I’m working on a project to get an oil temp display in my car (1999 BMW e46). My plan is to install a temperature sensor (thermistor) in the oil pan and then wire it up to an analog in pin using a voltage divider. I’ll use the analog signal to calculate resistance, and then calculate temperature from that using a best fit curve (see pic), so it’s really important that I can accurately calculate the resistance of the thermistor.
I’ll then display the temperature using an led matrix display. Overall this setup will probably pull about 2 amps. In case it’s useful, engine operating temperature is around 100C.
The issue I foresee here is the level of noise in the car’s ground. I don’t see a way around grounding everything to the body (the regulator’s ground passes straight through to the car), so I imagine my analog signal will be very noisy and almost useless. Before anyone suggests it, I’ve already tried to read oil temp from OBD2 and CAN-bus - it’s not broadcast over either of those
How can I mitigate this problem? I don’t want to have to run this off a 9v battery
EDIT: Would this (admittedly expensive) isolated DC converter work? Assuming I’d then ground everything to it.