From: Sumiec


>   So after that I decided to make a 7x60 matrix with the same principle of
>   Now the problem - when I try to turn on all the LED's they're all really
> dim.  From reading some of the previous messages on the list and actually
> reading the specs on the Optrex LED matrix's (<cough>for the first time) I
> found that I need to supply 100mA to each dot on the matrix with 1/10 duty
> cycle with a pulse of 0.1mS...  Now each pin of the pic can only source
> 20mA, and the decoders only sink 25mA.....
>
> Any suggestions on what I can do to 'fix' this?  Originally I wanted to
keep
> the number of chips to a minimal, so I didn't really pursue a huge shift
> register.  Are their LED matrix modules that could use a smaller Ipeak?
TIA
>
> Jerry

I did some repairwork on a 40 x 1 scrolling message board last year that
was suffering from heat exhaustion. Each 7 x 5 char was made up of
superbright yellow LEDs. I'm pretty sure the drivers were ULN2003
darlington ICs (7 per package, 500mA o/p). If you look into it you may
find driver ICs tidier than transistors. I'd suggest that if this unit of
yours is to be in service for some time put plenty of heatsinking in and let
it breathe. The resistors (1W/68R, I think) on the unit I repaired made
quite a mess of the tracks and PCB because of their heat. If they'd been
2W and mounted 5mm off the board and not slap-bang on it probably
would never had needed servicing.