The Sensirion Temp/Humidity Sensor is an efficient sensor that measure the ambient temperature and humidity of the surrounding area.
Humidity is notoriously difficult to measure. Some of the scientific and electronic considerations to measuring humidity include: analog to digital interface and external circuitry which might require op-amps or oscillator circuitry; temperature compensation adjustments to calculate dew point; calibration against a known humidity source; mounting, protection and response time in the real-world.
This sensor addresses many of these issues head on. It is a smart sensor for both humidity and temperature, and it comes from the factory in a tiny package that incorporates the analog to digital interface.
All the microcontroller has to do is read out the humidity and temperature values through the two-wire digital serial interface. The only math required is a simple scale and offset. This sensor is factory calibrated so that it returns temperature with a resolution of 0.01 degrees Celsius and relative humidity with a resolution of 0.03 percent with an accuracy that is better than most sensors. Worst-case temperature accuracy is +/- 2 degrees C - but in the "room temperature" range the accuracy better than +/- 1 degree C. The relative humidity sensor is similarly accurate: +/- 3.5% in the range 20% to 80%. This is quite remarkable for a low-cost sensor.