Digital Electronics: Principles, Devices and Applications

Computer Fundamentals 64315.9.1 Input DevicesAs mentioned before, input devices convert the raw data to be processed into a computer-understandableformat. Input devices can be broadly classified into various types, depending upon the type of inputdata they handle. Commonly used input devices include keyboard devices, pointing devices, imageand video input devices and audio input devices.15.9.1.1 Keyboard DevicesKeyboards are designed for the input of text and characters and also to control the operation of acomputer. Keyboards have an arrangement of keys where each press of a key corresponds to someaction. Keyboards are available in different types and sizes. Keyboard and pointing devices are alsoreferred to as data entry input devices.15.9.1.2 Pointing DevicesThese include the computer mouse, trackball, joystick, touch screen, light pen and so on. The mouseis a handheld device whose motion is translated into the motion of a pointer on the display. It is oneof the most popular input devices used with microcomputers. A joystick consists of a handheld stickthat pivots about one end and transmits its angle information to the computer. Touch screens are inputdevices that sense the touch event and send processing signals to the computer. Touch screens areavailable in various types including resistive, surface wave, capacitive, infrared, strain gauge, opticalimaging and so on. Light pens are devices that transmit their coordinates to the machine when placedagainst the CRT screen of the machine. Hence, they allow the user to point to displayed objects on thescreen or to draw on the screen, similarly to a touch screen but with greater position accuracy.15.9.1.3 Image and Video Input DevicesThese devices, as the name suggests, take some image or video as the input and convert it into a formatunderstandable by the computer. These include magnetic ink character recognition (MICR), opticalmark recognition (OMR), optical character recognition (OCR), scanners, digital cameras and so on.MICR devices are used to detect the printed characters with magnetically charged ink and convertthem into digital data. They are widely used in the banking industry for the processing of cheques. AnOMR device senses the presence or absence of a mark but not the shape of the character. It is a verypopular input device for surveys, census compilations and other similar applications. OCR devices areused for translating images of text or handwritten data into a machine-editable text or for translatingpictures or characters into a standard encoding scheme (ASCII or Unicode).A scanner is a device that analyses an image such as a photograph, printed text, etc., of an objectand converts it to a digital image. OCR, OMR and image scanners are also referred to as dataautomation input devices. A digital camera is an electronic device used to capture and store photographselectronically instead of using photographic film.15.9.2 Output DevicesOutput devices convert the processed data back into a user-understandable format. Like an inputdevice, an output device, too, acts as a human–machine interface. Printers, plotters and displays are