I thought I'd start a new thread since the last one from 2010 is locked (read only) http://forum.arduino.cc/index.php/topic,19961.0.html
I've been playing with a Sparkfun HIH-4030 to use as a humidstat. I see lots of different functions but not sure where the numbers are coming from. I'm using the following formula, directly from the spec sheet https://www.sparkfun.com/datasheets/Sensors/Weather/SEN-09569-HIH-4030-datasheet.pdf
float voltage = (5.0 * analog0) / 1023.0;
float rh = (voltage - 0.958) / 0.03068;
of course this could be rewritten as
float rh = (voltage - 0.958) * 32.5945;
This seems to be working but the RH values are about 2-3 % below what my desktop digital temp/humidity sensors read.
This seems reasonable as each sensor is different and may require calibration. What I have not done is account for temperature.
I put a 100K resistor across VO and GND per the spec recommendation. I also tried some capacitors 10uF on 5V and VO but they did not seem to help much.
I tried the formula on http://bildr.org/2012/11/hih4030-arduino/ and I get about +4% higher than my reference humidity readings.
The current issue I have is the relay I'm using throws off my RH reading
Any ideas on how to get more accuracy and or improvements would be nice