There was mention of a couple additional ICs you could use in your multi-plexing thread.Hmmm ... "minor" issue I've spotted:
Driving multiple LEDs via the I/O pins. Arduino does not like supplying over 200mA. At 20mA per LED, I'm limited to 10 LEDs.
Would some kind of transistor, using low-current from the I/O pins to switch on LEDs be a solution?
Or do I try to keep each LED below 20mA, maybe half that, and accept they won't be so bright?
Or is there a different solution?
(There is always a different solution! Is there a better solution? )
I think that's an ideal solution. Otherwise you can put a larger resistor in series with the LEDs to limit the current, or use a transistor for each LED. (I think the transistor method is a little clunky though, but is more than good enough for the direct Pin > LED approach during testing phases.)