The thermostat in my freezer said goodbye at the worst, with a lot of heat in July and an empty pocket after the summer break. So I started replacing, therm-mechanical element with an inexpensive ESP8266 system, which I can also monitor from anywhere (from home for now).

Step 1: Drawing the Scheme of the System

As you can see, the following list of materials is required:
1 dual power supply 5v and 3.3 volts dc.

1 Temperature sensor DS18b20 (Water proof is better with a couple of meters)

1 ESP8266-01

1 block of relay (I used a double because it is the one I had)

1 (4k7 ohm) resistor

Step 2: Assemble and Connect

As was urgent, I did not bother too much in the aesthetics of the whole, so I soldered with tin, cables and thermoplastic, on a piece of uniprint plate.

Note: Very important !!, be careful to connect the ESP8266 to 3.3volt DC and the block of relays to 5 volt DC, if done backwards it is very possible to destroy the microcontroller.

Step 3: Program ESP8266 With Arduino IDE

Using Arduino IDE and the appropriate libraries, the thermostat will easily be started, remember to connect the N / O normally open circuit of the relay to the old thermostat connections.

Important Note: To do this, remember to disconnect the main power from the refrigerator, to avoid damages by electric shocks.

Follow another better Instructable, to load the program via USB and serial port.
It is also possible to check the IP address of the thermostat. That IP address is where you can monitor temperature and the status of the relay through the wi-fi network., using http://ip_address/read