Analogue input of shared sensor

Using Arduino Sensors
#1

I'm trying to use an arduino uno to read the voltage of a sensor on an engine.
The temperature sensor on the engine is connected to the ECU which has an inbuilt 1k pullup resistor. I find that if I connect the sensor to the arduino, it changes the value that the ECU see.

I didn't think that the arduino would have an effect of the voltage of the sensor, but it's obviously is. Is there anyway around this?

#2

This is because the Arduino is only a 5V system and your car's ECU is not. It sounds like the Arduino input is clamping the sensor signal.

Try connecting the sensor to the Arduino through a potential divider circuit so that the Arduino never sees a voltage greater than 5V, that will stop the sensor voltage from being pulled down.

#3

You could use a op amp buffer so you read the ECU signal without loading it. Then voltage divider into the Arduino.

Weedpharma

#4

Yes but the input impedance of a digital input is very high so it is not actually loading the sensor is it.

#5

Grumpy_Mike:
Yes but the input impedance of a digital input is very high so it is not actually loading the sensor is it.

If the voltage is being clamped it is not high impedance.

Maybe I should have said buffer the voltage and do a level change.

Weedpharma

#6

Thanks for the feedback
The sensor on the engine is 5v, with a 1k pull up resistor from the ECU. I didn't think the arduino would have had this much affect on the voltage being read. What it the resistance of the analogue inputs?

#7

What it the resistance of the analogue inputs?

Well in excess of 10M, it is not having any loading effect on the sensor, your problem is something else.

#8