I am trying to learn how to design PCBs to create a RP2040 based microcontroller with the full pinout, but in the smallest form factor. Ever since the Teensy++ 2 was discontinued I have not been able to locate a 27+ GPIO MCU to facilitate full size keyboards using hardwired methods. My idea is having a small factor, but ample GPIO will allow for flexibility.
The goal is to create a drop in controller that can be use in any sized project (60%-100+%) and still have a few extra pins for rotary encoders or displays. The inspiration came from wanting to create a drop in controller for an Apple AEK (M3501) drop in PCB. I do not want USB built into the board, but rather break it out to save space, as in most instances the controller will be in a random spot on the board (wherever it can fit) and the daughterboard would be able to be manually populated with diodes, LEDS, USB connector, etc.
The board should have 2 buttons (reset and bootsel) for flashing. I am hoping to keep the form factor under 18mm x 54mm to fit in the preexisting cuts in the plates. I am hoping to make it a 2 layer board with all the components on a single side for cheaper manufacturing. I have taken a few Youtube courses on KiCad but it sure isn't easy. Any suggestions would be helpful. I can share any of the files I have created as well. I am trying to create this for the community and not for profit. I want this to be as open source as we can make it.
I have seen those RP2040 stamps, but I fear their footprint is too wide for my ideas.