Digital Electronics and Computer Interfacing PH 534

Digital Electronics and Computer Interfacing

PH 534

Tim Mewes

Spring 2011

01/11/2007 Digital Electronics and Computer Interfacing 2

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


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


1. LabVIEW Basics

1.1 Front panel

1.2 Block diagram

1.3 Getting help

1.4 Debugging

Experiment #1


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


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


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


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)


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


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.


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)


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.


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


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”


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


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


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


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


1. LabVIEW basics

1.2.3 Wiring objectsWiring “Hot Spot”

Clean Up Wiring

Left Click To Select Wires


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.


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!


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:


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

Documents

Digital Electronics and Computer Interfacing PH 534