Problem with DHT11 sensor

  • Hi

    Purchased a few DHT11's off ebay. I Know they work as when I test them with this code from exmples, below they work. When I test with the mysensor code they do not. Can someone help me out with the changes required. I think it is to do with the library being used.

    Example code

    #include <SimpleDHT.h>
    // for DHT11, 
    //      VCC: 5V or 3V
    //      GND: GND
    //      DATA: 2
    int pinDHT11 = 3;
    SimpleDHT11 dht11;
    void setup() {
    void loop() {
      // start working...
      Serial.println("Sample DHT11...");
      // read without samples.
      byte temperature = 0;
      byte humidity = 0;
      if (, &temperature, &humidity, NULL)) {
        Serial.print("Read DHT11 failed.");
      Serial.print("Sample OK: ");
      Serial.print((int)temperature); Serial.print(" *C, "); 
      Serial.print((int)humidity); Serial.println(" %");
      // DHT11 sampling rate is 1HZ.
     * 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 <>
     * Copyright (C) 2013-2015 Sensnology AB
     * Full contributor list:
     * Documentation:
     * Support Forum:
     * 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.
     * Version 1.0: Henrik EKblad
     * Version 1.1 - 2016-07-20: Converted to MySensors v2.0 and added various improvements - Torben Woltjen (mozzbozz)
     * This sketch provides an example of how to implement a humidity/temperature
     * sensor using a DHT11/DHT-22.
     * For more information, please visit:
    // 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 3
    // 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 = 60000;
    // 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
      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()
      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)
    void loop()      
      // Force reading sensor, so it works also after sleep()
      // 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: ");
      } else {
        // Increase no update counter if the temperature stayed the same
      // 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: ");
      } else {
        // Increase no update counter if the humidity stayed the same

    // Sleep for a while to save energy

  • Mod

    @lozzer65 "not working" really doesn't give us much information, so helping you is a bit hard. Could you describe in what way it is not working?

  • Thanks for the rely. Yes sorry for the sketchy info.

    When using the mysensors sketch and looking at the serial info, no values from the sensor were being reported. At first I thought it maybe the sensors being faulty. So I thought I would just test the sensors on their own to make sure it was not hardware. When using the example sketch the sensors outputs temp and humidity, but not on the mysensors sketch.

    Thanks for your help, Laurie

  • Mod

    @lozzer65 thanks for clarifying. Bu "no values", do you mean it prints just



    Is the node connecting with the gateway? Is there any other output that could give a clue to what is happening?

  • Instead of showing values it showed nan.

    The node was connecting to the gateway, but no sensor values were available to send.

    On the example sketch the sensor showed values without issue.

  • Mod

    @lozzer65 that's very strange. Are you sure the sketch above is what was uploaded to the Arduino?

    This code

      if (isnan(temperature)) {
        Serial.println("Failed reading temperature from DHT!");

    should guarantee that nan is never printed.

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