Digital Twins

A diploma work for Kyiv Politechnic Institute

Backend

Requirements: .NET 6 SDK

Commands for migrations using CLI:

1. Create migration:

dotnet ef migrations add {MigrationName} --project DigitalTwins.DAL --startup-project DigitalTwins.API

2. Update database:

dotnet ef database update --project DigitalTwins.DAL --startup-project DigitalTwins.API

Database

RDBMS: Microsoft SQL Server

Connection string for local database:

  "ConnectionStrings": {
    "DigitalTwinDBConnection": "Server=(localdb)\\MSSQLLocalDB;Database=DigitalTwinDB;Trusted_Connection=True;"
  }

Scheme: https://drawsql.app/teams/bsa2021/diagrams/digital-twin

MQTT

This project is using MQTT protocol and EMQX as message broker. Docker command for downloading EMQX broker:

1. Pull exqx:

docker pull emqx/emqx

2. Run exqx:

docker run -d --name emqx -p 1883:1883 -p 8083:8083 -p 8084:8084 -p 8883:8883 -p 18083:18083 emqx/emqx

Sample of code for Arduino project using subscribtion to MQTT topic:

#include <WiFi.h>
#include <PubSubClient.h>
#include <ArduinoJson.h>

// credentials for Wi-fi
const char* ssid = "yourSsid";
const char* password = "yourPassword";
// port and address of mqtt broker
const char* mqttServer = "broker.emqx.io";
const int mqttPort = 1883;
// topic name
const char* mqttTopic = "yourDeviceTopic";
// device status topic name
const char* statusTopic = "device/status";
// topic for sending statistic
const char* statsTopic = "device/stats";
// topic for sending error logs
const char* errorsTopic = "device/errors";
// unique indentifier
const char* guid = "yourDeviceGuid";
// credentials for broker
const char *mqtt_username = "emqx";
const char *mqtt_password = "public";


unsigned long lastMsg = 0;
int lightSwitchCount = 0;

WiFiClient espClient;
PubSubClient client(espClient);

enum Status {
    Online,
    Offline
};

void sendErrorLog(const String& errorMessage, const String& errorDescription) {
    DynamicJsonDocument doc(512);
    doc["Id"] = guid;
    doc["Error"] = errorMessage;
    doc["Description"] = errorDescription;

    char buffer[512];
    serializeJson(doc, buffer);

    client.publish(errorsTopic, buffer);
}


void sendStatus(Status status) {
    DynamicJsonDocument doc(256);
    doc["Id"] = guid;
    doc["Status"] = status;

    char buffer[256];
    serializeJson(doc, buffer);

    client.publish(statusTopic, buffer);
}

void setup_wifi() {
    delay(10);
    WiFi.begin(ssid, password);
    unsigned long startAttemptTime = millis();

    while (WiFi.status() != WL_CONNECTED && millis() - startAttemptTime < 10000) {
        delay(500);
        Serial.print(".");
    }

    if (WiFi.status() != WL_CONNECTED) {
        sendErrorLog("WiFi Connection Failed", "Could not connect to WiFi within 10 seconds");
    } else {
        Serial.println("WiFi connected");
    }
}

void callback(char* topic, byte* payload, unsigned int length) {
    Serial.print("Message arrived in topic: ");
    Serial.println(topic);

    Serial.print("Message:");
    for (int i = 0; i < length; i++) {
        Serial.print((char)payload[i]);
    }
    Serial.println();

    DynamicJsonDocument doc(1024);
    DeserializationError error = deserializeJson(doc, payload, length);
    if (error) {
        sendErrorLog("JSON Parsing Error", "Failed to parse incoming message: " + String(error.c_str()));
        return;
    }

    if (!doc.containsKey("Pin") || !doc.containsKey("Value")) {
        sendErrorLog("JSON content error", "Missing required values: Pin, Value");
        return;
    }

    int pin = doc["Pin"];
    bool value = doc["Value"];

    if (value) {
        lightSwitchCount++;
    }

    pinMode(pin, OUTPUT);
    digitalWrite(pin, value ? HIGH : LOW);

    Serial.println("Pin: " + String(pin) + " Value: " + value);
}

void setup() {
    Serial.begin(9600);
    setup_wifi();

    client.setServer(mqttServer, mqttPort);
    client.setCallback(callback);

    String client_id = "digital-twins";

    while (!client.connected()) {
        Serial.println("Connecting to MQTT Broker...");
        if (client.connect(client_id.c_str(), mqtt_username, mqtt_password)) {
            Serial.println("Connected");
            sendStatus(Status::Online);
        } else {
            sendErrorLog("MQTT Connection Failed", "Failed to connect to MQTT Broker with state " + String(client.state()));
            delay(2000);
        }
    }

    client.subscribe(mqttTopic);
}

void loop() {
    client.loop();

    unsigned long now = millis();
    if (now - lastMsg > 60000) {
        lastMsg = now;

        float heapUsed = ESP.getHeapSize() - ESP.getFreeHeap();
        float heapUsage = (heapUsed / ESP.getHeapSize()) * 100;
        float uptime = millis() / 1000.0;
        int rssi = WiFi.RSSI();

        DynamicJsonDocument doc(1024);
        doc["Id"] = guid;
        doc["Uptime"] = uptime;
        doc["HeapUsage"] = heapUsage;
        doc["Rssi"] = rssi;
        doc["LightSwitchCount"] = lightSwitchCount;
        lightSwitchCount = 0;

        char jsonBuffer[512];
        serializeJson(doc, jsonBuffer);

        client.publish(statsTopic, jsonBuffer);
    }
}

Frontend

Commands to run the client using the CLI:

1. Install all dependencies:

yarn install

2. Run client:

yarn dev

Authors

• Vasyl Pavliuk
• Vitalii Kovalov