CODEWITHSUNDEEP
androidbluetooth
N0xus
N0xus

Reputation: 2724

Finding out Android Bluetooth LE GATT Profiles

I've implemented the Android LE bluetooth example that find a heart rate monitor and connects to it. However, this example has a class that defines the GATT profile like this:

 private static HashMap<String, String> attributes = new HashMap();
public static String HEART_RATE_MEASUREMENT = "00002a37-0000-1000-8000-00805f9b34fb";
public static String CLIENT_CHARACTERISTIC_CONFIG = "00002902-0000-1000-8000-00805f9b34fb";

static {
    // Sample Services.
    attributes.put("0000180d-0000-1000-8000-00805f9b34fb", "Heart Rate Service");
    attributes.put("0000180a-0000-1000-8000-00805f9b34fb", "Device Information Service");
    // Sample Characteristics.
    attributes.put(HEART_RATE_MEASUREMENT, "Heart Rate Measurement");
    attributes.put("00002a29-0000-1000-8000-00805f9b34fb", "Manufacturer Name String");
}

public static String lookup(String uuid, String defaultName) {
    String name = attributes.get(uuid);
    return name == null ? defaultName : name;
}

Now, what I'm wanting to do is change it so that this program finds any device with bluetooth le but I have no idea how Google have gotten the information for the heart rate measurement of the client characteristic config.

Upvotes: 19

Views: 38937

Answers (3)

Godfrey Duke
Godfrey Duke

Reputation: 1545

The Bluetooth SIG maintains a list of "Assigned Numbers" that includes those UUIDs found in the sample app: https://www.bluetooth.com/specifications/assigned-numbers/

Although UUIDs are 128 bits in length, the assigned numbers for Bluetooth LE are listed as 16 bit hex values because the lower 96 bits are consistent across a class of attributes.

For example, all BLE characteristic UUIDs are of the form:

0000XXXX-0000-1000-8000-00805f9b34fb

The assigned number for the Heart Rate Measurement characteristic UUID is listed as 0x2A37, which is how the developer of the sample code could arrive at:

00002a37-0000-1000-8000-00805f9b34fb

Upvotes: 89

BoD
BoD

Reputation: 11035

In addition to @Godfrey Duke's answer, here's a method I use to extract the significant bits of the UUID:

private static int getAssignedNumber(UUID uuid) {
    // Keep only the significant bits of the UUID
    return (int) ((uuid.getMostSignificantBits() & 0x0000FFFF00000000L) >> 32);
}

Example of usage: 

    // See https://developer.bluetooth.org/gatt/services/Pages/ServiceViewer.aspx?u=org.bluetooth.service.heart_rate.xml
    private static final int GATT_SERVICE_HEART_RATE = 0x180D;

    (...)

        for (BluetoothGattService service : services) {
            if (getAssignedNumber(service.getUuid()) == GATT_SERVICE_HEART_RATE) {
                // Found heart rate service
                onHeartRateServiceFound(service);
                found = true;
                break;
            }
        }

Upvotes: 7

jnewt
jnewt

Reputation: 217

Here's the page on the gatt callback: https://developer.android.com/reference/android/bluetooth/BluetoothGatt.html

You need to use the BluetoothGatt.discoverServices();

and then in the callback onServicesDiscovered(...) i think you need to useBluetoothGatt.getServices();

Upvotes: -3

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