Anyone have any experience with this? I just started a project that will
be a cube with 6 led matrix displays, one on each side, using 5x7 led
modules. Each side will end up as a 35x35 matrix that will then display
a 3d rendered wireframe image of a cube. The part that makes it all
worth doing, is I'm incorporating a high-resolution 3-axis tilt sensor
into the center of all this, so while you can rotate the physical cube,
the virtual, rendered cube, will always remain stationary.

I'm using LEDs rather than off the shelf LCD displays, because finding
1-1 aspect ratio LCD's is rather hard, and the ones that I did find had
rectangular exteriors due to connectors and what not. Hard to make into
a nice, almost seemless cube.

The modules I got, the cheapest I could find, have 100ma peak currents
and 11ma average current ratings. So... I was going to base my design
around simple ULN200x and UDN200x source and sink drivers with 74hc574's
to drive them. The drivers can do 500ma source or sink so that should be
fine. 

5V is well above the LED's forward voltages, but of course they will
have an associated duty cycle so the average current is correct. My plan
is to make use of the watchdog timer, and have the first thing the pic
does is disable all outputs and wait for x cycles, so even in a reset
loop I won't fry my display. Disabling all outputs will work by pulling
the 74hc574 output enable lines low. Sounds reasonable to you guys? What
do commercial designs do? I found a bunch of current drivers in my
research, but they all seemed aimed at smaller LED displays, or even
just one or two LEDs, and were fairly expensive.

One challenge I see is power. Peak power, for all leds on, is about 16
amps per side! Or about 100amps for the whole board! That's just nuts...
Is there such a thing as a simple, self-contained switching regulator
that can handle a decent amount of current? I'd like something as simple
as a 3-pin regulator, no external components or anything. I'm trying to
have this thing completely built by March 11th, which I know is utterly
insane, but trying is fun!

Of course if all else fails if I just make the assumption that I'm
displaying wireframes, which means very few leds are on, and I reduce
the brightness, current requierments become *much* more reasonable, well
within the ability of a 7805 or two, but I'd like to avoid such
assumptions if it's reasonable.

The powercord going to this sucker will be fairly beefy BTW, it's gotta
allow the thing to hang off the ceiling... and be somewhat kid-proof.

-- 
pete@petertodd.ca http://www.petertodd.ca
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