Sketch for the ESP8266 to publish temperature and humidity values received from a DHT22 to MQTT

MQTT_ESP8266_temperature_humidity.ino

// Get ESP8266 going with Arduino IDE
// - https://github.com/esp8266/Arduino#installing-with-boards-manager
// Required libraries (sketch -> include library -> manage libraries)
// - PubSubClient by Nick ‘O Leary
// - DHT sensor library by Adafruit

#include <ESP8266WiFi.h>
#include <PubSubClient.h>
#include <DHT.h>

#define wifi_ssid "YOUR WIFI SSID"
#define wifi_password "WIFI PASSWORD"

#define mqtt_server "YOUR_MQTT_SERVER_HOST"
#define mqtt_user "your_username"
#define mqtt_password "your_password"

#define humidity_topic "sensor/humidity"
#define temperature_topic "sensor/temperature"

#define DHTTYPE DHT22
#define DHTPIN  14

WiFiClient espClient;
PubSubClient client(espClient);
DHT dht(DHTPIN, DHTTYPE, 11); // 11 works fine for ESP8266

void setup() {
  Serial.begin(115200);
  dht.begin();
  setup_wifi();
  client.setServer(mqtt_server, 1883);
}

void setup_wifi() {
  delay(10);
  // We start by connecting to a WiFi network
  Serial.println();
  Serial.print("Connecting to ");
  Serial.println(wifi_ssid);

  WiFi.begin(wifi_ssid, wifi_password);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }

  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}

void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) {
    Serial.print("Attempting MQTT connection...");
    // Attempt to connect
    // If you do not want to use a username and password, change next line to
    // if (client.connect("ESP8266Client")) {
    if (client.connect("ESP8266Client", mqtt_user, mqtt_password)) {
      Serial.println("connected");
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

bool checkBound(float newValue, float prevValue, float maxDiff) {
  return !isnan(newValue) &&
         (newValue < prevValue - maxDiff || newValue > prevValue + maxDiff);
}

long lastMsg = 0;
float temp = 0.0;
float hum = 0.0;
float diff = 1.0;

void loop() {
  if (!client.connected()) {
    reconnect();
  }
  client.loop();

  long now = millis();
  if (now - lastMsg > 2000) {
    lastMsg = now;

    float newTemp = dht.readTemperature();
    float newHum = dht.readHumidity();

    if (checkBound(newTemp, temp, diff)) {
      temp = newTemp;
      Serial.print("New temperature:");
      Serial.println(String(temp).c_str());
      client.publish(temperature_topic, String(temp).c_str(), true);
    }

    if (checkBound(newHum, hum, diff)) {
      hum = newHum;
      Serial.print("New humidity:");
      Serial.println(String(hum).c_str());
      client.publish(humidity_topic, String(hum).c_str(), true);
    }
  }
}

@ballob i have this error:

C:\Users\Paula Alves\Desktop\dddddd\dddddd.ino: In function 'void setup()':

dddddd:32: error: 'class PubSubClient' has no member named 'setServer'

client.setServer(mqtt_server, 1883);

      ^

C:\Users\Paula Alves\Desktop\dddddd\dddddd.ino: In function 'void reconnect()':

dddddd:62: error: no matching function for call to 'PubSubClient::connect(const char [14], const char [14], const char [14])'

 if (client.connect("ESP8266Client", mqtt_user, mqtt_password)) {

                                                             ^

C:\Users\Paula Alves\Desktop\dddddd\dddddd.ino:62:65: note: candidates are:

In file included from C:\Users\Paula Alves\Desktop\dddddd\dddddd.ino:8:0:

C:\Users\Paula Alves\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:111:9: note: bool PubSubClient::connect(String)

bool connect(String id);

     ^

C:\Users\Paula Alves\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:111:9: note: candidate expects 1 argument, 3 provided

C:\Users\Paula Alves\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:123:9: note: bool PubSubClient::connect(String, String, uint8_t, bool, String)

bool connect(String id, String willTopic, uint8_t willQos, bool willRetain, String willMessage);

     ^

C:\Users\Paula Alves\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:123:9: note: candidate expects 5 arguments, 3 provided

C:\Users\Paula Alves\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:185:9: note: bool PubSubClient::connect(MQTT::Connect&)

bool connect(MQTT::Connect &conn);

     ^

C:\Users\Paula Alves\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:185:9: note: candidate expects 1 argument, 3 provided

dddddd:66: error: 'class PubSubClient' has no member named 'state'

   Serial.print(client.state());

                       ^

C:\Users\Paula Alves\Desktop\dddddd\dddddd.ino: In function 'void loop()':

dddddd:101: error: invalid conversion from 'const char*' to 'const uint8_t* {aka const unsigned char*}' [-fpermissive]

   client.publish(temperature_topic, String(temp).c_str(), true);

                                                        ^

In file included from C:\Users\Paula Alves\Desktop\dddddd\dddddd.ino:8:0:

C:\Users\Paula Alves\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:144:9: error: initializing argument 2 of 'bool PubSubClient::publish(String, const uint8_t*, uint32_t, bool)' [-fpermissive]

bool publish(String topic, const uint8_t *payload, uint32_t plength, bool retained = false);

     ^

dddddd:108: error: invalid conversion from 'const char*' to 'const uint8_t* {aka const unsigned char*}' [-fpermissive]

   client.publish(humidity_topic, String(hum).c_str(), true);

                                                    ^

In file included from C:\Users\Paula Alves\Desktop\dddddd\dddddd.ino:8:0:

C:\Users\Paula Alves\Documents\Arduino\libraries\pubsubclient-master\src/PubSubClient.h:144:9: error: initializing argument 2 of 'bool PubSubClient::publish(String, const uint8_t*, uint32_t, bool)' [-fpermissive]

bool publish(String topic, const uint8_t *payload, uint32_t plength, bool retained = false);

     ^

exit status 1
'class PubSubClient' has no member named 'setServer'

Yes, that's perfect, but I don't know how to implement it with HomeAssistant Generic Thermostat, it requires a float, and don't know how change the code to do that...

@outrun0506

i think it's the MQTT_CALLBACK_SIGNATURE in pubsubclient. they are both being set to the same ID, so the MQTT server thinks you are already connected. when I unplug my 1st nodemcu the 2nd nodemcu stops getting the error. so it seems to be a first come, first serve(r)ed.

the script needs a way to pass in a DEVICE_ID of some kind to pubsubclient, so that it can used in the signature to differentiate them. not sure how to add that, python isn't my thing.

--stone

@outrun0506

well, it seems i spoke too soon, it does have a DEVICE_ID.

line 62: change "ESP8266Client" to "whateverYouLike2"
just so long as it's unique.

then both nodes should play well with each other.

I am successfully using this, but the temp and humidty values it reports are VERY jittery. Does anyone have a way to clean them up a little?

Depending on their values, taking an average could work.