💬 Air Humidity Sensor - DHT

[thomas schneider]

Hi everybody,

I try to uploaded the sketch on my arduino nano and I have an error with this line :dht.readSensor(true);

When I delete this line I have no error on the upload but the senosr has no refresh...

[carlos]

@thomas-schneider
Did you see the comments from Mikael?. Do you have the DHT library?.
What does the error say?

[thomas schneider]

Yes I saw the comments of Mickael. But sorry, I didn't understand how to download the library. Now all is done and ok ! We need to come back and download the entire folder. Why this library is not in mysensors library ? It's not easy for a newbie.

Thanks for the support and congratulations for the website.

[skywatch]

Can anyone please show how to connect more than one DHT with this sketch? What needs changing in the code? (I am OK with the hardware side of things).

Once I have an example I can work the rest out but at the moment this bit baffles me! ;)

Thank you :)

[mikeS]

@skywatch
I know what you mean, I was having the very same trouble with relay actuators, and that's where your solution lies. There is a sketch that allows you to name the number of relays, and then the sketch automatically names the children, you should be able to modify that, (or at least get an idea of how you have multiples of the same sensor on the same board) to add as many dht's as you have spare digital pins on your arduino. Good luck, hours of fun lies ahead ;)

[tiana]

Is exist some way to calibrate DHT sensors? today i make a experiment assemble 5 nodes with 5 DHT11 sensors put all nodes on one table and leave them for some hours, and the result is the every sensor give different values about temperature and humidity + - MAX 5 degree Celsius around the real temperature in the room. Hardware used Arduino Nano X 5pc., HDT11 X 5pc., the power supply is 12V 2,2A enough to power all of the arduinos.

[Anduril]

@tiana well you could simply calibrate the value you get in your sketch for every DHT on it's own. But you have to do a calibraton, meaning measure all of them at multiple temperatures and humidities.
If it's only a offset you can also use

// Set this offset if the sensor has a permanent small offset to the real temperatures
#define SENSOR_TEMP_OFFSET 0

to correct for this, otherwise you have to implement your calibration function on your own.

[tiana]

For some sensors is possible to make with offset, but some of the sensors changing their values 2 times in minute with + - 2 degree Celsius some times show more sometimes show less.

[Anduril]

well I think this kind of noise can not be calibrated. I thought they all have different values, but with offset, linear oder squared function for deviation.

[tiana]

I read datasheet for DHT11 and 2 degree deviation is ok for them. Now i playing with DHT22 I try this #define SENSOR_TEMP_OFFSET -1.3, but nothing is changed the sensor still give me same value.

[mfalkvidd]

@tiana try setting SENSOR_TEMP_OFFSET to a really big value, for example -30.8 to make sure that the change is large enough to be noticeable.

[pepson]

Where i can found good DHT library for this sketch ?

[mfalkvidd]

@pepson how about the library linked from the build page?

[pepson]

sorry i found

[Jim Danforth]

Using library linked above
Getting: no matching function for call to 'DHT::readSensor(bool)'

[ramoncarranza]

@hek
hi, how do I change the readings from C to F?
My sensor works fine, by I get the readings I celsius

[mikeS]

@ramoncarranza
Change the line in the sketch:

temperature = dht.toFahrenheit(temperature);

to

temperature = dht.toCelsius(temperature);

probably? I haven't checked it, just looked at the DHT library. You may need to comment the isMetric line earlier in the sketch too. But I think that's how you do it.

[ramoncarranza]

@mikeS Thanks so much for your reply, it's working perfectly now.

[meanmrgreen]

@Jim Danforth
Getting the same, have tried a number of different DHT libraries and cant get it to compile.

[mikeS]

@meanmrgreen The only DHT library that will work is the one from the link before the sketch. If you have used others chances are you need to move or rename those other DHT libraries as that is why the sketch cannot call that function.