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### Topic: DEW point using DHT22 sensor (Read 1 time)previous topic - next topic

##### Oct 10, 2017, 09:16 pmLast Edit: Oct 10, 2017, 09:25 pm by notfreeusername
Hi everyone,

I have a simple weather station. It measures the temperature and humidity using DHT22 sensor.
I want to detect fog in my garden. After doing some research I want to use dew point for the detection.
Using DHT22's values how can I get the dew point? After that how can I use those values to detect whether there is a fog or not?

Thanks

#### AWOL

#1
##### Oct 10, 2017, 09:21 pm
How many hits?
"Pete, it's a fool (who) looks for logic in the chambers of the human heart." Ulysses Everett McGill.
Do not send technical questions via personal messaging - they will be ignored.
I speak for myself, not Arduino.

#### groundFungus

#2
##### Oct 11, 2017, 12:21 am
I had a hard time finding a library for the DHT22 that included dew point when I made my weather station.  I ended up taking the dew point function from this DHT11 library and inserting it into the DHT22 library that I was using.

#### wvmarle

#3
##### Oct 11, 2017, 05:06 am
You can calculate the dew point with current temperature and humidity (if <100%). That means if the temperature drops below that point, you may start seeing fog, but likely well before that you'll have dew forming on your plants, which are normally experiencing a lower temperature (close to the ground) then where you will have mounted your sensor station (the normal height for measuring temperature is 1.5 meters above the ground).
Quality of answers is related to the quality of questions. Good questions will get good answers. Useless answers are a sign of a poor question.

#### criminalkaoz

#4
##### Oct 12, 2017, 04:31 pm
You can add this function to calculate the dewpoint:

Code: [Select]
`float calcDewpoint(float humi, float temp) {  float k;  k = log(humi/100) + (17.62 * temp) / (243.12 + temp);  return 243.12 * k / (17.62 - k);}`

#### aarg

#5
##### Oct 12, 2017, 06:05 pm
You can add this function to calculate the dewpoint:

Code: [Select]
`float calcDewpoint(float humi, float temp) {  float k;  k = log(humi/100) + (17.62 * temp) / (243.12 + temp);  return 243.12 * k / (17.62 - k);}`
In which measurement system?
... with a transistor and a large sum of money to spend ...
Please don't PM me with technical questions. Post them in the forum.

#### criminalkaoz

#6
##### Oct 13, 2017, 01:49 pm
In which measurement system?
ºC and %

#7
ºC and %