The project illustrates the control of a PC fan speed and using an Arduino microcontroller to read a LM35 temperature sensor. The use of an optocoupler is covered along with Pulse Width Modulation ...

The Sensiron SHT45 precision temperature and humidity sensor got featured here a couple of years ago, and wonderful Adafruit has picked up on it, and not only produces SHT4x breakout boards ( right ), ...