Output from DHT22

Mbed Studio
1

The output from dht sensor is always 0, no matter humidity or temperature. Can someone help me, thanks.

2

The cpp and header is from this website.
[DHT - Temp and Humidity sensor device driver. | Mbed]

3

And ouput is like this

截屏2022-04-09 20.31.31
截屏2022-04-09 20.31.311366×1022 160 KB

4

Hello,

usually is good to share also MbedOs version.

However, I tried that library with MbedOS 5.15.8 on Nucleo-F767ZI and output is OK

Temperature in Kelvin: 300.15, Celcius: 27.00, Farenheit 80.60
Humidity is 47.00, Dewpoint: 14.75, Dewpoint fast: 14.71

But you miss important part, you have to call readData() function. Without it you will read 0 every time because the rest of functions only calculate a conversion of measured data.

#include "mbed.h"
#include "DHT.h"
  
  DHT sensor(D4, DHT22);
  
  int main()
  {
      int error = 0;
      float h = 0.0f, c = 0.0f, f = 0.0f, k = 0.0f, dp = 0.0f, dpf = 0.0f;
 
      while(1) {
          thread_sleep_for(2000);
          error = sensor.readData();
          if (0 == error) {
              c   = sensor.ReadTemperature(CELCIUS);
              f   = sensor.ReadTemperature(FARENHEIT);
              k   = sensor.ReadTemperature(KELVIN);
              h   = sensor.ReadHumidity();
              dp  = sensor.CalcdewPoint(c, h);
              dpf = sensor.CalcdewPointFast(c, h);
              printf("Temperature in Kelvin: %4.2f, Celcius: %4.2f, Farenheit %4.2f\n", k, c, f);
              printf("Humidity is %4.2f, Dewpoint: %4.2f, Dewpoint fast: %4.2f\n", h, dp, dpf);
          } else {
              printf("Error: %d\n", error);
          }
      }
  }

For MbedOS6+ DHT - Fork of DHT component - https://os.mbed.com/teams… | Mbed also OK, but for that you also need to change printf lib in mbed_app.json

{
    "target_overrides": {
        "*": {
            "target.printf_lib": "std"
        }
    }
}

BR, Jan

5

Thanks for your reply, I just change all include mbed.json file. The version is mbed-os 6.13.0. But it shows “Error:1”. You can ignore other codes.

type or paste code here#include "mbed.h"
#include "Joystick.h"
#include "N5110.h"
#include "DHT.h"
//#include "ManMode.h"
// main() runs in its own thread in the OS
N5110 lcd(PC_7, PA_9, PB_10, PB_5, PB_3, PA_10);
Joystick joystick(PC_3, PC_2);
DHT sensor(PA_1,DHT22);
//void displayTMP();
void main_menu();
void select_term1();
void displayMain_menu();
// Manegement mode
int main_Man();
void menu_Man();
void select_term2();
void display_Manmode();
void set_triggerTMP();
void set_triggerHum();

int main_op();


    
int main()
{
    joystick.init();
    lcd.init(LPH7366_1);        //initialise for LPH7366-1 LCD (Options are LPH7366_1 and LPH7366_6)
    lcd.setContrast(0.55);      //set contrast to 55%
    lcd.setBrightness(0.5);
    lcd.clear();
    //oid main_menu();
   
    //while (true) {
     //main_menu(); 
     main_op() ; 
    //}
}
void main_menu(){
    displayMain_menu();
    //select_term1();
}
void displayMain_menu(){
    
    lcd.printString(" Select Mode ", 0, 1);
    lcd.printString(" Manage Mode ", 0, 3);
    lcd.printString("Operation Mode ", 0, 4);
    lcd.refresh();
}

/*void select_term1(){
    if (joystick.get_direction() == N){
        lcd.printString(" in Operation Mode ", 0, 2);
        
        printf(" Direction: N\n");
        main_Man();       
    }
      
}*/

int main_op(){
    int error =0;
    float h = 0.0f, c = 0.0f, f = 0.0f, k = 0.0f, dp = 0.0f, dpf = 0.0f;
       while(1) {
          thread_sleep_for(2000);
          error = sensor.readData();
          if (0 == error) {
              c   = sensor.ReadTemperature(CELCIUS);
              f   = sensor.ReadTemperature(FARENHEIT);
              k   = sensor.ReadTemperature(KELVIN);
              h   = sensor.ReadHumidity();
              dp  = sensor.CalcdewPoint(c, h);
              dpf = sensor.CalcdewPointFast(c, h);
              printf("Temperature in Kelvin: %4.2f, Celcius: %4.2f, Farenheit %4.2f\n", k, c, f);
              printf("Humidity is %4.2f, Dewpoint: %4.2f, Dewpoint fast: %4.2f\n", h, dp, dpf);
          } else {
              printf("Error: %d\n", error);
          }
      }
}