[dorkbotpdx-blabber] Kicked in the Charlieplex part II.

[Donald Delmar Davis]

It was not a general disgust it just doesn't scale economically.  
Anyone who will bring working stuff to a meeting gets much more  
credit in my book than I will give them out loud.

Let me rephrase the question.

If i have 50 bags of leds that I got for free and the easy solution  
costs me $30 per bag just to drive them (never mind the control part).
Who can write an art grant large enough to make this worth while?

I was really dissapointed in my ability to take a concept know that  
it is possible and on 5 shots of bushmills figure it out from scratch  
at 2 am.
In my day this would have not been a problem. Of course in my day I  
was not afraid of analog design with descrete components either.

I am currently looking at a 14046/74596 solution where driving 8 rows  
costs 1.60  and sinking the columns cost 60c with no resistors  
needed. So or the same 12 and  an extra 3 lines of io would drive a  
64 by 8 array. The other thing that sucks here is time. If I order  
them today and dont spend 20 shipping them here then it will take a  
week to do the experimentation.

Its kind of like the 75 free 250vac relays that I picked up where I  
then spent a whopping 25 bucks on the ul listed outlets.
64 house lamps later will get you an 8x8 array that will be blinding.

Don.




On Jan 8, 2007, at 7:09 PM, Jason Plumb wrote:

> Jared Boone wrote:
> <snip>
>> There is an upper limit to how many LEDs you can drive with this  
>> method.
>
> Sure...and I suspect that the limit is probably quite a bit *less*  
> than the theoretical when the pin count starts to go above some  
> vaguely smallish number.
>
>> Some other good references (oddly enough, all from Maxim):
> <snip>
> Wasn't Maxim the catalyst for all this?...eh?  Don's general  
> disgust with using a $12 chip to drive 64 LEDs that could have  
> otherwise been charlieplexed with a mere 9 I/O pins?  :)  That 8x8  
> grid at the last meeting sure looked bright and flicker-free and  
> easy to use tho!  :)
>
>> And now for some crazier ideas. I imagine using an FPGA and separate
>> driver ICs (to offload the current/heat) which implements a high- 
>> level
>> command set which could be used by a microcontroller.
>
> Crazy talk!
>
>> Kinda like an old-school frame buffer and blitter for LEDs.
>
> Frame buffer gooood.....blitter much more complicated.  It all  
> depends on what's available tho.
>
> I did a frame buffer with memory-mapped RAM on the PIC16f628 for my  
> LED sign reanimation:
> http://noisybox.net/electronics/LED_sign/
> The protocol/command set was stupid simple: read byte, write byte,  
> clear all, shift all left, shift all right.
>
> Of course, with a command-set this simple, the user requires some  
> brains...so all character generation in done with a PC in Perl  
> using a 5x7 figlet (http://www.figlet.org/) font set.  It's not  
> pretty, but the circuit is simple....
>
> On a side-note, I want my 3D-POV....
>
> -jason
> http://noisybox.net
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