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Output device. Monitors. The most obvious output device is a monitor. Whether you are writing in a word document, viewing images, watching a video or surfing the internet, you need a monitor to display all that you see and read.
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Monitors • The most obvious output device is a monitor. Whether you are writing in a word document, viewing images, watching a video or surfing the internet, you need a monitor to display all that you see and read. • There are two types of monitors – 1) Cathode Ray Tube (CRT) and 2) Flat Panel Display which uses LCD (Liquid Crystal Display) or Plasma screens.
Monitor - CRT • At the back of a CRT Monitor is a gun that shoots a beam of electrons through a magnetic coil which aims the beam at the front of the monitor. • There is a phosphorus sheet in between the glass screen and the magnetic coil. This sheet lights up when the electron hits the phosphorus sheet and produces a colour that we can see on the screen. • This image is produced via pixels, the more pixels you have the more clear the image. • The beam goes back and forth – left and right – along the screen to produce
Monitor – Liquid Crystal Display (LCD) • An LCD are transparent clear (white) crystals that when electrified they become opaque. • To be more precise, if we apply an electric charge to liquid crystal molecules untwist. When they straighten out, they change the angle of the light passing through. • When digital information is sent to the LCD, only parts of the crystals are hit with electricity to create an image that is displayed on the screen.
LCD - COlour • An LCD that can show colourmust have three subpixels with red, green and blue colour filters to create each colour pixel. • Through the careful control and variation of the voltage applied, the intensity of each subpixel can range over 256 shades. Combining the subpixels produces a possible palette of 16.8 million colours (256 shades of red x 256 shades of green x 256 shades of blue).
Video Controller • On the motherboard there is a chip called the video controller. It is a video- dedicated memory and other circuitry necessary to send information to the monitor for display on the screen. • This chip helps determine the refresh rate, resolution, and number of colours that can/need to be displayed. • The higher the resolution, the more pixels we require, the more clear/sharper the image. Ex. A resolution of 640x480 pixels is quite clear and easy to read. But, one that is 1024x768 pixels is much more crisp and clear. • Video Ram is also part of the controller; it sends a screen full of data to the monitor as fast as it receives the information. The more Video Ram you have the faster your screen can refresh.
Projector • Digital Light Projector acts exactly like a monitor. It takes the information from the monitor and uses LCD technology to project the image. • The problem with a Digital Light Projector is that its image is not all that crisp as it relies on light to be projected and spread out and blurry on a screen. • Digital Light Processing technology is coming out and it uses a microchip which uses mirrors to control the image. Because of using mirrors and a microchip it can create a more clear image on the screen.
Sound System • Sound Systems produce a sound from the computer for us to hear. A sound system requires speakers, sometimes a subwoofer, and a sound card. • The same sound card that is used with the microphone that converts an analog wave to digital format (ADC) also has the ability to convert digital information to analog (DAC). • The ability to convert the digital information to analog produces the sound we hear from the speaker.
Sound System The red line is the analog wave, the green bars are the conversion of the analog wave into digital information.
Printers • Printers are the final form out output device. • A printer produces a paper copy of information generated by a computer.
Printers Printers fall into two categories: • Impact printers use a device to strike an inked ribbon, pressing ink from the ribbon onto the paper. • Non-impact printers use different methods to place ink (or another substance) on the page.
Printers Some of the printers out in the market today include the following: • Dot Matrix Printers • Ink Jet Printers • Laser Printers • Snapshot Printers
Dot matrix printer – were once very popular, but have been replaced in popularity by ink-jet printers. Inside a dot-matrix printer a print head containing small blunt pins strikes an inked ribbon to stamp images on a page. Printers – Dot Matrix
Printers – Ink Jet Printer • Ink-jet Printer – An ink-jet printer produces high-quality documents at a relatively low price. You can use the documents produced by an ink-jet printer in most circumstances, except when only the highest quality is acceptable, such as for important business correspondence. • An ink-jet printer sprays ink through small nozzles onto a page to produce images.
Printers – Laser Printer • Laser Printer – A laser printer is a high-speed printer that is ideal for business documents and graphics. Laser printers produce the highest quality images, but are relatively expensive. • A laser printer works like a photocopier to produce images on a page. A laser beam draws images on a light-sensitive drum. The drum picks up a fine powdered ink called toner, and then transfers the toner to the paper to create the images. • Laser printers produce higher-quality print than ink jet printers, but are more expensive.
Printer – Photo Printer • Photo printers are small-format printers that print digital photographs. • Snapshot printers are fairly slower than other printers, and can be more expensive to operate.
