I've also been contemplating replacing the Nano with one of the STM32F103 "Blue Pill" Boards in the uBITX. I don't have the uBITX board dimensions but if you are interested I do have the Blue Pill board schematic icon and footprint in my public KiCAD repository at github.com/celeritous as well as schematic icons and footprints for several of the TFT displays with SPI interface.
I've also got an STM32F103 STM32CubeMX sample project in the repository as well as some other STM32 module boards that are released under the CERN OSH license. There is a 50mm x 50mm STM32F745 board with Ethernet interface, dual USB and uSD card and a low power STM32L151/152VDx processor? 50mm square board with USB abnd an optional uSD card and ESP07 WiFi module on it.? These both use 2 dual row 34 Pin 100 mil headers to bring out a lot of I/O. There are sample STM32CubeMX files with them.? There is also a 2.8" TFT LCD user interface board with 2 rotary encoders and 12 pushbutton array that I'm currently testing. It uses some passive and active de-bouncing so not a lot has to be done in software.
I'm also working on a board similar in size to the blue pill board that uses the STM32L152CCx processor which is lower power, 32MHz and has 256K of memory. It should be out in the next few days.? This is the one I was really intending to target the uBITX with. It was originally developed for a GPSDO project using the SIliabs SI534x Synthesizers with Holdover.? I've just been waiting on some enclosures from China to verify the size on everything before ordering some test boards.?
I should also have some STM32CubeMX? HAL compatible libraries for release soon for the ILI9341 and similar displays as well as the MCP23017 I2C digital IO expander and 25AA02 MAC EEPROM. I found most of the Adafruit ports to the STM32 lacking unless you use the Arduino environment.
We primarily use the STM32CubeMX to generate the initialization code and Atollic True Studio (Now free since ST acquired them) which is a good little development environment with actual hardware debugging. I've never really liked the Arduino and mBed style environment that don't provide for real hardware debugging.? I've been doing embedded design now for going on 40 years beginning with the Z80.
I hope that the more adventurous wanting to move to platforms with more than 32K of memory and faster speeds will find these of use. I did do some graphics tests with the ILI9341 driver and TFT displays on the blue pill boards and it is not hard to exceed the 64K (or even occasional 128K) memory on them with a few graphics and fonts.
Allen
K5ABL
