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what? Humidity sensing is simple, all you need is a humidity sensor/meter, then an ADC and a microcontroller.
Just create a program on reading an ADC be it serial, parallel, I2C or SPI. Calibrate the results to fit on your desired output, convert it to BCD, ASCII or whatever chracter fit for your display, then display into an LCD or an LED.
in honeywell humidity sensors available
i think the number is hih3160
search in the www.honeywell.com site
the sensor is linear and easy to use controller
On the mentioned above Sensirion web site there is a very good working example code for the humidity and temperature measurement with their SHT11 sensor. Buy the way, this sensor is best, compared with others by my experience. More, thanks to having both temperature and relative humidity sensors on one chip one can have a precise measurement of absolute humidity and even dewpoint. It costs about 17 EUR in small quantities.
I'm building a climate control that needs precise humidity readings, so I've done a lot of research about humidity sensors. I have found many information about them, and this is an interesting article for those who need to know more about: Choosing a Humidity Sensor: A Review of Three Technologies | Sensors Magazine
There is another option (which I'm using), the dry bulb/wet bulb method. You use two temperature sensors in a constant airflow, one of them wetted by a cottom strip. The temperature difference is a parameter that combined with air pressure in a complex formula gives the relative humidity and the dewpoint temperature, an extra parameters that can be useful. This method is complex, not as easy as capacitive sensors, but more precise and isn't affected by condensation like some of the capacitive sensors.
Resistive sensors are also interesting, but not easy to use, since you have to use alternate current to drive them. They also have a limited range of measuring.
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