Arduino for STM32

It can be done, but not without using LL or CMSIS and it will need way more flash and RAM then code written in "pure" c/c++.

There are many open source bootloaders that use SD card to flash firmware. You might even find one for your MCU or might need to tweak few lines of code.

Have you tried any DS3231 library ??

So that brings me to two new questions: 1. if using such a voltage divider circuit for multiple PCB's, how do you ensure consistency? Measure the actual resistance values prior to uploading code, and then hardcode the individual resistor values into the Arduino program for each PCB? I.e. calibratio...

1. Are you sure, the input voltage is exactly 3.3V ??
2. Are you sure that those resistors are exactly 4.7M and 2.2M ?

1. If you're using pullups, then with button pressed you get 0, and not pressed you get 1.
2. PC12-PC15 pins cannot source current, but they can sink, so pin provides GND to LED. 0 = on, 1= off

F072C8 has DFU bootloader, so just reset it into bootloader and you can flash it using USB.

Also STM does not provide software USB bootloaders.
You can probably make one using this: https://github.com/Serasidis/STM32_HID_Bootloader

PWM does not control voltage. You cannot use PWM to lower voltage, it only controls time how long power is turned on and off.
Voltage reading will depend on your meter, PWM frequency, board hardware and MCU.

No. .bin extension is for "binary". STM32 MCUs use binary files for firmware upload. You need .bin file if you want to upload firmware to STM32 MCU, unless you have an application that converts HEX file into binary format before uploading it.

dannyf wrote: ↑Tue Jul 18, 2023 10:53 am don't those chips come with a ST bootloader? ST has an application note on that.

They do, but it only supports UART and IIC.

Ground UART1 RX (PA10) pin while you reset board.
If MCU gets anything on UART it will start bootloader with UART enabled, not USB.