On Thu, Feb 23, 2006 at 12:33:14AM -0800, William Chops Westfield wrote: > > On Feb 22, 2006, at 11:45 PM, Peter Todd wrote: > > > 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 > > Hmm. That's equivalent to an LED-matrix sign 1 character high by > 210 characters wide, which is... very large for that sort of thing. Definetely, though size wise, it'll be only 4inches on each side, the dot pitch for the LED's is 0.1" > > One challenge I see is power. > > No Duh. 7350 LEDs. Ouch. It'll be the most LEDs I'll have had in any project! > > Peak power, for all leds on, is about 16amps 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. > > > Sure. There are LOTS of these little DC-DC converters aimed > at telco and comm equipment, that convert ~48V DC to your choice > of output voltage at frankly incredible efficiencies in amazingly > tiny packages. 200W per cubic inch or so. For instance, less > than 2.5x1.5x0.5 inches, 5V at 40A: > quarter_brick_48v_single_ultra_info.htm> Thanks! Those look excellent, exactly the sort of thing I've needed for this and a number of other projects. That said I'll do some looking to find some even smaller ones, those particular ones probably won't physically fit in my application, I genuinly need something the size of a 7805 or two. > We sprinkle them like candy through the larger cisco routers, > for instance. Don't ask how much they cost, though. And don't > ask me where you get the 48V supplies to provide at the input, > either... (On the other hand, these can frequently be found in > discarded last-generation comm gear. I could probably come up > with quite a few in a hour's worth of dumpster-diving (although > the current crop probably output 1.8 to 3.3V...) Digikey has nice ready-made 48V power supplies, seen 'em in the catelogs, lots of different types too. > Since this isn't the first time you've run into power problems, > I think you should do some research on distributed power. Just > because you need 5V at 100A doesn't mean you need a SINGLE 5V > regulator that can deliver 100A; a half-dozen 12A supplies MIGHT > be a lot easier... Probably true. I already want the power to be contained to each side, as I want to build all 6 sides using identical circuits. > Of course, you won't be doing "all LEDs on", since you said > "wireframe", and the peak current isn't appropriate since that's > for a momentary pulse in a multiplexed display (max 6*35 LEDs > on at a time at maybe 50mA; only about 10A required! Less than > that since the wireframe won't light up full rows on all sides > at once. Probably.) I hope you realize that this thing is > likely to be to hot to handle. That 10A at 5V works out to about > 50 watts, which will heat up something this size (less than 10inches > on a side?) quite happily to an impressive temperature. Not to mention getting power *too* it becomes quiet difficult, I was hoping to be able to use nice coiled up audio cables, they are very resilient and bouncy. Good point on the heat, didn't think of that one at all. LEDs are what, 10% or so efficient? Even assuming that much is turned into light energy, that's hot alright. And it's *4inches* on a side, even worse. Working through the numbers a little better... Peak current for the LEDs is 100ma. At that current the datasheet says my max duty cycle is 7% So I could apply the peak current to each row at 1/35th duty cycle and still be well within spec. 35 collums * 0.1A = 3.5A per side * 6 sides = 21A More reasonable... Something I realised right now reading the datasheet... That max peak current, of 100ma, is reached at a forward voltage of 2.75V So am I corrent in saying that I can't drive those LEDs from a 5V source, even if I used really low duty cycles, because the peak current would be well over that 100ma rating? > And it's already been done (in 2d, anyway) with laptops and their > internal 'drop sensors.' > http://osxbook.com/book/bonus/chapter10/ams2hid/ Er, funny story about that... I was telling this idea to my electronics teacher, who in the field of electro-mechanical art is very well known, and he said he thought it was brillient, I should totally do it. He also told me he had done almost the exact same thing, 10 years ago, with one rotating monitor held in a gyroscope-style mechanical movement with a 286 running the graphics and a joystick to move it. What's worse, is the guy who curated it, happens to be good friends with the same guy who I sell most of my work too... Fortunately his version never worked all that well, and didn't get much press. He also didn't think anyones done that idea as a proper handheld cube, so I'm still gonna make it. -- pete@petertodd.ca http://www.petertodd.ca -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist