Power supply ,Display adapter & IO devices

2K15-U1
UNIT – I
1.1.0 Understand Power supply and Display adapters

1.1.1 Draw the block diagram of an SMPS and explain its working

The use of IC’s and modular construction led to the introduction of switching mode power
supply to meet the DC requirements of equipments. These power supply circuit are smaller, lighter and
with less heat dissipation. These power supply offer high efficiency and more percentage of regulation.
The circuitry also avoids the need of bulky step down transformers with heavy iron core.

Basic principle of operation

In an SMPS the regulating elements consist of series connected transistor that act as rapidly
opening and closing switches. The input AC is first converted to unregulated dc, which is chopped by
the switching elements operating at a 20 KHz. The resultant 20 KHz pulse train is transformer coupled
to an output network which provides final rectification and smoothing of the Dc output. Regulation is
accomplished by control circuits which vary the duty cycle (ON-OFF) of the switching elements
depends on the variation of the output voltage.

Because of the use of high frequency in switching the transformer using will be a ferrite core
type and is very small and light. Also it helps the circuit from core and copper loss.

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SMPS advantages and disadvantages
The advantages of a SMPS over a conventional regulated power supply are;

1. The switching transistors are basically on-off devices and so dissipate only very little heat.
Efficiencies ranging from 65 to 85 percent. Other types of power supply can only offer 30 to
45 percent.
2. Because of the use of high switching rate of 20KHz, the power transformer, inductor and filter
capacitors are much smaller and lighter than normal transformer power supply type. Which
follows 50Hz line frequency? Typically SMPS is less than one third in size and weight of a
transformer power supply.
3. SMPS offers wide range of input voltages. It has a relatively long holdup period if input power
is lost momentarily.

Disadvantages

1. Electromagnetic interference is a natural problem with this off-off witching circuit with 20 KHz.
This interference can get coupled to various other equipments and may got malfunction.
2. Built in shields are necessary to avoid EMI and noise.
3. The control circuitry is expensive and with complex circuits.

SMPS circuit concept

The following figure contains the simplified circuit logic of an SMPS with associated
waveforms. The regulation in output is achieved by a pair of push pull switching transistors (Q1 and
Q2) operating under the control of a feedback network consisting of a pulse width modulator and a
voltage comparison amplifier.
The waveform illustrates the manner in which the duty cycle is controlled to deliver a constant
Dc output voltage. The voltage comparison amplifier continuously compares a fraction of the output
voltage with a stable reference source Vr1 and develops a control voltage Vcontrol for the turn on
comparator. The comparator compare the Vcontrol with a triangular ramp waveform at a frequency of
40Khz. When the ramp voltage is more positive than the control level, a turn on signal is generated.
Any increase or decrease in the control voltage will vary the width of the turn on voltage and this will
alter the width of drive pulses to both Q1 and Q2. Thus each switch operates at 20 Khz, one half of the
ramp frequency.

When Q1 is on , current flows through the upper half of the primary winding of T1, and
completes its path through the centre tap. Similarly, when Q2 conducts current flows in other direction
and the lower half of the same winding will be energized.

The DC out put is proportional to the duty cycle. By increasing the on period the output can be
increased and by decreasing the on period the output will be decreased. Thus the control voltage can
automatically monitor and maintain the duty cycle depends on the output variations.
The comparator, ramp generator and steering logic or control logic will be usually a common
IC. In modern designs more security options are also included with the same IC. In the PC SMPS, low
voltage, over current, high voltage protections are included in SMPS. They also generate a wide range
of voltages with different current handling capacities. PC SMPS are also categorized on the basis of
its power handling capacity and connector types. Also some special features like power management
facilities are also integrated with the circuit.

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1.1.2 List the voltage signals from an SMPS

The basic function of the power supply is to convert the type of electrical power available at the
wall socket to the type the computer circuitry can use. The power supply in a conventional desktop
system is designed to convert 230V (nominal) 50Hz AC power into +3.3V, +5V, and +12V DC (direct
current) power.

Computers power supplies are generally in TWO types, AT SMPS and ATX SMPS. The AT
generation design provides +5v, +12v, -5v and -12 v outputs. In ATX design, an additional +3.3v is
also available because of the need for modern processors and logic circuits as well as memory. The
total output voltage categories are as follows,

Positive DC Voltages

Usually, the digital electronic components and circuits in the system (motherboard, adapter
cards, and disk drive logic boards) use the +3.3V or +5V power, and the motors (disk drive motors and
any fans) use the +12V power. List of devices and their power consumptions are as follows.

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Negative DC Voltages

–5V and –12V are supplied to the motherboard via the power supply connectors, the
motherboard normally uses only the +3.3V, +5V, and +12V. The –5V is simply routed to the ISA bus
older floppy controllers uses –5V. The motherboard logic normally doesn’t use –12V it is used in some
board designs for serial port or LAN circuits.

The Power Good Signal

In addition to supplying electrical power to run the system, the power supply also ensures that
the system does not run unless the power supplied is sufficient to operate the system properly. In other
words, the power supply actually prevents the computer from starting up or operating until all the power
supply voltages are within the proper ranges. The power supply completes internal checks and tests
before allowing the system to start. If the tests are successful, the power supply sends a special signal
to the motherboard, called Power Good. This signal must be continuously present for the system to
run. Therefore, when the AC voltage dips and the power supply cannot maintain outputs within
regulation tolerance, the Power Good signal is withdrawn (goes low) and forces the system to reset.
The system will not restart until the Power Good signal returns.

The Power Good signal (sometimes called Power_-OK or PWR_OK) is a +5V (nominal) active
high signal (with variation from +2.4V through Power Good +6.0V generally being considered
acceptable) that is supplied to the motherboar
d when the power supply has passed its internal self tests and the output voltages have stabilized.
This normally takes place anywhere from 100ms to 500ms (0.1–0.5 seconds) after you turn on the
power supply switch.
The power supply then sends the Power Good signal to the motherboard, where the processor
timer chip that controls the reset line to the processor receives it. In the absence of Power Good, the
timer chip holds the reset line on the processor, which prevents the system from running under bad or
unstable power conditions. When the timer chip receives the Power Good signal, it releases the reset,
and the processor begins executing whatever code is at address FFFF:0000 (usually the ROM BIOS).
If the power supply cannot maintain proper outputs (such as when a brownout occurs), the
Power Good signal is withdrawn, and the processor is automatically reset. When the power output
returns to its proper levels, the power supply regenerates the Power Good signal and the system again
begins operation (as if you had just powered on). By withdrawing PowerGood before the output
voltages fall out of regulation, the system never sees the bad power because it is stopped quickly (reset)
rather than being allowed to operate using unstable or improper power levels, which can cause memory
parity errors and other problems.

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1.1.3 Identify the power connectors for various components in a PC

1.1.4 Explain the features of AT, ATX and NLX, SMPS illustrating the power supply connectors

Power Supply Form Factors

The shape and general physical layout of a component is called the form factor. Depends on the form
factors SMPS are categorized as XT, AT, ATX, NLX etc. They generally differ with the total case size,
connector types and the number of connectors provided.

1.1.5 Define the display adapter/display controller

A video card, video adapter, graphics-accelerator card, display adapter or graphics card
is an expansion card whose function is to generate output images to a display unit. The display adapter's
primary purpose is to continuously convert the graphic patterns (bitmaps) from the memory frame
buffers into signals for the monitor's screen. The high-end adapters provides texture and 2D and 3D
effects. The display adapter determines the maximum resolution of the image, refresh rate of the
monitor and number of colors that can be displayed, It also defines the monitor type to be supported.
An adapter can interface with the motherboard with several interfaces, such as ISA, PCI VESA etc.

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Some special purpose or dedicated BUS slost are available for the display adpters such as AGP, PCI
express etc.

Some modern motherboards integrated the display adapter hardware with the motherboard
circuit as an integrated function. ( onboard – display)Many video cards offer added functions, such as
3D and 2D graphics, video capture, TV-tuner adapter, MPEG-2/MPEG-4 decoding, FireWire, light
pen, TV output, or the ability to connect multiple monitors (multi-monitor)

A video card consists of a printed circuit board on which the components are mounted. These include:

1. Video controller OR Graphics processing unit (GPU)

1. Video BIOS
2. Video memory
3. RAMDAC
4. Output ports

The video controller is a microcontroller with its own RAM and ROM. The major activity of
this chip is to process the digital data stream from the main memory of the microprocessor and convert
it to the signal level which the monitor system accepts. This controller can directly read and write
system memory also. For modern cards, a dedicated processor is used as the GPU. This can effectively
process the floating point calculations they varies in speed from 250 MHz to 4 GHz also called as
graphics accelerator

The video BIOS or firmware contains the basic program, which governs the video card's
operations and provides the instructions that allow the computer and software to interact with the card.
It may contain information on the memory timing, operating speeds and voltages of the graphics
processor, RAM, and other information. During the boot process this program is initialized by the boot
loader routine and POST

All display cards contain a certain RAM chips as display memory Depends on the card
controller and features the capacity and type of chips will be varied Video memory is using for storing
the data from the motherboard before format conversion. Modern graphics cards contain 128 MB to 8
GB memory

Video Adapter Types

Depends on the mode of operation, the display systems can generate output as TEXT only mode and
GRAPHICS mode. In text only mode a monochrome display property is available and usually available
with DOS environment with command mode interface

Modes of operation

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1. Text mode

2. Graphics mode

The RAMDAC, or Random Access Memory Digital-to-Analog Converter, converts digital

signals to analog signals for use by a computer display that uses analog inputs such as CRT displays.
The RAMDAC is a kind of RAM chip that regulates the functioning of the graphics card.
Depending on the number of bits used and the RAMDAC-data-transfer rate, the converter will be
able to support different computer-display refresh rates. With CRT displays, it is best to work over
75 Hz and never under 60 Hz, in order to minimize flicker.

The most common connection systems between the video card and monitor are,

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1. Video Graphics Array (VGA) (DE-15)
2. Digital Visual Interface (DVI)
3. High-Definition Multimedia Interface (HDMI)
4. Composite video
5. Component video

Resolution Color depth (bits) Color support RAM required

640x480 4 16 256 K
640x480 8 256 512 K
640x480 16 65,536 1.0 Meg
640x480 24 16,777,216 1.0 Meg
800x600 4 16 256 K
800x600 8 256 512 K
800x600 16 65,536 1.0 Meg
800x600 24 16,777,216 1.5 Meg (2 Meg)
1024x768 4 16 512 K
1024x768 8 256 1.0 Meg
1024x768 16 65,536 1.5 Meg (2 Meg)
1024x768 24 16,777,216 2.5 Meg (4 Meg)
1280x1024 4 16 1.0 Meg
1280x1024 8 256 1.5 Meg (2 Meg)
1280x1024 16 65,536 2.5 Meg (4 Meg)
1280x1024 24 16,777,216 4.0 Meg
1600x1200 4 16 1.0 Meg
1600x1200 8 256 2.0 Meg
1600x1200 16 65,536 4.0 Meg
1600x1200 24 16,777,216 6.0 Meg
1.1.6 Compare the display adapters – MDA, CGA, HGA, EGA, VGA, SVGA on the basis of color,
mode, and RAM capability. RAM address,
Year Text Mode Graphics Mode Memory
(columns/lines) (resolution/colors)
MDA 1981 80×25 - 4 KB
CGA 1981 80×25 640×200 / 4 16 KB
HGC 1982 80×25 720×348 / 2 64 KB
PGA 1984 80×25 640×480 / 256 320 KB
EGA 1984 80×25 640×350 / 16 256 KB
8514 1987 80×25 1024×768 / 256 -
MCGA 1987 80×25 320×200 / 256 -
VGA 1987 80×25 640×480 / 16 256 KB
SVGA 1989 80×25 800×600 / 256 512 KB
(VBE 1.x) 640×480+ / 256+ 512 KB+
XGA 1990 80×25 1024×768 / 256 1 MB
XGA-2 1992 80×25 1024×768 / 65,536 2 MB
SVGA 1998 132×60 1280×1024 / 16.7M -
(VBE 3.0)

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Resolution
Resolution is the amount of detail a monitor can render. It is also termed as the ability of the
image reproducing system to represent the fine structure of an object. This quantity is expressed in the
number of horizontal and vertical picture elements, or pixels, contained in the screen. The greater the
number of pixels, the more detailed the images. The resolution required depends on the application.

Resolution Abbreviation Standard Designation

640x480 - VGA Video Graphics Array
800x600 - SVGA Super VGA
1,024x768 - XGA eXtended Graphics Array
1,280x1,024 - UVGA Ultra VGA

Dot pitch

Dot Pitch - also called Phosphor Pitch or Line Pitch - refers to the distance between the sub-
pixels (phosphor dots) or liquid crystal display cells of the same color inside a display screen. Expressed
in millimeters, technically, dot pitch is the sum of the size of a triad and the distance between the triads
(a triad is a cluster of three phosphor dots, colored Red, Green, and Blue inside a

Horizontal frequency

Horizontal scan rate, or horizontal frequency, usually expressed in kilohertz, is the frequency
at which a CRT moves the electron beam from the left side of the display to the right and back and
therefore describes the number of horizontal lines displayed per second

1.1.7 Draw the pin outs of various display adapters

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1.1.8
General operation

The typical VGA (Video Graphics Array) monitor is composed of three key sections: Video,
Time base, and Power. The Video Section receives the signal from the monitor cable and amplifies it
to a 50±60 VP-P grad running at 50 MHz to drive the electron gun. At the same time, it manages
Brightness Control ; Contrast Control ,AC gain control that sets the difference between white and black;
Blanking making sure the gun is turned off between each line drawn; and finally, DC Restoration the
feedback signal to ensure the black level remains consistent.

In the Time base Section, or deflection processor section, all activities in the monitor are
synchronized. These activities include Sync Recognition and Stripper where sync pulses can appear as
sync-on-green or separate H and V, Focus and Limiting. Also handled are Horizontal Deflection to
generate a high (1500V) voltage ramp to induce a magnetic field which aims the electron gun, and also,
Vertical Deflection similar in function to Horizontal Deflection but at a couple of hundred volts only.
The final section, Power Supply, must provide between 30W±100W of power and also supply a series
of voltages from 5V for the silicon, to 2 kV for the high voltage grid to accelerate the electrons in the
gun.

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1.1.9 Describe AGP

AGP bus. This is a high-speed 32-bit bus specifically for a video card. It runs at 66MHz (AGP
1x),133MHz (AGP 2x), 266MHz (AGP 4x), or 533MHz (AGP 8x), which allows for a bandwidth of
up to 2,133MB/second. It is connected to the North Bridge or Memory Controller Hub of the chipset
and is manifested as a single AGP slot in systems that support it.

The AGP was created by Intel as a new bus specifically designed for high-performance graphics
and video support. AGP is based on PCI, but it contains a number of additions and enhancements and
is, electrically, and logically independent of PCI.

The AGP connector is similar to PCI, although it has additional signals and is positioned
differently in the system. AGP is more of a point-to-point high-performance connection designed
specifically for a video card in a system because only one AGP slot is allowed for a single video card.

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The AGP specification 1.0 originally was released by Intel with pentium II design and defined a
66MHz clock rate with 1x or 2x signaling using 3.3 volts. AGP version 2.0 added 4x signaling as well
as a lower 1.5v operating capability

 AGP follows deeply pipelined memory read and write operations this hide access latency
 De-multiplexing of address and data on the bus helps 100 percent bus efficiency
 3.3v and 66MHz bus system allows 500MBps data transfer rate
 Modern AGP standard supports up to 2 GBPs or more data rate
 AGP is a dedicated bus slot for AGP cards only.

1.1.10 List the advantages of AGP

The Accelerated Graphics Port (also called Advanced Graphics Port, often shortened to
AGP) is a high-speed point-to-point channel for attaching a video card to a computer's motherboard,
primarily to assist in the acceleration of 3D computer graphics. Since 2004, AGP has been progressively
phased out in favor of PCI Express

The primary advantage of AGP over PCI is that it provides a dedicated interface , the point-to-
point connection allows for higher clock speeds, AGP uses sideband addressing, meaning that the
address and data buses are separated, an AGP card is capable of reading textures directly from
system RAM

Versions

AGP 1x
A 32-bit channel operating at 66 MHz resulting in a maximum data rate of 266 megabytes per
second (MB/s), doubled from the 133 MB/s transfer rate of PCI bus 33 MHz / 32-bit; 3.3 V
signaling.
AGP 2x
A 32-bit channel operating at 66 MHz double pumped to an effective 133 MHz resulting in a
maximum data rate of 533 MB/s; signaling voltages the same as AGP 1x;
AGP 4x
A 32-bit channel operating at 66 MHz quad pumped to an effective 266 MHz resulting in a
maximum data rate of 1066 MB/s (1 GB/s); 1.5 V signaling;
AGP 8x
A 32-bit channel operating at 66 MHz, strobing eight times per clock, delivering an effective
533 MHz resulting in a maximum data rate of 2133 MB/s (2 GB/s); 0.8 V signaling

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AGP vs. PCI

AGP PCI
Pipelined requests Non-pipelined
Address/data de-multiplexed Address/data multiplexed
Peak at 533MB/s in 32 bits Peak at 133MB in 32 bits
Single target, single master Multi-target, multi-master
Memory read/write only, no other I/O
Link to entire system
operations
High/low priority queues No priority queues

1.2.0 Understand I/ O Devices

1.2.1 Describe the matrix keyboard organization

A keyboard is a data entry electrical switch assembly similar to a traditional typewriter

keyboard. The keys include alphabets numbers and some special characters. Some control switches atr
also included as an ad-on feature. The total assembly usually includes an interface circuit which enables
it to communicate with the computer system digitally.

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1.2.2 Explain the method of encoding a keypress

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1.2.3 Discuss the keyboard controllers

1.2.4 Draw the typical keyboard connectors – 5 pin DIN, mini DIN (ps/2), USB

The Keyboard's Connector

The PC's AT Keyboard is connected to external equipment using four wires. These wires are
shown below for the 5 Pin DIN Male Plug & PS/2 Plug.

1. KBD Clock
1. KBD Clock
2. GND
2. KBD Data
3. KBD Data
3. N/C
4. N/C
4. GND
5. +5V (VCC)
5 Pin DIN 5. +5V (VCC) PS/2 6. N/C

A fifth wire can sometimes be found. This was once upon a time implemented as a Keyboard
Reset, but today is left disconnected on AT Keyboards. Both the KBD Clock and KBD Data
are Open Collector bi-directional I/O Lines. If desired, the Host can talk to the keyboard using
these lines.

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1.2.5 Describe the construction of mouse- optoelectronic mouse, optical mouse

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Working of Optical mouse

The main components of the optical mouse are:

 Inbuilt optical sensor

 High speed camera which can take 1000 pictures at a time
 LED

These optical mouse do have an inbuilt optical sensor. The optical sensor reads the movements
of the optical mouse (moved by the user) with the help of the light rays which comes out from the
bottom. ( The area in which a light glows). When the user moves the optical mouse, the LED (Light

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Emitting Diode) present inside the mouse emits the light according the minute movements. These
movements are send to the camera as light rays. The camera captures the difference in light rays as
images. When the camera captures the images, each and every pictures and compared to one another
with the digital technology. With the comparison, the speed of the mouse and the direction of the
movement of the mouse are rapidly calculated. According to the calculation, the pointer moves on the
screen

1.2.6 Interfacing of mouse – mouse connectors – serial, PS/2, Bus mouse, USB, wireless

1.2.7 Know the use of scanner

A scanner is a device that optically scans images, printed text, handwriting, or an object, and
converts it to a digital image.

1.2.8 Explain briefly the working of flat-bed and hand held scanners

The scanners are classified in to FOUR types depends on the size and operations.

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 Flatbed scanners, also called desktop scanners, are the most versatile and commonly used
scanners.
 Sheet-fed scanners are similar to flatbed scanners except the document is moved and the scan
head is immobile. A sheet-fed scanner looks a lot like a small portable printer.
 Handheld scanners use the same basic technology as a flatbed scanner, but rely on the user to
move them instead of a motorized belt. This type of scanner typically does not provide good
image quality. However, it can be useful for quickly capturing text.
 Drum scanners are used by the publishing industry to capture detailed images. They use a
technology called a photomultiplier tube (PMT). In PMT, the document to be scanned is
mounted on a glass cylinder. At the center of the cylinder is a sensor that splits light bounced
from the document into three beams. Each beam is sent through a color filter into a
photomultiplier tube where the light is changed into an electrical signal.

The basic principle of a scanner is to analyze an image and process it in some way. Parts of a typical
flatbed scanner include:

 Charge-coupled device (CCD) array

 Mirrors
 Scan head
 Glass plate
 Lamp
 Lens
 Cover
 Filters
 Stepper motor
 Stabilizer bar
 Belt
 Power supply
 Interface port(s)
 Control circuitry

CCD

The core component of the scanner is the CCD array. CCD is the most common technology for
image capture in scanners. CCD is a collection of tiny light-sensitive diodes, which convert photons
(light) into electrons (electrical charge).

The image of the scanned document reaches the CCD array through a series of mirrors,
filters and lenses. The exact configuration of these components will depend on the model of scanner,

The Scanning Process

Here are the steps that a scanner goes through when it scans a document:

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 The document is placed on the glass plate and the cover is closed. The inside of the cover in
most scanners is flat white, although a few are black. The cover provides a uniform background
that the scanner software can use as a reference point for determining the size of the document
being scanned. Most flatbed scanners allow the cover to be removed for scanning a bulky object,
such as a page in a thick book.

 A lamp is used to illuminate the document. The lamp in newer scanners is either a cold cathode
fluorescent lamp (CCFL) or a xenon lamp, while older scanners may have a standard
fluorescent lamp.

 The entire mechanism (mirrors, lens, filter and CCD array) make up the scan head. The scan
head is moved slowly across the document by a belt that is attached to a stepper motor. The
scan head is attached to a stabilizer bar to ensure that there is no deviation in the movement

 The image of the document is reflected by an angled mirror to another mirror. In some
scanners, there are only two mirrors while others use a three mirror approach. Each mirror is
slightly curved to focus the image it reflects onto a smaller surface.
 The last mirror reflects the image onto a lens. The lens focuses the image through a filter on
the CCD array.

Resolution and Interpolation

Scanners vary in resolution and sharpness. Most flatbed scanners have a true hardware
resolution of at least 800x600 dots per inch (dpi). The scanner's dpi is determined by the number of
sensors in a single row (x-direction sampling rate) of the CCD array by the precision of the stepper
motor (y-direction sampling rate).

Another term used when talking about scanners color depth. This simply refers to the
number of colors that the scanner is capable of reproducing. Each pixel requires 24 bits to create
standard true color.. Many of them offer bit depths of 30 or 36 bits.

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Image Transfer

Scanning the document is only one part of the process. For the scanned image to be useful, it
must be transferred to a computer. There are three common connections used by scanners:

 Parallel - Connecting through the parallel port is the slowest transfer method available.
 Small Computer System Interface (SCSI) - SCSI requires a special SCSI connection. Most
SCSI scanners include a dedicated SCSI card to insert into the computer and connect the scanner
 Universal Serial Bus (USB) - USB scanners combine good speed, ease of use and affordability
in a single package.
 FireWire - Usually found on higher-end scanners,FireWire connections are faster than USB
and SCSI. FireWire is ideal for scanning high-resolution images.

On the computer, there need software, called a driver, that knows how to communicate with
the scanner. Most scanners speak a common language, TWAIN. The TWAIN driver acts as an
interpreter between any application that supports the TWAIN standard and the scanner. This means
that the application does not need to know the specific details of the scanner in order to access it directly.
For example, it is possible to acquire an image from the scanner from within Adobe Photoshop because
Photoshop supports the TWAIN standard.

In addition to the driver, most scanners come with other software. Typically, a scanning utility
and some type of image editing application are included. A lot of scanners include OCR software. OCR
allows the user to scan in words from a document and convert them into computer-based text. It uses
an averaging process to determine what the shape

1.2.9 Discuss other input devices – digital camera

Digital Camera Basics

CCD and CMOS: Filmless Cameras

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Instead of film, a digital camera has a sensor that converts light into electrical charges.

The image sensor employed by most digital cameras is a charge coupled device (CCD). Some
cameras use complementary metal oxide semiconductor (CMOS) technology instead. Both CCD and
CMOS image sensors convert light into electrons. Once the sensor converts the light into electrons, it
reads the value (accumulated charge) of each cell in the image.

A CCD transports the charge across the chip and reads it at one corner of the array. An analog-
to-digital converter (ADC) then turns each pixel's value into a digital value by measuring the amount
of charge at each photosite and converting that measurement to binary form.

 CMOS devices use several transistors at each pixel to amplify and move the charge using more
traditional wires.

Differences between the two types of sensors:

 CCD sensors create high-quality, low-noise images. CMOS sensors are generally more
susceptible to noise.
 Because each pixel on a CMOS sensor has several transistors located next to it, the light
sensitivity of a CMOS chip is lower. Many of the photons hit the transistors instead of the
photodiode.
 CMOS sensors traditionally consume little power. CCDs, on the other hand, use a process that
consumes lots of power. CCDs consume as much as 100 times more power than an equivalent
CMOS sensor.
 CCD sensors have been mass produced for a longer period of time, so they are more mature.
They tend to have higher quality pixels, and more of them.

Digital Camera Resolution

The amount of detail that the camera can capture is called the resolution, and it is measured in
pixels. The more pixels a camera has, the more detail it can capture and the larger pictures can be
without becoming blurry or "grainy."

Some typical resolutions include:

 256x256 - Found on very cheap cameras, this resolution is so low that the picture quality is
almost always unacceptable. This is 65,000 total pixels.
 640x480 - This is the low end on most "real" cameras. This resolution is ideal for e-mailing
pictures or posting pictures on a Web site.
 1216x912 - This is a "megapixel" image size -- 1,109,000 total pixels -- good for printing
pictures.
 1600x1200 - With almost 2 million total pixels, this is "high resolution." You can print a 4x5
inch print taken at this resolution with the same quality that you would get from a photo lab.
 2240x1680 - Found on 4 megapixel cameras -- the current standard -- this allows even larger
printed photos, with good quality for prints up to 16x20 inches.
 4064x2704 - A top-of-the-line digital camera with 11.1 megapixels takes pictures at this
resolution. At this setting, you can create 13.5x9 inch prints with no loss of picture quality.

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1.2.10 Discuss the different classification of printers

A printer is the computer component that lets you create copies of information stored in the
computer on paper. The printed material is often called hard copy, to differentiate it from the data stored
on a disk, or held in the computer’s memory.

A basic classification of printers is the division into impact printers and non-impact printers.
The impact printer prints by mechanical impacts on the paper using needles or type wheels similar to
conventional type writers. For example, the dot–matrix printer creates text and images on the page by
hammering several small pins against the paper with an inked ribbon between the pins and the paper.
By pressing the inked ribbon against the paper, each pin leaves a dot on the paper. The more pins used,
the higher the resolution of the printed image – 9–pin and 24–pin was common options. Dot–matrix
printers are practically out of use because of development in inkjet and laser printing technology.
Nowadays these two methods are being low priced.

Inkjet printers do not use any mechanical impact and that’s why they are example of non-
impact printers. The non–impact printer prints without any mechanical impact. Laser printer uses
electrostatic forces to apply black or colored toner particles on the paper. Thermo printers are non–
impact printers, too. Non–impact printer is far more quite at work than impact printers.

Printer classification based on their technology. Typical printer types are:

1. Dot matrix printer

2. Ink-jet printer
3. Laser printer
4. Thermal printer

Dot Matrix Printer

Dot Matrix printers are impact printers that use a matrix or small pins to create precise dots.
They operate by using electromagnetic and small wires to press an ink ribbon onto the page to form a
series of dots to make up characters. dot matrix printers were most commonly used for home and
offices. This type of printers can print out on multi part carbon forms, it has low initial and running
cost but the print quality is low and it is noisy when printing.

Thermal Printers:
Thermal printers use a thermal ribbon which is soaked with a wax type ink which is melted
and then transferred to the paper. In some thermal printers a thermo sensitive paper is necessary. In
this case the paper passes over a thermal head and the carbon coating turns black in the heated areas.
Thermal printers have low noise, low cost while they are also compact. They are also known for their
low printing speed and high running cost.

Ink Jet Printers

Ink jet printers spray a very small amount of ink onto the media. This is done by using a
piezoelectric element. When voltage are applied to the element, in bends and creates a pressure wave
to force out a drop of ink. Ink jet printers have low cast, compact size, low noise. Their color printing
quality is affordable. Some ink jet printers may require special paper. Usually speed of ink jet printers
is slower than laser printers.

LaserPrinters:
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Laser printing is the most advance technology. In Laser printing, a computer sends data to the
printer. Printer translates this data into printable image data. This kind of printers uses xerographic
principle. A laser beam discharges photo sensitive drum. A Latent Image is created on drum, during
development process toner is attracted to the drum surface and then transferred to the paper.
Laser printing quality is high. These printers have low noise, high speed while they are more expensive
than ink jet or dot matrix printer and they are generally large in size.

1.2.12 Describe the different types of printers – Dot matrix, inkjet, laser printers

Inkjet printer

Inkjet printers use black or colored inks which are placed on the paper in fine droplets. The ink
is stored in an ink cartridge. The printer head is located the bottom side of the ink cartridge. The printer
head consists of many fine jets arranged in a matrix. Ink is fed from the cartridge reservoir through fine
channels to each jet. Just before the opening of each jet is a device which forces the ink
out of the jet opening and so squirts a drop of ink onto the paper.
Where the printer head works on the inkjet principle, a piezoelectric crystal is located just
before the jet opening around the ink channel. This Piezo–electrical crystal can be caused to produce a
single vibration by subjecting it to an electrical pulse. If the vibration causes the crystal to contract, the
crystal squeezes the channel together enough to force ink through the jet opening and a drop of ink is
squirted onto the paper.

Laser printers
Laser and LED printers use black or colored toner. Toner is fine ink dust which is applied to
the paper by electrostatic attraction and then fixed onto the paper by heat and pressure. The first step
involves transferring the digital image information onto a photoelectric drum (known as a
photoconductive drum) using a laser or a row of LEDs (Light Emitting Diodes). In the case of a Laser
printer, a laser beam is controlled by the data received by the printer. This laser beam is directed onto
the photoconductive drum via mirrors and lenses. As the drum turns, the laser strikes points in a line
at right angles across the surface of the drum.
The toner is negatively-charged and, due to the electrostatic force of attraction, adheres to all
the points on the drum surface where the laser beam has generated a positive charge. The next step
involves transferring the toner from the drum to the paper. The paper is given a positive charge by an
electrical field before it is fed past the drum. The positive charge on the paper is greater than
the positive charge at the points on the drum to which toner is adhering. When the drum carrying the
toner is rolled over the paper, the paper, which has the greater charge, exerts a stronger force of
attraction on the toner than the drum does.
The toner is released rom the drum and adheres to the paper. The drum is then cleaned of
residual toner and the original negative electrical charge is restored. Once the toner has been transferred
to the paper by electrostatic attraction, the toner must be fixed on the paper. This is achieved by pressure
and heat, for example. The heat melts the wax in the toner and the two rollers press the resin/toner
mixture onto the paper. The toner is bonded to the paper by the resin and pressure. The exposure of the
drum by Laser or LEDs, the transfer of toner onto the drum and finally the transfer of the toner from
the drum onto the paper form a single process in which ink can be transferred to the paper. A
monochrome printer performs this process once with black toner. A full color printer performs this
process four times with toner in one of the ink colors (yellow, magenta, cyan or black) being applied
to the paper at each pass.

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Thermal printers

Thermal printers use heat and special printer paper or transfer film to bring color on a copy.
Special printer paper is used for the thermal printers . This paper is already impregnated with the inks.
The external application of heat causes the ink emulsions in the various layers to reveal their color. The
resolution that can be achieved using the this method is determined by the design of the heating element.
Standard auto chrome printers for the private sector can achieve a resolution of just above 300 dpi and
use A6 format paper. With thermal transfer methods, the ink is transferred from a carrier film onto
the paper. The carrier film is coated in consecutive sections with yellow, magenta and cyan wax. The
paper is conveyed past one section of the carrier film at a time in three consecutive passes. A thermo
printer head is positioned at right angles across the back of the carrier film. Individual heating elements
melt the colored wax and thus transfer the ink from the carrier film onto the paper in the form of screen
dots. Thermo transfer printers achieve a resolution of 600 dpi for color printing. The thermo sublimation
process basically works in the same way as the thermo transfer process. There is colored ink on the
carrier foil instead of coloured wax. The coloured ink is heated so strongly by the heating elements that
the ink evaporates into the paper. Thermosublimation printers reach a resolution of up to 600 dpi and,
depending on their design, can print up to A3 sheet size.

1.2.11 Distinguish between impact and non-impact printer

Impact vs. Non-impact

There are several major printer technologies available. These technologies can be broken down into
two main categories with several types in each:
 Impact - These printers have a mechanism that touches the paper in order to create an image.
There are two main impact technologies:
 Dot matrix printers use a series of small pins to strike a ribbon coated with ink, causing the
ink to transfer to the paper at the point of impact.
 Character printers are basically computerized typewriters. They have a ball or series of bars
with actual characters (letters and numbers) embossed on the surface. The appropriate
character is struck against the ink ribbon, transferring the character's image to the paper.
Character printers are fast and sharp for basic text, but very limited for other use.
 Non-impact - These printers do not touch the paper when creating an image. Inkjet printers
are part of this group, which includes:
 Inkjet printers, which are described in this article, use a series of nozzles to spray drops of ink
directly on the paper.
 Laser printers, covered in-depth in How Laser Printers Work, use dry ink (toner), static
electricity, and heat to place and bond the ink onto the paper.
 Thermal printers have the color in the paper instead of in the printer. There are three layers
(cyan, magenta and yellow) in the paper, and each layer is activated by the application of a
specific amount of heat. The print head has a heating element that can vary in temperature.
The print head passes over the paper three times, providing the appropriate temperature for
each color layer as needed.

1.2.13 Explain the working of a dot-matrix printer

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Dot matrix printers are also known also as impact printers. Dot matrix printers are divided
on two main groups:

1. Serial Dot matrix Printer

2. line printers (or line dot matrix printer)
Line printers

Line printers as well as serial dot matrix printers use pins to strike against the inked ribbon,
making dots on the paper and forming the desired characters. The differences are that line printers use
hammer bank (or print-shuttle) instead of print head, this print-shuttle has hammers instead of print
wires, and these hammers are arranged in a horizontal row instead in vertical column.

The printing mechanism works as follow. The permanent magnetic field holds the hammer
spring in stressed, ready to strike position. The driver sends electrical current to hammer coil, which
then creates electromagnetic field opposite to the permanent magnetic field. When both fields equalize,
the energy stored in the spring is released to strike the hammer against the ribbon and prints a dot on
the paper. The hammer printhing mechanism is shown in action at the picture bellow.

The line printer mechanism

During printing process the print-shuttle vibrates in horizontal direction with high speed while
the print hammers are fired selectively. So each hammer may print a series of dots in horizontal
direction for one pass of the shuttle, then paper advances at one step and the shuttle prints the
following row of dots

The line printing process

Line matrix printers are the right solutions for high-volume impact printing and are superior in
speed, reliability and quality. As price-performance leaders, line printers cost less to service and less to
use. The fastest line matrix printers available on the market offers a claimed print speed between 1800
and 2000 lines per minute (lpm).

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Line dot matrix printer Features: Specifications

Print Technology: Line impact dot matrix

Print Speed
500 - 2000 lpm (draft)
LPM (lines per minute)

Graphics Resolution 60 - 240 DPI

Copies (Original +) 5-9

Serial dot matrix printers

In serial dot matrix printers the characters are formed by the print head . a print head has a
number of print wires (pins) arranged in vertical columns and electro-magnetic mechanism able to
shoot these wires.
There are two main printhead technologies - in the first one electromagnetic field shoots the print head's
wire. In the second one, the so called permanent magnet printheads, a spring shoots the printhead wire
and the magnetic field just holds the spring in stressed and ready to shoot position. When the
electromagnetic field equalizes the magnetic field, the spring is released to shoot the wire.

Classical print head mechanism The permanent magnet printer head mechanism

As the printer head moves in horizontal direction, the print head controller sends electrical
signals which forces the appropriate wires to strike against the inked ribbon, making dots on the paper
and forming the desired characters. The most commonly used printer heads has 9 print wires in one
column (9-pin print heads) or 24 print wires in two columns (24-pin print heads), for better print
quality. In some heavy-duty dot matrix printers there are also used 18 wire print heads (18-pin
printheads) which have 2 columns, 9 wires in each. The distance between wires in column may give
us the vertical printing resolution. That is dots/inch (dots per inch DPI)

1.2.14 Explain the working of an inkjet printers

Parts of a typical inkjet printer include:

 Print head assembly

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 Print head - The core of an inkjet printer, the print head contains a series of nozzles
that are used to spray drops of ink.

 Ink cartridges - Depending on the manufacturer and model of the printer, ink cartridges
come in various combinations, such as separate black and color cartridges, color and
black in a single cartridge or even a cartridge for each ink color. The cartridges of some
inkjet printers include the print head itself.
 Print head stepper motor - A stepper motor moves the print head assembly (print head
and ink cartridges) back and forth across the paper. Some printers have another stepper
motor to park the print head assembly when the printer is not in use. Parking means that
the print head assembly is restricted from accidentally moving, like a parking brake on
a car.

 Belt - A belt is used to attach the print head assembly to the stepper motor.
 Stabilizer bar - The print head assembly uses a stabilizer bar to ensure that movement
is precise and controlled.

 Paper feed assembly

 Paper tray/feeder - Most inkjet printers have a tray that you load the paper into. Some
printers dispense with the standard tray for a feeder instead. The feeder typically snaps
open at an angle on the back of the printer, allowing you to place paper in it. Feeders
generally do not hold as much paper as a traditional paper tray.
 Rollers - A set of rollers pull the paper in from the tray or feeder and advance the paper
when the print head assembly is ready for another pass.

 Paper feed stepper motor - This stepper motor powers the rollers to move the paper in
the exact increment needed to ensure a continuous image is printed.
 Power supply - While earlier printers often had an external transformer, most printers sold
today use a standard power supply that is incorporated into the printer itself.
 Control circuitry - A small but sophisticated amount of circuitry is built into the printer to
control all the mechanical aspects of operation, as well as decode the information sent to the
printer from the computer.

 Interface port(s) - The parallel port is still used by many printers, but most newer printers use
the USB port. A few printers connect using a serial port or small computer system interface
(SCSI) port.

Inkjet printer drop-on-demand technology with piezoelectric actuator

Bubble jet printer drop-on-demand technology

Canon developed the bubble jet printer technology, a drop-on-demand inkjet printing method
where ink drops were ejected from the nozzle by the fast growth of an ink vapor bubble on the top
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surface of a small heater. Shortly thereafter, Hewlett-Packard independently developed a similar inkjet
printing technology and named it thermal inkjet.

The most popular inkjet and bubble-jet printers use serial printing process. Similarly to dot
matrix printers, serial inkjet printers use print heads with a number of nozzles arranged in vertical
columns. The printing process is the same as in dot matrix printers.

The greatest advantages of inkjet printers are, quiet operation, capability to produce color
images even with photographic quality and the low printer prices. The down side is that although inkjet
printers are generally cheaper to buy than lasers, they are far more expensive to maintain. When it
comes to comparing the cost per page, ink jet printers work out many times more expensive than laser
printers.

Printer Features: Specifications

Print Technology: Inkjet or Bubble-jet

Print Speed
1 - 20 PPM
PPM (pages per minute)

Graphics Resolution 300 - 1200 DPI

Copies (Original +) 0

Workload (Duty cycle)

6,000 - 60,000 PPM
PPM (Pages per month)

1.2.15 Explain the working of a laser printer

The Major parts of a laser printer include,

1. Photoreceptor Drum ( Optical photo conductive drum or OPC)

2. Developer roller
3. Toner cartride
4. Laser scanning unit
5. Rotating mirror ( scanning mechanism)
6. Corona wire
7. Discharge lamp
8. Fuser
9. Paper feed mechaism

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The primary principle at work in a laser printer is static electricity The core component of this
system is the photoreceptor, typically a revolving drum or cylinder. This drum assembly is made out
of highly photoconductive material that is discharged by light photons.

Initially, the drum is given a total positive charge by the charge corona wire, a wire with an
electrical current running through it. the drum revolves, the printer shines a tiny laser beam across the
surface to discharge certain points. In this way, the laser "draws" the letters and images to be printed as
a pattern of electrical charges -- an electrostatic image.

After the pattern is set, the printer coats the drum with positively charged toner -- a fine, black
powder. Since it has a positive charge, the toner clings to the negative discharged areas of the drum,
but not to the positively charged "background."

With the powder pattern affixed, the drum rolls over a sheet of paper, which is moving along a
belt below. Before the paper rolls under the drum, it is given a negative charge by the transfer corona
wire (charged roller). This charge is stronger than the negative charge of the electrostatic image, so the
paper can pull the toner powder away. Since it is moving at the same speed as the drum, the paper picks
up the image pattern exactly.

Finally, the printer passes the paper through the fuser, a pair of heated rollers. As the paper
passes through these rollers, the loose toner powder melts, fusing with the fibers in the paper. The fuser
rolls the paper to the output tray, and finished page. The fuser also heats up the paper itself, which is
why pages are always hot when they come out of a laser printer or photocopier.

After depositing toner on the paper, the drum surface passes the discharge lamp. This bright
light exposes the entire photoreceptor surface, erasing the electrical image. The drum surface then
passes the charge corona wire, which reapplies the positive charge

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The traditional laser scanning assembly includes:

 A laser
 A movable mirror
 A lens

The laser receives the page data -- the tiny dots that make up the text and images -- one horizontal
line at a time. As the beam moves across the drum, the laser emits a pulse of light for every dot to be
printed, and no pulse for every dot of empty space.

Laser printer scanning assembly:

Laser printers rely on a laser beam and scanner assembly to form a latent image on the photo-
conductor bit by bit. The scanning process is similar to electron beam scanning used in CRT. The
laser beam modulated by electrical signals from the printer's controller is directed through a collimator
lens onto a rotating polygon mirror (scanner), which reflects the laser beam. Then reflected from the
scanner laser beam pass through a scanning lens
system, which makes a number of corrections to it and scans on the photoconductor.

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This technology is the major key for ensuring high precision in laser spot at the focal plane, accurate
dot generation at a uniform pitch and therefore better printer's resolution.

1.2.16 Describe the Centronics Interface, USB interface

Centronics Pinout, Connector Interface – 36 pin connector

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Centronics parallel interface

The Centronics parallel interface is an older and still widely-used standard I/O interface for
connecting printer s and certain other devices to computers. The interface typically includes a cable
and a 36- pin male and female connector at the printer or other device. The cable plugs into a 25-pin
parallel port on the computer. Data flows in one direction only, from the computer to the printer or
other device. In addition to eight parallel data lines, other lines are used to read status information and
send control signals. Centronics Corporation designed the original Centronics parallel interface for dot
matrix printers. In 1981, IBM used this interface as an alternative to the slower one-bit-at-a-time serial
interface.

USB (Universal Serial Bus)

Is a plug-and-play interface between a computer and add-on devices, such as media players,
keyboards, telephones, digital cameras, scanners, flash drives, joysticks and printers. USB supports
hot-swapping, which means that a new device can be added to your computer without having to add an
adapter card or even having to turn the computer off. The USB peripheral bus standard was developed
by Compaq, IBM, DEC, Intel, Microsoft, NEC, and Northern Telecom. The technology is available
without charge for all computer and device vendors. Since 1996, Windows operating systems have
been equipped with USB drivers or special software designed to work with specific input/output (I/O)
device types. Most new computers and peripheral devices are equipped with USB.

USB 3.0-

USB 3.0 is the next major revision of the ubiquitous Universal Serial Bus, created in 1996 by a
consortium of companies led by Intel to dramatically simplify the connection between host computer
and peripheral devices. Fast forwarding to 2009, USB 2.0 has been firmly entrenched as the de-facto
interface standard in the PC world for years (with about 6 billion devices sold), and yet still the need
for more speed by ever faster computing hardware and ever greater bandwidth demands again drive us
to where a couple of hundred megabits per second is just not fast enough.

USB 3.0 (Super-Speed USB) increases the data rate to 4.8 Gbit/s, 600 MB/s. USB 3.0 ports and cabling
will be designed to enable backward compatibility as well as future-proofing for optical capabilities
(USB 3.0 adds fiber). USB 3.0 connectors contain legacy pins to interface to USB 2.0 devices, and a
new set of pins for USB 3.0 connectivity (both sets reside in the same connector).

USB Pinout, Cable Assembly

Pin Signal Name Description
1 VBUS Red
2 D- White
3 D+ Green
4 GND Black
Shell Shield Drain

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