Class for DHT11, DHT21 and DHT22 (temperature & humidity)

[MaxG]

Hi Rob,

No disrespect... I appreciate putting your work out there for others to use!

I took the files from GitHub as they were yesterday...
Proceeded as described; got the same compile error  in both IDEs...
Looked for an alternative, tested the AdaFruit library... worked, done.

Cheers, Max

[robtillaart]

Thanks,

The latest version is an expirimental version,

The latest stable is - https://github.com/RobTillaart/Arduino/tree/master/libraries/DHTstable

[robtillaart]

Updated the DHTlib and DHTstable to support DHT12 and AM23XX.

- https://github.com/RobTillaart/Arduino/tree/master/libraries/DHTlib (experimental AVR version)
- https://github.com/RobTillaart/Arduino/tree/master/libraries/DHTstable (stable)


Comments and remarks as always welcome

[FooPlinger]

So, I have just gotten the DHT11 to work and display values on an OLED, but the sketch I am using helpfully puts an "F" after the temperature, but only displays the temp in Celcius.  I have been digging through posts and websites for the last couple of hours, but have been unsuccessful.  I keep seeing people say use float, but I have no clue what that means, others say it is part of the library, but they must be using a different library than I am.
Using this library, how can I make it display the temperature in Farenheit?

Code: [Select]


#include <U8glib.h>  // U8glib library
#include <dht.h>     // DHT library

#define dht_dpin 2  //  pin to which the sensor is connected
dht DHT;
               /*Uncomment and comment*/
//U8GLIB_SH1106_128X64 u8g(13, 11, 10, 9, 8);  // CLK=13, DIN=11, CS=10, DC=9, Reset=8
//U8GLIB_SSD1306_128X32 u8g(13, 11, 10, 9, 8); // CLK=13, DIN=11, CS=10, DC=9, Reset=8
U8GLIB_SSD1306_128X64 u8g(13, 11, 10, 9, 8); // CLK=13, DIN=11, CS=10, DC=9, Reset=8

void draw(void)
{
   u8g.setFont(u8g_font_fub11r);   // select font
   u8g.drawStr(0, 11, "Temp: ");   // put string of display at position X, Y
   u8g.drawStr(80, 11, "Humi: ");
   u8g.setFont(u8g_font_fub14r);
   u8g.setPrintPos(10, 45);        // set position
   u8g.print(DHT.temperature, 0);  // display temperature from DHT11 in Celsius
   u8g.println("F");
   u8g.setPrintPos(72, 45);        // set position
   u8g.print(DHT.humidity, 0);     // display humidity from DHT11
   u8g.println("%");
}
void setup(void)
{

}

void loop(void)
{
   DHT.read11(dht_dpin);  // Read dpin on DHT11
   u8g.firstPage(); 
   do
{
   draw();
}  while( u8g.nextPage() );
   delay(5000);  // Delay of 2 sec before accessing DHT11 (min - 2sec)
}
                           /*END OF FILE*/


[robtillaart]

>> Using this library, how can I make it display the temperature in Farenheit?

You can convert any Celsius temperature to Fahrenheit, that does not depend on the sensor.


float Tc = someObject.getTemperatureC(....);

float Tf = Tc * 1.8 + 32;

you should add this formula into your sketch.


Some interesting temperature is -40C as that is also -40F;  And 100F is about human body temperature.

The Celsius scale is based on the physics of water (melting/boiling)  @ 1013 hPa  or 1 atmosphere or sea level pressure.

More fun is the Kelvin scale as it has no negative temperatures in practice.

[FooPlinger]

After some trial and error, it seems that float is mostly working, but now it displays 32F all the time.  I changed the formula to add 33 in the conversion, and it displays 33.   Seems the float is being set to the last number in the conversion formula?

               /*Uncomment and comment*/
//U8GLIB_SH1106_128X64 u8g(13, 11, 10, 9, ;  // CLK=13, DIN=11, CS=10, DC=9, Reset=8
//U8GLIB_SSD1306_128X32 u8g(13, 11, 10, 9, ; // CLK=13, DIN=11, CS=10, DC=9, Reset=8
U8GLIB_SSD1306_128X64 u8g(13, 11, 10, 9, ; // CLK=13, DIN=11, CS=10, DC=9, Reset=8

float Tc = DHT.temperature;
float Tf =  (Tc*1.8+32);

void draw(void)
{
   u8g.setFont(u8g_font_fub11r);   // select font
   u8g.drawStr(0, 11, "Temp: ");   // put string of display at position X, Y
   u8g.drawStr(80, 11, "Humi: ");
   u8g.setFont(u8g_font_fub14r);
   u8g.setPrintPos(10, 45);        // set position
   u8g.print(Tf, 0);
//   u8g.print(DHT.temperature, 0);  // display temperature from DHT11 in Celsius
   u8g.println("F");
   u8g.setPrintPos(72, 45);        // set position
   u8g.print(DHT.humidity, 0);     // display humidity from DHT11
   u8g.println("%");

[FooPlinger]

After more searching and work, it seems I just don't understand float.   I finally got it working with the code below.
A few notes.   If I tried to print Tc, it shows 0.  If I print Tf, it shows 32.

Code: [Select]


#include <U8glib.h>  // U8glib library
#include <dht.h>     // DHT library

#define dht_dpin 2  //  pin to which the sensor is connected
dht DHT;
               /*Uncomment and comment*/
//U8GLIB_SH1106_128X64 u8g(13, 11, 10, 9, 8);  // CLK=13, DIN=11, CS=10, DC=9, Reset=8
//U8GLIB_SSD1306_128X32 u8g(13, 11, 10, 9, 8); // CLK=13, DIN=11, CS=10, DC=9, Reset=8
U8GLIB_SSD1306_128X64 u8g(13, 11, 10, 9, 8); // CLK=13, DIN=11, CS=10, DC=9, Reset=8

//float Tc = DHT.temperature;
//float Tf = Tc * 1.8 + 32;
//float Tf = (32 + (DHT.temperature * 1.8));

void draw(void)
{
   u8g.setFont(u8g_font_fub11r);   // select font
   u8g.drawStr(0, 11, "Temp: ");   // put string of display at position X, Y
   u8g.drawStr(80, 11, "Humi: ");
   u8g.setFont(u8g_font_fub14r);
   u8g.setPrintPos(10, 45);        // set position
//   u8g.print(Tc, 0);
//   u8g.print(Tf, 0);
   u8g.print((DHT.temperature * 1.8 + 32), 0);  // display temperature from DHT11 in Fahreneit
   u8g.println("F");
   u8g.setPrintPos(72, 45);        // set position
   u8g.print(DHT.humidity, 0);     // display humidity from DHT11
   u8g.println("%");
}
void setup(void)
{

}

void loop(void)
{
   DHT.read11(dht_dpin);  // Read dpin on DHT11
   u8g.firstPage(); 
   do
{
   draw();
}  while( u8g.nextPage() );
   delay(5000);  // Delay of 2 sec before accessing DHT11 (min - 2sec)
}
                           /*END OF FILE*/


[robtillaart]

Replace

Code: [Select]

u8g.print((DHT.temperature * 1.8 + 32), 0);  // display temperature from DHT11 in Fahreneit

by

Code: [Select]


float f = DHT.temperature * 1.8 + 32;
int whole = (int)f;  // take the whole part of the float
int decimal = (int) ((f-whole)*10);   // first decimal
u8g.print(whole);
u8g.print(".");
u8g.print(decimal);

splitting it up in pieces can help.


footnote:
The DHT11 has only integer values for temperature and humidity, so no need to use floats there.

[FooPlinger]

It looks like my problem was putting the float and calculations between lines 9 and 11, and then trying to print them later.  Once I moved your code all together inside the "void draw(void) " section, it works fine.

Thank you for the help, now I am off to see how to log this somewhere.  I have a dirt floor and cinder-block room under my brick porch on my new house that I want to use as a root cellar.  I am looking to log the data every x minutes (maybe ten, maybe 30) and keep those values so I can track it throughout the year.   I will also be putting a second dht11 outside of the root cellar to record the differences between the two.

Merry Christmas!

[robtillaart]

Better use a DHT22 as it more accurate and supports below zero (Celsius) temperatures.

did you do the storage math?

1 sample == 50 bytes? (including timestamp)

every 10 seconds --> 6 / minute  --> 360 / hour --> 9000 /day --> 3.300.000 / year ==> 165 MB