Basic connection between arduino and raspberry pi through Bluetooth

The hardware

• Raspberry pi 3b+ (it has inbuilt Bluetooth)
• Arduino micro
• HC-05 Bluetooth module

System requirements

• arduino-cli
• picocom
• python 3

Configurations for Bluetooth module HC-05

• Configure the module as master
• Set PIN

Configurations for Raspberry Pi

• Install and configure raspbian
• Configure python3 as default python interpreter
• Install Bluetooth packages
• Pair with HC-05 module
• Copy Bluetooth code

Configurations for arduino

• Install avr boards
• Make physical connections
• Copy arduino code and upload to arduino board

HC-05 Setup

First connect Bluetooth module to USB serial and press EN button, then send AT commands. Test AT commands in serial port from USB to serial converter. The default baud rate for AT commands is 38400

$ echo -e "AT\r" | picocom -b 38400 -qrx 1000 /dev/ttyUSB0
OK

Set with AT commands

$ echo -e "AT+NAME=ARDUINOBT\r" | picocom -b 38400 -qrx 1000 /dev/ttyUSB0
OK

Set password

$ echo -e "AT+PSWD=1379\r" | picocom -b 38400 -qrx 1000 /dev/ttyUSB0
OK

Set default baud rate

$ echo -e "AT+UART=115200,1,0\r" | picocom -b 38400 -qrx 1000 /dev/ttyUSB0
OK

Disconnect and test settings

Raspberry Pi Setup

Once installed raspbian and make the basic configurations, install Bluetooth required packages.

$ sudo apt install -y pi-bluetooth bluetooth bluez picocom blueman python3-pip

First edit Bluetooth service

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

Add the following lines

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

Reload systemd units

$ sudo systemctl daemon-reload

Enable Bluetooth service

$ sudo systemctl enable --now bluetooth

Edit the next file to load rfcomm automatically

$ sudo vi /etc/modules-load.d/modules.conf

Add the following line

rfcomm

Reboot the system

Pair with HC-05 module

Access to Bluetooth console

$ sudo bluetoothctl 

Pair with Bluetooth module

[bluetooth]# agent on
[bluetooth]# scan on
  Discovery started
  [NEW] Device 98:D3:31:50:4A:C1 98-D3-31-50-4A-C1
  [CHG] Device 98:D3:31:50:4A:C1 LegacyPairing: no
  [CHG] Device 98:D3:31:50:4A:C1 Name: ARDUINOBT
  [CHG] Device 98:D3:31:50:4A:C1 Alias: ARDUINOBT

[bluetooth]# scan off
  [CHG] Controller B8:27:EB:80:2D:06 Discovering: no
  Discovery stopped

[bluetooth]# pair 98:D3:31:50:4A:C1
  Attempting to pair with 98:D3:31:50:4A:C1
  [CHG] Device 98:D3:31:50:4A:C1 Connected: yes
  Request PIN code
  [agent] Enter PIN code: 1379
  [CHG] Device 98:D3:31:50:4A:C1 UUIDs: 00001101-0000-1000-8000-00805f9b34fb
  [CHG] Device 98:D3:31:50:4A:C1 ServicesResolved: yes
  [CHG] Device 98:D3:31:50:4A:C1 Paired: yes
  Pairing successful
  [CHG] Device 98:D3:31:50:4A:C1 ServicesResolved: no
  [CHG] Device 98:D3:31:50:4A:C1 Connected: no

[bluetooth]# trust 98:D3:31:50:4A:C1
  [CHG] Device 98:D3:31:50:4A:C1 Trusted: yes
  Changing 98:D3:31:50:4A:C1 trust succeeded

[bluetooth]# exit

Create a serial device

$ sudo rfcomm bind rfcomm0 <device's MAC>

If everything works, connect with picocom and test communication in both sides

Install pyserial library for python3

$ sudo pip3 install pyserial

Copy pythonClient dir to raspberry pi and execute client.py script

$ python pythonClient/client.py

Arduino Setup

Physical connections

Connections for HC-05 module

• GND -> GND Arduino
• VCC -> VCC Arduino
• RX -> D14 Arduino
• TX -> D15 Arduino
• EN -> N/C

Compile and upload the sketch

Upload the code to arduino board, considering serial port of arduino micro is /dev/ttyACM0

$ arduino-cli compile -b arduino:avr:micro -u -p /dev/ttyACM0 ~/WorkSpace/tutorials/rpi-arduino-bluetooth/arduinoBT-HC05

Test Communications

Raspberry pi output example

developer@raspberrypi:~ $ python pythonClient/client.py
  Enter your message below.
  Insert "exit" to leave the application.
  You message >> hi from raspberry pi
  Server Response >> hi
  
  You message >> test connection
  Server Response >> test connection from arduino
  
  You message >> exit

Arduino Output example

$ picocom -b 115200 /dev/ttyACM0
  Terminal ready
  Server response: hi from raspberry pi
  You response -> hi
  Server response: test connection
  You response -> test connection from arduino
  
  Terminating...
  Skipping tty reset...
  Thanks for using picocom