Partly out of curiosity, and partly to test some aspects of a workflow for other projects, I decided to create a custom RP2040 board. In most cases, there’s no need to do this; it may well be more expensive than simply using a ready-made Raspberry Pi Pico module and mounting it on a custom PCB, while saving a considerable amount of effort.
This short blog post describes how I’m approaching the project. It’s very much a work in progress.
The first thing I did was download the RP2040 hardware design guide PDF, and the minimal RP2040 design KiCad zip file from the Raspberry Pi website and extract and open the design with KiCad 10. This is what the minimal schematic looks like (click to enlarge):
The corresponding PCB layout is shown below. My plan is to reuse parts of this design while adapting it to fit the shape and requirements of my own PCB:
By examining the minimal PCB layout, it was possible to see that nearly all traces were on the top layer, with just a few on the underside, leaving the majority of the bottom copper being a ground plane.
Next, I modified the schematic by removing the components I didn’t need and adding the functionality I wanted. For example, I removed the pin headers and the Micro-B USB connector, replacing the latter with a USB-C connector. I also added RS-485 circuitry to one of the UART ports, since the board is intended to function as an RS-485 adapter.
You’ll also notice a 10-pin connector that appears to be underutilised. That’s intentional. I plan to route several unused GPIO pins to that connector in case I need them later. I haven’t assigned specific GPIOs yet; I’ll wait until the connector has been placed on the PCB so that I can choose whichever pins are physically closest. Anything that makes trace routing a little easier is worth considering!
With the schematic updated, I switched to the PCB editor and took a screenshot of the original layout for reference. I then selected the main central portion of the circuitry and moved it onto my new PCB outline.
The result looked promising:
The original design includes a top-layer +3.3 V copper fill zone, and I wanted to preserve part of that arrangement. To do this, I simply created a new fill zone and roughly followed the outline of the original design, almost like connecting the dots.
Once that was done, I moved the new fill zone into its final position. In hindsight, it would have been easier to create the fill zone first and move it together with the rest of the circuitry, but it only took a few moments to fix. The layout was already starting to come together nicely.
Next, I selected the voltage regulator section from the original PCB and moved it into the desired location on the new board. Since I no longer needed any of the remaining elements from the original PCB layout, I deleted them. At this point, the project had effectively become a normal PCB design exercise, with the remaining tasks being component placement and trace routing.
I’ll write a Part 2 (EDIT: Here is part 2: (+) Getting Custom RP2040 Boards Produced and Assembled with KiCad, Part 2! - element14 Community ) once the layout is complete. I suspect it will be an even shorter post, since everything appears to be progressing smoothly so far.
Thanks for reading!
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