I used an LCD shield to display the current temperature and speed of the fan, but you can use the circuit without the LCD display. You also need to select the transistor by the type of fan that you ...

Parts and tools Arduino UNO LM35 Temperature Sensor (Celsius) – datasheet Relay Module ( May refer to my previous post on how to make a relay module) A 9V battery (To supply to the coil of relay and ...

Alternatively, if the outside temperature is < desired temp, just blow air in regardless of the inside temp. All you need then is a temperature controlled fan.

To address this issue, he put together a simple but very elegant temperature controlled fan to vent the enclosure when the internal conditions go above the optimal temperature.