8.1 Hardware – Input Devices

By Ranjit Bassi

Mouse

• First prototype computer mouse was made by Douglas Englebert using a wooden shell with two metal wheels

• It was nicknamed the mouse due to a tail out of the end

• Works by detecting movement in the two axes x and y

• Wireless mice communicate by using a wireless signal instead of down a wire

Keyboard

• Used to enter text into a computer system• Components in the keyboard continually scan the

rows of keys to detect the pressing of a key or key combination

• The components identify which keys have been pressed and send the keys scan code to the computer

• Then software in the computer interprets the scan code and converts it into an ASCII code or Unicode code

Bar code reader

• An electronic device used for reading bar codes• A bar code is a sequence of white and black bars that

encodes information • A bar code reader consists of a light source, a lens,

photoelectric detectors (photodiodes)and decoder circuitry to analyse the bar code’s image data and generate character codes

• The scanner outputs the character codes as a sequence of binary digits for processing by a computer

Flatbed Scanner

• Uses a glass pane or platen illuminated from beneath a bright light, often xenon or cold-cathode fluorescent

• The reflected light from scanner is converted into a equivalent electrical signal

• Colour scanners usually contain three rows of sensors with red, blue and green filters (These measure the intensity of the primary colours in the reflected light)

• A digitised image of the entire scanned area is created, it can be stored and processed by the computer connected to the computer

Fingerprint Scanner

• Typically used as a security device• Takes a ‘picture’ of the ridges and valleys in

the finger so they can be analysed• The scanner consists of a sensor and decoder

circuitry• The scanner analyses the captured image data

and outputs it in a electrical form for processing

Retina Scanner

• Consists of a low energy infrared light source, photoelectric detectors and decoding circuitry

• The low energy infrared light is directed onto the retina of the eye

• The photoelectric detectors convert the reflected light into an electrical signal

• The decoding circuitry outputs an encoded form of the retinal pattern for storage or comparison by a computer

Iris Scanner

• The scanner uses a camera sensitive to infrared light

• An image of the iris is captured and stored electronically

• A complex algorithm is applied to the electronic image to create a code of normally 512 bytes

• This code is then compared with a database of iris codes to see if there is any match

Optical Mark reader

• This optically senses marks placed in predefined positions on a form

• Form is passed under a light source and the intensity of reflected light is measured and converted by photoelectric sensors into a electrical equivalent

• Pencil marks do not reflect as much light as the background colour of the form, this is used to detect the presence of the marks

• Optical mark recognition is used for processing multiple-choice answer grids

Optical Character reader (OCR)

• All of these types of systems use an optical scanner to input images of text then analyse the resulting digital images to recognise the characters.

• Some forms such as gas bills are pre-printed with the relevant customer details in a special font that is good for the OCR

• Then the forms can be processed automatically when returned

• OCR systems are used to automate postal sorting

Magnetic Stripe reader

• Magnetic stripe readers read information encoded magnetically in a stripe on the back of a plastic or cardboard card

• Stripe is composed of magnetic particles encased in tape made of plastic

• The orientation of the particles is used to encode binary data

• Stripes can normally store up to 2KB of data

Smart Card reader

• A smart card is a card that holds an integrated chip• The chip contains a microprocessor, little amount of

ROM, small amount of EEPROM, little amount of RAM and a computer bus system

• Applications are stored in the ROM and EEPROM• The microprocessor executes stored applications• Smart cards have enough processing power to encrypt

and decrypt data, so they are used in transactions that require a degree of security against fraud

RFID Reader

• Radio frequency identification uses radio frequencies to transmit data, a timing signal and energy between a reader and an RFID device

• RFID devices do not need a physical electrical contact to transfer data

• An RFID system has a transponder and a reader• The reader or interrogator may be able to read

data or to read and write data but it is always called a reader

Touch-sensitive screen• Is a type of visual display unit that allows a user to interact with a

application• The screen has been specially adapted so that the region just in

front of the screen is criss-crossed by horizontal and vertical beams of infrared light

• Breaking of these beams is detected at the receiving end of each beam by a series of photoelectric sensors

• An electronic circuit connected to these sensors correlates broken horizontal and vertical beams and tells the computer the coordinates.

• The executing application then maps the coordinates to an action

Graphics tablet

• Allows graphics to be drawn into a computer by hand like drawing with a pencil and paper

• Pressing the tip of the stylus against the surface operates a micro switch, which causes the movement to be recorded by computer

• These commands ,may be operating system commands or application commands such as drawing commands in a drawing package

• The board contains electronics to detect the position of the stylus tip

Voice Recognition

• A computer can be trained to recognise a persons voice

• The computer can do this be using a microphone, sound card and appropriate software

• All of the components and software can turn speech into text

• This system can be used to issue commands to the computer and to dictate sentences directly into applications

Digital Still Camera

• This is an electronic device used to capture and store photographs digitally on a memory card

• Most compact digital cameras are multifunctional (Can record sound and video as well as photographs)

• All use either a charge-coupled device(CCD) or a CMOS image sensor to sense the light intensities across the focal plane