Sorry, I did never found schematics from Yuneec drones (Blade 350QX is one predecessor of those, firmware was mads by Yuneec). I think that is and will be their secret. I can only guess that the voltage sensor is one of the analog inputs from the STM32 chip connected to a simple voltage divider (two resistors). The STM32 has an internal analog-digital converter (12bit). Most of the GPIO ports can be used as analog in/out pin. This is set by firmware how the pins are set-up. hard to say how the supplier has made that.Do you by any chance have a schematic diagram of this control board a friend of mine and I want to look into maybe replacing damage parts on the esc's and board instead of going the expensive way and replacing the whole thing.