CONSUMER ELECTRONICS

FACSIMILE (FAX)
Introduction
 In addition to basic signals consisting of speech, music, or telegraph
codes, a telecommunication system is often required to transmit signals
of a visual nature.
 Facsimile means an exact reproduction, and in facsimile transmission an
exact reproduction of a document or picture is provided at the receiving
end.
 Television means visually at a distance and a television system is used
to reproduce any scene at the receiving end.
 It differs from facsimile in that the scene may be live (i.e. include Fig. 4.1 Personal facsimile machine
movement).
 Information is transmitted at a much faster rate in television  The design of facsimile machines has been strongly influenced by the
transmission than it is in facsimile transmission. use of the PSTN (public switched telephone network).
 As a result, television transmission requires a much larger bandwidth,  Firstly, the network was designed for speech, not data. Therefore the
and special wideband circuits are required. power/frequency/time characteristics of the transmitted facsimile signal
 The small bandwidth required for facsimile makes it suitable for must be chosen to suit the network.
transmission over normal telephone lines.  Secondly, transmission time is expensive, so effective data compression
and channel modulation methods must be used.
FACSIMILE MACHINE  Thirdly, since the public network is switched, every facsimile machine
 An input scanner can be used to transmit images over a can in principle be connected to every other.
telecommunications link to a remote printer. This principle has been in  Rigorous development and application of international standards is
use commercially for news photograph transmission since 1930s. therefore necessary to ensure that this potential for interconnection is
 Combined send/receive machines suitable for office use became widely not wasted.
available in 1960s, and between 1980 and 1987 the number of machines  Fig. 4.2 shows the block diagram of a typical facsimile machine.
connected to the world-wide telephone network grew from a quarter of  When data is read from an input document it is first compressed and
a million to two million. then modulated on to an audio-frequency carrier prior to
 Facsimile provides very fast transmission of almost any documentary being coupled to the line. The receive path is the reverse of this.
material without specialist preparation. BASIC FAX MACHINE OPERATIONS
 However, between 2 million and 10 million bits are required for a raster  Essentially, a fax machine scans original documents, converts the
scan of an A4 page; this has to be compared with 20000 bits for a scanned images into electrical signals, and transmits them over
similar-sized page of ASCII-coded characters. telephone lines to a receiving fax machine shown in fig 4.3.
 This added transmission burden is somewhat alleviated by the ability to  The receiving fax machine in turn converts the received signals back
tolerate very high error rates. into the graphical images of the original document and prints them.
 The basic Group 3 fax machine operations for transmitting a page are
presented in Fig. 4.4.

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Fig. 4.4 Basic fax machine operations

 The handshake process:

Fig. 4.2 Block diagram of a typical facsimile machine o The sending and receiving fax-modems set up the transmission
protocols, transmission speed, and other settings between them
in a handshake process.
o If one modem cannot transmit at the highest speed of the other,
both modems agree to fallback to the next highest speed at
which both modems can transmit on the line.
 At the transmitting ends:
Scanning:
 The images on the page are scanned and transformed into analog
signals to begin the transmission process.
 Either a charge-coupled device or contact image sensor scanner
scans the page being sent.
 A photo sensor array of 1728 tiny sensors for A4 paper size (or 2048
for B4) targets very small picture elements (pixels) on a line of
page, one sensor per pixel, resulting in 1728 (or 2048) bits per line.
 The array determines whether each pixel is black or white and
accordingly generates a strong or weak electronic signal for that
Fig. 4.3 A fax machine is basically a scanner-copier machine that sends pixel.
and receives graphic images over telephone lines.  A page is scanned line-by-line with all the pixels in a thin strip from
0.13 to 0.25 mm high across the top of the page, or between 10 and
12 scan lines per line of text.

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 Successive strips are scanned until the whole page is converted into Modulation:
a series of electrical pulses.  The compressed digital signals are modulated by the modem into
 The amplitude of each pulse represents the brightness of the analog signals (a tone series) that can be sent over regular telephone
corresponding pixel. lines.
 This scanning operation takes between five and ten seconds per  Group 3 fax machines are half duplex and can either send or receive
page. at any time.
A/D Conversion: Transmission:
 The scanner signals are converted from analog to digital with  The analog signals are then transmitted over the phone lines from
typically from one to six bits per pixel. the sending modem to the receiving modem.
 After image processing is complete, one bit per pixel is produced. At the receiving end:
Video Processing: Demodulation:
 The processing of the scanner data can be done on the analog  A modem demodulates or decodes the received analog tone
scanner signal, the digital data, or both. signals regenerating the digital signals (bit streams) sent.
 It accommodates for the shading, distortions, and other aspects of Decompression:
the original image so that reproduction can be as accurate as  The next step is to expand the digital signals and reconstruct the
possible. page's images into black-and-white pixels which represent the
 Shading compensation checks for non uniformity in the scanner pixel's of the page's image.
optical system and corrects distortions due to both, light sources as Thermal printing:
well as nonuniformity in the scanner element.  The thermal printer converts the expanded bit stream into a copy of
Thresholding: the original page.
 The conversion of the scanner output from grey level to a black-and-  The printer's wires are spaced 203 to the inch, touching the
white level must also be performed. temperature-sensitive recording paper.
 It may include dithering (or half-toning), a method of generating  For black marking, the wires heat up when high current passes
pseudogrey scales. through them.
 Other video processing techniques include automatic background  The wires go from non-marking (white) to marking (black)
correction, automatic contrast control, edge enhancement and MTF temperature, and back again in a few milliseconds.
(modulation transfer function) correction. Resolution:
 These can be performed in one or two dimensions. Images may also  Standard resolution is 203 lines per inch across and 98 lines per inch
be reduced or enlarged. down the page.
Compressing the digital signals:  Fine resolution requires twice the number of lines (196 lines per
 The data compression operation can reduce the picture information inch) down the page.
by a factor of from 5 to 20, depending on the characteristics of the  Most group 3 fax machines include a high resolution option.
image.
 This operation generates code words containing the pixel
information in compressed digital signals.

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GROUP 3 FAX MACHINES
 Group 3 fax machines now comprise the overwhelming majority of fax
machines in operation worldwide.
 Group 3 refers to the digital standard that ensures compatibility among
fax machines.
 The Group 1 (1968) analog standard covered four and six minutes per
page fax machines, while the Group 2 (1976) analog standard covered
two and three minutes per page machines.
 The Group 3 digital standard was first adopted in 1980. It calls for the
ability to send an 8.5 × 11 inch page in approximately 30 seconds over a
voice grade telephone line.
 Group 3 fax machines actually do better. They can send an average page
of text in 10 to 30 seconds with about 15 seconds for the initial first
page handshake.
 The time per page really depends on how many black markings (text
and graphics images) are present, on their level of detail and on
the compression scheme used.
 Due to advancing technology the Group 3 standard has been revised Fig. 4.5 The Panasonic KX-580 BX facsimile system
several times since 1980.
 Most notable advances in VLSI chip technology and DSP have resulted XEROGRAPHIC COPIER
in increased data rates that significantly reduce transmission time. Introduction
 Group 4 fax machines, which transmit at 64,000 bps, will be suited to  The creation of an electrostatic image, which allows development by
computer controlled network communications. charged, pigmented particles, forms the basis of the xerographic
 First adopted in 1984, Group 4 fax machines are designed for process.
transmission over ISDN.  These particles can then be transferred to plain paper and subsequently
 While Group 3 machines excel at stand-alone, person-to-person fixed to provide permanent copy.
communications, Group 4 fax machines will be suited to computer-
controlled network communications. Xerographic process
 However the installed base of Group 4 machines today is very small  The basic steps in the xerographic process are depicted in fig. 1
compared to Group 3 machines and they are comparatively expensive.  Charging or sensitization of the photoconductor to a uniform surface
potential of 800 – 1000V is usually accomplished by corotron.
 It is a thin wire, stretched between terminals parallel to the
photoconductor surface, and driven at approximately 8000 V, the
corotron emits a corona of ions which deposit on the photoconductor
surface

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 The charged photoconductor must be kept in the dark to prevent
discharge.
 Exposure of the sensitized photoconductor to light reflected from the
original to be copied generates the required electrostatic image.
 Voltage decay occurs via photon absorption by the photoconductor
surface with the creation of an electron-hole pair.
 The hole, transported through the photoconductor neutralizes the
corresponding image charge at the photoconductor-substrate interface.
 To ensure selective development of the image, the black toner particles
are charged to a polarity opposite to that of the photoconductor surface.
 Toner consists of finely dispersed carbon black in a thermoplastic
polymer matrix.
 The toner particles are small to ensure that reasonable image, edge
definition and resolution performance are obtained.
 Transfer of the developed image from the photoconductor surface to
plain paper is affected by a corotron.
 Similar in design and process to the charge corotron, positive charger is
sprayed onto the back of the paper, which itself is in contact with the
developed photoconductor surface.
 Sufficient fields are generated to ensure that most, but not all, of the
toner will transfer to the paper
 Fusing the image into the surface of the paper is accomplished by heat
from a radiant fuser, or a combination of heat and pressure from a fuser
roll/backup roll combination.
 It is this step that will dictate the rheological requirements of the
thermoplastic resins used in toner manufacture.
 The process outlined above allows us to visualize the xerographic steps
required to produce a copy via a plate photoconductor in the static
mode.
Extension to a Dynamic Copier
 Dynamic operation of a copier places many constraints of space and
geometry on the elements of process design.
 A schematic representation of a copier is given in fig 4.7.
 Charging remains as discussed earlier with the rotation of the
photoreceptor now providing the linear motion underneath the corotron.
 Exposure represents more of a challenge. Fig 4.6 Basic steps of xerography

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 Fusing the toner image onto the paper is one of the major contributors to
power consumption within the copier and this led to the abandonment of
early, inefficient radiant oven furnace.
 Centrally heated polymer-coated steel or aluminium rolls now effect
fusing by a combination of heat and pressure.
 Release agent fluids are often used on these rollers to prevent toner
offsetting from the paper to the polymeric surface.

CALCULATORS
Introduction
 In a calculator there is battery, the tiny readout displays, a few wires
from the keyboard, and a printed circuit board with an IC attached.
 That singe IC is most of the digital system and contains an LSI chip that
performs the task of thousands of logic gates.
 The single IC performs the storage, processing and control functions of
the calculating system.
 The keyboard is the input and the displays are the output of the
calculator system.
Fig 4.7 Xerographic copier schematic STRUCURE OF A CALCULATOR
 With stationary platen copiers, the original document is scanned and  A calculator is really a special purpose computer containing a number
reflected light is transmitted via lens, mirrors and exposure slit to the of fixed program routines which may be initiated by entering such
photoreceptor. commands as +, –, ×, ÷. Numerical data are entered for the programs to
 Development of the electrostatic image has been extensively studied operate on.
following the trend towards, faster smaller copiers.  The structure is illustrated in Fig. 4.8
 Initial copier designs utilized a cascade development system which  Input Devices:
poured developer over the rotating photoreceptor. o The most common, input device to a calculator is keyboard.
 Cascading developer over the photoreceptor in the against mode o This is merely a group of key switches, each representing a digit
brought some relief for further speed enhancement but the resultant or an operation, which will be understood by the calculator when
development system remained bulky. a key is depressed.
 The trend toward magnetic brush development systems commenced o Each key, when depressed, causes a binary code to be generated
approximately 20 years ago. and passed to the processing section of the calculator.
 The latter, resulting mainly from the fibrous nature of the brush and o There is a unique code for each key so that the processor can
density of developer at the time of photoreceptor contact, has led to decode it and know how to handle the information.
almost all modern copiers using this form of development. o A more complex calculator may have other input devices such as
 A more recent development of this concept is the single-component magnetic or punched cards or tapes.
magnetic brush copiers used by the Japanese manufacturers.

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Fig. 4.9 Block diagram showing register structure of a calculator

o Figure 4.9 shows the basic register arrangement used in most of

our function calculators.
Fig. 4.8 Basic calculator structure
o The most important register is called the keyboard or display
 Data Storage :
register. It is also referred to as the accumulator register.
o When data is entered into the calculator it must be stored so that
o When you enter data via the keyboard the numbers are stored in
it can later be operated upon by the processor or arithmetic unit.
this register and the display is connected to this register so you
There are various ways in which the store may be arranged.
will see the numbers as they are entered.
o Basically, the arrangement may be such that groups of digits
o When you depress a function key and then begin entering the
may be conveniently accessed by the other processing units,
next number to be used in the calculation the first number is
each group representing either numbers to be operated upon or
transferred out of the accumulator into another register which we
the results of an operation.
can call the arithmetic register.
o The data storage area is generally made up of register stages.
o After the second number is entered the equals key is usually
 A register is a memory circuit used for remembering multi digit
depressed to initiate the computation, and the numbers stored in
numbers.
these two registers are then sent to the arithmetic unit which is
o Mostly four-function calculators have atleast three operating
an adder/subtractor.
registers that are used in entering the numbers to be used,
o The sum or difference, answer is stored back in the accumulator,
displaying them and carrying out the arithmetic operations.
and is displayed.
More sophisticated scientific calculators have more registers.

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o The number stored there previous to the calculation is lost; the  Output Devices :
number in the arithmetic register is retained but we usually o The most common output devices used with calculators are
cannot get to it. Only these two registers are used in addition and printers or luminous displays.
subtraction. o A printer has the obvious advantage of giving a permanent
o The third register is used when multiplication and division record of the data, this being typically a strip of paper containing
operations are performed. ten to fifteen digits per line of print.
o These functions are performed by successive additions and o Luminous displays, Fig. 4.8 , have the advantages of lower
subtractions. power consumption, so important for small calculators and fast
o Since the product or quotient numbers can be twice as long as response time.
the numbers you start, with additional memory space is required. o Data from the storage registers is output to the display device
o The product/quotient register provides this extra storage. under control of the calculator.
o The registers used in modern electronic calculators are called o The binary codes representing the numbers have to be decoded
shift registers since during data entry, transfer and calculation, by suitable logic circuits so that the required digit is displayed
the numbers are shifted into and out of the registers, a digit at a after it has been read out from the store.
time.
o The registers in a calculator are often referred to as the stack
register or the random access memory (RAM).
 The Arithmetic Unit :
o The arithmetic unit, as its name implies, performs arithmetic
operations on the data in the storage registers.
o It consists of an adder circuit, or an adder/subtractor, typically
resembling the serial or parallel adders.
o A single-bit storage register is usually included so that the carry Fig. 4.10 Seven segment display
condition from a previous operation may be remembered.  The Control Section :
o Data is passed to the arithmetic unit from the storage registers o The control section contains the programs which govern the
and is there operated upon, the result being passed back to the operations to be performed on data in order to produce the
appropriate register. answer to the required problem.
o This section of calculator is also used to detect the codes which o The program consists of many binary coded instructions held in
have been input from the keyboard. a read only memory (ROM).
o By adding numerical constants to the codes and detecting the o The instructions are read from this program memory
presence or absence of a carry generated, the code may be sequentially and decoded to perform the required control
identified and the appropriate action taken. functions.
o It is necessary, for example, to distinguish whether a keyboard o Such control functions include selecting the appropriate register
input is a digit or an operator. data and routing it to the adder, sending data back to the register,
outputting data to the display, selecting an add or subtract mode
for the adder, examining the carry bit and many more.

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o The instructions are executed sequentially by means of a  The 0010 is directed to the display register by the control circuitry and
program counter which selects one instruction after another from is stored in the display register.
the program memory.  This information is also applied to the seven-segment decoder and lines
o The apparently simple problem of adding together two numbers a, b, d, e, and g are activated.
would typically require a few hundred program steps to be  The first (Is display) seven-segment display shows a 2 when the scan
executed. line pulses that unit briefly.
o We can see how fast the individual operations are performed  The scanning continues at a high-frequency, and the display appears to
since the answer is calculated in a fraction of a second. be lit continuously even though it is being turned on and off many times
per second.
INTERNAL ORGANISATION OF A CALCULATOR  Next, we press + on the keyboard. This operation is transferred to and
 The diagram in Fig. 4.11 will help us figure out how a calculator works. stored in code form in an extra register (X register).
 Figure 4.11 shows three components :  Now we press 3 on the keyboard. The encoder translates the 3 to a BCD
o The keyboard, the seven-segment displays and the power supply. 0011.
 These parts are the only functional ones not contained in the single LSI  The 0011 is transferred to the display register by the controller and is
IC in most calculators. passed to the display decoder/driver which also places a 3 on the
 The keyboard is obviously the input device. The keyboard contains display.
simple normally open switches.  Meanwhile, the controller has moved the 0010 (decimal 2) to the
 The decimal display is the output. The readout unit in Fig. 4.11 contains operand register.
only six seven-segment displays.  Now we press = key. The controller checks the X register to see what to
 The power supply is a battery supply in most inexpensive hand-held do.
calculators.  The X register says to add the BCD numbers in the operand and display
 Many modern calculators use solar cells as their power supply. registers.
 CMOS ICs and LCD make this supply feasible.  The controller applies the contents of the display and operand registers
 The calculator chip (the IC) is divided into several functional to the adder inputs.
subsystems as shown in Fig. 4.11.  The results of the addition get collected in the accumulator register. The
 The organization shown is only one of several ways to get a calculator result of the addition is a BCD 0101.
to operate.  The controller routes the answer to the display register, shown in the
 The heart of the system is the adder/subtractor subsystem. The clock readout as 5.
subsystem pulses all parts of the system at a constant frequency.  For longer and more complex numbers containing decimal points, the
 The clock frequency is fairly high ranging from 25 to 500 kHz. controller follows directions in the instruction register.
 When the calculator is turned on, the clock runs constantly and the  For complicated problems the unit may cycle through hundreds of steps
circuit is idle until a command comes from the keyboard. as programmed into the ROM.
 Suppose we add 2 + 3 with this calculator.  Amazingly, however, even hundreds of operations take less than 1/10s.
 As we press the 2 on the keyboard, the encoder translates 2 to a BCD  Only the original IC designers need to know the organization of the
0010. subsystems in Fig. 4.11.

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 This organization is sometimes referred to as the architecture of the SERVICING ELECTRONIC CALCULATORS
calculator.  Small electronic calculators require more sophisticated troubleshooting
 Notice that all the elements of a system are present in this electronic techniques than those employed in servicing many other kinds of
calculator. electronic equipment.
 In addition to the basic procedures used in discrete transistor circuits,
calculator servicing requires some understanding of integrated circuitry
and logic.
 To service a defective calculator you will need a pencil-type soldering
iron (30 to 40 watts at about 700°F), small screwdrivers, solder
remover, sharp knife, diagonal cutters, and needle-nose pliers.
 A vom and oscilloscope are the only necessary pieces of test equipment,
but a frequency counter can come in handy at times.
 Some problems can be solved with no test equipment at all or possibly a
vom alone.
 A good example is the overflow indicator. If the readout devices do not
light, multiply two numbers whose product will give an overflow
indication.
 If the “Error” signal is displayed, the problem is not in the input,
control, or arithmetic sections of the machine.
 In this manner, possible causes of the trouble can be quickly identified.
 Finally, if a thorough visual inspection fails to reveal the problem, begin
troubleshooting at the point of the improper indication and work
backward, checking each associated component.
 Here is a typical example :
o In Fig. 46.6, the C segment in the display fails to light. Follow
these steps to isolate the trouble :
1. Check continuity from the C segment to the Q5 emitter
2. Check the Q5 base for proper incoming signal
3. Check Q5
4. Check R15
5. Check R14

Fig. 4.11 Internal Organization of Calculator

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DIGITAL CLOCK
Introduction
 In analog clocks the hands move continuously. In doing so they
indicate, or simulate the passage of time
 In digital clocks the time is shown in steps, as a digital process. No
times are displayed between one step and next
Frequency Division
 An interesting and common use of counters is for frequency division.
 An example of simple system using a frequency divider is shown in fig
4.14
 This system is the basis for and electric clock.
 The 60Hz input frequency formed into a square wave is divided by 60,
and output will be one pulse per second (1 Hz). This is a second’s timer.

Fig. 4.12 A typical hand-held calculator

Fig. 4.14 A Practical divide-by-60 circuit used as a 1-second timer

Block Diagram of Digital Clock

 Fig 4.15 (a) is a simple block diagram of a digital clock system. Many
clocks use 60Hz as their input or frequency standard
 This frequency is divided into seconds, minutes and hours by the
frequency divider section of the clock.
 The one-per second, one-per-minute and one-per-hour pulses are then
counted and stored in the count accumulator section of the clock.
 The stored contents of the count accumulator (seconds, minutes and
hours) are then decoded and correct time is shown on the output time
displays.
 The digital clock has the typical elements of a digital system.
 All system consists of logic gates, flip-flops and subsystems. The
diagram in 4.15 (b) shows how subsystems are organized to display
Fig. 4.13 Partial driver circuit for seven-segment readout

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time in hours, minutes and seconds. This is a more detailed block  The 1 pulse per second is fed into an up counter that counts from 00 to
diagram of digital clock 59 and then resets to 00.
 The seconds counters are then decoded and displayed on the 2 seven-
segment LED displays at the upper right.
 Consider middle frequency divider circuit in fig, the input to this divide-
by-60 circuits is 1 pulse per second, the output is 1 pulse per minute.
 The 1 pulse per minute output is transferred into the 0 to 59 counter that
counts from 00 to 59 and then resets to 00
 The minutes counters are then decoded and displayed on the 2 seven-
segment LED displays at the upper middle.
 The 1 pulse per hour output is transferred into the 0 to 23 counter that
counts from 00 to 23 and the resets to 00.
 The hour counters are the decoded and displayed on the 2 seven-
segment LED displays at the upper left.
 In many practical digital clocks the output may be in hours and minutes
only.
 Most digital clocks are based upon one of many inexpensive IC’s. Large
scale integrated clock chips have all the frequency dividers, count
accumulators, and decoders build into a single IC.
 A wave shaping circuit has been added to the block diagram. The IC
counters that make up the frequency-divider circuit do not work well
will a sine wave input.
 The sine wave input must be converted to a square wave. The wave-
shaping circuit changes the sine wave to a square wave. The square
wave will now properly trigger the frequency divider circuit as shown in
fig 4.16

Fig. 4.15 (a) Simplified Block diagram of Digital clock

(b) Detailed Block diagram of Digital clock

 The input is still a 60 Hz signal. The 60 Hz may be from the low-

voltage secondary coil of a transformer.
 The 60 Hz is divided by 60 by the frequency divider. The output of the
first divide-by-60 circuit is 1 pulse per second. Fig 4.16 Schmitt trigger inverter used as a wave shaper

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QUESTIONS
PART A
1. Write function of photocopy machine.
2. How does a copier work?
3. What is the difference between arithmetic and scientific calculator?
4. Differentiate digital clock and analog clock.
5. What are the basic operations performed by a calculator?
6. Draw the simplified block diagram of a digital clock.
7. Why wave shaping circuit is required?
8. Write short note on facsimile technology?
9. What does M+ mean on a calculator?
10. Draw the structure of the calculator.
11. What are the functions of a digital calculator?
12. Differentiate between static and dynamic xerographic copier.
13. Draw the basic structure of calculator.
14. Compare analog and digital clock.
15. What do you mean by decoder?
16. What is the basic operation performed by a calculator?
17. Give the basic principle of working of a Photostat machine.
18. What kind of oscillator is used in digital clocks and digital timers?
PART B
1. Explain the internal organization of calculator.
2. Explain the basic Xerographic Process.
3. Discuss the internal organization of a calculator.
4. Explain the operation and working principles of FAX machine.
5. Explain the steps involved in photocopying using Xerography
copier.
6. Write short notes on digital clock with a neat block diagram.
7. Explain briefly about the facsimile machine.
PART C
1. Draw the block diagram of digital clock and describe its block.
2. Sketch and explain the working function of Xerographic copier.
3. Discuss the structure and working of an electronic calculator.
4. Elucidate the construction and working of a Facsimile machine.
5. Briefly explain the servicing electronic calculators.
6. Outline the salient features of the Facsimile machine in detail.

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