Raspberry Pi Bluetooth Connection

Raspberry Pi 3 provides a built-in Bluetooth module. The latest Raspbian has been bundled with tools for enabling Bluetooth connection. The Bluetooth icon will be shown up on the top right corner of the desktop. It's a tool to discover available Bluetooth devices and connect Pi with Bluetooth devices. It is easy to connect any Bluetooth-enabled electronic device with Pi. But, sometimes Pi will fail to connect, especially for Bluetooth device that has no standardized services.

From a terminal, we can use the bluetoothctl tool to scan and connect with a Bluetooth device. You should make sure that the BlueZ protocol stack has been installed by running $ apt-get install bluez

1. Run bluetoothctl to enter the tool command window
2. Turn the power on by running power on
3. (Optional) You can set AutoEnable=true in /etc/bluetooth/main.conf if you want to make the Bluetooth auto power-on after reboot.
4. Run devices to see which devices have been paired
5. Run scan on if your desired device has not been paired yet.
6. Run agent on
7. Run pair <mac_address> to start pairing. Then, you need to enter the device PIN if it's needed.
8. Run trust <mac_address> manually if the device has no PIN.
9. Run connect <mac_address> to establish a connection.

The last step can fail for certain devices. I also failed to connect my Pi with my Arduino with the HC-06 Bluetooth module. If you use the GUI tool for Bluetooth, it may show you a notification message, "Connection failed: No usable services on this device". If you use the CLI tool (bluetoothctl), it may show you an error message, "Failed to connect: org.bluez.Error.NotAvailable". For the solution, you can try the following steps.

1. Edit the Systemd configuration of the Bluetooth service by:

   $ sudo nano /etc/systemd/system/dbus-org.bluez.service

2. Add compatibility flag "-C" and create a serial port profile. Find and edit or insert these lines.
   

   ExecStart=/usr/lib/bluetooth/bluetoothd -C
   ExecStartPost=/usr/bin/sdptool add SP

3. Save and reboot your Pi then run again previous steps for pairing Bluetooth device using bluetoothctl.
4. After the device is paired, you can run sudo rfcomm watch hci0 or sudo rfcomm connect 0 <mac_address> 1. This command will create an access channel in /dev/rfcomm0.
5. On another terminal, you can run rfcomm to see any created connection.

Finally, you can listen to /dev/rfcomm0 and send data through this channel using any tool like picocom by running $ sudo picocom -c /dev/rfcomm0.

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