💬 Air Humidity Sensor - DHT

[mfalkvidd]

@johnecy https://forum.mysensors.org/topic/5978/temperature-and-humidity-dht22

[donhuan78p]

Hello everybody,
hope, someone could help a newby :-)
I've installed the MQTT - GW and would use the Air/Humidity - sensor. But it doesn't work properly.
The Connection to the Gateway seems to be okay. But I get no Air/Humidity - Information.
The sensor does not measure anything.
I've tried to change the data - pin, I've tried the DHT11 and DHT22 - sensor. No choice.
I'm getting mad :-)

Thanks a lot.

[gohan]

Have you tried the basic arduino sketch that prints data to serial port?

[donhuan78p]

Hello,
thanks a lot for your answer.
Yes, I did. It produced the Messages as excepted.

[gohan]

So you'd better post your code so we can take a look at what is wrong with it.

[donhuan78p]

...sorry, Typo.
As expected :-)

[donhuan78p]

...no Problem:

/**
 * The MySensors Arduino library handles the wireless radio link and protocol
 * between your home built sensors/actuators and HA controller of choice.
 * The sensors forms a self healing radio network with optional repeaters. Each
 * repeater and gateway builds a routing tables in EEPROM which keeps track of the
 * network topology allowing messages to be routed to nodes.
 *
 * Created by Henrik Ekblad <henrik.ekblad@mysensors.org>
 * Copyright (C) 2013-2015 Sensnology AB
 * Full contributor list: https://github.com/mysensors/Arduino/graphs/contributors
 *
 * Documentation: http://www.mysensors.org
 * Support Forum: http://forum.mysensors.org
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * version 2 as published by the Free Software Foundation.
 *
 *******************************
 *
 * REVISION HISTORY
 * Version 1.0: Henrik EKblad
 * Version 1.1 - 2016-07-20: Converted to MySensors v2.0 and added various improvements - Torben Woltjen (mozzbozz)
 * 
 * DESCRIPTION
 * This sketch provides an example of how to implement a humidity/temperature
 * sensor using a DHT11/DHT-22.
 *  
 * For more information, please visit:
 * http://www.mysensors.org/build/humidity
 * 
 */

// Enable debug prints
#define MY_DEBUG

// Enable and select radio type attached 
#define MY_RADIO_NRF24
//#define MY_RADIO_RFM69
//#define MY_RS485
 
#include <SPI.h>
#include <MySensors.h>  
#include <DHT.h>

// Set this to the pin you connected the DHT's data pin to
#define DHT_DATA_PIN 2

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

// Sleep time between sensor updates (in milliseconds)
// Must be >1000ms for DHT22 and >2000ms for DHT11
static const uint64_t UPDATE_INTERVAL = 30000;

// Force sending an update of the temperature after n sensor reads, so a controller showing the
// timestamp of the last update doesn't show something like 3 hours in the unlikely case, that
// the value didn't change since;
// i.e. the sensor would force sending an update every UPDATE_INTERVAL*FORCE_UPDATE_N_READS [ms]
static const uint8_t FORCE_UPDATE_N_READS = 10;

#define CHILD_ID_HUM 0
#define CHILD_ID_TEMP 1

float lastTemp;
float lastHum;
uint8_t nNoUpdatesTemp;
uint8_t nNoUpdatesHum;
bool metric = true;

MyMessage msgHum(CHILD_ID_HUM, V_HUM);
MyMessage msgTemp(CHILD_ID_TEMP, V_TEMP);
DHT dht;


void presentation()  
{ 
  // Send the sketch version information to the gateway
  Serial.println("Presentation");
  sendSketchInfo("TemperatureAndHumidity", "1.1");
  
  // Register all sensors to gw (they will be created as child devices)
  present(CHILD_ID_HUM, S_HUM);
  present(CHILD_ID_TEMP, S_TEMP);
  
  metric = getConfig().isMetric;
}


void setup()
{
  Serial.println("vor Presentation");
  
  dht.setup(DHT_DATA_PIN); // set data pin of DHT sensor
  if (UPDATE_INTERVAL <= dht.getMinimumSamplingPeriod()) {
    Serial.println("Warning: UPDATE_INTERVAL is smaller than supported by the sensor!");
  }
  // Sleep for the time of the minimum sampling period to give the sensor time to power up
  // (otherwise, timeout errors might occure for the first reading)
  sleep(dht.getMinimumSamplingPeriod());
}


void loop()      
{  

  Serial.println("loop Anfang");
  
  // Force reading sensor, so it works also after sleep()
  dht.readSensor(true);
  
  // Get temperature from DHT library
  float temperature = dht.getTemperature();
  if (isnan(temperature)) {
    Serial.println("Failed reading temperature from DHT!");
  } else if (temperature != lastTemp || nNoUpdatesTemp == FORCE_UPDATE_N_READS) {
    // Only send temperature if it changed since the last measurement or if we didn't send an update for n times
    lastTemp = temperature;
    if (!metric) {
      temperature = dht.toFahrenheit(temperature);
    }
    // Reset no updates counter
    nNoUpdatesTemp = 0;
    temperature += SENSOR_TEMP_OFFSET;
    send(msgTemp.set(temperature, 1));

    #ifdef MY_DEBUG
    Serial.print("T: ");
    Serial.println(temperature);
    #endif
  } else {
    // Increase no update counter if the temperature stayed the same
    nNoUpdatesTemp++;
  }

  // Get humidity from DHT library
  float humidity = dht.getHumidity();
  if (isnan(humidity)) {
    Serial.println("Failed reading humidity from DHT");
  } else if (humidity != lastHum || nNoUpdatesHum == FORCE_UPDATE_N_READS) {
    // Only send humidity if it changed since the last measurement or if we didn't send an update for n times
    lastHum = humidity;
    // Reset no updates counter
    nNoUpdatesHum = 0;
    send(msgHum.set(humidity, 1));
    
   #ifdef MY_DEBUG
    Serial.print("H: ");
    Serial.println(humidity);
   #endif
  } else {
    // Increase no update counter if the humidity stayed the same
    nNoUpdatesHum++;
  }

  // Sleep for a while to save energy
  sleep(UPDATE_INTERVAL); 
}

[Arnold Šlepetis]

I am using dht22 outside. Does any one know how to change to whole number not decimal. The temperature outside change a lot. Let say temp 20.2 changed to 20.4 and still sends to getaway . If I do "send(msgTemp.set(temperature, 0));" and still receive both times 20 and 20, and I want only if change to 21 or 19.

[mfalkvidd]

@Arnold-Šlepetis change

float lastTemp;

to

signed int lastTemp;

and

float temperature = dht.getTemperature();

to

signed int temperature = dht.getTemperature() + 0.5; // Add 0.5 to get correct rounding

and

temperature = dht.toFahrenheit(temperature);

to

temperature = dht.toFahrenheit(temperature) + 0.5;

and

send(msgTemp.set(temperature, 1));

to

send(msgTemp.set(temperature));

You might also have to handle the isnan test.

[Arnold Šlepetis]

@mfalkvidd Thanks. It works like a charm

[jwosnick]

I've made a bit of an unusual observation in relationship to this script. I am running a fairly stripped-down version of it, but with the "standard" (not MySensors-customized) DHT library and its associated functions.

Here is the code:

// Enable debug prints
#define MY_DEBUG

// Enable and select radio type attached 
#define MY_RADIO_NRF24
//#define MY_RADIO_RFM69
//#define MY_RS485

#define MY_NODE_ID 47

#include <SPI.h>
#include <MySensors.h>  
#include <DHT.h>

// Set this to the pin you connected the DHT's data pin to
#define DHT_DATA_PIN 5

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

// Sleep time between sensor updates (in milliseconds)
// Must be >1000ms for DHT22 and >2000ms for DHT11
static const uint64_t UPDATE_INTERVAL = 10000;

#define CHILD_ID_HUM 0
#define CHILD_ID_TEMP 1

bool metric = true;

MyMessage msgHum(CHILD_ID_HUM, V_HUM);
MyMessage msgTemp(CHILD_ID_TEMP, V_TEMP);
DHT dht(DHT_DATA_PIN, DHT22);
float temperature;
float humidity;

void presentation()  
{ 
  // Send the sketch version information to the gateway
  sendSketchInfo("TemperatureAndHumidity", "1.1");

  // Register all sensors to gw (they will be created as child devices)
  present(CHILD_ID_HUM, S_HUM);
  present(CHILD_ID_TEMP, S_TEMP);

  metric = getControllerConfig().isMetric;
}


void setup()
{
  delay(100);
}


void loop()      
{  
  
  // Get temperature from DHT library
  temperature = dht.readTemperature();
  if (isnan(temperature))
  {
    Serial.println("Failed reading temperature from DHT!");
  }
    
  else
  {
    send(msgTemp.set(temperature,0));
    #ifdef MY_DEBUG
    Serial.print("T: ");
    Serial.println(temperature);
    #endif
  }  

  // Get humidity from DHT library
  
  humidity = dht.readHumidity();
  if (isnan(humidity))
  {
    Serial.println("Failed reading humidity from DHT!");
  }
    
  else 
  {
    send(msgHum.set(humidity,1));
    #ifdef MY_DEBUG
    Serial.print("H: ");
    Serial.println(humidity);
    #endif
  }

  // Sleep for a while to save energy
  sleep(UPDATE_INTERVAL); 
}

I find that if I leave the last line as
sleep(UPDATE_INTERVAL);
then the sensor node ends up sending the same temperature and humidity values, over and over again, even if the actual humidity and temperature change.

However, if I change the last line to
delay(UPDATE_INTERVAL);
then everything works as expected.

This is with known good DHT22 units, so I suspect there is something funny about the sleep() function and the operation of the standard (not customized) DHT library.

It took a lot of poking around to discover this, but is this in fact the reason why the MySensors customized DHT library is required for this script? Is that library necessary to make sleep() and DHT temperature measurements play nicely together?

[gohan]

What libraries versions are you using?

[mfalkvidd]

@jwosnick the example sketch has this:

  // Force reading sensor, so it works also after sleep()
dht.readSensor(true);

which is missing in your sketch. The comment suggests that it might be relevant.

[jwosnick]

@mfalkvidd

Yes, absolutely. But it appears that the dht.readSensor() function is not actually part of the standard DHT library, but rather something that only appears in the MySensors-customized version of it. I'm trying to get a handle on why there is a need for a customized library.

[mfalkvidd]

@jwosnick seems like the most recent version of the original library calls readSensor when getTemperature is called.

Maybe the most recent version can be used if the MySensors example sketch is rewritten to just use getTemperature? Would it be possible for you to test this? It would be great if we could get rid of the MySensors-custimized version of the library and just let people install the standard DHT library.

[jwosnick]

@mfalkvidd said in 💬 Air Humidity Sensor:

@jwosnick seems like the most recent version of the original library calls readSensor when getTemperature is called.

Yes, it does... but somehow that function is not "exposed" to the outside world. With a standard DHT test sketch (nothing to do with MySensors) calling readSensor throws an error.

[mfalkvidd]

@jwosnick yes. But since readSensor is called inside getTemperature, there should be no need to call it manually.

[avgays]

@jwosnick

As your set sensor model

DHT dht(DHT_DATA_PIN, DHT22);

it looks like you use "Adafruit DHT-sensor-library".
It's need dht.begin(); in setup(){ } which is missing in your sketch

[jwosnick]

@avgays
Good catch -- thanks. Yes, that is the library I am using.

Despite omitting that line, the script above works fine as long as the last line is a delay() function and not sleep(). If I use sleep(), it in fact appears to work, but sends the same temperature and humidity over and over again. So it is something about the sleep() function.

I will add in the dht.begin() and then put sleep() back in and see what happens.

[jwosnick]

@avgays Confirmed that even with dht.begin(); the script still sends the same temp and humidity info, over and over again, as long as the sleep() function is in there. As soon as sleep() is replaced by delay() it all works properly.

So I conclude from this that the MySensors-customized version of the DHT library must have something in it to make sleep() play nicely with the DHT unit. I wish I knew what that was. It would be ideal if this sensor (and the Dallas Semiconductor one) could be used with the MySensors system with their standard libraries.