For this project, you won’t be making use of any external sensors, so the hardware setup is relatively simple. However, it may be worth going through the primary guide for the STM32F405 Feather Express to make sure you've considered what headers to use, what pins are available, etc. etc.
Once you’ve set up your STM32 Feather the way you want, you’ll need to choose which of two programming options you’d like to use - the built in DFU-bootloader, or an external JLink Programmer. The DFU bootloader is built directly into the Feather, and allows you to skip purchasing a new programmer if you don’t have one. The JLink is more expensive, but faster, and it'll allow you to do more advanced debugging if you need to. Both are supported by the Zephyr West tool.
Cheap and easy (DFU Bootloader)
Out of the box, you have the DFU (Device Firmware Upgrade), a programming option over USB that’s available by default on all STM32F4 chips. Enabling it is very easy - just connect the Boot0 pin (B0) to 3.3V logic, which you can do by simply connecting a wire from the B0 pin to the 3.3V pin on your feather. Once you do, either power cycling or resetting the STM32 Feather and connecting to USB will put it in bootloader mode, and you can remove the jumper.
The Jlink is a great choice if you want to do something like debugging with GDB later. It also doesn't require any added wires, and it's much faster, but requires the purchase of the Jlink Programmer.
To get the Jlink working with the Feather F405 you’ll need to first solder on a SWD header on the bottom of the board. Make sure the gap in the SWD header plastic faces the end with the USB C connector.
Then, you can plug in your Jlink using the SWD adapter. Make sure you follow the Jlink instructions to install Jlink Server if you want to use debugging capabilities like GDB later.
Ready to Program!
Once you have one of your two programming options set up, your chip is now ready to be flashed - but you’ve got nothing to put on it yet! We’ll revisit programming the hardware once you’ve installed all the prerequisite tools and compiled your project.