Make Bluetooth Connections

Make Bluetooth Connections

Create a personal-area Bluetooth network to exchange files, send messages, and share network connections.

Bluetooth allows you to create short-range (usually 10-meter), low-bandwidth (1-2 megabits per second), ad hoc connections between devices. It's ideal for sending photos from your camera phone to your computer, or for using the wireless modem found in certain models of cell phones.

To get started with Bluetooth, first make sure it's working. Some computers have built-in Bluetooth adapters. If you are using an external USB Bluetooth dongle, after you insert it you may need to run this command to reset the Bluetooth Host Controller Daemon:

$ sudo killall -HUP hcid
         

Now, to make sure Bluetooth is really up and running, you need to make sure you have at least one device in the vicinity that is set as "discoverable" (this is a Bluetooth mode that allows devices to find one another). Check your device documentation for details on how to set discoverable mode.

Some devices allow you turn on discoverable mode only for a limited time (for example, two minutes). So, make sure you execute the next command quickly. The hcitool utility lets you manage Bluetooth connections. Run the command hcitool scan to enumerate the discoverable devices in your vicinity. Here, hcitool has found three devices (my Nokia 3650 cell phone, my Mac, and my Palm Treo):

bjepson@scoobuntu:~$ hcitool scan
Scanning ...
        00:60:57:50:AB:9C       BrianJ3650
        00:14:51:89:4D:C7       Jepstone
        00:07:E0:6A:FE:54       bjepson

Pairing

Now that you know Bluetooth is working, you can pair your Ubuntu system with one of the devices. Pairing creates a bond between the devices so that they can exchange data and connect to one another.

First, initiate pairing from the device you want to use. Each device is different. On the Treo, for example, you need to tap the Bluetooth icon and click Setup DevicesAdd Device. Figure shows my Palm Treo discovering several computers, including scoobuntu-0, my Ubuntu system. Select your Ubuntu system and tap OK. When prompted for your passkey, pick something at random. A dialog should pop up on your Ubuntu system asking for the passkey. Type the same thing into that dialog and click OK.

Palm Treo discovering nearby Bluetooth devices

Manual Pairing

If that dialog doesn't appear, you will need to take matters into your own hands. Cancel the pairing procedure on your device (or wait for it to time out), and go back to your Ubuntu system. Edit /etc/bluetooth/pin (you need to use sudo to edit this, as in sudo vi /etc/bluetooth/pin) and change the PIN code there to the PIN you want to use as the one-time password for pairing devices (some devices allow only numeric PINs).

Next, create a script called /usr/local/bin/bluepincat and make it executable:

#!/bin/sh
# file: /usr/local/bin/bluepincat

echo -n "PIN:" 
cat /etc/bluetooth/pin

Comment out the existing pin_helper line in /etc/bluetooth/hcid.conf (again, you need to use sudo to edit this file) and add the following:

pin_helper /usr/local/bin/bluepincat;

Next, reset the hcid daemon with sudo killall -HUP hcid and try to initiate pairing from your device again, this time using the PIN code that you put into /etc/bluetooth/pin as the passkey. Once you're done pairing devices, you should restore the original configuration and reset the hcid daemon again (this avoids the possibility of someone guessing your PIN and pairing with your computer without your knowledge or consent).

Bluetooth File Transfer

Suppose you have something on your cell phone, such as a photo you took, that you want to send to your computer. If you install the obexserver package, you can receive files sent over Bluetooth:

$ sudo apt-get install obexserver
            

To receive files, you need to register the OBEX (Object Exchange) push service. This needs to be done each time you restart your computer (or the Bluetooth subsystem):

$ sdptool add --channel=10 OPUSH
OBEX Object Push service registered

Now, when you want to receive a file, start the obexserver and send the file from the other device. The obexserver will terminate after the transfer:

$ obexserver
Waiting for connection...

...............................................................
...............................................................
...............................................................
...............................................................
...................................................HEADER_LENGTH = 307254
put_done() Skipped header 05
put_done() Skipped header 42
put_done() Skipped header c0
Filename = screenshot0000.bmp
Wrote /tmp/screenshot0000.bmp (307254 bytes)

$

Connect to the Internet

Many Bluetooth phones, including certain Treo models as well as many Nokia and Sony Ericsson phones, can act as a gateway between your computer and the Internet. In this configuration, the phone is commonly thought of as a "wireless modem," but in fact, the connection between your computer and the Internet is digital all the way. Still, because this configuration uses the same protocol (PPP) as most dial-up connections, it's easy and sometimes helpful to just think of it as a modem.

Before you try this, you need to contact your wireless provider to find out whether this service is supported and how much it will cost you. Some providers, such as T-Mobile in the U.S., have inexpensive flat-rate pricing of between $20 and $50 a month, depending on your level of service. But most providers will charge you by the kilobyte if you don't have a data plan on your account. If you're not totally clear on how much it will cost, be careful, since cellular bills of hundreds or even thousands of dollars are not unheard of, especially when you throw international roaming into the mix!

To make the connection, you first need to set up a link between your Ubuntu system and the paired device. Edit (using sudo) /etc/bluetooth/rfcomm.conf and add an entry for your device. You'll need to specify your phone's device ID (which you can get with hciutil scan, as shown earlier):

rfcomm0 {
  bind yes;
    # Bluetooth address of the device
    device 00:07:E0:6A:FE:54;
    # RFCOMM channel for the connection
    channel     1;
    # Description of the connection
    comment "My Treo";
}

Next, edit /etc/bluetooth/hcid.conf (using sudo), scroll to the bottom, and uncomment the auth and encrypt lines so they look like this:

    # Authentication and Encryption (Security Mode 3)
    auth enable;
    encrypt enable;

Then, run the command sudo killall -HUP hcid to reset the hcid daemon.

Next, use the command sudo rfcomm bind rfcomm0 to make the connection. Now you've got a modem you can use on /dev/rfcomm0. Next, you need to create some PPP scripts. The first one is a chat script. As root, create /etc/chatscripts/BluetoothPhone. You will need to replace APN with the Access Point Name that your cellular provider uses (contact your cellular provider to get this information, or check Opera's list of APNs at http://www.opera.com/products/mobile/docs/connect/):

TIMEOUT 10
ABORT   'BUSY'
ABORT   'NO ANSWER'
ABORT   'ERROR'
SAY     'Starting GPRS connect script\\n'

# Get the modem's attention and reset it.
""      'ATZ'

# E0=No echo, V1=English result codes
OK      'ATE0V1'

# Set Access Point Name (APN)
SAY     'Setting APN\\n'
OK  'AT+CGDCONT=1,"IP","APN"'

# Dial the number
ABORT   'NO CARRIER'
SAY     'Dialing...\\n'
OK      'ATD*99***1#'
CONNECT ''

The next is /etc/chatscripts/BluetoothPhone-Disconnect:

""      "\\K" 
""      "+++ATH0" 
SAY     "GPRS disconnected." 

Finally, you need a PPP peers script (/etc/ppp/peers/BluetoothPhone):

/dev/rfcomm0  # Bluetooth modem
115200        # speed
defaultroute  # use the cellular network for the default route
usepeerdns    # use the DNS servers from the remote network
nodetach      # keep pppd in the foreground
crtscts       # hardware flow control
lock          # lock the serial port
noauth        # don't expect the modem to authenticate itself
local         # don't use Carrier Detect or Data Terminal Ready
replacedefaultroute
debug

# Use the next two lines if you receive the dreaded messages:
#
#    No response to n echo-requests
#    Serial link appears to be disconnected.
#    Connection terminated.
#
lcp-echo-failure 4
lcp-echo-interval 65535

connect "/usr/sbin/chat -V -f /etc/chatscripts/BluetoothPhone" 
disconnect "/usr/sbin/chat -V -f /etc/chatscripts/BluetoothPhone-Disconnect"

With all these scripts in place and your rfcomm device connected using rfcomm bind, run the command sudo pppd call BluetoothPhone to connect to the Internet anywhere you have cellular service. When you are done, press Ctrl-C to terminate the connection.

For more information on working with cellular data connections and Bluetooth, see Linux Unwired by Roger Weeks et al. (O'Reilly).

Brian Jepson