1. ## 2 wire sensors

This is a stupid question that I should know the answer to but bear with me as I have spent as many years trying to forget this stuff since retiring than I spent learning it. In an automotive application you typically have 2 wire and 3 wire sensors, 2 wire sensors like thermistors for measuring temperatures are common. your temp sensor is a 3 wire sensor which makes it easy to hook up to a board that is set up for 3 wire analog inputs, but just the same, a 2 wire temp sensor is an analog input also.
Now if I wanted to utilize my already present ECT sensor can I just use the 5vdc and sensor return, disregarding the GND, or do I need to build some other circuit to interface it?

2. http://www.mp3car.com/vbulletin/docu...uspension.html

the fusion brain senses voltage, 2 wire sensors are variable resistance so they must be wired as part of a voltage divider

3. So looking at the schematic you provided in the link then my 2 wire resistive sensor would go between the GND and the Input terminals on the brain and the 5vdc terminal would connect to a resistor of which the other end would tie in with the input terminal right?
also is the value of R1 a constant or is this going to be something that depends on the resistive range of the thermistor and if so is there a formula to determine the proper value?

4. "also is the value of R1 a constant or is this going to be something that depends on the resistive range of the thermistor and if so is there a formula to determine the proper value?"

the latter, and you can certainly optimize, but a nice rule of thumb is R1 = highest resistance the sensor can be

5. So if I have a thermistor that reads roughly 13k at ambient temp and 60k at freezing, I should be able to replace R1 with a 100k pot and adjust that to get the most accurate temp readings across the range I will be using and then replace it with a resistor valued approximately at the resistance I find with the pot?

6. yup, that'd work

7. just one other problem, what if my thermistor is a negative temperature coefficient device?

8. why is that a problem?

9. because as the temperature rises the voltage goes down. with room temp I show about 60 degree F, if I stick the thermistor in ice water It jumps to 125!

10. Originally Posted by jimp
I show about 60 degree F, if I stick the thermistor in ice water It jumps to 125!
how are you converting to temperature?

it's not a problem, you just need a new formula to convert to temperature, utilizing the negative coefficient

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