cs320n –visual programming labview foundations. visual programminglabview foundations2 what we...

CS320n –Visual Programming

LabVIEW Foundations

Visual Programming LabVIEW Foundations 2

What We Will Do Today• Hand back and review the midterm

• Look at the basic tools in the LabVIEW programming environment


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


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


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


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


Selecting Advanced View

• Advanced View of front panelpalette

• When mouse rolls over buttontitle of sub palette shown


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


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


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


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


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)


Wire Color Scheme

Integer Floating Point Boolean String

Scalar

Array

2D Array


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


Adding Wires

Wire Icon

Wire from output of controlto input of indicator


Broken Wires• Errors in wiring are

shown graphically– loose ends– incorrect data

types– too many wires


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


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


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


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


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


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


Example of Multiple Inputs and Outputs

• In Range and Coerce

• 3 inputs, 2 outputs

• explanation of inputs and outputs available on context help


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


Example• Temperature conversion

• Celsius to Fahrenheit

• Degrees Fahrenheit = (1.8 * Degrees Celsius) + 32

• Input -> degrees Celsius

• Output -> degrees Fahrenheit


Conversion Formula• Two ways to handle formula

1. Use the primitive nodes and numerical constants

2. Use the formula express option


First Option

1.

4.

2.

3.


Bad Wires• If a wire connection is bad the wire will not

be solid, but a dashed line


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

<Control B>


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”


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 <shift-enter> to finish

• Changes label on corresponding componen


Free Labels• Not attached to a component

• For describing things about a program


Second Option


Formula Editor


Result of Second Option


Another Exercise• Simulate rolling a pair of dice


Expected Output?

• What next?


Expected Output?


Rounding


Making Two Dice• Copy and paste many

components


Finished Product


Always Another Way


Both Methods

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