Designed using KiCad.
While there are terminal boards out there for ESP32 dev boards they almost all are simply just bringing out all 38 pins. Not terribly useful when you want to use the ESP dev board for 3, 4, or perhaps a few more things. Their main limitations being you immediately run out of 3.3V terminals, and the 3.3V and Ground terminals are likely some distance away from the pin(s) that you do want to use.
The goal of this board is to provide the pins that are actually useful for ESPHome use. And more so for sensor inputs. Also to be as flexible as possible for typical sensor input use. Making it hyper compact was not a target goal. And neither was being low cost as possible.
Key Features:
Accommodations for both the wide (1”) and Narrow (.8”) 38 pin ESP32 dev boards.
2 – I2C bus screw terminals with 3.3V and Ground + adjacent .1” header.
8 – GPIO screw terminals with Grounds + adjacent .1” headers that include 3.3V.
1 – Dallas One wire screw terminal group with adjacent 3.3V and Ground + adjacent .1” header.
1 – Spare 4 terminal block.
Rows of holes next to the ones for the dev board module itself for “ooops I didn’t think about needing that pin” when designing the board.
A set of pins not dedicated and not connected in 16 groups of 4. These are for other on board things that you may need to add above and beyond what the ESP32 dev board board itself provides. One use I can think of is that they could be used for on board opto isolation (PC817’s for example). The groups are spaced to accommodate up to a 16 pin DIP package. I used the PC847 DIP package as the footprint.
While a bit “hacky”, I think that some strategic trace cutting could make the terminal blocks useful for something that may have to be routed through the “special circuits” area first. I don’t anticipate needing to do that very often. So a bit of board hacking and some wire runs don’t really bother me. My current terminal boards are all hand wired after all. And what a pain they were to make.
And my overall high level thinking is that in a majority cases the boards will not be fully populated with all the terminals or pin headers, but instead just the 3, 4, 5 or whatever pins that you want use with a single ESP32. In my current HA ESPHome configuration I have several ESP32’s that are doing 3 or 4 different things and using anywhere from 3 to 6 or so inputs.
My ESP32 deployments for sensors are typically in clusters and in fairly close proximity. Things like I2C I have not tried to push beyond about 3 feet of wire, and probably wouldn’t. But the GPIO’s I could see being useful for many 10’s of feet from the board. And that is where opto isolation could be useful.
I also avoided using any of the heavily restricted pins of the ESP32, for example have excluded all the GPIO’s that don’t have pull up or pull down capability. And also avoided pins related to the booting process of the ESP32 itself.
What I did NOT build in is support for relays on the board. Mainly because there are already a variety of ESP32 boards out there for handling relays. I was mostly motivated to pursue this because of there not being any boards that I could find to accommodate a multitude of inputs to a single ESP32. Particularly a mix of I2C, Dallas One Wire, in addition to some simple ground reference GPIO’s.
Some screenshots of board design so far. And a screenshot of the spreadsheet I used to figure out which pins to use, and which to avoid.
Schematic:
Proposed circuit board layout:
Pin usage table:
ToDo’s:
Mounting holes.
Schematic terminal labels.
Silk screening.
Remove board copper from the antenna end of the board.
???
What I’m looking for is some feed back and input of any flaws of this design. Things like what maybe should be included. And will there be concerns about on board capacitance with that amount of circuitry???
And also any mistakes on my thinking and analysis for which ESP32 pins to use like this.
This is my first attempt at CAD circuit design, and certainly KiCad. So I’m still not sure what I will be running into getting it to crank out the needed Gerbers for a prototype board house to make a small batch. And I don’t have a clear sense for how much that might cost. So some feedback on what to expect on that front would also be appreciated.
I have not yet attempted the routing either, I’m thinking that it is better to resolve any other issues that there may be first.
TLDR – Does this board plan look workable and sane, or not… 
TWT