Barcode reading, scanning and data processing

Equipment may be hand-held (where it is generally more convenient to take the reader to the product), desk-top fixed work station (where the barcoded product is passed by hand under or over the reader), or conveyor-mounted where the coded product can be taken to the reader. 

• A decoder, which is used to convert the barcode data to ASCII characters

• An interface, which provides the connection between the decoder and the terminal.

INPUT DEVICES

Different types of input device are available for a variety of different applications. In small convenience stores and some industrial applications, a typical input device would simply be a basic wand or pen scanner. The most common types of input devices are:

Pen or wand readers: The very simplest wand or pen-type readers look very much like an electronic pen or even a giant, oversized electric razor.

These types of devices shine red LED light onto the black and white barcode pattern and then read the pattern of reflected light with a light-sensitive CCD or a string of photoelectric cells.

With a pen scanner, it is passed across the barcode so it can reach each block of black or white lines in turn; with a wand scanner, the CCD or photocells read the entire code in one go.

Wand or pen-type readers are the most inexpensive input devices available. The reading head measures the intensity of the light reflected back from the light source as the tip crosses each bar and space in the printed code, 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 CCD or photo cells is a representation of the bar and space pattern in the barcode.

Pen or wand readers work well for low-volume scanning but do have some disadvantages.

They require a relatively flat surface, a fairly high quality barcode, and some skill on the part of the person operating it. However, in applications where someone must scan just one barcode on a sheet full of barcodes, these types of readers are a good choice.

They are inefficient for commercial applications like supermarket or grocery store scanning, or other businesses that require high-volume scanning because of the slow speed that will be required to scan the barcoded label properly.

Pen barcode readers are available in wired and wireless models, which can be connected to a computer or cash register using USB or ps2 port connections.

CCD Readers: CCD readers (Charge-Coupled Device) are the next step up from wand or pen type readers. They have the same width read head as the barcode and contain an array of hundreds of tiny light sensors lined up in a row in the head of the reader. 

Other examples of laser scanners are those used on conveyors to read the labels on cartons, pallets, packs or bags as they move along the line.

These kinds of scanners can be found in warehouses to control conveyors, in many manufacturing operations, and in the airline industry to process baggage.

Camera-based readers: Two-dimensional imaging scanners are the sixth and newest type of bar code reader. They use a small video camera and image processing techniques to capture an image. The reader then uses sophisticated digital image processing techniques to decode the barcode.

The information is then used to re-route items to another process or to a shipping location.

Today, there are also barcode scanning apps that can run on cell-phones. In use, the phone’s built in camera is used to photograph the code. 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 and DataMatrix codes which can be read quickly and accurately with or without auto-focus. 

Factors to be considered in selecting an input device will obviously include the type of barcode that is to be scanned. If the code is a one dimensional linear barcode it is not necessary to use a camera-based scanning system.

On the other hand, if 2D barcodes are to be read, then a camera-based scanner will be needed.

The quality of the barcode in relation to the input device is also important. If barcodes are of poor or low(ish) quality to start with, or are possibly prone to scratching or damage then, again, a high quality input device will be effective in reducing time and in minimizing reading errors.

The size of the barcode being read is also important. Small barcodes can usually be read by almost any type of reader. Large barcodes of many inches or centimetres in length will ideally require a laser scanner, as these have the ability to read barcodes of any size.

Each of these factors should be taken into account when selecting an input device. However, before making a final decision it is advisable to thoroughly test the proposed device or system in as many user-related conditions as possible, perhaps going as far as deliberately damaging or defacing codes, printing them with a worn ribbon or with low ink coverage, maybe making the reading/scanning head a bit dirty. Even asking an untrained colleague to take a reading.

Asking other employees, or even customers, what barcode reading problems they have experienced in the past can also be of help in making the right choice of input device that will give accurate readings in all expected conditions of use.

THE USE OF A CHECK DIGIT OR ‘CHECKSUM’

Checksums are additional characters that are appended to barcodes to guarantee good reads. They are located on the far right side of a barcode that the information on the barcode has been entered correctly. The barcode reader decoder calculates the checksum by performing a series of mathematical (see Figure 5.7).

The purpose of a check digit is to verify operations on the digits that precede the check digit, and comparing the result of the calculation to the value of the check digit. Typically, if the check digit matches the result of the calculation, the reader emits a signal (such as a beep) to acknowledge that the results match, and the scan has been successful.