LabVIEW User GroupUniversity of Bristol

Ben LavasaniAcademic Field Sales Engineer

NI UK

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Agenda

• LabVIEW Design Patterns Overview• Coffee break :)• LabVIEW for Multi-Touch Applications - David Carberry• LabVIEW in Teaching • LabVIEW Tips and Tricks

LabVIEW Design Patterns Overview

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What Is a Design Pattern?

• A template or framework for LabVIEW code• Widely accepted and well-known• Easily recognizable

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Benefits of Using Design Patterns

Simplify the development process Developers can easily understand code Don’t have to “re-invent the wheel” Pre-existing solutions to common problems

Reliability Many have been used for years - they are “tried and true” Large development community and resources online

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Getting Started: How Do I Pick?

• Identify most important aspect of your application: Processes that require de-coupling Clean, easy to read code Mission critical components

• Select a template based upon potential to improve

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Caution

You can needlessly complicate your life if you use an unnecessarily complex design pattern

Don’t forget the most common design pattern of all… dataflow!

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Basic Tools• Loops• Shift Registers• Case Structures• Enumerated Constants• Event Structures

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Today’s Discussion

• As we look at each design pattern, we’ll discuss A problem we are trying to solve Background How it works Technical implementation Demonstration Use cases / considerations

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Design Patterns

• Functional Global Variable• State Machine / Statecharts• Producer / Consumer

Functional Global Variables

How do I share data across a application without using Global or Local Variables?

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Background: Global and Local Variables

• Can cause race conditions• Create copies of data in memory• Cannot perform actions on data• Cannot handle error wires

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Breaking Down the Design Pattern

• While loop• Uninitialized shift

registers have memory• Case structure• Enumerated control

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DEMOUninitialized Shift Registers

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How It Works: Basic Actions

• Set the value of the shift register

INITIALIZE

INITIALIZE

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How It Works: Basic Actions

• Get the value currently stored in the shift register

GET

GET

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How It Works: Action Engine

• Perform an operation upon stored value and save result

• You can also output the new value

ACTION

ACTION

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1. Functional Global Variable is a Non-Reentrant SubVI2. Actions can be performed upon data3. Enumerator selects action4. Stores result in uninitialized shift register5. Loop only executes once

Technical Implementation

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DEMOFunctional Global Variables

Uninitialized shift register has memory

Action determines which case is executed

Only used in Initialize case

Loop only executes once

Examples of other ‘actions’

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Benefits: Comparison

Global and Local Variables• Can cause race conditions• Create copies of data in memory• Cannot perform actions on data• Cannot handle error wires• Drag and drop

Functional Global Variables• Prevent race conditions• No copies of data• Can behave like action engines• Can handle error wires• Take time to make

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Recommendations

Use Cases• Communicate data between code without connecting wires• Perform custom actions upon data while in storage

Considerations• All owning VIs must stay in memory• Use clusters to reduce connector pane• Using stacked shift registers will track multiple iterations

State Machine

I need to execute a sequence of events, but the order is determined programmatically

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Background

Dynamic Sequence: Allows distinct states to operate in a programmatically determined sequence

Static Sequence

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Soda Machine

Initialize

Wait

Change QuarterDime

Nickel

Exit

Vend

Soda costs $0.50

No input

Quarter Deposited

Total < 50

Total >= 50

Change Requested Dime Deposited

Nickel Deposited

Total < 50 Total < 50

Total >= 50Total >= 50

Total > 50

Total = 50

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Breaking Down the Design Pattern

• Case Structure inside of a While Loop• Each case is a state• Current state has decision making code that

determines next state• Use enumerators to pass value of next state to

shift registers

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Transition Code

How It Works

FIRST STATE

FIRST STATE

NEXT STATE

Step Execution

Shift registers used to carry state

Case structure has a case for every state Transition code determines next state based upon results of step execution

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Transition Code Options

Step Execution

Step Execution

Step Execution

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DEMOState Machine

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Recommendations

Use Cases• User interfaces• Data determines next routine

Considerations• Creating an effective State Machine requires the

designer to make a table of possible states.• Use LabVIEW Statechart to abstract this process for

more sophisticated applications

Producer / Consumer

I have two processes that need to execute at the same time, and I need to make sure one can’t slow the other down

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How It Works• One or more slave loops are told by

a master loop when they can run• Allows for a-synchronous execution

of loops• Data-independence breaks dataflow

and allows multi-threading• De-couples processes

Slave 1

Slave 2

Master

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Breaking Down the Design Pattern

• Data independent loops = Multithreading• Master / slave relationship• Communication and synchronization between

loops

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Loop Communication

• Variables• Occurrences• Notifier• Queues• Semaphores• Rendezvous

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QueuesAdding Elements to the Queue

De-queueing Elements

Reference to existing queue in memory

Select the data-type the queue will hold

Dequeue will wait for data or timeout (defaults to -1)

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Producer / Consumer

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Adding Your Own Design Patterns

C:\Program Files\National Instruments\LabVIEW 8.5\templates\Frameworks\DesignPatterns

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Resources

• Example Finder• New >> Frameworks >> Design Patterns• ni.com/labview/power• Expressionflow.com

• Visit ni.com/info and enter exhkqe

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LabVIEW in TeachingThe NI LabVIEW Academy

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The NI LabVIEW Academy program provides classroom curriculum, instructional materials, and hands-on exercises to high schools, community colleges, and universities for the specific purpose of teaching LabVIEW.

LabVIEW Academy is for anyone seeking LabVIEW education and knowledge through an academic institution.

What Is the NI LabVIEW Academy?

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What Does the NI LabVIEW Academy Do?

Increases the pool of qualified LabVIEW developers

Emphasises LabVIEW professional certification

Empowers institutions to teach LabVIEW

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Instructor Requirements

Two instructors must be Certified LabVIEW Associate Developers (CLADs) and teach at participating organisations

NI LabVIEW Academy Program Requirements

Program Requirements• Current teaching site license• At least one dedicated classroom (a computer lab will suffice)• 40 hours of classroom LabVIEW specific instruction time• One PC per student (with LabVIEW software) • NI DAQ equipment required for lab component (2:1 student ratio)• Submit course syllabus to NI for approval

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Instructor Materials

•LabVIEW Basics I & II Instructor Manual•LabVIEW Basics I & II Lecture Slides•LabVIEW Basics I & II Exercises and Solutions•Instructor Version of Student Workbook•50 LabVIEW Exam/Homework Questions

NI LabVIEW Academy Instructional Materials

Student Materials

•LabVIEW Academy Workbook (student purchase)• 300+ questions

•Recommended LabVIEW textbook (student purchase)

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NI LabVIEW Academy Teaching Materials

Curriculum for both learning LabVIEW and teaching LabVIEW

Recommended LabVIEW Textbooks

NI LabVIEW Academy Teaching Materials

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NI LabVIEW Academy CLAD Opportunity

The NI LabVIEW Academy gives students the opportunity to take the CLAD exam as part of the program

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“LabVIEW is getting more popular in academia and industry and many researchers and companies are on the lookout for competent LabVIEW programmers. This program will help bridge the gap between the two.”

– Khanjan Mehta, Professor, Penn State University

“In our exhaustive search for qualified LabVIEW developers to fill key roles in our organization, we greatly anticipate the new pool of qualified candidates coming out of the National Instruments LabVIEW Academy schools.“

– Marvin Landrum, Section Manager, Texas Instruments

Academic Industry

The NI LabVIEW Academy Bridging the Gap

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ni.com/academy

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Tips and Tricks to Speed NI LabVIEW DevelopmentUseful Nuggets to Save You Time

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Agenda

• 20 Tips and Tricks for LabVIEW Development Beginner: Simple tricks to save time Intermediate: LabVIEW tips you probably did not know about Advanced: Useful nuggets to put you ahead of the game

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Automatically Select the Right Tool

• Avoid manually switching among many tools

Operate Value Tool

Position/Size/Select Tool

Edit Text Tool

Connect Wire Tool

Auto Tool

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Hold down Ctrl + Space to launch Quick Drop

Quickly Drop Palette Objects2/ 20

• Ctrl + D – Create controls and indicators on selected diagram object(s)

• Ctrl + R – Remove diagram object(s) and reconnect wires

• Ctrl + T – Move control and indicator terminal labels to the left and right sides

Demo

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• Access via File New …• Well-known designs

Producer/Consumer State Machine Queued Message Handler

Design Pattern Templates3/ 20

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Switch Terminal Wires Easily

Hold Down Ctrl and Left-Click on Input Terminal

Note: This works only for functions with two inputs when bothinputs have already been wired

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Demo

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Easily Scroll Through Structures

• You can use Ctrl + Mouse Scroll to scroll through: Case Structures Event Structures Stacked Sequence Structures Diagram Disable Structures

Ctrl + Mouse Scroll Wheel

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Quickly Find the Right Palette

• Right-click on a block diagram object for a palette shortcut

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Add

To More Specific Class

Index Array

Demo

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Easily Navigate Arrays• Right-click on an array and select Visible Items >> Horizontal Scrollbar

(or Visible Items >> Vertical Scrollbar)• To view last element, select Advanced >> Show Last Element• Both horizontal and vertical scrollbars available (depending on array

dimensions)

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Demo

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Selective Insert Location

Right-Click Slightly above Wire

Right-Click Slightly below Wire

Wire Connected to Lower Terminal

Wire Connected to Upper Terminal

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Block Diagram Clean-Up• Click Clean Up Diagram button on toolbar or press

Ctrl + U• Highlight a portion of the diagram for partial cleanup• Right-click and select “Exclude from Diagram

Cleanup” option

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Note: Only available in LabVIEW 8.6 and later.

Demo

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Quickly Wire Multiframe Structures10/ 20

Note: Only available in LabVIEW 8.6 and later

• Right-click an output tunnel and select “Linked Input Tunnel » Create & Wire Unwired Cases”

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• Matrix Size function replaces old method• Assess size of 2D array regardless of data type

Easily Assess 2D Array Size11/ 20

Note: Only available in LabVIEW 2009 and later

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Breakpoint Manager

• Select View » Breakpoint Manager• Right-click and select Breakpoint » Breakpoint

Manager

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Note: Only available in LabVIEW 8.6 and later

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• Ctrl + Shift +E from an open VI with open project

Quickly Find VIs in the Project Window13/ 20

Note: Only available in LabVIEW 2009 and later

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Easily Add Enumeration Items

• Press Ctrl while hovering over an Enum to use the Text Tool

• Use Shift + Enter to repeatedly add items

Shift + Enter

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Demo

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• Highlight all desired front panel or block diagram objects

• Right-click and select “Properties”

Edit Multiple Objects Simultaneously15/ 20

Demo

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Automatically Create Control References

• Simply drag a control into a Control Refnum• Automatically creates a class-specific, type-specific

reference

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Note: To keep the original control, use Ctrl-Drag instead

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Drag and Drop to Save Time• Drag an image into your VI icon• Select a file and drag into a path constant• Take a URL from Internet Explorer and drag into a string constant• Drag items from disk or Project Explorer into a LabVIEW block diagram

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Quickly Browse Properties and Methods• View >> Class Browser• Shortcut: Ctrl + Shift + B• Drag a property or method directly into your

VI

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Demo

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Implement a For Loop Progress Bar

• Place Progress Bar VI inside a for loop• Opens automatically after a specified amount of time• Download sample code from ni.com/forums (search for “For Loop Progress Bar”)

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Demo

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Automatically Analyse Your VIs

• Tools >> VI Analyzer >> Analyze VIs– Check performance, style, UI, documentation, and more– Save LabVIEW VI Analyzer settings for later use

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Demo

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Other Resources

• Darren’s LabVIEW Nuggets (decibel.ni.com/content/docs/DOC-4002)

• LAVA: Favorite Tips and Shortcuts (forums.lavag.org)

• LabVIEW Wiki (labviewwiki.org)

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