Before try to increase resolution of sensor, two things you would better take care first;-
- Use separate power supply to power the Yun and Relay circuit.
- Optically isolated relay board is prefer. Now no common ground, no common power supply, Yun output optically isolated.
This is perfect way to eliminate electronic interference by connect two system via Opto-isolator.
Relay board, Price: $6.79 & FREE 2 day Shipping
http://forum.arduino.cc/index.php?topic=238992.msg1715853#msg1715853
Now you could use analogReference(INTERNAL) to increase resolution of sensor. Change sensor to LM35 for 0~1.1 V/ 0~110 Celsius range.
float tempC;
int reading;
int tempPin = 0; // switch to yun analog pin
void setup()
{
analogReference(INTERNAL);
}
void loop()
{
reading = analogRead(tempPin);
tempC = reading / 9.31;
}