For Computer hardware by Martin Robson at WQE

1. Input Devices

2. Mouse
Patented in 1970. Works by detecting the movement in two
axes, X and Y, of a hand-held mouse or, in the case of a
touchpad, a finger moving over the pad.
Also available as a wireless mouse.

3. Keyboard
Used to enter text into a computer. The electronic
components in the keyboard continually scan the rows of
keys to detect the pressing of a key or key combination. They
identify which key(s) have been pressed and send the key’s
scan code to the computer. Software in the computer
interprets the scan code and converts it into an ASCII code or
Unicode code.

4. Barcode Scanner/Reader (1)
A bar code reader or bar code scanner is an electronic
device for reading bar codes printed on items such as cans,
cardboard and plastic packaging and the covers of books or
magazines.
A bar code is a sequence of
white and black bars that
encodes information such as
a product identifier. The
product identifier is usually
printed in human-readable
form beneath the bar code.

5. Barcode Scanner/Reader (2)

6. • A bar code reader consists of a light source, lens, photoelectric
detectors (photodiodes) and decoder circuitry to analyse the bar
code’s image data and generate character codes.
• The scanner uses the light source to illuminate the black and
white bands.
• More light is reflected from a white band than from a dark band.
• The pattern of reflection is converted from optical form to
electrical form by photoelectric detectors in the bar code reader.
• The electrical form of the reflection data is analysed and the bar
code is decoded into character form
• The scanner then outputs the character codes e.g. ASCII codes
as a sequence of binary digits to be processed by a computer
Barcode Scanner/Reader (3)

7. Scanners
A scanner is a device that captures an electrical equivalent of a
picture, printed text, handwriting etc. It produces a digital
representation suitable for storing in a computer system. There
are different types:
1. Flatbed scanner
2. Fingerprint scanner
3. Retina scanner
4. Iris scanner
5. Optical mark reader
6. Optical character reader

8. Flatbed scanner
An item to be scanned is placed face down
on the glass pane, an opaque cover is
lowered over it to exclude external light, and
an array of light-detecting sensors spanning
the width of the glass pane is moved slowly
with the light source across the pane to read
the intensity of the reflected light from the
entire area. A digitised image is created
which can be stored by the computer
attached to the scanner. Colour scanners
contain sensors with red, green and blue
filters that measure the intensity of the
primary colours in the reflected light.

9. Fingerprint/Retina/Iris Scanners
Fingerprint reader: a security device that takes a ‘picture’ of
a finger so that the pattern of ridges and valleys in the
image can be analysed, encoded and stored.
Retina scanner: consists of a low-energy infrared light source
that is directed onto the retina in the back of the eye.
Photoelectric detectors convert reflected light into an
electrical signal that can be analysed, encoded and stored.
Blood vessels in the retina absorb more light than
surrounding tissue.
Iris scanner: the iris is the coloured part of the eye
surrounding the pupil. The iris is scanned using infrared
light. The image is analysed, encoded and stored.

10. Optical mark reader (1)
• Optically senses marks placed in predefined positions on a
form.
• The form is passed under a light source and the intensity of
the reflected light from each row of the form is measured and
converted by photoelectric sensors into an electrical
equivalent.
• Pencil marks do not reflect as much light as the background
colour of the form and this is used to detect the presence of
the marks.
• Optical mark recognition is used to process multiple choice
answer grids, national lottery tickets, some customer response
forms and for our school registration forms.

11. Optical mark reader (2)

12. Optical character reader (1)
• All optical character recognition (OCR) systems use an
optical scanner to input images of text and then analyse
the resulting digital images to recognise the characters.
• OCR systems are used to automate postal sorting. The
OCR system captures an image of the address on the
envelope and extracts the postal code before printing the
postcode in a machine-readable code of phosphor dots.
• The phosphor dots are used in the rest of the automatic
sorting process. It takes a fraction of a second as the
letter passes through the machine.

13. Phosphor dots
shown on stamp
Optical character reader (2)

14. Magnetic stripe reader (1)
• Magnetic stripes are usually found on the back of plastic or
cardboard cards of typically 8.5 cm x 6.5 cm in size and are
composed of magnetic particles encased in tape made of plastic.
• The magnetic particles are orientated in such a way so that they
encode binary data.
• Most stripes can store up to 2 KB of information.
• They are used in applications such as credit and debit cards,
library membership cards, railway tickets, bus tickets, phone
cards and hotel keys.
• They have to be slowly and steadily swiped through the magnetic
stripe reader to induce a current in the reader.
• Magnetic stripe cards are gradually being replaced by smart
cards.

15. Magnetic stripe reader (2)

16. Smart card reader (1)
• Smart cards are slowly replacing magnetic stripe cards.
• A smart card is a plastic card the size of a credit card
that holds an integrated circuit chip.
• The chip contains a microprocessor, a small amount of
ROM, a small amount of EEPROM, a small amount of
RAM and a computer bus system.
• The smart card reader provides power when the smart
card is inserted into the reader.
• Applications are stored in ROM and EEPROM.
• The EEPROM is mainly used to store persistent data
and the RAM is used as a scratch pad for temporary
data when the stored applications are executed.

17. • The microprocessor executes the stored applications.
• Smart cards are used in many applications, such as credit
and debit cards, mobile phone cards, railway tickets such
as the Oyster card and electronic cash.
• Smart cards have enough processing power to encrypt
and decrypt data, so they are used in transactions that
require security.
Smart card reader (2)

18. RFID reader (1)
• Radio frequency identification (RFID) uses radio frequencies (RF) to
energise a transponder located on the object to be identified so that the
transponder can respond with data which the RFID reader reads.
• The RFID reader can also supply a timing signal to the transponder so
that the transponder’s operations may be synchronised with those of its
reader.
• Reader and transponder do not need to be in physical contact because
data transmission is done via radio frequency waves. For this purpose,
both reader and transponder each use a small RF antenna and circuitry
for transmitting and receiving data.
• The RFID reader may also write data to the transponder’s memories
(volatile and non-volatile).

19. Computer
RFID
reader
Transponder
(Contactless
data carrier)
Data
Energy
RFID Device
RFID smart cards, such as Transport for London’s Oyster card, are used
as tickets for short journeys on public transport. RFID devices are
attached to products to respond with the product’s serial number when
interrogated. They can be used in security badges to give access to
protected premises. Electronic immobilisers for cars use RFID – the
ignition key is combined with a transponder. RFID devices can be placed
in animals under the skin or in the stomach for tracking and identification.
RFID reader (2)
Clock

20. Touch-sensitive screen
A touch-sensitive screen is a type of visual display unit that allows a user to
interact with an application.
•To initiate an action in an executing application a user touches regions of
the screen associated with the application.
•In one arrangement, the region just in front of the screen is criss-crossed
by horizontal and vertical beams of infrared light, invisible to the naked eye.
•The breaking of these beams by a finger or other passive pointing object,
e.g. pencil, is detected at the receiving end of each beam by a series of
photoelectric sensors, one per beam.
• An electronic circuit connected to these
sensors correlates broken horizontal and
vertical beams and signals the computer the
coordinates.
• The executing application then maps the
coordinates to an action

21. Graphics Tablet
A graphics tablet allows graphics to be drawn into a computer by hand
rather like drawing with pencil and paper. A flat board, the tablet, is
connected to the computer. Pressing the tip of the stylus against the
surface operates a micro switch which causes the movement to be
recorded by the computer. The board contains electronics to detect the
position of the stylus tip. A graphics tablet is used with a drawing package
to create line drawings.

22. Voice Recognition
A computer can be
trained to recognise a
person’s voice and to
turn speech into text
using a microphone,
sound card and
appropriate Voice
Recognition Software.
This system can be used
to issue commands to
the computer and to
dictate sentences
directly into applications.

23. Digital Still Camera
• The different colour arrays are
combined to form an image
• Once the RGB values have
been captured, they can then
be stored digitally using SD or
compact flash cards. Save
formats include JPEG or TIFF.
• Light is focused through the lens onto the image sensor at the back
of the camera.
• The image sensor is made up of an array of Red, Green and Blue
photosensors, called a Bayer filter. Each sensor will only record
values for that particular colour.

24. Output Devices

25. Visual Display Unit (VDU)
Computers require some form of visual display
unit (VDU) or monitor to show entered data and
the results of processing.
There are 3 main types:
1. Cathode-ray tube (CRT)
2. Flat screen (LCD)
3. Plasma screen

26. Cathode-Ray Tube (1)
A cathode-ray tube (CRT) is a vacuum tube with a
narrow neck and a flat rectangular base. The screen
is coated on the inside of the flat base with a
phosphor that emits light when struck by an electron
beam. The neck is surrounded by electromagnets
and inside the neck is an electron gun. The electron
beam is dragged across the screen from top to
bottom many times per second so that the image
does not appear to flicker to the eye.

27. Cathode-Ray Tube (2)

28. Colour CRT VDUs use three independent electron
guns: a red gun, a green gun and a blue gun. The
screen is made up of lines of phosphor dots
arranged in triplets and each triplet consists of one
red phosphor, one green phosphor and one blue
phosphor. Three independent electron beams are
arranged to strike their corresponding phosphor in
each triplet. The effect produced in the eye is a
combination of the received intensities of red, green
and glue light – the eye additively mixes these
primary colours to produce the required colour.
Cathode-Ray Tube (3)

29. LCD Flat Screen (1)
• Liquid-crystal display (LCD) technology uses a
property of liquid crystals to change the state of
polarisation of light when an electrical field is
applied to the crystals.
• The liquid-crystal material is sandwiched between
two crossed sheets of linearly polarised glass
(axes of polarisation are at right angles) so that
light from a back-light is normally blocked from
passing through the sandwich.

30. LCD Flat Screen (2)
• By applying an electrical voltage to the liquid
crystal, the angle of polarisation of the light
emerging from the first Polaroid sheet can be
rotated so that part of this light transmits through
the second Polaroid sheet.
• A greater amount of light emerges from the
second Polaroid sheet when a greater voltage is
applied to the liquid crystal because a greater
rotation of the axis of polarisation is produced.

31. LCD Flat Screen (3)
• An LCD flat screen is manufactured with an array
or matrix of these liquid crystal cells, each
constituting one pixel when the screen is used at
full resolution.
• Each pixel’s liquid crystal is connected to a
capacitor which stores the electrical charge which
produces the electrical voltage/field.
• More charge means more voltage which means the
passage of more light through the sandwich. The
charging of the capacitor is controlled by an
electrical switch which is a thin film transistor (TFT).

32. An exploded view of a single LCD pixel:
Flat Screen (4)

33. Compared with CRTs, LCD screens have the
following advantages:
1. Thinner display
2. Lower power consumption (30% lower)
3. Image does not need to be constantly redrawn
to remain visible so no flicker
4. Perfect screen geometry so no distortion in the
corners
Flat Screen (5)

34. Plasma Screen (1)
Plasma screens are ideal for large displays. Each pixel is
controlled by a miniature fluorescent light. When the
control voltage is applied, the gas becomes plasma and
releases ultraviolet light, which strikes phosphors on the
front of the screen to emit visible light. Unlike LCD
screens, plasma screens have a wide viewing angle and
produce colours similar to conventional CRTs. The
greatest limitation of plasma screns is pixel size, typically
0.8mm. This is unsuitable for smaller monitors viewed at
close range. Plasma screens generate a lot of heat,
enough to cause injury if touched.

35. Plasma Screen (2)

36. Speech Output
Words in electronic documents can be output as
spoken words using specialist speech synthesis
software, a sound card and speakers.

37. Electronic paper (1)
Electronic paper, e-paper and electronic ink are a
range of display technology which are designed to
mimic the appearance of ordinary ink on paper.
Unlike conventional backlit flat panel displays which
emit light, electronic paper displays reflect light like
ordinary paper. Many of the technologies can hold
static text and images indefinitely without using
electricity, while allowing images to be changed
later. Flexible electronic paper uses plastic
substrates and plastic electronics for the display
backplane.

38. Electronic paper is often considered to be more
comfortable to read than conventional displays. This
is due to the stable image, which has no need to be
refreshed constantly, a wider viewing angle, and
that it reflects ambient light rather than emitting its
own light. An ideal e-paper display can be read in
direct sunlight without the image appearing to fade.
There is ongoing competition among manufacturers
to provide full-colour ability.
Electronic paper (2)

39. Applications of electronic visual displays include
electronic pricing labels in retail shops, and digital
signage, time tables at bus stations, electronic
billboards, mobile phone displays, and e-readers
(e.g. Kindle) able to display digital versions of books
and e-paper magazines.
Electronic paper (3)
Electronic paper should not
be confused with digital
paper, which is a pad to
create handwritten digital
documents with a digital pen.

40. Impact Printer - Dot Matrix (1)
• Dot matrix printers remain in common use in businesses
where multi-part forms are printed, such as car rental
services, this allows several sheets of paper to be written
to with one strike of the printer head, it also allows for
carbon paper to be written to through sealed envelopes.
• Dot matrix printers use a print head containing a line of
pins.
• The number of pins can vary from 7 into the dozens.
• As the print head passes over the paper the pins impact
on the ink ribbon forming characters on the paper line by
line.

41. Impact Printer - Dot Matrix (2)

42. Inkjet Printer (1)
• Non-impact printers transfer ink to paper using
electrostatics or some other non-impact technique.
• An inkjet printer produces coloured output by
printing a line of colour at a time. Printing a line of
characters involves printing several lines of colour
before the whole line of characters emerges.
• Colour inkjet printers use 4 cartridges containing
cyan, magenta, yellow and black (CMYK) ink.
• Inkjet printers can be slow when printing in the
highest resolution and the ink can smudge.
• Cartridges for colour inkjet printers are still
relatively expensive.

43. Operation of an Inkjet Printer
• Heater behind the ink reservoir is warmed
• This vaporises a droplet of ink.
• The ink expands and is forced out as a small ink blob onto
the paper
• Different colours are produced from mixing of ink spots fired
together
• The heater is turned off – the ink cools and the remainder of
the droplet is sucked back in
• This process is repeated for all colours and each nozzle
• The print head moves across each line of paper
• The printer prints line by line
• The ink dries before the paper emerges from the printer
Inkjet Printer (2)

44. Laser Printer (1)
• A laser printer prints a whole page at a time.
• It prints high-quality text and graphics.
• A page description language usually describes the page to
be printed as lines, arcs and polygons.
• A processor in the laser printer generates a bitmap of the
page in the printer memory from the page description.
• A negative charge is applied to the photosensitive drum at
the heart of the printer – print drum is coated in negative
charge
• One or more laser beams are directed onto the rotating
drum’s surface.
• The lasers are modulated (turned on or off) at positions
determined by the bitmap data stored in the memory.

45. • The laser causes the negative charge to be neutralised or
reversed or removed at positions corresponding to the
black parts of the page to be printed.
• The resulting pattern of charges on the drum’s surface is an
image of the page to be printed.
• The toner consists of fine particles of dry plastic powder
mixed with carbon black or colouring agents.
• The toner is given a negative charge.
• The drum is exposed to the toner – the negatively charged
toner particles attach to the uncharged or positively charged
regions of the drum
• The toner is fused/bonded/melted/stuck to the paper by
heated rollers.
Laser Printer (2)