This simple project uses a Dallas DS1820 one wire temperature sensor and a pic 16f628 microprocessor. A simple temperature regulator where a LED symbolizes the Fan.
Data derived from the DS18s20 is a 9bit centigrade temperature measurement. As mentioned the temperature sensor communicates over a one Wire bus that requires only one data line and ground for communication with a central microprocessor.
The DS18S20 can use power directly from the data line (parasite power) wich eliminates the need for an external power supply. This is not used in this project though.
For more detail: DS1820 Temperature regulator using PIC16F628