DHT11 calibration

Other Hardware Sensors
1

Hi,

I bought 2 DHT11 sensors and they have a small electronic board attached to them like in this picture:


I can read the temp and humidity, but they are off.

room temp: 37.5 / sensor reading: 35
room humid: 22% / sensor reading: 27%

I also tried to keep the sensor in the hand and the temp spikes to 70-80C by the sensor reading. Also I put it in a container with ice and the temperature is actually going up to 37-40C. However the humidity is going down as expected. Both sensors are behaving the same.

Is there a way to calibrate them?

2

I forgot to mention that I do wait in the setup sequence 1 second and I read the sensor after 5 seconds in average, so it's not the timing that causes the problem...

3

Sorry, in my original post I made a mistake. The room temp is around 27 and the sensor reads 35...

room temp: 27.5 / sensor reading: 35
room humid: 22% / sensor reading: 27%

So, Any ideas on how to calibrate this DHT11? I read the data over digital.

4

Those sensors are not very accurate at all.
Their specified accuracy from the datasheet is HUM +- 5% and temp is +-2D C.
So you are doing pretty close as is.
If you want better accuracy use DHT22.

5

Hi,
Have you got the 5K or 4K7 resistor from data to 5V?
Have you added the 0.1uF capacitor between pin1 and pin4 of the DH11, right up close to it?
It only updates every second.

Can you please post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png or pdf?

Can you please post a copy of your sketch, using code tags?
Please use code tags.. See section 7 http://forum.arduino.cc/index.php/topic,148850.0.html

Tom.... :slight_smile:
The fact that both are the same is a worry.

6

It already has an electronics board attached to it. Why do you have to connect more resistors and capacitors?

7

Hi,
Has the board got a 5K or 4K7 from data to 5V.
The resistor is needed to bias the communication line, look up the spec for the DHT11 and it will tell you ALL about the one-wire com system.

Tom... :slight_smile: