Automotive: Signal Regulation/Protection and Analogue Sensors

Projects General Guidance
1

Hi, I've got a few questions.

  1. I'm attempting to read my car's Tach signal and VSS, I've found a few options but would like some help learning the pros/cons of each so I can select the correct one and know which one to use in future projects. The signal is a ~12v square wave with some overshoot (unsure how much, but apparently nothing major) on the leading edge. These are the options I was able to find.
    a) Transistor
    b)Zener diode
    c)Opto-Isolator
    d) CD4049
    I've thrown out voltage dividers as the offer no surge protection (Not common but a possibility)

  2. Eventually this project will evolve in to a full DAQ system taking in a number of parameters. For this I'll probably have to move to something such as a Leaf Maple, which unfortunately does not have VRef on it's onboard ADC's. What I'm wondering is are car sensors (MAP, TPS, Temp, etc.) sent a consistent 12v from the ECU or are they powered by the battery voltage (Ranges from 12v-14.5v). If it's the latter what are my options for correctly reading these values, as I'd assume of Vin changes then the output of the sensor could mean different values at the same output. I have one idea, reading vBatt and using it to scale, but I'm unsure how accurate/feasible that would be.

Thanks!
-Nigel

2

Opto Isolator would do nicely.

3

Thanks for the response.

I've looked into the optocoupler and it seems that they're more for when you're trying to completely isolate. I'll probably getting power and sharing a ground with the car, so would this not defeat the point? Also with ~14.5V input I'll need a fairly large resistor to properly limit the current.

Can someone elaborate on the downside of using zeners? From my research they seem like a solid option but they're rarely recommended. Thanks!

-Nigel

4

Basically, any power coming into the arduino will be running through a regulator anyway, so its isolated, ground itself is not dangerous to the chip, but signal leads are, hence the optoisolator being your best protection.