The bar code reader consists of a light source and a photo diode that are placed next to each other in the tip of a pen or wand. To read the bar code, the tip of the pen has to be dragged across all the bars in an even and steady manner. The photo diode measures the intensity of the light reflected back from the light source and generates a wave form that is used to measure the widths of the bars and spaces in the barcode. Dark bars in the barcode absorb light and the white spaces reflect the light so that the voltage wave form generated by the photodiode is an exact duplicate of the bar and space pattern in the barcode. This waveform is decoded by the scanner in a manner to similar to the way Morse code dots and dashes are decoded.
Laser scanners work the same way as pen type readers except that they use a laser beam as the light source and typically employ either a reciprocating mirror or a rotating prism to scan the laser beam back to and forth across the barcode. Just the same as with the pen type reader, a photo diode is used to measure the intensity of the light reflected back from the bar code. In both pen readers and laser scanners, the light emitted by the reader is turned to a specific frequency and the photo diode is designed to detect only this same frequency light.
Pen type readers and laser scanners are available with different resolutions to enable them to read bar codes of different sizes. The scanner resolution is measured by the size of the dot of light emitted by the reader. The dot of light should be equal to or slightly smaller than the narrowest element width ("X" dimension). If the dot is wider than the width of the narrowest bar or space, then the dot will overlap two or more bars at the same time thereby causing the scanner to not be able to distinguish clear transitions between bars and spaces. If the dot is too small, then any spots or voids in the bars can be misinterpreted as light areas also making the barcode unreadable. The most commonly used X dimension is 13 mils (roughly 4 printer dots on a 300dpi printer). Because this X dimension is so small, it is extremely important that the bar code is created with a program that creates high resolution graphics (like B-coder).
3.2 bar code scanner:
A barcode scanner is a device that uses a laser or other technology to collect and interpret barcodes on customer products, shipping labels and many other items. Barcode scanner is used around the world because they can collect information quickly and accurately. Barcode scanners are used everywhere, from retail checkout counters to delivery companies to movie and sports tickets to medical information bracelets.
how does a bar code scanner WORK?
A bar code scanner scans a barcode using a laser or other technology. Before the information contained in the barcode can be used, it may be decoded by the software which is either incorporated within the barcode scanner itself or in the form of software on a desktop, laptop, server, PDA or other computers. This turns the alternating black and white bars seen on a product into a string of letter and / or numbers that can then be used to look up pricing, inventory or other information for the product.
bar code scanner types:
Laser bar code scanner:
A laser barcode scanner uses a rapidly-moving laser to shine a particular frequency of light at black and white bars of a barcode. The laser light is reflected off the bar code and read by a photo diode in the bar code scanner. The barcode scanner then interprets a reflection data and decodes it into useful data. To use a laser barcode scanner, simply hold it near the barcode and click the button or trigger. A laser barcode scanner is suitable for almost any use, reads barcodes quickly and is very affordable.
CCD bar code scanner:
A CCD barcode scanner works much like a laser barcode scanner, but instead of shining a laser at the barcode, the CCD barcode scanner measures light reflected from a series of light-emitting diodes (LED's). This technology and not as fast as a laser barcode scanner, but usually costs less. Some CCD barcode scanner can read 2D barcodes. To use a CCD barcode scanner, hold it near the barcode and click the button or trigger.
USB Bar code scanner:
A USB bar code scanner uses the computer USB port to transmit data from the barcode scanner to the computer. The USB is a fast, easy to use connection which uses the computers own power supply to power the barcode scanner. Through the use of the USB hub, many USB peripherals can be connected to the same computer at the same time.
PS2 Keyboard Wedge Bar code scanner:
A PS2 keyboard wedge barcode scanner to the keyboard port on the computer. When a barcode is scanned, the data appears on the screen just as a though it had been entered via the keyboard. The keyboard wedge barcode scanners come with a "Y" connecter which allows the keyboard and the scanner to be connected and used at the same time. This is a very simple and easy to install type of barcode scanner, but it does not allow any modification or re-ordering of the barcode's data before displaying it on the screen.
Wireless Bar code scanner:
A wireless barcode scanner (also known as an RF barcode scanner or a cordless barcode scanner) operate on wireless frequencies like a cordless phone. A wireless barcode scanner transmits data to a base station which is connected to computer. The base station also doubles as a battery charger for the scanner. Wireless barcode scanner models vary by transition rate and by battery life, and are ideal for warehouses and retail stores.
Bluetooth Bar code scanner:
A bluetooth barcode scanner is very similar to a wireless barcode scanner but uses bluetooth technology to transmit its data. The bluetooth interfaced has a shorter range than other wireless technologies but is found in small devices such as mobile phones and PDA's. This makes the bluetooth barcode scanner flexible since it can interact with a much wider array of devices.
SPECIFICATION OF BAR CODE SCANNER (QUICKSCAN® QS6500):
Mechanical:
Dimensions
Height: 6.0" / 16.5cm
Width: 2.9" / 7.4 cm
Length: 3.9" /9.9 cm
Weight
6.4 oz. /181.4 g
Electrical:
Operating Voltage
+4.5 to 14VDC ±5%
Operating Current
300mA @ 5VDC
Idle Current
200mA @ 5VDC
Environmental:
Temperature Rating
Operating: 32° to 122° F /0° to 50°C
Storage: -40° to 158° F /-40° to 70° C
Humidity
Operating: 5 to 95% NC
Storage/Transport: 5 to 95% NC
Vibration
Meets MIL STD-810E
Mechanical Shock
Withstands 50 drops from 5' / 1.5m to concrete
ESD Protection
Functional after multiple 25kV discharges.
Water & Dust
IEC529 Rating IP52DW
Communications
RS-232
Keyboard Wedge
IBM 46XX
IBM USB
USB
Optical
Ambient Light Immunity
Artificial & Sunlight: 86,000 Lux
Light Source
630nm Visible Red Diode
Scan Rate
450 scans/sec max
Sensor
2048 pixel linear imager
Scan Width
6.3" /16.5cm @ 7" /17.8 cm from nose
Resolution
5 mils /.13mm
Print Contrast
30% or greater
Pitch
±60°
Skew
±55°
Depth of Field*
LABEL DENSITY
RANGE* 1D MODELS
RANGE* PDF MODELS
5 mil Linear
2.0 - 5.0" / 5.1 - 12.7 cm
2.0 - 4.5" / 5 - 11.4 cm
7.5 mils
1.0 - 7.0" / 2.5 - 17.8 cm
1.0 - 6.0" / 2.5 - 16.2 cm
10 mils
0 - 12" / 0 - 30.5 cm
0 - 10.5" / 0 - 26.7 cm
13 mils / 100% UPC
0 - 15" / 0 to 38 cm
0 - 13" / 0 - 33 cm
20 mils
Up to 24" / 61.0 cm
Up to 21" / 53.3 cm
40 mils
Up to 40" / 101.6 cm
Up to 35" / 89 cm
* Minimum distance determined by symbol length and scan angle. Printing resolution, contrast, and ambient light dependent.
Decoding Capability
1D Versions
UPC A, E / EAN 8, 13 / JAN 8, 13
Add-ons (sub 2 or P2, sub 5 or P5 & C128)
RSS-14, Expanded, Stacked, Limited
ISBN / Bookland EAN
Code 39 (with full ASCII)
Pharmacode 39
Code 128
Code 93
Interleaved 2 of 5
Standard 2 of 5
IATA
Code 16K
Code 11
Codabar/NW7
UK/Plessey
MSI/Plessey
PDF Models support these additional symbologies:
RSS Composites
PDF-417
Micro-PDF
Safety & Regulatory
Electrical: Complies to:
EN60950
CSA60950
UL60950
Emissions: Complies to:
FCC-A
EN 55022-B
BSMI 13438
AS/NZS 3548
VCCI-B
ICES-003
Laser Classification
IEC 60825 Class 1 LED
3.3 BAR CODE LABEL:
A barcode label is a printed version of the Morse code. Different bar and space patterns are used to represent different characters. Sets of these patterns are grouped together to form a "symbology". There are many types symbologies each having their own special characteristics and features. Most symbologies were designed to meet the need of a specific application or industry.
Bar code label types:
Code 39 (Normal and full ASCII versions) :
The normal code 39 is a variable length symbology that can encode the following 44 characters: 1234567890ABCDEFGHIJKLMNOP QRSTUVWXYZ-.*$/+%. Code 39 is the most common symbology in the non retail world and is used extensively for in manufacturing, military and health applications. Each code 39 is framed by a start/stop character represented by an asterisk (*). The asterisk is reserved for this purpose and may not be used in the body of the message. Bar coder automatically adds the start and stop character to each bar code. Therefore one should not include them as part of the bar code message. If the NORMAL version of CODE 39 and the barcode text contains lower case characters, decoder will concert them to upper case. If the barcode message contains any invalid characters, the barcode-decoder will prompt with a warning message.
Code 39 optionally allows for a check character incase where data security is important. The health care industry has adopted the use of this check character for health care applications. Another feature of code 39 allows for concatenation of two or more bar codes. It is sometimes advantages to take long message into multiple shorter messages.
CODABAR:
CODABAR is a variable length symbology that allows encoding of the following: 123456789-$:/.+ABCD. CODABAR is commonly used in libraries, blood banks, and the air parcel business. Codabar uses the characters ABC & D A as start and stop characters. Thus, the first and last digits of a Codabar message must be A B C & D. and the body of the message should not contain these characters. Bar-coder will allow any length of Codabar message as long as it contains valid characters and starts and ends with a valid start/stop character. If you use lower case letters for A B C or D, bar coder will convert to upper case.
INTERLEAVED 2 0F 5:
Interleaved 2 0f 5 is a high density variable length numeric only symbology that encodes digit pairs in an interleaved manner. The odd position digits are encoded in the bars and the even position digits are encoded in the spaces. Because of this, 1 2 of 5 bar codes have a slight chance of being decoded as a valid bar code, readers are usually said to read a fixed (even) number of digits are usually predefined for a particular application and all readers used in this application are programmed to only accept 1 2 of 5 bar cods of chosen length. Shorter data can be left padded away with zeros to fit the proper length.
CODE 93:
CODE 93 is a variable length symbology that can encode the complete 128 ASCII character set. CODE 93 was developed an enhancement to CODE 39 symbology by providing a slightly higher character density than CODE 39. CODE 93 also incorporates two check digits as an added measure of security. Although CODE 93 is considered more robust than CODE 39, it has never achieved the same popularity as CODE 39. CODE 93 bar codes are framed by a special start/stop character. B-coder will automatically add the start stop characters as well as the check digits to each CODE 93 bar code, therefore it is not necessary to include them as a part of the message.
CODE 128:
CODE 128 is a variable length high density, alphanumeric symbology. CODE 128 has 106 different bar and space patterns and each pattern can have one of three different meanings, depending on which of three character sets is employed. Special start characters tell the readers which of the character sets is initially being used and three special shift codes permit changing character sets inside a symbol. One character sets encodes all upper case and ASII control characters, another encodes all upper case and lower case characters and the third set encodes all numeric pairs 00 through 99. The CODE 128 allows special characters for application specific purposes.
DATA MATRIX:
The data matrix is a high density two dimensional matrix style, bar code symbology, that can be encode up to 3116 characters from the entire 256 byte ASCII character set, the symbol is built on a square grid arranged with a finder pattern around the perimeter of the bar code symbol.
There are two types of data matrix symbols each using a different error checking and correction scheme (ECC). The different types of data matrix symbols are identified using the terminology (ECC) followed by a number representing the type of error correction that is used by the encoding software. ECC 000 to 140 are the original type of data matrix symbols and are now considered obsolete. The newest version of the data matrix is called ECC 200 and is recommended for all new data matrix applications. The ECC 200 version of data matrix uses a much more efficient algorithm for encoding data in a symbol as well as an advanced error checking and correction scheme.
Interfacing of the Bar Code scanner :
The barcode scanner is interfaced with the PC using a converter cable that converts PS2 to RS-232 standard, for the PC to be able to communicate successfully with the barcode scanner. The data received by the PC is sent to the PLC through a special communication channel available in Windows XP, called the "Hyper Terminal". The hyper terminal allows data present on the hyper terminal screen to be transferred to any other location. In this particular application the data i.e. the data sent by the barcode scanner, is sent to a variable memory in the PLC, the data in the PLC is then used by the program to generate the right sequence of PTO output.
