I have pt100 sensor connected to fez spider analog input. The resistance of sensor changes, along with temperature. I have 110 ohm resistor connected in series, so i am meassuring voltage drops. The problem is, that my readings are inconstitent , from 20 to 30C. Like that some kind of noise is present. I am just starter in electronic, so i had no idea, what causes this voltage up and downs. Is the 3.3v voltage reference ?