Use Microsoft Office for Your Next Automation Project

David Novak — Sun, 29 Aug 2010 16:02:02 +0000

Automate with Office

If a software development platform can call a DLL, it can be used to control the Expert I/O 1000. Microsoft Office with Visual Basic for Applications (VBA) is no exception.

For most people, Office would be the last tool they would consider for PC based automation, but in some cases it might be the best. For example, you could easily log data to an Excel spreadsheet or Access database as you collect it and once it’s in these applications, it’s simple to manipulate, plot and report the data.

Office provides two big advantages.

Low start up cost.
Short learning curve.

The main advantage of Office is its low start up cost. Practically every computer in existence has Microsoft Office installed. If you don’t need the features of a full fledged software development suite, you can save a bunch of money by using a tool that is already on your computer.

The other big advantage of Office is that many people who aren’t software engineers know a great deal about VBA. It is used all the time for office automation by non-engineers. Microsoft has given us a development tool that can be used by everyone, not just geeky software engineers.

Controlling the Expert I/O using VBA in Excel is very easy. Here is the entire code of a VBA macro I created. The entire subroutine is only about a dozen lines.

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' Expert I/O API.
Declare Function eioOpen Lib "eio.dll" () As Long
Declare Function eioClose Lib "eio.dll" () As Long
Declare Function eioClaimInterfaceEz Lib "eio.dll" (ByVal ModelId As Integer, ByVal SerialNumber As Long, ByRef Handle As Long) As Long
Declare Function eioReleaseInterface Lib "eio.dll" (ByVal Handle As Long) As Long
Declare Function eioDioSetPull Lib "eio.dll" (ByVal Handle As Long, ByVal Port As Long, ByVal PullLevel As Long) As Long
Declare Function eioDioSet Lib "eio.dll" (ByVal Handle As Long, ByVal Port As Long, ByVal PinLevels As Byte) As Long
Declare Function eioDioGet Lib "eio.dll" (ByVal Handle As Long, ByVal Port As Long, ByRef PinLevels As Byte) As Long

' Constants
Const MODEL_ID As Integer = 1
Const SERIAL_NUMBER As Long = 99
Const INPUT_PORT As Long = 0
Const OUTPUT_PORT As Long = 2
Const eioDIO_PULL_3_3 As Long = 1
Const eioDIO_PULL_GND As Long = 2

Sub DigitalIo()
Dim Handle As Long
Dim PinLevels As Byte
Dim ReturnCode As Long

' Open API and get handle. Normally, this would be done only once at the
' beginning of the program. It has been included here to keep the
' example as simple as possible.
ReturnCode = eioOpen()
ReturnCode = eioClaimInterfaceEz(MODEL_ID, SERIAL_NUMBER, Handle)

' Set digital pulls.
ReturnCode = eioDioSetPull(Handle, INPUT_PORT, eioDIO_PULL_3_3)
ReturnCode = eioDioSetPull(Handle, OUTPUT_PORT, eioDIO_PULL_3_3)

' Set output levels equal to cell in spreadsheet.
PinLevels = Cells(3, 5)
ReturnCode = eioDioSet(Handle, OUTPUT_PORT, PinLevels)

' Get input levels and set spreadsheet cell to the value read.
ReturnCode = eioDioGet(Handle, INPUT_PORT, PinLevels)
Cells(5, 5).Value = PinLevels

' Clean up. Normally, this would be done only once at the end of the
' program. It has been included here since we included eioOpen() and
' eioClaimInterfaceEz() in this subroutine.
ReturnCode = eioReleaseInterface(Handle)
ReturnCode = eioClose()

End Sub

Lines 27 and 28 initialize the Expert I/O API. Lines 31 and 32 set the output voltage level and input pull up state. These lines would normally be placed in a subroutine that runs once at the beginning of the macro. The initialization does not need to be performed for every I/O access.

Lines 35 and 36 set a digital output port to the value in the spreadsheet at E3.

Lines 39 and 40 read a digital input port and write its value to the spreadsheet at E5.

The interface is released and the API is closed with lines 45 and 46. As with the initialization, this cleanup only needs to be performed once at the end of the macro.

As you can see, writing a VBA macro to control the Expert I/O is an incredibly simple task. So for your next automation project, don’t forget to consider Microsoft Office. It might be just what you need.

Click here to download the Excel file that contains this macro.

Understanding Expert I/O 1000 Access Times

David Novak — Fri, 14 Aug 2009 19:06:38 +0000

Expert I/O Timing

I often get questions about the Expert I/O 1000’s access time characteristics. The short answer is that you can change outputs at a rate of 100Hz and you can read inputs at 50Hz. However, the complete answer is more complicated.

When dealing with MS Windows on a PC, it’s not possible to get absolute realtime results. You will always have some variability in timing. However, Dajac’s USB implementation directly associates the timing to guaranteed values in the USB specification. Therefore, we know the guaranteed worst case access times at the USB level.

Nothing prevents Windows from providing faster access, but it’s not guaranteed and will depend on such things as processor load and software implementation techniques.

Obviously, the Expert I/O 1000 is not the fastest device you’ll find, but we knew that would be the case when we designed it. A very large number of applications exist where the Expert I/O 1000 is plenty fast enough and in our experience, guaranteed latency has always been more important than raw speed. You’ll also pay a great deal more for faster solutions.

Here are access time test results. I included ADC inputs and digital I/O, but these numbers will hold for all inputs and outputs.

Sample an Analog Input
Number of Accesses: 1000
Minimum Access Time: 9475.5 us (105.54 Hz)
Maximum Access Time: 23847 us (41.935 Hz)
Average Access Time: 21519 us (46.47 Hz)

Set a Digital Output Port
Number of Accesses: 1000
Minimum Access Time: 3430.1 us (291.54 Hz)
Maximum Access Time: 15876 us (62.987 Hz)
Average Access Time: 10673 us (93.697 Hz)

Sample a Digital Input Port
Number of Accesses: 1000
Minimum Access Time: 15210 us (65.745 Hz)
Maximum Access Time: 23915 us (41.815 Hz)
Average Access Time: 21527 us (46.452 Hz)

If you have concerns about timing, keep in mind that if the Expert I/O 1000 doesn’t work for you, return it within 30 days and we’ll give you a full refund.

What other aspects of the Expert I/O 1000 would you like more detail about? Put your suggestions in the comments below and I’ll address them in future articles.

PC Based Automation » access

Use Microsoft Office for Your Next Automation Project

Understanding Expert I/O 1000 Access Times