An Introduction To Using
LabView - Adding Two Numbers
This note is for those just starting to
program in LabVIEW. In this exercise, you will create a vi (Virtual Instrument)
that adds two numbers. You have to take care of the following tasks.
You need to input two numbers You need to add the two
numbers that were put in in the first step. You need to display the
results (sum).
In the process, you should create a diagram like the
one below. Follow the steps below, which tell you what you need to do, and
which provide explanations of what is going on as you do things.
Start LabView.
Choose New vi. On the
Front Panel of that
new vi, add two numeric controls and a numeric indicator. You may need
to get the Controls Palette using
Window-Show Controls Palette to show the
controls palette, then click to show all functions and open the
Numeric sub-palette
to get the numeric control tool to place numeric controls on the front
panel.
You will use
the two numeric controls
to input the two numbers that you want to add. You will do that on
the front panel when you run the program. When you add the numeric
controls on the front panel, you will find that you have added the
elements shown above on the block diagram. If the block diagram is
not showing, then click Window-Show
Block Diagram (from the menus on the
front panel!) to show the block diagram. In the diagram
above, those controls are labelled "A" and "B". We used the
Text Tool to
change to those labels from the default labels. If the text tool is
not showing, click on Window-Show Tools
Palette to show the tools palette, and
click on the panel in that palette that shows the letter A to
indicate the text tool. Add a
numeric indicator
to show the result on the front panel. Find the numeric indicator
tool and add one numeric indicator to the front panel. Again, you
can change the label to "C" - as we did above.
Now, you need to go
to the block diagram. If the block diagram is not showing use
Window-Show Block Diagram
to show the block diagram. (Or, if you have the windows not taking up
the full screen, you can just click between them. On the
Block Diagram, add
the addition element - the "summer". You will need to show the
Functions Palette using Window - Show
Functions Palette (using the block diagram
menus).
This is the element
that will actually do the addition. In the diagram above,
the yellow triangle with the "+" sign is the addition element.
Wire the output of the
two numeric controls to the addition element. You need to locate the
wiring tool (It looks like a spool of wire.), then wire your circuit by
holding down the mouse button as you drag the tool from connector to
connector on the various elements. Wire the output of the
summer to the numeric control.
Note the following:
The two numeric
controls that you use for input and the numeric indicator that you use
for output must all be put onto the front panel. You can't add them to
the block diagram. When you add these elements to the front panel, the
terminals for
these elements appear on the diagram at an arbitrary position, and you
will need to position those elements where you want them. The summer appears only
on the block diagram. There is no indication that it even exists if you
look on the front panel. You can make a better
looking program by putting some appropriate label(s) on the elements on
the front panel.
Now, you can run the
program. Do the following:
What can go wrong?
You might mis-wire
something. Then the run button will have a broken arrow, but if you
click it anyway you will get an error message that points to where
things have gone wrong. You might have used a
wrong element. For example, you might have used the multiplier element
instead of the summer. Then you would get one of those hard-to-debug
kinds of problems. Note that you can always right-mouse-click on an
element to get help.
There are some other
considerations with the vi that you have just constructed and run.
The data representation is a "double" i.e.
a more precise floating point representation. You can right-mouse-click on the
icon on the block diagram and change the representation (and there are numerous
choices.)
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