ok, more reading has yielded more questions, mostly current-capacity related.
I'm looking at using LEDs like these superbrights from adafruit
, or these 5mm from superbrightleds
, or super flux ones like these
. I think using anything 10 candellas or above is going to be out of my budget. This LED Matrixing article
suggests that multiplexed LED’s can be driven with currents above their peak continuous current, because they’re only flashed briefly, to make them appear brighter. So now I’m trying to figure out what 595 configuration I can use if I want to deliver, say 40mA (the super flux spec a max of 100mA), to my LEDs.
I was thinking about 8 rows, 24 columns. With three 74HC595s each driving 8 columns and a TPIC6B595 sinking one row on each of its 8 pins. I’d be cycling through the rows rather than the columns so my led’s would be lit 1/8th of the time instead of a 24th of the time. But I saw somewhere that the 74HC595 is only good for providing 20mA per pin. And even if I could get 40mA out of it, if I lit a whole row at once, that would be roughly 1A trying to sink into one of my sink pins spec’d at 150mA.
If I instead used three MAX7219s, each controlling an 8x8 grid, and got them to somehow cycle through their rows in sync with each other, the specs look better. Each one could easily supply 40mA to all their columns, and sink the maximum 320mA coming from their rows. And I could pretty much copy the MAX72XX schematics in the playground
directly. And I’d only need 3 resistors instead of 24. But I get the impression that 595s are simpler and easier to troubleshoot if something doesn’t go as expected. Not sure the difference in programming difficulty.
Either way, I’m worried about putting too much current through the arduino board. So I should find a way to supply a regulated +5V to the drivers, in addition to the 7 to 12V needed for the arduino, right?