OUTPUT DEVICES

OUTPUT DEVICES

Working of CRT Monitor

Working of LCD Monitor

Working of Dot Matrix Printer

Daisy wheel Printer

Working of Drum Printer

Working of Chain Printer

Inkjet Printer

Working of Laser Printer

The output device receives information from the computer and provides them to users. The computer sends information to the output devices in binary coded from. The output devices than convert them into a form, which can be use by users. Output can exist in two forms:

• Softcopy output
• Hardcopy output

a) Softcopy Output

Softcopy Output refers to the output display on the screen. The output on the screen is lost when the computer is turned off. The most commonly used softcopy output devices is monitor.

i) Monitor

Monitor display the video adapter output. The onscreen display enables us to see how application are processing our data, but important to remember that the screen display isn't permanent record.
How CRT Monitor works?
CRT monitor look like TV screen. This kind of screen uses the Cathode Ray Tube (CRT) technology. CRT is a partially evacuated glass tube which is filled with an inert gas at very low pressure. Images are formed in this CRT by an electron gun shooting a stream of electrons at the surface of phosphorescent. Deflection coils are used to divert electron beam and strike on the exact position of phosphorescent surface.
The CRT screen can be classified into two types in terms of colors capability :
Monochrome Monitor:
Monochrome monitor actually display only two colors, one for the background and other for the foreground.
Color Monitor:
Color Monitor display color but the number of color they can display depends on the video adaptor capabilities as well as the monitors. Color monitor can display from 1 to 16 million different colors. Color monitor are sometime called RGB monitors because they accept three separate signal RED, GREEN and BLUE
Most of the monitors use in today PC are color monitor and capable of displaying 16.7 million colors.

ii) LCD (Liquid crystal display)

The thinner monitor use on note book and other small computers are known as flat panel display. Compared to CRT based monitor, flat panel display consumes less electricity and to be up much less room. Most flat panel display use LCD technology.
In LCD or liquid crystalline material is sandwich between two glass or plates as shown in figure2(LCD Monitor). The front plate is transparent and the back plate is reflective. The less expenses LCD's are called passive matrix LCD's. The expensive LCD's are called active matrix LCD's (also called thinfil transistor - TFT) used transistor to control the color of each screen pixel. Speed and color quality is improved on passive matrix LCD's.

b) Hardcopy

Hard copy is a permanent reproduction, or copy in the form of a physical object, of any media suitable for direct use by a person (in particular paper). Examples of hard copy include teleprinter pages, continuous printed tapes, computer printouts, ect.
Magnetic tapes, diskettes, and non printed punched paper tapes are not hard copies.

Printer:

Printer is a peripheral which produces a hard copy (permanent readable text and/or graphics) of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most newer printers, a USB cable to a computer which serves as a document source. Some printers, commonly known as network printers, have built-in network interfaces (typically wireless and/or Ethernet), and can serve as a hardcopy device for any user on the network. Individual printers are often designed to support both local and network connected users at the same time. In addition, a few modern printers can directly interface to electronic media such as memory sticks or memory cards, or to image capture devices such as digital cameras, scanners; some printers are combined with a scanners and/or fax machines in a single unit, and can function as photocopiers.
i) Impact printers
An impact printer is like a typewriter and the characters are formed by physically striking the type devices against an inked ribbon. Impact printers can produce a page, a line, or a character at a time. Print quality is low, but these printers are mainly used for printing backup copies of large amounts of data.
Some of the examples of impact printers are:

• Dot Matrix Printer
• Daisy Wheel Printers
• Drum Printers
• Chain Printers

a) Dot-Matrix Printer:
In the general sense many printers rely on a matrix of pixels, or dots, that together form the larger image. However, the term dot matrix printer is specifically used for impact printers that use a matrix of small pins to create precise dots. The advantage of dot-matrix over other impact printers is that they can produce graphical images in addition to text; however the text is generally of poorer quality than impact printers that use letterforms (type).
At one time, dot matrix printers were one of the more common types of printers used for general use - such as for home and small office use. Such printers would have either 9 or 24 pins on the print head. 24-pin print heads were able to print at a higher quality. Once the price of inkjet printers dropped to the point where they were competitive with dot matrix printers, dot matrix printers began to fall out of favor for general use.
Dot matrix printers are still commonly used in low-cost, low-quality applications like cash registers, or in demanding, very high volume applications like invoice printing. The fact that they use an impact printing method allows them to be used to print multi-part documents using carbonless copy paper (like sales invoices and credit card receipts), whereas other printing methods are unusable with paper of this type.
b) Daisy Wheel Printer
Daisy-wheel printers operate in much the same fashion as a typewriter. A hammer strikes a wheel with petals (the daisy wheel), each petal containing a letter form at its tip. The letter form strikes a ribbon of ink, depositing the ink on the page and thus printing a character. By rotating the daisy wheel, different characters are selected for printing.
These printers were also referred to as letter-quality printers because, during their heyday, they could produce text which was as clear and crisp as a typewriter (though they were nowhere near the quality of printing presses). The fastest letter-quality printers printed at 30 characters per second.
c) Drum printer
In a typical drum printer design, a fixed font character set is engraved onto the periphery of a number of print wheels, the number matching the number of columns (letters in a line) the printer could print. The wheels, joined to form a large drum (cylinder), spin at high speed and paper and an inked ribbon are stepped (moved) past the print position. As the desired character for each column passes the print position, a hammer strikes the paper from the rear and presses the paper against the ribbon and the drum, causing the desired character to be recorded on the continuous paper. Because the drum carrying the letterforms (characters) remains in constant motion, the strike-and-retreat action of the hammers had to be very fast
Often the character sequences are staggered around the drum, shifting with each column. This obviates the situation whereby all of the hammers fire simultaneously when printing a line that consists of the same character in all columns, such as a complete line of dashes ("----").
D) Chain (train) printer
Chain printers (also known as train printers) placed the type on moving bars (a horizontally-moving chain). As with the drum printer, as the correct character passed by each column, a hammer was fired from behind the paper. Compared to drum printers, chain printers had the advantage that the type chain could usually be changed by the operator. By selecting chains that had a smaller character set (for example, just numbers and a few punctuation marks), the printer could print much faster than if the chain contained the entire upper- and lower-case alphabet, numbers, and all special symbols.

ii) Non-Impact Printer:

A type of printer that does not operate by striking a head against a ribbon we call this kind of printer, Non-Impact Printer. These printers are the most widely used printers for PCs to day. It can produce both text and images. Because nothing strikes the paper, Non-Impact Printers are quite. The characters are formed by using heat, laser, ink spray and so on.
Some of the examples of Non-Impact Printers are:

• Ink Jet Printers
• Laser Printers

1) Ink Jet Printer:
Inkjet printers operate by propelling variably-sized droplets of ink onto almost any sized page. They are the most common type of computer printer for the general consumer due to their low cost, high quality of output, capability of printing in different colors.
A typical inkjet receives control info from your printer driver/PC, or may process the printout in its onboard electronics. Either way, rollers advance a page from your paper tray (1) under a sliding printhead/cartridge assembly (2). Then, the printhead stepper motor (3) kicks in, drawing the assembly on a sliding rod (4) to its starting position, usually via a belt (5).
The printhead (6) proper is an incredible piece of miniaturization, in some cases fabricated via an etching process similar to semiconductor manufacture. On some printers, the head and ink cartridge (7) are one unit. The head's microscopic nozzles (8)-anywhere from dozens to literally thousands-are outlets for incredibly tiny ink chambers (9), which are fed by the cartridge's reservoirs. Microscopic droplets (10), measured in millionths of a millionth of a liter (no, that's not a typo), fire through the nozzles.
2) Laser Printer
A laser printer is a common type of computer printer that rapidly produces high quality text and graphics on plain paper. Laser Printers are more expensive then ink jet printers, their print quality is higher, and most are faster. The quality and speed of laser printers make them ideal for office environment.
Static electricity is the principle behind laser printers. A revolving drum or cylinder builds up an electrical charge. A tiny laser beam pointed at the drum discharges the surface in the pattern of the letters and images to be printed creating a surface with positive and negative areas. The surface is then coated with toner, a fine powder that is positively-charged so it clings only to the negatively-charged areas, and is then passed onto the paper to form the positive image. The paper then passes through heated rollers fusing the toner to the paper. Color lasers make multiple passes, in order to mix the different color toners.