Digital Signal Processing with

LabVIEW 8.6

Lab # 02

Structures

Adnan Niazi

Lab Engineer

Signal Processing/Signal & Systems Lab

CECOS University of IT & Emerging Sciences

13th- 14th Feb 2009

Contact: [email protected]

CECOS University of IT & Emerging Sciences

Agenda

▌ What are Loops

▌ What is shift register

▌ What are Sequence structures

▌ What is case structure

▌ What are tunnels

▌ What is Mathscript window

▌ What is Mathscript node

▌ What is formula node

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Loops

▌ Loops are used to perform some task over and over

again

▌ Loops help in creating a compact code

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Loops

While Loop

▌ Most widely used loop in LabVIEW

▌ Used whenever the number of times a loop will execute,

is unknown before runtime

Current loop

Conditional stop

count

terminal

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Shift Register

▌ Shift register shifts the output of one iteration of the

loop to the next iteration

▌ Right click on the loop boundary and select Add Shift

Shift register

Loop

iteration

Conditional terminal

count

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While loop

Scenario: Design a VI that adds 2 to the results of the

previous iteration of the loop until a stop button is pressed

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While loop with no timing controls

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Loops

Untimed Loops: loop with no timing controls

▌ Untimed loops Run without any time interval between

successive iteration

▌ This results in a 100% processor Usage which leaves no

processor real-estate for other processes

▌ Always use some kind of timing controls in untimed

loops or use timed loops instead.

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While loop with no timing controls

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Timing control

▌ Insert delay between two successive loop iterations

using timing control

Wait (ms)

Timer value(ms)

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While loop with timing controls

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Loops

For Loop

▌ Used whenever the number of times a loop will execute

is known to you

▌ Loop count starts from 0 to N-1 in LabVIEW

Number of Iterations

Current loop count

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For Loop

Scenario: Design a VI that blinks an LED 10 times

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Case Structure

▌ Case structure is used different sections of code

depending on value of the select terminal

▌ By default the select terminal is Boolean so there are

only two cases , TRUE and FALSE

▌ There must always be a default case

▌ Select terminal can be of 4 types:

 Boolean

 Numeric

 String

 Enum

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Case Structure

Scenario: Design a VI that performs 10+5 if the user

selects True and 10- 5 if the user selects False

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CECOS University of IT & Emerging Sciences

Case Structure

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Tunnels

▌ Tunnel are used to transport the data into and out of the

loops

Output

Input

Tunnel

Tunnels

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CECOS University of IT & Emerging Sciences

Case Structure

▌ Scenario: We need to add, sub and multiply two

numbers(constants) depending on the value of the

numeric input that the user specifies

 If the numeric input is 0, then add the two numbers

 If the numeric input is 1 ,then subtract the two numbers

 If the numeric input is 2, then multiply the two numbers

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CECOS University of IT & Emerging Sciences

Case Structure

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Sequence Structure

▌ Executes sections of code in a sequence

▌ Type of sequence structures

 Flat Sequence Structures

 Stacked Sequence Structure

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Flat Sequence Structure

▌ Used to execute code in a left to right sequence

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Flat Sequence Structure

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Stacked Sequence Structure

▌ Works the same as flat sequence structure

▌ Sequences are stacked over one another rather than

being spread from left to right

▌ Results in more compact code than in flat sequence

structure

▌ Being more compact, its difficult to understand

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CECOS University of IT & Emerging Sciences

Stacked Sequence Structure

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CECOS University of IT & Emerging Sciences

Mathscript Window

▌ Its a Matlab like window where Matlab code could

written, tested and debugged just as in standard Matlab

▌ Matlab Engine run behind the scene

▌ Not all Matlab functions are supported in Mathscript

▌ However, with each new release of LabVIEW, the support

for Matlab functions grows

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CECOS University of IT & Emerging Sciences

Mathscript Window

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CECOS University of IT & Emerging Sciences

Mathscript Node

▌ Mathscript node allows you to integrate Matlab code

within the block diagram

▌ You can copy existing Matlab code and paste it within

Mathscript node in block diagram

▌ This integration of Matlab within block diagram reduces

the need to reinvent the wheel

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CECOS University of IT & Emerging Sciences

Mathscript Node

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CECOS University of IT & Emerging Sciences

Formula Node

▌ Formula node is used to integrate C-like code within

LabVIEW

▌ Its very cumbersome to graphically write complex and

long equations such as

▌ Use formula node for writing these cumbersome and

long equation

Contact: [email protected]

CECOS University of IT & Emerging Sciences

Task 1

▌ Design a VI that takes two numeric inputs x and y and

one string input from the user.

 If the string entered is add then the vi display x+y in the

result indicator

 If the string entered is sub then the vi displays x-y in the

result indicator

 In the string entered is mean or any other string (including

the empty string) then the result displayed is (x+y)/2

 Refer to Task 1.vi in the Tasks folder if you have any

confusion about how the VI should behave

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CECOS University of IT & Emerging Sciences

Hints for task 1

▌ Use case structure

▌ Use string as a case selector

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CECOS University of IT & Emerging Sciences

Lab report for Task 1

The lab report must contain

▌ Picture of the front panel

▌ Picture of the add case

▌ Picture of the sub case

▌ Picture of the mean case

 Note: Always write the question before beginning the

answer

Contact: [email protected]

CECOS University of IT & Emerging Sciences

Task 2

Answer the following question

▌ Question 1: What is an Array in LabVIEW

▌ Question 2: In which situation an array is likely to be

used

▌ Question 3: What is Cluster in LabVIEW

▌ Question 4: In which situation a cluster is likely to be

used

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CECOS University of IT & Emerging Sciences

Lab Report for Task 2

The lab report for task 2 must contain

▌ Give precise answers to the questions asked

▌ No long stories required

▌ Include pictures if possible

▌ Instead of long paragraphs use bullets format

 Important point 1

 Important point 2

 Important point 3

 Note: Always write the question in the lab report so that I

can know which question are you answering to

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CECOS University of IT & Emerging Sciences

Ball Sorting Demo at NI week 2005

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CECOS University of IT & Emerging Sciences