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Topic: [SOLVED]Ethernet cable for sensor (Read 1 time) previous topic - next topic

kris92

Oct 10, 2013, 09:20 pm Last Edit: Oct 12, 2013, 06:01 pm by kris92 Reason: 1
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 ?

Regards,

MarkT

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 will NOT respond to personal messages, I WILL delete them, use the forum please ]

kris92

I don't use capacitor....
In attachment how i've wired everythings

kris92

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


kris92

#4
Oct 12, 2013, 06:01 pm Last Edit: Oct 12, 2013, 07:12 pm by kris92 Reason: 1
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 !


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