Here you see that most discrete components are SMD and the MAX485 as well. Also the 7805 had to go to the back side.Note that I accidently also used an SMD LED which is also on the bottom side :( The diodes on the right are to protect the 3.3V extension module against the 5V of the controller. In a future double sided PCB it would probably be possible to replace the 7805 with an SMD. It will be difficult however to also have mounting holes.