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Bluetooth Connection

Exploiting the fact that on the MBot robot the USB Serial port shares its tx and rx with the bluetooth module, it is possible to setup a serial bluetooth connection that behaves exactly as the USB serial of the Arduino.

Using the standard linux tools for the bluetooth communications it is possible to connect to a bluetooth serial and setup a device /dev/rfcomm0 that behaves like a regular serial interface.

The two robots can be connected using this technique, since the lego robot runs a linux os.

Requirements

  • bluez library
  • rfcomm binary from bluez-utils or bluez-utils-compat
  • python3-pyserial for serial communication and the miniterm utility

To install all the requirements on the ev3dev linux (and every Debian-based distros):

$ sudo -i
# apt install bluez bluez-utils bluez-utils-compat python3-pyserial

Setup

Use the bluetoothctl utility to scan for nearby bluetooth devices

$ bluetoothctl
[bluetooth]# scan on

Find the Makeblock MAC address in the discovered devices and pair it

[bluetooth]# scan off
[bluetooth]# trust 00:1B:10:30:4B:17
[bluetooth]# pair 00:1B:10:30:4B:17

If you are setting up the connection directly on the lego robot, a new pop-up window should appear on the LCD display asking to accept the pairing. Once accepted the two devices are successfully paired.

The next step is to setup /dev/rfcomm0 device

# rfcomm connect /dev/rfcomm0 00:1B:10:30:4B:17
# chmod 777 /dev/rfcomm0

And test the connection

python3 -m serial.tools.miniterm /dev/rfcomm0 115200

You should have now a fully working serial console connected to the MBot robot.

To use this new device in your python scripts you can use the pyserial python module (https://pythonhosted.org/pyserial/shortintro.html#opening-serial-ports)