saturno:
After several hours around the build of the matrix (mine is 475 x 475 mm), I've just managed to see the result of half of the matrix (just one MAX completely connected by now).
The result is not what I was expecting. Without thinking or questioning, I used the diagram presented in the file "Clock7.pdf" to wire the first max to the arduino and as I can now see, my assumption was not correct.
The schematic was the one I used to build both clocks so should work. It is based on this article. What you may have done (I did it first time) is forget that when your wiring the back of the board the SegX are reversed.
Here is what I have done:
Since we usually read from left to right, I supposed that since you placed the IC1 at the right side of IC2, the schematic was drawn as seen from the back, i.e. when you see the watch from the front, the IC1 becomes the left and the IC2 on the right; and I wired my matrix exactly as in the schematic. At the moment, only the IC1 that, seen from the back of the watch, it is on the right side (right half) and when we turn around to see the "lights", it is on the left side.
I'm not sure what the effect would be with only one chip as the matrix information is cascaded through one MAX into the next from right to left when LED's viewed from the front.Well the problem is that I missed something and now I have the initial string appearing from the left to the right (wrong) and, even worse all the characters are backwords (like mirrored). To see the characters correctly, I would need to turn around and see the watch from it's back...
All you need to do is reverse the order of the 8/16 SegX pins and it should come good.