The OS on icub-head - Configure the Bluetooth

Introduction

The Bluetooth connection is used on icub-head to communicate with the battery pack (so we can check the battery in our software); it can be also used to connect a joypad to the robot. The icub-head board has an onboard BT controller and antenna, so no external dongle is required.

The BT configuration relies on hardware address, so it is to be done on each robot after you installed iCubOS.

Generic Bluetooth device configuration

This procedure shows how to pair a bluetooth device on icub-head.

Install the following packages
```
bluetooth bluez bluez-tools
```
Open Bluetooth control and search for the device
```
bluetoothctl
  scan on
```
Wait that the device address to show up, note it, then stop scanning
```
scan off
```
Trust the device using its address (replace ADDRESS with the addres you noted on point 3. )
```
trust ADDRESS
```
Pair the device using its address (replace ADDRESS with the addres you noted on point 3. ). It may prompt to enter yes to verify that the passcode is correct
```
pair ADDRESS
```
Connect the device using its address (replace ADDRESS with the addres you noted on point 3. ).
```
connect ADDRESS
```
Check status
```
devices
```
If everything is ok, the above command shows the device as PAIRED AND CONNECTED, then quit Bluetooth control
```
quit
```

The configuration is now saved into the system and the device will be connected automatically.

Battery device configuration

This procedure shows how to pair the bluetooth on icub-head with the BCB board to retrieve the battery status. The BCB board is not a standard Bluetooth device, so some additional passages are necessary.

Scan for available devices and search for the battery device. It should have the prefix RNBT.
```
hcitool scan | grep RNBT
```
After a while, you should see the BT address of the battery (it look very similar to a MAC address), please take note of it. Usually, the range of these devices is large, hence the BCB board of other robots may also be visible.
Follow the instructions from point 2 to 4 of the above section. If you attempt also point 5, you will get the following error:
```
Failed to connect: org.bluez.Error.NotAvailable
```
In fact, it is not possible to connect since the board is not compatible with BlueZ.
If the pairing went ok, the battery device should be PAIRED but not connected. Quit Bluetooth control
```
quit
```

In order to use it as a serial device, it is possible to use rfcomm. In order to check if the connection to the BCB board works, run the following command:

sudo rfcomm -r connect 0 RNBT_ADDRESS

This connects to the Bluetooth and creates a serial device named /dev/rfcomm0 in raw mode. If this test is working, the terminal should be blocked, displaying a message like

Waiting for connection on channel 0
Connection from RNBT to /dev/rfcomm0
Press CTRL-C for hangup

On the robot side, whenever we connect to the BCB board, a blue LED should light up between the "Motors" and "CPU" button. By pressing CTRL+C, the connection is interrupted.

The problem with rfcomm connect is that it keeps the connection with the Bluetooth board even when not necessary, and it is blocking for the terminal that called it. Alternatively, it is possible to use

sudo rfcomm bind 0 RNBT
sudo stty -F /dev/rfcomm0 raw

This connects to the Bluetooth only when the port /dev/rfcomm0 is opened. The second command makes sure that the port is interpreted as a raw serial port and not as TTY. After launching those commands, the /dev/rfcomm0 should be visible.

The connections made via rfcomm get reset when shutting down. In order to have them working at startup follow the next section.

Connect to the BCB board automatically

The connections made via rfcomm get reset when shutting down. In order to have them working at startup, create a system service as follows. First create the file bt-battery.service in the folder /etc/systemd/system/ as here

This service runs once the bt-battery_connect.sh script at startup after running the bluetooth service. You can find the script here, and it needs to be saved in the /etc/rc.iCub.d system folder. ⚠️ You need to change RNBT_ADDRESS with the address you noted, keeping the ".

The scripts first tries to connect using rfcomm connect. If it works (hence rfcomm connect is still alive), releases the connection. Then it tries running rfcomm bind and stty checking the outputs in case of errors. If there is any error, it tries again at most 10 times.

You can try to run this script with the command

sudo bash ~/bt-battery_connect.sh

If the connections was successfull, you should see stty successfull and the /dev/rfcomm0 should be available.

This service can be enabled at startup with

sudo systemctl enable bt-battery.service

and started with

sudo systemctl start bt-battery.service

In case there were errors starting the service, it is possible to inspect the output of the script with

systemctl status bt-battery.service

This script can also be run after startup in case the connection is not working, with

sudo bash ~/bt-bluetooth_connect.sh