[magicalhippo]

I tested a few STM32F103 dev boards, using a Siglent SDM3055 multimeter and Siglent SPD330X power supply.

The chip has a 12bit SAR ADC. Layout and board design mattered a lot, but even the worst ones had 10 bits worth, and the best one had nearly 12 bits effective.

That was without doing too much on the software side, meaning the other modules weren't running, besides a single serial output. On the bad boards the serial affected it, but on the good board very little.