Air Humidity Sensor - DHT

written by hek
The most basic DHT humidity and temperature sensor comes in two variants with different levels of accuracy. There are better alternatives to this sensor, like the [Si7021](/build/humidity_si7021), so please consider using them first.
DHT-11 DHT-22
Humidity range 20%-80%RH (±5%RH) 0%-100%RH (±2%RH)
Temperature range 0-50°C (±2°C) -40-80°C (±0.5°C)
Measurement time 1s per sample 2s per sample

There's more humidity sensors around which requires less power to operate, like BME280 or Si7021. See this comparison for in-depth information on their accuracy.

Wiring Things Up

Start by connecting the radio module.

Sensor Arduino Comment
- GND Marked black
+ VCC (3.3 - 5.5V) Marked red
out (middle) Digital pin 3 Marked green


This example uses a modified version of the external DHT library, which is included in the MySensors external examples. Please install it and restart the Arduino IDE before trying to compile.

For the DHT-11, you can find an example created by michlb1982 here.

 * 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 <[email protected]>
 * 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_RF24
//#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.
// In Celsius degrees (as measured by the device)

// 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;

    // apply the offset before converting to something different than Celsius degrees
    temperature += SENSOR_TEMP_OFFSET;

    if (!metric) {
      temperature = dht.toFahrenheit(temperature);
    // Reset no updates counter
    nNoUpdatesTemp = 0;
    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


NameSize# Downloads
DHT11.pdf677.52 kB4734
DHT22.pdf896.87 kB6008

Shopping Guide

DHT11 Module
Humidity range: 20%-80%RH (±5%RH). Temperature range: 0-50°C (±2°C).
Unavailable   Buy
undefined   Buy
DHT22 Module
Humidity range: 0%-100%RH (±2%RH). Temperature range: -40-80°C (±0.5°C).
Unavailable   Buy
undefined   Buy


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