The system uses an Arduino board (~$30) and special sensors that are able to take measurements and report the data without additional hardware. This is done using a MicroLan or "One wire" network. It allows many sensors to be connected using one data line an a ground wire.
Old household telephone cables have 4 wires, only 2 of which are usually used, so you should be able to use the other 2 wires to communicate with the sensors, this allows you to have cheap sensors that plug into the phone jacks and send the data to an Arduino board plugged into another phone jack.
The Temperature sensors cost about $4USD. Humidity sensors are also available.
I was unable to get this to work in my house, I think this was because of the phone wires (we broke some when we removed the wallpaper), so I was not able to get the full system to work. I am posting an outline of the system, hopefully someone will find this interesting or useful.
Arduino UNO R3 board with DIP ATmega328P
DS18B20 Wire Digital Temperature Sensor IC
Step 1: Wire the Sensor
I used a surface mount version because I had one on hand. There is a through hole version that is easier to work with.
The data sheet is here;
You can buy it here for $4.25:
Step 2: Connect to Phone Cable
Step 3: Wire to Arduino
From the sensor: Ground and Vdd both go to the Arduino Ground. DQ goes to digital pin 10. A resistor goes from pin 10 to 5V.
Step 4: Program the Arduino
You can get it here:
Also you need this library:
Step 5: Test It Out
Step 6: Try It With the Wires You Already Have in the Wall
Step 7: Fix the Wires - Outside and Inside the House
Every phone jack had its own cable, that ran to two grey boxes on the side of the house. All the cables had been cut, some in multiple spots. I used a wire nuts to connect all the black wires to each other, and all the yellow wires.
Inside the house the house, I took off all the phone jacks and reconnected the wires has needed. In one spot 3 cables came together behind one jack. Several wires had to be reconnected.
Step 8: Success!
I have thermometers (4$ each) plugged into 3 unused phone jacks, in different rooms. At another jack I have an Arduino streaming the data to a laptop.
I am just using the example program included in the One Wire library. It shows the address of each chip, the raw data, and the temperature in C and F.
Step 9: Now What....
Step 10: Plot
I am not sure of the timescale -- this is either 30 min (until the screen saver came on) or 3 days.....