[ESP8266] Node MCU + DHT22 （OS X)

最近有個需求如下：

1.需要在工作站偵測溫、溼度。

2.需要用MQTT協定回傳資料。

3.無線傳輸。

4.可以用Arduino IDE來寫程式

因而選用Node MCU 搭配DHT 22 。

以下是Node MCU的連結
http://www.nodemcu.com/index_cn.html

Node MCU 可以用Lua語言進行開發，亦可用Arduino IDE進行開發，本篇使用後者。

本次購買的是 LoLin V3 NodeMcu Lua WIFI Development Board

接線圖如下（我買的模組己經裝4.7K做在電路板上了，這只是示意圖）












DHT22 可以運作在3.3 及5V，所以不必擔心電壓問題。

這裡紀錄一個遇到的問題，在程式碼，我指定DHT22 的腳位為2 , 但指的不是D2, 而是GPIO2(D4), 參考下圖（圖片取自網路，如有侵權請來信告知）。

























接下來在Arduino IDE中安裝相關的Lib

Adafruit_Sensor
從以下URL下載ZIP檔
https://github.com/adafruit/Adafruit_Sensor





DHT-sensor-lib

https://github.com/adafruit/DHT-sensor-library

下載此ZIP檔

加入.ZIP程式庫。

找到剛才下載的ZIP檔

接下來下載pubsubclient
https://github.com/knolleary/pubsubclient

接下來安裝板子, 打開Arduino的偏好設定，在額外的板子管理員網址加入一行

http://arduino.esp8266.com/stable/package_esp8266com_index.json

按下"好"

接著到板子管理員

安裝一下ESP8266

接下來將板子選擇為Node MCU 1.0 （ESP-12E Module)

接下來要安裝一下USB to UART 驅動，它用的不是和Arduino的一樣，需要額外裝，

否則在序列埠中什麼都看不到。

到這個網址，下載驅動程式，安裝完成後一定要"重開機"

http://www.wch.cn/download/CH341SER_ZIP.html

重開機後開啟Arduino ，輸入以下程式碼。每六秒左右，就會送一次溫溼度到MQTT Server

程式碼如下：

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

#define DHTPIN 2     // what digital pin we're connected to

#define DHTTYPE DHT22   // DHT 22  (AM2302), AM2321

// NOTE: If using a board with 3.3V logic like an Arduino Due connect pin 1
// to 3.3V instead of 5V!
// Connect pin 2 of the sensor to whatever your DHTPIN is
// Connect pin 4 (on the right) of the sensor to GROUND

// Initialize DHT sensor.
// Note that older versions of this library took an optional third parameter to
// tweak the timings for faster processors.  This parameter is no longer needed
// as the current DHT reading algorithm adjusts itself to work on faster procs.
DHT dht(DHTPIN, DHTTYPE);

// Update these with values suitable for your network.
const char* ssid = "your ssid";
const char* password = "your pw";
const char* mqtt_server = "MQTT Server IP";
const char* topic="your Topic";

// WiFi Client 

WiFiClient espClient;

// PubSub Client
PubSubClient client(espClient);
long lastMsg = 0;
char msg[50];
int value = 0;

void setup() {
  Serial.begin(9600);
  Serial.println("DHTxx test!");
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);

  dht.begin();
}

void loop() {
  // Wait a few seconds between measurements.
  delay(2000);
 //Check Wi-Fi is Connected 
  if (WiFi.status() != WL_CONNECTED)
  {
    setup_wifi();
  }
  //Check MQTT Connection 

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

  // Reading temperature or humidity takes about 250 milliseconds!
  // Sensor readings may also be up to 2 seconds 'old' (its a very slow sensor)
  float h = dht.readHumidity();
  // Read temperature as Celsius (the default)
  float t = dht.readTemperature();
  // Read temperature as Fahrenheit (isFahrenheit = true)
  float f = dht.readTemperature(true);

  // Check if any reads failed and exit early (to try again).
  if (isnan(h) || isnan(t) || isnan(f)) {
    Serial.println("Failed to read from DHT sensor!");
    return;
  }

  // Compute heat index in Fahrenheit (the default)
  float hif = dht.computeHeatIndex(f, h);
  // Compute heat index in Celsius (isFahreheit = false)
  float hic = dht.computeHeatIndex(t, h, false);

  Serial.print("Humidity: ");
  Serial.print(h);
  Serial.print(" %\t");
  Serial.print("Temperature: ");
  Serial.print(t);
  Serial.print(" *C ");
  Serial.print(f);
  Serial.print(" *F\t");
  Serial.print("Heat index: ");
  Serial.print(hic);
  Serial.print(" *C ");
  Serial.print(hif);
  Serial.println(" *F");

   long now = millis();
  // read DHT22 sensor every 6 seconds
  if (now - lastMsg > 6000) {
     lastMsg = now;
     String msg=String(h)+","+String(t);
     Serial.println(msg);
     char message[msg.length()];
     msg.toCharArray(message,msg.length());
     //publish sensor data to MQTT broker
    client.publish(topic, message); 
  }
}

void setup_wifi() {
   delay(100);
  // We start by connecting to a WiFi network
    Serial.print("Connecting to ");
    Serial.println(ssid);
    WiFi.begin(ssid, password);
    while (WiFi.status() != WL_CONNECTED) 
    {
      delay(500);
      Serial.print(".");
    }
  randomSeed(micros());
  Serial.println("");
  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}
// recieve Topic message handler , I don't implements it 
void callback(char* topic, byte* payload, unsigned int length) 
{
  
}  

void reconnect() {
  // Loop until we're reconnected
  while (!client.connected()) 
  {
    Serial.print("Attempting MQTT connection...");
    // Create a random client ID
    String clientId = "ESP8266Client-";
    clientId += String(random(0xffff), HEX);
    // Attempt to connect
    //if you MQTT broker has clientID,username and password
    //please change following line to    if (client.connect(clientId,userName,passWord))
    if (client.connect(clientId.c_str()))
    {
      Serial.println("connected");
     //once connected to MQTT broker, subscribe command if any
      client.subscribe(topic);
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 6 seconds before retrying
      delay(6000);
    }
  }
} //end reconnect()

燒錄完成後，建議按一下RST按鈕，讓它重啟。