Opto Isolator question I'm building a CANBUS network based on an arduino to go into an offroad racing truck. The vehicle has two separate battery systems, and I would like to monitor the voltage while still electrically isolating them from the arduino itself. For the voltage monitoring itself, I assume I can use a simple voltage divider into an Analog pin. To electrically isolate the arduino, would an Opto Isolator work? I found this one: https://www.sparkfun.com/products/9118 But it appears that it's designed for low voltage to control high voltage, as opposed to the other way around.
An optoisolator is good for digital signals, but won't transfer an analog signal accurately.  

Instead, you could put ADCs on the different circuits and optoisolate their communication with a master Arduino.