Serial Bluetooth Terminal on Linux

In this article we will look at how to establish a serial connection with devices via bluetooth .

Device Pairing

We need to pair the device before starting the communication

You can pair the device using standard bluetooth GUI utilities or command line utilties.In this article we will look at command-line utilities to do so.

[BlueZ](https://apps.ubuntu.com/cat/applications/bluez/) is the official Linux Bluetooth protocol stack This package contains tools and system daemons for using Bluetooth devices.

• Install this package on your system.

sudo apt-get install bluez bluez-tools

• Get the Bluetooth adapter details on linux

The hciconfig command gives the Bluetooth adapter details.

#hciconfig
hci0:	Type: BR/EDR  Bus: USB
	BD Address: 18:F4:6A:DE:EB:9D  ACL MTU: 1021:8  SCO MTU: 64:1
	UP RUNNING PSCAN ISCAN 
	RX bytes:2492 acl:3 sco:0 events:99 errors:0
	TX bytes:1421 acl:2 sco:0 commands:82 errors:0

hci0 is out bluetooth adapter name .

• Get the Bluetooth device Mac Address

The hcitool scan command gives us the bluetooth device mac address and name

hcitool scan
Scanning ...
	98:D3:31:30:1A:BA	HC-05

98:D3:31:30:1A:BA is the mac address of HC-05 bluetooth module

• Pairing the devices

bluez-simple-agent utility can be used to pair to the device with mac address 98:D3:31:30:1A:BA using the adapter hci0

bluez-simple-agent hci0 98:D3:31:30:1A:BA
RequestPinCode (/org/bluez/3772/hci0/dev_98_D3_31_30_1A_BA)
Enter PIN Code: 1234
Release
New device (/org/bluez/3772/hci0/dev_98_D3_31_30_1A_BA)

To remove a paired device enter the command

bluez-simple-agent hci0 98:D3:31:30:1A:BA remove

RFComm communication protocol

RF Comm protocol handles the transmission of information and control commands from one communication device to another communication device (such as from a computer to an accessory device) that is performed serially (one bit at a time).

The Bluetooth system uses radio frequency communication (RFComm) protocol to setup and coordinate the transfer of serial data.

RFCOMM is intended to cover applications that make use of the serial ports of the devices in which they reside.In the present application the Bluetooth Device used is HC-05 which communicates using UART protocol with devices.

RFCOMM only allows one connected client per channel and supports up to 60 simultaneous connections between two BT device

• Configure Rfcomm First Step is to configure the rfcomm module on linux to communicate with our Bluetooth module

In /etc/bluetooth/rfcomm.conf file make the following entry

rfcomm0 {
        bind no;
        device 98:D3:31:30:1A:BA;
        channel 1;
        comment "Serial Port";
        }
        

98:D3:31:30:1A:BA is the mac address of our device.

The “bind no” is important, otherwise it will try to automatically bind to device and not when the user wants.

• Start the connection

Type the command sudo rfcomm connect 0 to start the communication

#sudo rfcomm connect 0
Connected /dev/rfcomm0 to 98:D3:31:30:1A:BA on channel 1
Press CTRL-C for hangup

This will also create a serial device file /dev/rfcomm0 ,though which we can communicate with the bluetooth device.

If you have errors, restart the bluetooth service and enter the above command again

Communication with Bluetooth Device

User graphical serial terminal like CuteCom

use the /dev/rfcomm0 device to communicate with the bluetooth device.

You can send and receive commands in ASCII or HEX format via serial terminal interface.

Various bluetooth devices will correspond to different serial device files though which we can communicate with them.