The Communication Protokoll

We created a test setup for I²C and MQTT communication. In this setup, the Master sends a "get" request over I²C to retrieve temperature and humidity data from the Slave. Upon receiving the request, the Slave reads the data from the DHT22 sensor and publishes it to the MQTT broker.

Since the Master is subscribed to the temperature and humidity topics, it receives the newly published data and displays it on the screen. Additionally, for debugging purposes, we included another I²C message from the Master to the Slave with the payload "Data Acquired."

Master

On the Master side we needed to connect the dislplay, which is an OLED I²C Display, like in Lysanders Assignment, to the Pins GP6 for SDA and GP7 for SCL which are pin 7 and 8 on the Breakout pins. For the I²C Connection of master and slave, the pins GP4 and GP5 (SDA/SCL) are used which are pin 5 and 6 on the Breakout pins.

The code

                    
#include 
#include 
#include 
#include 
#include 
#include 

uint32_t delayMS;  //start to count

int sending_request_ms = 20000;

// WiFi-Credentials
const char *ssid = "xxxxxxxxxxxxxx";
const char *password = "xxxxxxxxxxxxxxxx";

// MQTT Broker IP address
const char *mqtt_identifier = "xxxxxxxxxxxxx";
const char *mqtt_server = "xxxxxxxxxxxxxxx";
const char *mqtt_user = "xxxxxxxxxxx";
const char *mqtt_pass = "xxxxxxxxxxxxxxxxx";


WiFiClient espClient;
PubSubClient client(espClient);
char msg[50];
char topic[50];
long lastMsg = 0;


bool gotTemp = false;
bool gotHum = false;
String latestTemp = "";
String latestHum = "";

#define SLAVE_ADDR 0x10


//OLED Setup
#define SCREEN_WIDTH 128
#define SCREEN_HEIGHT 64

#define OLED_SDA 6  // Yellow wire GP6
#define OLED_SCL 7  // Purple wire GP7

Adafruit_SSD1306 display(SCREEN_WIDTH, SCREEN_HEIGHT, &Wire1, -1);



void setup(void) {

  Serial.begin(115200);

//I2C channel 1 start as Master
  Wire.begin();

//I2C channel 2 start for the OLED
  Wire1.setSDA(OLED_SDA);
  Wire1.setSCL(OLED_SCL);
  Wire1.begin();

  if (!display.begin(SSD1306_SWITCHCAPVCC, 0x3C)) {
    Serial.println("SSD1306 OLED failed to start");
    while (1)
      ;  // Stop here if OLED fails
  }

  display.clearDisplay();
  display.setTextSize(1);
  display.setTextColor(WHITE);
  display.setCursor(0, 20);
  display.println("Waiting...");
  display.display();

  //Wifi and MQTT connection
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  client.setCallback(callback);
  delay(2000);
}

void loop() {


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

  // Display of the Data on the Screen and "Data Acquired"
  if (gotTemp && gotHum) {

    Wire.beginTransmission(SLAVE_ADDR);  // Address of the slave
    Wire.write("Data Aquired");          // Send 5 bytes
    Wire.endTransmission();              // Stop condition
    Serial.println("Sent: Data Acquired");

    gotTemp = false;
    gotHum = false;

    display.clearDisplay();
    display.setCursor(0, 40);
    display.println("Temp in *C: " + latestTemp);
    display.setCursor(0, 20);
    display.println("Hum in %: " + latestHum);
    display.display();
  }

  //get request after 20 seconds
  long now = millis();
  if (now - lastMsg > sending_request_ms) {
    lastMsg = now;

    Wire.beginTransmission(SLAVE_ADDR);  // Address of the slave
    Wire.write("get");                   // Send 5 bytes
    Wire.endTransmission();              // Stop condition
    Serial.println("Sent: get");
  }
}

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

  WiFi.begin(ssid, 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 (client.connect(mqtt_identifier, mqtt_user, mqtt_pass)) {
      Serial.println("connected");
      // Subscribe to the Temp and Hum topics for the callback
      strcpy(topic, mqtt_identifier);
      strcat(topic, "/humidity");
      client.subscribe(topic);

      strcpy(topic, mqtt_identifier);
      strcat(topic, "/temperature");
      client.subscribe(topic);
    } else {
      Serial.print("failed, rc=");
      Serial.print(client.state());
      Serial.println(" try again in 5 seconds");
      // Wait 5 seconds before retrying
      delay(5000);
    }
  }
}

void callback(char *incomingTopic, byte *message, unsigned int length) {
  Serial.print("Message arrived on topic: ");
  Serial.print(incomingTopic);
  Serial.print(". Message: ");

  String messageTemp;
  for (int i = 0; i < length; i++) {
    Serial.print((char)message[i]);
    messageTemp += (char)message[i];
  }
  Serial.println();

  String expectedTopicTemperat = String(mqtt_identifier) + "/temperature";
  String expectedTopicHumi = String(mqtt_identifier) + "/humidity";

  if (String(incomingTopic) == expectedTopicTemperat) {
    Serial.println("Temperature: " + messageTemp);

    gotTemp = true;

    latestTemp = String(messageTemp);
  }

  if (String(incomingTopic) == expectedTopicHumi) {
    Serial.println("Humidity: " + messageTemp);

    gotHum = true;

    latestHum = String(messageTemp);
  }
}

Slave

On the Slave side we needed to connect the DHT22, which is an humidity and Temperature Sensor, like in Mikas Assignment, to pin GP3 which is pin 4 on Breakout pins. For the I²C Connection of master and slave, the pins GP4 and GP5 (SDA/SCL) are used which are pin 5 and 6 on the Breakout Pins.

The code

                    
                        #include 
#include 
#include 
#include 
#include 
#include 
#include 

//DHT22 setup

#define DHTPIN 3  // Digital pin connected to the DHT sensor

#define DHTTYPE DHT22  // DHT 22 (AM2302)
DHT_Unified dht(DHTPIN, DHTTYPE);

// WiFi-Credentials
const char *ssid = "xxxxxxxxxxxxxx";
const char *password = "xxxxxxxxxxxxxxxx";

// MQTT Broker IP address
const char *sub_identifier = "xxxxxxxxxxxx";
const char *mqtt_identifier = "xxxxxxxxxxxxx";
const char *mqtt_server = "xxxxxxxxxxxxxxx";
const char *mqtt_user = "xxxxxxxxxxx";
const char *mqtt_pass = "xxxxxxxxxxxxxxxxx";


WiFiClient espClient;
PubSubClient client(espClient);
char msg[50];
char topic[50];
int value = 0;

#define SLAVE_ADDR 0x10
String receivedText = "";

void setup(void) {

  Serial.begin(115200);

  //Wifi,MQTT and dht begin
  setup_wifi();
  client.setServer(mqtt_server, 1883);
  dht.begin();

  //I2C channel 1 start as Slave with a specific adress
  Wire.begin(SLAVE_ADDR);
  Wire.onReceive(receiveEvent);

  delay(2000);
}

void loop() {


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


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

  WiFi.begin(ssid, 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 (client.connect(mqtt_identifier, mqtt_user, mqtt_pass)) {
      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);
    }
  }
}

void receiveEvent(int numBytes) {

    //recieves a message through I2C
  receivedText = "";
  while (Wire.available()) {
    char c = Wire.read();
    if (isPrintable(c)) {
      receivedText += c;
    }
  }

  Serial.print("Received: ");
  Serial.println(receivedText);

  receivedText.trim();

  //checks if it is the "get" request
  if (receivedText == "get") {
    //get temperature

    sensors_event_t event;

    dht.temperature().getEvent(&event);


    // Convert the value to a char array
    char tempString[8];
    dtostrf(event.temperature, 1, 2, tempString);
    Serial.print("Temperature: ");
    Serial.println(tempString);

    //changes the topic to publish to
    strcpy(topic, sub_identifier);
    strcat(topic, "/temperature");

    //and publish it to MQTT
    client.publish(topic, tempString);

    //get humidityy
    dht.humidity().getEvent(&event);

    // Convert the value to a char array and publish it to MQTT
    char humString[8];
    dtostrf(event.relative_humidity, 1, 2, humString);
    Serial.print("Humidity: ");
    Serial.println(humString);

    //changes the topic to publish to
    strcpy(topic, sub_identifier);
    strcat(topic, "/humidity");

    //and publish it to MQTT
    client.publish(topic, humString);
  }
}

Result

In the Video u see everything working. The top rigth window is the serial output of the Slave. After receiving the "get", it reads the temperature and publishes them. After that it gets "Data Acquired"

Under the Slave is the Master, Where you can see, that "get" was sent, the Data was read through MQTT and then "Data Acquired" sent to the Slave

On the left you see MQTT-Explorer(look in Mikas Repo for more Information). We used it for Debugging, to see if the Data was sent to the MQTT Broker. As you see, it worked.

Source Code for Download

Master: Arduino sketch for master code
Slave: Arduino sketch for slave code

Group Assignment: Week 11

Networking & Communication

As this week is about networking and communication, we had an assignment to complete that regarded different communication protocols between microcontroller. Here, the assignment were:

The Communication Protokoll

Master

The code

Slave

The code

Result

Source Code for Download