Here is the first design of the PCB, adjusted after discussion on the Hacker Channel this morning, for which many thanks, and studying the guidelines for PCB design https://hackaday.io/project/6936-pcb-design-guidelines.

Considerations:

- No surface mount (too little experience)

- Three functional groups: power supply (left), CPU (center), and RF part (Thunder click) as far from the rest as possible (it will actually stick out over the board with its RF part).

- Made supply lines wider

- Removed straight angles and replaced them with 45 degrees

- Hi frequency ground (crystal and GND of CPU) is isolated from the rest of the ground; only connected at one point to rest of GND

Unfortunately, with apologies to Yann Guidon, we do use the bottom side as well. You are probably right that it can be avoided but that will be the next version... Fortunately, at OSH Park, the price for two-sided is the same as for one-sided (about $10 per PCB).

Next steps, put all material on Github and order PCB and parts....