GATTCCharacteristic

The smallest concept in GATT is the Characteristic, which encapsulates a single data point (though it may contain an array of related data, such as X/Y/Z values from a 3-axis accelerometer, longitude and latitude from a GPS, etc.).

The following class allows you to manage characteristics from a Client.

Methods

characteristic.uuid()

Returns the UUID of the service. In the case of 16-bit or 32-bit long UUIDs, the value returned is an integer, but for 128-bit long UUIDs the value returned is a bytes object.

characteristic.instance()

Returns the instance ID of the service.

characteristic.properties()

Returns an integer indicating the properties of the characteristic. Properties are represented by bit values that can be OR-ed together. See the constants section for more details.

characteristic.read()

Read the value of the characteristic, sending a request to the GATT server. Returns a bytes object representing the characteristic value.

characteristic.value()

Returns the locally stored value of the characteristic without sending a read request to the GATT server. If the characteristic value hasn’t been read from the GATT server yet, the value returned will be 0.

characteristic.write(value)

Writes the given value on the characteristic. For now it only accepts bytes object representing the value to be written.

characteristic.write(b'x0f')

characteristic.callback(trigger=None, handler=None, arg=None)

This method allows to register for notifications on the characteristic.

• trigger can must be Bluetooth.CHAR_NOTIFY_EVENT.
• handler is the function that will be executed when the callback is triggered.
• arg is the argument that gets passed to the callback. If nothing is given, the characteristic object that owns the callback will be used.

characteristic.read_descriptor(uuid)

Returns the value of the descriptor specified by the uuid parameter. If no descriptor found for the characteristic returns None.

descriptor = char.read_descriptor(0x2900)
if(descriptor != None):
    print("Characteristic Extended Properties: " + str(binascii.hexlify((descriptor))))

descriptor = char.read_descriptor(0x2901)
if(descriptor != None):
    print("Characteristic User Description: " + str(binascii.hexlify((descriptor))))

descriptor = char.read_descriptor(0x2902)
if(descriptor != None):
    print("Client Characteristic Configuration: " + str(binascii.hexlify((descriptor))))

descriptor = char.read_descriptor(0x2904)
if(descriptor != None):
    print("Characteristic Presentation Format: " + str(binascii.hexlify((descriptor))))