Best practice for auto sensor interfacing.

Hello, I'm fairly new to all of this, but I'm planning on something of a dash/data logger for my car, and every day, I think of more than I can monitor.

So far, my plan is ESP32 based, with ADS1115 external ADC's for the measurements. My circuit includes, OPAMP buffers for each input signal to prevent loading the sensor that I want to monitor, since I want to use the majority of already installed sensors where I can.

At the moment, I suddenly remembered while reading some information on one of the sensors that I'll be monitoring, that factory ECU's usually use 2 wire sensors for earth plausibility monitoring.

So this got me thinking, should I just measure the voltage on the sensors, or should I be feeding the sensor earth into the ADC's with the high side and do a differential measurement with the ADC's to eliminate any plausibility concerns?

Also, instead of using 2 wires for each sensor, and a pair of ADC pins for each measurement, can I just measure the sensor earth in single wire mode, then subtract from sensor readings in my code?

Since most engine sensors all share a common sensor ground, then this would save a few pins, otherwise, I can see that I might need to use more than 4 ADC's, and that creates a whole new headache with having to multiplex the ADC's.

Is your car a truly ancient vehicle?

If not, you might consider reading the data via the built in OBD interface, which makes essentially every measurement of interest accessible.

The automotive electrical environment is very harsh. Anything you built yourself needs to be protected from voltage transients possibly higher than 200V, polarity reversals and other calamities. Those considerations include the "12V" supply.

I had considered that, but not all sensors that I want to monitor are broadcast over OBD. I figured that it may not be worth the added complexity, and might be simpler to monitor all sensors using the same method.

Example is, I do have an oil temperature sensor in the car, but it doesn't get broadcast.

The 12v supply is pretty solid, with both reverse polarity, and over voltage protections on the input before the 5V reg.

And reference voltages are buffered, and as far as I know, should be fairly smooth, but will still need to test.

Mostly, a lot of this project, is about learning something new.

A learning experience is guaranteed!

Here is an overview of the hazards you will encounter and protection methods now in use.

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