The Arduino/MQTT temperature reading program

mqtt_temp_read.ino

/*
  Sensor to MQTT basic example
*/

#include <SPI.h>
#include <Ethernet.h>
#include <PubSubClient.h>

// Update these with values suitable for your network.
byte mac[]    = {  0xDE, 0xED, 0xBA, 0xFE, 0xFE, 0xED };
byte server[] = { 192, 168, 111, 50 };
byte ip[]     = { 192, 168, 111, 240 };

int sensorPin=5;
int lastTemperature;
unsigned long lastTime;
char buffer[10];

void callback(char* topic, byte* payload, unsigned int length) {
  // handle message arrived (no messages expected though)
}

EthernetClient ethClient;
PubSubClient client(server, 1883, callback, ethClient);

void setup() {
  Ethernet.begin(mac, ip);
  if (client.connect("arduinoClient")) {
    client.publish("demo/status/arduino01","online");
    lastTemperature=0;
    lastTime=0;
  }
}

void loop() {
  int reading=analogRead(sensorPin);
  int temperature = ((reading * 0.004882)-0.50)*100;
  if(temperature!=lastTemperature) {
    if(millis()>(lastTime+1000)) {
      sprintf(buffer,"%d",temperature);
      client.publish("demo/device/arduino01",buffer);
      lastTemperature=temperature;
      lastTime=millis();
    }
  }
  client.loop();
}