I'm trying to build a circuit that can scale down several lipo batteries (5 cell) up to 22V max to be safe to either 3.3V or 5V for measuring with a PIC microcontroller using the analog to digital converter.
Now the problem is I have more than one battery for each motor and each battery is isolated from one another. There is no common ground between them.
Can someone offer some advice on how I can measure the voltage of these batteries using the PIC's ADC. Some form of voltage divider will of course be needed and suggestions on this are welcome.
My analog circuitry skills are extremely weak so please provide as much detail and or references. Any calculations would also be appreciated.
I'd like to ensure some level of filtering/isolation is present due to the LiPos obvious high current usage and noise of the motor.
PS: I know there are very cheap LED voltmeteres on ebay for this but I want to be able to send the sampled voltages back to a base in my project.