Hello,
> apologies if this question is very stupid. :)
> I have been toying with electronics for a little while, but I know I
> lack some basic knowledge to wrap everything up together so... here is
> my doubt.
>
> I am designing some Christmas decoration with a bunch of LEDs driven by
> an array of 74HC595s (controlled by an ATtiny45). The whole thing will be
>
> I did something similar in the past, using three 595s to control three
> 7-segment LED displays, but I did it fairly randomly: I just connected
> each output to each segment, with a resistor between the two.
> Since this thing I'm planning to do is going to be simple yet much
> bigger -- involving twelve 595s -- I'd like to do things properly.
> The 96 LEDs could and probably will be all on at some point, so
> considering a current draw of 15 mA for each LED, the whole thing would
> draw a total of about 15 A
96 x 15mA = 1.44A
15mA is actually a lot for a LED, you can run them at much lower current for a roughly proportional drop in luminosity. High efficiency LED's can be insanely bright at only several mA.
Dave.