At 04:09 PM 2/4/02 +1300, you wrote:

>The scanning frequency itself shouldn't make a difference. What
>will affect the brightness is the off to on ratio, and you'll have to
>work out what other work the PIC has to do while it is maintaining
>regular pulses to the display. For example, shifting new data bits.
>Evenly spacing the pulses is also important, so as to keep the
>display looking good

Mostly what affects the brightness (assuming a reasonable and even refresh
rate) is

1)      Average LED current

2)      LED technology -Ultra-Bright, super-bright, normal high-efficiency,
         old fashioned GaAs 8-(

An average current of  1-20mA/LED is reasonable, so for 1024 LEDs you're
looking
at a total current of 1A ~ 20A. A PIC port is capable of a couple hundred
mA tops.
At 150mA, the average LED current (all on) would be only 150 microamps, which
is enough to see the LED in a dim room IF it's a super-bright or better,
but not
enough to really get it bright. Commercial outdoor displays use efficient
LEDs and
run them at high current (with all kinds of thermal management problems with
so many watts per m^2 of display area).

Best regards,


Spehro Pefhany --"it's the network..."            "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com
9/11 United we Stand

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