Peripherals I

Content of the lesson:

Monitors

Monitor (or screen) is a device which is used to display the input, job processes and output of computers. It is being connected to graphic cards which prepare data for it to be able to display it as text and graphical information for users. We can say that the graphic card translates data for the monitor. It provides an output from the computer so it is an output device (peripheral).

Important Parameters of Monitors:

• Resolution - This parameter informs us about the number of points on the monitor, which means how many of them are in the horizontal and vertical directions. It is being indicated as value x value, for example 1024 x 768. This parameter is quite variable, it depends on the settings of each graphic card and also on the fact whether the monitor is able to display the setting. There is so called native resolution at LCD monitors. This is a resolution which indicates the physical number of pixels of the monitor. If you change the resolution, the image will be recalculated and the result will be worse.
• Diagonal size - It is usually written in inches and tells you theoretically how big the monitor is, what is the distance between two non-adjacent corners of the screen. You can have a 22" monitor but it tells you nothing about the fact whether the aspect ratio is 4:3 or 16:9.
• Refresh rate - This is the speed how fast the monitor is able to redraw the whole screen. This is important especially for CRT monitors but you can find it also at LCD screens. However, the way of drawing the final image here is quite different.
• Response - This value tells how long it takes until one pixel changes for example from white color to black and back. Sometimes only without the reversing. In case that the response time was high, result would not be sharp because the monitor would no be able to react for example during quick scenes in films or games.
• Other - Other important parameters are for example number of input ports and their types (in case you want to connect more computers to one monitor), possibility to attach shading constructions (for graphic designers), possibility to rotate it in vertical and horizontal direction, size of pedestal (how much space will be taken), accessibility of buttons (for example buttons from the bottom or from the rear side are not ideal) and more.

CRT (Cathode Ray Tube) Monitor

This is an older type of monitors which works on the principle of cathode tube (it is a kind of vacuum tube). They are not sold anymore and their use is waived because of several reasons:

• size - CRT monitors are much larger than LCD monitors because of the principle how the image is created
• weight - this is connected to the size and limits the possibility of manipulation (of course bigger change to break it)
• dangerous waves - dangerous waves are emitted from the rear side of CRT monitors and they can cause several health problems (especially in offices where people work opposite each other)

     
CRT monitor (source: barang-bagus.co.cc, www.pctechguide.com)

The image is created by so called electron gun which emits electrons. They are being streamlined to a narrow volume and have to go through a mask before falling on the shade. There are different types of masks - Delta (Invar), Trinitron (developed by Sony), In-Line (combination of previous). Single points are drawn into lines using this way and the whole screen is redrawn several times per second - the refresh rate indicates how many times per second.

Animation (CRT monitor)

Alternativní obsah, třeba obrázek.

LCD (Liquid Crystal Display) Monitor

This is a newer type of monitors which works on the principle of optical and electromagnetic properties of liquid crystals. The optical properties mean that if a polarized light goes through crystals it is rotated because of them. To be more accurate, not single crystals rotate the light but their molecules. To be able to use this property, crystals are into a liquid phase (something between solid and liquid state - crystals are liquid but have properties of solid materials).

     
LCD monitor (source: www.geekwithlaptop.com, www.soundandvisionmag.com)

Light inside a LCD monitor travels from the rear part to the front one and goes through two polarization filters to streamline the direction of oscillation. According to the rotation of the filters, a color pixel (composited from color filters - red, green and blue) is made or the result pixel can be black (light will not fall on that place).

     
LCD monitor - principle (source: www.svethardware.cz, www.svethardware.cz)

Division of LCD Monitors:

• STN (Supertwist Nematic, passive) and DSTN (Double Super Twisted Nematic, passive) - They are not used in monitors, only in the cheapest portable computers. Their brightness is low and the response time is high.
• TFT (Thin Film Transistor, active) - This technology can control the brightness of each pixel independently using transistors. Each image point has its own transistor which can set the requested voltage and control the amount of light which goes through. In detail, all three subpixels which create the final pixel have their own transistor because each pixel needs its color filters (red, green, blue) and thanks to this a color image is drawn on the monitor.
  
  
  pixel inside LCD monitor (source: easyhdtv.blogspot.com)
  

Division of LCD Monitors:

• Reflexive - This LCD uses the surrounding light only. The light goes through the display, is reflected from the rear reflexive layer and then returned back to the front part with image points.
• Transmissive - This LCD uses background lamps which are located in the rear part of the monitor.
• Transreflective - Combination of previous ones, it uses the surrounding light as well as a background lamp
  
  Division of LCD (source: www.auo.com)
  

Animation (LCD monitor)

Alternativní obsah, třeba obrázek.

Monitors with LED Backlight (LED LCD monitors)

This is a newer technology for LCD monitors which uses similar procedure as the classical LCD monitors. The difference it in the backlight which is realized using LED diodes. Such a monitor has several advantages:

• lower energy consumption - LED diodes use not so much energy as fluorescent lamps in classical LCD monitors
• higher contrast - thanks to the possibility to control the lightness of each pixel these monitors offers darker black color
• longer life - LED diodes can work longer than classical lamps so the whole life time of these monitors is usually longer
• thinner construction - monitors with LED backlight can be even thinner than classical LCD monitors

OLED (Organic light-emitting diode) Monitors

A new technology which works on the principle of organic electroluminescent diodes (organic diodes) which emit light. These display devices are extremely thin and use a different procedure to create image than LCD monitors. Brightness and color are generated using the organic material in pixel together for all three subpixels.

     
OLED technology (source: www.avsforum.com, www.avsforum.com)

     
OLED technology (source: express.howstuffworks.com, www.wired.com)

What are the advantages?

• Much better color balance because more than 16 million can be displayed.
• No problem to observe from a high angle (around 160°), which means better readability from different positions.
• Clear and bright image.
• More mechanically resistant - ideal for pocket computers and mobile phones.
• Fast response.
• Low energy consumption.
• Well readable in case of direct daylight.
• Possibility to bend or shape the devices.
• Additional source of light is not needed so they are thinner and lighter.

Types of OLED?

• Passive matrix (PMOLED) - Simpler variant which is used for devices which do not require lot of details - especially for texts.
• Active matrix (AMOLED) - Variant for demanding graphic designers who require high resolution. They are designed to work with graphics or videos in high resolution.

     
OLED technology (source: www.svethardware.cz, www.svethardware.cz)

Projector

This device allows you to project image for example on a canvas placed on a wall instead of displaying it on a screen. Projector is used because you can get larger projection area. It is used for presentations, in schools for educational purposes etc.

Except from classical projectors, there are also so called 3D projectors which project a specially adjusted image. If the viewer uses special glasses he can see fictive 3D objects which do not exist in the real.

What to look for when buying a projector?

• resolution - mostly SVGA (800×600), XGA (1024×768), SXGA (1280×1024), UXGA (1600×1200)
• light power - important parameter, it is indicated in so called lumens and says how the final image is bright
• contrast - ratio of the brightest and the darkest point, nowadays usually around 1000:1 (the lightest point is 1000x brighter than the darkest one)
• dimensions and weight
• endurance of the lamp
• interface - which connectors can be used to connect the projector to a computer (VGA, DVI, HDMI, ...)

Other Display Devices

Plasma Screens

Plasma screen or also plasma display is a type of flat display device used for TV with large diagonal size (at least 80 cm) - these devices can be connected to computer of course. The name plasma is derived from the used technology which uses small cells with electrically charged particles of ionized gas.

  
plasma screen (source: www.seznamzbozi.cz), its principle (source: www.pise.cz)

3D Monitors

These monitors are able to simulate 3D image because they display different images for each eye. Human brain then combines both images and creates an illusion of the third dimension. This technology does not allow the viewer to move a lot and also special glasses are required. 3D image is only virtual - similarly as if you wanted to create surround sound using only 2 speakers.

  
3d monitor (source: www.links.hr), its principle (source: www.cnews.cz)

Holographic Projectors

A holographic projector is a display device which can draw real 3D objects which can be seen without any glasses or other tools. It also allows you to observe the objects from all sides at once (for example a conference, lecture). These devices are extremely expensive and their development is still at the beginning. However, in the future they will probably be used for scientific and medical purposes. It is also possible that we will be able to touch the objects.

Holografický projektor - animace.
source: www.vimeo.com

Array of Monitors

This is a situation when more monitors are connected to one computer (3, 6, 9, 16, ...). This solution offers a large workspace which can be used for various purposes - displaying a large part of a map for emergency services or police, details of all appliances while doing a large experiment, communication between doctors in different parts of the world during operation with the current situation in detail, flight simulators for training pilots and more. You have to realize that more than 2 monitors usually cannot be connected to one graphic card so you have to buy a special hub. Also the data transmission is very demanding so it is usually not possible to share the screen via the Internet.

array of monitors (source: www.tinypic.com)

Keyboard

Keyboard is being connected to a computer via the serial interface PS/2 or via the universal serial bus (USB). You can also use wireless variants of course. Keys which are located on the keyboard can be divided to alphanumerical, cursor, numerical and functional parts. There are also additional keys which have special roles (Enter, Space, BackSpace, Esc, Del, Insert, CTRL, ALT, SHIFT, Caps Lock). The principle is that conductive paths are connected when a key is pressed because of a special carbon membrane. Pressing a key generates code which is evaluated by a computer. This is based on an interruption event.

Several modern keyboards contain also multimedia buttons which can for example control volume, launch favorite programs (browser, player, e-mail client, document and more) or switch computer to power saving mode or to hibernation mode.

How to choose a keyboard?

• Wired or wireless? - This option depends on the fact whether you will place it on one place and will not move it or if you want to have a mobile keyboard and be able to move it permanently (for example when watching a film from your bed). If you choose a wireless one, you will have to still observe the state of batteries.
• Interface for connection? - This depends on the availability of ports in your computer. There is practically no computer without USB port nowadays. However, you can also connect your keyboard via Bluetooth - this requires a Bluetooth adapter which can be connected using a USB port.
• Common or multimedia? - A common keyboard is usually very cheap. However, if you pay extra, you can get control over several programs in your computer via your keyboard. Multimedia keyboards contain special buttons for this purpose (sometimes they can also be programmed).
• Soft or hard? - You can buy a classical keyboard with hard keystroke which makes more noise or you can buy a keyboard similar to keyboards in notebooks which has softer keystroke and makes less noise but its endurance is shorter.
• With or without backlight? - Backlight can be useful at the night when you do not want to turn on a light but need to use the keyboard (and do not remember the whole layout of keys). A keyboard with backlight is more expensive of course.

Keyboard (source: myego.cz)

Mouse

Mouse belongs between positioning devices and is used to control the cursor on the screen. We can divide mouses to optical-mechanical (with ball) and optical (infrared, laser, optical). They are connected via the serial interface designed for this purpose (PS/2) or by the universal serial bus (USB). There are different levels of accuracy and sometimes they can even be set (they are indicated in units DPI - dots per inch). Mouses contain two buttons (left and right) and also roller button between the two previous ones.

Better mouses can contain for example buttons for movement back and forward in browsers, or programmable buttons. Also quality gaming mouses usually contain a set of weights which can be placed inside to gain an optimally balanced mouse according to the needs of each user. Mouses are made for right-handed and left-handed people and or you can buy so called universal ones which can be used in both cases (they are symmetrical).

How to choose a mouse?

• Optical or laser or even with a ball? - Mouses with a ball belong to the museum. Optical mouses contain a diode which emits light in visible spectrum, laser and infra ones emit invisible light. Laser mouses offer high resolution and sensitivity and also function well on a glossy surface. However the accuracy is not ideal, sometimes the cursor skips on other place than you wanted. Optical mouses are older, have lower resolution but their accuracy is better. Infra mouses are quite new and their principle is similar to optical ones.
• Wired or wireless? - This option depends on the fact whether you will place it on one place and will not move it or if you want to have a mobile mouse and be able to move it permanently (for example when watching a film from your bed). If you choose a wireless one, you will have to still observe the state of batteries.
• Interface for connection? - Similarly as for the keyboard, it depends on the availability of ports in your computer. There is practically no computer without USB port nowadays. However, you can also connect your keyboard via Bluetooth - this requires a Bluetooth adapter which can be connected using a USB port.
• Which shape to choose? - There are different dimensions of mouses and several ones are ergonomically shaped. It depends on every user which type does he like. There are also mouses with the possibility to change hardness of surfaces, to add weight to gain optimal weight balance etc.

Mouse (source: pretaktovani.cz)

Other Input Devices

There is plenty of input devices, several more types are described in the following lesson (Peripherals II), but you can see several alternatives for already mentioned keyboard and mouse. For example disabled people cannot use classical mouse or keyboard so additional devices were developed for this purposes - these devices can fully replace a keyboard or a mouse.

Mouse for Legs

People who cannot use standard mouse for hands can use this alternative. This is a full replacement for a mouse. The device can also be used together with a classical mouse by common users.

source: www.abilityhub.com

Head Movement Tracker

This device tracks any movement of head (it is usually necessary to wear a special reflexive tool, glasses or something similar). You can move the cursor using your head but it is usually not possible to click. This device can be used in case that someone cannot move with the mouse and needs to work with computer. The principle is simple, you have to fix a tracking head on the top of monitor or notebook which will track the movement of the reflexive tool.

source: www.dansdata.com

Keyboard for Disabled

Users who cannot move with fingers can use the following device which can be controlled even by mouth because of the special pen. There is no need to put any pressure to it, the device automatically recognizes when the pen is above any key.

source: www.magicwandkeyboard.com

Laser Keyboard

This is a device which emits two laser beams. The first of them draws a virtual keyboard on any surface and the second one in the bottom captures presses of virtual keys. The device is compatible not only with computer but also with mobile phones and PDA via the Bluetooth interface. You can enable sounds for keys or change keys layout at more expensive models.

source: www.samuraj.com

Additional Texts

Questions

1. What is the difference between CRT and LCD monitors?
2. What is the principle of a LCD monitor?
3. Which advantages do OLED monitors have?
4. How can we choose the right projector?
5. How can we connect a keyboard and a mouse to a computer?
6. Which alternatives do you know for mouses and keyboards?