulb. Forgoing special analog hardware to programmatically dim LEDS, most approaches use a technique called Pulse-Width Modulation (PWM) where you affect the "duty cycle" of the LED. Instead of giving a device half power, you give it full power, half of the time. By cycling the device on and off, faster than what the human eye can perceive, we create the illusion of a solidly-mixed color.

To drive LEDs in this manner, most all cases you will see use a micro-controller or chip capable of PWM dimming on output pins for each LED. So for an RGB LED, you would need at least 3 outputs each doing PWM dimming on their respective color elements.

The Big Picture:

Now some very clever people realized, "Hey we have dots of light that can be any color, some might call such a thing a pixel!", and the first LED displays were born. If you've ever seen one of those massive Jumbo-Trons at sports stadiums, nowadays those are basically very big, VERY expensive, RGB LED arrays/matrices. Believe it or not those used to be made of tiny CRT's!

Here's the key factor though, people are realizing we now have pixels that don't necessarily have to be arranged in the normal 2D display paradigm. Ever seen a 3D voxel display? A voxel is a volumetric pixel, i.e. a color element with 3D coordinates. People are now using this to build 3D visualizations/light objects, the most notable being Mark Lottor's Cubatron that first appeared at the Burning Man festival in 2004 and variations of it have been back each year since.

Of course some the effect is lost watching this on a 2D screen.

The quintessential problem in driving this many LEDs is dimming and addressing them all. You'll never find a single micro-controller with enough PWM output pins to drive such massive arrays of LEDS, so what most people do is chain up ICs. You can read how they attacked this problem with the Cubatron. Basically each RGB element was driven with a small PIC chip that handled all the PWM/dimming. They then were chained up on a common bus it seems.

For a short time, the maker's of the Cubatron manufactured a product called Triklits which was almost exactly the hardware used in the Cubatron, and could be programmed/driven from a PC. I spit my drink all over my keyboard when I found out about these-- 'cause I've had A LOT of lighting installation/interactive ideas I've wanted to do, but my electrical engineering skills are not enough to design a system like this from scratch. Not to mention, that building large arrays of RGB LEDs CHEAPLY is a tough task that requires smart design and wise choices in components. If you don't believe me, check out prices for LED sports stadium screens. Unfortunately, they had some manufacturing issues, and perhaps it wasn't cost effective for one reason or another, but you can no longer buy these.

A (not so) Shifty Solution:
This guy Garrett Mace, created a product called ShiftBrites, which largely accomplishes what the Triklits did and it's about as cost effective. Basically this is a breakout board for the guy that does the real work, the A6281 IC from Allegro. This is a great little chip, that comes in a QFN package-- and if you've ever tried to interface to a chip of this type, you'll quickly realize the advantage of buying a ShiftBrite module with it pre-mounted.

The awesome advantage this gives, is that you can can just chain up your LED modules, and each module/chip acts as a 32-bit shift register. So if you want to send color data for just one module, push out a 32 bit packet of color data. 2 Modules? Push out 64 bits. Once the first module grabs its bits, it just passes the rest down the line. Translation: an easy way to drive a large amount of RGB LEDs where each module is addressable. This approach also cuts down on wires, and makes it easier to produce light chains.

The Allegro chip gives you 10-bit brightness values per color-- thats 30 bit color!