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Programming for Bluetooth
By Anurag Phadke

With more and more computing devices featuring Bluetooth connectivity, it's about time you provide some serious thought to programming for Bluetooth devices. Here are some snippets of code that will get you started

As per expert estimates, come 2002 and over 100 million mobile phones and mobile computing devices all over the world will be Bluetooth enabled. What we all are striving for today is a world without wires, full of various frequencies establishing connection between various handheld devices. Though, Captain John Lu Picard's Starship seems to be somewhere in the distant future, Bluetooth and the SIG developers are certainly moving at warp speed to turn some of the futuristic sci-fi fantasies into reality.

Using a 2.4GHz ISM frequency band Bluetooth targets mainly small mobile devices that require very little power to sustain. The technology is much similar to our TV Remote Control using IR (Infra Red Rays) or our cordless phones that use a particular frequency. Also, this technology is well accepted as an industry standard with companies such as Nokia, Motorola, Toshiba, etc developing products based of this wireless connectivity platform.

So, what actually does a Bluetooth device comprise of? Does it make use of any programming language? To understand Bluetooth is to understand its architecture.

Bluetooth System Architecture
The Bluetooth Architecture comprises of a number of layers interlinked to one another.

Radio stack at the bottom of the layer is the interface responsible for the physical connection. Baseband and Link Manager protocol (LMP) are used to establish control links between bluetooth devices. The firmware/hardware comprises of three layers, the Host Control Layer is used to interface the Bluetooth hardware to the upper L2CAP (Logical Link Control and Adaptation Control Protocol). Presence of host controller is a requisite only if L2CAP resides in software in host. (Read Bluetooth: Connectivity without wires for details on various layers in the Bluetooth Stack)

Get down to coding
Once you have familiarized yourself with the different layers in the Bluetooth stack and their functionality, you can make use of the various stacks and then build your own customized programs. Stacks are like functions/programs created by other programmers and prove helpful as it does away with the need for tedious redundant programming. They are similar to #include files that come with "C" language.

Lets begin with a small program in ActiveX used for finding various Bluetooth enabled devices in the vicinity of 10m. Once a device is found it is assigned a value and then functions such as File Transfer, Viewing Directory Contents and other similar things can be performed.

Used to convert a byte into a HEX string with zero padding

Option Explicit
'Global Variable
Dim intCmdresult As Integer
Function ByteHex(ByVal byteI As Byte) As String
ByteHex = Hex(byteI)
If Len(ByteHex) < 2 Then
ByteHex = "0" & ByteHex
End If
End Function
Opening the Com Port for Communication.
Function OpenComPort()
objBT.ComPort = 2 'Opens COM2 port
objBT.ComPortBaudrate = 3 'Baud Rate of 57600
Call objBT.API_OpenComPort(intCmdresult)
If (intCmdresult < 0) Then

MsgBox ("Could not open com port no 2. If this is not the port number your device is connected to, connect it to com port number 2 or open the visual basic project and change the com port number to the correct one, then recompile the project. (error: " & intCmdresult & ")")

End If

End Function

The following code is used to start a stack. Once a stack is started it needs to be reset and then initialized before

further use.

Function StartStack()

'Start the Bluetooth stack

Call objBT.API_StartStack(1, intCmdresult)

If (intCmdresult < 0) Then

MsgBox ("Could not start the stack. (Internal Error: " & intCmdresult & ")")

End If

End Function

Function ResetStack()

'Reset the Bluetooth stack

Call objBT.API_Reset(intCmdresult)

If (intCmdresult < 0) Then

MsgBox ("Could not reset the stack. You probably do not have a bluetooth module connected to this PC. (error: " & intCmdresult & ")")

End If

End Function

Function InitStack()

'Initialise the Bluetooth stack

Call objBT.API_Init(intCmdresult)

If (intCmdresult < 0) Then

MsgBox ("Could not initialise the stack. (Internal Error: " & intCmdresult & ")")

End If

End Function

Function AllowScan()

'Variables

Dim byteSwitch As Byte

byteSwitch = 3

'Request scanning to be enabled

Call objBT.WriteScanEnable_Issue(byteSwitch, intCmdresult)

intCmdresult = -24

Do While intCmdresult = -24

Call objBT.WriteScanEnable_Result(intCmdresult)

Loop

'if the WriteScanEnable failed

If intCmdresult <> 0 Then

MsgBox ("Scanning not enabled on your device, others module will not be able to see you (error: " & intCmdresult & ")")

End If

End Function

Private Sub Form_Load()

'The following functions:

'OpenComPort(), StartStack(), ResetStack(), InitStack()

'AllowScan() are used to get the bluetooth device ready to

'communicate. those functions are defined in GENERAL

Call OpenComPort 'Open communication port

'If com port open

If intCmdresult = 0 Then

Call StartStack 'Start Stack

End If

'If the stack started well

If intCmdresult = 0 Then

Call ResetStack 'Reset Stack

End If

'If the module has been reset succesfully

If intCmdresult = 0 Then

Call InitStack 'Init Stack

End If

'If the module has been initialised sucessfully

If intCmdresult = 0 Then

Call AllowScan 'Allow this device to be visible

End If

End Sub

Once the bluetooth devices are properly initialized, the program can then be made to search for various devices in the 10m range. If found, a low '0' is generated else a high '1' is generated.

Private Sub Button_Search_Click()

'Command to search for Bluetooth devices within range

'of the locally connected device. This function

'send out a general enquiry and then waits for

'responses from bluetooth devices. All replies

'are then added to the list box for display.

'this define standard lap (Lower Address Part) values

'those values should be recognised by any bluetooth device

Dim byteLap(3) As Byte

byteLap(0) = &H33

byteLap(1) = &H8B

byteLap(2) = &H9E

'other useful variables

Dim intI, intJ As Integer

Dim strBDAddr As String

Dim varNumResps As Variant

Dim varBDAddrs As Variant

'These variables are used by the function

'Inquiry_Result_Event()

Dim varPSRModes As Variant

Dim varPSPModes As Variant

Dim varPSModes As Variant

Dim varCoDs As Variant

Dim varClkOffsets As Variant

'clear the listbox of previous results

SearchResultListBox.Clear

'Send a general enquiry so that any bluetooth

'device in the area will respond.

Call objBT.Inquiry_Issue(byteLap, 3, 0, intCmdresult)

If (intCmdresult < 0) Then

MsgBox (" error = " & intCmdresult)

End If

'We now wait for the result from our enquiry and

'also for the replies from any bluetooth device

'in the area.

intCmdresult = -24

Do While intCmdresult = -24

Call objBT.Inquiry_Result(varNumResps, intCmdresult)

DoEvents

Loop

'the inquiry is finished, all other

'devices have responded, or the inquiry

'was cancelled or there was an error

If (intCmdresult < 0) Then

If (intCmdresult = -18) Then

MsgBox (" Inquiry cancelled ")

Else

MsgBox (" error = " & intCmdresult)

End If

Else

'populate listbox with information about the devices

'get the information about every present device

intCmdresult = 0

Do While intCmdresult <> -24

Call objBT.InquiryResult_Event(varNumResps, _

varBDAddrs, varPSRModes, _

varPSPModes, varPSModes, _

varCoDs, varClkOffsets, _

intCmdresult)

'if we have received data accurately

'we add the bluetooth addresses of the

'devices detected to the listbox after

'converting them to hexadecimal format

If intCmdresult = 0 Then

'for every bluetooth device found, add them in the

list box

For intI = 0 To varNumResps - 1

'set bluetooth address to nothing

strBDAddr = ""

'the bluetooth address is returned

'its format is a bidimensionnal array (x,6)

'we convert every byte to hexadecimal

'then we concatenate every 6 bytes

For intJ = 0 To 5

strBDAddr = strBDAddr & ByteHex(varBDAddrs(intI, intJ))

Next intJ

'we add the result to the list box

SearchResultListBox.AddItem strBDAddr

Next intI

End If

Loop

End If

End Sub

Once a device is found, it can be completely controlled by the above mentioned code. This helps us to achieve wireless communication between two or more PC's or laptops making the task of connecting various wires a hassle free experience.

Anurag Phadke can be reached at cbca@mantraonline.com

Testing your code
Be sure that your Bluetooth device is connected to COM1 port. Start the program and click on Search. The device shall now attempt to search for other Bluetooth-enabled devices in the vicinity of 10m. On a successful attempt of finding a similar device, the corresponding "6-byte" (or 12 digit) address (in HEX format) of the "found" device is displayed on the screen. To find more devices, press refresh. This shall show you the address of the local Bluetooth device in succession to the other devices found.

(The program listed above performs the basic function of finding Bluetooth devices. To perform File Operations there's another program which over 1000 lines and reproducing it in the magazine is not a viable option).