Computer Input Devices:
Input devices allow users and other applications to input data into the computer, for processing. Input devices are classified as follows-
(1) Human Data Entry Devices:
(ii) Pointing Devices- Mouse, Joystick, Trackball, Digitizing Tablet, Light Pen, Touch Screen.
(2) Source Data Entry Devices:
|(i) Audio input- Speech Recognition.|
(ii) Video input- Digital Camera.
(iii) Scanner- Hand-Held Scanner, Flat-Bed Scanner, Sheet-Fed Scanner, Drum Scanner.
(iv) Optical Scanner- OCR, OMR, MICR, Barcode Reader.
The keyboard is perhaps the most popular and widely used computer input device for entering data and instructions in a computer system. A keyboard is similar to the keyboard of a typewriter. It contains alphabets, digits, special characters, and some control keys. A general-purpose keyboard normally contains cursor control keys and function keys. Function Keys allow users to enter frequently used operations in a single keystroke, and cursor-control keys can be used to select displayed objects or coordinate positions by positioning the cursor on the screen.
|Presently a standard computer keyboard known as the QWERTY keyboard is used. This keyboard derived its name from the first six keys in its top row which are Q, W, E, R, T and Y.|
Some of the special purpose keys are listed below:
|Alt Key||It performs a specific task in conjunction with other keys.|
|Arrow Key||To move the cursor in the top, down, left and right directions in a document.|
|Backspace Key||It deletes the character just to the left of the cursor (or insertion point) and moves the cursor to that position.|
|Caps Lock Key||It displays all alphabetic characters in upper case.|
|Ctrl Key||It produces control characters in combination with other keys.|
|Del Key||To delete the character from the current position of the cursor.|
|End Key||To move the cursor to the end of the line.|
|Enter Key||To start a new paragraph in a document.|
|Esc Key||It sends special codes to devices and exits (or escape) from programs and tasks.|
|Shift Key||To type the special characters above the numeric keys. If you press this key along with a number key, the special character above that number will be typed. For example- To type “$”, you have to press the shift key and the number key 4.|
|Num Lock||It switches between numbers to arrow keys. When this key is enabled, the numbers are active and when disabled the arrow keys are active.|
|Space Bar||To enter a space.|
|Tab Key||To enter multiple spaces between two words in a document.|
|Function Keys||They comprise different keys like F1, F2, F3, F4 and so on. These keys have different functions according to the program running.|
A mouse is a small rectangular-shaped hand-held pointing device, with a rubber ball embedded at its lower side and buttons on the top. Usually, a mouse contains two or three buttons, which can be used to input commands or the data. Different types of mouse available are Mechanical Mouse, Optical, Laser Mouse, Air Mouse, 3D Mouse, Tactile Mouse, Ergonomic Mouse and Gaming Mouse.
|(i) Mechanical Mouse- It comprises a rubber ball at the bottom surface. As the mouse is moved on a flat surface, the rubber ball rotates to move the mouse pointer on the screen. A mechanical mouse is the most common and least expensive pointing device.|
(ii) Optical Mouse- It uses a light beam instead of a rotating ball to detect movement. As the user rolls the mouse on a flat surface, the cursor on the screen also moves in the direction of the mouse.
A mouse allows to create graphic elements on the screen such as lines, curves and freehand shapes. Since it is an intuitive device, it is easier and more convenient to work as compared to the keyboard. Like a keyboard, it is also supplied with a computer, therefore, no additional cost is incurred. However, it needs a flat space close to the computer. The mouse cannot easily be used with laptops (notebooks) or palmtop computers. These types of computers need a trackball or a touch-sensitive pad called a touchpad.
Like a mouse, a joystick is also a pointing device that controls the movement of the cursor. The only difference between a mouse and a joystick is that a joystick enables the user to control movement on the screen by manoeuvring a small lever instead of using the mouse. A joystick is usually used to play video games or computer games that require fast reflexes and decision-making.
A joystick provides three types of control.
|(i) Digital Control- It allows movement in a limited number of directions such as up, down, left and right.|
(ii) Glide- It allows movement in all directions (360 degrees).
(iii) Direct Control- It allows all direction movement similar to glide. In addition, it has the ability to respond to the distance and speed with which the user moves the stick.
A trackball is similar to the upside-down design of the mouse. The user moves the ball directly, while the device itself remains stationary. The user spins the ball in various directions to navigate the screen movements. The main advantage of a trackball is that it requires less desk space than a mouse.
A light pen is also a pointing device. The light pen consists of a photocell mounted in a pen-shaped tube. When the pen is brought in front of a picture element of the screen, it senses light coming from a limited field of view. The light coming from the screen causes the photocell to respond by generating a pulse. This electric response is transmitted to a processor that identifies the pixel (graphic point) the light pen is pointing to. Thus, to identify a specific location, the light pen is very useful. But the light pen provides no information when held over a blank part of the screen because it is a passive device with a sensor only.
The light pen is also used to draw images on the screen. With the movement of the light pen over the screen, the lines are drawn.
A touch screen is a display device that allows the user to interact with a computer by using a finger. It can be quite useful as an alternative to a mouse or keyboard for navigating a Graphical User Interface (GUI). Touch screens are used on a wide variety of devices such as computers, laptops, monitors, smartphones, tablets, cash registers, and information kiosks. Some touch screens use a grid of infrared beams to sense the presence of a finger instead of utilizing touch-sensitive input.
A digital camera is a device that stores images digitally. It comprises an electrical sensor and a memory card. The images are stored in the memory card that can be seen after they are captured. The images can also be transferred to the computer to print, view, edit, or send images over the Internet.
The data in the digital camera is recorded in the form of pixels (which are small squares of light). The advantage of a digital camera is that images can be viewed after they are clicked/captured on the screen provided in the camera. Also, in these cameras, the “developing” of photos is both inexpensive and fast because there is no film processing (as these cameras do not require a camera film roll).
The webcam also called a web camera is a loosely used term for any camera that generates images that can be accessed by and displayed on the World Wide Web through a server. They are video capturing devices connected to computers or computer networks, often using USB or, if they connect to networks, Ethernet or Wi-Fi, and gather a series of images for remote display elsewhere. Some webcams capture a still image only once every 30 seconds, while others provide streaming video by capturing 30 images per second. Webcam technology is widely used by all sorts of people for all sorts of reasons. Webcams are being used for security purposes and also for video conferencing.
Optical Character Reader (OCR):
An optical character reader is used to read characters of special type font (or fonts) printed on conventional paper with conventional ink. The printed characters are examined by passing them under a strong light and a lens system, which differentiates light (no ink) from inked areas, and a logical system that attempts to determine which of the possible characters is being examined. The systems in actual use depend heavily on the fact that only a limited number of characters in a particular font are used, but such systems are still quite useful. The standard type of font was agreed on by the ANSI optical character committee. The major advantage of using an optical character reader is that it reduces data entry errors. As a result, an OCR provides accurate data.
Optical Mark Reader (OMR):
In this method, special preprinted forms are designed with boxes that can be marked with a dark pencil or ink. Each box is annotated distinctly so that the user clearly understands what response he is marking. Such a document is read by a document reader, called an optical mark reader (OMR) which transcribes the marks into electrical pulses which are transmitted to the computer.
Such documents are mostly used in areas where responses are one out of a small number of alternatives and the volume of data to be processed is larger. Therefore, OCRs are best suited for:
- Objective type answer papers in examinations in which a large number of candidates appear.
- Various types of surveys where responses can be restricted to one or more out of a few possibilities.
- Order forms containing a small choice of items.
- Timesheets of employees where the start and stop times may be marked.
The main advantage of OMR is that the information is entered at its source and no further transcription is required. This minimizes the unreliability of data. The main disadvantage is the need for accurate alignment of printing on forms and the need for good quality expensive paper. The form cannot be redesigned frequently because any changes will require reprinting of the form, which is expensive.
Magnetic Ink Character Reader (MICR):
A Magnetic Ink Character Reader is an input device that is used to read the characters printed in magnetic ink. A Magnetic Ink Character Reader is extensively used to read the check number and branch code which are located at the bottom of the cheques. A Magnetic Ink Character Reader provides a secure, high-speed method of reading and processing information. A Magnetic Ink Character Reader reads these characters by examining their shapes in a matrix form and the information is then passed on to the computer. The major advantage of a Magnetic Ink Character Reader is that it can be directly used for the computer input, as magnetic ink characters are machine-readable.
A barcode is a machine-readable code in the form of parallel vertical lines of varying widths. It is commonly used for labelling goods that are available in supermarkets and numbering books in libraries. This code is sensed and read by a barcode reader using reflective light. The information recorded in the bar code reader is then fed into the computer, which recognizes the information from the thickness and spacing of the bars. The barcode readers are either hand-held or fixed-mount. Hand-held scanners are used to read barcodes on stationery items. With fixed-mount scanners, the items having barcodes are passed by the scanner- by hand as in retail scanning applications or by conveyor belt in many industrial applications.
Barcode data collection systems provide enormous benefits for every business with a barcode data collection solution; capturing data is faster and more accurate. A barcode scanner can record the data 5 to 7 times faster than a skilled typist. A barcode data entry has an error rate of about 1 in 3 million. Bar coding also reduces the cost in terms of labour and revenue losses resulting from the data collection errors. The barcode readers are widely used in supermarkets, department stores, libraries and other places. You must have seen barcode on the back cover of certain books and grinding cards. Retail and grocery stores use a barcode reader to determine the items being sold and to retrieve the price of an item from a computer system.
Scanners are used to enter the information directly into the computer’s memory. This device works like a Xerox machine. The scanner converts any type of printed or written information including photographs into a digital format, which can be manipulated by the computer.
Types of Scanners:
|(i) Hand-Held Scanners are small in size and are available in different resolutions (measures the quality of an image). These scanners are available in either grayscale or colour. While scanning a document, this can is moved a number of times over the document to obtain the best results.|
(ii) Flatbed Scanners are more expensive than hand-held scanners. These scanners scan the document, image, or text in one go. While scanning, the document is placed on the flat glass surface and the light sensors move over the document to scan it.
(iii) Sheet-Fed Scanners are similar to a flatbed scanner. However, while scanning a document, unlike the flatbed scanner, the document is moved across a stationary scan head. It allows only the paper to be scanned rather than books or other thick objects.
(iv) Drum Scanners are very expensive and produce high-resolution images. They have a scanning photomultiplier tube. While scanning a document, a drum rolls over the entire document around the tube. Since drum scanners provide high resolution, they are used when a scanned image has to be enlarged.
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