Core and memory budget for the BOM
The STM32L100R8T6A: An additional 2K x 8 EEPROM block stores calibration constants or configuration data without wearing the flash.
Housed in a 64-LQFP package with a 10x10 mm body and 0.50 mm pitch, the STM32L100R8T6A requires a four-layer PCB for reliable fan-out of the inner rows.
At 32 MHz the core draws roughly 10 mA in active mode; the brown-out detect and POR blocks add negligible overhead, so a 200 mAh coin cell can power a sensor node for several months if the duty cycle is low.
It is ROHS3 compliant, meeting the latest EU restriction on hazardous substances.