Digital Electronics and Computer Interfacing

PH 534

Tim Mewes

Spring 2011

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Digital Electronics

• Binary systems with two possible values (logic states):– High/Low– ON/OFF– 1/0– TRUE/FALSE

• First part of the course, after introduction to LabVIEW

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Computer interfacing

• Connects the digital world to the analog world• One way to communicate with Laboratory equipment is

by using GPIB-commands (General Purpose Instrumentation Bus)

• Data acquisition cards (DAQ-cards) provide another interface between the computer and the outside world

• Second part of the course

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1. LabVIEW Basics

1.1 Front panel

1.2 Block diagram

1.3 Getting help

1.4 Debugging

Experiment #1

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1. LabVIEW Basics

Together these two parts constitute a Virtual Instrument – short: VI

A VI is typically build by using other VIs which are then called subVIs

Block diagram:contains the graphicalprogram code

Front panel:the interface to theprogram

<CTRL>-E switches between Block diagram and Front panel

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1.1 Front panel

1. LabVIEW basics

Toolbar

Pull-down menus

VI icon (right click for short cut menu)

Window title

Area that holdscontrols/indicatorsenables user interaction

(Numeric) controls:Enable the user to enter data

(Numeric) indicator:Displays data

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run button

broken run buttonindicates coding errors

run continuously button

abort execution button

pause/resume button

1. LabVIEW basics

text settings

align objects

distribute objects

resize objects

reorder objects

show/hide context help

1.1.1 Front panel toolbar

indicates running top level VI

indicates that a VI caller is running

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1. LabVIEW basics

1.1.2 Controls palette• right clicking in an empty area of the front panel opens the controls palette• choose the general type of control/indicator:

1

1. Numeric controls & indicators

2

2. Boolean controls & indicators

33. String & Path controls & indicators

4 4. Array, Matrix & Cluster controls & indicators

5 5. Graphs (indicators)

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3 4

5

1 2

1. LabVIEW basics

1.1.2 Controls palette• right clicking in an empty area of the front panel opens the controls palette• choose the general type of control/indicator:

• place the object on the front panel:

left click

• type in a name for the control, finish with or by clicking on an empty spot of the front panel avoid using generic names like “Numeric”!

1. Numeric controls & indicators

• from the submenu choose the desired control/indicator

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1. LabVIEW basics

1.1.3 Short cut menus• right clicking in different areas of a control opens different short cut menus

• changes a control into an indicator and vice versa

• opens the properties dialog box

Can be used to change the default value, data range, label, documentation and many more properties of objects.

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1. LabVIEW basics

1.1.4 VI icon and connector pane• right click on the icon opens the short cut menu

• always design your own icon for your VIs avoid using the standard icons!• many times you will only see the icon of your VIs

• opens the icon editor:

• shows the connector pane of the VI

the connector pane is used to define inputs and outputs of subVIs(will be discussed in detail later)

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1. LabVIEW basics

1.1.5 Icon editorPencil: Draws and erases pixel by pixel.

Line: Draws straight lines.

Color Copy: Copies the foreground color from an element in the icon.

Fill: Fills an outlined area with the foreground color.

Rectangle: Draws a rectangular border in the foreground color.

Filled Rectangle: Draws a rectangle with a foreground color frame and filled with the background color.

Select: Selects an area of the icon to cut, copy, move, or make other changes. Text: Enters text into the icon. Double-click this tool to

select a different font. While text is active, you can move the text by pressing the arrow keys.

Copy from: Copies from a color icon to a black and white icon and from a black and white icon to a color icon.

Foreground/Background: Displays the current foreground and background colors. Click each rectangle to access a color picker from which you can select new colors.

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1. LabVIEW basics

1.1.6 Tools palette

• <SHIFT> + right-click or select it in the “View” pull-down menu• Used to modify the cursor appearance and its functionality

Operating Tool

Positioning/Resizing Tool

Labeling Tool

Wiring Tool

Shortcut Menu Tool

Scrolling Tool

Breakpoint Tool

Probe Tool

Color Copy Tool

Coloring Tool

Automatic Selection Tool (off): Keep it on!<SHIFT>+<TAB> turns it back on

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1.2 Block diagram

1. LabVIEW basics

Toolbar

Pull-down menus

VI icon (right click for short cut menu)

Window title

Control terminals

wire

function node

Indicator terminal

This is where the program code is “written”

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debugging features

Step Over executes a node and pauses at the next node

Execution highlighting enabled

retain wire values saves data values

1. LabVIEW basics

Highlight execution buttonenables/disables execution highlightingdata flow will be visible

Step Into opens a node and pauses

Step Out finishes executing the current node and pauses

1.2.1 Block diagram toolbar

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1. LabVIEW basics

1.2.2 Functions palette

• right clicking in an empty area of the block diagram opens the functions palette• choose the general type of node you want to insert:

1. Structures (For Loop, While Loop, Event Structure, etc.)1

2. Array functions (Array size, Index Array, Build Array, etc.)2

3. Cluster & Variant functions

3

4. Numeric functions (Add, Subtract, Multiply, etc.)

4

5. Boolean functions (AND, OR, XOR, etc.)

5

6. String functions (String length, Concatenate Strings, etc.)

6

7. Comparison functions (Equal, NOT equal, greater, etc.)

7

8. Instrument I/O (Data acquisition & interfacing)

8

9. User Libraries (your own VIs)

9 • place the actual object on the block diagram

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1. LabVIEW basics

1.2.3 Wiring objects

• once you move the cursor over an input (or output) terminal it changes to the wiring tool

• left click starts a wire

• moving the mouse creates a wire (dashed line)

• left click again over an output (or input) terminal

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1. LabVIEW basics

1.2.3 Wiring objects

• wiring errors are indicated by broken wires

• moving the wiring tool over a broken wire displays a tip strip that describes why the wire is broken

• <CTRL>-B removes all broken wires on the Block diagram

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1. LabVIEW basics

1.2.3 Wiring objectsWiring “Hot Spot”

Clean Up Wiring

Left Click To Select Wires

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1. LabVIEW basics

1.2.4 Short cut menus• right clicking on terminals, function nodes and wires opens different short cut menus

• terminals: - find the corresponding object on the front panel - hide the corresponding object on the front panel - change the properties of the object etc.

• function nodes: - create a constant, control or indicator for a particular input or output – very useful etc.

• wires: - create a constant, control or indicator - clean up the wire - set/clear breakpoints etc.

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1. LabVIEW basics

1.3 Help

• <CTRL>+H, or “Show Context Help” from the Help pull-down menu toggles the Context Help on and off• Move the cursor over the Block diagram object you are interested in

• Using <CTRL>+?, F1 or “Search the LabVIEW…” from the Help pull-down menu you can get more detailed help• Besides help for different LabVIEW components tutorials are also available (PDF-files) try for example to search for “getting started how-to”

• Use “Find examples” from the Help pull-down menu to find example VIs for a specific task

• Make yourself familiar with the LabVIEW help!

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1. LabVIEW basics

1.4 Debugging

• Click on broken Run button: a Window that explains the error and possible solutions appears

Locating errors:

• Click on Execution Highlighting button; data flow is animated using bubbles. Values are displayed on wires.

Execution Highlighting:

• Right-click on wire to display probe and it shows data as it flows through wire segment

• You can also select Probe tool from the Tools palette and click on the wire

• If retain wire values is on the last data flowed through the wire at the last VI execution is shown immediately

Probes:

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1. LabVIEW basics

1.4 DebuggingBreak points:

• Right-click on a wire or node to set/clear a break point

Continue execution until the next break point or the end of the program

Step Over executes a node and pauses at the next node

Step Into opens a node and pauses

Step Out finishes executing the current node and pauses