The LabVIEW Programming Environment and

Basic Operations
Sarah Fenney 
Arizona State University

Instructor’s Portion
Summary
The students will learn about the two parts of the LabVIEW programming 
environment, the front panel and block diagram.  They will also write a 
simple Virtual Instrument (VI) to incorporate basic operations in 
LabVIEW.  Finally, the students will convert their programs into subVIs 
by creating an icon and connector pane.   

Uses
This homework applies to all general instrumentation courses. 

Equipment List
 Computer with LabVIEW 6.1

References
 Getting Started with LabVIEW.  November 2001. Part Number
321527E-01. http://www.ni.com/manuals.

 LabVIEW User’s Manual. November 2001. Part Number

320999D-01. http://www.ni.com/manuals.

 LabVIEW Student Edition. http://www.ni.com/labviewse.

 LabVIEW Introduction Course - Six Hours.

 LabVIEW Introduction Course - Three Hours.

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Student’s Portion
Introduction
In this homework, you will learn about the LabVIEW programming 
environment.  You will also write a simple Virtual Instrument (VI) to 
incorporate basic operations in LabVIEW.  Finally, you will convert your 
programs into subVIs.  

Objectives
 Learn the three parts of a VI. 

 Learn the three palettes.

 Learn how data is passed in LabVIEW.

 Distinguish between controls and indicators on the front panel and 
block diagram.

 Create a subVI using two different methods. 

Theory
LabVIEW Programming Basics

Introduction

LabVIEW is a graphical programming language that uses icons instead of 
lines of text to create applications. In contrast to text­based programming 
languages, where instructions determine program execution, LabVIEW 
uses dataflow programming, where the flow of data determines execution.

In LabVIEW, you build a user interface by using a set of tools and objects.
The user interface is known as the front panel. You then add code using 
graphical representations of functions to control the front panel objects.
The block diagram contains this code. In some ways, the block diagram 
resembles a flowchart.

LabVIEW programs are called virtual instruments, or VIs, because their 
appearance and operation imitate physical instruments, such as 

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oscilloscopes and multimeters. Every VI uses functions that manipulate 
input from the user interface or other sources and display that information 
or move it to other files or other computers.

A VI contains the following three components:
• Front panel—Serves as the user interface.

• Block diagram—Contains the graphical source code that defines the 
functionality of the VI.
• Icon and connector pane—Identifies the VI so that you can use the VI 
in another VI. A VI within another VI is called a subVI. A subVI 
corresponds to a subroutine in text­based programming languages.

Front Panel

The front panel is the user interface of the VI. You build the front panel 
with controls and indicators, which are the interactive input and output 
terminals of the VI, respectively. Controls are knobs, pushbuttons, dials, 
and other input devices. Indicators are graphs, LEDs, and other displays. 
Controls simulate instrument input devices and supply data to the block 
diagram of the VI. Indicators simulate instrument output devices and 
display data the block diagram acquires or generates.

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Block Diagram

After you build the front panel, you add code using graphical 
representations of functions to control the front panel objects. The block 
diagram contains this graphical source code. Front panel objects appear as 
terminals on the block diagram. 

Additionally, the block diagram contains functions and structures from 
built­in LabVIEW VI libraries. Wires connect each of the nodes on the 
block diagram, including control and indicator terminals, functions, and 
structures.

LabVIEW Palettes

LabVIEW palettes give you the options you need to create and edit the 
front panel and block diagram. 

The Tools palette is available on the front panel and the block diagram.
A tool is a special operating mode of the mouse cursor. When you select a 
tool, the cursor icon changes to the tool icon. Use the tools to operate and 
modify front panel and block diagram objects.

Select Window»Show Tools Palette to display the Tools palette. You can
place the Tools palette anywhere on the screen.

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If automatic tool selection is enabled and you move the cursor over objects
on the front panel or block diagram, LabVIEW automatically selects the 
corresponding tool from the Tools palette.

The Controls palette is available only on the front panel. The Controls 
palette contains the controls and indicators you use to create the front 
panel. Select Window»Show Controls Palette or right­click the front 
panel workspace to display the Controls palette. You can place the 
Controls palette anywhere on the screen.

The Functions palette is available only on the block diagram. The 
Functions palette contains the VIs and functions you use to build the 
block diagram. Select Window»Show Functions Palette or right­click 
the block diagram workspace to display the Functions palette. You can 
place the Functions palette anywhere on the screen.

Dataflow Programming

LabVIEW follows a dataflow model for running VIs. A block diagram 
node executes when all its inputs are available. When a node completes 
execution, it supplies data to its output terminals and passes the output 
data to the next node in the dataflow path.

Creating SubVIs

Introduction

After you build a VI and create its icon and connector pane, you can use it
in another VI. A VI called from the block diagram of another VI is called a
subVI. A subVI corresponds to a subroutine in text-based programming
languages. A subVI node corresponds to a subroutine call in text-based
programming languages. The node is not the subVI itself, just as a
subroutine call statement in a program is not the subroutine itself.

Setting up the Connector Pane

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To use a VI as a subVI, you need to build a connector pane. The connector
pane is a set of terminals that corresponds to the controls and indicators of
that VI, similar to the parameter list of a function call in text-based
programming languages. The connector pane defines the inputs and
outputs you can wire to the VI so you can use it as a subVI.

Define connections by assigning a front panel control or indicator to each

of the connector pane terminals. To define a connector pane, right-click
the icon in the upper right corner of the front panel window and select
Show Connector from the shortcut menu. The connector pane replaces
the icon. Each rectangle on the connector pane represents a terminal. Use
the rectangles to assign inputs and outputs. The number of terminals
LabVIEW displays on the connector pane depends on the number of
controls and indicators on the front panel.

The connector pane has, at most, 28 terminals. If your front panel contains
more than 28 controls and indicators that you want to use
programmatically, group some of them into a cluster and assign the cluster
to a terminal on the connector pane.

Select a different terminal pattern for a VI by right-clicking the connector

pane and selecting Patterns from the shortcut menu. Select a connector
pane pattern with extra terminals. You can leave the extra terminals
unconnected until you need them. This flexibility enables you to make
changes with minimal effect on the hierarchy of the VIs.

If you create a group of subVIs that you use together often, give the
subVIs a consistent connector pane with common inputs in the same
location to help you remember where to locate each input. If you create a
subVI that produces an output another subVI uses as the input, align the
input and output connections to simplify the wiring patterns. Place the
error in clusters on the lower left corner of the front panel and the error
out clusters on the lower right corner.

Setting Required, Recommended, and Optional Inputs and Outputs

You can designate which inputs and outputs are required, recommended,
and optional to prevent users from forgetting to wire subVI connections.

Right-click a terminal in the connector pane and select This Connection

Is from the shortcut menu. A checkmark indicates the terminal setting.
Select Required, Recommended, or Optional.

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For terminal inputs, required means that the block diagram on which the
subVI is dropped will be broken if the required inputs are not wired.
Required is not available for terminal outputs. For terminal inputs and
outputs, recommended means that the block diagram on which the subVI
is dropped can be run if the input is not wired but the Warnings dialog
box will generate a warning that the input has not been wired. Optional
means that the block diagram on which the subVI is dropped can be run
and will not generate any warnings if the terminal input or output is not
wired.

Inputs and outputs of VIs in vi.lib are already marked as Required,

Recommended, or Optional. LabVIEW sets inputs and outputs of VIs
you create to Recommended by default. Set a terminal setting to required
only if the VI must have the input or output to run properly.

In the Context Help window, required connections are bold,

recommended connections are plain text, and optional connections are
dimmed if you have the Detailed view selected or do not appear if you
have the Simple view selected.

Creating an Icon

Every VI displays an icon in the upper right corner of the front panel and
block diagram windows. An icon is a graphical representation of a VI. It
can contain text, images, or a combination of both. If you use a VI as a
subVI, the icon identifies the subVI on the block diagram of the VI.

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The default icon contains a number that indicates how many new VIs you
have opened since launching LabVIEW. Create custom icons to replace
the default icon by right-clicking the icon in the upper right corner of the
front panel or block diagram and selecting Edit Icon from the shortcut
menu or by double-clicking the icon in the upper right corner of the front
panel.

You also can drag a graphic from anywhere in your file system and drop it
in the upper right corner of the front panel or block diagram. LabVIEW
converts the graphic to a 32 X 32 pixel icon.

Depending on the type of monitor you use, you can design a separate icon
for monochrome, 16-color, and 256-color mode. LabVIEW uses the
monochrome icon for printing unless you have a color printer.

Creating SubVIs from Sections of a VI

Convert a section of a VI into a subVI by using the Positioning tool to

select the section of the block diagram you want to reuse and selecting
Edit»Create SubVI. An icon for the new subVI replaces the selected
section of the block diagram. LabVIEW creates controls and indicators for
the new subVI and wires the subVI to the existing wires.

Creating a subVI from a selection is convenient but still requires careful

planning to create a logical hierarchy of VIs. Consider which objects to
include in the selection and avoid changing the functionality of the
resulting VI.

Equations

Converting ºC to ºF

The formula for converting degrees Celsius to degrees Fahrenheit is as 
follows: 
°F = (1.8 * °C) + 32

For example, to convert a Celsius temperature of 100 degrees into degrees 
Fahrenheit, first multiply the Celsius temperature reading by 1.8 to get 
180. Then add 32 to 180 and get 212 degrees Fahrenheit. 

Slope of a Line

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The formula for the slope of a line is as follows:

Slope = (Y2 – Y1) / (X2 – X1) 

where (X1, Y1) and (X2, Y2) are points on the line. 

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Homework Procedure
Part 1. Converting ºC to ºF

In Part 1, you will create a VI that can be used as a sub­VI.  

1. Launch LabVIEW from Start»Programs»National Instruments 
LabVIEW 6.1.  Click New VI to open a new front panel.

2. (Optional) Select Window»Tile Left and Right to display the front 
panel and block diagram side by side.

3. Create a numeric digital control. You will use this control to enter the 
value for degrees Centigrade.

a. Select the digital control on the Controls»Numeric palette. If 
the Controls palette is not visible, right­click an open area on the 
front panel to display it.

b. Move the control to the front panel and click to place the 
control.

c. Type deg C inside the label and click outside the label or click 
the Enter button on the toolbar, shown at left. If you do not type 
the name immediately, LabVIEW uses a default label. You can 
edit a label at any time by using the Labeling tool, shown at left.

4. Create a numeric digital indicator. You will use this indicator to display 
the value for degrees Fahrenheit.

a. Select the digital indicator on the Controls»Numeric palette.

b. Move the indicator to the front panel and click to place the 
indicator.

c. Type deg F inside the label and click outside the label or click 
the Enter button.

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LabVIEW creates corresponding control and indicator terminals on the 
block diagram. The terminals represent the data type of the control or 
indicator. For example, a DBL terminal, shown at left, represents a 
double­precision, floating­point numeric control or indicator.

5. Display the block diagram by clicking it or by selecting Window»
Show Diagram.

6. Select the Multiply and Add functions on the Functions»Numeric 
palette and place them on the block diagram. If the Functions palette is 
not visible, right­click an open area on the block diagram to display it.

7. Select the numeric constant on the Functions»Numeric palette and 
place two of them on the block diagram. When you first place the numeric
constant, it is highlighted so you can type a value.

8. Type 1.8 in one constant and 32.0 in the other.

If you moved the constants before you typed a value, use the Labeling tool
to enter the values.

9. Use the Wiring tool to wire the icons as shown in the block diagram.

• To wire from one terminal to another, use the Wiring tool to click
the first terminal, move the tool to the second terminal, and click 
the second terminal, as shown in the following illustration. You 
can start wiring at either terminal.

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• You can bend a wire by clicking to tack the wire down and 
moving the cursor in a perpendicular direction. Press the spacebar 
to toggle the wire direction.

• To identify terminals on the nodes, right­click the Multiply and 
Add functions and select Visible Items»Terminals from the 
shortcut menu to display the connector pane. Return to the icons 
after wiring by right­clicking the functions and selecting Visible 
Items»Terminals from the shortcut menu to remove the 
checkmark.

• When you move the Wiring tool over a terminal, the terminal 
area blinks, indicating that clicking will connect the wire to that 
terminal and a tip strip appears, listing the name of the terminal.

• To cancel a wire you started, press the <Esc> key, right­click, or 
click the source terminal.

10. Display the front panel by clicking it or by selecting Window»Show 
Panel.

11. Save the VI because you will use this VI later in the course.  Select 
File»Save.  Type Convert C to F.vi in the dialog box.  Click the 
Save button.

12. Enter a number in the digital control and run the VI.

a. Use the Operating tool or the Labeling tool to double­click the 
digital control and type a new number.

b. Click the Run button to run the VI.

c. Try several different numbers and run the VI again.

13. Right­click the icon in the upper right corner of the front panel and 
select Edit Icon from the shortcut menu. The Icon Editor dialog box 
appears.

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14. Double­click the Select tool on the left side of the Icon Editor dialog 
box to select the default icon.

15. Press the <Delete> key to remove the default icon.

16. Double­click the Rectangle tool to redraw the border.

17. Create the following icon.

a. Use the Text tool to click the editing area.

b. Type C and F.

c. Double-click the Text tool and change the font to

Small Fonts.

d. Use the Pencil tool to create the arrow.

Note To draw horizontal or vertical straight lines, press the

<Shift> key while you use the Pencil tool to drag the
cursor.

e. Use the Select tool and the arrow keys to move the
text and arrow you created.

f. Select the B&W icon and select 256 Colors in the

Copy from field to create a black and white icon,
which LabVIEW uses for printing unless you have a
color printer.

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g. When the icon is complete, click the OK button to
close the Icon Editor dialog box. The icon appears in
the upper right corner of the front panel and block
diagram.

18. Right-click the icon on the front panel and select Show
Connector from the shortcut menu to define the
connector pane terminal pattern.
LabVIEW selects a connector pane pattern based on the
number of controls and indicators on the front panel. For
example, this front panel has two terminals, deg C and
deg F, so LabVIEW selects a connector pane pattern with
two terminals.

19. Assign the terminals to the digital control and digital

indicator.

a. Select Help»Show Context Help to display the

Context Help window. View each connection in the
Context Help window as you make it.

b. Click the left terminal in the connector pane. The

tool automatically changes to the Wiring tool, and
the terminal turns black.

c. Click the deg C control. The left terminal turns

orange, and a marquee highlights the control.

d. Click an open area of the front panel. The marquee

disappears, and the terminal changes to the data
type color of the control to indicate that you
connected the terminal.

e. Click the right terminal in the connector pane and

click the deg F indicator. The right terminal turns
orange.

f. Click an open area on the front panel. Both

terminals are orange.

g. Move the cursor over the connector pane. The

Context Help window shows that both terminals are
connected to floating-point values.

20. Select File»Save to save the VI.  

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21. Select File»Close to close the VI.

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Part 2. Calculating the Slope of a Line

Using the techniques you learned in Part 1, create a VI to calculate the 
slope of a line.  Then, transform the code into a subVI using the 
Edit»Create SubVI method.  Save the VI as Slope.vi.  Save the subVI
as SlopeSub.vi.  The equation for slope is given in the Theory section.

Open a new VI and complete the front panel and block diagram as 
follows:

  Front Panel

  Block Diagram before subVI

After creating the subVI, your block diagram will resemble the one below.

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Block Diagram with subVI

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Part 3. Calculator VI

Write a VI that adds, subtracts, multiplies, divides, and averages two input
numbers and displays the results on the front panel.  Save your VI as 
Calculator.vi. 

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Homework Report
For your homework report, email the VIs and the answers to the questions 
below to the instructor no later than <date>.

Data Sheet
Questions

1. What is a VI? What are the three main parts of a VI? Briefly describe 
each.

2. What are the three palettes?  Briefly describe each.  

3. How is data passed in LabVIEW?

4. How can you tell the difference between controls and indicators on the 
front panel? On the block diagram?

5.  Explain the two methods of creating a subVI.  

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