Impact Dot Matrix
For many years, Impact Dot Matrix has been the workhorse of low cost printers. This printing method uses a ribbon which contains ink, and a print head with a series of "pins" which are fired onto the ribbon, pressing the ribbon against the paper. Where the ribbon contacts the paper, under pressure from these pins, an impression is made on the paper.

Dot matrix printers are required in cases where multiple layer pre-carbonised paper is used to produce a second copy of what is printed. Other printing technologies to not apply pressure to the paper which is needed to make the second copy readable.

Dot Matrix printers are noisy, slow and produce poor quality printing with limited or no graphics capability. The color of the printouts comes from the ribbon color and usually single color, with some printers able to use a dual color ribbon.

They are relatively low in cost to operate, though ribbons need to be replaced at regular intervals.

Some models have relatively complex paper feed mechanisms which can make it difficult to load paper, and make the printer susceptible to paper jams.

Many models are extremely reliable, and in cases where multi-part stationery is required, dot matrix printers are the only option to consider.

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Direct Thermal
Direct thermal printers have largely replaced dot matrix receipt printers at the point of sale.

They are relatively low cost, fast, quiet and usually have very easy paper load mechanisms where you insert the paper and close the printer.

These printers work using special thermal paper which changes color when heated. Thermal paper is slightly more expensive than ordinary paper, however no ribbon, ink or toner cartridge is required.

Direct Thermal printers are capable of quite good graphics for logos etc. and some such printers have non volatile RAM which can be used to store logos in the printer which can be printed quickly without being sent from the controller each time the image is used. This feature is of limited benefit however, because the communication speed of parallel and USB interfaces makes this unnecessary. You should be careful about using such features for images which change frequently, because some such printers have a limited number of cycles where the image in non-volatile RAM can be updated.

SELLmatix does not normally use non-volatile RAM for storing images in printers (though it could be set up that way if required), and instead sends the image to printer each time it is printed. As a result, this limitation with those printers would not normally be an issue with SELLmatix.

Dual color thermal printing is starting to emerge as an option. This uses paper which uses coatings which respond to two different temperatures from the print head. Use of this feature requires a printer which is able to use two different temperatures in the print head. Such printers include the Epson TM-T90 and Star Micronics TSP600 and TSP 700 models.

Quite stunning effects can be produced using dual color thermal printing, particularly where the graphics are optimised for the colors in use. We have worked with black/red, black/blue and black/green combinations with good effect.

There are however, a couple of points to be careful of with dual color thermal printing. The manuals for the Epson TM-T90 carry a warning that if the printer is set to dual color mode, but is in fact only using single color thermal paper, that print head life will be very substantially reduced. This is buried in the fine print of the documentation and would be easy to overlook. The Star TSP600 and TSP700 printers do not need to switch mode between dual color and single color paper, and carry no such warning.

As of early 2004, dual color thermal paper was not widely available, and cost so much more than single color thermal paper that it would not usually be commercially viable in a production environment. This is expected to change, and that if you are able to purchase a dual color thermal printer for similar cost to a single color printer, use could be made of this feature in the future.

Thermal printers have one disadvantage, and that is that the print fades over time when exposed to sunlight. In most cases this is acceptable, as indicated by the wide use of these printers particularly in convenience, grocery, fuel outlets and Bank ATM's. If however, this is an issue, then you are better off to consider other receipt printing options.

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Thermal Transfer
Thermal transfer printers are similar to direct thermal printers, except that they do not use thermal paper, but do have a ribbon which is similar to the carbon ribbons used on old IBM golfball typewriters, and the heating action on the print head bonds the color from the thermal ribbon to the paper.

Thermal Transfer printers are usually used for printing barcode labels and these printers produce very crisp lines and edges which are easy to read by barcode scanners.

Another important feature with thermal transfer printers is that the labels do not fade. Usually thermal transfer printers can also operate as direct thermal printers, with a configuration setting. Of course in that case the thermal ribbon would not be used, but thermal paper would be required.

The cost of consumables for thermal transfer printing is similar to direct thermal printing. You save money on the paper (thermal paper is more expensive), but you do have to buy ribbons, so the cost evens out. Thermal transfer printers, however do cost more on the initial purchase.

Thermal transfer printers are normally used for label printing, and they produce a particularly crisp result which is ideal for printing barcodes.

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Ink Jet printers work by spraying a pattern of ink onto the paper. They are quiet, and faster than Impact Dot Matrix printers.

Very few POS printers use inkjet technology, and the cost of ink is a major consideration. Dot Matrix and Direct Thermal printers tend to have significantly lower operating cost.

Prices for Ink Jet Page printers start lower than any other type of page printer, however the cost of Ink can make these printers extremely expensive to operate.

Some color Ink Jet printers are capable of extremely good photo quality reproduction but to achieve this quality special paper is normally required because the ink is absorbed into the paper and bleeds onto other parts of the paper before drying.

Many low cost Ink Jet printers use one black ink cartridge, and one color ink cartridge which in fact contains three separate ink colors, Cyan, Magenta and Yellow. The problem with these cartridges is that it lasts only as long as the most used ink color.

Virtually all Ink Jet printer manufacturers strongly suggest that you only use genuine ink cartridges, but if the printer does not use separate cartridges for each ink cartridge, and they can't be re-inked, then the operational cost can be very high.

While the capital cost of low end Ink Jet printers can make them appear attractive, the main advantages of Ink Jet printing are not normally realised in Point of Sale applications, and the operational cost can be a trap.

Inkjet Page Printers can be used for printing barcode labels, but they are not a particularly good choice because the ink tends to bleed along the edges of the bars, making the labels harder for scanners to read than Thermal Transfer or Laser printed labels.

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Laser printers are probably the best choice as a page printer, particularly where color is not required. Even where color is needed the capital cost of color lasers has fallen sharply over the last few years.

Laser printers win over Ink Jet printers in two areas. Firstly, they produce a much sharper image, because the print does not bleed into the paper. This can be particularly useful with barcode printing.

The second area where laser printers win over Ink Jet printers is in the cost of consumables. Even so it is useful to calculate the cost of fuser units, toner etc. to work out the actual cost per page when comparing different units.

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Serial
Serial RS-232 interfaces are perhaps the oldest, lowest cost, most reliable and flexible way for digital devices to communicate... Provided the technician installing the equipment knows what they are doing, and frankly, most of them just plug cables and hope it works.

Serial interfaces are bi-directional and can be used equally effectively for sending and receiving data. Cable lengths can be very long, though the communication rate needs to be reduced and distance increases.

For character based devices such as ticket printers, barcode scanners, pole displays and modems, the communication speed is more than adequate. For graphics intensive data transfer, such as to a printer using a Windows driver or anything using bitmapped graphics, serial communication is barely adequate, even at the fastest speed, 115Kb.

Most modern serial devices use fairly standard cables and connectors. The RS-232 specification however does not even specify a connector type, so there is a lot of variation particularly in older devices. The good news is, however, that you can always make the connection work if you know how to figure out the interface.

With serial devices transferring any volume of data, you should always use hardware handshaking to prevent buffer overflow. Software handshaking via XON/XOFF is a slimy hack at best. On devices with very low data transfer, such as barcode scanners, pole displays, handshake really doesn't matter.

Serial cables can be plugged and unplugged from the devices without damaging the equipment, though data may be lost if the devices are trying to communicate when the connection is made or broken.

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Parallel interfaces are used mainly for printers. They are much faster than serial communications, good for graphics intensive data transfer, very cheap and reliable.

Parallel interfaces transfer date in one direction, from a computer to a printer. Backward communication (from the printer to the computer) very limited, and while there have been a couple of attempts to improve the back channel, this usually does not work very well. Parallel interfaces are not useful for devices such as barcode scanners, pole displays etc.

Cable lengths for parallel interfaces should be 5 meters or less, and 5 meters is pushing things.

Parallel cables can be plugged and unplugged from the devices without damaging the equipment, though data may be lost if the devices are trying to communicate when the connection is made or broken.

There are no cabling issues with parallel devices. If they don't work you just replace the cable.

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USB is relatively new. It is much faster than normal serial interfacing, and power is carried in the cable which reduces the need for other power sources on devices like barcode scanners etc.

USB interfaces generally cost a few dollars more than parallel or serial, but if you need additional ports in a computer into which to plug the devices, USB will usually cost less than adding serial or parallel ports to the computer.

USB cables can be plugged and unplugged from the devices without damaging the equipment, though data may be lost if the devices are trying to communicate when the connection is made or broken. Some USB devices need to be "shut down" via a software command on the computer to prevent data loss.

We have seen some USB devices which do not power up correctly if they are left plugged into the computer, and which need to be unplugged and replugged after the computer has been started, in order for the device to work. This is rare and probably is the result of poor software drivers supplied with the device.

USB devices require a software driver supplied by either the operating system vendor (Microsoft) or the hardware manufacturer. Serial and Parallel devices can be controlled in raw mode directly from a program such as SELLmatix. USB devices do require drivers.

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Overview
There are thousands of different models of printers, and none of them work in exactly the same way. When a software program needs to control a device such as a printer, it needs to send commands to the printer in the way that printer understands. Drivers are programs or tables which software uses to translate what it wants into the commands which the printer understands.

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Raw drivers allow a program to directly send commands to the printer to invoke features such as bold print, underlined print, italic print etc. The raw commands can generally be found in printer manuals.

In theory, you can obtain the best possible results by using raw drivers. In reality, however, the raw commands that are actually used are a very limited subset of what the printer is capable of doing, and the amount of work required to achieve optimal results is not justified because the same work would be required for every different printer model.

Normally you would use raw drivers, where a windows driver did not exist for that particular model of printer, or where the windows printer driver was too slow. This could well happen with serial printers installed a long distance from the computer.

Raw drivers can not be used with USB devices, and in general, where a windows driver is available, it should be used instead of a raw driver.

Printers using raw drivers can only be controlled by the computer to which they are connected, and they cannot be shared with other computers over the local LAN.

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For programs such as word processors, spreadsheets, accounting systems and so forth, Windows uses what could be called a "virtual printer" which programs can use. Printer manufacturers provide a Windows printer driver which works between the Windows "virtual printer" and the actual printer hardware.

While this description greatly oversimplifies the way that printing works for Windows programs, it does mean that application programs have a consistent way to determine printer capabilities and control a printer. The application program does not need to know what type of printer is being used, because as long as the application program works with the Windows "virtual printer" correctly, the output will be correct provided that the printer manufacturer has written a good Windows driver that operates between the Windows "virtual printer" and the printer hardware.

Of course, not all printer manufacturers supply perfect Windows drivers, and issues with printer drivers do arise from time to time. As a general rule, however, if a Windows driver is available, it is a good idea to use it.

Windows drivers also have the advantage that they can be shared over a network, and used by more than one computer.

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Overview
Barcode readers send out a beam of light, and detect differences in the light reflected back to the scanner. The bars on a barcode do not reflect light as well as the spaces on the barcode, and the scanner measures the relative widths of the bars and spaces to detect a pattern which it can decode. Barcodes have checksums which enable the barcode reader to determine if the pattern it has detected are valid, and when a valid pattern is detected, the scanner "beeps" and sends the data it has read back to the device connected to the barcode scanner.

There are a number of different barcode symbologies or "languages". All of these have at least 2 different bar widths, and sometimes different widths for the spaces. The actual size of the bars and spaces is not important for the barcode scanner, and this varies with the size of printed barcode, and how far the scanner is from the barcode when it is scanned.

What is important for the barcode scanner is the size ratio between width of narrow bars, the width of medium bars and the width of wide bars.

There are three factors which are very important in printing a barcode where a scanner can quickly, easily and reliably detect the pattern and decode the data. These are:-

Pure Color All parts of the bars must reflect light consistently, and all parts of the spaces must reflect light consistently, and the difference between the light reflected from the bars, and the light reflected from the spaces must be easy for the scanner to detect. Of course pure black bars and pure white spaces are a good example, but other color combinations work just as well. Shading, dithering or color changes within the bars reflect light differently however and make it much more difficult for the scanner to read the barcode.

Clear, Crisp Edges are needed so that the scanner can detect precisely where a bar starts and ends, and hence accurately calculate the ratios between wide and narrow bars. Most printing designed for human readers has the edges softened by gradual color changes over several pixels. This is pleasing to the eye and helps to "round" curves. Barcode scanners are simply looking for a bar or a space and softened edges which transition gradually from the dark bar to the light space make it difficult for the barcode scanner to detect precisely where the bar starts and ends. And this is critical to a barcode reader, because it is calculating the ratio between wide and narrow bars.

Precise Dimensions The specifications for each of the barcode symbologies contain precise tolerance ranges for the ratios between narrow bars, wide bars and spaces etc. that the scanner sees. The reflected light which the barcode scanner sees, however, depends on the angle of the scanner to the barcode, any curve or twist in the packaging, little Johnnie's finger marks, and the condensation which forms on that is removed from a refrigerator.

With all of these obstacles for the barcode scanner, it is important that the printing on the barcode is exactly in the middle of the published tolerance ranges. If the printing of the barcode approaches either side of the tolerance range, the other factors which are involved will make it difficult or impossible for the scanner to decode.

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There are literally thousands of different fonts available for Windows producing an almost infinite range of ways in which text appears. Virtually all of these are TrueType Fonts which means they can be infinitely scaled to different size, and still retain their appearance to the eye. This is big advantage over other types of fonts which could only be scaled in steps, which did not necessarily fit well into the space available on the page.

There are a number of Barcode Fonts available, some quite expensive, which display characters as barcode symbols. It would be wonderful if we could simply select a barcode font, and then print barcodes which could be scanned reliably with a barcode scanner. Unfortunately it does not work that way.

The smallest unit of resolution on a printer is a pixel, or "dot". You can't print smaller than a pixel. In order to retain the accuracy required in the ratios between wide bars, medium bars and narrow bars, when printing barcodes it is necessary to have bar widths which are exact multiples of pixels. Barcodes can be scaled in size, but only in certain steps which are multiples of the pixel resolution if they are to remain within the tolerances required by barcode readers.

As the resolution of a printer increases, the steps in which a barcode must be scaled become smaller. At a resolution of 100,00dpi (dots per inch) these steps would be so small that they would appear infinite to the eye. But at a resolution of 300dpi or even 1200dpi, the steps at which a barcode can be scaled are noticeable.

TrueType fonts interpolate and make approximations when scaling text, and while this appears OK to the eye, it puts the printed "barcode" out of tolerance for the barcode scanner. Unfortunately, without having each printed result tested by a barcode analyser, there is no way to tell if the result is in tolerance. Consequently, some barcodes will scan, but many will not, and most scanners will have great difficulty trying to decode a barcode printed using a barcode font.

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