Hello everyone, I am a new user from Italy. :-)
I realized a thermostat controllable by web using an arduino with wifi shield.
My house is divided into two zones (day and night) controlled by two programmable thermostats.
I often travel for work and sometimes happen to get home earlier or later than I thought. Hence the need to have a thermostat controllable by the web.
Looking around I found great thermostats wifi with web interface but very expensive (500-700 euros), so I decided to realize this project and it works!
Materials:
Product Price Qty Price Tot
-------------------------------------------------- ---------------------------------------------
Arduino Uno 29,90 1 29,90
Wifi Shield 56,00 1 56,00
Temperature Sensor DS18B20 2,00 2 4,00
Power Supply AC/DC 3-12V 500mA 9,90 1 9,90
Relay 220V 8,00 3 24,00
Switch 30,00 1 30,00
Switch Contact 1NO/1NC 5,00 2 10,00
Mini adhesive backed PCB support 14.3mm 4,50 1 4,06
Box 9,00 1 9,00
-------------------------------------------------- ----------------------------------------
Total 176,86
I installed the Arduino + wifishield, the three relays and the switch in the box.
I placed the two temperature sensors side by side with traditional thermostats, one in the day zone and the other in the night zone.
The switch is used to include/exclude the arduino or the traditional thermostats.
I then added a third relay (on the web page "auxiliary") to turn on/off a pellet stove.
Screenshot of the webpage:

I attach the code, libraries and some pdf, please use arduino-0023 (with Arduino-1.0 does not work the wifi shield library).
I also used a modified OneWire library because the original one doesn't work with long wires (about 10 meters from arduino to temperature sensors).
Suggestions for improvement are welcome!