GSM Based Irrigation System

GSM BASED IRRIGATION SYSTEM

THE INSTITUTION OF ELECTRONICS AND TELECOMMUNICATION ENGINEERS

NEW DELHI

PROJECT REPORT ON

“GSM Based Irrigation System” Submitted to, to,

The Institution of Electronics & Telecommunication Engineers, Engineers, New Delhi at Rajkot center towards center towards the partial fulfillment of the Degree of The Institution of Electronics & Telecommunication Engineers in “Electronics & Telecommunication Engineering”

Guided By.

Submitted LAKHANI ARCHITA M

Dr. H.N. Pandya (Ms.C., Ph. D) H.O.D. Electronics. (Saurashtra Univerity) Rajkot. I.E.T.E. RAJKOT SUBCENTER

(Mem. No.SG-172792)

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NEW DELHI

CERTIFICATE

This is to certify that this is a bonafide record of the project work done satisfactorily by LAKHANI ARCHITA (Mem. No.SG- 172792) towards the partial fulfillment fulfillment of her AMIETE examination. examination. This report has not been submitted for any other examination and is not from a part of any other course undergone by the candidate.

Guided By. Dr. H.N. Pandya (Ms.C., Ph. D) H.O.D. Electronics. (Saurashtra Univerity) Rajkot.

I.E.T.E. RAJKOT SUBCENTER

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NEW DELHI

CERTIFICATE

This is to certify that this is a bonafide record of the project work done satisfactorily by LAKHANI ARCHITA (Mem. No.SG- 172792) towards the partial fulfillment fulfillment of her AMIETE examination. examination. This report has not been submitted for any other examination and is not from a part of any other course undergone by the candidate.

Guided By. Dr. H.N. Pandya (Ms.C., Ph. D) H.O.D. Electronics. (Saurashtra Univerity) Rajkot.


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NEW DELHI

DECLARATION

GSM Based Irrigation System I hereby hereby declare declare that the work presented presented in this project project report report entitled entitled “GSM Based irrigation System” is a partial fulfillment of my AMIETE in Electronics institution of

Electronics and Telecommunication and is an authenticated record of

my own work carried

out under the valuable guidance of Dr. H. N. PANDYA The

matter embodied in the report has not been submitted for the award of any other

degree or diploma.

Submitted By:- LAKHANI ARCHITA M I.E(Mem. .T.E. RNo.SG-172792) AJKOT SUBCENTER

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PREFACE At present because of rapid globalization and industrialization there is a big need of skilled and trained engineers. All industries need good and trained engineers because of this reason “IETE” has adopted Degree in Electronics and Telecommunication.

Degree in Electronics and Telecommunication is a unique course in reputed IETE centers in India. This course provides both theoretical and practical knowledge about Electronics. Student can get theoretical knowledge by experienced and learned professors of IETE centers.

As a part of fulfillment of the degree I have selected a project Work on “GSM BASED IRRIGATION SYSTEM” after the enough discussion

with my guide Mr. H. N. Pandya.

Describing the various methods of irrigation I have constructed on “GSM BASED IRRIGATION SYSTEM” , I have used AT89 C2051 as Micro-

Controllers. Using different types of sensors the moisture is sensed and thus water supply is control to soil.


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ACKNOWLEDGEMENT It is a great opportunity for a Degree student to prepare “Project Report” to know about of practical aspects of the field.

First of all I am very much thankful to “IETE” to include this kind of subjects in Degree syllabus in which students can get practical knowledge. I humbly pay my respect to IETE authority and director for giving me such opportunity to prepare my report.

I am thankful to Prof Dr. H. N. PANDYA for giving me his valuable time and co-operation to develop the project on object counter by giving guidance.


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CONTENS Sr No

Name

Page .No

1

PREFACE ACKNOWLEDGEMENT INTRODUCTION GENERAL OVERVIEW PROJECT MEANS ABSTRACT MAIN OVERVIEW

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LIST OF COMPONENTS USED

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CIRCUIT DESCRIPTION AND

24

2 3 4

5

5 7 18 19 21 22

OPERATION 6

7

MATERIALS OVERVIEW MICROCONTROLLER LED DIODE RESISTOR CAPACITOR TRANSSFORMER DATASHEET OVERVIEW MICROCONTROLLER

29 30 46 51 67 73 79 90 93

AT89C2O51 SINGLE TIMER CIRCUIT SYMBOLE 8

REFERENCE BOOKS AND

106 116 120

WEBSITES

INTRODUCTION

Types of irrigation


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Basin flood irrigation of wheat

Various types of irrigation techniques differ in how the water obtained from the source is distributed within the field. In general, the goal is to supply the entire field uniformly with water, so that each plant has the amount of water it needs, neither too much nor too little.

•

Surface irrigation

Main article: Surface irrigation

In surface irrigation systems water moves over and across the land by simple gravity flow in order to wet it and to infiltrate into the soil. Surface irrigation can be subdivided into furrow, borderstrip or basin irrigation. It is often called flood irrigation when the irrigation results in flooding or near flooding of the cultivated land. Historically, this has been the most common method of irrigating agricultural land. Where water levels from the irrigation source permit, the levels are controlled by dikes, usually plugged by soil. This is often seen in terraced rice fields (rice paddies), where the method is used to flood or control the level of water in each distinct field. In some cases, the water is pumped, or lifted by human or animal power to the level of the land.


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Localized irrigation

Spray Head Localized irrigation is a system where water is distributed under low pressure through a piped network, in a pre-determined pattern, and applied as a small discharge to each plant or adjacent to it. Drip irrigation, spray or microsprinkler irrigation and bubbler irrigation belong to this category of irrigation methods.

•

Drip Irrigation

Main article: Drip Irrigation

Drip Irrigation - A dripper in action Drip irrigation, also known as trickle irrigation, functions as its name suggests. Water is delivered at or near the root zone of plants, drop by drop. This method can be the most water-efficient method of irrigation, if managed properly, since evaporation and runoff are minimized. In modern agriculture, drip irrigation is


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often combined with plastic mulch, further reducing evaporation, and is also the means of delivery of fertilizer. The process is known as fustigation.

Drip Irrigation Layout and its parts Deep percolation, where water moves below the root zone, can occur if a drip system is operated for too long of a duration or if the delivery rate is too high. Drip irrigation methods range from very high-tech and computerized to low-tech and relatively labor-intensive. Lower water pressures are usually needed than for most other types of systems, with the exception of low energy center pivot systems and surface irrigation systems, and the system can be designed for uniformity throughout a field or for precise water delivery to individual plants in a landscape containing a mix of plant species. Although it is difficult to regulate pressure on steep slopes, pressure compensating emitters are available, so the field does not have to be level. Hightech solutions involve precisely calibrated emitters located along lines of tubing that extend from a computerized set of valves. Both pressure regulation and filtration to remove particles are important. The tubes are usually black (or buried under soil or mulch) to prevent the growth of algae and to protect the polyethylene from degradation due to ultraviolet light. But drip irrigation can also be as low-tech as a porous clay vessel sunk into the soil and occasionally filled from a hose or bucket. Subsurface drip irrigation has been used successfully on lawns, but it is more expensive than a more traditional sprinkler system.


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Surface drip systems are not cost-effective (or aesthetically pleasing) for lawns and golf courses. In the past one of the main disadvantages of the subsurface drip irrigation (SDI) systems, when used for turf, was the fact of having to install the plastic lines very close to each other in the ground, therefore disrupting the turf grass area. Recent technology developments on drip installers like the drip installer at New Mexico State University Arrow Head Center, places the line underground and covers the slit leaving no soil exposed.

Sprinkler irrigation

Sprinkler irrigation of blueberries in Plainville, New York

A traveling sprinkler at Millets Farm Centre, Oxford shire, UK


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In sprinkler or overhead irrigation, water is piped to one or more central locations within the field and distributed by overhead high-pressure sprinklers or guns. A system utilizing sprinklers, sprays, or guns mounted overhead on permanently installed risers is often referred to as a solid-set irrigation system. Higher pressure sprinklers that rotate are called rotors and are driven by a ball drive, gear drive, or impact mechanism. Rotors can be designed to rotate in a full or partial circle. Guns are similar to rotors, except that they generally operate at very high pressures of 40 to 130 lbf/in² (275 to 900 kPa) and flows of 50 to 1200 US gal/min (3 to 76 L/s), usually with nozzle diameters in the range of 0.5 to 1.9 inches (10 to 50 mm). Guns are used not only for irrigation, but also for industrial applications such as dust suppression and logging. Sprinklers may also be mounted on moving platforms connected to the water source by a hose. Automatically moving wheeled systems known as traveling

sprinklers may irrigate areas such as small farms, sports fields, parks, pastures, and cemeteries unattended. Most of these utilize a length of polyethylene tubing wound on a steel drum. As the tubing is wound on the drum powered by the irrigation water or a small gas engine, the sprinkler is pulled across the field. When the sprinkler arrives back at the reel the system shuts off. This type of system is known to most people as a "water reel" traveling irrigation sprinkler and they are used extensively for dust suppression, irrigation, and land application of waste water. Other travelers use a flat rubber hose that is dragged along behind while the sprinkler platform is pulled by a cable. These cable-type travelers are definitely old technology and their use is limited in today's modern irrigation projects.

Center pivot irrigation I.E.T.E. RAJKOT SUBCENTER

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The hub of a center-pivot irrigation system. Center pivot irrigation is a form of sprinkler irrigation consisting of several segments of pipe (usually galvanized steel or aluminum) joined together and supported by trusses, mounted on wheeled towers with sprinklers positioned along its length. The system moves in a circular pattern and is fed with water from the pivot point at the center of the arc. These systems are common in parts of the United States where terrain is flat.

Center pivot with drop sprinklers. Photo by Gene Alexander, USDA Natural Resources Conservation Service.


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Most center pivot systems now have drops hanging from a u-shaped pipe called a gooseneck attached at the top of the pipe with sprinkler heads that are positioned a few feet (at most) above the crop, thus limiting evaporative losses. Drops can also be used with drag hoses or bubblers that deposit the water directly on the ground between crops. The crops are planted in a circle to conform to the center pivot. This type of system is known as LEPA (Low Energy Precision Application). Originally, most center pivots were water powered. These were replaced by hydraulic systems ( T-L

Irrigation) and electric motor driven systems ( Lindsay , Reinke, Valley , Zimmatic , Pierce, Grupo Chamartin. Most systems today are driven by an electric motor mounted low on each span. This drives a reduction gearbox and transverse driveshafts transmit power to another reduction gearbox mounted behind each wheel. Precision controls, some with GPS location and remote computer monitoring, are now available.

Wheel line irrigation system in Idaho. 2001. Photo by Joel McNee, USDA Natural Resources Conservation Service.

Lateral move (side roll, wheel line) irrigation A series of pipes, each with a wheel of about 1.5 m diameter permanently affixed to its midpoint and sprinklers along its length, are coupled together at one


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edge of a field. Water is supplied at one end using a large hose. After sufficient water has been applied, the hose is removed and the remaining assembly rotated either by hand or with a purpose-built mechanism, so that the sprinklers move 10 m across the field. The hose is reconnected. The process is repeated until the opposite edge of the field is reached. This system is less expensive to install than a center pivot, but much more labor intensive to operate, and it is limited in the amount of water it can carry. Most systems utilize 4 or 5-inch (130 mm) diameter aluminum pipe. One feature of a lateral move system is that it consists of sections that can be easily disconnected. They are most often used for small or oddly-shaped fields, such as those those foun found d in hill hilly y or moun mounta tain inou ous s regi region ons, s, or in regi region ons s wher where e labo laborr is inexpensive.

Sub-irrigation Sub irrigation also sometimes called seepage irrigation has been used for many years in field crops in areas with high water tables. tables. It is a method of artificially raising the water table to allow the soil to be moistened from below the plants' plants' root \zone. Often those systems are located on permanent grasslands in lowlands or river river valle valleys ys and combin combined ed with with draina drainage ge infras infrastruc tructur ture. e. A system system of pumpin pumping g stations, canals, weirs and gates allows it to increase or decrease the water level in a network of ditches and thereby control c ontrol the water table. Sub-irrigation is also used in commercial greenhouse production, usually for potted plants. plants . Water is delivered from below, absorbed upwards, and the excess collected for recycling. Typically, a solution of water and nutrients floods a container or flows through a trough for a short period of time, 10-20 minutes, and is then pumped back into a holding tank for reuse. Sub-irrigation in greenhouses requires fairly sophisticated, expensive equipment and management. Advantages are water


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Manual irrigation using buckets or watering cans ca ns These systems have low requirements for infrastructure and technical equipment but need high labor inputs. Irrigation using watering cans is to be found for example in peri-urban agriculture around large cities in some African countries.

Automatic, non-electric irrigation using buckets and ropes Besides the common manual watering by bucket, an automated, natural version of this also exist. Using plain polyester ropes combined with a prepared ground mixture can be used to water plants from a vessel filled with water. The ground mixture would need to be made depending on the plant itself, yet would mostly consist of black potting soil, vermiculite vermiculite and perlite. perlite. This system would (with certain crops) allow you to save expenses as it does not consume any electricity and only little water (unlike sprinklers, water timers, ...). However, it may only be used with with cert certai ain n crop crops s (pro (proba babl bly y most mostly ly larg larger er crop crops s that that do not not need need a humi humid d environment; perhaps e.g. paprika's).

Irrigation using stones to catch water from humid air In countries where at night, humid air sweeps the countryside, stones are used to catch water from the humid air by transpiration transpiration.. This is for example practiced in the vineyards at Lanzarote Lanzarote..

Dry terasses for irrigation and water distribution In subtropical countries as Mali and Senegal Senegal,, a special type of terrassing (without flood irrigation or intent to flatten farming ground) is used. Here, a 'stairs' is


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made trough the use of ground level differences which helps to decrease water evaporation and also distributes the water to all patches (sort of irrigation).

Sources of irrigation water Sources of irrigation water can be groundwater extracted from springs or by using wells wells,, surfac surface e water water withdr withdrawn awn from from rivers rivers,, lakes or reservoirs or nonnonconventional sources like treated wastewater , desalinated water or drainage water . A spec special ial form form of irri irriga gati tion on usin using g surfa surface ce wate waterr is spate irrigation irrigation,, also called floodwater harvesting. harvesting . In case of a flood (spate) water is diverted to normally dry river beds (wadi’s) using a network of dams, gates and channels and spread over large areas. The moisture stored in the soil will be used thereafter to grow crops. Spate irrigation areas are in particular located in semi-arid or arid, mountainous regions. While floodwater harvesting belongs to the accepted irrigation methods, rainwater rainwa ter harve harvesting sting is usually not considered as a form of irrigation. Rainwater harv harves esti ting ng is the the coll collec ectio tion n of runo runoff ff wate waterr from from roof roofs s or unus unused ed land land and and the the concentration of this water on cultivated land. Therefore this method is considered as a water concentration method.

How an in-ground irrigation system works Most commercial and residential irrigation systems are "in " in ground" ground" systems, which means that everything is buried in the ground. With the pipes pipes,, sprinklers sprinklers,, and irrigation valves being hidden, it makes for a cleaner, more presentable landscape without garden hoses or other items having to be moved around manually.

Water source and piping The beginning of a sprinkler system is the water source. water source. This is usually a tap into an existing (city) water line or a pump that pulls water out of a well or a pond.


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The water travels through pipes from the water source through the valves to the sprinklers. The pipes from the water source up to the irrigation valves are called "mainlines", and the lines from the valves to the sprinklers are called "lateral lines". Most piping used in irrigation systems today are HDPE and MDPE or PVC or PEX plastic pressure pipes due to their ease of installation and resis tance to corrosion.


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PROJECT MEANS:I.E.T.E. RAJKOT SUBCENTER

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ABSTRACT

This system is a remote controlled pump control system. The remote control media used is the regular GSM cell phone.

The system installed at the farm has four moisture sensors which analyse the moisture content of the soil.

When the sensors are dry, a buzzer is activated. When the user call up the phone kept in the system, he hears the buzzer which will let him know that the farm has dried up.

Then by pressing a particular switch on his phone he can switch on the water pump. The pump can be switched off in the same manner.

This system, if implemented, will save a lot of time, energy and money of the farmers by automation of the job. A simple modification can also make the system completely automatic.


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LIST OF COMPONENTS USED

FOR THE GSM BASED IRRIGATION SYSTEM (1)

DIODE

(2)

TRANSISTOR (i)PNP (ii)NPN

(3)

TRAMSFORMER 230V 12-0-12V/500 MA CAPACITOR (i)

10 µ

(ii)

100 µ

(iii)

0.1 µ

(iv)

22 µ

(v)

(4)

RESISTOR (i)

100KΩ

(ii)

10K

(iii)

2k2

(iv)

220k

(v)

1k

(6)

Cell phone interface

(7)

DTMF decoder section

(8)

Moisture sensors

(9)

Main controller section

(10)

Indicator section

(11)

Relay driver and the pump control section

(12)

Power supply section


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CIRCUIT DESCRIPTION AND OPERATION

This system can be used in fields for providing them with water by switching on and off the pumps at the field using a mobile phone. For this purpose a cell phone with a sim card is to be attached to the system and placed at the farm itself. The system has moisture sensors with variable sensitivity that can detect moisture levels in the soil. Multiple sensors are used so that moisture in the soil can be measured at more than one place. The system gives audible clues to the user about the moisture content and the pump status to the user or the person who call up the phone that is attached to the system and placed at the field.

For better understanding the system can be divided in to smaller parts. Segregation according to small functional blocks c an be done as below.

1. The cell phone interface 2. The DTMF decoder section 3. The moisture sensors 4. The main controller section 5. The indicator section 6. The relay driver and the pump control section 7. The power supply section

The cell phone interface: this section is the heart of the entire circuit. It is the section with which the cell phone is attached to the system and through which it communicates with the system. The cell phone that is attached to the system is kept


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in auto answer mode after connecting a hands free set to it. Whenever this phone is called up, it picks up the phone after which the DTMF tones generated by the calling cell phone will also be produced at the cell phone connected to the system. This fact is the essence behind the working of the entire project. The DTMF tones from the switches depressed at the calling cell phone are transmitted to the system cell phone via the GSM network. Initially this system would seem rather costly as whenever a pump is to be switched on or off or the status of the field is to be known, a call has to be made. But since nowadays call costs are going so low that this is not much of a problem. Moreover when the call cost is compared with the cost of physical visit of the farmer to the field, it proves to be much cheaper. Also more and more telecom service providers are giving CUG plans in which call rates are negligible or even zero. The cell phone hands free is attached to a microphone is the system. The mic picks up the DTMF tones from the hands free speaker. These tones are very small in amplitude thus a single transistor collector feedback biased amplifier stage has been employed for amplifying the signals to a specific level so that they can be applied to the DTMF decoder for decoding.

The DTMF decoder section: this section is fed input from the single stage transistor amplifier output. The output of the amplifier and thus the input to the decoder are the DTMF tones from the system cell phone which are in turn the tones which were send from the caller cell phone. The decoder is built around a very popular ASIC the MT8870. This chip accepts DTMF tones and converts them into BCD data corresponding to the switch that was depressed at the caller phone. Along with this data, the decoder also generates one specific high signal called the StD signal from its pin 15. This signal is generated whenever the chip receives any valid DTMF tone and last for the instant for which the tone lasts. This signal is used to convey the micro controller that a new data nibble has arrived. The decoder exactly decodes the DTMF tones by the help of an in built oscillator that generates a very stable frequency with the help of an externally connected crystal resonator of 3.5795MHz. the output of the DTMF decoder is fed to the controller for further processing.


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The moisture sensors: there are three moisture sensors employed in the system. The concept of multiple sensors is based on the fact that different parts of the field may have different amount of moisture at the same time and that has to be taken into consideration. As many no. of sensors can be used in the system although here only four are employed. The sensors actually measure the soil resistivity to gauge the amount of moisture present in it. Each sensor has been made using a 555 timer employed as a schmitt trigger. The sensitivity of each sensor is adjustable using a preset. Moreover each sensor has been fitted with fail safe mechanism in the form of a 0.1uF capacitor to prevent false triggering. The outputs of the sensors are active high which can be seen on an LED which has been connected on the output pin of each sensor so that the status of the sensor can be easily seen. These LEDs also help in setting the sensitivity of the sensors. The sensors are fed from the probes that are to be inserted in the soil for measuring the resistance between the two points at which the probes are entered. The probes can be of any conductive material, but material which are not corrosive or prone to rusting must be used. The best alternative is to use graphite rods as sensor probes. These rods can be easily available by breaking exhausted dry batteries. The outputs of the sensors are also fed to the microcontroller for further processing.

The main controller section: this section controls the entire system. It actually integrates the individual components and then unifies their functions as one. The controller that has been used here is the 89C2051 which belongs to the very popular 8051 series of micro controllers from Intel. The 2051 has been utilized because it is a 20 pin controller and thus far smaller in size than the usual 40 pin version. The main purpose of the controller to be used in this project is that by its usage further advancement and modification of the project becomes easy and feasible. Moreover the component count of the entire system remains small in the scenario when a micro controller is used. Less no of components mean less no of failure points which increases the system reliability. The micro controller is clocked by a 12MHz quartz crystal resonator. Other associated circuitry for the controller like the power-on-reset network and the manual reset network are also connected to the controller.


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The controller accepts input on its port 1 which has been configured as the input port. The first nibble to the input port is the data from the sensors whereas the second nibble is the data obtained from the DTMF decoder section. The StD output of the DTMF decoder is applied as interrupt to the controller. As the entire 8051 family is built in such a way as to accept active low interrupts, the signal from the DTMF decoder is first inverted with the help of a single npn transistor and then applied to interrupt the controller.

The indicator section: contrary to other type of indicators, usually visual in the form of leds, here audible indication is used. This is due to the fact that an audible clue about the status is to be given to the user on the phone. To accomplish this two different buzzers are implemented. One of the buzzers indicates that the pump has been started and running. This buzzer plays a music to distinguish it from the other continuous buzzer It stays on for the time the pump is on. The other buzzer is a continuous one which rings when all the sensors are dry. Display LEDs are also utilized for visual indication of the status.

The relay driver and the pump control section: this section is connected to the output of the controller and is used to control the relay which in turn controls the pump. There are two problems in driving the relay directly from the controller. The first is that the outputof the controller is in the vicinity of +5V which will not be able to drive the 12V /200ohm relay. The other thing is that the controller is also not able to provided that high amount of current that is required by the magnetizing coils of the relay.

The power supply section. The system requires two distinct dc voltages to function- +5V dc for the entire circuit except the relay driver section and the relays themselves as both are rated at 12V. The transformer used is the 12-0-12V/500mA which is more than enough. The output ac voltage of the mains transformer is fed to a rectifier for converting it into dc. This impure unregulated dc is applied to a large value filter capacitor which smoothes the dc voltage. Finally the unregulated dc is then applied to the 7805 voltage regulator chip so as to obtain the necessary +5 volts needed by the electronics circuit.


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MICROCONTROLLER Microcontroller is a computer on a single chip. Micro suggests that the device is small and controller indicates that the device can be used to control the events, proce processe sses s or obje objects cts.. Micro Microco cont ntro roll ller er is becom becomin ing g a key key compo compone nent nt in many many electr electroni onics cs produc products ts like washin washing g machin machine, e, un-inte un-interru rrupte pted d power power supply supply,, color color television, television, CD player, player, remote remote control, control, robots, robots, CNC machines, modems, printers, keyboards, advertisement displays. Temperature indicator and controller, pressure monito monitor, r, elevat elevators, ors, engine engine manage managemen mentt system system in automo automobil biles, es, measur measureme ements nts instruments, mobile phones, security system, fire alarm system and many others. The use of microcontroller is so widespread that it is almost impossible to work in electronics field without utilizing it.


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Overview Of Microcontroller

A microcontroller is an integrated chip that is often part of an embedded system. The microcontroller includes a CPU, RAM, ROM, I/O ports and timers like a standard computer but because they are designed to execute only a single specific task to control a single system, they are much smaller and simplified so that they can include all the functions required on a single chip.

Early controllers controllers were built from discrete components components and they were large in size. Later microprocessors were build and microcontrollers were able to fit onto a circuit board. Microcontroller now places all of the needed components onto a single chip. chip. With With the the adve advent nt of VLSI VLSI tech techno nolo logy, gy, micr microco ocont ntro roll ller er chip chip are are beco becomin ming g essentially single chip microcomputers. Microcontrollers collect data from the input devices, process the data and make decision based on the result of process. The input may be for sensing and measurement of some aspects of the environment and output may be generation of one or more control signals that effect the environment in a desirable manner. Input may be simple binary valued signal from switch, group of binary digits from ADC, serial data from computer, pulses from infrared receiver or signa signals ls from from sens sensor ors. s. Outp Output ut may may be sole soleno noid id,, rela relay, y, LCD, LCD, LED, LED, indi indica cato tors, rs, Optodevices, motors etc. Assembly language is stored in either internal ROM or external ROM. Internal RAM is used for processing and temporary storage.

Microcontrollers have become common in many areas, and can be found in variet variety y of applica applicatio tions ns like like interc intercom, om, teleph telephone ones, s, mobile mobiles, s, securit security y system, system, door door openers, openers, curtain controller, controller, answering answering machines, fax, television, television, CNC machines, machines, washing washing machines, machines, VCR/VCD, VCR/VCD, DVD players, players, remote remote controls, controls, musical musical instruments, instruments, sewing machine, camera, Microwave ovens, laser printers computer equipments, instr instrum umen enta tati tion on and and many many othe otherr home home appl applia ianc nces es.. They They are are wide widely ly used used in auto autom mobil obiles es and and have ave beco becom me a cent centra rall part art of ind industr ustria iall robo obotics tics.. The microcontrollers is most essential IC for continuous process- based industries like chemical refinery, pharmaceuticals, steels, programmable logic control system(PLC) and distributed control system(DCS). I.E.T.E. RAJKOT SUBCENTER

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Microcontrollers do not require significant processing power because they are usually used to control a single process and execute simple instructions.

The automotive automotive market has been a major driver driver of microcontrollers, microcontrollers, many of which have been developed developed for automotive automotive applications. applications. Because Because of automotive automotive microcontrollers have to withstand harsh environmental conditions, they may be highly reliable and durable. Automotive microcontrollers, like their counterparts are very inexpensive and are able to deliver powerful features that would otherwise be impossible, or too costly to implement.

•

Brief History Of 8051 Microcontroller Family:-

Intel Intel Corpor Corporati ation on introd introduce uced d an 8 bit 8051 8051 microco microcontr ntroll oller er in 1981. 1981. This This microcontroller has 128 byte RAM, 4K bytes ROM, two timers one serial ports and four I/O ports on single chip.8051 is a 8 bit processor because CPU can work 8 bit data at a time. If data is larger then 8 bit, it has to be broken into pieces of 8 bit. Intel allowed other manufacturers to make flavors of 8051 with the condition that it should be code compatible with Intel 8051. There are 20 vendors like Philips, siemens; Dallas, OKI, Fujitsu, Atmel, etc. are building their own versions of the 8051.

Comparison Of Some 8051 Family.

Chip 8031 8032 8051 8052 8751 8752 89C51 89C52 89C1051

ROM(bytes) --4K 8K 4K(EPROM) 8K(EPROM) 4K flash 8K flash 1K flash

RAM(bytes) 128 256 128 256 128 256 128 256 64

Timers 2 3 2 3 2 3 2 3 1

I/O pins 32 32 32 32 32 32 32 32 15

(20 pin) 89C2051 89S51

2K flash 4K flash

128 128

2 2

15 40


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Reasons For The Success Of Microcontroller:-

•

Microcontrollers have powerful, cleverly chosen electronics which is able to

control a variety of processes and devices( industrial automatics, voltage, temperature, engines, etc) independently or by means of I/O instruments such as switches, buttons, sensors, LCD screens, relays…. Etc. •

Their low cost makes them suitable for installing in places, which attracted no

such interest in the past. This is the fast accountable for today’s market being swamped with cheap automation and “intelligent” toys. •

Writing and loading a program into microcontroller is very easy. All that is

required is; any PC (software is very friendly and intuitive) and one simple device (programmer) for loading a written program in microcontroller.

•

Block Diagram Of Microcontroller:-

A microcontroller is an integrated chip that is often part of an embedded system. The microcontroller includes a CPU, RAM, ROM, I/O ports and timers like a standard computer, but because they are designed to execute only a single specific task to control a single system, they are much smaller and simplified so that they can include all the functions required on a single chip. Simplified block diagram of the microcontroller is shown in figure1.


33


Fig 1: simplified block diagram of the microcontroller

Microcontroller incorporates all features found in microprocessor Such as ALU, General purpose registers, accumulators, program counters, stack pointer, timing control unit, interrupts etc. In addition to these microcontrollers incorporates ROM, RAM, I/O, serial I/O, timers etc.

Parallel Serial Input-Output Port:-

Microcontroller contains parallel input

output ports to interface it with real world. For Example: 8051 contains 4 parallel input-output ports to interface with I/O devices. The 8085 microprocessor requires separate chips such as 8255 (programmable peripheral interface) to interface it with I/O devices. Microcontroller also has in built serial port. Serial communication with microcontroller is simpler.

•

Timers: Microcontroller has inbuilt timers. 8051 has 2 16 bit timers. Timers provide real time interrupt to the processor for specific events. It can be used as a counter to count number of events. Typical example is object counter. Interrupt is generated when count value overflows.


34

GSM BASED IRRIGATION SYSTEM •

ROM: Microcontroller has inbuilt Read only memory (ROM) which is used to store program code and data required during execution such as look up

tables. 8051 microcontrollers has 4K-ROM, 8751 has 4K EPROM (erasable programmable read only memory), 89C51 has 4K flash memory. ROM is programmed during manufacturing process. EPROM can be programmed using EPROM programmer. It needs to erase using ultraviolet eraser. 89C51 is very popular version of 8051 because it contains flash memory. It is ideal for fast development since flash memory can be erased and programmed in seconds. Erasing and programming can be done by microcontroller programmer unit itself.

•

RAM: Microcontroller has inbuilt Random Access Memory. It is used to store information for temporary use. CPU can write RAM as well as read it. Any information stored in the RAM is lost when power is switched off. 8031/8051has 128 bytes Ram while 8032/8052 has 256 byte of RAM.

•

General Microcontroller based System:-


35


Fig 2: general microcontroller based system

Microcontroller are dedicated to one task and run one specific program. The program is stored in ROM (read only memory) and generally does not change. Microcontroller often uses flash, EEPROM or EPROM as their storage device to allow field programmability so they are flexible to use.

Once program is tested and found correct i.e. prototype is developed then OTP (one time programmable) microcontrollers can be used because they are chip.

These are multiple architecture used in microcontrollers, the predominant architecture is CISC (complex instruction set computer), which allows the microcont-


36


roller to contain multiple control instructions that can be executed with a single macro instruction. Another is RISC (reduced instruction set computer ) architecture, which implements fewer instructions, but delivers greater simplicity and lower power consumption. A highly integrated chip that contains all the components comprising a controller . Typically this includes a CPU, RAM, some form of ROM, I/O ports, and timers. Unlike a general-purpose computer, which also includes all of these components, a microcontroller is designed for a very specific task -- to control a particular system. As a result, the parts can be simplified and reduced, which cuts down on production costs. Microcontrollers are sometimes called embedded microcontrollers, which just means that they are part of an embedded system -- that is, one part of a larger device or system.

•

MicroMo Electronics: Microcontrollers :Specializes in the design, assembly and application of high precision,

miniature DC drive systems, components, and motion control systems.

•

Parallax Microcontrollers:Broad-line distributor web site features real-time stock status and

pricing, online ordering, RFQ, technical support, product datasheets and photos.


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MICROCONTROLLER


38


A Microcontroller (also MCU or µC) is a computer -on-a-chip. It is a type of microprocessor emphasizing high integration, low power consumption, selfsufficiency and cost-effectiveness, in contrast to a general-purpose microprocessor (the kind used in a PC). In addition to the usual arithmetic and logic elements of a general purpose

microprocessor, the microcontroller typically integrates additional elements such as read-write memory for data storage, read-only memory, such as flash for code storage, EEPROM for permanent data storage, peripheral devices, and input/output interfaces. At clock speeds of as little as a few MHz or even lower, microcontrollers often operate at very low speed compared to modern day microprocessors, but this is adequate for typical applications. They consume relatively little power (militates), and will generally have the ability to sleep while waiting for an interesting peripheral event such as a button press to wake them up again to do something. Power consumption while sleeping may be just nano watts, making them ideal for low power and long lasting battery applications. Microcontrollers are frequently used in automatically controlled products and devices, such as automobile engine control systems, remote controls, office machines, appliances, power tools, and toys. By reducing the size, cost, and power consumption compared to a design using a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to electronically control many more processes.


39


EMBEDDED DESIGN:- The majority of computer systems in use today are embedded in other machinery, such as telephones, clocks, appliances, and vehicles. An embedded system may have minimal requirements for memory and program length. Input and output devices may be discrete switches, relays, or solenoids. An embedded controller may lack any human-readable interface devices at all. For example, embedded systems usually don't have keyboards, screens, disks, printers, or other recognizable I/O devices of a personal computer . Microcontrollers may control electric motors, relays or voltages, and may read switches, variable resistors or other electronic devices.

HIGHER INTEGRATION:- In contrast to general-purpose CPUs, microcontrollers may not implement an external address or data bus as they integrate RAM and non-volatile memory on the same chip as the CPU. Using fewer pins, the chip can be placed in a much smaller, cheaper package. Integrating the memory and other peripherals on a single chip and testing them as a unit increases the cost of that chip, but often results in decreased net cost of the embedded system as a whole. Even if the cost of a CPU that has integrated peripherals is slightly more than the cost of a CPU + external peripherals, having fewer chips typically allows a smaller and cheaper circuit board, and reduces the labor required to assemble and test the ci rcuit board.


40


A microcontroller is a single integrated circuit, commonly with the following features:•

central processing unit - ranging from small and simple 4-bit processors to complex 32- or 64-bit processors

•

discrete input and output bits, allowing control or detection of the logic state of an individual package pin

•

serial input/output such as serial ports (UARTs)

•

other serial communications interfaces like I²C, Serial Peripheral Interface and Controller Area Network for system interconnect

•

peripherals such as timers, event counters, PWM generators, and watchdog

•

volatile memory (RAM) for data storage

•

ROM, EPROM, [EEPROM] or Flash memory for program and operating parameter storage

•

clock generator - often an oscillator for a quartz timing crystal, resonator or RC circuit

•

many include analog-to-digital converters

•

in-circuit programming and debugging support

This integration drastically reduces the number of chips and the amount of wiring and PCB space that would be needed to produce equivalent systems using separate chips. Furthermore, and on low pin count devices in particular, each pin may interface to several internal peripherals, with the pin function selected by software. This allows a part to be used in a wider variety of applications than if pins had dedicated functions. Microcontrollers have proved to be highly popular in embedded systems since their introduction in the 1970s. Some microcontrollers use a Harvard architecture: separate memory buses for instructions and data, allowing accesses to take place concurrently. Where a Harvard architecture is used, instruction words for the processor may be a different bit size than the length of internal memory and registers; for example: 12-bit instructions used with 8-bit data registers.


41


The decision of which peripheral to integrate is often difficult. The microcontroller vendors often trade operating frequencies and system design flexibility against time-to-market requirements from their customers and overall lower system cost. Manufacturers have to balance the need to minimize the chip size against additional functionality. Microcontroller architectures vary widely. Some designs include general-

purpose microprocessor cores, with one or more ROM, RAM, or I/O functions integrated onto the package. Other designs are purpose built for control applications. A microcontroller instruction set usually has many instructions intended for bit-wise operations to make control programs more compact. For example, a general purpose processor might require several instructions to test a bit in a register and branch if the bit is set, where a microcontroller could have a single instruction that would provide that commonly-required function .

LARGE VOLUMES Microcontrollers take the largest share of sales in the wider microprocessor market. Over 50% are "simple" controllers, and another 20% are more specialized digital signal processors (DSPs)[citation needed ]. A typical home in a developed country is likely to have only one or two general-purpose microprocessors but somewhere between one and two dozen microcontrollers. A typical mid range automobile has as many as 50 or more microcontrollers. They can also be found in almost any electrical device: washing machines, microwave ovens, telephones etc.


42


Manufacturers have often produced special versions of their microcontrollers in order to help the hardware and software development of the target system. These have included EPROM versions that have a "window" on the top of the device through which program memory can be erased by ultra violet light, ready for reprogramming after a programming ("burn") and test cycle. An economical option for intermediate levels of production (usually a few score to a few thousand parts) is a one-time programmable (OTP) microcontroller. This uses the same die as the UV EPROM version of the part, and is programmed on the same equipment, but the package does not include the expensive quartz window required to admit UV light on to the chip. Other versions may be available where the ROM is accessed as an external device rather than as internal memory. A simple EPROM programmer, rather than a more complex and expensive microcontroller programmer, may then be used, however there is a potential loss of functionality through pin outs being tied up with external memory addressing rather than for general input/output. These kind of devices usually carry a higher cost but if the target production quantities are small, certainly in the case of a hobbyist, they can be the most economical option compared with the set up charges involved in mask programmed devices. A more rarely encountered development microcontroller is the "piggy back" version. This device has no internal ROM memory; instead pin outs on the top of the microcontroller form a socket into which a standard EPROM program memory device may be installed. The benefit of this approach is the release of microcontroller pins for Input and output use rather than program memory. These kinds of devices are normally expensive and are impractical for anything but the development phase of a project or very small production quantities.


43


The use of field-programmable devices on a microcontroller may allow field update of the firmware or permit late factory revisions to products that have been assembled but not yet shipped. Programmable memory also reduces the lead time required for deployment of a new product. Where a large number of systems will be made (say, several thousand), the cost of a mask-programmed memory is amortized over all products sold. A simpler integrated circuit process is used, and the contents of the read-only memory are set In the last step of chip manufacture instead of after assembly and test. However, mask-programmed parts cannot be updated in the field. If product firmware updates are still contemplated, a socket may be used to hold the controller which can then be replaced by a service technician, if required.

PROGRAMMING ENVIRONMENTS Microcontrollers were originally programmed only in assembly language, but various high-level programming languages are now also in common use to target microcontrollers. These languages are either designed specially for the purpose, or versions of general purpose languages such as the C programming language. Compilers for general purpose languages will typically have some restric tions as well as enhancements to better support the unique characteristics of microcontrollers. Interpreter firmware is also available for some microcontrollers. The Intel 8052 and Zilog Z8 were available with BASIC very early on, and BASIC is more recently used in the BASIC Stamp MCUs. Some microcontrollers have environments to aid developing certain types of applications, e.g. Analog Device's

Blackfin processors with the

LabVIEW

environment and its programming language "G".


44


Simulators are available for some microcontrollers, such as in Microchip's MPLAB environment. These allow a developer to analyse what the behaviour of the microcontroller and their program should be if they were using the actual part. A simulator will show the internal processor state and also that of the outputs, as well as allowing input signals to be generated. While on the one hand most simulators will be limited from being unable to simulate much other hardware in a system, they can exercise conditions that may otherwise be hard to reproduce at will in the physical implementation, and can be the quickest way to debug and analyse problems. Recent microcontrollers integrated with on-chip debug circuitry accessed by In-circuit emulator via JTAG enables a programmer to debug the software of an embedded system with a debugger .

INTERRUPT LATENCY In contrast to general-purpose computers, microcontrollers used in embedded systems often seek to minimize interrupt latency over instruction throughput. When an electronic device causes an interrupt, the intermediate results, the registers, have to be saved before the software responsible for handling the interrupt can run, and then must be put back after it is finished. If there are more registers, this saving and restoring process takes more time, increasing the latency. Low-latency MCUs generally have relatively few registers in their central processing units, or they have "shadow registers", a duplicate register set that is only used by the interrupt software.


45


What is Inside an LED? LED's are special diodes that emit light when connected in a circuit. They are frequently used as "pilot" lights in electronic appliances to indicate whether the circuit is closed or not. A a clear (or often colored) epoxy case enclosed the heart of an LED, the semi-conductor chip.

The two wires extending below the LED epoxy enclosure, or the "bulb" indicate how the LED should be connected into a circuit. The negative side of an LED lead is indicated in two ways: 1) by the flat side of the bulb, and 2) by the

shorter of the two wires extending from the LED. The negative lead should be connected to the negative terminal of a battery. LED's operate at relative low voltages between about 1 and 4 volts, and draw currents between about 10 and 40

mill amperes. Voltages and currents substantially above these values can melt a LEDchip.


46


The most important part of a light emitting diode (LED) is the semiconductor chip located in the center of the bulb as shown at the right. The chip has two regions separated by a junction. The p region is dominated by positive electric charges,

The n region is dominated by negative electric charges. The junction acts as a barrier to the flow of electrons between the p and the n regions. Only when sufficient voltage is applied to the semi-conductor chip, can the current flow, and the electrons

cross

the

junction

into

the

p

region.

In the absence of a large enough electric potential difference (voltage) across the LED leads, the junction presents an electric potential barrier to the flow of electrons.

LED leads

<-- --> side lead on flat side of bulb = negative


47


•

What Causes the LED to Emit Light and What Determines the Color of the Light? When sufficient voltage is applied to the chip across the leads of the LED,

electrons can move easily in only one direction across the junction between the p and n regions. In the p region there are many more positive than negative charges. In the n region the electrons are more numerous than the positive electric charges. When a voltage is applied and the current starts to flow, electrons in the n region have sufficient energy to move across the junction into the p region. Once in the p

region the electrons are immediately attracted to the positive charges due to the mutual Coulomb forces of attraction between opposite electric charges. When an electron moves sufficiently close to a positive charge in the p region, the two charges"re-combine".

Each time an electron recombines with a positive charge, electric potential energy is converted into electromagnetic energy. For each recombination of a negative and a positive charge, a quantum of electromagnetic energy is emitted in the form of a photon of light with a frequency characteristic of the semi-conductor material (usually a combination of the chemical elements gallium, arsenic and phosphorus). Only photons in a very narrow frequency range can be emitted by any material. LED's that emit different colors are made of different semi-conductor materials, and require different energies to light them.


48


DESCRIPTION A miniaturized receiver for infrared remote control and IR data transmission. PIN diode and preamplifier are assembled on lead frame. The epoxy package is designed as IR filter. The demodulated output signal can directly be decoded by a microprocessor. The main benefit is the operation with high data rates and long distances .

•

•

FEATURES o

Photo detector and preamplifier in one package

o

Internal band filter for PCM frequency

o

Internal shielding against electrical field disturbance

o

TTL and CMOS compatibility

o

Output active low

o

Small size package

SPECIAL FEATURES o

Supply voltage 5.5 V

o

Short settling time after power on

o

High envelope duty cycle can be received

o

Enhanced immunity against disturbance from energy

o

saving lamps

o

B.P.F Center Frequency 38khz

o

Peak Emission Wavelength 940nm


49


APPLICATION

•

•

o

AV instruments such as Audio, TV, VCR, CD, DVD,

o

MD etc.

o

Home appliances such as Air conditioner, Fan etc.

o

The other equipments with wireless remote control.

o

CATV set top boxes.

o

Multi-media Equipment.

o

Sensors and light barrier systems for long distances

IR RECEIVER CODES

o

Best works with: Rc6 Code, Rcmm Code, Sony 15bit

o

Code

o

Also suitable for: Grundig Code, Nec Code, Rc5

o

Code, R-2000 Code, Rca Code, Sharp Code, Sony

o

12bit Code, Zenith Code

o

Not recommended for: Rcs-80 Code, High Data Rate

o

Code


50


Diode

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

Figure 2: Various semiconductor diodes. Bottom: A bridge rectifier


51


Figure 3: Structure of a vacuum tube diode 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). Thus, the diode can be thought of as an electronic version of a check valve. 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.Early diodes included “cat’s whisker” crystals and vacuum tube devices (also called thermionic valves). Today the most common diodes are made from semiconductor materials such as silicon or germanium.

•


52


History Although the crystal diode was popularized before the thermionic diode,

harmonic and solid state diodes were developed in parallel. The principle of operation of harmonic diodes was discovered by Frederick Guthrie in 1873. [1] The principle of operation of crystal diodes was discovered in 1874 by the German scientist, Karl Ferdinand Braun.[2] Thermion diode principles were rediscovered by Thomas Edison on February 13, 1880 and he was awarded a patent in 1883 ( U.S. Patent 307,031 ), but developed the idea no further. Braun patented the crystal rectifier in 1899 [1]. Braun's discovery was further developed by Jag dish Chandra Bose into a useful device for radio detection. The first radio receiver using a crystal diode was built around 1900 by Greenleaf Whittier Pickard. The first thermionic diode was patented in Britain by John Ambrose Fleming (scientific adviser to the Marconi Company and former Edison employee[2]) on November 16, 1904 (U.S. Patent 803,684 in November 1905). Pickard received a patent for a silicon crystal detector on November 20, 1906 [3] (U.S. Patent 836,531 ). At the time of their invention, such devices were known as rectifiers. In 1919, William Henry Eccles coined the term diode from Greek roots; di means "two", and

ode (from odos) means "path".


53


Thermionic and gaseous state diodes

Figure 4: The symbol for an indirect heated vacuum tube diode. From top to bottom, the components are the anode, the cathode, and the heater filament. Thermionic diodes are thermionic valve devices (also known as vacuum tubes), which are arrangements of electrodes surrounded by a vacuum within a glass envelope. Early examples were fairly similar in appearance to incandescent light bulbs. In thermionic valve diodes, a current is passed through the heater filament. This indirectly heats the cathode, another filament treated with a mixture of barium and strontium oxides, which are oxides of alkaline earth metals; these substances are chosen because they have a small work function. (Some valves use direct heating, in which a tungsten filament acts as both cathode and emitter.) The heat causes thermionic emission of electrons into the vacuum. In forward operation, a surrounding metal electrode, called the anode, is positively charged, so that it electrostatically attracts the emitted electrons. However, electrons are not easily released from the unheated anode surface when the voltage polarity is reversed and hence any reverse flow is a very tiny current. For much of the 20th century, thermionic valve diodes were used in analog signal applications, and as rectifiers in many power supplies. Today, valve diodes


54


are only used in niche applications, such as rectifiers in guitar and hi-fi valve amplifiers, and specialized high-voltage equipment.

Semiconductor diodes Most 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 characteristic A 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 electronhole pair that recombines, a positively-charged dopant ion is left behind in the Ndoped 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.


55


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 5: 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.


56


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 i s 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.


57


Schottky diode equation The Shockley ideal diode equation or the diode law (named after transistor co-inventor William Bradford Shockley, not to be confused with tetrode inventor Walter H. Scotty) is the I–V characteristic of an ideal diode in either forward or reverse bias (or no bias). The equation is:

where

I is the diode current, I S is a scale factor called the saturation current , V D is the voltage across the diode, V T is the thermal voltage, and n is the emission coefficient , also known as the ideality factor . The emission coefficient n varies from about 1 to 2 depending on the fabrication process and semiconductor material and in many cases is assumed to be approximately equal to 1 (thus the notation n is omitted). The thermal voltage V T is approximately 25.85 mV at 300 K, a temperature close to “room temperature” commonly used in device simulation software. At any temperature it is a known constant defined by:

where

q is the magnitude of charge on an electron (the elementary charge), I.E.T.E. RAJKOT SUBCENTER

58


k is Boltzmann’s constant,

T is the absolute temperature of the p-n junction in kelvins The Shockley ideal diode equation or the diode law is derived with the assumption that the only processes giving ris e to current in the diode are drift (due to electrical field), diffusion, and thermal recombination-generation. It also assumes that the recombination-generation (R-G) current in the depletion region is insignificant. This means that the Shockley equation doesn’t account for the processes involved in reverse breakdown and photon-assisted R-G. Additionally, it doesn’t describe the “leveling off” of the I–V curve at high forward bias due to internal resistance. Under reverse bias voltages (see Figure 5) the exponential in the diode equation is negligible, and the current is a constant (negative) reverse current value of -I S. The reverse breakdown region is not modeled by the Shockley diode equation.For even rather small forward bias voltages (see Figure 5) the exponential is very large because the thermal voltage is very small, so the subtracted ‘1’ in the diode equation is negligible and the forward diode current is often approximated as

The use of the diode equation in circuit problems is illustrated in the article on diode modeling.

Small-signal behavior For circuit design, a small-signal model of the diode behavior often proves useful. A specific example of diode modeling is discussed in the article on small-signal circuits.


59


Types of semiconductor diode:-

Diode

Light-emitting diode

Zener

Schottky

Tunnel

diode

diode

diode

Photodiode

Varicap

Silicon controlled rectifier

Figure 7: Some diode symbols There are several types of junction diodes, which either emphasize a different physical aspect of a diode often by geometric scaling, doping level, choosing the right electrodes, are just an application of a diode in a special circuit, or are really different devices like the Gunn and laser diode and the MOSFET: Normal (p-n) diodes which operate as described above. Usually made of doped silicon or, more rarely, germanium. Before the development of modern silicon power rectifier diodes, cuprous oxide and later selenium was used; its low efficiency gave it a much higher forward voltage drop (typically 1.4–1.7 V per “cell”, with multiple cells stacked to increase the peak inverse voltage rating in high voltage rectifiers), and required a large heat sink (often an extension of the diode’s metal substrate), much larger than a silicon diode of the same current ratings would require. The vast majority of all diodes are the p-n diodes found in CMOS integrated circuits, which include two diodes per pin and many other internal diodes.


60


Avalanche Diodes:Diodes that conduct in the reverse direction when the reverse bias voltage exceeds the breakdown voltage. These are electrically very similar to Zener diodes, and are often mistakenly called Zener diodes, but break down by a different mechanism, the avalanche effect . This occurs when the reverse electric field across the p-n junction causes a wave of ionization, reminiscent of an avalanche, leading to a large current. Avalanche diodes are designed to break down at a well-defined reverse voltage without being destroyed. The difference between the avalanche diode (which has a reverse breakdown above about 6.2 V) and the Zener is that the channel length of the former exceeds the “mean free path” of the electrons, so there are collisions between them on the way out. The only practical difference is that the two types have temperature coefficients of opposite polarities.

•

Cat’s whisker or crystal diodes:These are a type of point contact diode. The cat’s whisker diode consists of a thin or sharpened metal wire pressed against a semiconducting crystal, typically galena or a piece of coal.[4] The wire forms the anode and the crystal forms the cathode. Cat’s whisker diodes were also called crystal diodes and found application in crystal radio receivers. Cat’s whisker diodes are obsolete.

•

Constant current diodes:These are actually a JFET with the gate shorted to the source, and function like a two-terminal current-limiting analog to the Zener diode; they allow a current through them to rise to a certain value, and then level off at a specific


61


value.

Also

called

CLDs,

constant-current

diodes,

diode-connected

transistors, or current-regulating diodes.

•

Esaki or tunnel diodes these have a region of operation showing negative resistance caused by quantum tunneling, thus allowing amplification of signals and very simple bistable circuits. These diodes are also the type most resistant to nuclear radiation.

•

Gunn diodes:These are similar to tunnel diodes in that they are made of materials such as GaAs or InP that exhibit a region of negative differential resistance. With appropriate biasing, dipole domains form and travel across the diode, allowing high frequency microwave oscillators to be built.

•

Light-emitting diodes (LEDs):In a diode formed from a direct band-gap semiconductor, such as gallium arsenide, carriers that cross the junction emit photons when they recombine with the majority carrier on the other side. Depending on the material, wavelengths (or colors) from the infrared to the near ultraviolet may be produced. The forward potential of these diodes depends on the wavelength of the emitted photons: 1.2 V corresponds to red, 2.4 to violet. The first LEDs were red and yellow, and higher-frequency diodes have been developed over time. All LEDs produce incoherent, narrow-spectrum light; “white” LEDs are actually combinations of three LEDs of a different color, or a blue LED with a yellow scintillator coating. LEDs can also be used as low-efficiency photodiodes in signal applications. An LED may be paired with a photodiode or phototransistor in the same package, to form an opto-isolator .


62


•

Laser diodes:When an LED-like structure is contained in a resonant cavity formed by polishing the parallel end faces, a laser can be formed. Laser diodes are commonly used in optical storage devices and for high speed optical communication.

•

Peltier diodes:Are used as sensors, heat engines for thermoelectric cooling. Charge carriers absorb and emit their band gap energies as heat.

•

Photodiodes:All semiconductors are subject to optical charge carrier generation. This is typically an undesired effect, so most semiconductors are packaged in light blocking material. Photodiodes are intended to sense light( photodetector ), so they are packaged in materials that allow light to pass, and are usually PIN (the kind of diode most sensitive to light). A photodiode can be used in solar cells, in photometry, or in optical communications. Multiple photodiodes may be packaged in a single device, either as a linear array or as a twodimensional array. These arrays should not be confused with charge-coupled devices.

•

Point-contact diodes :These work the same as the junction semiconductor diodes described above, but their construction is simpler. A block of n-type semiconductor is built, and a conducting sharp-point contact made with some group-3 metal is placed in contact with the semiconductor. Some metal migrates into the semiconductor to make a small region of p-type semiconductor near the contact. The long-


63


popular 1N34 germanium version is still used in radio receivers as a detector and occasionally in specialized analog electronics.

•

PIN diodes:A PIN diode has a central un-doped, or intrinsic , layer, forming a ptype/intrinsic/n-type structure. They are used as radio frequency switches and attenuators. They are also used as large volume ionizing radiation detectors and as photodetectors. PIN diodes are also used in power electronics, as their central layer can withstand high voltages. Furthermore, the PIN structure can be found in many power semiconductor devices, such as IGBTs, power MOSFETs, and thyristors.

•

Switching diodes:Switching diodes, sometimes also called small signal diodes, are a single p-n diode in a discrete package. A switching diode provides essentially the same function as a switch. Below the specified applied voltage it has high resistance similar to an open switch, while above that voltage it suddenly changes to the low resistance of a closed switch. They are used in devices such as ring modulation.

•

Schottky diodes:Schottky diodes are constructed from a metal to semiconductor contact. They have a lower forward voltage drop than p-n junction diodes. Their forward voltage drop at forward currents of about 1 mA is in the range 0.15 V to 0.45 V, which makes them useful in voltage clamping applications and prevention


64


of transistor saturation. They can also be used as low loss rectifiers although their reverse leakage current is generally higher than that of other diodes.

Schottky diodes are majority carrier devices and so do not suffer from minority carrier storage problems that slow down many other diodes — so they have a faster “reverse recovery” than p-n junction diodes. They also tend to have much lower junction capacitance than p-n diodes which provides for high switching speeds and their use in high-speed circuitry and RF devices such as switched-mode power supply, mixers and detectors.

•

Super Barrier Diodes:Super barrier diodes are rectifier diodes that incorporate the low forward voltage drop of the Schottky diode with the surge-handling capability and low reverse leakage current of a normal p-n junction diode.

•

Gold-doped” diodes:As a dopant, gold (or platinum) acts as recombination centers, which help a fast recombination of minority carriers. This allows the diode to operate at signal frequencies, at the expense of a higher forward voltage drop. Gold doped diodes are faster than other p-n diodes (but not as fast as Schottky diodes). They also have less reverse-current leakage than Schottky diodes (but not as good as other p-n diodes).[7].[3] A typical example is the 1N914.

•

Snap-off or Step recovery diodes:The term ‘step recovery’ relates to the form of the reverse recovery characteristic of these devices. After a forward current has been passing in an SRD and the current is interrupted or reversed, the reverse conduction will cease very abruptly (as in a step waveform). SRDs can therefore provide very


65


fast voltage transitions by the very sudden disappearance of the charge carriers.

•

Transient voltage suppression diode (TVS):These

are

avalanche

diodes designed specifically to protect

other

semiconductor devices from high-voltage transients. Their p-n junctions have a much larger cross-sectional area than those of a normal diode, allowing them to conduct large currents to ground without sustaining damage.

•

Varicap or varactor diodes:These are used as voltage-controlled capacitors. These are important in PLL (phase-locked loop) and FLL (frequency-locked loop) circuits, allowing tuning circuits, such as those in television receivers, to lock quickly, replacing older designs that took a long time to warm up and lock. A PLL is faster than an FLL, but prone to integer harmonic locking (if one attempts to lock to a broadband signal). They also enabled tunable oscillators in early discrete tuning of radios, where a cheap and stable, but fixed-frequency, crystal oscillator provided the reference frequency for a voltage-controlled oscillator .

•

Zener diodes:Diodes that can be made to conduct backwards. This effect, called Zener breakdown, occurs at a precisely defined voltage, allowing the diode to be used as a precision voltage reference. In practical voltage reference circuits Zener and switching diodes are connected in series and opposite directions to balance the temperature coefficient to near zero. Some devices labeled as high-voltage Zener diodes are actually avalanche diodes (see below). Two


66


(equivalent) Zeners in series and in reverse order, in the same package, constitute a transient absorber (or Transorb, a registered trademark). The Zener diode is named for Dr. Clarence Melvin Zener of Southern Illinois University, inventor of the device.

RESISTOR

A 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. Resistors are used as part of electrical networks and electronic circuits.

•

IDENTIFYING RESISTORS

Most axial resistors use a pattern of colored stripes to indicate resistance. Surface-mount ones 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.


67


FOUR-BAND AXIAL RESISTORS

Color Black Brown Red Orange Yellow Green Blue Violet Gray White Gold Silver None

1st band 2nd band 3rd band (multiplier) 4th band (tolerance) Temp. Coefficient 0 0 ×100 1 1 ×10 1 ±1% (F) 100 ppm 2 2 2 ×10 ±2% (G) 50 ppm 3 3 ×10 3 15 ppm 4 4 ×10 4 25 ppm 5 5 5 ×10 ±0.5% (D) 6 6 6 ×10 ±0.25% (C) 7 7 7 ×10 ±0.1% (B) 8 8 ×108 ±0.05% (A) 9 9 ×109 ×10-1 ±5% (J) -2 ×10 ±10% (K) ±20% (M)

Electronic Color Code I.E.T.E. RAJKOT SUBCENTER

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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. 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%.

PREFERRED VALUES :Preferred Number Resistors are manufactured in values from a few milliohms to about a gigaohm; only a limited range of values from the IEC 60063 preferred number series are commonly available. These series are called E6, E12, E24, E96 and E192. The number tells how many standardized values exist in each decade (e.g. between 10 and 100, or between 100 and 1000). So resistors conforming to the E12 series, can have 12 distinct values between 10 and 100, whereas those confirming to the E24 series would have 24 distinct values. In practice, the discrete component sold as a "resistor" is not a perfect resistance, as defined above. Resistors are often marked with their tolerance (maximum expected variation from the marked resistance).

•

NOISE


69


In precision circuits, electronic noise becomes of utmost concern. As dissipative elements, resistors will naturally produce a fluctuating "noise" voltage across their terminals. This Johnson–Nyquist noise is predicted by the FluctuationDissipation theorem and is a fundamental noise source present in all resistors which must beconsidered in constructing low-noise electronics. For example, the gain in a simple (non-)inverting amplifier is set using a voltage divider. Noise considerations dictate that the smallest practical resistance should be used, since the noise voltage scales with resistance, and any resistor noise in the voltage divider will be impressed upon the amplifier's output.

Although Johnson-Nyquist noise is a fundamental noise source, resistors frequently exhibit other, "non-fundamental" sources of noise. Noise due to these sources is called "excess noise." Thick-film and carbon composition resistors are notorious for excess noise at low frequencies. Wire-wound and thin-film resistors, though much more expensive, are often utilized for their better noise characteristics .

•

FAILURE MODES AND PITFALLS


70


Like every part, resistors can fail; the usual way depends on their construction. Carbon composition resistors and metal film resistors typically fail as open circuits. Carbon-film resistors typically fail as short circuits. Various effects become important in high-precision applications. Small voltage differentials may appear on the resistors due to thermoelectric effect if their ends are not kept at the same temperature. The voltages appear in the junctions of the resistor leads with the circuit board and with the resistor body. Common metal film resistors show such effect at magnitude of about 20 µV/°C. Some carbon composition resistors can go as high as 400 µV/°C, and specially constructed resistors can go as low as 0.05 µV/°C. In applications where thermoelectric effects may become important, care has to be taken to e.g. mount the resistors horizontally to avoid temperature gradients and to mind the air flow over the board.

CAPACITOR


71


Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; throughhole tantalum at top right; through-hole electrolytic at bottom right. Major scale divisions are cm. A 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 electrical circuit and electronic circuits as energy-storage devices. They can also be used to differentiate between highfrequency 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. I.E.T.E. RAJKOT SUBCENTER

72


•

CAPACITANCE The 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:

C=

Q V

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).

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 has been moved from one plate to the other. This electric field creates a potential difference V = E·d between the plates of this simple parallel-plate capacitor. I.E.T.E. RAJKOT SUBCENTER

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The capacitance is proportional to the surface area of the conducting plate and inversely proportional to the distance between the plates. It is also proportional to the permittivity of the dielectric (that is, non-conducting) substance that separates the plates. The capacitance of a parallel-plate capacitor is given by:

C=

A ε d

; A

> >

d

2

where ε is the permittivity of the dielectric (see Dielectric constant), A is the area of the plates and d is the spacing between them.

In the diagram, the rotated molecules create an opposing electric field that partially cancels the field created by the plates, a process called dielectric polarization.

•

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:


74


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, all capacitors made with the same dielectric have about the same maximum energy density (joules of energy per cubic meter).

1

Estored= 2 CV

2

=

1

Q2

2

C

=

1 2

VQ

DC SOURCES:The dielectric between the plates is an insulator and blocks the flow of electrons. A steady current through a capacitor deposits electrons on one plate and removes the same quantity of electrons from the other plate. This process is commonly called 'charging' the capacitor. The current through the capacitor results in the separation of electric charge within the capacitor, which develops an electric field between the plates of the capacitor, equivalently, developing a voltage

difference between the plates. This voltage V is directly proportional to the amount of charge separated Q. Since the current I through the capacitor is the rate at which charge Q is forced through the capacitor (dQ/dt), this can be expressed mathematically as:

I=

dQ dt

=

C

dV dt

Where I is the current flowing in the conventional direction, measured in amperes, dV /dt is the time derivative of voltage, measured in volts per second, and

C is the capacitance in farads. I.E.T.E. RAJKOT SUBCENTER

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For circuits with a constant (DC) voltage source and consisting of only resistors and capacitors, the voltage across the capacitor cannot exceed the voltage of the source. Thus, an equilibrium is reached where the voltage across the capacitor is constant and the current through the capacitor zero. For this reason, it is commonly s dV /dt is the time derivative of voltage, measured in volts per second, and C is the capacitance aid that capacitors block DC.

AC SOURCES:The current through a capacitor due to an AC source reverses direction periodically. That is, the alternating current alternately charges the plates: first in one direction and then the other. With the exception of the instant that the current changes direction, the capacitor current is non-zero at all times during a cycle. For this reason, it is commonly said that capacitors "pass" AC. However, at no time do electrons actually cross between the plates, unless the dielectric breaks down. Such a situation would involve physical damage to the capacitor and likely to the circuit involved as well. Since the voltage across a capacitor is proportional to the integral of the current, as shown above, with sine waves in AC or signal circuits this results in a phase difference of 90 degrees, the current leading the voltage phase angle. It can be shown that the AC voltage across the capacitor is in quadrature with the

alternating current through the capacitor. That is, the voltage and current are 'out-ofphase' by a quarter cycle. The amplitude of the voltage depends on the amplitude of the current divided by the product of the frequency of the current with the capacitance, C. I.E.T.E. RAJKOT SUBCENTER

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APPLICATIONS (1) ENERGY STORAGE:A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery. Capacitors are commonly used in electronic devices to maintain power supply while batteries are being changed. (This prevents loss of information in volatile memory.)

(2) POWER CONDITIONING:-


77


Capacitors are used in power supplies where they smooth the output of a full or half wave rectifier . They can also be used in charge pump circuits as the energy storage element in the generation of higher voltages than the input voltage. Capacitors are connected in parallel with the power circuits of most electronic devices and larger systems (such as factories) to shunt away and conceal current fluctuations from the primary power source to provide a "clean" power supply for signal or control circuits. Audio equipment, for example, uses several capacitors in this way, to shunt away power line hum before it gets into the signal circuitry. The capacitors act as a local reserve for the DC power source, and bypass AC currents from the power supply. This is used in car audio applications, when a stiffening capacitor compensates for the inductance and resistance of the leads to the leadacid car battery.

TRANSFORMER Transformer is a device that transfers electrical energy from one circuit to another through inductively coupled wires. 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 V S is scaled from the primary V P by a factor ideally equal to the ratio of the number of turns of wire in their respective windings: I.E.T.E. RAJKOT SUBCENTER

78


By appropriate selection of the numbers of turns, a transformer thus allows an alternating voltage to be stepped up — by making N S more than N P — or stepped down, by making it less. A key application of transformers is to reduce the current before transmitting electrical energy over long distances through wires. Most wires have resistance and so dissipate electrical energy at a rate proportional to the square of the current through the wire. By transforming electrical power to a high-voltage, and therefore low-current form for transmission and back again afterwards, transformers enable the

economic

transmission

of

power over

long

distances.

Consequently,

transformers have shaped the electricity supply industry, permitting generation to be located remotely from points of demand. All but a fraction of the world's electrical power has passed through a series of transformers by the time it reaches the consumer.

Transformers are some of the most efficient electrical 'machines', with some large units able to transfer 99.75% of their input power to their output. Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tonnes 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 PRINCIPLES:-


79


The transformer is based on two principles: first, that an electric current can produce a magnetic field (electromagnetism) and, second, 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, one changes the strength of its magnetic field; since the secondary coil is wrapped around the same magnetic field, a voltage is induced across the secondary.An ideal step-down transformer showing magnetic flux in the core A simplified transformer design is shown to the right. 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. INDUCTION LAW:The voltage induced across the secondary coil may be calculated from Faraday's law of induction, which states thatWhere V S is the instantaneous voltage,

N S is the number of turns in the secondary coil and Φ equals the total magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicular to the

magnetic field lines, the flux is the product of the magnetic field strength B and the area A through which it cuts. The area is constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer, the instantaneous voltage across the primary winding equals


80


Taking the ratio of the two equations for V S and V P gives the basic equationfor stepping up or stepping down the voltage

•

IDEAL POWER EQUATION


81


The ideal transformer as a circuit element If the secondary coil is attached to a load that allows current to flow, electrical power is transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is perfectly efficient; all the incoming energy is transformed from the primary circuit to the magnetic field and thence to the secondary circuit. If this condition is met, the incoming electric power must equal the outgoing power

P incoming = I PV = P outgoing = I S VS P giving the ideal transformer equation Thus, if the voltage is stepped up ( V S > V P) , then the current is stepped down (I S < I P) by the same factor. In practice, most transformers are very efficient (see below), so that this formula is a good approximation. The impedance in one circuit is transformed by the square of the turns ratio. For example, if an impedance Z S is attached across the terminals of the secondary coil, it ppears to the primary circuit to have an impedance of . This relationship is reciprocal, so that the impedance Z P of the primary circuit appears to the secondary to be .

TECHNICAL DISCUSSION:The simplified description above avoids several complicating factors, in particular the primary current required to establish a magnetic field in the core, and the contribution to the field due to current in the secondary circuit. Models of an ideal transformer typically assume a core of negligible reluctance with two windings of zero resistance.[7] When a voltage is applied to the primary winding, a small current flows, driving flux around the magnetic circuit of the I.E.T.E. RAJKOT SUBCENTER

82


core. The current required to create the flux is termed the magnetising current ; since the ideal core has been assumed to have near-zero reluctance, the magnetising current is negligible, although a presence is still required to create the magnetic field. The changing magnetic field induces an electromotive force (EMF) across each winding. Since the ideal windings have no impedance, they have no associated voltage drop, and so the voltages V P and VS measured at the terminals of the transformer, are equal to the corresponding EMFs. The primary EMF, acting as it does in opposition to the primary voltage, is sometimes termed the " back EMF".This is due to Lenz's law which states that the induction of EMF would always be such that it will oppose development of any such change in magnetic field.

PRACTICAL CONSIDERATIONS:-


83


Flux leakage in a two-winding transformer

FLUX LEAKAGE:

•

Leakage Inductance The ideal transformer model assumes that all flux generated by the primary

winding links all the turns of every winding, including itself. In practice, some flux traverses paths that take it outside the windings. Such flux is termed leakage flux , and manifests itself as self-inductance in series with the mutually coupled transformer windings. Leakage results in energy being alternately stored in and discharged from the magnetic fields with each cycle of the power supply. It is not itself directly a source of power loss, but results in poorer voltage regulation, causing the secondary voltage to fail to be directly proportional to the primary, particularly under heavy load. Distribution transformers are therefore normally designed to have very low leakage inductance

However, in some applications, leakage can be a desirable property, and long magnetic paths, air gaps, or magnetic bypass shunts may be deliberately introduced to a transformer's design to limit the short-circuit current it will supply. Leaky transformers may be used to supply loads that exhibit negative resistance, such as electric arcs, mercury vapor lamps, and neon signs; or for safely handling loads that become periodically short-circuited such as electric arc welders. Air gaps are also used to keep a transformer from saturating, especially audio-frequency transformers that have a DC component added. I.E.T.E. RAJKOT SUBCENTER

84


EFFECT OF FREQUENCY The time-derivative term in Faraday's Law shows that the flux in the core is the integral of the applied voltage. An ideal transformer would, at least hypothetically, work under direct-current excitation, with the core flux increasing linearly with time. In practice, the flux would rise very rapidly to the point where magnetic saturation of the core occurred, causing a huge increase in the magnetising current and overheating the transformer. All practical transformers must therefore operate under alternating (or pulsed) current conditions. Transformer universal EMF equation If the flux in the core is sinusoidal, the relationship for either winding between its rms EMF E, and the supply frequency f, number of turns N, core cross-sectional area a and peak magnetic flux density B is given by the universal EMF equation:

. The EMF of a transformer at a given flux density increases with frequency, an effect predicted by the universal transformer EMF equation. By operating at higher frequencies, transformers can be physically more compact because a given core is able to transfer more power without reaching saturation, and fewer turns are needed to achieve the same impedance. However properties such as core loss and conductor skin effect also increase with frequency. Aircraft and military equipment traditionally employ 400 Hz power supplies which are less efficient but this is more than offset by the reduction in core and I.E.T.E. RAJKOT SUBCENTER

85


winding weight. In general, operation of a transformer at it s designed voltage but at a higher frequency than intended will lead to reduced magnetising current. At a frequency lower than the design value, with the rated voltage applied, the magnetising current may increase to an excessive level. Operation of a transformer at other than its design frequency may require assessment of voltages, losses, and cooling to establish if safe operation is practical. For example, transformers may need to be equipped with "volts per hertz" over-excitation relays to protect the transformer from overvoltage at higher than rated frequency. Knowledge of natural frequencies of transformer windings is of importance for the determination of the transient response of the windings to impulse and switching surge voltages.

ENERGY LOSSES:An ideal transformer would have no energy losses, and would therefore be 100% efficient. Despite the transformer being amongst the most efficient of electrical machines, with experimental models using superconducting windings achieving

efficiencies of 99.85%,energy is dissipated in the windings, core, and surrounding structures. Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 95%. A small transformer, such as a plug-in "power brick" used for low-power consumer electronics, may be no more than 85% efficient; although individual power loss is small, the aggregate losses from the very large number of such devices is coming under increased scrutiny. Transformer losses are attributable to several causes and may be differentiated between those originating in the windings, sometimes termed copper I.E.T.E. RAJKOT SUBCENTER 86


loss, and those arising from the magnetic circuit, sometimes termed iron loss. The losses vary with load current, and may furthermore be expressed as "no-load" or "full-load" loss, respectively. Winding resistance dominates load losses, whereas hysteresis and eddy currents losses contribute to over 99% of the no-load loss. The no-load loss can be significant, meaning that even an idle transformer constitutes a drain on an electrical supply, and lending impetus to development of low-loss transformers (also see energy efficient transformer ).

Losses in the transformer arise from:

•

Winding Resistance :-

Current flowing through the windings causes resistive heating of the conductors. At higher frequencies, skin effect and proximity effect create additional winding resistance and losses.

•

Hysteresis losses :Each time the magnetic field is reversed, a small amount of energy is lost due to hysteresis within the core. For a given core material, the loss is proportional to the frequency, and is a function of the peak flux density to which it is subjected.

•

Eddy Currents :-


87


Ferromagnetic materials are also good conductors, and a solid core made from such a material also constitutes a single short-circuited turn throughout its entire length. Eddy currents therefore circulate within the core in a plane normal to the flux, and are responsible for resistive heating of the core material. The eddy current loss is a complex function of the square of supply frequency and inverse square of the material thickness.

•

Magnetostriction:Magnetic flux in a ferromagnetic material, such as the core, causes it to

physically expand and contract slightly with each cycle of the magnetic field, an effect known as magnetostriction. This produces the buzzing sound commonly associated with transformers,[6] and in turn causes losses due to frictional heating in susceptible cores.

•

Mechanical losses :In addition to magnetostriction, the alternating magnetic field causes fluctuating

electromagnetic forces between the primary and secondary windings. These i ncite vibrations within nearby metalwork, adding to the buzzing noise, and consuming a small amount of power. [19]

•

Stray losses :-

Leakage inductance is by itself lossless, since energy supplied to its magnetic fields is returned to the supply with the next half-cycle. However, any leakage flux that intercepts nearby conductive materials such as the transformer's support structure will give rise to eddy currents and be converted to heat.


88



89



90



91



92



93



94



95


v


96



97



98



99



100



101



102



103



104



105



106



107



108



109



110



111



112



113



114



115



116



117


Circuit Symbols Circuit symbols are used in circuit diagrams which show how a circuit is connected together. The actual layout of the components is usually quite different from the circuit diagram. To build a circuit you need a different diagram showing the layout of the parts on strip board or printed circuit board. Resistors Component

Circuit Symbol

Function of Component A resistor restricts the flow of current, for example to limit the current

Resistor

passing through an LED. A resistor is used with a capacitor in a timing circuit. This type of variable resistor with 2 contacts (a rheostat) is usually used to

Variable Resisto r (Rheostat)

control current. Examples include: adjusting lamp brightness, adjusting motor speed, and adjusting the rate of flow of charge into a capacitor in a timing circuit. This type of variable resistor with 3

Variable Resisto r (Potentiometer)

contacts (a potentiometer) is usually used to control voltage. It can be used like this as a transducer converting position (angle of the control spindle) to an electrical signal. This type of variable resistor (a preset) is operated with a small screwdriver or

Variable Resisto r (Preset)

similar tool. It is designed to be set when the circuit is made and then left without further adjustment. Presets are cheaper than normal variable resistors so they are often used in projects to reduce the cost.


118


Capacitors Component

Circuit Symbol

Function of Component A capacitor stores electric charge. A capacitor is used with a resistor in a

Capacitor

timing circuit. It can also be used as a filter, to block DC signals but pass AC signals. A capacitor stores electric charge. This type must be connected the correct way round. A capacitor is

Capacitor,

used with a resistor in a timing

polarized

circuit. It can also be used as a filter, to block DC signals but pass AC signals.

Variable Capacito

A variable capacitor is used in a

r

radio tuner. This type of variable capacitor (a trimmer) is operated with a small

Trimmer

screwdriver or similar tool. It is

Capacitor

designed to be set when the circuit is made and then left without further adjustment.

Diodes Component

Circuit Symbol

Diode LED Light Emitting Diod e

Function of Component A device which only allows current to flow in one direction. A transducer which converts electrical energy to light. A special diode which is used to

Zener Diode

maintain a fixed voltage across its terminals.


119


Photodiode

A light-sensitive diode.

Transistors Component

Circuit Symbol

Function of Component A transistor amplifies current. It can be used with

Transistor NPN

other components to make an amplifier or switching circuit. A transistor amplifies current. It can be used with

Transistor PNP

other components to make an amplifier or switching circuit.

Pezos Transducer

A transducer which converts electrical energy to sound. An amplifier circuit with one input.

Amplifier (general symbol)

Really it is a block diagram symbol because it represents a circuit rather than just one component.

Earphone


A transducer which converts electrical energy to sound.

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Books 1. Electronics projects September 2004 edition 2. Principal of electronics By. V.K. Mehta, 3. Electronics devices and circuits By. J.B. Gupta, 4. Computer fundamental By. B. Ram I.E.T.E. RAJKOT SUBCENTER

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GSM Based Irrigation System

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