I'm just writing to tell you I finally figured out how you suggested
to multiplex digits. I have 8 outputs that are connected to the
8 segments (7 segments + 1 dot) of all the digits at the same
time. and the common ground of each digit is controlled by
8 other outputs. That makes 16 outputs for 8 digits !

I will run about 25 mA into each segment, for about 1/8 of
the time, but since I will use it in my car, it will be visible
in the night.

A big thanks for the help, I already had started soldering 96
resistors when I asked my question ! It is a lot simpler now !

Patrick Lamontagne