Project Report

MAJOR PROJECT REPORT ON TELEMETRY

SUBMITTED IN THE PARTIAL FULLFILLMENT OF THE REQUIREMENT OF THE AWARD OF

THE DEGREE OF BACHELOR OF TECHNOLOGY

ELECTRONICS & COMMUNICATION ENGINEERING

UNDER THE GUIDANCE OF ER. ASHISH JASUJA(PROJECT INCHARGE)

SUBMITTED BY:- GAURAV SINGH(1404226) RAJAT KAUSHIK(1404263) MANISH DESWAL(1404282)

DEPTT OF ELECTRONICS & COMMUNICATION SHRI KRISHAN INSTITUTE OF ENGG. & TECH.

KURUKSHETRA(136118) SESSION(2004-2008)

DEPARTMENT OF ELECTRONICS AND COMMUNICATION SHRI KRISHAN INSTITUTE OF ENGG. & TECH. KURUKSHETRA. SESSION(2004-2008)

TO WHOM SO EVER IT MAY CONCERN

THIS IS TO CERTIFIED THAT PROJECT ENTITLED “TELEMETRY” MADE

BY GAURAV SINGH (1404226), RAJAT KAUSHIK(1404263),

MANISH DESWAL(1404282) FINAL YEAR STUDENTS IN ELECTRONICS AND

COMMUNICATION ENGG. IN THE PARTIAL FULLFILLMENT OF THE

REQUIREMENT FOR THE AWARD OF THE DEGREE OF BACHELOR OF

TECHNOLOGY IS A RECORD OF BONAFIDE WORK CARRIED OUT BY

THEM UNDER MY GUIDANCE AND SUPERVISION. THEY COMPLITED THE

WORK EFFICIENTLY AND SINCERELY. THEIR CONDUCT DURING THE

PROJECT WAS FOUND VERY GOOD.

ER. ASHISH JASUJA (PROJECT INCHARGE.)

ACKNOWLEDGEMENT

WHILE EXPERIENCING OUR GRATITUDE AND INDEBTEDNESS TO ALL

THOSE TEACHERS AND LAB TECHNICIANS OF SHRI KRISHAN INSTITUTE

OF ENGG. & TECH WHO HAVE GIVEN THEIR VALUABLE TIME, FOR

RENDERING US THEIR NEEDY SERVICES, GUIDELINES DURING THE

COURSE OF IMPARTING US IN MALOR PROJECT. WE WOULD ALSO LIKE TO THANK OUR NOBLE AND BENEVOLENT

TEACHERS , ER. ASHISH JASUJA (Project Incharge) & MR. BALVINDER

WHO HAVE INSPIRED US FOR ACHIEVING OUR GOAL BY GIVING THEIR

PROPER GUIDANCE & CO-OPERATION DURING THE MAJOR PROJECT.

ABOVE ALL WE LIKE TI THANK THE ALMIGHTY GOD WITH THOSE

BLESSING ONLY WE HAVE BEEN ABLE TO COMPLETE OUR PROJECT

SUCCESSFULLY.

PLACE : KURUKSHETRA GAURAV SINGH(1404226) RAJAT KAUSHIK(1404263) MANISH DESWAL(1404282)

CONTENTS TOPICS PAGE NO.

1. Telemetry. 1-4

2. Project Intro & Theory. 5-10

3. PCB Fabrication. 11-17

4. Component Description. a) Relay. 18-23

b) Resistor. 24-28

c) Transistor. 29-34

d) Capacitor. 35-37

e) Diode. 38-44

f) 7-Segment Display. 45-49

g) Transformer. 50-53

5. Soldering. 54-61

6. References. 62 7. Appendix 63

a) Photographs of circuit b) Datasheets of IC’s

TelemetryTelemetry is a technology that allows the remote measurement and reporting of information of interest to the system designer or operator. The word is derived from Greek roots tele = remote, and metron = measure. Systems that need instructions and data sent to them in order to operate require the counterpart of telemetry, telecommand.

ExplanationTelemetry typically refers to wireless communications (i.e. using a radio system to implement the data link), but can also refer to data transferred over other media, such as a telephone or computer network or via an optical link.

Applications

AgricultureGrowing crops has become high-tech business. Most activities related to healthy crops and good yields depend on the timely availability of weather and soil data. Therefore wireless weather stations play a major role in disease prevention and precision irrigation. These stations transmit back to a base station the major parameters needed for good decisions: air temperature and relative humidity, precipitation and leaf wetness data

(needed for disease prediction models), solar radiation and wind speed (needed to calculate evapotranspiration), and sometimes also soil moisture, crucial for proper irrigation decisions in order to understand the progress of water into the soil and towards the roots.

Because local micro-climates can vary significantly, such data needs to

come from right within the crop. Monitoring stations usually transmit data back by terrestrial radio though occasionally satellite systems are used. Solar power is often employed to make the station independent from local infrastructure.

Water ManagementTelemetry has become indispensable for water management applications, including water quality and stream gauging functions. Major applications include AMR (Automatic Meter Reading), groundwater monitoring, leak detection in distribution pipelines and equipment surveillance. Having data available in almost real time allows quick reactions to occurrences in the field.

Defense, space and resource exploration systemsTelemetry is an enabling technology for large complex systems such as missiles, RPVs, spacecraft, oil rigs and chemical plants because it allows automatic monitoring, alerting, and record-keeping necessary for safe, efficient operations.

Space agencies such as NASA, ESA, and other agencies use telemetry/telecommand systems to collect data from operating spacecraft and satellites.

Telemetry is vital in the development phase of missiles, satellites and aircraft because the system might be destroyed after/during the test. Engineers need critical system parameters in order to analyze (and improve) the performance of the system. Without telemetry, these data would often be unavailable.

Enemy intelligenceTelemetry was a vital source of intelligence for the US and UK when

Soviet missiles were tested. For this purpose, the US operated a listening post in Iran. Eventually, the Soviets discovered this kind of US intelligence gathering and encrypted their telemetry signals of missile tests. Telemetry was a vital source for the Soviets who would operate listening ships in Cardigan Bay to eavesdrop on the UK missile tests carried out there.

Motor racingTelemetry has been a key factor in modern motor racing. Engineers are able to interpret the vast amount of data collected during a test or race, and use that to properly tune the car for optimum performance.

Systems used in some series, namely Formula One, have become advanced to the point where the potential lap time of the car can be calculated and this is what the driver is expected to meet. Some examples of useful measurements on a race car include accelerations (G forces) in 3 axes, temperature readings, wheel speed, and the displacement of the suspension. In Formula 1, the driver inputs are also recorded so that the team can assess driver performance and, in the case of an accident, the FIA can determine or rule out driver error as a possible cause.

In addition, there exist some series where "two way" telemetry is allowed. Two way telemetry suggests that engineers have the ability to update calibrations on the car in real time, possibly while it is out on the track. In Formula 1, two-way telemetry surfaced in the early nineties from TAG electronics, and consisted of a message display on the dashboard which the team could update. Its development continued until May 2001, at which point it was first allowed on the cars. By 2002 the teams were able to change engine mapping and deactivate particular engine sensors from the pits while the car was on track. For the 2003 season, the FIA banned two-way telemetry from Formula 1, however the technology still exists and could eventually find its way

into other forms of racing or road cars.

In addition to that telemetry has also been applied to the use of Yacht racing. The technology was applied to the Oracle's USA-76.

INTRODUCTION

TEMPERATURE can be measured with the help of a commercially available like AD590 and LM337. Here’s a simple temperature sensor built around a transistor (used as a diode) and a single chip analog -to- digital converter ADC cum 3 ½-digit LED driver IC7107. Apart from displaying the temperature with a resolution of 0.1 degree C , this circuit provides for temperature based relay activation for controlling heaters, coolers etc. The trip-point temperature, set for activating the relay, can also be displayed with simple flick of a switch. The circuit can be calibrated to have an accuracy of + 2 degree C with an operating range of -25 degree C to 125 degree C.

CIRCUIT OPERATION :

Fig. 1 shows the circuit diagram of the temperature measurement system –using transistor T2 as a sensor. The base and collector of T2 have been shorted so that it is reduced to a diode. The forward voltage drop of the diode changes with temperatures. The rate of change in voltage drop is around -2mV/0C. Thus, the forward voltage of the diode changes with temperature. This principle is used in this circuit to measure temperature with reasonable accuracy.

A small signal transistor provides the best characteristics suitable for use as a temperature sensor. As a matter of fact, any small signal transistor can be used in place of the BC 547 in the circuit with similar results. The base-emitter diode is used as the sensing element in this circuit. This diode ahs a nominal forward voltage drop of around 0.6V at room temperature. The diode is forward biased with a current of 100µA, derived from the internal reference of ADC ICL 7107. The Voltage drop of around 2mV for every 0Crise in temperature.

This voltage is connected to the IN LO input of the ICL 7104CPL. (ICL7107CPL is an LSI ADC chip with necessary circuitry built into it, so a simple 3½ digit ADC can be implemented with just a handful of components . ICL 7107 CPL is the LED –driver of popular ICL 7106 , which is commonly used in low cost LCD digital multimeters )The IN HI Signal is connected to a trimpot , which is set such that at 00C the potential difference between in HI and IN LO is 0V.

With increase in temperature, the voltage drop in the base emitter diode of transistor reduces and hence the potential difference between in HI and 1N LO increase. The ADC, as per following relationship, converts this potentials difference into a digital value :

(IN HI-IN LO) / (REF HI –REF LO) * 1000 counts Where REF HI and REF LO are the voltage levels as pins 36 and 35 of ICI , respectively. A reference voltage is critical in all analogue to digital conversions. The ICL 7107 CPL has an internal band gap reference that provides as stable output of around 2.8V , as measured from the positive voltage rail (+5V). The analog common (AC) is used for all the analog circuitry. Thus, at nay point of time , the potential between the AC and the +5V rail is maintained at a constant 2.8V by the internal reference . Trimpot VR1 is connected between the AC and +5V sets the reference voltage for the analogue –to-digital convesion (REF H1-REF LO).

ADC PARAMETERS :The ADC requires a fairly stable clock, which is

generated by using a simple RC combination. With the components shown across pins 38 and 39 ICI in the circuit, a clock frequency of about 48kHZ. is obtained . For all ranges of the frequency, a 100 K resistor is recommended and the capacitor value is calculated from the equation f= 0.45 /RC. This gives a conversion rate of 3 readings per second. Since this is an integrating type ADC, an integrating capacitor (C4, 0.22µF) is used here. As the accuracy of the ADC greatly depends on the type of the capacitor, the capacitor must be low dielectric.

Absorption, such as polypropylene, polystyrene, polyester capacitor will provide erroneous results. The 47K resistor (R4) sets the integrating current. The auto-zero capacitor has some influence on the noise of the system. For 200m V full scale, where low noise is very important, a 0.47µF polyester capacitor (C3) is recommended. A 0.1 µF polyester capacitor (C1) is used for the internal reference circuitry. Since the ADC output section switches large currents, a 0.1 µF ceramic disk decoupling capacitor is connected close to lC1.

The ADC has 23 outputs that directly interface with LTS 542 common anode 7-segment displays (DIS1 to DIS 3) and ½ digit common anode display (DIS4). You can use LTS 542 by using its segment b,c and g in place of ½ digit display with a b and POL (MINUS) segments, respectively . The result of the conversion along with polarity is displayed on these four 7 segment displays.

CALIBRATION :After assembling the circuit, dip sensor transistor T2 in

ice-cold water at 00C , taking care not to short the base and emitter leads of the transistor, and adjust trimpot VR2 until the display reads 00.0 . After this dip sensor transistor T2 in boiling water (1000c) and adjust trimpot VR1 such that the display reads 100.00

Since the sensor diode takes some time to settle to the final temperature, the sensor should be kept in ice or boiling water for at least 10 to 20 seconds before adjusting VR1 or VR2 . Once calibration is done the circuit is ready to measure the temperature of the desired medium.

RELAY CONTROLLER :This circuit can be used to control a heater (shown as

load) using the relay contacts , The simple voltage comparator circuit built around LM 311 (IC2) compares the temperature measured by sensor transistor T2 and trip-point voltage set by VR3 . if the actual temperatures measured by the sensor is less than the trip point, the relay remains energized . On reaching the trip point, the comparator switches off the relay, which, in turn, switches off the heater. To monitor the trip point temperature on display, press push –to-changeover switch S. This shifts switch S connection from position A to position B and connects the ADC input pin 30 of ICI (INLO) to the trip point voltage set by VR3. The trip point temperature is now displayed on the four 7 segment displays (DI-SI to DIS4) . On releasing switch S, the ADC input pin 30 (INLO) returns to position A, and now the ADC normally displays the sensor temperature. A positive feedback is used in the comparator to produce clean transitions at the output.

BUZZER SYSTEM

A Buzzer system in also employed with the CKT, as soon as the temp reaches the max pt.& relay is operated & cut the heater supply a Buzzer system get activated on the Panel using IC Um 3561,which is used to produce different type of sound, simple SPDT switch is also employed to switch off the Buzzer, this buzzer in placed outside the heating chamber but we want to activate the Buzzer at the control room also there for we send the IC Um 3561 signal through Radio wave with the help of a transmitter which operate at 96MHz.. These signal are received by the Radio receiver (KIT) which

has IC CX A1619 & IC CTC 810, IC CXA, 1619 BS is used here as an receiver which demodulate the sound signal . The signal received here are very weak so it is to amplified which is done with the help of IC CTC 810.The O/P is obtained on the speaker hence we get the same O/P at both side with the help of radio waves.

CAUTION :1 To ensure correct and accurate operation, select

appropriate capacitors for the ADC.2 Trimpots VR1 and VR2 must be of low –drift type.

VR3 can be wire-wound type which will greatly improve the stability of the circuit.

3 Take care while handling ICL 7107 CPL, as it is susceptible to electrostatic charge. Always use a shielded cable from the sensor to the PCB.

4 Analog common (AC) and digital ground (GND) should not be connected together.

5 The load currents should be within the relay contact ratings.

6 The sensors must never be kept floating in air if the air temperature is to be measured . Otherwise the sensor will not give a stable output, leading to excessive rolling of ADC outputs. To achieve a sable ouput attach the sensor to a metallic device, which in turn, may be exposed to the medium whose temperature is to be measured.

Printed circuit board

PCB Layout ProgramA printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, or traces, etched from copper sheets laminated onto a non-conductive substrate. Alternative names are printed wiring board (PWB),and etched wiring board. A PCB populated with electronic components is a printed circuit assembly (PCA), also known as a printed circuit board assembly (PCBA).

PCBs are rugged, inexpensive, and can be highly reliable. They require much more layout effort and higher initial cost than either wire-wrapped or point-to-point constructed circuits, but are much cheaper and faster for high-volume production.

Much of the electronics industry's PCB design, assembly, and quality control needs are set by standards that are published by the IPC organization.

Manufacturing

Materials

Conducting layers are typically made of thin copper foil. Insulating materials have a wider scale: phenolic paper, glass fibre and different plastics are commonly used. Usually PCB factories use prepregs (short for preimpregnated), which are a combination of glass fibre mat, nonwoven material and resin. Copper foil and prepreg are typically laminated together with epoxy resin. Well known prepreg materials used in the PCB industry are FR-2 (Phenolic cotton paper), FR-3 (Cotton paper and epoxy), FR-4 (Woven glass and epoxy), FR-5 (Woven glass and epoxy), FR-6 (Matte glass and polyester), G-10 (Woven glass and epoxy), CEM-1 (Cotton paper and epoxy), CEM-2 (Cotton paper and epoxy), CEM-3 (Woven glass and epoxy), CEM-4 (Woven glass and epoxy), CEM-5 (Woven glass and polyester). Other widely used materials are polyimide, teflon and some ceramics.

A PCB as a design on a computer (left) and realized as a board assembly with populated components (right). The board is double sided, with through-hole plating, green solder resist, and white silkscreen printing. Both surface mount and through-hole components have been used.

Patterning (etching)The vast majority of printed circuit boards are made by bonding a layer of copper over the entire substrate, sometimes on both sides, (creating a "blank PCB") then removing unwanted copper after applying a temporary mask (eg. by etching), leaving only the desired copper traces. A few PCBs are made by adding traces to the bare substrate (or a substrate with a very thin layer of copper) usually by a complex process of multiple electroplating steps.

There are three common "subtractive" methods (methods that remove copper) used for the production of printed circuit boards:

1. Silk screen printing uses etch-resistant inks to protect the copper foil. Subsequent etching removes the unwanted copper. Alternatively, the ink may be conductive, printed on a blank (non-conductive) board. The latter technique is also used in the manufacture of hybrid circuits.

2. Photoengraving uses a photomask and chemical etching to remove the copper foil from the substrate. The photomask is usually prepared with a photoplotter from data produced by a technician using CAM, or computer-aided manufacturing software. Laser-printed transparencies are typically employed for phototools; however, direct laser imaging techniques are being employed to replace phototools for high-resolution requirements.

3. PCB milling uses a two or three-axis mechanical milling system to mill away the copper foil from the substrate. A PCB milling machine (referred to as a 'PCB Prototyper') operates in a similar way to a plotter, receiving commands from the host software that control the position of the milling head in the x, y, and (if relevant) z axis.

Data to drive the Prototyper is extracted from files generated in PCB design software and stored in HPGL or Gerber file format.

"Additive" processes also exist. The most common is the "semi-additive" process. In this version, the unpatterned board has a thin layer of copper already on it. A reverse mask is then applied. (Unlike a subtractive process mask, this mask exposes those parts of the substrate that will eventually become the traces.) Additional copper is then plated onto the board in the unmasked areas; copper may be plated to any desired weight. Tin-lead or other surface platings are then applied. The mask is stripped away and a brief etching step removes the now-exposed original copper laminate from the board, isolating the individual traces.

The additive process is commonly used for multi-layer boards as it facilitates the plating-through of the holes (to produce conductive vias) in

the circuit board.

LaminationSome PCBs have trace layers inside the PCB and are called multi-layer PCBs. These are formed by bonding together separately etched thin boards.

DrillingHoles, or vias, through a PCB are typically drilled with tiny drill bits made of solid tungsten carbide. The drilling is performed by automated drilling machines with placement controlled 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 the location and size of each drilled hole.

When very small vias are required, drilling with mechanical bits is costly because of high rates of wear and breakage. In this case, the vias may be evaporated by lasers. Laser-drilled vias typically have an inferior surface finish inside the hole. These holes are called micro vias.

It is also possible with controlled-depth drilling, laser drilling, or by pre-drilling the individual sheets of the PCB before lamination, to produce holes that connect only some of the copper layers, rather than passing through the entire board. These holes are called blind vias when they connect an internal copper layer to an outer layer, or buried vias when they connect two or more internal copper layers and no outer layers.

The walls of the holes, for boards with 2 or more layers, are plated with copper to form plated-through holes that electrically connect the conducting layers of the PCB. For multilayer boards, those with 4 layers or more, drilling typically produces a smear comprised of the bonding agent in the laminate system. Before the holes can be plated through, this smear must be removed by a chemical de-smear process, or by

plasma-etch.

Exposed conductor plating and coatingThe places to which components will be mounted are typically plated, because bare copper oxidizes quickly, and therefore is not readily solderable. Traditionally, any exposed copper was plated with solder by hot air solder levelling (HASL).

This solder was a tin-lead alloy, however new solder compounds are now used to achieve compliance with the RoHS directive in the EU, which restricts the use of lead. Other platings used are OSP (organic surface protectant), immersion silver (IAg), immersion tin, electroless nickel with immersion gold coating (ENIG), and direct gold. Edge connectors, placed along one edge of some boards, are often gold plated.

Electrochemical migration (ECM) is the growth of conductive metal filaments on or in a printed circuit board (PCB) under the influence of a DC voltage bias.

Solder resistAreas that should not be soldered to may be covered with a polymer solder resist (solder mask) coating. The solder resist prevents solder from bridging between conductors and thereby creating short circuits. Solder resist also provides some protection from the environment.

Screen printingLine art and text may be printed onto the outer surfaces of a PCB by screen printing. When space permits, the screen print text can indicate component designators,switch setting requirements, test points, and

other features helpful in assembling, testing, and servicing the circuit board.

Screen print is also known as the silk screen, or, in one sided PCBs, the red print.

Lately some digital printing solutions have been developed to substitute the traditional screen printing process. This technology allows printing variable data onto the PCB, including serialization and barcode information for traceability purposes.

Protection and packagingPCBs intended for extreme environments often have a conformal coat, which is applied by dipping or spraying after the components have been soldered. The coat prevents corrosion and leakage currents or shorting due to condensation. The earliest conformal coats were wax. Modern conformal coats are usually dips of dilute solutions of silicone rubber, polyurethane, acrylic, or epoxy. Some are engineering plastics sputtered onto the PCB in a vacuum chamber.

Many assembled PCBs are static sensitive, and therefore must be placed in antistatic bags during transport. When handling these boards, the user must be earthed; failure to do this might transmit an accumulated static charge through the board, damaging or destroying it. Even bare boards are sometimes static sensitive. Traces have gotten so fine that it's quite possible to blow an etch off the board (or change its characteristics) with a static charge. This is especially true on non-traditional PCBs such as MCMs and microwave PCBs.

Relay

Automotive style miniature relayA relay is an electrical switch that opens and closes under the control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts. It was invented by Joseph Henry in 1835. Because a relay is able to control an output circuit of higher power than the input circuit, it can be considered to be, in a broad sense, a form of an electrical amplifier.

Operation

When a current flows through the coil, the resulting magnetic field attracts an armature that is mechanically linked to a moving contact. The movement either makes or breaks a connection with a fixed contact. When the current to the coil is switched off, the armature is returned by a force approximately half as strong as the magnetic force to its relaxed position. Usually this is a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing.

If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a

spike of voltage and might cause damage to circuit components. Some automotive relays already include that diode inside the relay case. Alternatively a contact protection network, consisting of a capacitor and resistor in series, may absorb the surge.

If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle.[1]

By analogy with the functions of the original electromagnetic device, a solid-state relay is made with a thyristor or other solid-state switching device. To achieve electrical isolation an optocoupler can be used which is a light-emitting diode (LED) coupled with a photo transistor.

Overload protection relayOne type of electric motor overload protection relay is operated by a heating element in series with the electric motor . The heat generated by the motor current operates a bi-metal strip or melts solder, releasing a spring to operate contacts. Where the overload relay is exposed to the same environment as the motor, a useful though crude compensation for motor ambient temperature is provided.

Pole & Throw

Circuit symbols of relays. "C" denotes the common terminal in SPDT and DPDT types.

Since relays are switches, the terminology applied to switches is also applied to relays. A relay will switch one or more poles, each of whose contacts can be thrown by energizing the coil in one of three ways:

Normally-open (NO) contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. It is also called a Form A contact or "make" contact.

Normally-closed (NC) contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. It is also called a Form B contact or "break" contact.

Change-over, or double-throw, contacts control two circuits: one normally-open contact and one normally-closed contact with a common terminal. It is also called a Form C contact or "transfer" contact. If this type of contact utilizes a "make before break" functionality, then it is called a Form D contact.

The following types of relays are commonly encountered:

SPST - Single Pole Single Throw. These have two terminals which

can be connected or disconnected. Including two for the coil, such a relay has four terminals in total. It is ambiguous whether the pole is normally open or normally closed. The terminology "SPNO" and "SPNC" is sometimes used to resolve the ambiguity.

SPDT - Single Pole Double Throw. A common terminal connects to either of two others. Including two for the coil, such a relay has five terminals in total.

DPST - Double Pole Single Throw. These have two pairs of terminals. Equivalent to two SPST switches or relays actuated by a single coil. Including two for the coil, such a relay has six terminals in total. It is ambiguous whether the poles are normally open, normally closed, or one of each.

DPDT - Double Pole Double Throw. These have two rows of change-over terminals. Equivalent to two SPDT switches or relays actuated by a single coil. Such a relay has eight terminals, including the coil.

QPDT - Quadruple Pole Double Throw. Often referred to as Quad Pole Double Throw, or 4PDT. These have four rows of change-over terminals. Equivalent to four SPDT switches or relays actuated by a single coil, or two DPDT relays. In total, fourteen terminals including the coil.

ApplicationsRelays are used:

to control a high-voltage circuit with a low-voltage signal, as in some types of modems.

to control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile.

to detect and isolate faults on transmission and distribution lines by

opening and closing circuit breakers (protection relays).

ResistorA resistor is a two-terminal electrical or electronic component that opposes an electric current by producing a voltage drop between its terminals in accordance with Ohm's law: The electrical resistance is equal to the voltage drop across the resistor divided by the current through the resistor while the temperature remains the same. Resistors are used as part of electrical networks and electronic circuits.

Identifying resistorsMost axial resistors use a pattern of colored stripes to indicate resistance. Surface-mount resistors are marked numerically. Cases are usually brown, blue, or green, though other colors are occasionally found such as dark red or dark grey.

One can also use a multimeter or ohmmeter to test the values of a resistor.

Four-band axial resistorsElectronic color code

Four-band identification is the most commonly used color coding scheme on all resistors. It consists of four colored bands that are painted around the body of the resistor. The scheme is simple: The first two numbers are the first two significant digits of the resistance value, the third is a multiplier, and the fourth is the tolerance of the value.

(e.g. green-blue-yellow red : 56 x (10^4) ohms = 56 x 10000 ohms = 560 kohms ±2%). Each color corresponds to a certain number, shown in the chart below. The tolerance for a 4-band resistor will be 1%, 5%, or 10%.

Color1st

band2nd

band3rd band

(multiplier)4th band

(tolerance)Temp.

Coefficient

Black 0 0 ×100    

Brown 1 1 ×101 ±1% (F) 100 ppm

Red 2 2 ×102 ±2% (G) 50 ppm

Orange 3 3 ×103   15 ppm

Yellow 4 4 ×104   25 ppm

Green 5 5 ×105 ±0.5% (D)  

Blue 6 6 ×106 ±0.25% (C)  

Violet 7 7 ×107 ±0.1% (B)  

Gray 8 8 ×108 ±0.05% (A)  

White 9 9 ×109    

Gold     ×10-1 ±5% (J)  

Silver     ×10-2 ±10% (K)  

None       ±20% (M)  

5-band axial resistors5-band identification is used for higher precision (lower tolerance) resistors (1%, 0.5%, 0.25%, 0.1%), to notate the extra digit. The first three bands represent the significant digits, the fourth is the multiplier, and the fifth is the tolerance. 5-band standard tolerance resistors are sometimes encountered, generally on older or specialized resistors. They can be identified by noting a standard tolerance color in the 4th band. The 5th band in this case is the temperature coefficient

Surface mounted resistors are printed with numerical values in a code related to that used on axial resistors. Standard-tolerance Surface Mount Technology (SMT) resistors are marked with a three-digit code, in which the first two digits are the first two significant digits of the value and the third digit is the power of ten (the number of zeroes). For example:

"334" = 33 × 10,000 ohms = 330 kiloohms"222" = 22 × 100 ohms = 2.2 kiloohms"473" = 47 × 1,000 ohms = 47 kiloohms"105" = 10 × 100,000 ohms = 1 megaohm

Resistances less than 100 ohms are written: 100, 220, 470. The final zero represents ten to the power zero, which is 1.

For example:

"100" = 10 × 1 ohm = 10 ohms"220" = 22 × 1 ohm = 22 ohms

Sometimes these values are marked as "10" or "22" to prevent a mistake.

Resistances less than 10 ohms have 'R' to indicate the position of the decimal point (radix point). For example:

"4R7" = 4.7 ohms"0R22" = 0.22 ohms"0R01" = 0.01 ohms

Precision resistors are marked with a four-digit code, in which the first three digits are the significant figures and the fourth is the power of ten. For example:

"1001" = 100 × 10 ohms = 1 kiloohm"4992" = 499 × 100 ohms = 49.9 kiloohm"1000" = 100 × 1 ohm = 100 ohms

"000" and "0000" sometimes appear as values on surface-mount zero-ohm links, since these have (approximately) zero resistance.

Power dissipationThe power dissipated by a resistor is the voltage across the resistor multiplied by the current through the resistor:

All three equations are equivalent. The first is derived from Joule's law, and other two are derived from that by Ohm's Law.

Carbon compositionCarbon composition resistors consist of a solid cylindrical resistive element with embedded wire leadouts or metal end caps to which the leadout wires are attached, which is protected with paint or plastic.

The resistive element is made from a mixture of finely ground (powdered) carbon and an insulating material (usually ceramic). The mixture is held together by a resin. The resistance is determined by the ratio of the fill material (the powdered ceramic) and the carbon. Higher concentrations of carbon, a weak conductor, result in lower resistance. Carbon composition resistors were commonly used in the 1960s and earlier, but are not so popular for general use now as other types have better specifications, such as tolerance, voltage dependence, and stress (carbon composition resistors will change value when stressed with over-voltages).

TransistorA transistor is a semiconductor device, commonly used to amplify or switch electronic signals. The transistor is the fundamental building block of computers, and all other modern electronic devices. Some transistors are packaged individually but most are found in integrated circuits.

Introduction

An electrical signal can be amplified by using a device that allows a small current or voltage to control the flow of a much larger current. Transistors are the basic devices providing control of this kind. Modern transistors are divided into two main categories: bipolar junction transistors (BJTs) and field effect transistors (FETs). Applying current in BJTs and voltage in FETs between the input and common terminals increases the conductivity between the common and output terminals, thereby controlling current flow between them. The characteristics of a

transistor depend on its type.

The term "transistor" originally referred to the point contact type, which saw very limited commercial application, being replaced by the much more practical bipolar junction types in the early 1950s. Today's most widely used schematic symbol, like the term "transistor", originally referred to these long-obsolete devices.[1]

In analog circuits, transistors are used in amplifiers, (direct current amplifiers, audio amplifiers, radio frequency amplifiers), and linear regulated power supplies.

Transistors are also used in digital circuits where they function as electronic switches, but rarely as discrete devices, almost always being incorporated in monolithic Integrated Circuits. Digital circuits include logic gates, random access memory (RAM), microprocessors, and digital signal processors (DSPs).

AdvantagesThe key advantages that have allowed transistors to replace their vacuum tube predecessors in most applications are:

Small size and minimal weight, allowing the development of miniaturized electronic devices.

Highly automated manufacturing processes, resulting in low per-unit cost.

Lower possible operating voltages, making transistors suitable for small, battery-powered applications.

No warm-up period for cathode heaters required after power application.

Lower power dissipation and generally greater energy efficiency. Higher reliability and greater physical ruggedness. Extremely long life. Some transistorized devices produced more

than 30 years ago are still in service. Complementary devices available, facilitating the design of

complementary-symmetry circuits, something not possible with

vacuum tubes. Though in most transistors the junctions have different doping

levels and geometry, some allow bidirectional current

Ability to control very large currents, as much as several hundred amperes.

Insensitivity to mechanical shock and vibration, thus avoiding the problem of microphonics in audio applications.

More sensitive than the hot and macroscopic tubes

Disadvantages Silicon transistors do not operate at voltages higher than about 1

kV, SiC go to 3 kV. The electron mobility is higher in a vacuum, so that high power,

high frequency operation is easier in tubes.

Types

PNP P-channel

NPN N-channel

BJT JFET

BJT and JFET symbols

Bipolar junction transistorThe bipolar junction transistor (BJT) was the first type of transistor to be mass-produced. Bipolar transistors are so named because they conduct by using both majority and minority carriers. The three terminals of the BJT are named emitter, base and collector. Two p-n junctions exist inside a BJT: the base/emitter junction and base/collector junction. "The [BJT] is useful in amplifiers because the currents at the emitter and collector are controllable by the relatively small base current." In an NPN transistor operating in the active region, the emitter-base junction is forward biased, and electrons are injected into the base region. Because the base is narrow, most of these electrons will diffuse into the reverse-biased base-collector junction and be swept into the collector; perhaps one-hundredth of the electrons will recombine in the base, which is the dominant mechanism in the base current. By controlling the number of electrons that can leave the base, the number of electrons entering the collector can be controlled.

Unlike the FET, the BJT is a low–input-impedance device. Also, as the base–emitter voltage (Vbe) is increased the base–emitter current and hence the collector–emitter current (Ice) increase exponentially according to the Shockley diode model and the Ebers-Moll model. Because of this exponential relationship, the BJT has a higher transconductance than the FET.

Bipolar transistors can be made to conduct by exposure to light, since absorption of photons in the base region generates a photocurrent that acts as a base current; the collector current is

approximately beta times the photocurrent.

Devices designed for this purpose have a transparent window in the package and are called phototransistors.

Semiconductor materialThe first BJTs were made from germanium (Ge) and some high power types still are. Silicon (Si) types currently predominate but certain advanced microwave and high performance versions now employ the compound semiconductor material gallium arsenide (GaAs) and the semiconductor alloy silicon germanium (SiGe). Single element semiconductor material (Ge and Si) is described as elemental.

CapacitorA capacitor is an electrical/electronic device that can store energy in the electric field between a pair of conductors (called "plates"). The process of storing energy in the capacitor is known as "charging", and involves electric charges of equal magnitude, but opposite polarity, building up on each plate.

Capacitors are often used in electric and electronic circuits as energy-storage devices. They can also be used to differentiate between high-frequency and low-frequency signals. This property makes them useful in electronic filters.

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

Diagram of a parallel-plate capacitor

A capacitor consists of two conductive electrodes, or plates, separated by a dielectric.

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

In SI units, a capacitor has a capacitance of one farad when one coulomb of charge is stored due to one volt applied potential difference across the plates. Since the farad is a very large unit, values of capacitors are usually expressed in microfarads (µF), nanofarads (nF), or picofarads (pF).

Stored energy

As opposite charges accumulate on the plates of a capacitor due to the separation of charge, a voltage develops across the capacitor due to the electric field of these charges. Ever-increasing work must be done against this ever-increasing electric field as more charge is separated. The energy (measured in joules, in SI) stored in a capacitor is equal to the amount of work required to establish the voltage across the capacitor, and therefore the electric field. The energy stored is given by:

where V is the voltage across the capacitor.

The maximum energy that can be (safely) stored in a particular capacitor is limited by the maximum electric field that the dielectric can withstand before it breaks down. Therefore, capacitors made with the same dielectric have about the same maximum energy density (joules of energy per cubic meter), if the dielectric volume dominates the total volume.

Diode

Figure 1: Closeup of the image below, showing the square shaped semiconductor crystal

In electronics, a diode is a two-terminal device (except that thermionic

diodes may also have one or two ancillary terminals for a heater). Diodes have two active electrodes between which the signal of interest may flow, and most are used for their unidirectional current property. The varicap diode is used as an electrically adjustable capacitor.

The directionality of current flow most diodes exhibit is sometimes generically called the rectifying property. The most common function of a diode is to allow an electric current to pass in one direction (called the forward biased condition) and to block it in the opposite direction (the reverse biased condition).. Real diodes do not display such a perfect on-off directionality but have a more complex non-linear electrical characteristic, which depends on the particular type of diode technology. Diodes also have many other functions in which they are not designed to operate in this on-off manner.

Today the most common diodes are made from semiconductor materials such as silicon or germanium.

Semiconductor diodesMost modern diodes are based on semiconductor p-n junctions. In a p-n diode, conventional current can flow from the p-type side (the anode) to the n-type side (the cathode), but cannot flow in the opposite direction. Another type of semiconductor diode, the Schottky diode, is formed from the contact between a metal and a semiconductor rather than by a p-n junction.

Current–voltage characteristicA semiconductor diode's current–voltage characteristic, or I–V curve, is related to the transport of carriers through the so-called depletion layer or depletion region that exists at the p-n junction between differing

semiconductors. When a p-n junction is first created, conduction band (mobile) electrons from the N-doped region diffuse into the P-doped region where there is a large population of holes (places for electrons in which no electron is present) with which the electrons "recombine". When a mobile electron recombines with a hole, both hole and electron vanish, leaving behind an immobile positively charged donor on the N-side and negatively charged acceptor on the P-side. The region around the p-n junction becomes depleted of charge carriers and thus behaves as an insulator.

However, the depletion width cannot grow without limit. For each electron-hole pair that recombines, a positively-charged dopant ion is left behind in the N-doped region, and a negatively charged dopant ion is left behind in the P-doped region.

As recombination proceeds and more ions are created, an increasing electric field develops through the depletion zone which acts to slow and then finally stop recombination. At this point, there is a "built-in" potential across the depletion zone.

If an external voltage is placed across the diode with the same polarity as the built-in potential, the depletion zone continues to act as an insulator, preventing any significant electric current flow. This is the reverse bias phenomenon. However, if the polarity of the external voltage opposes the built-in potential, recombination can once again proceed, resulting in substantial electric current through the p-n junction.

For silicon diodes, the built-in potential is approximately 0.6 V. Thus, if an external current is passed through the diode, about 0.6 V will be developed across the diode such that the P-doped region is positive with respect to the N-doped region and the diode is said to be "turned on" as it has a forward bias.

Figure : I–V characteristics of a P-N junction diode (not to scale).

A diode’s I–V characteristic can be approximated by four regions of operation (see the figure at right).

At very large reverse bias, beyond the peak inverse voltage or PIV, a process called reverse breakdown occurs which causes a large increase in current that usually damages the device permanently. The avalanche diode is deliberately designed for use in the avalanche region. In the zener diode, the concept of PIV is not applicable. A zener diode contains a heavily doped p-n junction allowing electrons to tunnel from the valence band of the p-type material to the conduction band of the n-type material, such that the reverse voltage is "clamped" to a known value (called the zener voltage), and avalanche does not occur. Both devices, however, do have a limit to the maximum current and power in the clamped reverse voltage region.

The second region, at reverse biases more positive than the PIV, has only a very small reverse saturation current. In the reverse bias region for a normal P-N rectifier diode, the current through the device is very low (in the µA range).

The third region is forward but small bias, where only a small forward current is conducted.

As the potential difference is increased above an arbitrarily defined "cut-in voltage" or "on-voltage", the diode current becomes appreciable (the level of current considered "appreciable" and the value of cut-in voltage depends on the application), and the diode presents a very low resistance.

The current–voltage curve is exponential. In a normal silicon diode at rated currents, the arbitrary "cut-in" voltage is defined as 0.6 to 0.7 volts. The value is different for other diode types — Schottky diodes can be as low as 0.2 V and red light-emitting diodes (LEDs) can be 1.4 V or more and blue LEDs can be up to 4.0 V.

At higher currents the forward voltage drop of the diode increases. A drop of 1 V to 1.5 V is typical at full rated current for power diodes.

Types of semiconductor diode

DiodeZenerdiode

Schottkydiode

Tunneldiode

Light-emittingdiode

Photodiode Varicap Silicon controlled rectifier

Figure : Some diode symbols

Radio demodulationThe first use for the diode was the demodulation of amplitude modulated (AM) radio broadcasts. The history of this discovery is treated in depth in the radio article. In summary, an AM signal consists of alternating positive and negative peaks of voltage, whose amplitude or “envelope” is proportional to the original audio signal, but whose average value is zero. The diode (originally a crystal diode) rectifies the AM signal, leaving a signal whose average amplitude is the desired audio signal.

The average value is extracted using a simple filter and fed into an audio transducer, which generates sound.

Power conversion

Rectifiers are constructed from diodes, where they are used to convert alternating current (AC) electricity into direct current (DC). Automotive alternators are a common example, where the diode provides better performance than the commutator of earlier dynamo. Similarly, diodes are also used in Cockcroft–Walton voltage multipliers to convert AC into higher DC voltages.

Temperature measuringA diode can be used as a temperature measuring device, since the forward voltage drop across the diode depends on temperature, as in a Silicon bandgap temperature sensor. From the Shockley ideal diode equation given above, it appears the voltage has a positive temperature coefficient (at a constant current) but depends on doping concentration and operating temperature (Sze 2007). The temperature coefficient can be negative as in typical thermistors or positive for temperature sense diodes down to about 20 kelvins.

Seven-segment display

A typical 7-segment LED display component, with decimal point.

A seven-segment display (abbreviation: "7-seg(ment) display"), less commonly known as a seven-segment indicator, is a form of display device that is an alternative to the more complex dot-matrix displays. Seven-segment displays are commonly used in electronics as a method of displaying decimal numeric feedback on the internal operations of devices.

The individual segments of a seven-segment display.

A seven segment display, as its name indicates, is composed of seven elements. Individually on or off, they can be combined to produce simplified representations of the Hindu-Arabic numerals. Often the seven segments are arranged in an oblique, or italic, arrangement, which aids readability.

Each of the numbers 0, 6, 7 and 9 may be represented by two or more different glyphs on seven-segment displays.

LED-based 7-segment display showing the 16 hex digits.

The seven segments are arranged as a rectangle of two vertical segments on each side with one horizontal segment on the top and bottom. Additionally, the seventh segment bisects the rectangle horizontally. There are also fourteen-segment displays and sixteen-segment displays (for full alphanumerics); however, these have mostly been replaced by dot-matrix displays.

The segments of a 7-segment display are referred to by the letters A to G, as shown to the right, where the optional DP decimal point (an "eighth segment") is used for the display of non-integer numbers.

The animation to the left cycles through the common glyphs of the ten decimal numerals and the six hexadecimal "letter digits" (A–F). It is an image sequence of a "LED" display, which is described technology-wise in the following section. Notice the variation between uppercase and lowercase letters for A–F; this is done to obtain a unique, unambiguous shape for each letter.

Seven-segment displays may use liquid crystal display (LCD), arrays of light-emitting diodes (LEDs), and other light-generating or controlling techniques such as such as cold cathode gas discharge, vacuum fluorescent, incandescent filaments, and others. For gasoline price totems and other large signs, electromagnetically flipped light-reflecting segments (sometimes called "vanes") are still commonly used. An alternative to the 7-segment display in the 1950s through the 1970s was the cold-cathode, neon-lamp-like nixie tube. Starting in 1970, RCA sold a display device known as the Numitron that used incandescent filaments arranged into a seven-segment display.

In a simple LED package, each LED is typically connected with one terminal to its own pin on the outside of the package and the other LED terminal connected in common with all other LEDs in the device and brought out to a shared pin. This shared pin will then make up all

of the cathodes (negative terminals) OR all of the anodes (positive terminals) of the LEDs in the device; and so will be either a "Common Cathode" or "Common Anode" device depending how it is constructed. Hence a 7 segment plus DP package will only require nine pins to be present and connected.

Integrated displays also exist, with single or multiple digits. Some of these integrated displays incorporate their own internal decoder, though most do not – each individual LED is brought out to a connecting pin as described. Multiple-digit LED displays as used in pocket calculators and similar devices used multiplexed displays to reduce the number of IC pins required to control the display. For example, all the anodes of the A segments of each digit position would be connected together and to a driver pin, while the cathodes of all segments for each digit would be connected. To operate any particular segment of any digit, the controlling integrated circuit would turn on the cathode driver for the selected digit, and the anode drivers for the desired segments; then after a short blanking interval the next digit would be selected and new segments lit, in a sequential fashion. In this manner an eight digit display with seven segments and a decimal point would require only 8 cathode drivers and 8 anode drivers, instead of sixty-four drivers and IC pins. Often in pocket calculators the digit drive lines would be used to scan the keyboard as well, providing further savings; however, pressing multiple keys at once would produce odd results on the multiplexed display.

Seven segment displays can be found in patents as early as 1908 (in U.S. Patent 974,943   , F W Wood invented an 8-segment display, which displayed the number 4 using a diagonal bar), but did not achieve widespread use until the advent of LEDs in the 1970s. They are sometimes even used in unsophisticated displays like cardboard "For sale" signs, where the user either applies color to pre-printed segments, or (spray)paints color through a seven-segment digit template, to compose figures

such as product prices or telephone numbers.

For many applications, dot-matrix LCDs have largely superseded LED displays, though even in LCDs 7-segment displays are very common. Unlike LEDs, the shapes of elements in an LCD panel are arbitrary since they are formed on the display by a kind of printing process. In contrast, the shapes of LED segments tend to be simple rectangles, reflecting the fact that they have to be physically moulded to shape, which makes it difficult to form more complex shapes than the segments of 7-segment displays. However, the high common recognition factor of 7-segment displays, and the comparatively high visual contrast obtained by such displays relative to dot-matrix digits, makes seven-segment multiple-digit LCD screens very common on basic calculators.

TransformerA transformer is a device that transfers electrical energy from one circuit to another through inductively coupled electrical conductors. A changing current in the first circuit (the primary) creates a changing magnetic field; in turn, this magnetic field induces a changing voltage in the second circuit (the secondary). By adding a load to the secondary circuit, one can make current flow in the transformer, thus transferring energy from one circuit to the other.

The secondary induced voltage VS is scaled from the primary VP by a factor ideally equal to the ratio of the number of turns of wire in their respective windings:

By appropriate selection of the numbers of turns, a transformer thus allows an alternating voltage to be stepped up — by making NS more than NP — or stepped down, by making it less.

Transformers are some of the most efficient electrical 'machines',[1] with some large units able to transfer 99.75% of their input power to their output.[2] Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of national power grids. All operate with the same basic principles, though a variety of designs exist to perform specialized roles throughout home and industry.

Basic principlesThe transformer is based on two principles: firstly that an electric current can produce a magnetic field (electromagnetism) and secondly that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). By changing the current in the primary coil, it changes the strength of its magnetic field; since the changing magnetic field extends into the secondary coil, a voltage is induced across the secondary.

An ideal step-down transformer showing magnetic flux in the coreA

simplified transformer design is shown to the left. A current passing through the primary coil creates a magnetic field. The primary and secondary coils are wrapped around a core of very high magnetic permeability, such as iron; this ensures that most of the magnetic field lines produced by the primary current are within the iron and pass through the secondary coil as well as the primary coil.

Construction

Cores

Laminated core transformer showing edge of laminations at top of unit.

Laminated steel coresTransformers for use at power or audio frequencies typically have cores made of high permeability silicon steel. The steel has a permeability many times that of free space, and the core thus serves to greatly reduce the magnetising current, and confine the flux to a path which closely couples the windings. Early transformer developers soon realised that cores constructed from solid iron resulted in prohibitive eddy-current losses, and their designs mitigated this effect with cores consisting of bundles of insulated iron wires.Later designs constructed the core by stacking layers of thin steel laminations, a principle that has remained in use. Each lamination is insulated from its neighbors by a thin non-conducting layer of insulation.The universal transformer equation indicates a minimum cross-sectional area for the core to avoid saturation.

The effect of laminations is to confine eddy currents to highly elliptical paths that enclose little flux, and so reduce their magnitude. Thinner laminations reduce losses, but are more laborious and expensive to construct. Thin laminations are generally used on high frequency transformers, with some types of very thin steel laminations able to operate up to 10 kHz.

Laminating the core greatly reduces eddy-current losses

Soldering

Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a relatively low melting point. Soft soldering is characterized by the melting point of the filler metal, which is below 400 °C. The filler metal used in the process is called solder.

Soldering is distinguished from brazing by use of a lower melting-temperature filler metal; it is distinguished from welding by the base metals not being melted during the joining process. In a soldering process, heat is applied to the parts to be joined, causing the solder to melt and be drawn into the joint by capillary action and to bond to the materials to be joined by wetting action. After the metal cools, the resulting joints are not as strong as the base metal, but have adequate strength, electrical conductivity, and water-tightness for many uses. Soldering is an ancient technique mentioned in the Bible and there is evidence that it was employed up to 5000 years ago in Mesopotamia.

ApplicationsThe most frequent application of soldering is assembling electronic components to printed circuit boards (PCBs). Another common application is making permanent but reversible connections between copper pipes in plumbing systems. Joints in sheetmetal objects such as food cans, roof flashing, rain gutters and automobile radiators have also historically been soldered, and occasionally still are. Jewelry and small

mechanical parts are often assembled by soldering. Soldering is also used to join lead came and copper foil in stained glass work. Soldering can also be used to effect a semi-permanent patch for a leak in a container cooking vessel.

SoldersSoldering filler materials are available in many different alloys for differing applications. In electronics assembly, the eutectic alloy of 63% tin and 37% lead (or 60/40, which is almost identical in performance to the eutectic) has been the alloy of choice. Other alloys are used for plumbing, mechanical assembly, and other applications.A eutectic formulation has several advantages for soldering; chief among these is the coincidence of the liquidus and solidus temperatures, i.e. the absence of a plastic phase. This allows for quicker wetting out as the solder heats up, and quicker setup as the solder cools. A non-eutectic formulation must remain still as the temperature drops through the liquidus and solidus temperatures.

Any differential movement during the plastic phase may result in cracks, giving an unreliable joint. Additionally, a eutectic formulation has the lowest possible melting point, which minimizes heat stress on electronic components during the soldering process.

Lead-free solders are suggested anywhere children may come into contact (since children are likely to place things into their mouths), or for outdoor use where rain and other precipitation may wash the lead into the groundwater. Common solder alloys are mixtures of tin and lead, respectively:

63/37: melts between 180–185 °C (356–365 °F) 60/40: melts between 183–190°C (361–374 °F) 50/50: melts between 185–215°C (365–419 °F)

Lead-free solder alloys melt around 250 °C (482 °F), depending on their composition.

For environmental reasons, 'no-lead' solders are becoming more widely used. Unfortunately most 'no-lead' solders are not eutectic formulations, making it more difficult to create reliable joints with them. See complete discussion below; see also RoHS.

Other common solders include low-temperature formulations (often containing bismuth), which are often used to join previously-soldered assemblies without un-soldering earlier connections, and high-temperature formulations (usually containing silver) which are used for high-temperature operation or for first assembly of items which must not become unsoldered during subsequent operations.

Specialty alloys are available with properties such as higher strength, better electrical conductivity and higher corrosion resistance.

FluxIn high-temperature metal joining processes (welding, brazing and soldering), the primary purpose of flux is to prevent oxidation of the base and filler materials. Tin-lead solder, for example, attaches very well to copper, but poorly to the various oxides of copper, which form quickly at soldering temperatures. Flux is a substance which is nearly inert at room temperature, but which becomes strongly reducing at elevated temperatures, preventing the formation of metal oxides. Secondarily, flux acts as a wetting agent in the soldering process, reducing the surface tension of the molten solder and causing it to better wet out the parts to be joined.

Fluxes currently available include water-soluble fluxes (no VOC's required for removal) and 'no-clean' fluxes which are mild enough to not require removal at all. Performance of the flux needs to be carefully evaluated; a very mild 'no-clean' flux might be perfectly acceptable for production equipment, but not give adequate performance for a poorly-controlled hand-soldering operation.

Traditional rosin fluxes are available in non-activated (R), mildly activated (RMA) and activated (RA) formulations. RA and RMA fluxes

contain rosin combined with an activating agent, typically an acid, which increases the wettability of metals to which it is applied by removing existing oxides.

The residue resulting from the use of RA flux is corrosive and must be cleaned off the piece being soldered. RMA flux is formulated to result in a residue which is not significantly corrosive, with cleaning being preferred but optional.

Basic soldering techniques

MethodsSoldering operations can be performed with hand tools, one joint at a time, or en masse on a production line. Hand soldering is typically performed with a soldering iron, soldering gun, or a torch, or occasionally a hot-air pencil. Sheetmetal work was traditionally done with "soldering coppers" directly heated by a flame, with sufficient stored heat in the mass of the soldering copper to complete a joint; torches or electrically-heated soldering irons are more convenient. All soldered joints require the same elements of cleaning of the metal parts to be joined, fitting up the joint, heating the parts, applying flux, applying the filler, removing heat and holding the assembly still until the filler metal has completely solidified. Depending on the nature of flux material used, cleaning of the joints may be required after they have cooled.

The distinction between soldering and brazing is arbitrary, based on the melting temperature of the filler material. A temperature of 450 °C is usually used as a practical cut-off.

Different equipment and/or fixturing is usually required since (for

instance) a soldering iron generally cannot achieve high enough temperatures for brazing. Practically speaking there is a significant difference between the two processes—brazing fillers have far more structural strength than solders, and are formulated for this as opposed to maximum electrical conductivity. Brazed connections are often as strong or nearly as strong as the parts they connect, even elevated temperatures.

"Hard soldering" or "silver soldering" (performed with high-temperature solder containing up to 40% silver) is also often a form of brazing, since it involves filler materials with melting points in the vicinity of, or in excess of, 450 °C. Although the term "silver soldering" is used much more often than "silver brazing", it may be technically incorrect depending on the exact melting point of the filler in use. In silver soldering ("hard soldering"), the goal is generally to give a beautiful, structurally sound joint, especially in the field of jewelry. Thus, the temperatures involved, and the usual use of a torch rather than an iron, would seem to indicate that the process should be referred to as "brazing" rather than "soldering", but the endurance of the "soldering" apellation serves to indicate the arbitrary nature of the distinction (and the level of confusion) between the two processes.

Induction soldering is a process which is similar to brazing. The source of heat in induction soldering is induction heating by high-frequency AC current. Generally copper coils are used for the induction heating. This induces currents in the part being soldered. The coils are usually made of copper or a copper base alloy.

The copper rings can be made to fit the part needed to be soldered for precision in the work piece. Induction soldering is a process in which a filler metal (solder) is placed between the faying surfaces of (to be joined) metals. The filler metal in this process is melted at a fairly low temperature. Fluxes are a common use in induction soldering.This is a process which is particularly suitable for soldering continuously. The process is usually done with coils that wrap around a cylinder/pipe that needs to be soldered. Some metals are easier to solder than others. Copper, silver, and gold are easy. Iron and nickel are found to be more

difficult. Because of their thin, strong oxide films, stainless steel and aluminum are a little more difficult. Titanium, magnesium, cast irons, steels, ceramics, and graphite can be soldered but it involves a process similar to joining carbides. They are first plated with a suitable metallic element that induces interfacial bonding.

Soldering defectsVarious problems may arise in the soldering process which lead to joints which are non functional either immediately or after a period of use. The most common defect when hand-soldering results from the parts being joined not exceeding the solder's liquidus temperature, resulting in a "cold solder" joint. This is usually the result of the soldering iron being used to heat the solder directly, rather than the parts themselves. Properly done, the parts to be connected are heated by the iron, which in turn melts the solder, guaranteeing adequate heat in the joined parts for thorough wetting.

An improperly selected or applied flux can cause joint failure, or if not properly cleaned off the joint, may corrode the metals in the joint over time and cause eventual joint failure. Without flux the joint may not be clean, or may be oxidized, resulting in an unsound joint. Movement of metals being soldered before the solder has cooled will cause a highly unreliable cracked joint.

REFRENCES:-

ELECTRONICS FOR YOU EDITION-MAY 2003.

ELECTRONICS FOR YOU VOLUME-10.

ELECTRONICS FOR YOU VOLUME-11.

F.M RECEIVER BY RAJESH AGGARWAL.

GOOGLESEARCH :- ELECTRONICS ENCYCLOPEDIA.

WWW. DATASHEETS.IN

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