DESCRIPTION: 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. If you're interested in the
details see Tracy Allen's web site (EME
Systems) for his discussion.
The Sensirion SHT1x 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 that the
BASIC Stamp 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. The SHT1x 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. The accuracy is better than most other sensors too.
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. Excellent for commercial or home-based projects
that require such readings.
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