[SOLVED]Ethernet cable for sensor

Hi, I have a TMP36 sensor running on my Arduino, connected with jumper wires. Today i've tried to connect my TMP36 to my Arduino using a 5 meter length Ethernet cable. The result was : 110°C !! Normally it should be around 20°C.

Any idea about things to consider for long wire cable, and about what's wrong ?


Firstly ethernet cable is unshielded which is bad news for sensitive precision signals.

But one thing you should do is use a 4-wire connection to the sensor, power and ground on one twisted pair, signal and signal-ground on another twisted pair. You use two analog inputs for signal and signal ground and take the difference. Then the voltage error caused by sharing grounds goes away.

However that may not be the problem - did you decouple at the sensor end? The device requires 0.1uF decoupling capacitor (and decoupling has to be close-by to work).

I don’t use capacitor…
In attachment how i’ve wired everythings

I dont’ instinctively think about reading datasheets !
…so i had a look at the TMP36 datasheet (see below) : maybe here is the answer ?


Hi, Today i've added a 0.1uF capacitor just like the datasheet says. Works like a charm with an Ethernet cable up to 15 meter !!! Great :) Many thanks !