Modbus_to_IoTHub.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>netcoreapp2.1</TargetFramework>
    <RootNamespace>iothub_serviceclient</RootNamespace>
    <LangVersion>7.3</LangVersion>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Azure.Devices" Version="1.16.0" />
    <PackageReference Include="Microsoft.Azure.Devices.Client" Version="1.17.0" />
    <PackageReference Include="ModbusTcp" Version="1.0.3" />
  </ItemGroup>

</Project>

Program.cs

using System;
using System.Text;
using Microsoft.Azure.Devices.Client;
using Microsoft.Azure.Devices.Shared;
using Newtonsoft.Json;
using ModbusTcp;
using System.Threading.Tasks;
using System.Linq;
using System.Collections.Generic;
using Newtonsoft.Json.Linq;

namespace modbus_notmodbus
{
    class Program
    {
        public static uint pollingInterval = 11; // seconds
        public static string deviceId = "ModbusCollector";
        public static string modbusHost = "127.0.0.1";
        public static int modbusPort = 502;
        public static string deviceConnStr = ".........................";
        static DeviceClient c;

        static async Task Main(string[] args)
        {
            ModbusClient m = new ModbusClient(modbusHost, modbusPort);
            m.Init();

            c = DeviceClient.CreateFromConnectionString(deviceConnStr);
            Twin twin = await c.GetTwinAsync();
            if (twin.Properties.Desired["pollingInterval"] != Program.pollingInterval)
            {
                Console.WriteLine("[DEBUG] Setting new pollingInterval: " +
                    $"{twin.Properties.Desired["pollingInterval"]} seconds");
                try
                {
                    Program.pollingInterval = twin.Properties.Desired["pollingInterval"];
                }
                catch (Exception ex)
                {
                    Console.WriteLine($"[EXCEPTION] Unable to set pollingInterval: {ex.Message}");
                }
            }
            await c.SetDesiredPropertyUpdateCallbackAsync(OnDesiredPropertyChanged, null);

            while (true)
            {
                object telemetryObject = await GetModbusData(m);

                Console.WriteLine("[DEBUG] Serialized telemetry object:\n" +
                    JsonConvert.SerializeObject(telemetryObject, Formatting.Indented));

                byte[] payload = Encoding.ASCII.GetBytes(JsonConvert.SerializeObject(telemetryObject));
                Message message = new Message(payload);

                Console.WriteLine("Sending message to Azure IoT Hub...");
                await c.SendEventAsync(message);
                Console.WriteLine("OK");

                await SleepSpinner(pollingInterval);
            }
        }

        static async Task<object> GetModbusData(ModbusClient m)
        {
            Console.WriteLine("Fetching MODBUS data...");
            // Reading might throw System.IO.IOException. Handle it.
            // Fingers crossed for a short int
            short[] voltage = await m.ReadRegistersAsync(40001, 3);
            short[] current = await m.ReadRegistersAsync(41001, 3);
            string hardwareId = "Function Code 0x2b (43)";

            return new
            {
                deviceId = deviceId,
                voltage = voltage,
                current = current,
                hardwareId = hardwareId
            };
        }
        static async Task SleepSpinner(uint pollingInterval)
        {
            Console.Write($"Sleeping for {pollingInterval} seconds  ");
            for (byte i = 0; i < pollingInterval; i++)
            {
                foreach (string s in new string[] { "|", "/", "-", "\\" })
                {
                    await Task.Delay(250);
                    Console.Write($"\b{s}");
                }
            }
            Console.Write("\n");
        }

        static async Task OnDesiredPropertyChanged(TwinCollection desiredProperties, object userContext)
        {
            Console.WriteLine();
            foreach (var prop in desiredProperties)
            {
                var pair = (KeyValuePair<string, object>)prop;
                var value = pair.Value as JValue;
                Console.WriteLine($"[DEBUG] desiredProp: {pair.Key} = {pair.Value.ToString()}");
            }

            if (desiredProperties["pollingInterval"] != Program.pollingInterval)
            {
                Console.WriteLine($"[DEBUG] Setting new pollingInterval: {desiredProperties["pollingInterval"]}");
                try
                {
                    Program.pollingInterval = desiredProperties["pollingInterval"];
                }
                catch (Exception ex)
                {
                    Console.WriteLine($"[EXCEPTION] Unable to set pollingInterval: {ex.Message}");
                }
            }

            TwinCollection reportedProperties = new TwinCollection();
            reportedProperties["pollingInterval"] = Program.pollingInterval;
            await c.UpdateReportedPropertiesAsync(reportedProperties);
        }
    }
}