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JUCE Bluetooth LE module

JUCE module for interacting with Bluetooth LE devices on macOS and Windows.

Dependencies

The project depends on a few third-party libraries.

• JUCE *
• GSL
• fmt
• range-v3

The CMake build script uses CPM to fetch these dependencies. If you use a different build system, you will have to make sure these libraries are available and linked properly as part of your appliation build step.

* JUCE will only be fetched if juce_bluetooth is loaded as a top-level project. If you're consuming it in your project, JUCE will surely already be available.

The project assumes a CMake-based environment.

Installing

In order to install the module in your system

cmake -B build -DCMAKE_INSTALL_PREFIX=/usr/local
sudo cmake --build build --target install

Then, in your project juce_bluetooth may be found using find_package. See the using_find_package example.

Quickstart

At the heart of your application you'll instantiate a BleAdapter to manage discovery and connections.

genki::BleAdapter adapter;

This module uses JUCE's ValueTrees to pass messages back-and-forth, so make sure to listen to changes on the adapter's state.

genki::ValueTreeListener listener{adapter.state};

listener.property_changed = [&](juce::ValueTree& vt, const juce::Identifier& id)
{
    if (vt.hasType(ID::BLUETOOTH_ADAPTER) && id == ID::status)
    {
        const auto is_powered_on = AdapterStatus((int) vt.getProperty(id)) == AdapterStatus::PoweredOn;

        fmt::print("{}\n", is_powered_on
                           ? "Adapter powered on, starting scan..."
                           : "Adapter powered off/disabled, stopping scan...");

        adapter.scan(is_powered_on);
    }
    else if (vt.hasType(ID::BLUETOOTH_DEVICE) && id == ID::last_seen)
    {
        if (vt.getProperty(ID::name).toString().isNotEmpty())
        {
            fmt::print("{} {} - rssi: {}\n",
                    vt.getProperty(ID::name).toString().toStdString(),
                    vt.getProperty(ID::address).toString().toStdString(),
                    (int) vt.getProperty(ID::rssi));
        }
    }
};

After discovery, you can connect to a BLE device

const BleDevice::Callbacks ble_callbacks{
    .valueChanged = [this](const juce::Uuid& uuid, gsl::span<const gsl::byte> data)
    {
        // Called when data is received on a characteristic via notifications or indications
    },
    .characteristicWritten = [this](const juce::Uuid& uuid, bool success)
    {
        // Called when a characteristic write has successfully been delivered to the peripheral
    },
};

listener.child_added = [&](juce::ValueTree&, juce::ValueTree& vt)
{
    if (vt.hasType(ID::BLUETOOTH_DEVICE))
    {
        const auto name = vt.getProperty(ID::name).toString();

        if (name.containsIgnoreCase(my_device_name))
        {
            device = adapter.connect(vt, ble_callbacks);
        }
    }
};

You'll receive ValueTree changes for all devices on the BleAdapter.state as well

After connecting to a device, you initiate service discovery

listener.property_changed = [&](juce::ValueTree& vt, const juce::Identifier& id)
{
    if (vt.hasType(ID::BLUETOOTH_ADAPTER) && id == ID::status)
    {
        ...
    }
    else if (vt.hasType(ID::BLUETOOTH_DEVICE))
    {
        if (id == ID::is_connected && vt.getProperty(id))
        {
            genki::message(vt, ID::DISCOVER_SERVICES);
        }
    }
};

which will emit a message with ID::SERVICES_DISCOVERED on the device node, allowing us to discover characteristics for a given service

listener.child_added = [&](juce::ValueTree&, juce::ValueTree& vt)
{
    if (vt.hasType(ID::BLUETOOTH_DEVICE))
    {
        ...
    }
    else if (vt.hasType(ID::SERVICES_DISCOVERED))
    {
        const auto dev = vt.getParent(); // dev should be the same node as device->state
        jassert(dev.hasType(ID::BLUETOOTH_DEVICE));

        if (const auto srv = dev.getChildWithProperty(ID::uuid, HeartRateServiceUuid.toDashedString()); srv.isValid())
            genki::message(srv, ID::DISCOVER_CHARACTERISTICS);
    }
};

and finally enable notifications on the characteristic

listener.child_added = [&](juce::ValueTree&, juce::ValueTree& vt)
{
    if (vt.hasType(ID::BLUETOOTH_DEVICE))
    {
        ...
    }
    else if (vt.hasType(ID::SERVICES_DISCOVERED))
    {
        ...
    }
    else if (vt.hasType(ID::CHARACTERISTIC))
    {
        if (juce::Uuid(vt.getProperty(ID::uuid).toString()) == HeartRateCharacteristicUuid)
            genki::message(vt, ID::ENABLE_NOTIFICATIONS);
    }
};