I use humidity sensor dht11 to measure humidity of a room, it was working good for almost a month. and suddenly the reading drop down to 10% and **** there. I calibrated it using procedures in its datasheet but the problem still exists. it works for 2 hours then drop to 10%. what is the deal?
Check how much power supply drops. If you are using PIC then PIC can work from 3.3V to 5V. So, if power supply drops by 1V then your PIC will be still working and also Lcd but not DHT11 properly.
Not sure if related, the humidity sensor I have has a little ...flaw?. I've attached the datasheet for you to compare and consider if it may be the same issue. View attachment Sensor Humidity HIH5030-100 Honeywell.pdf Notes on page 2 say:
3. Non-condensing environment. When liquid water falls on the humidity sensor die, output goes to a low rail condition indicating no humidity.
Extended exposure to >90 % RH causes a reversible shift of 3 % RH.
There are application notes that may be of some or no use to you...