Thanks a lot for al the input and ideas. Helps a lot, because a lot of this is new for me.
Yes, I'm using buck converters (the mini-360), and it does seem like the already have capacitors.
DrAzzy:
Every digital IC should have a 0.1uF ceramic cap across supply right next to it minimizing length of traces. Unless the datasheet specifies some other value. Even when the datasheet doesn't spec any decoupling cap, you probably ought to use one.
Does this mean I have to check the modules I'm using, to see if they have caps next to the IC on it? And if not, place one 0.1uF ceramic cap close to the vcc and gnd pin?
As far as I can tell only the relay module and the EEPROM adapter don't have there own caps...
DrAzzy:
For ESP8266 modules, especially the ESP-01, I would use a 10uF ceramic, not a 0.1uF one - the module already has 0.1uF ones; what it seems to lack is a larger value decoupling cap (the sudden current surges that that module can pull are sort of shocking - it can go from 30mA to 300mA in an instant when it transmits.
When I google "ESP8266 capacitor" I see a lot of guys advising to add in a 0.1uF AND bigger cap like the 47uF electrolytic. Some even say to use a 470uF. So I don't understand why you are telling me to drop both and add in a 10uF ceramic cap. Can you explain this to me? (as you can see I'm obviously a bit clueless with electronics)
DrAzzy:
And - yes, use a ground ground plane (aka pour) on both sides, except close to where the antenna of the ESP8266 would be; ideally you don't want any copper right around where it's antenna will sit, as that can reduce wifi performance.
The ground plane sounds like a good idea, but its new for me, so I will start look in to this and try and find out how to implement this. (I will keep in mind to put the ESP on the edge of the PCB)
Paul__B:
A couple of things fascinate me about the general design here.
The ESP-01 alone contains vastly more computing power than an Arduino Mega including EEPROM capability, and I am wondering why you would use a Mega rather than a Nano? It would seem the only reason for using an Arduino at all would be to provide lots of pins, but a WeMOS D1 Mini and a couple of shift registers should be able alone to fulfil all the requirements.
In any case, it has been mentioned that there should be no fill under the ESP-01. Better still, there should be no traces - nothing - under the ESP-01; the best place to mount it would be in an open corner and/ or overhanging the PCB.
I guess you're absolutely right, but I started this project with an Uno, ran out of pins so continued with the Mega and later on I discovered the existence of the ESP8266 and decided to add this to my project as well for communication with the app I'm also building.