CS320n –Visual Programming

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CS320n Visual Programming

• LabVIEW Foundations

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What We Will Do Today

• Hand back and review the midterm
• Look at the basic tools in the LabVIEW
  programming environment

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LabVIEW Programming Elements

• Controls and Indicators arranged on palettes
  according to function
• Controls inputs (from user or other devices)
  source terminals
• Indicators outputs destinations or sinks
• They are not interchangeable

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Controls

• On front panel
• White background
• values may be typed in
• Increment / decrement control
• can hide by right clicking, selecting visible
  items, and unchecking
• On Block Diagram
• thick border
• arrow on right hand side, going out of icon

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Indicators

• On front panel
• background is gray
• no way to type in value
• On block diagram
• thin border
• arrow on left hand side, going into icon
• DBL indicates data type is a double, a number
  with a fractional component

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Adding Components on Front Panel

• Express view of palette
• Change to advanced view by clicking options
  button and selecting Advanced from pull down menu
  for Palette View

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Selecting Advanced View

• Advanced View of front panelpalette
• When mouse rolls over buttontitle of sub palette
  shown

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Adding Components

• Clicking on a button for a sub palette brings up
  that sub palette
• Get back to the previous palette using the up
  arrow
• right clicking on a palette button brings up the
  sub palette while keeping the original palette
  visible

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Adding Components

• Once correct component found click on it and drag
  to front panel
• Adding to front panel places corresponding
  terminal on the block diagram
• can alter characteristics of component by right
  clicking on it or
• alter font by selecting text and change Text
  Settings
• can change label and value in control / indicator

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Making Things Pretty

• Components on front Panel can be aligned and
  distributed
• Select components by clicking mouse and dragging
  box around them

align objects distribute objects resize
objects
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Wires

• Data is moved around a LabVIEW program via wires
• Wires are placed on the block diagram
• Wires take information from controls to nodes and
  indicators
• Wires are color coded based on the type of data
  they carry

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Wire Color Scheme

• Wires have a color and a width based on data type
  and data structure
• data types
• floating point numbers, integer numbers,
  Booleans, Strings
• data structures
• scalar (single value), array (list of values), 2D
  array (table of values)

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Wire Color Scheme

• Integer Floating Point Boolean
  String

Scalar Array 2D Array
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Wiring Components

• LabVIEW has an automatic tool selection option.
  (Selected by default)
• Cursor turns into tool necessary based on
  position of cursor
• When cursor moved over terminal it becomes a
  spool of wire
• click to start wiring
• drag wire from one terminal to another

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Adding Wires
Wire Icon
Wire from output of controlto input of indicator
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Broken Wires

• Errors in wiring are shown graphically
• loose ends
• incorrect data types
• too many wires

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Help

• Context Help is a feature of LabVIEW to provide
  help based on the situation you are in
• enable context help by pressing control and H or
  by selecting the Help menu and selecting Show
  Context Help
• Tries to explain errors
• shows information about icons / controls /
  indicators / data type of wire / sub VIs

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Nodes

• Nodes are program execution elements
• Like actions in Alice or statements in text based
  languages
• Nodes exist for all sorts of operations, from
  simple to complex
• add
• transpose the elements of a table

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Data flow

• LabVIEW programs are driven by data flow
• operations are not performed until the data to
  perform them is available
• Alice (and most text based languages) use
  sequential flow of control
• statements executed in the order they appear in
  the program

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Example of Data Flow

• Which gets executed first the add operation or
  the divide operation?
• The answer is, it depends.
• On which operation has the data to perform the
  operation first
• Sometimes when the program is run the add could
  be performed first and other times it could be
  the multiplication

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Cascading Data Flow

• Outputs of nodes can be feed to other nodes
• (x y) x y2
• multiplication not performed until addition
  complete

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Multiple Inputs and Outputs

• Operations (nodes) in LabVIEW can have more than
  input and more than one output
• multiple outputs are like multiple parameters in
  an Alice method or function
• Alice functions had no equivalent to the multiple
  outputs

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Example of Multiple Inputs and Outputs

• In Range and Coerce
• 3 inputs, 2 outputs
• explanation of inputs and outputs available on
  context help

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sub VIs

• As virtual instruments are created they can be
  used like the built in components
• packaged into a sub program
• create an icon with inputs and outputs
• analogous to class level methods in Alice
• code reuse
• LabVIEW contains a large library of sub VIs

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Example

• Temperature conversion
• Celsius to Fahrenheit
• Degrees Fahrenheit (1.8 Degrees Celsius)
  32
• Input -gt degrees Celsius
• Output -gt degrees Fahrenheit

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Conversion Formula

• Two ways to handle formula
• Use the primitive nodes and numerical constants
• Use the formula express option

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First Option
1.
2.
4.
3.
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Bad Wires

• If a wire connection is bad the wire will not be
  solid, but a dashed line

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Incorrect Programs

• A LabVIEW program that has wiring (or other
  format errors) cannot be run
• Clicking on the broken arrow brings up a list of
  errors
• Clicking on an error displays more information
  about the error
• Edit menu has Remove Broken Wires option or
  ltControl Bgt

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Adding Components Automatically

• Some components can be added automatically
  instead of from a palette
• In the temperature example
• after adding the multiplication node right click
  on one input
• from the pop up menu select Create and then
  Constant

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Changing Labels

• When component added to front panel it is given a
  default name
• change name to be more descriptive
• After entering text click off of control or press
  ltshift-entergt to finish
• Changes label on corresponding componen

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Free Labels

• Not attached to a component
• For describing things about a program

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Second Option
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Formula Editor
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Result of Second Option
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Another Exercise

• Simulate rolling a pair of dice

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Expected Output?

• What next?

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Expected Output?
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Rounding
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Making Two Dice

• Copy and paste many components

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Finished Product
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Always Another Way
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Both Methods