Digital Signal Processing with
LabVIEW 8.6
Lab # 05
Variables, State Machines, Dialog Boxes,
Tab Control
Designed by
Adnan Niazi
Lab Engineer
Signal Processing/Signal & Systems Lab
CECOS University of IT & Emerging Sciences
27th- 28th Feb 2009
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Agenda
▌ What is a Tab Control
▌ How to use Tab Control
▌ What are variables
▌ Types of variables
▌ What are dialog boxes
▌ How to use Dialog Boxes
▌ What is a State Machine
▌ How to make a State Machine
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Tab Control
▌ Tab control helps to organize and front panel into logical
blocks
▌ Instead of one very long front panel you can divide the
front panel into pages with each page containing only a
portion of the front panel objects
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Block diagram Without Tab Control
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Arranging Block Diagram with Tab Control
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Arranging Block Diagram with Tab Control
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Variable in LabVIEW
▌ There are three types of variable in LabVIEW
Local Variable
Global Variable
Shared Variable
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Local variable
▌ Local variable transfers data within a VI
▌ Allows programmer to access data from a control or
indicator at multiple locations in the block diagram
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How to make a Local Variable :
Method # 01
▌ Right click on an existing control and select Local
Variable from the create Submenu
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How to make a Local Variable :
Method # 02
▌ Drag a Local variable from the structures palette
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How to make a Local Variable :
Method # 02
▌ Right Click this Local Variable and assign it a control
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Local Variable
▌ Local Variables can be written to or read from
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Example of a Local Variable
Scenario
▌ Lets make a VI with two while loops running in parallel
with each other independently. Each while loop will have
its own stop button. We can’t stop these two loops
simultaneously because we can’t work with both the
stop buttons at exactly the same time
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Example of a Local Variable
Both Loops are running in
Parallel with each other.
Consequently y same result
is shown in both the indictors
No matter How Hard you Try,
you can’t stop these two
loops at the same time using
two Stop Buttons
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Use Local Variable to solve this
Problem
Now Both Loops can be
stopped simultaneously by
using just one stop button
with the help of a local
variable
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Caution
▌ By Default the stop button has a latch Action
▌ Local Variables can’t work with Latch type Buttons
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Caution
▌ To successfully run the VI, you need to change the latch
action to a switch action
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Global Variable
▌ Global Variable transfers data within multiple VIs on a
single computer
▌ Global variables are built-in LabVIEW objects.
▌ Global variables have a front panel but no block diagram
▌ Can contain multiple data types
▌ Retain whatever values are set as default
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How to make Global Variables
▌ Step 1: Place a Global variable from the structures
palette onto the block diagram
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How to make Global Variables
▌ Step 2: Double click the Global Variable to open its front
panel and place any control that you want to convert to
Global
Variable
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How to make Global Variables
▌ Step 3: Save and close the front panel for the global
variable
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Caution
▌ Avoid use of Global variables whenever possible
▌ Use Functional Global Variables instead of Global
Variables
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Shared Variable
▌ Transfer data within multiple VIs to multiple computers
over a network.
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Where to find Tab Control
Tab Control
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Type Definition or Type Def
▌ Type definition is custom control file that has been
marked as a Type Def
▌ Instances of Type Def are Linked to their definition
▌ Changes in definition cause all the instances to be
updated
▌ Enumerated constants with type def are widely used in
Enum Driven state Machine Architecture
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How to Make Type Def of a CTL
▌ Step 1: Follow this path
Right click the control >>> Advanced >>> Customize
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How to Make Type Def of a CTL
▌ Change the control to Type Def
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How to Make Type Def of a CTL
▌ Any changes made to the type definition will result in
the automatic update of all the instances of that type def
▌ This saves a lot of time as you only need to change the
definition. All instance of the type def will automatically
update themselves.
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Dialog Boxes
▌ Dialog boxes Pop Up during runtime
▌ They inform the user that something has happened
▌ They require a certain response from the user
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Types of Dialog Boxes
There are Four types of Dialog Boxes
▌ 1- One Button Dialog Box
▌ 2- Two button Dialog Box
▌ 3- Three button Dialog Box
▌ 4- Prompt Dialog Box
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One Button Dialog Box
▌ One Button Dialog Box is used to show some
information to the user and getting back some
acknowledgment
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One Button Dialog Box
▌ Two button dialog box lets the user select one of two
different options
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Three Button Dialog Box
▌ It allows user to select one of the three available options
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Prompt Dialog Box
▌ Enables user to specify some input
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Prompt Dialog Box
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State Machine
▌ A state machine or Finite State machine (FSM) consists
of States, Actions and transitions between the different
states
▌ The current state is defined by the previous states
▌ Each state may lead to one or multiple states
▌ A State Machine relies on user input or in-state
calculation to determine which state to go to next
▌ Commonly used for making user interfaces
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State Machine for an Oven
Power Up
Routine
Cook Food or
Shutdown?
Shutdown
Routine
Set Cooking
Timer
Start
Food
Cooking
Beep
Cooked
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State Machine for an Oven
State 1: Power Up Routine
▌ In this state the ovens electronics are powered up
▌ Soft Start circuit supplies power to the electronics (LCD
display etc…) after a certain delay when all the
transients have settled down
▌ A delay of 1000ms simulates the delay introduced by the
soft start circuitry
▌ After the soft start has started the electronics, a
Powered up! message is displayed for 1000ms
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State Machine for an Oven
State 1: Power Up Routine
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State Machine for an Oven
State 2: Cook Food or Shutdown?
▌ In this state the user is presented with a dialog box
asking the user whether he wants to cook food or just
want to shutdown the oven
▌ If the user Presses Cook Food then the state machine
goes to Set Cooking Timer State otherwise it goes to the
Shutdown Routine state
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State Machine for an Oven
State 2: Cook Food or Shutdown?
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State Machine for an Oven
State 3: Set Cooking Timer
▌ In this state the user is presented with a dialog box
asking the user to set Cooking Time in Seconds
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State Machine for an Oven
State 3: Set Cooking Timer
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State Machine for an Oven
State 4: Start Cooking
▌ After the user specifies the cooking time, the oven’s
heating mechanism is started and the food starts to
cook.
▌ The remaining cooking time is displayed on the front
panel
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State Machine for an Oven
State 4: Start Cooking
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State Machine for an Oven
State 5: Beep
▌ When the Food has been cooked for the specified
amount of time, an alarm, in the form of three beeps, is
sounded to alert the user near by
▌ Mean while The front displays Food Cooked! message
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State Machine for an Oven
State 5: Beep
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State 6: Power down Routine
▌ The oven is shut down in this state.
▌ A message Shutting Down is displayed for 2 seconds
and then the display is cleared(simulating the turning off
of the LCD display) and then the VI aborts
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State Machine for an Oven
State 6: Shutdown Routine
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Task 1
▌ Design a LabVIEW VI that mimics the behavior of the
following state transition diagram
User chooses to go
to next State
State 1
User chooses to go
to previous State
User chooses
Abort or Quit
State 2
State 5
Abort
State 3
State 4
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Lab Report
The lab report must contain
▌ Block Diagram for State 1
▌ Block Diagram for State 2
▌ Block Diagram for State 3
▌ Block Diagram for State 4
▌ Block Diagram for state 5
▌ Black Diagram for Abort State
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Hints For the Task
▌ First Define six states in an Enumerated Type Def. The
states should be:
State 1
State 2
State 3
State 4
State 5 &
Abort
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Hints For the Task
▌ Use Three Button Dialog Box to ask the user whether he
wants to go to next state, previous state or want to abort
the state machine
▌ You can use case structure with the output of the three
button dialog box in order to select the Next, Previous or
Abort States
If you have any problem understanding how the VI should
behave then, refer to the project Task 1.lvprj in the Tasks
folder.
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Brain Control with LabVIEW
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CECOS University of IT & Emerging Sciences
