Who wants an eagle routing challenge? (PM me)
I’m currently trying out 2 layer, but i don’t think it’ll be possible 
3 Likes
I wish I have time 
and I am sure it can be done 2 layers.
Sure i can do 2 layers.
With the cost these days for a 4 layer board and the better EMC and easier power routing it makes no sense to consider 2 layer boards for anything other than simply designs.
How many power rails does the design have? You can still do this with 4 layer and split planes. I often route 5V and 12V on the inner power plane.
A good test that I find is to run the auto router for a 2 layer board and see if this can route the board. I never use this for finished boards but it is a good check for routing capability and then I unroute and manually layout the board.
PS. See your 2 resistors for the USB differential pair, your tracks are likely to end up different lengths and possibly fail the max length difference. Even on short runs, I would try and keep these as close to each other, length wise, as possible to ensure a stable USB connection. 
12V, 5V, 3V3, the 12V is 1.6mm i think it will be OK.
Yeah that was just first placement, saw the pair when i started routing.
So here it is, gonna order a prototype tomorrow. 
4 Likes
Nice work indeed. Not much space left for a ground plane which is why I like 4 layer but this is nicely done on 2 layers.
I see you have what looks like decoupling caps for the SD card. I would move those closer to the connection at the SD card socket itself. My first ever use of SD was without any decoupling and I had many read/write issues. After I added the caps next to the connection, rock solid. You can never have too many decoupling caps on your boards.