[dorkbotpdx-blabber] another LED array question

[Mr.T]

you may want to think about somthing like the TLC5947:

http://focus.ti.com/lit/ds/symlink/tlc5947.pdf

or look for one here:

http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=480&uiTemplateId=NODE_STRY_PGE_T

maxim has tons too:
http://www.maxim-ic.com/products/display/


plus most of 'em are I2C controlable

-eric

_____________________________
Drtwist:
drtwist at aracnet.com

On Mon, 15 Dec 2008, Paul Stoffregen wrote:

> I would try a big 120 bit shift register, probably built out of 15 
> TPIC6C596N chips, which costs about $16.
> 
> The AVR can shift out 8 bits in 17 cycles, so running at 16 MHz in 
> theory the whole shift register could be updated 62754 times per second, 
> if you didn't have to do anything else.  In practice, I'd imagine 
> getting between 1/4 to 1/3 of that if you're writing in C.  If you're 
> willing to do a bit of assembly (or copy mine from the recent LCD 
> project) you can write to the SPI data register exactly every 17 
> cycles.  Just copy the code 15 times.
> 
> I'd probably go for 32 levels of light (not necessarily linearly 
> distributed).  If you're reading bit patterns from a table and putting 
> them out to the shift register, you can do a lot better than PWM.  For 
> example, if you want 50% brightness, shift out 1,0,1,0,1...  if you want 
> 40%, shift out 1,0,1,1,0.  The patterns could go in a lookup table 
> (which can be any distribution of intensities that "look" even to the 
> human eye even if they're not linear) that you index by the desired 
> brightness, so each time you build another 15 bytes to shift out, you do 
> 120 lookups and shifts and probably some other simple stuff.  Even if 
> you only manage to get all 15 bytes computed and shifted out 1000 times 
> per second (only 1/60th of the theoretical max) if you scatter the bits 
> like that there shouldn't be any visible flicker, except maybe at very 
> low brightness where it's only 1 or 2 on and many off in the pattern.
> 
> The other (much harder) idea that comes to mind is actually building 120 
> PWM timers inside a FPGA!
> 
> 
> -Paul
> 
> 
> 
> >
> > i'm sizing up a project for LIGHTBAR that involves an array
> > of 40 RGB LEDs, each of which i want to control in complete
> > gradations of brightness, and i want them to be arrayed
> > on an 8x5 matrix inscribed on a sphere, approximately.
> > so that's 120 variable-brightness or PWM pins i need to
> > be able to control.
> >
> > i'm considering using blinkMs, since the wiring and programming
> > would both be significantly simpler.  but the cost goes through
> > the roof if i do that. (i'm asking thingM to give me the blinkMs
> > for free, but that trick almost never works.  =)
> >
> > is there something like an analog shift register that i can
> > interface to a dorkboard, that will let me set these 120 different
> > pin voltages individually, rapidly, easily?  is there some
> > clever textbook solution to such a problem that i should know about?
> >
> > and will i ever figure out anything myself, or will i just keep
> > bothering all of you busy people?
> >
> > seasons blinkings,
> > -m-
> > ---
> > HELP!  A Bear is Eating Me!
> > http://helpabeariseatingme.com
> >
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