One of the steppng stones to utilizing a computer for data acquisition and device control is the ability to receive input from its ports. After becoming familiar with programming for a PC's ports, you can start to design programs and hardware to meet the needs of your applications.
To do this, it is assumed that you already:
The rest of the tutorial is presented as follows:
All that is required for this tutorial are the following:
The game port was originally designed to relive the erial port of devices like joysticks and MIDI devices. It eventually became the standard port for interfacing with a joystick or other game controller. The address for the game port is 0201 (Hex). The following diagram shows the pins for the game port and there respective functions:
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The axis pins generally receive analog input from a pot on the joystick. The button pins receive a digital input. This information is primarily background, and will not greatly affect the actual programming.
Start Visual Basic. At the Window that appears, choose "Standard EXE" as shown in Figure 1.
This should bring you to a screen with a blank form. The program we will be constructing will be a form with a dot that moves around in it based in input from the joystick. In the properties box on the right, change the width of the form to 8200 and height to 6600 as shown in Figure 2.
From the toolbox on the left, select the timer (clock icon). Click in the form and drag to place a clock icon on the form. This adds a timer to the form to perform repeated tasks. Select the timer icon on the form. In the properties window on the right on the right, change the interval to 100.
Now right click the form and select "View Code". This is where we will enter our code for the form. From the drop down list at the top of the window, select form. This is the area to enter code for when the form is originally loaded. You should have a screen that looks similar to Figure 4.
The following is the code for the form. It will be explained in detail later.
Dim x, xg As Long
Dim y, yg As Long
Dim start As Long
Dim status, i As Integer
Dim PortBits(8) As Integer
Dim PortNum As Long
Dim r As Long
Dim temp As Long
Dim xmax As Long
Dim xmin As Long
Dim xratg As Double
Dim ymax As Long
Dim ymin As Long
Dim yratg As Double
Dim formh As Long
Dim formw As Long
Dim ji As JOYINFOEX
Dim caps As JOYCAPS ' joystick capabilities
Dim rc As Long
Private Sub Form_Load()
ji.dwSize = Len(ji)
ji.dwFlags = JOY_RETURNALL
' Get the current joystick data
rc = joyGetPosEx(JOYSTICKID1, ji)
If (rc <> 0) Then
MsgBox "Couldn't detect the joystick"
End
Else
temp = MsgBox("Hold the joystick to the right and click 'OK'", vbOKOnly, "Calibrate X")
rc = joyGetPosEx(JOYSTICKID1, ji)
xmax = ji.dwXpos
temp = MsgBox("Hold the joystick to the left and click 'OK'", vbOKOnly, "Calibrate X")
rc = joyGetPosEx(JOYSTICKID1, ji)
xmin = ji.dwXpos
temp = MsgBox("Hold the joystick down and click 'OK'", vbOKOnly, "Calibrate Y")
rc = joyGetPosEx(JOYSTICKID1, ji)
ymax = 32600 'ji.dwYpos
temp = MsgBox("Hold the joystick up and click 'OK'", vbOKOnly, "Calibrate Y")
rc = joyGetPosEx(JOYSTICKID1, ji)
ymin = 0 'ji.dwYpos
End If
formw = 8200
formh = 6300
xratg = formw / (xmax - xmin)
yratg = formh / (ymax - ymin)
r = 50
End Sub
Private Sub Timer1_Timer()
' Initialize struct
ji.dwSize = Len(ji)
ji.dwFlags = JOY_RETURNALL
' Get the current joystick data
rc = joyGetPosEx(JOYSTICKID1, ji)
x = ji.dwXpos
y = ji.dwYpos
If ji.dwButtons = 1 Then
r = r + 50
Else
If ji.dwButtons = 2 Then
If r >= 100 Then
r = r - 50
End If
End If
End If
xg = Round((x - xmin) * xratg)
yg = Round((y - ymin) * yratg)
Form1.Circle (x, y), r
End Sub
VARIABLE DECLERATIONS
The first portion of code goes above the "From_Load()" sub. This declares all the variables to be used in the program. Their meaning will become evident as we progress through the code.
Dim x, xg As Long Dim y, yg As Long Dim start As Long Dim status, i As Integer Dim PortBits(8) As Integer Dim PortNum As Long Dim r As Long Dim temp As Long Dim xmax As Long Dim xmin As Long Dim xratg As Double Dim ymax As Long Dim ymin As Long Dim yratg As Double Dim formh As Long Dim formw As Long Dim ji As JOYINFOEX Dim caps As JOYCAPS ' joystick capabilities Dim rc As LongFORM LOAD
The next portion of code defines a script that will run as soon as the form is started (in other words, when the program first starts). Does a calibration to set up constants to be used later.
Private Sub Form_Load()
ji.dwSize = Len(ji)
ji.dwFlags = JOY_RETURNALL
' Get the current joystick data
rc = joyGetPosEx(JOYSTICKID1, ji)
If (rc <> 0) Then
MsgBox "Couldn't detect the joystick"
End
Else
temp = MsgBox("Hold the joystick to the right and click 'OK'", vbOKOnly, "Calibrate X")
rc = joyGetPosEx(JOYSTICKID1, ji)
xmax = ji.dwXpos
temp = MsgBox("Hold the joystick to the left and click 'OK'", vbOKOnly, "Calibrate X")
rc = joyGetPosEx(JOYSTICKID1, ji)
xmin = ji.dwXpos
temp = MsgBox("Hold the joystick down and click 'OK'", vbOKOnly, "Calibrate Y")
rc = joyGetPosEx(JOYSTICKID1, ji)
ymax = 32600 'ji.dwYpos
temp = MsgBox("Hold the joystick up and click 'OK'", vbOKOnly, "Calibrate Y")
rc = joyGetPosEx(JOYSTICKID1, ji)
ymin = 0 'ji.dwYpos
End If
The beginning of this code initializes the joystick variables. It tells the joystick function to return all flags (status of the joystick, max and min values, etc.). It then goes through a standard error handling process to ensure that the joystick was detected. If the joystick was detected, a series of message boxes appear. Each message box asks that the user hold the joystick to an extreme and click "ok". When the user clicks "ok", the value for the respective access is read and stored in a variable.
formw = 8200
formh = 6300
xratg = formw / (xmax - xmin)
yratg = formh / (ymax - ymin)
r = 50
End Sub
The last part of the form load code sets up two ratios. These ratios relate the joystick value returned and to a position within the form. These will be used to scale the input from the joystick. Finally, the radius of the dot is initialized to 50.
UTILIZING INPUT FROM THE JOYSTICK
The remainder of the code is a simple application that places a circle on the form who's position is directed by the joystick. The circle changes color and size based on which buttons are pressed.
Private Sub Timer1_Timer() ' Initialize struct ji.dwSize = Len(ji) ji.dwFlags = JOY_RETURNALL ' Get the current joystick data rc = joyGetPosEx(JOYSTICKID1, ji) x = ji.dwXpos y = ji.dwYpos
It should first be noted that this code is contained within the timer sub. This will cause the code to be run with every cycle of the timer (and thereby read a new joystick position and redraw the dot). The joystick is initialized and the postion from the joystick is read and stored in the variables x and y.
If ji.dwButtons = 1 Then r = r + 50 Else If ji.dwButtons = 2 Then If r >= 100 Then r = r - 50 End If End If End If
Based on which button is hit, the radius of the circle is either increased or decreased, but the radius is never allowed to drop below 50.
xg = Round((x - xmin) * xratg)
yg = Round((y - ymin) * yratg)
Form1.Circle (x, y), r
End Sub
The input from the joystick is scaled and rounded to the nearest integer. This will give us a position we can use on the form. A circle is then drawn at this position, with the appropriate radius.
After completing this tutorial you should be familiar with the the gameport, be able to program in Visual Basic to receive input from a joystick and apply that input to an application.
If you have questions about this tutorial you can email me at Keithicus@drexel.edu.