This is a thermometer for ambient temperature; it uses a thermistor and displays temperatures from 0 to 40 degrees Celsius.
Step 1: Materials and Schematic
Seeeduino (or Arduino) X1
10k resistor X1
50k Thermistor X1
All materials except the board come from Seeedstudio's Sidekick Kit, which can be found here:
The picture illustrates the schematic
Step 2: Code
The code is included in the file. It's modified based on Adafruit's tutorial on thermistors, which can be found here:
It's the most detailed tutorial I've come across, and it explains very clearly the concept of a thermistor, how to connect it to the board, and how to convert the readings into temperatures.
Step 3: Final Step
With the parts working, we just need to add a box outside of the board to protect the wires, and a panel on the servo that marks the temperatures. The servo's arm will point to the number that corresponds to the ambient temperature, with a range from 0 to 40 degrees Celsius.