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[Reply #15 on:]

i was thinking right outside the ground terminal on the arduino. I don't know, but i suspect sending a potentially large current into my arduino's ground could be a bad thing? Maybe i'm being overly paranoid?

[Reply #16 on:]

You're probably right about large current damaging your Arduino, but the few times I've used multiple power supplies I've just connected all grounds and nothing else. I think it's an issue if there could be a path for the high amperage circuit through your low voltage's ground path but if you keep the busses completely separate except for a single link between two ground points you should be ok.

My notes say I followed this when I made a plant light timer that needed 2 power supplies:

http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1247091107

[Reply #17 on:]

Thanks for the relevant link and insight. I think i've got everything now except for a long enough proto-board. I'm building a 6x6 proof of concept this weekend and when i get it up and running i will update this thread as well as begin work on the full sized 6x24.

[Reply #18 on:]

Alright, I have all the parts in hand 2 74hc595s and 1 74hc4052 (with some external modification to make it 1 to that i already had. I already have the LEDs soldered together hopefully sometime today i will the ICs breadboarded and ready to go. Thanks again for all the help.

[Reply #19 on:]

alright the matrix is together and i have tested all the individual LEDs... no shorts or open circuits now i'm having trouble with the electronics part of it. I'm linking up my test sketch with this post. It's going to be running on an UNO. I'm working on a more clear computer generated schematic so that i can have a more clean approach this time I'll link that up when i'm done.