- 1.Magnetic Disk The primary computer storage device. Like tape,
it is magnetically recorded and can be re-recorded over and over.
Disks are rotating platters with a mechanical arm that moves a
read/write head between the outer and inner edges of the platter's
surface. It can take as long as one second to find a location on a
floppy disk to as little as a couple of milliseconds on a fast hard
disk. Tracks and Spots The disk surface is divided into concentric
tracks (circles within circles). The thinner the tracks, the more
storage. The data bits are recorded as tiny magnetic spots on the
tracks. The smaller the spot, the more bits per inch and the
greater the storage. Example Hard disk in computer Floppy Disk
2. Tape Recorders An audio tape recorder, tape deck,
reel-to-reel tape deck, cassette deck or tape machine is an audio
storage device that records and plays back sounds, including
articulated voices, usually using magnetic tape, either wound on a
reel or in a cassette, for storage. The use of magnetic tape for
sound recording originated around 1930. Magnetisable tape
revolutionized both the radio broadcast and music recording
industries. The alternative recording technologies of the era,
transcription discs and wire recorders, could not provide anywhere
near this level of quality and functionality. 3. Tape Recorders In
its present day form, it records a fluctuating signal by moving the
tape across a tape head that polarizes the magnetic domains in the
tape in proportion to the audio signal. It gave artists and
producers the power to record and re-record audio with minimal loss
in quality as well as edit and rearrange recordings with ease.
However, as of the first decade of the 21st century, analog
magnetic tape is largely being replaced by digital recording
technologies for most sound recording purposes 4. CRT 5. Structure
of Cathode Ray Tube Etymology: Cathode rays in a vacuum tube.
Cathode rays are high energy electrons emitted from the heated
cathode (-) of a vacuum tube 6. How Does it Work Electron gun is
weak particle accelerator (only electrons(-)). Aims electrons at
phosphor screen where they light up the image Small heater heats
cathode (-), emits electron cloud that is focused into an electron
beam by two anodes(+): accelerating anode and focusing anode.
Black-and-white monitors only have one electron gun; color monitors
have three (RGB). 7. Variations of CRTs Metal screen filled with
holes sitting just behind phosphor layer. Electron guns each send
beam through hole to a single pixel triad of tubes phosphor layer.
Aperture Grill - Looks kind of like a grill; with lines jutting
down the screen packed together in strips Shadow Mask - packed
together in clusters. If you look closely, you can see little
individual dots, known as pixels 8. Advantages of CRT The cathode
rayed tube can easily increase the monitors brightness by
reflecting the light. They produce more colours The Cathode Ray
Tube monitors have lower price rate than the LCD display or Plasma
display. The quality of the image displayed on a Cathode Ray Tube
is superior to the LCD and Plasma monitors. The contrast features
of the cathode ray tube monitor are considered highly excellent. 9.
Disadvantages of CRT They have a big back and take up space on
desk. The electromagnetic fields emitted by CRT monitors constitute
a health hazard to the functioning of living cells. CRTs emit a
small amount of X-ray band radiation which can result in a health
hazard. Constant refreshing of CRT monitors can result in headache.
CRTs operate at very high voltage which can overheat system or
result in an implosion Within a CRT a strong vacuum exists in it
and can also result in a implosion They are heavy to pick up and
carry around 10. Digital Plotter and Printer The plotter is a
computer printer for printing vector graphics. In the past,
plotters were used in applications such as computer-aided design,
though they have generally been replaced with wide-format
conventional printers. A plotter gives a hard copy of the output.
It draws pictures on paper using a pen. Plotters are used to print
designs of ships and machines, plans for buildings and so on.
Digital printing refers to methods of printing from a digital-based
image directly to a variety of media. It usually refers to
professional printing where small-run jobs from desktop publishing
and other digital sources are printed using large-format and/or
high-volume laser or inkjet printers. Digital printing has a higher
cost per page than more traditional offset printing methods. 11.
Some of the more common printing technologies are: blueprint and
related chemical technologies daisy wheel where pre-formed
characters are applied individually dot-matrix which produces
arbitrary patterns of dots with an array of printing line printing
where formed characters are applied to the paper by lines heat
transfer such as early fax machines or modern receipt printers that
apply heat to special paper, which turns black to form the printed
image inkjet including bubble-jet, where ink is sprayed onto the
paper to create the desired image electrophotography where toner is
attracted to a charged image and then developed laser a type of
xerography where the charged image is written pixel by pixel using
a laser solid ink printer where cubes of ink are melted to make ink
or liquid toner 12. LCD 13. LCD History Liquid crystals were first
discovered in 1888 by Austrian botanist Friedrich Reinitzer. Melt
cholesterol-like substance. When cooled, the liquid turned blue
before finally crystallizing. RCA made the first experimental LCD
in (1968). Manufacturers have been developing creative variations
and improvements since on LCDs. 14. LCD Technology Used for
displays in notebooks, small computers, pagers, phones and other
instruments. Uses a combination of fluorescent-based backlight,
color filters, transistors, and liquid crystal to create and
illuminate images. Until recently, was only used on notebook
computers and other portable devices. In 1997, manufactures began
to offer full size LCD monitors as alternatives to CRT monitors.
15. Advantages of LCDs Power Consumption and Radiation Emission
Consume less energy and more durable A typical CRT losses
approximately 50% of its brightness after 10,000 hours. An LCD bulb
will maintain its brightness anywhere from 25,000 to 50,000 hours.
LCD consumes fewer watts than a CRT. LCD will use an average 30
watts compared to 120 watts for the CRT. Can reduce electric bill
by 40-85%. Uses a combination of fluorescent-based backlight, color
filters, transistors, and liquid crystal to create and illuminate
images. It blocks light rather emit light 16. Advantages of LCDs
Power Consumption and Radiation Emission Does not emit Radiation
Not subject to Electromagnetic Interference Viewing Cause less
eyestrain Does not flicker or glare 17. How does it work &
display Liquid crystal displays work by the tiny pixels on the
screen showing more than 20,000,000 colours an LCD screen is a
multilayered, sideways sandwich. A fluorescent light source, known
as the backlight. This light passes through the first of two
polarizing filters. The polarized light then passes through a layer
that contains thousands of liquid crystal pixels arrayed in tiny
containers called cells. The cells are, in turn, arrayed in rows
across the screen; one or more cells make up one pixel. Electric
leads around the edge of the LCD create an electric field that
twists the crystal molecule, which lines the light up with the
second polarizing filter and allows it to pass through it. 18.
Advantages of LCD The sharpness of a LCD display is at maximum
tweakness. Zero geometric distortion at the native resolution of
the panel. High peak intensity produces very bright images. Best
for brightly lit environments. Screens are perfectly flat. Thin,
with a small footprint. Consume little electricity and produce
little heat The LCD display unit is very light and can be put
anywhere or moved anywhere in the house. Lack of flicker and low
glare reduce eyestrain. 19. Disadvantages of LCD After a while the
LCD display the some of the pixels will die you will see a
discoloured spot on a black spot on the display. The cost of a LCD
is considerably at a high price. The LCD display will have slow
response times. The LCD display has a fixed resolution display and
cannot be changed. LCDs use analog interface making careful
adjustment of pixel tracking/phase in order to reduce or eliminate
digital noise in the image. The viewing angle of a LCD display is
very limited due to the Automatic pixel tracking/phase controls.
20. CRO 21. CRO - Functional Units a) Electron Gun b) Evacuated
Tube c) Deflecting Systemd) Time Base e) Trigger Circuit 22.
Electron Gun 23. Evacuated Tube Vacuum space Screen Graphite inner
wall Shielded from electric and magnetic fields 24. Deflecting
System X-plates Y-plates X and Y Deflection Amplifiers X-shift
Control Y-shift Control Sensitivity Control 25. Time Base Sawtooth
potential difference Time period control 26. Trigger Circuit
Maintain a stable trace Trig level control Trigger time base
automatic triggering 27. USES OF CRO a) Voltmeter b) Display of
waveforms c) Measurement of short time intervals d) Measurement of
frequency e) Display of phase relationship f) Comparison of
frequencies 28. LIGHT EMITTING DIODES 29. A light emitting diode
(LED) is essentially a PN junction opto-semiconductor that emits a
monochromatic (single color) light when operated in a forward
biased direction. LEDs convert electrical energy into light energy.
They are frequently used as "pilot" lights in electronic appliances
to indicate whether the circuit is closed or not.29 30. About LEDs
(1/2) The most important part of a light emitting diode (LED) is
the semi-conductor chip located in the center of the bulb as shown
at the right. The chip has two regions separated by a junction. The
p region is dominated by positive electric charges, and the n
region is dominated by negative electric charges. The junction acts
as a barrier to the flow of electrons between the p and the n
regions. Only when sufficient voltage is applied to the
semi-conductor chip, can the current flow, and the electrons cross
the junction into the p region.30 31. How Does A LED WorkWhen
sufficient voltage is applied to the chip across the leads of the
LED, electrons can move easily in only one direction across the
junction between the p and n regions. In the p region there are
many more positive than negative charges. When a voltage is applied
and the current starts to flow, electrons in the n region have
sufficient energy to move across the junction into the p region.31
32. How Does A LED Work Each time an electron recombines with a
positive charge, electric potential energy is converted into
electromagnetic energy. For each recombination of a negative and a
positive charge, a quantum of electromagnetic energy is emitted in
the form of a photon of light with a frequency characteristic of
the semi-conductor material (usually a combination of the chemical
elements gallium, arsenic and phosphorus)..32 33. Applications
Sensor Applications Mobile Applications Sign Applications
Automative Uses LED Signals Illuminations Indicators33 34. DOT
MATRIX DISPLAY A dot-matrix display is a display device used to
display information on machines, clocks, railway departure
indicators and many other devices requiring a simple display device
of limited resolution. The display consists of a dot matrix of
lights or mechanical indicators arranged in a rectangular
configuration (other shapes are also possible, although not common)
such that by switching on or off selected lights, text or graphics
can be displayed. A dot matrix controller converts instructions
from a processor into signals which turns on or off lights in the
matrix so that the required display is produced. 35. Usual
resolutions: 12816 (Two lined) 12832 (Four lined) 12864 (Eight
lined)Usual character resolutions: A common size for a character is
57 pixels, either separated with blank lines with no dots (in most
textonly displays), or with lines of blank pixels (making the real
size 6x8). This is seen on most graphic calculators, such as Casio
calculators or TI-82 and superior. A smaller size is 35 (or 4x6
when separated with blank pixels). This is seen on the TI-80
calculator as a "pure", fixed-size 35 font, or on most 75
calculators as a proportional (15 to 55) font. The disadvantage of
the 75 matrix and smaller is that lower case characters with
descenders are not practical. A matrix of 119 is often used to give
far superior resolution. Dot matrix displays of sufficient
resolution can be programmed to emulate the customary sevensegment
numeral patterns.
