Example code for a NodeMCU type ESP8266 board programmed in the

Arduino environment to sample a RHT03 Temperature/Humidity Sensor
and publish the temp/humidity values as a MQTT topic.

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examples/esp8266/temp_sensor/temp_sensor.ino

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+#include <PubSubClient.h>
+
+/**
+ * IoT Kit - Temperature and Humidity Logger
+ * Author: Shawn Hymel (SparkFun Electronics)
+ * Date: October 30, 2016
+ * 
+ * Log temperature and humidity data to a channel on
+ * thingspeak.com once every 20 seconds.
+ * 
+ * Connections:
+ *   Thing Dev |  RHT03
+ *  -----------|---------
+ *      3V3    | 1 (VDD) 
+ *        4    | 2 (DATA)
+ *      GND    | 4 (GND)
+ *      
+ * Development environment specifics:
+ *  Arduino IDE v1.6.5
+ *  Distributed as-is; no warranty is given.  
+ */
+
+#define NODEMCU_D0 16
+#define NODEMCU_D1 5
+#define NODEMCU_D2 4
+#define NODEMCU_D3 0
+#define NODEMCU_D4 2
+#define NODEMCU_D5 14
+#define NODEMCU_D6 12
+#define NODEMCU_D7 13
+#define NODEMCU_D8 15
+#define NODEMCU_D9 3
+#define NODEMCU_D10 1
+#define NODEMCU_D12 10
+
+#include <ESP8266WiFi.h>
+#include <SparkFun_RHT03.h>
+#include <PubSubClient.h>
+
+// CHANGE THESE VALUES FOR YOUR INSTALLATION!
+// WiFi and Channel parameters
+const char WIFI_SSID[] = "<your 2.4Ghz SSID>";
+const char WIFI_PSK[] = "<your SSID password>";
+const char* mqtt_server = "<your mqtt broker>";
+
+// Pin definitions
+const int RHT03_DATA_PIN = 4;
+const int LED_PIN = 5; //16;  // was 5
+
+// Global variables
+WiFiClient client;
+PubSubClient pubSubClient(client);
+RHT03 rht;
+
+char tempCStr[7];
+char tempFStr[7];
+char humiStr[7];
+
+char mac_addr[18];
+
+void setup() {
+  Serial.begin(115200);
+  Serial.println();
+
+  // Set up LED for debugging
+  pinMode(LED_PIN, OUTPUT);
+
+  // Connect to WiFi
+  connectWiFi();
+
+  byte mac[6];
+  WiFi.macAddress(mac);
+  sprintf(mac_addr, "%02x:%02x:%02x:%02x:%02x:%02x", mac[0],mac[1],mac[2],mac[3],mac[4],mac[5]);
+
+  pubSubClient.setServer(mqtt_server, 1883);
+  //pubSubClient.setCallback(callback);
+
+  // Call rht.begin() to initialize the sensor and our data pin
+  rht.begin(RHT03_DATA_PIN);
+
+}
+
+void loop() {
+
+  if (!client.connected()) {
+    reconnect();
+  }
+  pubSubClient.loop();
+
+  // Flash LED to show that we're sampling
+  digitalWrite(LED_PIN, LOW);
+
+  // Call rht.update() to get new humidity and temperature values from the sensor.
+  int updateRet = rht.update();
+
+  // If successful, the update() function will return 1.
+  if (updateRet == 1)  {
+     publishTemps();
+  } else  {
+    // If the update failed, try delaying for some time
+    delay(RHT_READ_INTERVAL_MS);
+  }
+
+  // Turn LED off when we've posted the data
+  digitalWrite(LED_PIN, HIGH);
+
+  // ThingSpeak will only accept updates every 15 seconds
+  delay(20000);
+}
+
+void publishTemps(){
+    // The tempC(), tempF(), and humidity() functions can be 
+    // called after a successful update()
+    float temp_c = rht.tempC();
+    float temp_f = rht.tempF();
+    float humidity = rht.humidity();
+
+    char tempTopic[100];
+    char rhtTopic[150];
+    snprintf(tempTopic, 99, "sensors/temp/%s/%3.2f", mac_addr, temp_f);
+    snprintf(rhtTopic, 149, "sensors/rht/%s/%3.2f/%3.2f", mac_addr, temp_f, humidity);
+
+    Serial.print("publishing topic: ");
+    Serial.println(tempTopic);
+    pubSubClient.publish(tempTopic, "");
+    Serial.print("publishing topic: ");
+    Serial.println(rhtTopic);
+    pubSubClient.publish(rhtTopic, "");
+}
+
+// Attempt to connect to WiFi
+void connectWiFi() {
+
+  byte led_status = 0;
+
+  // Set WiFi mode to station (client)
+  WiFi.mode(WIFI_STA);
+
+  // Initiate connection with SSID and PSK
+  WiFi.begin(WIFI_SSID, WIFI_PSK);
+
+  // Blink LED while we wait for WiFi connection
+  while ( WiFi.status() != WL_CONNECTED ) {
+    digitalWrite(LED_PIN, led_status);
+    led_status ^= 0x01;
+    delay(100);
+  }
+
+  // Turn LED off when we are connected
+  digitalWrite(LED_PIN, HIGH);
+}
+
+void reconnect() {
+  // Loop until we're reconnected
+  while (!pubSubClient.connected()) {
+    Serial.print("Attempting MQTT connection...");
+    // Create a random client ID
+    String clientId = mac_addr; //"ESP8266Client-";
+    //clientId += "-";
+    //clientId += String(random(0xffff), HEX);
+    Serial.print(clientId);
+    Serial.print("...");
+    // Attempt to connect
+    if (pubSubClient.connect(clientId.c_str())) {
+      Serial.println("connected");
+      // Once connected, publish an announcement...
+      pubSubClient.publish("outTopic", "hello world");
+      // ... and resubscribe
+      //client.subscribe("inTopic");
+    } else {
+      Serial.print("failed, rc=");
+      Serial.print(pubSubClient.state());
+      Serial.println(" try again in 5 seconds");
+      // Wait 5 seconds before retrying
+      delay(5000);
+    }
+  }
+}
+
+