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winlinvip / SimpleDHT

Simple, Stable and Fast Arduino Temp & Humidity Sensors for DHT11 and DHT22. http://learn.adafruit.com/dht
MIT License
144 stars 61 forks source link

diff values for Humidity for dht11&dht22 #17

Closed enginm closed 6 years ago

enginm commented 6 years ago

Hi, thanks for library,

i have an issue that i don't understand,

i am reading different Humidity values on same breadboard with diff sensor,

here is the result: Sample RAW Bits: 0100 0011 0000 0000 0001 0101 0000 0000 0101 1000 Sample OK for DHT11: 21 C, 67 % Sample RAW Bits: 0000 0001 1110 1011 0000 0000 1100 1001 1011 0101 Sample OK for DHT22: 20 C, 49 %

Rayzor53 commented 6 years ago

As I understand it, the DHT11 gives its measurements as absolute humidity, and the DHT22 gives relative humidty, which is affected by temperature.

On Wed, Jan 3, 2018 at 2:46 PM, enginm notifications@github.com wrote:

Hi, thanks for library,

i have an issue that i don't understand,

i am reading different Humidity values on same breadboard with diff sensor,

here is the result: Sample RAW Bits: 0100 0011 0000 0000 0001 0101 0000 0000 0101 1000 Sample OK for DHT11: 21 C, 67 % Sample RAW Bits: 0000 0001 1110 1011 0000 0000 1100 1001 1011 0101 Sample OK for DHT22: 20 C, 49 %

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DaleSchultz commented 1 year ago

well, I was reading the lines in SimpleDHT.h and its states:

//      For DHT11, in H, such as 35H.
//      For DHT22, in RH%, such as 53%RH.

However, the data sheet states it returns Relative Humidity. See https://www.electronicoscaldas.com/datasheet/DHT11_Aosong.pdf

I get a value of 35 right now at 23°C - and if that was absolute humidity the RH% would be well over 100%

So this means the original posters question is unresolved, and I want to suggest that the .h file get updated as a simple documentation issue.

winlinvip commented 1 year ago

Patch welcome.