Language - Visual Basic .NET

Preamble about the language and its general strengths and weaknesses.

Assessment for use with Phidgets

Our honest opinion on how well this language is suited to controlling Phidgets. If it is a poor choice, suggest and link similar (better) languages.

Support

Visual Basic .NET has a complete API and sample code for all Phidgets devices.

For a complete list of our supported languages and their support status, click here.

Restrictions

In this section, list any restrictions or limitations that this particular language may impose. For example, incompatibility with certain operating systems.

Development Environments and Compilers

Describe each major compiler and notable differences or important information. (eg. framework versions) If there are known issues/workarounds mention them and link to the corresponding issue at the bottom of the page.

Drivers, Libraries and Resources

Before you can run your program, you need to set up the proper environment and get the necessary files off the Phidgets website. Visit the drivers section at www.phidgets.com and get the latest:

• Phidget Framework

You will need the Phidget Framework to use and to program with Phidgets. We also recommend that you download the following reference materials:

• API Manual
• API Reference
• VB.NET Sample Code
• You can find a high level discussion about programming with Phidgets in general on the General API page.
• The Device Functionality page explains the general operational information for your device.

You may want to have these pages open while working through these instructions.

Getting Started

The Phidget examples were written using Visual Basic .NET 2005 and this tutorial assumes its use. Newer versions of Visual Studio Express are freely available for download from Microsoft. Older versions of Visual Studio work as well and would be set up in a similar manner (Note: you would have to recreate the user interface in the examples for Visual Studio versions earlier than 2005).

In Visual Studio:

• Generate a new VB.NET Windows Application with a descriptive name such as PhidgetTest.
• Launch the Add Reference window (Project | Add Reference).
• Under the .NET tab, select the most recent Phidget21.NET library. If it does not appear in this list, then you can Browse to the Phidget Framework installation directory and add the Phidget21.NET.dll. For earlier versions of Visual Studio, you will want to use the Phidget21.NET1.1.dll instead.
• Place a TextBox on your main form for the purpose of capturing output.
• Hook the form's Load and FormClosing events. Phidget initialization and shutdown will take place there.

The project now has access to Phidgets and we are ready to begin coding.

Coding For Your Phidget

A Phidget object will fist need to be declared and then initialized. For example, we can declare a PhidgetInterfaceKit inside our form with:

  Public Class Form1
       'The Phidget object declaration
  Dim WithEvents ifKit As Phidgets.InterfaceKit
       '... Form1_Load and Form1_OnClosing here
  End Class

The object name for any type of Phidget is listed in the API manual. Every type of Phidget also inherits functionality from the Phidget base class.

Connecting to the Phidget

Next, the program needs to try and connect to the Phidget through a call to open(). Open will tell the program to continuously try to connect to a Phidget, based on the parameters given, even trying to reconnect if it gets disconnected. This means that simply calling open does not guarantee you can immediately use the Phidget. We can handle this by using event driven programming and tracking the AttachEvents and DetachEvents, or by calling waitForAttachment. WaitForAttachment will block indefinitely until a connection is made to the Phidget, or an optional timeout is exceeded.

       
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        ifKit = New Phidgets.InterfaceKit
        ifKit.open()
        ifKit.waitForAttachment(3000)
    End Sub

The different types of open can be used with parameters to try and get the first device it can find, open based on its serial number, or even open across the network. The API manual lists all of the available modes that open provides. One important thing to remember is that when working with Phidgets, a local connection will reserve the device until closed. This prevents any other instances from retrieving data from the Phidget, including other programs. The one connection per device limit does not apply when exclusively using the Phidget Webservice.

Event Driven Programming

We recommend the use of event driven programming when working with Phidgets. In VB.NET we can hook an event handler with the following code:

    Private Sub ifKit_SensorChange(ByVal sender As Object, ByVal e As Phidgets.Events.SensorChangeEventArgs) Handles ifKit.SensorChange
        TextBox1.Text = "Index " + e.Index.ToString() + " Value: " + e.Value.ToString()
    End Sub

With this function, the code inside ifKit_SensorChange will get executed every time the PhidgetInterfaceKit reports a change on one of its analog inputs. Some events such as Attach and Detach belong to the base Phidget object and thus are common to all types of Phidgets. Please refer to the API manual for a full list of events and their usage. At the end of your program, unhook any events and call Application.DoEvents(). This will make sure there are no outstanding events being processed before calling close.

    Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        RemoveHandler ifKit.SensorChange, AddressOf ifKit_SensorChange
        Application.DoEvents()
        ifKit.close()
    End Sub

Working directly with the Phidget

Some values can be read and sent directly to the Phidget, simply use the instance members and properties. This is also how you would set properties on the Phidget such as the output state or sensor sensitivity. These functions can be used inside a polling loop as an alternative to event driven programming.

  Dim val As Integer = ifKit.sensors(0).Value

Working with multiple Phidgets

Multiple Phidgets of the same type can easily be run inside the same program. In our case, it requires another PhidgetInterfaceKit instance to be defined and initialized. The new instance can then be set up, opened and used in the same process as the previous one. If the application needs to distinguish between the devices, open can be called with the serial number of a specific Phidget.

Other Phidgets

The design given in this document can also be followed for almost all Phidgets. For example, if you were using a PhidgetRFID instead of an PhidgetInterfacekit, you would declare an RFID object instead of an InterfaceKit. The methods and events available would change but they can be accessed in a similar manner.

Building your Project

Describe the different ways a project could be built using this language.

Common Problems and Solutions/Workarounds

Here you can put various frequent problems and our recommended solutions.