Pencom - Visual Basic for Application Serial Port Software API Example

Visual Basic for Applications API Serial Port Software Example

We will continue the serial port control demonstration using the windows API functions. We only need the CommIO.bas file to continue this demonstration, unpack this file in a blank directory so it will be easy to find. Our screen should look like the following picture, with a blank user form loaded.

Note: as stated before this example is tailored to the first time Visual Basic for applications user, but the information is useful for the advanced user that is unfamiliar with serial port control. Click here if you're familiar with VBA and want to jump directly to the code segment.

Click on the command button icon in the tool box (rectangular box) and place two buttons on the user form. Click on CommandButton1 and the options will appear in the properties window. Click to the right of the Caption in the properties window and change commandButton1 to "All Relays ON". Click on the commandButton2 or select this name from the pull down at the top of the properties window, and change this to read "All Relays OFF" as shown in the picture below.

Right Click in the Project window, select >> Import File... >> and navigate to the CommIO.bas file. Click OK to add this file to the project window. If you expand the tree by clicking on the + box you will see that the modCOMM module is loaded, as shown below.

From the menu at the top of the Visual Basic for Applications screen select View >> Code or press F7, and a code window will be displayed where the form currently resides. Click in the following box and select the contents of the box by holding the left mouse button and dragging down over the contents. Hold the Ctrl Button down and press "C'' to copy the contents to the clipboard.

'Set up variables Public intPortID As Integer ' Ex. 1, 2, 3, 4 for COM1 - COM4 Public lngStatus As Long Public strError As String Public strData As String 'Transmit/receive variable Private Sub CommandButton1_Click() 'Send data to serial board to turn ON Relays strData = "A" + "H" + "0" + Chr$(13) 'set strData variable to AH0<cr> ' Write data to serial port. lngSize = Len(strData) lngStatus = CommWrite(intPortID, strData) If lngStatus <> lngSize Then ' Handle error. 'Place error handler in your software here End If End Sub Private Sub CommandButton2_Click() 'Send data to serial board to turn ON Relays strData = "A" + "L" + "0" + Chr$(13) 'set strData variable to AL0<cr> ' Write data to serial port. lngSize = Len(strData) lngStatus = CommWrite(intPortID, strData) If lngStatus <> lngSize Then ' Handle error. 'Place error handler in your software here End If End Sub Private Sub UserForm_Initialize() 'Initialize serial port when form is loaded 'Set to Com Port #1 intPortID = 1 ' Initialize Communications baud=9600 parity=N data=8 stop=1 lngStatus = CommOpen(intPortID, "COM" & CStr(intPortID), _ "baud=9600 parity=N data=8 stop=1") If lngStatus <> 0 Then ' Handle error. lngStatus = CommGetError(strError) MsgBox "COM Error: " & strError End If End Sub Private Sub UserForm_Terminate() 'Close serial port on form exit (X on userform) Call CommClose(intPortID) End Sub

Switch to Visual Basic for Applications and click inside the code window and highlight any information in this window -- press Ctrl "V" to paste the contents into the code window. The window should now look like the following picture.

That's all the code that is required to turn all the relays ON and OFF on our relay boards, it will work on the 1, 2 & 8 Channel relay boards. Select File >> Save Book1 from the pull down menu to save your project before you attempt to run the program.

All that's left to do is run our program, but first make sure the relay board is connected to com1 on the the back of your computer using the 9 pin serial to modular cable adapter. Connect the modular cable from the adapter to the input of the relay board. Plug the wall transformer cable into the board and the wall transformer into the wall receptacle or apply power to the board if your using the internal transformer version.

Assuming that everything is connected up properly, press the blue right arrow at the top of the screen and our program will run. To stop the program click the box on the top right of the user form, DO NOT close the program using the blue square box in the VBA editor. If you would close the program using the blue box the serial port will not be closed properly and it will not operate correctly if you would restart the program.

The running program is shown below.

Click the "All Relays ON" button and you will hear an audible click from the relays that is turning them ON and pressing the "All Relays OFF" button will turn them OFF.

Congratulations on your first Visual Basic For Applications control program using the Windows API. We're sure you will find many practical applications for using your RS232 serial controlled relay board.

If you have any other questions you may contact the support dept at or you may request information using our feedback form.

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