I'm designing a CAN circuit that will connect a series string of 12V batteries together. The first battery will be tied to a common ground (think vehicle chassis) that will connect to the CAN ground which is shared separately across the batteries.
I'm trying to design a circuit that will activate a GPIO pin if CAN activity is detected. At it's simplest, I believe this is achievable with the use of a differential amplifier with low gain - such that the inputs are buffered and summarised independent of the amplifier circuit's ground.
What happens however if the CAN voltages are offset - i.e. if we consider CAN to be +2.5V and -2.5V relative to the source ground - in the 4th battery in the string the difference becomes 38.5 and 33.5 relative to that batteries ground (and well above rail voltage)
Is an instrumentation amplifier or differential the right circuit for this application? Ideally I want a buffered circuit where if the difference between Vin(A) and Vin(B) > 4V, an output gets pulled high.