This is easy to build a simple digital thermometer with only two parts – microcontroller, temperature sensor and display. Here is one small project that can be put together in less than hour.
It is based on PIC16F628A which reads temperature from DS18B20 1-wire digital sensor. Temperature is displayed on four seven segment display which can output temperature values from -55 to 125 degrees. Probably most work that needs to be done here is interfacing the display which cathodes are switched though BC337 transistor keys. The keying is needed to dynamically switch between separate digits. This way less microcontroller pins are required. Source code is ready for download so all you need is to plug pickit3 or other programmer and have temperature output immediately.