Barcode Reader
Luz Tonks
A barcode reader or barcode scanner is an optical scanner that can read printed barcodes, decode the data contained in the barcode to a computer. Like a flatbed scanner, it consists of a light source, a lens and a light sensor for translating optical impulses into electrical signals. Additionally, nearly all barcode readers contain decoder circuitry that can analyse the barcode's image data provided by the sensor and send the barcode's content to the scanner's output port.
Pen-type readers consist of a light source and photodiode that are placed next to each other in the tip of a pen. To read a barcode, the person holding the pen must move the tip of it across the bars at a relatively uniform speed. The photodiode measures the intensity of the light reflected back from the light source as the tip crosses each bar and space in the printed code. The photodiode generates a waveform that is used to measure the widths of the bars and spaces in the barcode. Dark bars in the barcode absorb light and white spaces reflect light so that the voltage waveform generated by the photodiode is a representation of the bar and space pattern in the barcode. This waveform is decoded by the scanner in a manner similar to the way Morse code dots and dashes are decoded.
Laser barcode scanners utilize a semiconductor laser diode to produce a laser beam. This beam is directed by a deflection mirror onto a polygon mirror wheel. The design may include a focusing device, enabling the scanner to adjust the beam to scan at various distances.[1]
The scanner deflects the laser beam using a rotating mirror wheel. This wheel deflects the beam line by line over the barcode at frequencies between 200 Hz and 1200 Hz in most scanners. The deflected beam exits the scanner spread at an opening angle, which is dependent on scanner design. The deflection allows it to traverse the barcode in a reading plane, effectively turning it into a "reading beam." To accommodate stationary items, laser scanners incorporate oscillating mirrors that provide additional deflection perpendicular to the main scanning line. These mirrors function at frequencies that can vary from 0.1 Hz to about 5 Hz, ensuring that barcodes can be read at different orientations.[1]
Charge-coupled device (CCD) readers use an array of hundreds of tiny light sensors lined up in a row in the head of the reader. Each sensor measures the intensity of the light immediately in front of it. Each individual light sensor in the CCD reader is extremely small and because there are hundreds of sensors lined up in a row, a voltage pattern identical to the pattern in a barcode is generated in the reader by sequentially measuring the voltages across each sensor in the row. The important difference between a CCD reader and a pen or laser scanner is that the CCD reader is measuring emitted ambient light from the barcode whereas pen or laser scanners are measuring reflected light of a specific frequency originating from the scanner itself. LED scanners can also be made using CMOS sensors, and are replacing earlier Laser-based readers.[2][better source needed]
Video camera readers use small video cameras with the same CCD technology as in a CCD barcode reader except that instead of having a single row of sensors, a video camera has hundreds of rows of sensors arranged in a two dimensional array so that they can generate an image.
Large field-of-view readers use high resolution industrial cameras to capture multiple bar codes simultaneously. All the bar codes appearing in the photo are decoded instantly (ImageID patents and code creation tools) or by use of plugins (e.g. the Barcodepedia used a flash application and some web cam for querying a database), have been realized options for resolving the given tasks.
Omnidirectional scanning uses "series of straight or curved scanning lines of varying directions in the form of a starburst, a Lissajous curve, or other multiangle arrangement are projected at the symbol and one or more of them will be able to cross all of the symbol's bars and spaces, no matter what the orientation.[3] Almost all of them use a laser. Unlike the simpler single-line laser scanners, they produce a pattern of beams in varying orientations allowing them to read barcodes presented to it at different angles. Most of them use a single rotating polygonal mirror and an arrangement of several fixed mirrors to generate their complex scan patterns.
Omnidirectional scanners are most familiar through the horizontal scanners in supermarkets, where packages are slid over a glass or sapphire window. There are a range of different omnidirectional units available which can be used for differing scanning applications, ranging from retail type applications with the barcodes read only a few centimetres away from the scanner to industrial conveyor scanning where the unit can be a couple of metres away or more from the code. Omnidirectional scanners are also better at reading poorly printed, wrinkled, or even torn barcodes.
While cell phone cameras without auto-focus are not ideal for reading some common barcode formats, there are 2D barcodes which are optimized for cell phones, as well as QR Codes (Quick Response) codes and Data Matrix codes which can be read quickly and accurately with or without auto-focus.[4]
Currently any camera equipped device or device which has document scanner can be used as Barcode reader with special software libraries, Barcode libraries. This allows them to add barcode features to desktop, web, mobile or embedded applications. In this way, combination of barcode technology and barcode library allows to implement with low cost any automatic document processing OMR, package tracking application or even augmented reality application.
Early barcode scanners, of all formats, almost universally used the then-common RS-232 serial interface. This was an electrically simple means of connection and the software to access it is also relatively simple, although needing to be written for specific computers and their serial ports.
As the PC with its various standard interfaces evolved, barcode readers began to use keyboard serial interfaces. The early "keyboard wedge" hardware plugged in between the PS/2 port and the keyboard, with characters from the barcode scanner appearing exactly as if they had been typed at the keyboard. Today the term is used more broadly for any device which can be plugged in and contribute to the stream of data coming "from the keyboard". Keyboard wedges plugging in via the USB interface are readily available. In many cases, a choice of USB interface types (HID, CDC) are provided.
There are a few other less common interfaces. These were used in large EPOS systems with dedicated hardware, rather than attaching to existing commodity computers. In some of these interfaces, the scanning device returned analog signal proportional to the intensities seen while scanning the barcode. This was then decoded by the host device. In some cases the scanning device would convert the symbology of the barcode to one that could be recognized by the host device, such as Code 39.
Some modern handheld barcode readers can be operated in wireless networks according to IEEE 802.11g (WLAN) or IEEE 802.15.1 (Bluetooth). Some barcode readers also support radio frequencies viz. 433 MHz or 910 MHz. Readers without external power sources require their batteries be recharged occasionally, which may make them unsuitable for some uses.
The scanner resolution is measured by the size of the dot of light emitted by the reader. If this dot of light is wider than any bar or space in the bar code, then it will overlap two elements (two spaces or two bars) and it may produce wrong output. On the other hand, if a too small dot of light is used, then it can misinterpret any spot on the bar code making the final output wrong.
I have an application that uses a barcode reader to enter part numbers. I have been asked by manglement if I can lock-out the keyboard to prevent the users from typing in the part numbers (too prone to error in typing). As the barcode reader is a separate USB port from the keyboard, is there a way to identify the keyboard port and disable it programmatically?
Most bar code readers set them self up as a key board wedge at the operating system level. LabVIEW can not select between the key board or the bar code reader. To LabVIEW they seem to be the same input device.
Since your barcode reader is USB, you may have the ability to set it up as a COM port. Several USB readers will either behave as a keyboard or a COM port. You would then have to modify your software to look at the COM Port. You can change the control to an indicator and the user will not be able to do anything.
The other option, which is what I typically do, is to add prefix and suffix characters to the barcode scanner. I pick a prefix that corresponds to a LabVIEW Key Navigation settign to set focus to the control. This way, whenever the barcode scanner scans, the control is automatically highlighted and the barcode fills end. I usually use a suffix of the ENTER key so the data is entered.
This way, you can hide your control off-screen so users cannot see it. Use an indicator on-screen. You can even set the off-screen control to be skipped while tabbing. The other nice thing with the prefix is I can simulate the barcode with the keyboard by using the special key navigation sequence. This is not 100% tamper-proof, but most operators aren't going to know what you are doing to skip the barcode reader unless you show them.
I have a data card value that I want linked to a barcode reader. I unlocked the advanced properties of the data card and set the default to BarcodeReader1. I followed a video exactly and am getting an error. The troubleshooting says:
Barcode scanners can be connected to a computer through a serial port, keyboard port or interface device called a wedge. A barcode reader works by directing a beam of light across the barcode and measuring the amount and pattern of the light that is reflected.
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