> perhaps it is possible to have some LED's on completely,
> while strobing only the ones needed to fill out the character
> or pattern......?

Yes it is. Any LED that's on is part of a pattern

You'll see in my circuit that the 75R is lower than what you'd
expect for an LED running on 5V. This is because the LED
does not see a constant 5V, but pulses. Which is why I mentioned
the current/time/efficiency relationship the other day. When you
say "on completely" then you'll have to consider the series
resistance

(btw, the 56R/220p on the row control inputs is just a simple
noise filter and has nothing to do with brightness)

> here I actually was wondering if a 4mhz 16F84 is fast/powerful
> enough to present a good display.....now that my little
> experimenter set up is working

What will ultimately affect the quality of the display is how long
the refresh cycle is, which depends on how many shift registers
you need to get data to and how fast an effect like scrolling is
performed. A fast scroll needs faster updating (hence the tilted
characters seen when the updating is not fast enough). You
could drop in an F84A-20 if you wanted to

> could a darlington transistor array be used in this application?
> I was looking at a ULQ2003A, and was wondering if that could
> be connected somehow...

Those drivers are quite common in displays. However, I have
repaired displays in which the driver chips got too hot (the
individual transistors can handle a reasonable amount of power,
but you have to watch the dissipation for the whole chip) and have
either died or scorched the board and caused dry joints, which
can get nasty. With individual transistors you have the opportunity
for better cooling. Also, the faster the transistor switches, the less
time it will spend between on and off and so run cooler

> I get the idea of how the individual transistors make the circuit,
> but this array isn't obvious to me how to hook it up....

How do you mean ?

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