Today I will show you how to make a very simple temperature control fan speed circuit. I use very minimal parts and works in real life.
This circuit change 12 volts DC fan speed by temperature. The hotter the temp, the faster fan speed. The circuit principle is a voltage divider between T1 and 20 K potentiometer. When temperature increase, the Thermistor resistance decrease and make the voltage set point between T1 and R1 increase until it is higher than a Mosfet Vgs threshold and make a Mosfet change to ON state and conduct current to a fan.
Below picture is the parts you need.