National Instruments NI myRIO, Essentials Manual

Page: 77 / 163

CHAPTER 9. POS TERMINAL 71
These LabVIEW techniques are also required for this project:
•
Add Custom Data Lane
9
– Create a custom control for the Barcodes
Vision Assistant script output and insert this into the data highway
•
Create Formatted Text String
10
– Format Into String
•
Overlay Text
11
– Use IMAQ Overlay Text to insert a text string into the
nondestructive image overlay
• Select Overlay Text Font
12
– Select the “NI Vision” font and adjust its size
•
Create “Inventory” Cluster of Arrays
13
– Create a cluster of arrays to store
the product inventory with item codes, names, and values
9.2 Development Tips
Representative Images
•
Gather at least five items that contain barcodes.
•
Conduct an Internet search to learn more about the structure of an EAN-13
barcode and write a paragraph to describe your findings. Also look for
a site that can generate an EAN-13 barcode given a user-supplied value.
•
Determine the camera distance and camera mode (resolution and frame
rate) that achieves your required spatial resolution while maximizing the
frame rate.
• Experiment with your barcode items to determine a suitable background
color; you may find that a piece of white paper works well to protect the
surface of the table-top camera copy stand. Ambient room light should suf-
fice; keep the lighting as uniform as possible to avoid lighting “hot spots.”
• Use a line grid target to align the camera so as to minimize perspective
distortion.
•
Adjust the camera attributes to maximize the contrast of the barcode’s
black-and-white pattern. The NI Vision Assistant
Barcode Reader step is
robust and should be able to ignore the other features visible on the object.
9
http://youtu.be/GkqjZCj3xck
(2:58)
10
http://youtu.be/VqH0SSK1fHY
(1:44)
11
http://youtu.be/SS72-mKX6fQ
(2:15)
12
http://youtu.be/lEKJcR553zA
(2:48)
13
http://youtu.be/DJB1otFHnbA
(5:03)