I’m gonna start by saying the author of this project was very inventive by using this method. I never thought something like this is possible: by using a piece of paper the system detects the humidity by taking pictures before and after the humidification. The system is able to take 1500 photographs per second and analyze them. The whole system is based on dsPIC30F2012 a powerful microcontroller from Microchip.
Humidity Meter for Soils Takes Pictures Using A Computer Optical Mouse: