so, I was thinking of getting another peggy 2 le and use a 12x12 grid of 10mm rgb leds taking up 4 led locations each.

what would be better? common cathode or common anode? I'm guessing common anode since all connections are brought low to activate the leds. I was thinking of using the same method I did with my peggy 2 rgb color mixing board except cut off every other row or col and jumping adjacent rows or col together to make it one row or col.

I know I'll have to modify libs and stuff and I don't have massive programing skills, so the common choice should take that into account as well.

also, can you recommend a good book on using bitwise and interrupts in a time critical manner? (like for peggy). most c++ books just have an appendix on it with no examples.

thanx

so, I was thinking of getting another peggy 2 le and use a 12x12 grid of 10mm rgb leds taking up 4 led locations each.

We did a demo just like that on the Peggy 2, using four (full size) LED locations, with independent LEDs: http://www.evilmadscientist.com/article.php/peggyRGB

It's not actually straightforward to use a grid of four LEDs (two columns, two rows) with one RGB LED, because the common anode can only be in one row, not both. You could certainly wire it off-board with each RGB LED taking up three columns in a single row.

what would be better? common cathode or common anode? I'm guessing common anode since all connections are brought low to activate the leds.

Yes, that's correct.

I know I'll have to modify libs and stuff and I don't have massive programing skills, so the common choice should take that into account as well.

Not necessarily-- you could start with our RGB example, which defines pixel colors in clusters of four LEDs.

also, can you recommend a good book on using bitwise and interrupts in a time critical manner? (like for peggy). most c++ books just have an appendix on it with no examples.

Not really-- bitwise operations are pretty straightforward-- there are all kinds of good references on those. Like here, for example: http://www.arduino.cc/playground/Code/BitMath

For interrupts, I'm not sure that there's any particularly good reference in the context of AVR. These are a bit harder, and it's best to learn about them by reading the AVR's datasheet, or by studying examples where they are used in code that you want to understand.