LM35 and instability below 6 degree...

[mark_s]

I found it was very important to have a bypass capacitor (0.1uf) right at the power leads of the LM35. If you don't already have one it might help the stability.

[synsyn]

I have try to do some experiment and i have find than if i measure the output voltage from lm35 with a multimeter i get the correct one. So the problem is not in the probe(thank's Mark for the tips with capacitor) but in adc reading of my 16f676 :-(
The strange thing is if i try to take some measure with a trimmer tied from vcc and gnd i will get always the correct and stable measure but when i try do measure the output voltage from lm35 i read different voltage variations +/- 2v and the measure is very unstable. I don't know more what i can try for have a decent measure from lm35.

[AvionicsMaster1]

In these two measurements are you using the same power supply? You say you use a pot and it was good but using the LM35 you get erroneous voltages.

I wonder if when troubleshooting you used different power supplies and the DC voltage may be from an analog supply in the first case and a switcher the second. If so the switcher may need an electrolytic on the supply to the LM35.

In the last part of your post, how and where are you measuring the voltage? Could your meter/probe be loading the output of LM35? It would be interesting if you'd show some sketches of how you measured those voltages and what's connected to the LM35.

Just some thoughts.