There is a mystique surrounding bar codes which intimidates many people. Let's eliminate it quickly. First the bar code usually doesn't contain descriptive data, (just like your social security number or car's license plate number doesn't have anything about your name or where you live). The data in a bar code is just a reference number which the computer uses to look up associated computer disk record(s) which contain descriptive data and other pertinent information.

For example, the bar codes found on food items at grocery stores don't contain the price or description of the food item; instead the bar code has a "product number" (12 digits) in it. When read by a bar code reader and transmitted to the computer, the computer finds the disk file item record(s) associated with that item number. In the disk file is the price, vendor name, quantity on-hand, description, etc. The computer does a "price lookup" by reading the bar code, and then it creates a register of the items and adds the price to the subtotal of the groceries purchased. (It also subtracts the quantity from the "on-hand" total.)

Another example of bar code data might be in a quality reporting application, the bar code may have only a single digit in it, but it may be titled "Failed Vibration Test". The computer associates the single digit with the test result.

So, bar codes typically have only ID data in them; the ID data is used by the computer to look up all the pertinent detailed data associated with the ID data.

When a bar code scanner is passed over the bar code, the light source from the scanner is absorbed by the dark bars and not reflected, but it is reflected by the light spaces. A photocell detector in the scanner receives the reflected light and converts the light into an electrical signal.

As the wand is passed over the bar code, the scanner creates a low electrical signal for the spaces (reflected light) and a high electrical signal for the bars (nothing is reflected); the duration of the electrical signal determines wide vs. narrow elements. This signal can be "decoded" by the bar code reader's decoder into the characters that the bar code represents. The decoded data is then passed to the computer in a traditional data format.

Many of this booklet's readers have to comply with their customer's or industry's bar coding specifications; no choice is possible, just compliance. Look at the following samples of printed bar codes:

The classic bar code type is Code 39, (also called Code 3 of 9) which has 9 bars and spaces; three are wide, and the other 6 are narrow. In Code 39, 3 of 9 total bars and spaces are wide; hence the name, Code 3 of 9. For example, look at the following character representations with Code 39:

Notice there are two widths of bars and two widths of spaces. If you wished to print a bar code of ABCD, you would need to start and end it with a special Start/Stop code character - the * (asterisk) is used for Code 39. So to print a bar code of ABCD, it would need to be printed as *ABCD*. There should be at least 1/4" of white space to the left and right of the code; this helps the reader pick out where a bar code begins and ends.

Other bar code types are similarly constructed. UPC and EAN bar codes have four widths of bars and spaces; so does Code 128.

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For new bar coding projects that don't have industry or customer standards, Code 39 is the typical non-food standard, because almost all bar code equipment reads/prints Code 39. However, Code 39 produces relatively long bar codes; it is not particularly efficient in bar code density, (the maximum density is 9.4 characters per inch including 2 start/stop characters).

Where the label width is an issue and there is numeric data or lower case data, Code 128 is the best alternative; Code 128 also has an extra efficient numeric only packing scheme to produce very dense bar codes, and Code 128 has all 128 ASCII characters.

Not all readers read Code 128, so before you settle on it as a standard, be sure that your reader is 128 capable. Code 93 has been promoted by only one vendor; it requires two characters to make Full ASCII; and it doesn't have a numeric packing option. For these reasons, Code 128 is preferable over Code 93.

The larger the width of the elements, the more space it takes to print the bar code; therefore, the lower the bar code density. The thinner the bar and spaces, the less space is required and the higher the bar code density. Look at the samples below of different densities:

Lower density bar codes are more reliably printed and more consistently read than higher density bar codes, because minor variations (due to printing or damage) are much more serious with high density bar codes - the percentage of distortion is larger.

There are three basic types of bar code readers: fixed, portable batch, and portable RF.

Fixed readers remain attached to their host computer and terminal and transmit one data item at a time as the data is scanned.

Portable batch readers are battery operated and store data into memory for later batch transfer to a host computer. Some advanced portable readers can operate in non-portable mode too, often eliminating the need for a separate fixed reader.

Portable RF Readers are battery operated and transmit data real-time, on-line. More importantly, the real-time, two-way communication allows the host to instruct the operator what to do next based on what just happened.

A basic bar code reader consists of a decoder and a scanner, (a cable is also required to interface the decoder to the computer or terminal). The basic operation of a scanner is to scan a bar code symbol and provide an electrical output that corresponds to the bars and spaces of a bar code.

A decoder is usually a separate box which takes the digitized bar space patterns, decodes them to the correct data, and transmits the data to the computer over wires or wireless, immediately or on a batch basis.

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Personal Computer Keyboard Wedge Readers

If the bar code reader is attached through the keyboard interface, the bar code reader sends data in key codes, exactly as though the data had been keyed on the keyboard. Keyboard interface readers are nicknamed "wedge readers", because they physically wedge between the keyboard and the computer (or mainframe terminal) and attach as a 2nd keyboard.

The great advantage of "wedge readers" is that bar code reading can be added with no software changes necessary; the software thinks that the data received was produced by a fast typist. (Of course the keyboard remains usable too!). With a wedge reader, any program that accepts keyed data will accept bar code data with no change. The following figure shows a keyboard wedge reader attachment.

A keyboard wedge reader which emulates all of the keys including function keys, Ctrl, Alt, Page Up, etc. is preferable. You cannot place a keyboard wedge reader more than 10 feet from the computer. You can get an extension cable for the scanner, allowing you to range up to 35-100 feet from the computer.

For these applications a cordless radio frequency wand would be better; the wand has a transmitter and the decoder has a receiver so that the wand can transmit digitized data to the decoder over RF instead of a cord. RF wand readers transmit up to 150 feet; at these distances the trick is to hear the decoder's beep.

Serial Bar Code Readers

Another method of data transmission from the bar code reader to the computer is by RS-232 Serial ASCII format. If you have a multi-user computer, (for example a UNIX system), with serial ASCII terminals for each user, the bar code reader can attach between the terminal and host computer, transmitting ASCII data just like the terminal; in fact the bar code data looks just like keyed data. when attached like the following figure:

Single user computers without an external keyboard (most notebooks) must use the serial port for interface of a bar code reader; to get the bar code data to appear as keyed data, a TSR or device driver program is also necessary. Typically requiring only 2K of RAM memory, the program takes data from the COM port and places it into the keyboard data buffer, so bar code data appears to have been keyed. If your computer program can read a serial port directly, no additional program is necessary.

Serial readers can be placed several hundred feet from the computer, (keyboard wedge readers cannot be placed beyond 10 feet.). Also multiple serial readers can be attached to the same computer, (keyboard wedge readers cannot). The PC runs a program to poll the readers one at a time.

MainFrame Bar Code Readers

Mainframe computers often have terminals with unique data connectors and data formats, (different from ASCII or PC key codes). The IBM System 36-38, AS/400, 4300, 9000, etc., have such terminals. To use bar codes with these computer systems, you must use a keyboard wedge reader specifically designed for the terminal to be attached to. Vendors such as Compsee, Intermec, and Welch-Allyn specialize in readers which attach to mainframe terminals.

The alternative is to have a PC with a terminal emulation card in it attached to the mainframe; then a less expensive PC bar code reader and laser printer can be used on the PC.

Portable Readers

Portable readers are handheld battery operated readers which store the data in memory for later uploading. In addition to a bar code scanner, a portable reader usually has an LCD display to prompt the user what to do; and they usually have a keyboard to enter variable data such as quantities.

Ease of programmability is a key issue in selecting a portable, and that depends on your programming abilities; lots of vendors say it's easy, (as long as you can program in C++ or go to their two week school). Other variables to consider are: battery life (at least 20,000 scans), ease of reading the display, size/weight of the unit, who repairs it, and where it is to be repaired in the event of a malfunction.

Radio Frequency Readers

Radio frequency readers are the ultimate solution to many applications' needs - especially any computer remote application that can benefit from the computer checking and instructing the operator.

Warehousing applications such as picking, put-aways, shipping, and receiving are typically better performed by RF readers because the computer can instruct the operator where to go and what to do, plus the computer files are current as to exact status and location of available inventory.

RF Readers are like on-line terminals, but wireless. The user can roam around his local facility scanning and keying data and getting a response from the computer with each entry. Therefore the computer can very carefully edit the data for errors as well as prompt the user for what to do next considering the data that has just been entered.

The classic RF applications and associated advantages are:

There are two basic types of RF Readers on the market:

• Readers that emulate terminals or PCs, and
• Simpler Readers which talk to a computers serial port. A brief explanation follows:

RF Readers that Emulate Terminals
These readers started out as mainframe terminal emulators such as IBM 3270 or 5250 terminal emulation. To emulate an IBM mainframe terminal is no easy task, so the cost was very high,

Today there are several emerging terminals that emulate PC workstations on NT or Netware Local Area Networks. These machines are 486 computers with lots of memory and download their software from the network server. They are relatively expensive,  require an operating LAN, mostly require applications to be written to the upper left hand corner of the screen, and usually require a network controller that is $3k-$10k in cost.

These terminals almost always require a C++ program to be written on the terminal and the host programs to be modified to just use the upper left hand corner of the screen. Competent network management personnel are also required for each location.

RF Readers that Talk to a Serial Port
These readers require programming on the host computer to read and write to a serial port. Such programming is relatively trivial and can be written in almost any language or any platform. Existing application packages can be modified to include these simple RF readers, but programming is required.

It could be argued that the amount of effort is considerably less than with terminal emulation, because all programming is on the host computer; the terminal emulation programs require host programming (for the upper left hand corner) and programming on the terminal too.

Readers that communicate to the host by serial port are usually less than 1/2 the price of the more complicated "Terminal Emulators"; they also often have faster response time due to less software overhead. No network is required - even a slow can drive them at maximum speed. They are far simpler - thus less costly, BUT they do require programming to get their full potential. Even though you can run them in "One-Way" mode without programming, that misses the greatest potential of computer-led activities, (often referred to Event Driven Applications).

Spread Spectrum Terminals vs. Narrow Band Terminals
Narrow band refers to radios that operate within a narrow band of radio frequencies. Spread spectrum refers to radios that jump around on a wide band of frequencies to avoid interference. Narrow band can be licensed at high power and unlicensed at low power.

Spread spectrum is almost always unlicensed at high power. Spread spectrum is superior for very large networks of RF terminals - 150 plus terminals in the same building. For terminal networks below that number, unlicensed narrow band is usually less expensive, far less difficult to program and it usually transmits just as far with considerably less power and battery size/weight.

Narrow band radios with a user changeable frequency has the same advantage as spread spectrum in avoiding interference. In fact, it can be argued that 10 plus channels of user selectability are at least as safe as spread spectrum with a fixed pattern. What you really want to avoid is narrow band terminals with a fixed frequency that cannot be changed unless sent back to the manufacturer. More and more devices are going wireless; so, the channel interference is expected to increase substantially in the future.

Wand Scanners are the least expensive and the oldest type of bar code scanner. A wand is typically made from 1/2" stainless steel tubing or from plastic; optics are in the front with a cord out the back. The wand scanner must be moved by the user's hand across and in contact with the bar code. While the wand is moving across the bar code, the reflected light is converted to electrical signals through a photocell in the wand.

A wand requires a little technique; it is not a "can't miss" scanner. Even without directions, most people can master the use of a wand in 30-45 seconds; but some need directions and training for a few minutes to learn the proper wanding techniques. These techniques are detailed in most product manuals, but consist of common sense rules such as:

Wands can read any length of bar code. Wands typically can read through laminates of thickness up to 1/10" inch. Many wands can read through CD cases and audio tape cases. You can't judge a wand by whether it is steel or plastic. Most plastic wands are inferior, but not all steel wands are superior. Check out the warranty period and check out if there is a flat rate repair charge after the warranty. Wands are more likely to deteriorate than decoders.

Wand Resolutions

Wands come in a variety of resolutions, usually low, medium, and high resolution; this allows for reading bar codes printed by different methods and for reading very small element widths, (high density). Low resolution wands have a larger diameter aperture for the reflected light to pass through to the photocell; therefore, if there is a void (tiny white space) in a dot matrix printed bar, the bar is still interpreted as a bar.

A high resolution wand has a smaller diameter aperture and sees the same void in a bar as a space - thus it can't read dot matrix code as well as lower resolution wands.

A low resolution wand will have an aperture opening so large that it will view very narrow bars and spaces at the same time - thus being unable to decode a high density bar code. A high resolution wand will see only one bar or space element at a time, thus it is able to decode a high density bar code correctly. So, if you are reading dot matrix codes only, use low resolution. If you are reading laser or thermal only, use high resolution. If you are reading a mixture of dot matrix with other types of printed codes, use a medium resolution wand.

Wand type with associated resolutions and uses are:

*A mil is 1/1000 of an inch

Type of Wand	Aperture Diameter	Use
Low Resolution	10 to 16 mils*	For dot matrix only
Medium	8 mils	Mixtures of printer types
High	6 mils	Thermal or laser only
Ultra High	4 mils	For ultra high density codes

Some Xerox high speed mainframe laser printers (not the desktop laser printers from HP et al.) can produce bars with voids in them also, (just like dot matrix printers); high resolution wands would not be satisfactory for such codes.

Scanner Light Source
Wands also vary with the type of light used. Today, most wands are have with visible red light (670nm) as the light source reflect from the spaces and bars. If you can see the light being emitted from a visible wand's tip; it is red. Visible light can read any bar code that you can see.

It can read thermal printed bar codes, whereas wands with infrared light (870nm) cannot read thermal printed bar codes; you cannot see light emitted from an infrared wand's tip. One advantage of infrared light wands is reading bar codes that can't be photocopied.

A bar code can be printed with infrared absorbing ink (carbon based) and covered with a black laminate window which is infrared blind, giving you a security bar code for use on badges that you don't want to be photocopied. A "black on black" bar code requires infrared scanners to be read.

Switch Scanners
With the typical wand on most bar code readers, power is always applied to the wand unless power is turned off at the computer or terminal. This should be of no concern to the user; the LED will last 20 years.

However, with a portable bar code reader, battery power is to be conserved. A wand with a switch is the best solution. No power is lost as long as the switch is open or off. When the user wants to read, the switch is depressed to provide power to the wand.

When finished reading, the switch is released turning off power.

Cordless RF Wands are used for tetherless scanning. The wand has a battery, antenna, and transmitter built-in. The radio simply substitutes for the cord between the wand and the decoder.

There is not a beeper in the wand to confirm a "good read"; since it is exactly like a corded wand with the radio substituting for the cord, the base station/decoder beeps to confirm a "good read". Therefore the operating distance is limited by being able to hear the "good read" beep. Amplified external speakers can be added to the base station and Range Extenders can be added to increase the operating range.

Slot badge scanners require only one hand for operation; the user simply slides his badge with a bar code on the bottom edge through the scanner.

These are typically used in unattended entry/exit stations for payroll, club membership accounting, school lunch assistance programs, etc. Slot badge scanners are similar to wand scanners, but usually refined so that one resolution can read most types of bar codes with no difficulty; utilising the additional space for larger optics, a slot badge scanner usually has a vertical aperture to look at the elements, thus allowing a high resolution slot badge scanner to read almost all types of printed bar codes, from dot matrix to high density.

Slot badge scanners also come with visible or infrared light sources. Visible can read any bar code which can be seen with the eye including bar codes printed on thermal printers, (infrared cannot read thermal printed bar codes); infrared slot badge scanners would be used for security "black on black" bar codes, (the black bar code is covered by a black window on the badge, but the black window looks clear under infrared light).

Laser scanners have a very precise beam of light which can be reflected accurately several inches to several feet. Almost all laser scanners today have a moving beam which sweeps back and forth, (some older laser scanners required the user to move the beam across the bar code). The advantages of moving beam laser scanners are:

• Reading bar codes from a distance (typically 3-18 inches, or up to 17 feet with reading low density bar codes).
• Reading moving objects on an assembly line.
• No-hands operation. Some lasers can be mounted to turn on automatically when an object passes under the scanner. Typically used in blood banks, library check out, etc.
• Reading through glass windows or thick laminates.
• Reading bar codes on curved surfaces, (bags of parts).
• Reading bar codes inside difficult to reach enclosures.

Laser scanners emit a laser light beam which sweeps back and forth across the bar code 36 times per second. At this rate, unsuccessful reading attempts go unnoticed; you will only be aware of the one successful decode. Once a read has occurred, the laser turns off, requiring you to release and pull the trigger again to reactivate the laser scanner.

The lower the density of the bar code, the further the laser scanner can read a bar code. The higher the density of the bar code, the closer to the bar code the laser scanner must be.

Triggered Laser Scanners

Triggered Laser Scanners are virtually "can't miss". Just "point and shoot". Face the bar code so that the bars point up (the laser light will then form a red line across the bar code when the trigger is pulled). Aim the gun scanner at a bar code and pull the trigger; reading is instantaneous. You may have to move the scanner closer to the bar code to get a read, but that's it.

Triggered laser scanners are about 5-10 times more expensive than a wand scanner, but scanning is significantly easier. Pay attention to the length of the warranty on laser scanners; it could prove to be very important with heavy usage.

The basic laser scanners read up to 10-20" distance, depending on the brand of the laser scanner. There are hand held triggered long range laser scanners that can read up to 33 feet distance, (using retro-reflective low density bar codes) or 10 feet distance using paper low density bar codes. Long range laser scanners are naturally more expensive than the standard laser scanners.

Cordless RF Laser and CCD Scanners

There are at least four RF Laser Scanners available on the market. These units have decoder, battery, and transmitter built into the laser scanner - allowing tetherless laser scanning back to a base station/decoder. The range varies from 20-30 feet from the base station.

RF Laser Scanners cost considerably more. The two-way version has a confirmation "good read" beeper in the laser scanner, so you always know that the host has received the data. The Base Station connects to a PC or Mac in series with the keyboard or it connects to a serial port. Multiple two-way laser scanners per base station are possible.

Supermarket Slot Scanners
These devices are continuously emitting multi-directional light beams to maximize the reading of a bar code regardless of the orientation of the bar code to the scanner. Unless the bar code is on the surface of the item pointing straight up, the bar code reader has a good chance of reading it. These devices are required to be integrated into the sales counter. They typically directly interface with a retail POS terminal.

On Counter Scanners
These devices are the smaller cousins of the Supermarket Slot Scanner. They were developed for the convenience stores that wanted automation but didn't have the counter space required for a slot scanner installation. They also have a omnidirectional light source to free the user to present the bar code in any orientation. They sit on a counter, or they sit on a stand that sits on the counter. Items are passed a few inches in front of the scanner to get a successful read.

Industrial Scanners
There are also a whole line of scanners made just for industrial applications including small under $1000 scanners that read a few inches distance and large $20,000 long range scanners that read twenty feet away. These are typically mounted adjacent to conveyor lines to read bar codes on passing items; the host computer then directs the items to the appropriate branching line. A classic example of such scanners use is airport baggage sortation; (those bar codes that are placed on your luggage are actually used in the large airports to get your luggage to the right place.

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CCD Scanners are a "can't miss" scanner too. Most have to be placed on the code for reading, but some have "laser like" distance reading. Some are triggerless and some require the trigger or button to be pushed to initiate reading. CCD scanners have an LED array with CCD light detectors for the reflected light. There are no moving parts in a CCD Scanner.

Most CCD scanners have a "depth of field", (how far you can be away from the bar code and still get a read), of only 1/2". They have to be placed directly on the code to get a read. In the last 2-3 years CCD Scanners have been developed with a depth of field up to 8 inches. We have manufactured such a unit and have put it in the same case as our laser scanner. It has less depth of field than a laser scanner and it doesn't read very high density bar codes, but it does cost less - an excellent trade off for most people.

Most CCD Scanners have a front opening, typically 2 inches or 3 inches. If you suddenly need to read a larger bar code than the width of the CCD scanner front opening, it can't be done. Recent developments in CCD scanners which can read from a distance (up to 5"), are able to read bar codes up to 4.2" wide.

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