[IoT] IoT 쌩초보 - MQTT를 이용한 데이터 전송과정

MQTT

MQTT(Message Queueing Telemetry Transport)는 머신 대 머신 통신에 사용되는 표준 기반 메시징 프로토콜이다.
출처: https://aws.amazon.com/ko/what-is/mqtt/

ThingsBoard의 경우 MQTT를 이용한 데이터 전송 방식을 추천한다. 이는 MQTT 방식이 IoT 장치에 가장 적합한 방식이기 때문인데 MQTT는 다른 방식보다 필요로 하는 리소스가 적다. 따라서 IoT에서 주로 사용되는 작은 마이크로컨트롤러에서도 사용할 수 있고 전력 소비량도 적기 때문에 IoT 장치를 개발하는 경우 MQTT를 활용하는 것이 좋은 방법이다.

MQTT의 원리

MQTT는 Publish/Subscribe의 방식으로 구성되어 있다. MQTT의 구성요소로는 Client와 Broker가 있다.

Client

MQTT의 Client는 네트워크를 통해 MQTT를 사용하여 통신하는 모든 디바이스라고 할 수 있다. Client는 Subscriber(구독자)일 수도 있고 Publisher(게시자)일 수도 있다.
Client가 특정 주제에 대해 메세지를 게시하는 경우 Publisher가 될 수 있고 특정 주제를 구독하여 해당 주제에 대한 게시된 메세지를 받아오는 경우 Subscriber로의 역할을 할 수 있다.

Broker

MQTT에서 Broker는 백엔드 시스템이다. 메세지 수신, 필터링, 구독 클라이언트 식별, 메세지 전송, Client 권한 부여 및 인증 등의 역할을 한다.
MQTT의 경우 클라이언트끼리 직접 연결되는 것은 아니고 Broker에만 연결된다. Broker는 Client로부터 메세지를 수신하여 메세지에 관심이 있는 구독 Client로 전달한다.

RESTful vs MQTT?

REST(Representational State Transfer)는 네트워크 통신에 대한 아키텍처 접근 방식으로 메세지 발신자와 수신자간의 요청-응답 패턴의 통신을 사용한다.
MQTT는 애플리케이션 계층에서 게시/구독 모델 통신을 사용하고 메세지를 푸시 방식으로 전송하기 때문에 고정된 TCP 연결을 필요로 한다. MQTT5에서는 REST와 유사한 방식의 요청/응답 메서드가 존재한다.

ThingsBoard의 좋은 점은 시각화 부분도 있지만 예시 코드가 잘 되어 있다는 것이다.
다음은 Arduino IDE에 ThingsBoard Library를 추가하였을 때 File > Examples > ThingsBoard > 0003-esp8266_esp32_send_data에서 찾을 수 있는 데이터 전송 예시 코드이다.

#if defined(ESP8266)
#include <ESP8266WiFi.h>
#elif defined(ESP32)
#include <WiFi.h>
#include <WiFiClientSecure.h>
#endif


// Sending data can either be done over MQTT and the PubSubClient
// or HTTPS and the HTTPClient, when using the ESP32 or ESP8266
#define USING_HTTPS false

// Wheter the given script is using encryption or not,
// generally recommended as it increases security (communication with the server is not in clear text anymore),
// it does come with an overhead tough as having an encrypted session requires a lot of memory,
// which might not be avaialable on lower end devices.
#define ENCRYPTED false


#if USING_HTTPS
#include <ThingsBoardHttp.h>
#else
#include <ThingsBoard.h>
#endif


// PROGMEM can only be added when using the ESP32 WiFiClient,
// will cause a crash if using the ESP8266WiFiSTAClass instead.
#if defined(ESP8266)
constexpr char WIFI_SSID[] = "YOUR_WIFI_SSID";
constexpr char WIFI_PASSWORD[] = "YOUR_WIFI_PASSWORD";
#elif defined(ESP32)
constexpr char WIFI_SSID[] PROGMEM = "YOUR_WIFI_SSID";
constexpr char WIFI_PASSWORD[] PROGMEM = "YOUR_WIFI_PASSWORD";
#endif

// See https://thingsboard.io/docs/getting-started-guides/helloworld/
// to understand how to obtain an access token
constexpr char TOKEN[] PROGMEM = "YOUR_DEVICE_ACCESS_TOKEN";

// Thingsboard we want to establish a connection too
constexpr char THINGSBOARD_SERVER[] PROGMEM = "demo.thingsboard.io";
#if USING_HTTPS
// HTTP port used to communicate with the server, 80 is the default unencrypted HTTP port,
// whereas 443 would be the default encrypted SSL HTTPS port
#if ENCRYPTED
constexpr uint16_t THINGSBOARD_PORT PROGMEM = 443U;
#else
constexpr uint16_t THINGSBOARD_PORT PROGMEM = 80U;
#endif
#else
// MQTT port used to communicate with the server, 1883 is the default unencrypted MQTT port,
// whereas 8883 would be the default encrypted SSL MQTT port
#if ENCRYPTED
constexpr uint16_t THINGSBOARD_PORT PROGMEM = 8883U;
#else
constexpr uint16_t THINGSBOARD_PORT PROGMEM = 1883U;
#endif
#endif

// Maximum size packets will ever be sent or received by the underlying MQTT client,
// if the size is to small messages might not be sent or received messages will be discarded
constexpr uint32_t MAX_MESSAGE_SIZE PROGMEM = 128U;

// Baud rate for the debugging serial connection
// If the Serial output is mangled, ensure to change the monitor speed accordingly to this variable
constexpr uint32_t SERIAL_DEBUG_BAUD PROGMEM = 115200U;

#if ENCRYPTED
// See https://comodosslstore.com/resources/what-is-a-root-ca-certificate-and-how-do-i-download-it/
// on how to get the root certificate of the server we want to communicate with,
// this is needed to establish a secure connection and changes depending on the website.
constexpr char ROOT_CERT[] PROGMEM = R"(-----BEGIN CERTIFICATE-----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=
-----END CERTIFICATE-----
)";
#endif


// Initialize underlying client, used to establish a connection
#if ENCRYPTED
WiFiClientSecure espClient;
#else
WiFiClient espClient;
#endif
// Initialize ThingsBoard instance with the maximum needed buffer size
#if USING_HTTPS
ThingsBoardHttpSized<MAX_MESSAGE_SIZE> tb(espClient, TOKEN, THINGSBOARD_SERVER, THINGSBOARD_PORT);
#else
ThingsBoardSized<MAX_MESSAGE_SIZE> tb(espClient);
#endif


/// @brief Initalizes WiFi connection,
// will endlessly delay until a connection has been successfully established
void InitWiFi() {
  Serial.println("Connecting to AP ...");
  // Attempting to establish a connection to the given WiFi network
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  while (WiFi.status() != WL_CONNECTED) {
    // Delay 500ms until a connection has been succesfully established
    delay(500);
    Serial.print(".");
  }
  Serial.println("Connected to AP");
#if ENCRYPTED
  espClient.setCACert(ROOT_CERT);
#endif
}

/// @brief Reconnects the WiFi uses InitWiFi if the connection has been removed
/// @return Returns true as soon as a connection has been established again
const bool reconnect() {
  // Check to ensure we aren't connected yet
  const wl_status_t status = WiFi.status();
  if (status == WL_CONNECTED) {
    return true;
  }

  // If we aren't establish a new connection to the given WiFi network
  InitWiFi();
  return true;
}

void setup() {
  // If analog input pin 0 is unconnected, random analog
  // noise will cause the call to randomSeed() to generate
  // different seed numbers each time the sketch runs.
  // randomSeed() will then shuffle the random function.
  randomSeed(analogRead(0));
  // Initalize serial connection for debugging
  Serial.begin(SERIAL_DEBUG_BAUD);
  delay(1000);
  InitWiFi();
}

void loop() {
  delay(1000);

  if (!reconnect()) {
    return;
  }

#if !USING_HTTPS
  if (!tb.connected()) {
    // Connect to the ThingsBoard
    Serial.print("Connecting to: ");
    Serial.print(THINGSBOARD_SERVER);
    Serial.print(" with token ");
    Serial.println(TOKEN);
    if (!tb.connect(THINGSBOARD_SERVER, TOKEN, THINGSBOARD_PORT)) {
      Serial.println("Failed to connect");
      return;
    }
  }
#endif

  Serial.println("Sending data...");
  // Uploads new telemetry to ThingsBoard using MQTT.
  // See https://thingsboard.io/docs/reference/mqtt-api/#telemetry-upload-api
  // for more details
  tb.sendTelemetryInt("temperature", random(10, 31));
  tb.sendTelemetryInt("humidity", random(40, 90));
  tb.sendAttributeString("version", "1.0");

#if !USING_HTTPS
  tb.loop();
#endif
}

주석까지 정말 친절하게 잘 나와있다.
이제 앞서서 작성했던 IMU와 FSR의 값을 가져오는 코드와 합치기만 하면 된다.
내가 작성한 코드는 다음과 같다.

#if defined(ESP32)
#include <WiFi.h>
#include <WiFiClientSecure.h>
#endif


// Sending data can either be done over MQTT and the PubSubClient
// or HTTPS and the HTTPClient, when using the ESP32 or ESP8266
#define USING_HTTPS false

// Wheter the given script is using encryption or not,
// generally recommended as it increases security (communication with the server is not in clear text anymore),
// it does come with an overhead tough as having an encrypted session requires a lot of memory,
// which might not be avaialable on lower end devices.
#define ENCRYPTED false


#if USING_HTTPS
#include <ThingsBoardHttp.h>
#else
#include <ThingsBoard.h>
#endif


// PROGMEM can only be added when using the ESP32 WiFiClient,
// will cause a crash if using the ESP8266WiFiSTAClass instead.
#if defined(ESP8266)
constexpr char WIFI_SSID[] = "your Wifi Name";
constexpr char WIFI_PASSWORD[] = "your Wifi Password";
#elif defined(ESP32)
constexpr char WIFI_SSID[] PROGMEM = "your Wifi Name";
constexpr char WIFI_PASSWORD[] PROGMEM = "your Wifi Password";
#endif

// See https://thingsboard.io/docs/getting-started-guides/helloworld/
// to understand how to obtain an access token
constexpr char TOKEN[] PROGMEM = "your ThingsBoard Device Token";

// Thingsboard we want to establish a connection too
constexpr char THINGSBOARD_SERVER[] PROGMEM = "demo.thingsboard.io";
#if USING_HTTPS
// HTTP port used to communicate with the server, 80 is the default unencrypted HTTP port,
// whereas 443 would be the default encrypted SSL HTTPS port
#if ENCRYPTED
constexpr uint16_t THINGSBOARD_PORT PROGMEM = 443U;
#else
constexpr uint16_t THINGSBOARD_PORT PROGMEM = 80U;
#endif
#else
// MQTT port used to communicate with the server, 1883 is the default unencrypted MQTT port,
// whereas 8883 would be the default encrypted SSL MQTT port
#if ENCRYPTED
constexpr uint16_t THINGSBOARD_PORT PROGMEM = 8883U;
#else
constexpr uint16_t THINGSBOARD_PORT PROGMEM = 1883U;
#endif
#endif

// Maximum size packets will ever be sent or received by the underlying MQTT client,
// if the size is to small messages might not be sent or received messages will be discarded
constexpr uint32_t MAX_MESSAGE_SIZE PROGMEM = 128U;

// Baud rate for the debugging serial connection
// If the Serial output is mangled, ensure to change the monitor speed accordingly to this variable
constexpr uint32_t SERIAL_DEBUG_BAUD PROGMEM = 115200U;

#if ENCRYPTED
// See https://comodosslstore.com/resources/what-is-a-root-ca-certificate-and-how-do-i-download-it/
// on how to get the root certificate of the server we want to communicate with,
// this is needed to establish a secure connection and changes depending on the website.
constexpr char ROOT_CERT[] PROGMEM = R"(-----BEGIN CERTIFICATE-----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jh8BCNAw1FtxNrQHusEwMFxIt4I7mKZ9YIqioymCzLq9gwQbooMDQaHWBfEbwrbw
qHyGO0aoSCqI3Haadr8faqU9GY/rOPNk3sgrDQoo//fb4hVC1CLQJ13hef4Y53CI
rU7m2Ys6xt0nUW7/vGT1M0NPAgMBAAGjQjBAMA4GA1UdDwEB/wQEAwIBBjAPBgNV
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hkiG9w0BAQsFAAOCAgEAVR9YqbyyqFDQDLHYGmkgJykIrGF1XIpu+ILlaS/V9lZL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=
-----END CERTIFICATE-----
)";
#endif


// Initialize underlying client, used to establish a connection
#if ENCRYPTED
WiFiClientSecure espClient;
#else
WiFiClient espClient;
#endif
// Initialize ThingsBoard instance with the maximum needed buffer size
#if USING_HTTPS
ThingsBoardHttpSized<MAX_MESSAGE_SIZE> tb(espClient, TOKEN, THINGSBOARD_SERVER, THINGSBOARD_PORT);
#else
ThingsBoardSized<MAX_MESSAGE_SIZE> tb(espClient);
#endif



#define FORCE_SENSOR_PIN1 36 // ESP32 pin GIOP36 (ADC0): the FSR and 10K pulldown are connected to A0
#define FORCE_SENSOR_PIN2 39 // ESP32 pin GIOP39 (ADC3): the FSR and 10K pulldown are connected to A3
#define FORCE_SENSOR_PIN3 34 // ESP32 pin GIOP36 (ADC6): the FSR and 10K pulldown are connected to A6
#define FORCE_SENSOR_PIN4 35 // ESP32 pin GIOP36 (ADC7): the FSR and 10K pulldown are connected to A7



/// @brief Initalizes WiFi connection,
// will endlessly delay until a connection has been successfully established
void InitWiFi() {
  Serial.println("Connecting to AP ...");
  // Attempting to establish a connection to the given WiFi network
  WiFi.begin(WIFI_SSID, WIFI_PASSWORD);
  while (WiFi.status() != WL_CONNECTED) {
    // Delay 500ms until a connection has been succesfully established
    delay(500);
    Serial.print(".");
  }
  Serial.println("Connected to AP");
#if ENCRYPTED
  espClient.setCACert(ROOT_CERT);
#endif
}

/// @brief Reconnects the WiFi uses InitWiFi if the connection has been removed
/// @return Returns true as soon as a connection has been established again
const bool reconnect() {
  // Check to ensure we aren't connected yet
  const wl_status_t status = WiFi.status();
  if (status == WL_CONNECTED) {
    return true;
  }

  // If we aren't establish a new connection to the given WiFi network
  InitWiFi();
  return true;
}

void setup() {
  // If analog input pin 0 is unconnected, random analog
  // noise will cause the call to randomSeed() to generate
  // different seed numbers each time the sketch runs.
  // randomSeed() will then shuffle the random function.
  randomSeed(analogRead(0));
  // Initalize serial connection for debugging
  Serial.begin(SERIAL_DEBUG_BAUD);
  delay(1000);
  InitWiFi();
}

void loop() {
  delay(500);

  if (!reconnect()) {
    return;
  }

#if !USING_HTTPS
  if (!tb.connected()) {
    // Connect to the ThingsBoard
    Serial.print("Connecting to: ");
    Serial.print(THINGSBOARD_SERVER);
    Serial.print(" with token ");
    Serial.println(TOKEN);
    if (!tb.connect(THINGSBOARD_SERVER, TOKEN, THINGSBOARD_PORT)) {
      Serial.println("Failed to connect");
      return;
    }
  }
#endif
  int analogReading1 = analogRead(FORCE_SENSOR_PIN1);
  int analogReading2 = analogRead(FORCE_SENSOR_PIN2);
  int analogReading3 = analogRead(FORCE_SENSOR_PIN3);
  int analogReading4 = analogRead(FORCE_SENSOR_PIN4);  

  Serial.println("Sending data...");
  // Uploads new telemetry to ThingsBoard using MQTT.
  // See https://thingsboard.io/docs/reference/mqtt-api/#telemetry-upload-api
  // for more details
  tb.sendTelemetryInt("yellow", analogReading1);
  tb.sendTelemetryInt("green", analogReading2);
  tb.sendTelemetryInt("gray", analogReading3);
  tb.sendTelemetryInt("purple", analogReading4);

  tb.sendTelemetryJson();
  


#if !USING_HTTPS
  tb.loop();
#endif
}