Wet bulb humidity sensor

Robert Graham describes (with pictures) how to measure humidity with a couple of DS18S20 sensors, a fan and some PVC pipe. Here on the Wet Bulb Humidity page.

This "modern" way requires a humidity sensor and another sensor (DS2438) to meaure voltage and temperature. See this.

A more complex experiment on the subject can be found at Thermistor Psychrometer Lab.