This is intended mostly as an aide-memoir to myself – your mileage may vary!
boot
partition and edit cmdline.txt
console=serial0,115200
config.txt
and add the following to the end of the file: enable_uart=1 dtoverlay=pi3-disable-bt
pi
, password raspberry
)sudo systemctl disable serial-getty@ttyAMA0.service sudo systemctl disable hciuart