I have made one STM32 DIY hardware for my daughter charity sale in school.

That use STM32F103 development board, BMP280/AHT20 sensor, OLED display, three buttons, two pin female connector. All are soldered in one 5cm*7cm Perfboard.

The hardware can use two AA batteries connect to two pin female connector as power. And can use type C USB to supply power.

Simply usage: SW1 reboot MCU. Display button toggle OLED on or off. Temperature button toggle BMP280 temperature show or hide. Energy saving button toggle energy saving on (after 30 second clear OLED display) or off.

Fritzing breadboard sketch included in source code files.

The source code is hosted on codeberg.org.