OpenThings 2.2.1

OpenThings

A .net core library for encoding and decoding OpenThings messages. See specification.

Installing OpenThings

Install the OpenThings package via nuget package manager console:

Install-Package OpenThings

Supported .Net Runtimes

The OpenThings package is compatible with the following runtimes:

• .NET Core 7.0

Encoding

var messageHeader = new MessageHeader(0x55, 0xAA, 0x0000, 0xFEEDED);

var message = new Message(messageHeader);

message.Records.Add(
    new MessageRecord(
        new Parameter(OpenThingsParameter.Temperature),
        new MessageRecordDataFloat(RecordType.UnsignedX4, 20.5f)));

message.Records.Add(
    new MessageRecord(
        new Parameter(OpenThingsParameter.Debug),
        new MessageRecordDataString("TEST")));

message.Records.Add(
    new MessageRecord(
        new Parameter(OpenThingsParameter.Frequency),
        new MessageRecordDataUInt(120)));

message.Records.Add(
    new MessageRecord(
        new Parameter(OpenThingsParameter.Level),
        new MessageRecordDataInt(-50)));

List<Byte> encodedMessageBytes = openthingsMessageEncoder.Encode(message);

// A random seed source for linear encrypt encryption
ushort seed = GetSeed();

// Alternatively apply linear shift encryption to message 
List<Byte> encodedMessageBytes = openthingsMessageEncoder.Encode(message, 0x45, seed);

Decoding

// List of manufacturer Ids to PID's for linear shift decryption
List<PidMap> pidMaps = new List<PidMap>()
{
    new PidMap(0xAA, 1)
}

List<Byte> payload = GetPayloadFromSource();

var openthingsMessage = _decoder.Decode(payload, pidMaps);

Console.WriteLine($"Message: {openthingsMessage}");

Adding Extended Parameters And Commands

The OpenThings specification specifies a number of parameter types out of the box, however there are situations when new parameters are required to be added to support a custom sensor type. There are a number of steps required to support additional parameter types encoding and decoding.

Extend Parameter Identifiers

To support the encoding and decoding of custom parameter types first extend the ParameterIdentifiers base class and add the additional parameters.

internal class ExtendedParameterIdentifiers : ParameterIdentifiers
{
    /// <summary>
    /// The devices battery voltage
    /// </summary>
    public const byte BatteryVoltage = 0x7D;

    /// <summary>
    /// The Indoor air quality
    /// </summary>
    public const byte Iaq = 0x7E;

    /// <summary>
    /// The estimated carbon dioxide level
    /// </summary>
    public const byte eCo2 = 0x7F;

    /// <summary>
    /// The equivalent ethanol level
    /// </summary>
    public const byte EtOH = 0x80;

    /// <summary>
    /// The total volatile organic compounds
    /// </summary>
    public const byte TVOC = 0x81;
}

Extend Commands

To support encoding of command type parameters extend the DefaultCommands type.

internal class ExtendedCommands : DefaultCommands
{
    /// <summary>
    /// A command to execute the devices boot loader
    /// </summary>
    public const byte ExecuteBootLoaderCommand = 0xFF;
}

Extend Parameter Definitions

To support the encoding and decoding of custom parameter types the OpenThings library contains a collection of the default parameters called DefaultParameters. This class implements the interface IParameters interface.

Create a derived type from the DefaultParameters type and add the custom parameters to the collection via the Add method.

internal class ExtendedParameters : DefaultParameters
{
    public ExtendedParameters()
    {
        Add(new Parameter(
            ExtendedParameterIdentifiers.BatteryVoltage, 
            nameof(ExtendedParameterIdentifiers.BatteryVoltage), "V"));

        Add(new Parameter(
            ExtendedParameterIdentifiers.Iaq,
            nameof(ExtendedParameterIdentifiers.Iaq), string.Empty));

        Add(new Parameter(
            ExtendedParameterIdentifiers.eCo2,
            nameof(ExtendedParameterIdentifiers.eCo2), "ppm"));

        Add(new Parameter(
            ExtendedParameterIdentifiers.EtOH,
            nameof(ExtendedParameterIdentifiers.EtOH), "ppm"));

        Add(new Parameter(
            ExtendedParameterIdentifiers.TVOC,
            nameof(ExtendedParameterIdentifiers.TVOC), "mg/m^3"));

        Add(new Parameter(
            ExtendedCommands.ExecuteBootLoaderCommand,
            nameof(ExtendedCommands.ExecuteBootLoaderCommand), string.Empty));
    }
}

An instance of this custom ExtendedParameters type is then injected into the OpenThingsDecoder instance either directly or via a DI framework.