Input Devices
... issue commands to the computer directly (e.g scroll down’) • To allow the user to select from a range of menu items and activate specified commands With the advent of graphical user interfaces, a means of pointing to various places on the screen became necessary. The mouse fulfils this function well. Most modern software includes an option to use it Some users dislike having to shift constantly from keyboard to mouse and will tend therefore to use keyboard shortcuts Hand-to-eye coordination is an issue for some users Optical mice have several benefits over wheeled mice: (1) No moving parts means less wear and a lower chance of failure (2) There’s no way for dirt to get inside the mouse (3) Increased tracking resolution means smoother response. Joystick • A joystick is a device which enables the user to control movement on the screen by maneuvering a small lever(called the stick). • The device is either held in the hand or stands on a desk • Mainly used for games, virtual reality walk-throughs and controlling robots Enables simulation Provides a full range of movement Great fun to use With practice very good control can be achieved Can be difficult to control movement Limited use Cheaper models are easily broken or damaged Digital Camera • The pattern of light associated with the image is stored digitally rather than on film • The image, now stored in a standardized format, can be imported into a range of different applications and modified to suit the user’s needs • Everyday personal use, e.g weddings, holidays, etc • For engineers to communicate to clients the progress of a project • For estate agents to update websites using digitally captured images • Speed cameras and number plate recognition The image can be used flexibly in a wide range of applications It can be modified using specially designed applications It can be attached as a file to an e-mail Image files can be ‘memory-heavy’ Quality of output will depend on quality of printer and paper Optical Character Recognition (OCR) • A scanner device reads the reflected light from characters on a page. These may have been typed or hand-written • The scanner creates an image of the character. Software then tries to match it against a ‘library’ of similar character shapes • When a match is found, it inputs the appropriate character • This method is used to input large blocks of text held in ‘hard copy’ format • It is also used to input data captured on forms. Often these forms require the person filling it in to write each character in a box. This is because OCR systems need to be able to read each character individually. An example of this is the passport application form This method can speed up an otherwise lengthy process of keying in The documents do not have to be designed so precisely for OCR Documents can be read directly into a computer without any tying e.g documents received by fax, old books, etc It often misreads letters, and documents captured in this way almost always have to be proof-read afterwards For capturing hand-written text, the cursive style must be clear and the document must be ‘clean’ i.e not contain any marks or smudges that could be interpreted as characters Optical Mark Recognition(OMR) • This method works on the same principle as OCR but instead of trying to interpret characters, OMR systems read marks made at specified points on a specially designed form • These marks equate to pre-set values and once read can be sent for processing • It is used for examination papers where multiple choice questions are used and for submitting grades to examination boards • School registers Avoids need for file transfer This can be an extremely quick way of entering large amounts of data Fewer mistakes are made by machines reading marks than are made reading handwritten characters Data can be prepared without any special equipment The input forms necessarily limit the range of permissible responses Incorrect marking of the sheet will lead to the data being rejected Documents for mark readers are complicated to design. If an item has several values, then the form has to have a different box to mark for each possible value. Sensors • Sensors are devices which read changes in the environment around them • There are a wide range of sensors which can detect changes in light, air pressure, temperature, humidity, speed etc • Sensors are frequently used in control systems. They can be used to measure the temperature of a room. This input can then be used to trigger a control system which adjusts the heating • Other examples include humidity sensors in an art gallery and movement sensors in a security system Sensors are a necessary element of any control system and can also be used for data logging Data can be captured cheaply and with little human effort They are limited in the type of data they can collect They can ‘misread’ environmental changes, e.g a car alarm activated by a strong gust of wind Voice Recognition Systems • The data is inputted in audio form, either directed, via a microphone, or indirectly, via an audio tape. • Software analyses the inputted sound and matches it against a library of sounds • When a match is found the value is sent for processing • A voice recognition system allows users to dictate text straight into the computer. The resulting text can then be edited using standard word-processing applications • It has also been used in control systems e.g instructions to robots in the manufacturing industry • It is sometimes used in security systems A user can speak much more quickly than even the most skilled of typists can type At present the method does not give good results. Relatively few words can be recognised and the error rate is high. The human voice is not uniform. We speak in different styles and different accents. Voice recognition software has to be ‘trained’ to recognize the voice patterns of individual users. This can take a long time. The system is not suitable for use in noisy places without a shielded mouthpiece Touch Screens • Values are associated with different positions on a VDU via a ‘grid’ of infrared beams across the front of the screen. • When the user touches a particular part of the screen, the associated value is sent to be processed. • Touch screens are...