Peripheral Devices

A computer peripheral is a device that is connected to a computer but is not part of the core computer architecture. 

There are many different peripheral devices, but they fall into three general categories:-

• Input devices, such as a mouse and a keyboard
• Output devices, such as a monitor and a printer
• Storage devices, such as a hard drive or flash drive

Printer

A printer is an electromechanical device which converts the text and graphical documents from electronic form to the physical form.

Categories of Printer

Impact Printer

In the case of impact printers, printing is performed  by means of an impregnated ribbon; therefore, there is a mechanical contact between the printing assembly, inked ribbon, and paper.

E.g.-Dot-Matrix, Daisy-wheel

Non-Impact Printer

In the case of non-impact printers, there is no direct contact between the printing assembly and paper.

   E.g. - Ink-Jet Printer, Laser Printer 

General Structure of a Printing Engine

Types of Printer

Daisy-Wheel Printer:-

Daisy wheel printers print only characters and symbols and cannot print graphics. They are generally slow with a printing speed of about 10 to 75 characters per second is very similar to typewriters.

A circular printing element (known as daisy wheel, shown in the below image) is the heart of these printers that contains all text, numeric characters and symbols mound on each petal on the circumference of the circle.

   

               

Dot-Matrix Printer:-

It is a popular computer printer that prints text and graphics on the paper by using tiny dots to form the desired shapes. 

It uses an array of metal pins known as print head to strike an inked printer ribbon and produce dots on the paper.These combinations of dots form the desired shape on the paper.

     

                   

Ink-Jet Printer: -

It prints characters by spraying patterns of ink on the paper from a nozzle or jet. 

It prints from nozzles having very fine holes, from which a specially made ink is pumped out to create various letters and shapes. The ink comes out of the nozzle in a form of vapors. After passing through a reflecting plate, it forms the desired letter/shape at the desired place.         

              

There are mainly two technologies that are used to spray the ink by nozzles. These are:

Thermal Bubble

This technology is also known as bubble jet is used.When printer receives commands to print something, the current flows through a set of tiny resistors and they produce heat.This heat in turn vaporizes the ink to create a bubble.

As the bubble expands, some of the ink moves out of the nozzle and gets deposited over the paper. Then the bubble collapses and due to the vacuum it pulls more ink from ink cartridge.

            

Piezoelectric 

In the piezoelectric technology, a piezo crystal is situated at the end of the ink reservoir of a nozzle. When printer receives the command to print, an electric charge is applied to the crystal which in turn starts vibrating and a small amount of ink is pushed out of the nozzle. When the vibration stops the nozzle pulls some more ink from the cartridge to replace the ink sprayed out.

          

Laser Printer:-

 A type of printer that utilizes a laser beam to produce an image on a drum. The light of the laser alters the electrical charge on the drum wherever it hits.

The drum is then rolled through a reservoir of toner, which is picked up by the charged portions of the drum. Finally, the toner is transferred to the paper through a combination of heat and pressure. This is also the way copy machines work. Because an entire page is transmitted to a drum before the toner is applied, laser printers are sometimes called page printers. 

   

                         

                                  Some special types of printers

Photo Printer: – 

                           These inkjet printers are color printers that produce photo lab quality pictures on photo papers. Although they can also be used to print documents but they are specially designed for printing the photo. 

                            

Dye Sublimation Printers: – 

                        These are latest innovative printers that are specially designed for high quality photo printing. They magnetize the ink over a charged paper to produce a very high quality picture. These printers are suitable to photo hobbyists but are a quite expensive.

            

Portable Printers: - 

                               They are small light weight inkjet or thermal printers specially designed for the users to carry out with the laptops while travelling. Generally these printers have a lower quality for image printing and higher cost because of its compact design.

         

Monitor

A computer monitor, technically termed as visual display unit is an output device that presents the information from the CPU on the screen working as an interface between CPU and the user. These monitors employ the CRT technology to create a display.

The operation of a  A cathode ray tube consists of one or more electron guns, possibly internal electrostatic deflection plates and a phosphor target. CRT has three electron beams – one for each (Red, Green, and Blue). The electron beam produces a tiny, bright visible spot when it strikes the phosphor-coated screen. In every monitor device the entire front area of the tube is scanned repetitively and systematically in a fixed pattern called a raster.

      





                  

Mouse

• A mouse is an Input device which allows the user to control a cursor to manipulate data without complicated commands (i.e. to position the screen cursor).

• There are 2 cylindrical rollers attached to the mouse ball, which rotate along their respective axes, when the mouse is moved. There are perforated wheels attached to rollers and they rotate simultaneously (but independently) with rollers.

• When we move the mouse, the red beams (infraredLEDs) get interrupted and the quantum of motion is sensed. This is sensed and converted to a signal pulse. Entire plane of computer screen is covered in this way.

        

Keyboard

Keyboard is an input device that functions in accordance to the instructions of the user.

     

Inside the keyboard, there are metallic plate, circuit board and processor, which are responsible for transferring information from the keyboard to the computer.

Depending upon the working principle, there are two main types of keys, namely, capacitive and hard-contact. When a capacitive key is pressed, the metal plunger applies a gentle pressure to the circuit board.

The pressure is identified by the computer and the circuit flow is initiated, resulting in the transfer of information from the circuit to the currently installed software.