I am well aware, that I'd need a multiplexer for that, but still - is it capable to do it with a single ATmega328? Will I have to multiplex the multiplexers?
I'd be using small, like 12mm high displays.
I'd like to show on a single board:
-Date (8 displays)
-Time (6 displays)
-Temperature (5 displays, 3 digits + "°" + "C")
-Humidity (3 displays...and any got idea, show to show a sign for percentage "%" ? Maybe 2x 2mm LED and a LED "bar"?)
-Barometer (8 digits (to show "0900 - 1050" + another 4 to say "mbar")
Yes but the display will be very dim because you will have to multiplex them at a ratio of 26:1. That means that any one display will only be on one twentysixth of the time.
Better solutions are:-
a long chain of shift registers and drive the segments from them so they are on all the time.
use the MAX2819 chip to drive 8 display digits at a time. You can string as many chips as you like on the the SPI bus.