RKDF YASH SYNP

8/2/2019 RKDF YASH SYNP

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Component list

S.no. Name of the component Quantity Cost of the

components in

(Rs.)

1)- PCB Board (Single Sided) 1 40/-

2)- SCR of Specification as-

2P4M.2 /-

3)- Resistors of 10 kilo Ohms 2 1/-

4)- Resistors of 150 Ohms. 6 2/-

5)- Capacitor s of 22 F. 2 5/-

6)- Capacitors of 1 F. 6 10/-

7)- Transistor BC548 4 20/-


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Introduction

8)- Band Wire 1m 10/-

10)- Push to On Switches 2 8/-

11)- RJ 7 Connectors 3 15/-

12)- Heat Sink 2 4/-

13)- Leds 2 4/-

11)- Plastic Case 1 40/-

14)- Push to on switches 2 8/-


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This circuit provides secrecy when two or more telephones

are connected in parallel with telephone line. The circuit

also prevents incoming calls to as well as outgoing calls

from other Telephones are connected in parallel, except

from the one lifted first and also provide some extension so

that we can operate the telephone at any corner of our

home. This circuit is very convenient and reliable for home

application and with certain modification can be

implemented for office and for some big scale use. By the

use of this we can prevent the unauthorized person to hear

our voice and at a same time it avoid to make call. When

one phone is in use no one can use another phone until

he/she has to press the switch. The phone appears in dead

state until it is in use or it has been not triggered on by the

switch. This circuit does not require any external power

supply and have least maintenance.

This circuit doesnt produce distortion neither introduce

any noise in telephone channel, thus very fit for use.

Furthermore it is very handy and easily installing device.


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SCHEMATIC CIRCUIT DIAGRAM


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LAYOUT diagram


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Diagram as in Diptrace PCB software


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WORKING This circuit provides secrecy when two or more

telephones are connected in parallel to a telephone line.

The circuit also prevents incoming calls to as well as

outgoing calls from other telephones connected in parallel

thats why this circuit is called as Extension Parallel

Phone Switcher with Secrecy and Call- Prevention

.By the use of this we can prevent the unauthorized person

to hear our voice and at a same time it avoid to make calls.

When someone picks up the handset of the telephone

connected in parallel to the original (master) phone for

making an outgoing call, no dial tone is heard and the

phone appears to be dead. But when a call comes, the ring

signal switches the SCRs on and conversation can be

carried out. As soon as the handset is kept on the hook, the

SCR goes off and the telephone can again only receive

incoming calls

When a call comes, conversation can be made only

from the telephone which is lifted up first. To carry out

conversation from the other telephone, the handset of the

telephone that was lifted up first has to be placed on the

hook and then the push-to-on switch of the associated

circuit of the other telephone has to be pressed after lifting


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up its handset. Thus the circuit ensures privacy because

both the telephones cannot be active

At the same time.

TECHNICAL DESCRIPTION

The no-load voltage at the telephone line, when thetelephone handset is on- hook, is around 48 volts.

However, when the handset is off-hook, terminalvoltage drops to between 5 volts and 15 volts.

This is due to the impedance of telephone line and thetelephone set. The voltage of the telephone line is the

key factor that controls the operation of this circuit.

Lifting the handset causes the terminal voltage to dropfrom 48V to about 10V.

Current flows through resistor R3, triggering SCR1and providing a link to the telephone set connected to

lines L1 (a) and L2 (a).

However, once the SCR is on, it will remain in thatstate as long as the current flowing through it does not

fall to near zero level. Thus the link continues.

The low off-hook voltage of the line will disable theother extension phones.


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The Silicon-Controlled Rectifier(SCR)

Shockley diodes are curious devices, but rather limited in

application. Their usefulness may be expanded, however,by equipping them with another means of latching. In doingso, they become true amplifying devices (if only in an on/offmode), and we refer to them as silicon-controlled rectifiers,or SCRs.

The progression from Shockley diode to SCR is achievedwith one small addition; actually nothing more than a third

wire connection to the existing PNPN structure:

If an SCR's gate is left floating (disconnected), it behavesexactly as a Shockley diode. It may be latched by breakovervoltage or by exceeding the critical rate of voltage risebetween anode and cathode, just as with the Shockleydiode. Dropout is accomplished by reducing current until


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one or both internal transistors fall into cutoff mode, alsolike the Shockley diode. However, because the gate terminalconnects directly to the base of the lower transistor, it maybe used as an alternative means to latch the SCR. Byapplying a small voltage between gate and cathode, thelower transistor will be forced on by the resulting basecurrent, which will cause the upper transistor to conduct,which then supplies the lower transistor's base withcurrent so that it no longer needs to be activated by a gatevoltage. The necessary gate current to initiate latch-up, ofcourse, will be much lower than the current through the

SCR from cathode to anode, so the SCR does achieve ameasure of amplification.

This method of securing SCR conduction is calledtriggering, and it is by far the most common way that SCRsare latched in actual practice. In fact, SCRs are usuallychosen so that their breakover voltage is far beyond thegreatest voltage expected to be experienced from the powersource, so that it can be turned on onlyby an intentionalvoltage pulse applied to the gate.

It should be mentioned that SCRs may sometimes beturned off by directly shorting their gate and cathodeterminals together, or by "reverse-triggering" the gate with anegative voltage (in reference to the cathode), so that thelower transistor is forced into cutoff. I say this is"sometimes" possible because it involves shunting all of the

upper transistor's collector current past the lowertransistor's base. This current may be substantial, makingtriggered shut-off of an SCR difficult at best. A variation ofthe SCR, called a Gate-Turn-Off thyristor, or GTO, makesthis task easier. But even with a GTO, the gate currentrequired to turn it off may be as much as 20% of the anode(load) current! The schematic symbol for a GTO is shown inthe following illustration:


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SCRs and GTOs share the same equivalent schematics (twotransistors connected in a positive-feedback fashion), theonly differences being details of construction designed togrant the NPN transistor a greater than the PNP. Thisallows a smaller gate current (forward or reverse) to exert agreater degree of control over conduction from cathode toanode, with the PNP transistor's latched state being moredependent upon the NPN's than vice versa. The Gate-Turn-Off thyristor is also known by the name of Gate-ControlledSwitch, or GCS.

A rudimentary test of SCR function, or at least terminalidentification, may be performed with an ohmmeter.

Because the internal connection between gate and cathodeis a single PN junction, a meter should indicate continuitybetween these terminals with the red test lead on the gateand the black test lead on the cathode like this:


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All other continuity measurements performed on an SCRwill show "open" ("OL" on some digital multimeter displays).It must be understood that this test is very crude and doesnotconstitute a comprehensive assessment of the SCR. It ispossible for an SCR to give good ohmmeter indications andstill be defective. Ultimately, the only way to test an SCR isto subject it to a load current.

If you are using a multimeter with a "diode check" function,the gate-to-cathode junction voltage indication you get mayor may not correspond to what's expected of a silicon PN

junction (approximately 0.7 volts). In some cases, you will

read a much lower junction voltage: mere hundredths of avolt. This is due to an internal resistor connected betweenthe gate and cathode incorporated within some SCRs. Thisresistor is added to make the SCR less susceptible to falsetriggering by spurious voltage spikes, from circuit "noise" orfrom static electric discharge. In other words, having aresistor connected across the gate-cathode junctionrequires that a strongtriggering signal (substantial current)be applied to latch the SCR. This feature is often found inlarger SCRs, not on small SCRs. Bear in mind that an SCRwith an internal resistor connected between gate andcathode will indicate continuity in both directions betweenthose two terminals:


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"Normal" SCRs, lacking this internal resistor, aresometimes referred to as sensitive gate SCRs due to their

ability to be triggered by the slightest positive gate signal.

The test circuit for an SCR is both practical as a diagnostictool for checking suspected SCRs and also an excellent aidto understanding basic SCR operation. A DC voltage sourceis used for powering the circuit, and two pushbuttonswitches are used to latch and unlatch the SCR,respectively:


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Actuating the normally-open "on" pushbutton switchconnects the gate to the anode, allowing current from thenegative terminal of the battery, through the cathode-gatePN junction, through the switch, through the load resistor,and back to the battery. This gate current should force theSCR to latch on, allowing current to go directly fromcathode to anode without further triggering through thegate. When the "on" pushbutton is released, the loadshould remain energized.

Pushing the normally-closed "off" pushbutton switchbreaks the circuit, forcing current through the SCR to halt,

thus forcing it to turn off (low-current dropout).

If the SCR fails to latch, the problem may be with the loadand not the SCR. There is a certain minimum amount ofload current required to hold the SCR latched in the "on"state. This minimum current level is called the holdingcurrent. A load with too great a resistance value may notdraw enough current to keep an SCR latched when gate

current ceases, thus giving the false impression of a bad(unlatchable) SCR in the test circuit. Holding currentvalues for different SCRs should be available from themanufacturers. Typical holding current values range from 1milliamp to 50 milliamps or more for larger units.

For the test to be fully comprehensive, more than thetriggering action needs to be tested. The forward breakover

voltage limit of the SCR could be tested by increasing theDC voltage supply (with no pushbuttons actuated) until theSCR latches all on its own. Beware that a breakover testmay require very high voltage: many power SCRs havebreakover voltage ratings of 600 volts or more! Also, if apulse voltage generator is available, the critical rate ofvoltage rise for the SCR could be tested in the same way:subject it to pulsing supply voltages of different V/time


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rates with no pushbutton switches actuated and see whenit latches.

In this simple form, the SCR test circuit could suffice as a

start/stop control circuit for a DC motor, lamp, or other

practical load

Some device or circuit sensing the output voltage will beconnected to the gate of the SCR, so that when an

overvoltage condition occurs, voltage will be appliedbetween the gate and cathode, triggering the SCR andforcing the fuse to blow. The effect will be approximatelythe same as dropping a solid steel crowbar directly acrossthe output terminals of the power supply, hence the nameof the circuit.

Most applications of the SCR are for AC power control,

despite the fact that SCRs are inherently DC(unidirectional) devices. If bidirectional circuit current is


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required, multiple SCRs may be used, with one or morefacing each direction to handle current through both half-cycles of the AC wave. The primary reason SCRs are usedat all for AC power control applications is the uniqueresponse of a thyristor to an alternating current. As we sawin the case of the thyratron tube (the electron tube versionof the SCR) and the DIAC, a hysteretic device triggered onduring a portion of an AC half-cycle will latch and remainon throughout the remainder of the half-cycle until the ACcurrent decreases to zero, as it must to begin the next half-cycle. Just prior to the zero-crossover point of the current

waveform, the thyristor will turn off due to insufficientcurrent (this behavior is also known as naturalcommutation) and must be fired again during the nextcycle. The result is a circuit current equivalent to a"chopped up" sine wave. For review, here is the graph of aDIAC's response to an AC voltage whose peak exceeds thebreakover voltage of the DIAC:

With the DIAC, that breakover voltage limit was a fixedquantity. With the SCR, we have control over exactly whenthe device becomes latched by triggering the gate at anypoint in time along the waveform. By connecting a suitablecontrol circuit to the gate of an SCR, we can "chop" the sinewave at any point to allow for time-proportioned power

control to a load.


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Take the following circuit as an example. Here, an SCR ispositioned in a circuit to control power to a load from anAC source:

Being a unidirectional (one-way) device, at most we canonly deliver half-wave power to the load, in the half-cycle of

AC where the supply voltage polarity is positive on the topand negative on the bottom. However, for demonstratingthe basic concept of time-proportional control, this simplecircuit is better than one controlling full-wave power (whichwould require two SCRs).

With no triggering to the gate, and the AC source voltagewell below the SCR's breakover voltage rating, the SCR will

never turn on. Connecting the SCR gate to the anodethrough a normal rectifying diode (to prevent reversecurrent through the gate in the event of the SCR containinga built-in gate-cathode resistor), will allow the SCR to betriggered almost immediately at the beginning of everypositive half-cycle:


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We can delay the triggering of the SCR, however, byinserting some resistance into the gate circuit, thusincreasing the amount of voltage drop required before thereis enough gate current to trigger the SCR. In other words, ifwe make it harder for electrons to flow through the gate by

adding a resistance, the AC voltage will have to reach ahigher point in its cycle before there will be enough gatecurrent to turn the SCR on. The result looks like this:


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With the half-sine wave chopped up to a greater degree bydelayed triggering of the SCR, the load receives less averagepower (power is delivered for less time throughout a cycle).By making the series gate resistor variable, we can makeadjustments to the time-proportioned power:

Unfortunately, this control scheme has a significantlimitation. In using the AC source waveform for our SCR


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triggering signal, we limit control to the first half of thewaveform's half-cycle. In other words, there is no way forus to wait until after the wave's peak to trigger the SCR.

This means we can turn down the power only to the pointwhere the SCR turns on at the very peak of the wave:

Raising the trigger threshold any more will cause the circuitto not trigger at all, since not even the peak of the ACpower voltage will be enough to trigger the SCR. The resultwill be no power to the load.

An ingenious solution to this control dilemma is found inthe addition of a phase-shifting capacitor to the circuit:


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The smaller waveform shown on the graph is voltage acrossthe capacitor.

For the sake of illustrating the phase shift, I'm assuming acondition of maximum control resistance where the SCR isnot triggering at all and there is no load current, save forwhat little current goes through the control resistor andcapacitor.

This capacitor voltage will be phase-shifted anywhere from0o to 90o lagging behind the power source AC waveform.When this phase-shifted voltage reaches a high enoughlevel, the SCR will trigger.

Assuming there is periodically enough voltage across the

capacitor to trigger the SCR, the resulting load currentwaveform will look something like this:

Because the capacitor waveform is still risingafter the main

AC power waveform has reached its peak, it becomespossible to trigger the SCR at a threshold level beyond that


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peak, thus chopping the load current wave further than itwas possible with the simpler circuit. In reality, thecapacitor voltage waveform is a bit more complex that whatis shown here, its sinusoidal shape distorted every time theSCR latches on. However, what I'm trying to illustrate hereis the delayed triggering action gained with the phase-shifting RC network, and so a simplified, undistortedwaveform serves the purpose well.

SCRs may also be triggered, or "fired," by more complexcircuits. While the circuit previously shown is sufficient fora simple application like a lamp control, large industrial

motor controls often rely on more sophisticated triggeringmethods. Sometimes, pulse transformers are used tocouple a triggering circuit to the gate and cathode of anSCR to provide electrical isolation between the triggeringand power circuits:

When multiple SCRs are used to control power, theircathodes are often not electrically common, making itdifficult to connect a single triggering circuit to all SCRs

equally. An example of this is the controlled bridge rectifiershown here:


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In any bridge rectifier circuit, the rectifying diodes (or inthis case, the rectifying SCRs) must conduct in oppositepairs. SCR1 and SCR3 must be fired simultaneously, andlikewise SCR2 and SCR4 must be fired together as a pair. As

you will notice, though, these pairs of SCRs do not sharethe same cathode connections, meaning that it would notwork to simply parallel their respective gate connections

and connect a single voltage source to trigger both:

Although the triggering voltage source shown will triggerSCR4, it will not trigger SCR2 properly because the twothyristors do not share a common cathode connection to


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reference that triggering voltage. Pulse transformersconnecting the two thyristor gates to a common triggeringvoltage source willwork, however:

Bear in mind that this circuit only shows the gateconnections for two out of the four SCRs. Pulsetransformers and triggering sources for SCR1 and SCR3, aswell as the details of the pulse sources themselves, havebeen omitted for the sake of simplicity.

Controlled bridge rectifiers are not limited to single-phasedesigns. In most industrial control systems, AC power isavailable in three-phase form for maximum efficiency, andsolid-state control circuits are built to take advantage ofthat. A three-phase controlled rectifier circuit built withSCRs, without pulse transformers or triggering circuitryshown, would look like this:


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REVIEWA Silicon-Controlled Rectifier, or SCR, is essentially aShockley diode with an extra terminal added. This extra

terminal is called the gate, and it is used to trigger the


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device into conduction (latch it) by the application of a

small voltage.

To trigger, orfire, an SCR, voltage must be appliedbetween the gate and cathode, positive to the gate and

negative to the cathode. When testing an SCR, a

momentary connection between the gate and anode is

sufficient in polarity, intensity, and duration to trigger it.

SCRs may be fired by intentional triggering of the gateterminal, excessive voltage (breakdown) between anode and

cathode, or excessive rate of voltage rise between anode and

cathode. SCRs may be turned off by anode current falling

below the holding current value(low-current dropout), or by

"reverse-firing" the gate (applying a negative voltage to the

gate). Reverse-firing is only sometimes effective, and always

involves high gate current

A variant of the SCR, called a Gate-Turn-Off thyristor(GTO), is specifically designed to be turned off by means of

reverse triggering. Even then, reverse triggering requires

fairly high current: typically 20% of the anode current.SCR terminals may be identified by a continuity meter:the only two terminals showing any continuity between

them at all should be the gate and cathode. Gate and

cathode terminals connect to a PN junction inside the SCR,

so a continuity meter should obtain a diode-like reading

between these two terminals with the red (+) lead on the


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gate and the black (-) lead on the cathode. Beware, though,

that some large SCRs have an internal resistor connected

between gate and cathode, which will affect any continuity

readings taken by a meter.

SCRs are true rectifiers: they only allow current throughthem in one direction. This means they cannot be used

alone for full-wave AC power control.

If the diodes in a rectifier circuit are replaced by SCRs, you have the makings of a controlled rectifier circuit,

whereby DC power to a load may be time-proportioned by

triggering the SCRs at different points along the AC power

waveform

Resistor

A resistor is a two-terminal electronic component designedto oppose an electric current by producing a voltage dropbetween its terminals in proportion to the current, that is,in accordance with Ohm's law: V= IR
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Resistors are used as part of electrical networks andelectronic circuits. They are extremely commonplace inmost electronic equipment. Practical resistors can be madeof various compounds and films, as well as resistance wire(wire made of a high-resistivity alloy, such asnickel/chrome).

The primary characteristics of resistors are their resistanceand the power they can dissipate. Other characteristicsinclude temperature coefficient, noise, and inductance.Less well-known is critical resistance, the value belowwhich power dissipation limits the maximum permittedcurrent flow, and above which the limit is applied voltage.Critical resistance depends upon the materials constituting

the resistor as well as its physical dimensions; it'sdetermined by design.

Resistors can be integrated into hybrid and printedcircuits, as well as integrated circuits. Size, and position ofleads (or terminals) are relevant to equipment designers;resistors must be physically large enough not to overheatwhen dissipating their power.

Capacitor
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A capacitor or condenser is a passive electroniccomponent consisting of a pair ofconductors separated bya dielectric. When a voltage potential difference existsbetween the conductors, an electric field is present in thedielectric. This field stores energy and produces amechanical force between the plates. The effect is greatestbetween wide, flat, parallel, narrowly separated conductors.

An ideal capacitor is characterized by a single constantvalue, capacitance, which is measured in farads. This is theratio of the electric charge on each conductor to thepotential difference between them. In practice, the dielectric

between the plates passes a small amount of leakagecurrent. The conductors and leads introduce an equivalentseries resistance and the dielectric has an electric fieldstrength limit resulting in a breakdown voltage.

The properties of capacitors in a circuit may determine theresonant frequency and quality factor of a resonant circuit,power dissipation and operating frequency in a digital logic

circuit, energy capacity in a high-power system, and manyother important aspects.

A capacitor is an electrical/electronic device that can storeenergy in the electric field between a pair of conductors(called "plates"). The process of storing energy in thecapacitor is known as "charging", and involves electriccharges of equal magnitude, but opposite polarity, building

up on each plate.

Capacitors are often used in electric and electronic circuitsas energy-storage devices. They can also be used todifferentiate between high-frequency and low-frequencysignals. This property makes them useful in electronicfilters.

Capacitors are occasionally referred to as condensers. Thisis considered an antiquated term in English, but most
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other languages use an equivalent, like "Kondensator" inGerman, "Condensador" in Spanish, or "Kondensa" in

Japanese.

Early capacitors were also known as condensers, a termthat is still occasionally used today. It was coined byAlessandro Volta in 1782 (derived from the Italiancondensatore), with reference to the device's ability to storea higher density of electric charge than a normal isolatedconductor. Most non-English European languages still usea word derived from "condensatore".

Condensers patented by Nikola Tesla in U.S. Patent

567,818, Electrical Condenser, in 1896 on September 15.

Capacitance

The capacitor's capacitance (C) is a measure of the amountof charge (Q) stored on each plate for a given potentialdifference or voltage(V) which appears between the plates:

In SI units, a capacitor has a capacitance of one faradwhen one coulomb of charge is stored due to one volt
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applied potential difference across the plates. Since thefarad is a very large unit, values of capacitors are usuallyexpressed in microfarads (F), nanofarads (nF), orpicofarads (pF).

When there is a difference in electric charge between the

plates, an electric field is created in the region between the

plates that is proportional to the amount of charge that hasbeen moved from one plate to the other. This electric field

creates a potential difference V= Edbetween the plates of

this simple parallel-plate capacitor.

The capacitance is proportional to the surface area of theconducting plate and inversely proportional to the distancebetween the plates. It is also proportional to the permittivityof the dielectric (that is, non-conducting) substance thatseparates the plates.

The capacitance of a parallel-plate capacitor is given by:

[2]
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where is the permittivity of the dielectric (see Dielectricconstant), A is the area of the plates and d is the spacingbetween them.

In the diagram, the rotated molecules create an opposingelectric field that partially cancels the field created by theplates, a process called dielectric polarization

Electric circuits

The electrons within dielectric molecules are influenced by

the electric field, causing the molecules to rotate slightly

from their equilibrium positions. The air gap is shown for

clarity; in a real capacitor, the dielectric is in direct contact

with the plates. Capacitors also allow AC current to flowand block DC current.

DC sources

The dielectric between the plates is an insulator and blocksthe flow of electrons. A steady current through a capacitor
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deposits electrons on one plate and removes the samequantity of electrons from the other plate. This process iscommonly called 'charging' the capacitor. The currentthrough the capacitor results in the separation of electriccharge within the capacitor, which develops an electric fieldbetween the plates of the capacitor, equivalently,developing a voltage difference between the plates. Thisvoltage V is directly proportional to the amount of chargeseparated Q. Since the current I through the capacitor isthe rate at which charge Q is forced through the capacitor(dQ/dt), this can be expressed mathematically as:

where Iis the current flowing in the conventional directionmeasured in amperes, dV/dt is the time derivative ofvoltage measured in volts per second, and C is thecapacitance in farads.

For circuits with a constant (DC) voltage source andconsisting of only resistors and capacitors, the voltageacross the capacitor cannot exceed the voltage of thesource. Thus, an equilibrium is reached where the voltageacross the capacitor is constant and the current throughthe capacitor is zero. For this reason, it is commonly saidthat capacitors block DC.

AC sources

The current through a capacitor due to an AC sourcereverses direction periodically. That is, the alternatingcurrent alternately charges the plates: first in one directionand then the other. With the exception of the instant thatthe current changes direction, the capacitor current is non-

zero at all times during a cycle. For this reason, it is
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commonly said that capacitors "pass" AC. However, at notime do electrons actually cross between the plates, unlessthe dielectric breaks down. Such a situation would involvephysical damage to the capacitor and likely to the circuitinvolved as well.

Since the voltage across a capacitor is proportional to theintegral of the current, as shown above, with sine waves inAC or signal circuits this results in a phase difference of 90degrees, the current leading the voltage phase angle. It canbe shown that the AC voltage across the capacitor is inquadrature with the alternating current through the

capacitor. That is, the voltage and current are 'out-of-phase' by a quarter cycle. The amplitude of the voltagedepends on the amplitude of the current divided by theproduct of the frequency of the current with thecapacitance, C.

Impedance

The ratio of the phasor voltage across a circuit element tothe phasor current through that element is called theimpedanceZ. For a capacitor, the impedance is given by

Where is the capacitive reactance, is the angularfrequency, f is the frequency), C is the capacitance infarads, andjis the imaginary unit.

While this relation (between the frequency domainvoltageand current associated with a capacitor) is always true, the
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ratio of the time domainvoltage and current amplitudes isequal to XConly for sinusoidal (AC) circuits in steady state.

See derivation Deriving capacitor impedance.

Hence, capacitive reactance is the negative imaginarycomponent of impedance. The negative sign indicates thatthe current leads the voltage by 90 for a sinusoidal signal,as opposed to the inductor, where the current lags thevoltage by 90.

The impedance is analogous to the resistance of a resistor.

The impedance of a capacitor is inversely proportional tothe frequency -- that is, for very high-frequency alternatingcurrents the reactance approaches zero -- so that acapacitor is nearly a short circuit to a very high frequencyAC source. Conversely, for very low frequency alternatingcurrents, the reactance increases without bound so that acapacitor is nearly an open circuit to a very low frequencyAC source. This frequency dependent behavior accounts for

most uses of the capacitor (see "Applications", below).

Reactance is so called because the capacitor doesn'tdissipate power, but merely stores energy. In electricalcircuits, as in mechanics, there are two types of load,resistive and reactive. Resistive loads (analogous to anobject sliding on a rough surface) dissipate the energydelivered by the circuit as heat, while reactive loads

(analogous to a spring or frictionless moving object) storethis energy, ultimately delivering the energy back to thecircuit.

Also significant is that the impedance is inverselyproportional to the capacitance, unlike resistors andinductors for which impedances are linearly proportional toresistance and inductance respectively. This is why theseries and shunt impedance formulae (given below) are the
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inverse of the resistive case. In series, impedances sum. Inparallel, conductances sum.

Series or parallel arrangements

Main article:Series and parallel circuits

Capacitors in a parallel configuration each have the samepotential difference (voltage). Their total capacitance (Ceq) isgiven by:

The reason for putting capacitors in parallel is to increasethe total amount of charge stored. In other words,increasing the capacitance also increases the amount ofenergy that can be stored. Its expression is:

The current through capacitors in series stays the same,

but the voltage across each capacitor can be different. Thesum of the potential differences (voltage) is equal to thetotal voltage. Their total capacitance is given by:
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In parallel the effective area of the combined capacitor has

increased, increasing the overall capacitance. While inseries, the distance between the plates has effectively beenincreased, reducing the overall capacitance.

In practice capacitors will be placed in series as a means ofeconomically obtaining very high voltage capacitors, forexample for smoothing ripples in a high voltage powersupply. Three "600 volt maximum" capacitors in series will

increase their overall working voltage to 1800 volts. This isof course offset by the capacitance obtained being only onethird of the value of the capacitors used. This can becountered by connecting 3 of these series set-ups inparallel, resulting in a 3x3 matrix of capacitors with thesame overall capacitance as an individual capacitor butoperable under three times the voltage. In this application,a large resistor would be connected across each capacitor

to ensure that the total voltage is divided equally acrosseach capacitor and also to discharge the capacitors forsafety when the equipment is not in use.

Another application is for use of polarized capacitors inalternating current circuits; the capacitors are connected inseries, in reverse polarity, so that at any given time one ofthe capacitors is not conducting...
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By dielectric material

1. Vacuum: Two metal, usually copper, electrodes areseparated by a vacuum. The insulating envelope is usuallyglass or ceramic. Typically of low capacitance - 10 - 1000pF and high voltage, up to tens of kilovolts, they are most

often used in radio transmitters and other high voltagepower devices. Both fixed and variable types are available.Vacuum variable capacitors can have a minimum tomaximum capacitance ratio of up to 100, allowing anytuned circuit to cover a full decade of frequency. Vacuum isthe most perfect of dielectrics with a zero loss tangent. Thisallows very high powers to be transmitted withoutsignificant loss and consequent heating.2. Air: Air dielectric capacitors consist of metal platesseparated by an air gap. The metal plates, of which theremay be many interleaved, are most often made ofaluminum or silver-plated brass. Nearly all air dielectriccapacitors are variable and are used in radio tuningcircuits.3. Plastic film: Made from high quality polymer film(usually polycarbonate, polystyrene, polypropylene,polyester (Mylar), and for high quality capacitors
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polysulfone), and metal foil or a layer of metal deposited onsurface of the plastic film in a the metalized film type.

They have good quality and stability, and are suitable fortimer circuits. Their inductance limits use at highfrequencies.4. Mica: Similar to glass. Often high voltage. Suitable forhigh frequencies. Expensive. Excellent tolerance & stability.5. Paper: Used for relatively high voltages. Known forlong term failures.6. Glass: Used for high voltages. Expensive. Stabletemperature coefficient in a wide range of temperatures.7.

Ceramic: Chips of alternating layers of metal andceramic, or disks of ceramic with metal on both sides of thedisk. Characteristics vary widely depending on the type ofceramic dielectric. The dielectrics are broadly categorized asClass 1 or Class 2. Class 2 ceramic capacitors have strongvariation of capacitance with temperature, high dissipationfactor, high frequency coefficient of dissipation, and theircapacitance depends on applied voltage and changes with

aging. However they find massive use in common low-precision coupling and filtering applications. Suitable forhigh frequencies.8. Aluminum electrolytic: Polarized. One electrodemade of aluminum foil, etched aluminum to acquire muchlarger surface area. The dielectric is oxide grown on theetched aluminum plate, and the second electrode is a liquidelectrolyte. They can achieve high capacitance but suffer

from poor tolerances, high instability, gradual loss ofcapacitance especially when subjected to heat, and highleakage current. The conductivity of the electrolyte drops atlow temperatures, increasing equivalent series resistance.Bad frequency characteristics make them unsuited forhigh-frequency applications. Special types with lowequivalent series resistance are available.9. Tantalum electrolytic: Similar to the aluminumelectrolytic capacitor but with better frequency andtemperature characteristics. High dielectric absorption and
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high leakage [4]. Although they share many of thedisadvantages of aluminum electrolytics, they performbetter on most attributes; for example, they have muchbetter performance at low temperate

Led

A light-emitting diode (LED) is an electronic light source. The LED was first invented in Russia in the 1920s, andintroduced in America as a practical electronic componentin 1962. Oleg Vladimirovich Losev was a radio technicianwho noticed that diodes used in radio receivers emittedlight when current was passed through them. In 1927, he

published details in a Russian journal of the first ever LED.
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Blue, green, and red LEDs; these can be combined to produce any color, including white. Infrared and

ultraviolet (UVA) LEDs are also available.

A light-emitting diode, usually called an LED (pronounced

/lidi/)[1], is a semiconductor diode that emits incoherent

narrow-spectrum light when electrically biased in theforward direction of the p-n junction, as in the commonLED circuit. This effect is a form ofelectroluminescence.

A LED is usually a small area light source, often with extraoptics added to the chip that shapes its radiation pattern. [2]

[3] LEDs are often used as small indicator lights on
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electronic devices and increasingly in higher powerapplications such as flashlights and area lighting. The colorof the emitted light depends on the composition andcondition of the semiconducting material used, and can beinfrared,visible, or ultraviolet. LEDs can also be used as aregular household light source. Besides lighting, interestingapplications include sterilization of water and disinfectionof devices.[

There are two types of LED panels: conventional, usingdiscrete LEDs, and surface mounted device (SMD) panels.Most outdoor screens and some indoor screens are built

around discrete LEDs, also known as individually mountedLEDs. A cluster of red, green, and blue diodes is driventogether to form a full-color pixel, usually square in shape.

These pixels are spaced evenly apart and are measuredfrom center to center for absolute pixel resolution. Thelargest LED display in the world is over 1,500 foot(457.2 m) long and is located in Las Vegas, Nevada coveringthe Fremont Street Experience.

Most indoor screens on the market are built using SMDtechnologya trend that is now extending to the outdoormarket. An SMD pixel consists of red, green, and bluediodes mounted on a chipset, which is then mounted onthe driver PC board. The individual diodes are smaller thana pinhead and are set very close together. The difference isthat the maximum viewing distance is reduced by 25%

from the discrete diode screen with the same resolution.

LED panels allow for smaller sets of interchangeable LEDs

to be one large display.

Indoor use generally requires a screen that is based onSMD technology and has a minimum brightness of 600candelas per square meter (unofficially called nits). This

will usually be more than sufficient for corporate and retail
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applications, but under high ambient-brightnessconditions, higher brightness may be required for visibility.Fashion and auto shows are two examples of high-brightness stage lighting that may require higher LEDbrightness. Conversely, when a screen may appear in ashot on a television show, the requirement will often be forlower brightness levels with lower color temperatures(common displays have a white point of 6500 to 9000 K,which is much bluer than the common lighting on atelevision production set).

For outdoor use, at least 2,000 units are required for mostsituations, whereas higher brightness types of up to 5,000units cope even better with direct sunlight on the screen.(The brightness of LED panels can be reduced from thedesigned maximum, if required.)

Suitable locations for large display panels are identified by

factors such as line of sight, local authority planningrequirements (if the installation is to become semi-permanent), vehicular access (trucks carrying the screen,truck-mounted screens, or cranes), cable runs for powerand video (accounting for both distance and health andsafety requirements), power, suitability of the ground forthe location of the screen (if there are no pipes, shallowdrains, caves, or tunnels that may not be able to support

heavy loads), and overhead obstructions.


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Like a normal diode, the LED consists of a chip ofsemiconducting material impregnated, or doped, withimpurities to create a p-n junction. As in other diodes,current flows easily from the p-side, or anode, to the n-side,or cathode, but not in the reverse direction. Charge-carrierselectrons and holesflow into the junction from

electrodes with different voltages. When an electron meets ahole, it falls into a lower energy level, and releases energyinthe form of a photon.

The wavelength of the light emitted, and therefore its color,depends on the band gap energy of the materials formingthe p-n junction. In silicon or germanium diodes, theelectrons and holes recombine by a non-radioactive

transition which produces no optical emission, becausethese are indirect band gap materials. The materials usedfor the LED have a direct band gap with energiescorresponding to near-infrared, visible or near-ultravioletlight.

LED development began with infrared and red devicesmade with gallium arsenide. Advances in materials sciencehave made possible the production of devices with ever-shorter wavelengths, producing light in a variety of colors.

LEDs are usually built on an n-type substrate, with anelectrode attached to the p-type layer deposited on itssurface. P-type substrates, while less common, occur aswell. Many commercial LEDs, especially GaN/InGaN, alsouse sapphire substrate. Substrates that are transparent tothe emitted wavelength, and backed by a reflective layer,

increase the LED efficiency. The refractive index of the
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package material should match the index of thesemiconductor, otherwise the produced light gets partiallyreflected back into the semiconductor, where it may beabsorbed and turned into additional heat, thus loweringthe efficiency. This type of reflection also occurs at thesurface of the package if the LED is coupled to a mediumwith a different refractive index such as a glass fiber or air.

The refractive index of most LED semiconductors is quitehigh, so in almost all cases the LED is coupled into a muchlower-index medium. The large index difference makes thereflection quite substantial (per the Fresnel coefficients),

and this is usually one of the dominant causes of LEDinefficiency. Often more than half of the emitted light isreflected back at the LED-package and package-airinterfaces. The reflection is most commonly reduced byusing a dome-shaped (half-sphere) package with the diodein the center so that the outgoing light rays strike thesurface perpendicularly, at which angle the reflection isminimized. An anti-reflection coating may be added as well.

The package may be cheap plastic, which may be colored,but this is only for cosmetic reasons or to improve thecontrast ratio; the color of the packaging does notsubstantially affect the color of the light emitted. Otherstrategies for reducing the impact of the interfacereflections include designing the LED to reabsorb andreemit the reflected light (called photon recycling) andmanipulating the microscopic structure of the surface to

reduce the reflectance, either by introducing randomroughness or by creating programmed moth eye surfacepatterns.

Conventional LEDs are made from a variety of inorganic

semiconductor materials, producing the following colors:
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Aluminum gallium arsenide (AlGaAs)red and infraredAluminum gallium phosphide (AlGaP)greenAluminium gallium indium phosphide (AlGaInP)high-brightness orange-red, orange, yellow, and greenGallium arsenide phosphide (GaAsP)red, orange-red,orange, and yellowGallium phosphide (GaP)red, yellow and greenGallium nitride (GaN)green, pure green (or emeraldgreen), and blue also white (if it has an AlGaN QuantumBarrier)Indium gallium nitride (InGaN)
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Transistor bc548

In electronics, a transistor is a semiconductor device

commonly used to amplify or switch electronic signals. A

transistor is made of a solid piece of a semiconductor

material, with at least three terminals for connection to an

external circuit. A voltage or current applied to one pair of

the transistor's terminals changes the current flowing

through another pair of terminals. Because the controlled

(output) power can be much larger than the controlling

(input) power, the transistor provides amplification of a

signal. The transistor is the fundamental building block of

modern electronic devices, and is used in radio,telephone,

computer and other electronic systems. Some transistors

are packaged individually but most are found in integrated

circuits.
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PRINTED CIRCUIT BOARDPRINTED CIRCUIT BOARDS or PCBs are used tomechanically support and electrically connect electronics

components using conductor pathways, or traces, etchedfrom copper sheets laminated onto a non-conductivesubstrate. Alternative names are PRINTED WIRING BOARD(PWB) and ETCHED WIRING BOARD (EWB). Populating theboard with the electronics components forms a PRINTEDCIRCUIT ASSEMBLY (PCA). Also known as a PRINTEDCIRCUIT BOARD ASSEMBLY (PCBA). Sometimesabbreviated as PCB, it is a thin plate on which chips and

other electronics components are placed. Computersconsist of one or more boards, often called cards oradapters. PCBs are laminated. This means that they aremade from two or more sheets of material stuck together,often copper or fiber glass.

PHYSICAL COMPOSITION OF THE PCB

Most PCBs are composed if between one and twenty-four

conductive layers separated and supported by layers of


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insulating material which is the substrates that arelaminated that is glued with heat, pressure & sometimesvacuum together.

Layers may be connected together through drilled holescalled vias. To form an electrical connection, the holes areeither electroplated or small rivets are inserted. Eventhough they may not form electrical connections to alllayers, these holes are typically drilled completely throughthe PC board. The exception are high-density PCBs, whichmay have blind vias, which are visible only on one surface,or buried vias which are visible on neither.

TYPES OF BOARDS

Printed Circuit Boards are found virtually in all electronicequipments. They are also the most custom-designed partof any electronic equipment, PCBs provide mechanicalsupport apart from the functional inter connection between

components. A PCB is a dielectric substrate with metalliccircuitry photo-chemically formed upon that substrate.

Typically, there are two major types of board materials thatis dielectric substrates that are used for the baseboards (1)Fiber Glass (Glass Epoxy) (2) Phenolic Paper. Thebaseboard is also known as copper clad. There are 3 typesof PCBs available today. They are

1. SINGLE SIDED BOARDS:

When the entire circuit is laid on the one side of the boardand there may or may not be holes on the board formounting of components, or for the interconnection ofcomponents then such a PCB is called as SINGLE SIDEDBOARDS. The single sided PCB are mostly used inEntertainment Electronics where the manufacturing costshave to be kept minimum. However in IndustrialElectronics cost factors cannot be neglected. These boars


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should be iced where a particular circuit can beaccommodated on them.

2. DOUBLE SIDED BOARDS:.

With the circuit on both sides of boards an electricalconnection is established through the board and platingcopper through the holes then PCB is called as DOUBLESIDED BAORD. These can be with or without being platedthrough holes. The production of boards with platedthrough holes is fairly expensive. Therefore plated throughholes boards are only chosen when there cannot be any

trade of between circuit complexities and density ofcomponents.

3. MULTILAYER BOARDS:

Two or more pieces of dielectric materials with circuitryformed on them are stacked up and bonded together.Electrical connections are established from one side to theother, and to the inner layer circuitry by drilled holes which

are subsequently plated through with copper.PCB DESGNING AND MANUFACTURING

PCB DESINGING

PRINTED CIRCUIT BOARD (PCB) is the component made ofone or more layers of insulating material with electricalconductors. The insulator is made up of various materialsthat are based on fiber glass, plastic or ceramic. Duringmanufacturing the portion of the conductors that are notneeded are etched of, leaving printed circuits that connectelectronic components. The main generic standard for theprinted circuit board design is IPC-2221A. This standardprovides the rules for the manufacturability and qualitiessuch as requirement for the material properties, criteria forsurface plating, conductor thickness, componentsplacement, dimensions and tolerance rules but does notprovide any information as to how to properly route the


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board. Good PCB layout techniques require understandingof effects of non-zero trace impedance and coupling ofsignals from one circuit to another through parasiticcapacitance and radio transmission, as well as basicunderstanding of circuit operation. When the routing isdone the conductors width should be chosen based on theselected temperature rise at the rated current andacceptable impedance. The spacing between the PC tracesis determined by the peak working voltage, the type of thecircuit and the safety requirements. The minimum possiblewidth of the traces and spacing between them are limited

by the minimum possible width of the traces and spacingbetween then are limited by the manufacturing capabilities.Modern technology allows as low as 2 mils for both widthand spacing although typical minimum values are at least6/6 mils.

The main purpose of printed circuit is in the routing ofelectrical currents and signal through a thin copper layerthat is bounded firmly to an insulating base material

sometimes called the substrate. This base is manufacturedwith integrally bounded layers of thin copper foil which hasto be partly etched or removed to arrive at a pre-designedpattern to suit the circuit connections or other applicationsas required.

The term printed circuit board is derived from the originalmethod where a printed pattern is used as the mask over

wanted areas of copper. The PCB provides an idealbaseboard upon which to assemble and hold firmly most ofthe small components.

From the constructors point of view, the main attraction ofusing the PCB is its role as the mechanical support forsmall components. There is less need for complicated andtime consuming metal work of chassis contraception exceptperhaps in providing the final enclosure. Most straightforward circuit designs can be easily converted in to printed


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wiring layer the thought required to carry out the inversionca footed high light as possible error that would otherwisebe missed n conventional point to pint wiring. The finishedproject is usually neater and truly a work of art.

Actual size PCB layout for the circuit is drawn on thecopper board. The board is then immersed in FeCl3 solutionfor 12 hours. In this process only the exposed copperportion is etched out by the solution. Now the petrolwashes out the paint and the copper layout on PCB isrubbed with a smooth sand paper slowly and lightly suchthat only the oxide layers over the Cu are removed. Now the

holes are drilled at the respective places according tocomponent layout.

LAYOUT DESIGN

The connections on the PCB should be identical to thecircuit diagram, but while the circuit diagram is arrangedto be readable, the PCB layout is arranged to be functional,so there is rarely any visible correlation between the circuit

and the layout. PCB layout can be performed manually(using CAD) or in combination with auto router. The bestresults are usually still achieved using at least somemanual routingsimply because the design engineer has afar better judgment of how to arrange circuitry.Surprisingly, many author routed boards are oftencompletely illogical in track routing the program hasoptimized the connections, and sacrificed any small

amount of order that may have been put in place bymanual routing. Generally auto routed boards are slightlyharder for a technician to repair or debug, for this reason.Historically, PCBs used to be laid out by drawing or usingstick on paper shaped on Mylar film. The CAD PCB layoutconsists of several layers, for illustration purpose the holes,outline and the component identification layers can becombined into one diagram.


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When designing the layout, one should observe theminimum size (components body length and weight). Beforestarting to design the layout we need all the requiredcomponents in hand so that an accurate assessment ofspace can be made. Other space considerations might alsobe included from case to case of mounted components overthe printed circuit board or to access path of presentcomponents.

It might be necessary to turn some components around toa different angular position so that terminals are closer tothe connections of the components. The scale can be

checked by positioning the components on the squaredpaper. If any connection crosses, then one can reroute toavoid such conditions.

All common or earth lines should be ideally connected to acommon line routed around the perimeter of the layout.

This will act as the ground plane. If possible try to route theouter supply lines around the opposite edge of the layout

through the center. The first set is tearing the circuit toeliminate the crossover without altering the circuit detailsin anyway.

Plan the layout looking at the topside to this board. Firstthis should be translated inversely; later for the etchingpattern large areas are recommended to maintain goodcopper adhesion. It is important to bear in mind alwaysthat copper track width must be according to the

recommended minimum dimensions and allowance mustme made for increased width where termination holes areneeded. From this aspect, it can become little tricky tonegotiate the route to connect small transistors.

There are basically two ways of copper interconnectionpatterns underside the board. The first is the removal ofonly the amount of copper necessary to isolate the

junctions of the components to one another. The second isto make the interconnection pattern looking more


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conventional point wiring by routing uniform width ofcopper from component to component.

SCREEN PRINTING

Line art and text may be printed onto the outer surfaces ofa PCB by screen printing. When space permits the screenprint text can indicate component designators, switchsetting requirements, test points and other features helpfulin assembling, test and servicing the circuit board. Screenprinting is also known as silk screening or, in one sidedPCBs, the red printing. Screen printing or serigraphy is aprintmaking technique that creates a sharp edged imageusing a stencil. A screen printing or serigraph is an imagecreated using this technique. In electronics, the termscreen printing often refers to the writing on a PCB. Screenprinting may also be used in the process of etching copperwiring on the board or computer chips.

PATTERNING (ETCHING)

The vast majority of printed circuit boards are made byadhering layer of copper over the entire substrate,sometimes on both sides, creating a blank PCB then

removing unwanted copper after applying a temporarymask by etching, leaving only the desired copper traces. Afew PCBs are made by adding traces to the bare substrateor a substrate with a very thin layer of copper usually by acomplex process of multiple electroplating steps. There are

three common subtractive methods to remove copperwhich are used for the production of printed circuit boards.


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1. Silkscreen Printing uses etch-resistant inks to protectthe copper foil. Subsequent etching removes the unwantedcopper. Alternatively, the ink may be conductive, printed ona blank non-conductive board. The latter technique is alsoused in manufacture of hybrid circuits.

2. Photo-Engraving uses a photo mask and chemicaletching to remove the copper foil from the substrate. Thephoto mask is usually prepared with photo plotter fromdata produced by a technician using CAM, or computer-aided manufacturing software. Laser-printedtransparencies are typically employed for photo-tools;

however, direct laser imaging techniques are beingemployed to replace photo tools for high resolutionrequirements.

3. PCB Milling uses a two or three-axis mechanical millingsystem to mill away copper foil from the substrate. A PCBmilling machine referred to as a PCB Prototype operates ina similar way to plotter, receiving commands from the host

software that controls the position of the milling head inthe x, y, and if relevant z axis. Data to drive the prototype isextracted from the files generated in PCB design softwareare stored HPGL or Gerber file format.

A PCB as a design on a computer (left) and realized as a

board assembly with populated components (right). The


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board is double sided, with through-hole plating, greensolder resist, and white silkscreen printing. Both surfacemount and through-hole components have been used.

Etching process requires the use of chemicals. Acidresistant dishes and running water supply. Ferric chlorideis mostly used solution but other etching materials such asammonium per sulphate can be used. Nitric acid can beused but in general is not used due to poisonous fumes.

The pattern prepared is glued to the copper surface of theboard using latex tape of adhesive that can be cubed after

use. The pattern is laid firmly on the copper using a verysharp knife to cut around the pattern carefully to removethe paper corresponding to the required copper patternareas. Then apply the resistant solution, which can be akind of ink solution for the purpose of maintain smoothclean outlines as far as possible.

Before going to next stage, check the whole pattern andcross check with the circuit diagram. Check for any free

metal on the copper. The etching bath should be in a glassor enamel disc. If using crystal of ferric chloride, theseshould me thoroughly dissolved in water to the proportionsuggested. There should be 0.5ltrs of water for 125gm ofcrystal.

To prevent the particles of copper hindering furtheretching, agitate the solutions carefully by gently twisting or

rocking the tray.

The board should not be left in the bath a moment longerthan needed o remove just the right amount of copper. Inspite of there being resistive coating, there is no protectionagainst etching away through exposed copper edges. Thisleads to over etching. Have running water ready so thatboard can be removed properly and rinsed. This will haltitching immediately.


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DRILLING

Holes or vias through a PCB are typically drilled with tinydrill bits made of solid tungsten carbide. The drilling isperformed byautomated drilling machines with placementcontrolled by a drill tape or drill file. These computer-generated files are also called numerically controlled drill(NCD) files or "Excellon files". The drill file describes thelocation and size of each drilled hole. These holes are oftenfilled with annular rings to create vias. Vias allow theelectrical and thermal connection of conductors on oppositesides of the PCB.

When very small vias are required, drilling with mechanical

bits is costly because of high rates of wear and breakage. Inthis case, the vias may be evaporated by lasers. Laser-drilled vias typically have an inferior surface finish insidethe hole. These holes are called micro vias.

It is also possible with controlled-depth drilling, laserdrilling, or by pre-drilling the individual sheets of the PCBbefore lamination, to produce holes that connect only some

of the copper layers, rather than passing through the entireboard. These holes are called blind viaswhen they connectan internal copper layer to an outer layer, or buried viaswhen they connect two or more internal copper layers andno outer layers.

The walls of the holes, for boards with 2 or more layers, areplated with copper to form plated-through holesthat

electrically connect the conducting layers of the PCB. Formultilayer boards, those with 4 layers or more, drilling
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typically produces a smearcomprised of the bonding agentin the laminate system. Before the holes can be platedthrough, this smear must be removed by a chemical de-smearprocess, or byplasma-etch.

SOLDER RESIST

Areas that should not be soldered to may be covered with apolymer solder resist (solder mask) coating. The solderresist prevents solder from bridging between conductorsand thereby creating short circuits. Solder resist alsoprovides some protection from the environment.

POPULATING (MOUNTING)

After the printed circuit board (PCB) is completed,electronic components must be attached to form afunctional printed circuit assembly, or PCA (sometimescalled a "printed circuit board assembly" PCBA). In through-hole construction, component leads are inserted in holes.

In surface-mount construction, the components are placedonpadsor landson the outer surfaces of the PCB. In bothkinds of construction, component leads are electrically andmechanically fixed to the board with a molten metal solder.

Often, through-hole and surface-mount construction mustbe combined in a single PCA because some requiredcomponents are available only in surface-mount packages,while others are available only in through-hole packages.

JEDEC guidelines for PCB component placement,soldering, and inspection are commonly used to maintainquality control in this stage of PCB manufacturing.

After the board is populated, the interconnections betweenthe traces and the ICs may be tested by boundary scantechniques. In boundary scan testing, test circuitsintegrated into various ICs on the board form temporary

connections between the PCB traces to test that the ICs are
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mounted correctly. Boundary scan testing requires that allthe ICs to be tested use a standard test configurationprocedure, the most common one being the Joint TestAction Group (JTAG) standard.

There could be damage such as hairline crack on PCB. Ifthere are, then they can be repaired by soldering a shortlink of bare copper wire over the affected part. The mostpopular method of holding all the items is to bring thewires far apart after they have been inserted in theappropriate holes. This will hold the component in positionready for soldering.

Some components will be considerably larger. So it is bestto start mounting the smallest first and progressingthrough to the largest. Before starting, be certain that nofurther drilling is likely to be necessary because access maybe impossible later.

Next will probably be the resistor, small signal diodes or

other similar size components. Some capacitors are alsovery small but it would be best to fit these afterwards.When fitting each group of components mark off each oneon the circuit as it is fitted so that if we have to leave the

job we know where to recommence.

Although transistors and integrated circuits are smallitems, there are good reasons for leaving the soldering of

these until the last step. The main point is that thesecomponents are very sensitive to heat and if subjected toprolonged application of the soldering iron they could beinternally damaged.

All the components before mounting are rubbed withsandpaper so that oxide layer is removed from the tips.Now they are mounted according to the component layout.
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ASSEMBLY AND TESTING

COMPONENTS ASSEMBLY

From the greatest variety of electronic componentsavailable, which runs into thousands of different types it, isoften a perplexing task to know which is right for a given

job. There could be damage such as hairline crack on PCB.If there are, then they can be repaired by soldering a shortlink of bare copper wire over the affected part.

The most popular method of holding all the items is to

bring the wires apart after they have been inserted in theappropriate holes. This will hold the component in positionready for soldering.

Some components will be considerably larger. So it is bestto start mounting the smallest first and progressingthrough to the largest. Before starting, be certain that nofurther drilling is likely to be necessary because access may

be impossible later.

Next will probably be the resistor, small signal diodes orother similar size components. Some capacitors are alsovery small but it would be best to fit these afterwards.When fitting each group of components mark off each oneon the circuit as it is fitted so that if we have to leave the

job we know where to recommence.

Although transistors and integrated circuits are smallitems, there are good reasons for leaving the soldering ofthese until the last step. The main point is that thesecomponents are very sensitive to heat and if subjected toprolonged application of the soldering iron they could beinternally damaged.


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All the components before mounting are rubbed withsandpaper so that oxide layer is removed from the tips.Now they are mounted according to the component layout.

PRECAUTIONS FOR SOLDERING

1. The wattage of soldering iron should be selected asminimum as permissible for that soldering place.

2. We should select the soldering wire with proper ratio oflead (Pb) and tin (Sn) to provide the suitable meltingtemperature.

3. Proper amount of good quality flux must be applied onthe soldering point to avoid dry soldering.

APPLICATIONS


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1) Having multiple extension telephones at home is very

convenient. You can make or receive phone calls practically

anywhere in the house.

This circuit disables other telephones connected to the

phone line whenever a telephone (either the master or any

extension phone) is in use.

The circuit is guaranteed to keep the phone conversation

private

2). It can be used to prevent, some other unauthorized

person to hear the conversation in our parallel telephone

network.

3). This circuit system is very compact and easy to install

at small level organization

4). This circuit gives privacy for both, incoming and

outgoing call.

MERITS


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1. This is a low cost circuit.

2. This circuit is highly efficient.

3. This circuit has a simple working architecture.

4. It is not bulky therefore can be installed easilyanywhere.

5. This circuit has a simple circuitry.

6.The circuit does not need an external power supply. It

gets its power from the telephone line.

LIMITATIONS

1. The only limitation of this particular circuit is that when

any of the telephone is dead because of any technical

reason, the whole network connect to extension switch is

failed.

FUTURE SCOPE


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Having multiple extension telephones at home is very

convenient. You can make or receive phone calls practically

anywhere in the house. This circuit disables other

telephones connected to the phone line whenever a

telephone (either the master or any extension phone) is in

use. The circuit is guaranteed to keep the phone

conversation private. The circuit does not need an external

power supply.

It gets its power from the telephone line. The no-load

voltage at the telephone line, when the telephone handset is

on-hook, is around 48 volts. However, when the handset

is off-hook, terminal voltage drops to between 5 volts and

15 volts.

With some more modification the overall performance of

this circuit can be enhanced and can be use for some more

complex level.


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BIBLIOGRAPHY

We express our sincere gratitude towards the following

sources for helping us out immensely in the project.

1. Electronics for U.

2. www.electronicsforu.com

3. www.national.com

4. www.wikipedia.org5. Express PCB (software).
http://www.electronicsforu.com/http://www.national.com/http://www.wikipedia.org/http://www.wikipedia.org/http://www.national.com/http://www.electronicsforu.com/

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