This is my first project where the microcontroller is powered directly from the battery. PCB is driven by STM32L412KB chip. It is low power ARM Cortex-M4. Power consumption in run mode is 120uA/MHz so 9,6mA at 80MHz. PCB has micro USB to upload new firmware, also it has capative touch button to interact with user. The board had to be simple as possible and have minimum number of connection because routing can only be on one side of the board without vias. Also I don't want to pay extra for 4 layer board. Due to imposed constraints, three of the route must be wired on the board. So far I don't have many time to run a USB or capative sensor, but when I find more time I will definitely do it :D.

In next verison I want use LIR2032 (li-ion battery)  and add simple charging circuit on board. It will be charge by micro USB connector.  Also next version should have connector for programing the STM if possible and be 2x smaller.

All of file is in GitLab repo.

TODO:

1.  Touch Sensor fix
2. USB fix
3.  Optimize power management
4. Add solder mask under TopOverlay