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Home >> What's a Barcode? What's a Barcode?Check out our Glossary of Industry Terms by Clicking Here.  What is a Bar Code? A bar code is a machine readable code consisting of a series of bars and spaces printed in defined ratios. Bar code symbologies are essentially alphabets in which different widths of bars and spaces are combined to form characters and, ultimately, a message. Because there are many ways to arrange these bars and spaces, numerous symbologies are possible. Common linear symbologies include UPC/EAN, Interleaved 2 of 5 (I of 5), Codebar, Code 39, and Code 128. While each symbology is in some way unique, the composition of a complete message (bar code) is surprisingly similar regardless of the symbology used. For example, all bar codes are based on some "X" dimension. The "X" dimension is the narrowest bar or space in the bar code. Designated in "mils" (thousandths of an inch), symbology standards usually specify a minimum value "X" to insure compatibility between reading and printing equipment used in open systems. The "X" dimension determines a bar code's density. Density refers to the amount of information that can be captured in the bar code in a particular space, usually a linear inch. While not intuitively obvious, high density bar codes have low numbers (e.g., 5 mil) and low density bar codes have high numbers (e.g., 55 mil). This is because individual characters consist of some combination of bars and spaces that are each multiples of "X". When "X" is small, the area required for each character is less than when "X" is large; thus the bar code can hold more per linear inch and is said to be of higher density. Similarly, increasing the width of the narrowest element ("X") increases the space required for each character and reduces the number of characters per inch. Because the resulting code is often quite large, very low density codes are often associated with applications such as warehousing that require reading bar codes from a significant distance (3 to 30 feet).  All bar codes have start/stop characters that allow the bar code to be read from both left to right and right to left. Unique characters placed at both the beginning and end of each bar code, the stop/start characters provide timing references, symbology identification, and direction of read information to the scanner. By convention, the unique character on the left of the bar code is considered the "start" and the character on the right of the bar code is considered the "stop." Immediately preceding the start character and following the stop character is an area of no markings called the quiet zone. Because there is no printing in this area, a scanning signal is not produced, thus the term "quiet." The quiet zone helps the scanner find the leading edge of the bar code so reading can begin. As a rule, the quiet zone should be ten times the "X" dimension or 1/4", whichever is greater. Putting all these components together, we get a complete bar code such as the one found below. Notice the leading quiet zone followed by a start character, data, a stop character, and a final quiet zone.  Bar Code Scanners The function of the bar code scanner is to "read" the image presented by the bar code. In its most basic form, the scanner sees and measures the absence or presence of light in the code's bars and spaces, and converts that information into an electrical signal that can be translated into recognizable or computer-compatible data. Common hand held scanning technologies include wands, lasers, and CCDs. While they are all dedicated to the same task, reading a bar code , each scanner type offers both advantages and disadvantages, and none is clearly superior in all cases. The following discussion outlines how each technology works and the relative advantages/disadvantages of each. For information on selecting an appropriate scanner for a specific application see "Which Bar Code Reader is Right for You?"  Wands Hand-held contact scanners, or wands, are the oldest and most cost effective method of bar code scanning. How Wands Work An operator manually places the scanner in contact with the bar code label. A tiny spot of light is projected through the scanner lens. As the scan spot is drawn across the bar code, reflections from each white space and light absorption from each black bar produce voltage variations that are amplified and shaped for decoding (see "Decoding and Interfacing" below). Wand technology is an excellent choice for many bar code applications. Specific advantages include: contact with the code makes it easy to determine which bar code is being read, and allows the operator to read bar codes of virtually any length; relative cost is low when compared to other scanning technologies; and with no moving parts, wands are the most rugged, compact and lightweight of the technologies available. Wands are not completely without their limitations, however. Some applications are simply not appropriate for contact scanning. Bar codes need to be of good quality, of a particular density (wand dependent), and reside on a flat hard surface if acceptable scanning performance is to be achieved. Some training is required for operators to develop an appropriate scanning technique since factors such as scan speed, wand angle, and pressure can adversely affect scanning performance if not performed properly. Finally, because this is a contact device, damage to the bar code label can occur if the proper paper stock or protective coating has not been used. Lasers Hand held laser scanners are the most expensive of the scanning devices, but offer the largest depth of field making them an appropriate choice for a wide variety of non-contact applications. How Lasers Work Hand held laser scanners use a laser diode to create a scan line by projecting a beam of energy off a rotating prism or oscillating mirror. The beam is reflected out the scanner window onto the bar code, where light energy from the bars and spaces is reflected back to the scanner, collected on a mirror, focused, and read by a photodetector. The resulting signal may then be read using decoding software within the scanner or at the terminal or host. Laser technology is an excellent choice for non-contact applications, and the only choice for applications that require reading distances of a foot (.3048m) or more. Available in both hand held and fixed mount form, lasers are easy to use, read a wide variety of code densities, and allow for easy reading of bar codes from irregular surfaces or through glass. Because they are non-contact devices, lasers will not wear out repeatedly scanned labels. The two disadvantages inherent in laser scanning are durability and cost. Because lasers use both moving parts and mirrors, they are not as rugged as CCDs or wands. The reality is that hand held scanners will be dropped no matter how diligent the operator, and even if the internal parts do not break, misalignment of the laser can easily reduce performance or render the scanner unusable. Finally, laser technology is the most expensive, both in terms of initial purchase price and product life costs. CCDs Charge coupled devices (CCDs) are extremely durable scanners for near contact and contact applications. Less expensive than their laser counterparts, CCDs having no moving parts to wear out or break. How CCDs Work CCD scanners use one or more LEDs to flood the bar code area with light, and an image of the code is transferred to an array of photodetectors. The characteristics of the bar code are determined by electronically sampling each individual photodetector which interprets each bar and space by the number of adjacent detectors sensing black or white. In other words, instead of reading each bar and space in succession, the CCD "takes a picture" of a very thin portion of the complete bar code which it then converts into a signal that may be decoded. CCDs offer numerous advantages over competing technologies. Though less expensive than lasers CCDs also read various code densities, are easy to use, and require very little training. They are lighter and more rugged than lasers and, unlike wands, may be used for non-contact applications. New models offer depth of field that is well suited for most retail, banking and manufacturing applications. Welch Allyn's 3400LR, for example, reads low density codes to 12 inches (30.48 cm) and 100% UPC to 6 inches (15.24 cm). Limitations to CCD technology include depth of field and scan width. While CCDs are an excellent choice for the applications listed above, they are not appropriate for long range scanning applications such as warehousing. CCDs are also not the best technology choice for applications in which a wide variety of label lengths and formats are used. Long messages or very low density codes can easily result in bar codes that exceed the width of the scan head, rendering them unreadable. The Common Denominator - Decoding and Interfacing While each technology uses a different method for reading bar codes, all result in a digital signal that must be translated into recognizable, or computer-compatible, data. This is accomplished using decoding software that resides in the scanner itself, or in a separate device placed between the scanner and the terminal or host. Using an algorithm, the decoder identifies and interprets each bar coded message, and transmits that data to the host computer. Transmitting the data requires a link, or interface, to the host computer. Every interface has two different "layers": a physical connection (hardware), and a logical communications protocol. Common interfaces for bar code scanners include keyboard wedge, serial wedge, and direct connect. The term "wedge" refers to any device inserted between the keyboard and the terminal that translates digital signals into keyboard codes. In a keyboard wedge application, the data resulting from the scanning of a bar code symbol is treated by the PC or terminal as if it originated from the keyboard, while the keyboard itself remains fully functional. Because the terminal or PC cannot differentiate between bar coded data and actual keyboard data, a keyboard wedge interface allows bar code reading capability to be rapidly added to an existing computer without changing the application software. An ASCII or serial wedge is an RS-232 scanner that is connected between the ASCII terminal and a host controller. This connection is used when keyboard wedge transmission is too slow, or when the interface is not supported by the product. The term direct connect actually has two meanings. To some, direct connect refers to decoded output, or the ability of the scanner to read a bar code and output data directly to the host without an external decoder. Direct connect has also been used to describe a decoded output scanner connecting to a PC or host without a keyboard. Some Other Common Terms Dual Interface: The ability of the scanner to connect directly to either of two different host devices and to automatically configure itself to communicate with each host. For example, a hand-held CCD may be attached to an IBM POS (Point of Sale) terminal during the day, and a portable data terminal for maintaining inventory at night. A built-in dual interface makes it easy to move a scanner between applications. Flash Memory: A memory chip that holds its content without power. The term was coined by Toshiba for the chip's ability to be erased "in a flash". Flash memory is used by Welch Allyn in most products as an alternative to PROMs (Programmable Read Only Memory) because flash memory can be easily updated. Flash capability allows cloning, PC Menuing and full firmware updates. HHLC (Hand Held Laser Compatible): "Dumb" or undecoded lasers have a unique way of communicating with an external decoder. This protocol, also known as laser emulation, is used by devices such as CCD's or decoded output lasers to communicate with external decoders. RS-232 (Recommended Standard 232): TIA/EIA standard for serial transmission between computers and peripheral devices such as barcode scanners, modems, and mice. RS-232 uses a 25-pin DB-25 or 9-pin DB-9 connector. RS-232 is generally used for distances of 50 feet (15.24 m) or less from the host, though this distance may be extended if high quality cable is used. Snappiness: A term used to reference the speed of the scanner. Depending on the testing method employed, snappiness may be measured by reads per minute, trigger to beep time, or trigger to output time. Various factors can affect snappiness, including ease of use (aiming), decoding software, bar code quality, and interface speed. Wand Emulation: When a wand scans a bar code, it sends a digital picture of the bar code to an external decoder. When a decoded output scanner connects to an external decoder (such as a portable data terminal), wand emulation mode is used. The decoded output scanner decodes the bar code and outputs the information as a digital picture just as if a wand had scanned the bar code. SELECTING A HAND HELD SCANNER Which Bar Code Reader is Right For You? How to pick a hand held scanner that is compatible with your symbology and ideal for your application. Hand held bar code readers have been a key part of automatic identification applications since the inception of the industry, and they remain a crucial part of bar code systems in a range of industries and applications. Today's manufacturers offer customers a variety of choices and price/performance options for tailoring hand held scanner solutions to individual requirements. There are three primary types of hand held readers: contact wands, CCD readers, and laser scanners. In considering which of these readers offers the best solution for your scanning activities, it is useful to understand the key functional components of a hand held reader: 1) illumination and image or code capture; 2) decoding, and 3) connectivity. The three types of hand held readers are differentiated by the type of "reader engine" used to illuminate and read the bar code. A contact wand uses a light emitting diode (LED), the CCD's engine reader is a charge-coupled device (CCD) and the laser scanner uses a visible laser diode (VLD). The type of reader engine is a primary factor in the hand held reader's price / performance and also determines its appropriateness for individual applications. By understanding the distinctions, users can select a hand held reader offering the best fit and value. To successfully match reader choices to project requirements, users need to consider three key application criteria: working distance, label size, and label density. Working distance refers to the distance between the label and the reader while scanning. There may be none (contact) or several feet, but each requires a different reader. Label size refers to the width of the bar codes being read, while label density addresses the minimum resolution of the bar/space patterns. Each of these criteria is interrelated. For example, the larger the label and the bigger the bar/space pattern, the greater the attainable working distance. Contact wands, CCD readers and laser scanners offer different levels of scanning performance, and, given different price points and life cycle costs, there are a variety of trade offs to consider. Working Distance The required working distance should be clearly defined. Will the operator bring the reader in contact with the label, or will he/she scan the bar code from a distance? Retail point of sale, office, and factory applications often support contact scanning, while warehousing, distribution, and transportation applications typically require greater working distances. Working distance is the primary differentiator of the three reader types. As the name implies, contact wands require that the label be brought into contact with the reader. Until recently, CCD readers were limited to working distances of one to two inches, but the newest generation of scanners has extended that range significantly (7 in/17.78 cm). Laser scanners, offer the greatest working distances averaging 8 to 30 inches (20.32 to 76.2 cm)standard. There are also specialty laser guns that can be matched up with special large, reflective labels to achieve scan distances of many feet. Differences in working distance are reflected in the cost of the readers. While there are exceptions, contact wands are generally the most economical of the readers, and laser guns the most expensive, both in terms of initial cost and overall life cycle. CCD readers are priced somewhere between wands and lasers. Because these readers feature solid-state designs, they offer excellent life cycle costs as well. Label Size/Label Density Label density refers to the minimum width of a bar/space element, and is measured in thousandths of an inch , or "mils". For linear or one-dimensional bar codes, the key size consideration is label width. High-density codes (under 7.5 mil) tend to be read at closer working distances; low-density codes (above 15 mil) can be read from greater distances. Total code width is particularly important to know when selecting a CCD reader. In most cases, the widest label a CCD reader will support is limited to the width of the reader's scanner opening, though some custom readers have been designed to read substantially larger codes. Since wand scanners are moved across the target code, and laser guns project light to move across the code, these two readers can handle broader code widths. If you decide a contact wand is ideal for your application, you must consider the wand's aperture width when you make your hardware selection. The aperture should be approximately the same size as the narrow bar (X dimension) of the bar code it is to read. If it is much wider, adjacent bars may appear in the scanning window at the same time, making it harder to read the symbol. If the aperture is too small, the scanner may see a printing defect as a bar or space where none exists. Decoding the Image Once the reader's illumination and acquisition system has captured the code's bar/space pattern, the information must be converted into a signal with a format that can be understood by the host computer system. This is called decoding. The decoding function identifies the type of symbology being scanned (auto discrimination), loads the appropriate decoding algorithms, and decodes the data encoded on the label. Decoded information is typically formatted as serial RS-232 data, or is converted into keyboard commands for transmission to the host system. The decoded signal is transmitted via an interface cable to an RS-232 communication port (serial data) or to the terminal's keyboard port via a "Y-cable" (keyboard data). The term "wedge" is used to refer to one technique for interfacing the bar code reader to the host system or terminal. A "serial" wedge inserts the scanned data in an RS-232 signal between a host computer and terminal, while a "keyboard" wedge presents the data as a series of key strokes. Software in the readers are programmed via a bar code menu to select terminal and interface parameters. Until a few years ago, the decoding and wedge functions were typically handled by separate devices. The bar code reader would output a hand held laser-compatible (HHLC) or wand emulation (Wand Em) signal to an external decoder bow, which performed the decoding and wedging functions. Today, reader manufacturers have integrated the decoding in all three reader types, resulting in a one-piece, decoded output scanner (DOS). Decoded output readers offer the same decoding performance of box decoders in a single package at a lower overall price. External wedge decoders are necessary when two or more different types of scanning devices are required at each decoding station (e.g., a badge swipe reader and contact wand), or when an AUX port is required (for integration of scales, printers, or other serial I/O devices). But for ease of integration and a lower overall system cost, integrated decoded readers offer excellent value. Connectivity Once a reader has decoded the label data, the information must be transmitted to the host system. The serial and keyboard wedge functions for electronically formatting decoded output data are described above. Of course, the reader must also be physically connected to the host system, so customers will need to specify the physical interface type of the terminal, PC, or system. Since manufacturers of hand held readers support hundreds of terminal types, they also carry hundreds of interface cables. Customers should work with the equipment supplier to identify and order the correct cable. Since decoded output readers typically support many terminal interfaces in a single device, some manufacturers of CCD and laser hand held readers have standardized common cabling schemes so that customers can stock fewer cable and use common cable on both CCD and laser scanners to save both time and money. All three types of hand held readers -contact wands, CCD readers and laser scanners - offer excellent price/performance for particular applications. Understanding a few key functional and price point differences, however, can help you select the best hand held scanner for your requirements. All Barcode Systems is your single source for zebra printers, intermec printers, barcode scanners and barcode software.
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