btzen

BTZen is a library to asynchronously access Bluetooth devices using Python language. It provides simple API over complex D-Bus Bluez interface.

Features

The main features of BTZen are

• Connect and access multiple Bluetooth devices in parallel with Python asynchronous coroutines.
• GATT notification interface integrated into main API of the library.
• Automatic reconnections to devices.
• Access to serial devices implementing Stollmann (Telit) protocol.
• Support for devices, which do not follow the Bluetooth specification fully like SensorTag (CC2650STK) or Thingy:52.
• Support for Bluez managed interfaces of devices, i.e. battery level.
• Allow to implement support for new devices easily.

The library can be used with any Bluetooth Smart device. It was tested with

• SensorTag (CC2650STK) to read temperature, pressure, humidity, light, accelerometer data and state of the buttons.
• Thingy:52 to read temperature, pressure, humidity, light data and state of the button.
• Mi Smart Scale to read weight data.
• OSTC dive computer to read serial device data using Stollmann (Telit) protocol.

The library is tested with default asyncio event loop and its drop-in replacement uvloop <https://github.com/MagicStack/uvloop>_. Use of uvloop increases performance of the library.

The scripts in scripts directory demonstrate reading data from various devices.

NOTE: The first version of SensorTag (CC2541DK) is not supported at the moment. If you still own the device and would like it to be supported, please raise an issue <https://github.com/wrobell/btzen/issues>_.

API Changes

Please note that since version 0.6.0 the API changed. The benefits are

• support different makes of devices with single API
• it is much easier to implement functionality for new devices
• shutting down of BTZen connection sessions is more reliable

If pre-0.6.0 version of BTZen is required, then use appropriate versioning in installation requirements of your project.

Documentation

This project's documentation is lacking at the moment. Some useful tips might be found in this README file and files at

https://github.com/wrobell/btzen/tree/master/doc

Installation

Use pip to install BTZen library (Cython needs to be installed first), for example::

pip install --user cython
pip install --user btzen

BTZen uses experimental API of Bluez adapter interface to connect to Bluetooth devices. The bluetoothd daemon has to be started with experimental option on. This can be permanently achieved by setting Experimental to true in /etc/bluez/main.conf file.

Change AutoEnable option to true in /etc/bluetooth/main.conf to automate powering up of Bluetooth controllers. Otherwise a controller might need to be switched on manually with bluetoothctl tool. BTZen library does not perform this operation.

Connection Management

BTZen uses ConnectDevice method of Bluez adapter interface to discover and connect to Bluetooth devices. MAC address of a device needs to be known in order to connect.

BTZen connection manager allows to connect and disconnect Bluetooth devices without restarting of an application. If an application is reading data from multiple Bluetooth devices, the application can continue working if, for example, a sensor requires battery change.

Please note

• when trying to connect to a device using BTZen library, do not start scan with other programs, i.e. bluetoothctl
• if a device is disconnected with an external program, the external program has to be used to reconnect

Obtaining MAC Address

If Bluetooth device MAC address is not known

• Start bluetoothctl.
• Start scan.
• Save discovered MAC address.
• Optionally, remove device with remove command of bluetoothctl utility.
• Start BTZen based application using the discovered MAC address.

Performance

The library enables programmers to communicate with mutliple devices in parallel without using threads. This avoids context switching of threads and minimizes memory requirements, which makes BTZen more efficient than other, similar libraries. To keep the library as fast as possible, Cython is used to access Bluez D-Bus API. BTZen can be used with uvloop for even more increased performance of an application.

Support for GATT notification interface allows efficient use of Bluetooth devices. For example, data from sensors like accelerometers can be read only when sensor wakes up and transmits data after sensor has been moved. This limits amount of transferred data and avoids draining battery of the sensor, which will happen if data is polled at regular, short intervals.

Requirements

BTZen library requires the following software components

• Python 3.11
• bluez 5.68
• sd-bus (kart of systemd)
• Cython 3.0.0

License

BTZen library is licensed under terms of GPL license, version 3, see COPYING <https://www.gnu.org/licenses/gpl-3.0.en.html>_ file for details.