Help! PIC Controlled LED Array Circuit - 100 LED's??

Hi Scott,
I may have come a little late on this thread but I did this LED thing 
just recently. I used an 8-pin PIC (12C675) driving an array of 64 LEDs 
using 74HC164 serial to parallel shift registers. These are more common 
and cheaper (real cheap) than other types but do not have any kind of 
output enable or buffer register so I simply used a P-channel FET to 
drive the anodes of all the  LEDs. This allows me to blank the LEDs when 
I am clocking plus I can also execute PWM in s/w to control the brightness.

Sure, you require a resistor per LED but when you do it with SMD then it 
really is quite simple. There is no problem with chaining this array out 
to any practical length.

Note that there is a limit to the total amount of current that you can 
pass through the substrate of any IC. For most 74HC devices this is 
around 50ma total which means you should limit LED current to about 
6ma/LED. As the LEDs I was using were around 200mcd I didn't have a 
problem with that.

I can give you schematics and source code if you like.


--
Peter Jakacki

Scott Hooper wrote:
> I am new to electronics, but a programmer by trade. I am trying to
> achieve a circuit of up to 100 independently controlled LED's (not
> segmented display modules). Ideally the circuit would be controlled by
> one or more PIC microcontrollers as I have a Willem II programmer. My
> application is artistic in nature and requires the leds to be spread
> out over a wide area as opposed to being in a grid formation.
> 
> I have heard a lot of conflicting reports about Maxim's MAX721xx chips
> for this job. Some say it's the one I want, but others (including an
> actual Maxim tech-supporter) say it's more suited to the segmented
> displays. I have experimented with this chip with little success.
> 
> Has anybody achieved anything like this? I have scoured the Internet
> and newsgroups for literally weeks looking for a matching schematic
> and source module. I have found a few Basic Stamp modules but I'm not
> setup for that at all and would rather stick with native PIC. The only
> compiler I have is MPLab's MPASM.
> 
> Many thanks to anyone that can help