I have an arduino which I have set up to monitor humidity and temperature inside and out. 4 sensors in total which switch a fan on via a relay.
I have the code and sensors working fine but on building the project by putting the extrnal lm35 on a 5m wire it now reads 0. I tried adding it again on a short wire and it works fine.
The setup has a 4 core burglar alarm cable. @ wires for + and - and the other two for humidity and temp sensing.
the humidity sensors work fine.
Check the sensor with a short cable?
Check the cable with a Digital MultiMeter (DMM)
Did you connect the cable properly?
To the right pin?
double checked?
And first before first --> READ THE DATASHEET of the LM35.
ALL IS EXPLAIN page 7 (National Semiconductor edition). You have to protect the LM35 from capacitive load.
National recommends a serial resistor of 2kohms .
With 50 m Cat 5 ethernet cable I found an optimum for R = 4.7 kohms.
Other solution see picture.
In my opinion it is the best because it is independent of the length of the cable.
LM35 Output impedance as a value near from 0 Ohms so the line have to be matched by 100 ohms.
Arduino input impedance is > 100kohms so the line have to be AC matched by 100ohms.
