Peripherals II

Content of the lesson:

Printers

The possibility to print a document is considered as one of the standard functions of a personal computer. Thanks to this printers belong to the basic accessories for computers.

Dot-Matrix

An old type of printer but still used. The principle is similar to typing machine. The printed document is created using a head with needles which draw points on a paper gradually through ribbon. The final document or image is created from these points. You can see this type of printer for example at bus stations in machines or inside cash registers in shops.

Inkjet

Inkjet printer offers a quality and quick printing. This type is very popular nowadays. The price of inkjet printer is quite favorable. Inkjet printers also offer color printing. The disadvantage is higher cost of printing (the ink is expensive). Because of this they are not suitable for large amounts of printed documents. They are suitable for home usage or for smaller offices.

The basic element of inkjet printing is the printing head. It consists of a cartridge which contains ink and of a single head which transfers the ink to a paper. The whole device is placed on a special handle and moves in horizontal direction above the paper (the movement of paper is perpendicular to the movement of the head). Ink is injected on the paper using small jets with diameter around 1 µm. The number of jets differs but it is usually between 21 and 256 jets for each color. Several printers have more jets for the cartridge with black inkjet to increase the speed of black and white printing.

• Thermal inkjet printers - A drop of ink is injected by an expanding bubble of fluxed ink. This technology was first invented by company Hewlett-Packard and was called as Bubble-Jet. These printers are being called bubble printers according to it.
• Piezoelectric inkjet printers - By deforming the piezoelectric crystal, pressure waves are formed in the jet chamber with ink and a blob of ink is injected. This technology is used for example by company Epson.

Animation (inkjet printer)

Alternativní obsah, třeba obrázek.

Laser

Laser printers offer very quality printing compared to the other types. The image is "created" optically using the laser ray and then transferred to the paper by a special cylinder. Finally it is ironed using a high temperature. The final documents are sharp, contrast, still, accurate and very quality (300 - 1200 dpi). The printing is even cheap because you can print hundreds or thousands of pages from one magazine of paint in powder (toner). Laser printers are also quite fast, they can print up to 20 pages per minute. The disadvantage is still the higher cost of laser printers.

The base of laser printers is a selenium cylinder which is charged with a static charge. It is rotated using constant speed. Using a rotating mirror the laser ray burns the final image on the photosensitive layer at first. Places hit with the laser ray are discharged. Then the rotating cylinder goes around the magazine with toner (special paint in powder) which is pulled up to the surface of the cylinder because of the static electricity (toner has the same charge as the previous surface of cylinder so it is pulled up only by areas hit by the laser ray). Then the cylinder transfers the toner on the paper which was previously charged with the static electricity. Then the paper goes through an ironing cylinder at the end to adhere the powder to the paper (using a temperature around 200 °C). The whole process is being called electrophotographic and is very similar to the process inside copiers.

Before printing, all data is transferred to printer and the printer creates the whole page at once. Because of this, laser printers usually have their own processor which computes the points which will be printed. It also has an operating memory of course which is used for this calculation. Several printers also have a hard drive where each printing task is saved and you can then adjust the settings of the printer. The cheapest printers do not have a processor and the complete calculation of printing is done by computer processor. Once the page is completed, the printing process is launched.

Animation (laser printer)

Alternativní obsah, třeba obrázek.

Parameters of Printers

• Color Print - At least four color cartridges of regime CMYK (subtractive model of color composition) are used for color printing. Single colors are Cyan, Magenta, Yellow and blacK. Several printers use two additional colors for better color reproduction for photos. This model is being called as CMYKcm and the letters "c" and "m" mean a light variant of cyan and magenta. Single colors are not mixed, they are only composed into the grid at medium where they partly interact together. The situation inside color laser printers is more complicated. The printer contains four separated magazines of toner and the photosensitive cylinder is separately lit for each color. After placing all colors on the paper, the image is fixed by the ironing cylinder.
• Resolution of printing - This is the main criteria for the quality of printing. It is given by the amount of printed points which can be created by the printer on a particular area and is being indicated in dots per inch (DPI – Dots Per Inch). For example a printer with resolution 300 x 300 is able to print 300 points per inch in vertical and horizontal direction which means 90 000 points inside the area of inch². Nowadays printers reach values of 4800 x 2400 dpi (inkjet printers) and 1200 x 1200 dpi (laser printers). The resolution of black and white printing is usually higher than the resolution of color printing. The quality of printing is not only given by the physical resolution but also by other techniques (quality of ink, management of the volume of ink blobs etc.) There are also several different technologies of photographic printing (PhotoREt III, ColorSmart II).
• Volume of ink blobs - This is very important for the quality of print. The volume of injected blobs has been dramatically reduced since the printers were invented from previous 180 pl to current 2 - 5 pl. The technology of changeable volume of blobs was developed recently. In case that a larger area is filled with one color, large blobs are used, but in case you need details, a smaller blob is used and the final image is very quality and also quickly printed.
• Speed of printing - It depends on the fact whether you use black and white or color printing. Black and white printers reach speed around 30 pages/min (inkjet printers) or 20 pages/min (laser printers). Color printers generally reach speed around 20 pages/min (inkjet printers) or 15 pages/min (laser printers). The speed of printing is affected by the speed of printing head and movement of paper, also by the fact whether the printing head can print in both directions and partly by the interface which is used to connect the printer to computer.
• Communication interface - The oldest and slowest one is the classical parallel interface LPT which is not used anymore. The most of printers use USB interface, in version USB 1.1 or USB 2.0.
• Memory - It is used in laser printers and affects the speed of printing. The cheapest printers have around 2 MB RAM ant this means that a part of document is loaded to memory and the rest is being loaded while printing. The larger memory the bigger part of document can be loaded -> faster printing.
• Maximal load - This is a recommended value of printed pages per month. A general value for inkjet printers is around 5 000 pages/month. Laser printers can print much more pages, around 70 000 pages/month.
• Price of printed page - The total costs can be calculated from the prices of ink and paper. Laser printers are more economic in this way.

Plotter

A plotter is a device similar to a printer. Unlike a printer its head is movable and carries a special pen. The head then moves above the paper using the same way as when you hold a pencil in hand and manipulate with it. The process is similar to drawing. The required motive is created using this pen.

Plotters differ according to the fact whether the head moves horizontally and vertically at once or horizontally only and the vertical movement is done by rolling the paper by cylinders which hold it.

• Table plotter (desk) - Paper is placed inside the whole area of plotter and is fixed electrostatically. Above this area is the construction which holds the head with pen.
• Floor plotter - This type does not have the whole drawing area on a desk but the paper goes through a special rack where the head moves along one axis. The second axis is created by moving the paper. There are special pressure cylinders or several plotters attach the paper electrostatically. Not so large area is needed as for table plotters but there is a risk of paper deflection when it is moving.

Plotter (source: Wikimedia Commons)

Scanner

This device is used for capturing any image or text information and saving it to computer. It can differ in the quality of captured data.

• Manual scanner - Very simple scanner, you can capture images up to the format A4. In case that your image is larger, there is software which can capture it separately and then complete all parts. It is not expensive, usually has lower resolution and allows you to capture not so many colors.
• Flat scanner - Table scanner which is much spread. Its principle is similar as capturing image in a copier. It offers high resolution and can also be equipped with a feeder which can make the scanning process faster and more comfortable.

The principle is similar to digital cameras. There is a chip which is sensitive to light and a optical set before it. The source of light is placed to create ideal lighting conditions for the scanning process.

Scanner (Photo: Michal Mikláš)

Speakers

This device is used to convert electrical energy to mechanical one which can causes vibrations of a membrane. The membrane causes moving air particles and creates the sound. To have functional speakers you have to plug the cable to the right port in computer. To be able to hear a sound you have to have a functional sound card. You also have to set it properly. You need to install drivers (special software) which allow the computer to communicate with the sound card. Drivers are usually a part of your operating system, in case of a new computer, they are provided on additional medium. In case of emergency you can use the Internet and search for correct drivers and then install them.

How to choose Speakers?

• Passive small speakers (dimensions apx. 7x9 cm) - Usually called as "rattles", made of plastics. You can get sound from them but the quality is poor. The advantage is a minimal price. They are not suitable for longer usage.
• Passive bigger speakers (dimensions apx. 9x12 cm) - No miracle but suitable for sound from computer games or software. You can get several low tones from them.

Passive speakers need an amplifier inside the sound card. The prices are usually several hundreds of Kč.

• Active speakers (20 - 40W, height apx. 15 to 20cm) - The performance is not large, they can endure much less (for example around 1-2W), then you can hear rattling in the output sound. They have their own amplifier, the sound is much better but you cannot turn it loud.
• Active speakers (60 - 120W, height over 25cm) - They also have own amplifier and listening to music is no problem. Nothing extra but this solution is enough for a general sound.
• Active speakers in wood (height over 25cm) - They have own amplifier and are designed for more demanding users. Prices are usually between 2 - 6 thousand Kč (according to the type).

Speakers (source:Wikimedia Commons)

Microphone

This device is on the contrary used to convert mechanical energy to electric one. You can use a small microphone with small frequency range for your computer. You can connect it by a thin cable to the proper port. You can also see a microphone which is a part of headphones. In this case it has a stronger cable which is divided at the end - there are two plugs labeled with the correct color to be connected to the right port. These microphones are mostly used only for communication between users using the Internet; they are not suitable for any recordings.

Microphone (source: Wikimedia Commons)

Tablet

This is a positioning device. We can say that it is similar to mouse (it controls the cursor) but tablet has much better accuracy and can be used for example when drawing by hand because the drawn image is transferred to a computer using the correct software. This device consists of a solid base which contains the capturing area which is usually rectangular or square and of a special pen which allows you to change the strength of pressure and create lines of different widths.

Tablet (source: Wikimedia Commons)

Web Camera

Or webcamera if you want. This is a common part of computer equipment nowadays. It can be used to transfer moving image or to capture single images. The quality is not very good but it is enough for communication when you want to see the person behind the other computer (for example when calling somebody via Skype). The price is quite low; you can buy it for several hundreds of Kč. Webcameras are used for several conferences or as a cheap solution to protect your property.

Web camera (source: Wikimedia Commons)

Joystick

This is a leverage controller mostly used for playing games (especially flight simulators). You can swing the lever to each side and transfer the movement into your computer. Inside a flight simulator you will lean the plane according to the direction you move the lever. Joystick is usually supplemented by buttons which can be used for different actions - according to the user settings.

Joystick (source: Wikimedia Commons)

Bar Codes Analyzer

This device offers automatic input of data which is contained in bar codes. You can connect it to a computer using a cable or wirelessly. They differ according to the type of scanning (CCD or laser). Laser ones are bigger and have larger depth of reading range. They can also read much thicker codes.

Bar codes analyzer (source: Wikimedia Commons)

Memory Card Reader

It is usually used to transfer photos from memory cards to a computer. Several computers also have built-in readers but you can buy them externally and connect to your computer using a cable. When you have a reader you do not have to connect your camera to your computer and install additional software to be able to copy your photos. You simply insert your memory card inside the reader which is quick and comfortable. You can use readers not only to copy photos but also to process any other data.

Memory Card Reader(Source: Wikimedia Commons)

Questions

1. Are dot-matrix printers still used?
2. Describe the principle of laser printers.
3. Which parameters of printers do you know?
4. How can you use a scanner? Name several types.
5. What is the difference between passive and active speakers?
6. How would you use a tablet?