Reading car coolant temp sensor

Official Hardware Nano Family Nano 33 IoT
1

Hi,

I am trying to read the car coolant sensor resistance (voltage) but I want to try and do it without affecting the car dashboard that is using the same sensor. The sensor has one terminal and is getting constant 10.3 V from the car dashboard instruments cluster. At room temperature (20c) the resistance is 1020Ω when the engine is hot the resistance drop to around 30Ω. Below is the circuit I thought about. I think that I do need another voltage divider in the case of low temp and assuming I will get the 10.3V. In that case, my divider will output 3.3V

Attached please see the circuit I am thinking to use. Will that work?

Thanks,

Ofer

Screen Shot 2020-06-24 at 3.55.38 PM.png
Screen Shot 2020-06-24 at 3.55.38 PM.png1488×918 86.8 KB

Screen Shot 2020-06-24 at 3.55.38 PM.png
Screen Shot 2020-06-24 at 3.55.38 PM.png1488×918 86.8 KB

2

Two additional measurements I just did.

  1. when measuring the voltage on the sensor the voltage goes down as the resistance is going down. So at 44 Ω the voltage is going down from 10.2V to 6.5V
  2. measuring the voltage on the sensor with a Fluke is not affecting what the car dashboard is showing. So there is a way to do it and minimizing the effect on the dashboard function.