Nuts & Volts - July 2005

Project

ing time is spent here during its execution. Listing 2 is the routine that is called when a character is received into the serial buffer of the computer from the interface board. After the computer tells the interface board to begin analyzing, the interface board starts to send data samples to the computer. Every data sample received is handled by the routine in Listing 2.

Listing 2 is an event procedure that is associated with a control called “CommX1.” CommX1 provides the means for your VB program to use the serial port of the computer for communication. CommX1 is a third party tool that does not come with VB and must be added to the programming environment before it can be used. VB comes with its own Comm Control, but it is only available with the more expensive versions of the program. The VB “learning addition” is what most beginners start out with, but does not have this needed tool. One of the nice fea-

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NUTS & VOLTS E v e r y t h i n g

tures of VB though, is that it’s designed to support programming tools from other vendors. Lucky for us CommX1 can be downloaded for free from MCS Electronics so that even the beginner versions of VB can be used to develop some respectable control applications.

After the computer starts the analyzing process by sending the proper control word to the interface board, it waits until a data value is received at the serial port and then processes it. Note.1 of Listing 2 is where the serial data is retrieved and stored at variable “volt.” Between note.1 and note.2, the ASCII data from the interface board must be converted into a numeric value so a voltage level can be calculated from the ADC value. Once a voltage value is obtained, it is displayed on the computer monitor.

Between note.2 and note. 3, the voltage data is used to calculate where to plot the voltage measurement on the graph. The program uses the default VB unit of screen measurement called “twips.” Each vertical volt designation is equal to 500 twips of resolution. The discharge graph time resolution is in the horizontal direction or X plot position, while the voltage measurement is in the vertical direction or Y plot position. If the voltage measured is five volts, the Y plot position will be 2,500 twips up from the zero level.

Between note. 4 and note. 5, the program will set the first X plot point at the zero time designation and the Y plot point will depend on the voltage value.

Between note. 5 and note. 6 is where the graph gets drawn by calculating a Y plot point (voltage) from each measurement, moving the X plot point (time) a defined number of twips to the right, and then connecting the plot points using the line method. This will continue until it reaches the end of the graph, is stopped by the user, or falls below the cut-off voltage. This section of code is also responsible for filling a table with voltage values that can be printed for record keeping (more on this later).

Code between note. 6 and note. 7 is executed when plotting reaches the end of the graph or the battery voltage falls below the cut-off level. The program will then halt testing by sending the “stop” command to the interface board and closing the serial connection.

Listing 2. VB Serial Communications sub-routine.

Private Sub CommX1_OnReceive(ByVal DATA As String)
Dim volt As Integer
Dim volt2 As Single
Dim volt3 As String
Dim volt4 As Single
Dim volt5 As Integer
Static x As Integer
volt = Val(DATA)                              ‘**NOTE 1**
volt2 = (volt * 0.004888) * (2)
volt3 = Str(volt2)
volt3 = Left$(volt3, 5)
Label28.Caption = volt3
volt4 = Val(volt3)                            ‘**NOTE 2**
volt5 = volt4 / 0.01  ‘convert to twips
volt5 = volt5 * 5    ‘1volt=500 twips         ‘**NOTE 3**
If check = 0 Then                             ‘**NOTE 4**
    Form1.CurrentX = 1000
    Form1.CurrentY = 6000 - volt5
    check = 1
Else                                         ‘**NOTE 5**
     vertical = 6000 - volt5
     Line -(Form1.CurrentX + 50, vertical)
     MDIForm1.frm.grdTable.Row = Tr
     MDIForm1.frm.grdTable.Col = Tc
     MDIForm1.frm.grdTable.Text = volt3
     Tr = Tr + 1
     If Tr = 13 Then
        Tc = Tc + 1
        Tr = 1
     End If
     x = x + 1
     If x = 120 Then                         ‘**NOTE 6**
        x = 0
        CommX1.SEND “Stop” + Chr(13)
        CommX1.Close
        Command2.Enabled = False
        Command3.Enabled = False
        MDIForm1.mnuPrint.Enabled = True
        Form1.Caption = Format$(Now, “mmmm dd yyyy h:mm a/p”)
        MDIForm1.frm.Caption = Format$(Now, “mmmm dd yyyy h:mm a/p”)
        MDIForm1.frm.grdTable.Enabled = False
        Label36.Caption = “STOPPED”
        Label36.ForeColor = &HFF&
        Exit Sub
     End If
End If
If (volt4 < Cutoff) Or (volt4 = Cutoff) Then    ‘** NOTE 7**
    Call Command3_Click
End If
End Sub