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CHAPTER 9. POS TERMINAL 69
(a) Representative images
(b) Vision Assistant script
(c) LabVIEW project file set
9.1 Technical Approach
NI Vision Assistant Script
NI Vision Assistant provides the Barcode Reader step as a flexible and easy-to-
use method to detect 1-D barcodes from among ten different standards including
“EAN 13” (European Article Number) and the essentially equivalent “UPC-A”
(Universal Product Code). This step can even detect multiple barcodes of differ-
ent types, all within the same image. The Barcode Reader step is scale invariant
(the barcode can be any size) as well as rotation invariant (the barcode angle does
not matter); the only requirement is that the barcode must be in focus with suffi-
cient spatial resolution to resolve the black and white bar pattern. Study
EAN-13
(UPC-A) Barcode Reader
1
to learn how to set up the Barcode Reader step.
The Vision Assistant Express VI offers two indicators for the Barcode
Reader ; use the Barcodes output. This output is an array because the reader
can read multiple barcodes at once. Use the following techniques to interpret
the barcode output:
1. Use the
Index Array
function to retrieve a single barcode and connect this
to a custom control in the data highway,
T
IP
: Use the “Quick Drop” shortcut (Ctrl + space bar) to look up
and place a LabVIEW element by name. See Appendix C on page 139
for more LabVIEW tips.
2. The “Data” element of the barcode output is a string that contains the nu-
merical code. Use the
Empty String/Path?
function to determine whether
or not a valid barcode is in view, and
3. Use the Decimal String To Number function to convert the “Data” element
string to an [I64] integer; wire a zero-valued constant of this data type to
the
default
input.
1
http://youtu.be/hLSla3C-6V4
(1:29)