Top Banner
CHAPTER 1 Introduction 1.1 Literature Review 1.2 Aim 1.3 Block Diagram 1.4 Description Of Block Diagram 1.5 Circuit Diagram 1.6 List of Components Page | 1
176
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: Final Profect Report

CHAPTER 1

Introduction1.1 Literature Review1.2 Aim1.3 Block Diagram1.4 Description Of Block Diagram1.5 Circuit Diagram1.6 List of Components

Introduction

Page | 1

Page 2: Final Profect Report

The remote control technologies have been used in the fields like factory automation, space exploration, in

places where human access is difficult. As this has been achieved in the domestic systems partially, many

corporations and laboratories are researching the methods which enable human to control and monitor

efficiently and easily in the house or outdoor. Controlling the domestic system regardless of time and space

is an important challenge. As the mobile phone enables us to connect with the outside devices via mobile

communication network regardless of time and space, the mobile phone is a suitable device to control

domestic systems. This paper proposes a method to control a domestic system using a mobile phone,

irrespective of the phone model and mobile phone carrier. The system suggested consists of the mobile

phone normally registered in communication service and a computer that can receive a call from another

phone. Existing methods for control and monitoring, using mobile phones have usage problems because

the cost and need for continuous control. One of the disadvantages, being the lack of feedback during the

process. This paper proposes to solve the problems of existing methods of control that use simple voice

call and SMS. Method proposed uses the DTMF (Dual Tone Multi Frequency) [2], [3], [4] generated when a

keypad button of the mobile phone is pressed by the user. The mobile phone user controls the system by

sending the DTMF tone to the access point. Mobile communication network coverage is larger than that of

LANs, thus user can take advantage of mobile phones to control the system.

DTMF BasicsDTMF is a generic communication term for touch tone (a Registered Trademark of AT&T). The tones

produced when dialing on the keypad on the phone could be used to represent the digits, and a separate

tone is used for each digit. However, there is always a chance that a random sound will be on the same

frequency which will trip up the system. It was suggested that if two tones were used to represent a digit,

the likelihood of a false signal occurring is ruled out. This is the basis of using dual tone in DTMF

communication. DTMF dialing uses a keypad with 12/16 buttons. Each key pressed on the phone

generates two tones of specific frequencies, so a voice or a random signal cannot imitate the tones. One

tone is generated from a high frequency group of tones and the other from low frequency group. The

frequencies generated on pressing different phone keys are shown in the Table 1.

Table 1 – Frequencies Generated on Key Presses

Page | 2

Page 3: Final Profect Report

Each row and column of the keypad corresponds to a certain tone and creates a specific frequency. Each

button lies at the intersection of the two tones as shown in Table 2.

Table 2 – Row and Column Frequency Correspondence

When a button is pressed, both the row and column tones are generated by the telephone instrument.

These two tones will be unique and different from tones of other keys. So, whenever we say that there is a

low and high frequency associated with a button, it is actually the sum of two waves is transmitted.

This fundamental principle can be extended to various applications. DTMF signals can be transmitted over

a radio to switch on or switch off home appliances, flash lights, motors, cameras, warning systems,

irrigation systems and so on. These encoded data can be stored in a microcontroller and can be

transmitted serially to another system for processing.

Page | 3

Page 4: Final Profect Report

The decoder used is M-8870. For operating functions see Fig. 3 – Structure of M-8870. M-8870 includes a

band split filter that separates the high and low tones of the received pair, and a digital decoder that verifies

both the frequency and duration of the received tones before parsing the resulting 4-bitcode to the output

bus.

The M-8870 decoder uses a digital counting technique to determine the frequencies of the limited tones

and to verify that they correspond to standard DTMF frequencies. A complex averaging algorithm is used to

protect against tone simulation by extraneous signals (such as voice) while tolerating small frequency

variations [6], [7].

The algorithm ensures an optimum combination of immunity to talk off and tolerance to interfering signals

(third tones) and noise. When the detector recognizes the simultaneous presence of two valid tones (known

as signal condition), it raises the Early Steering flag (Est.). Any subsequent loss of signal condition will

cause ESt to fall.

SIGNAL CONDITIONINGBefore a decoded tone pair is registered, the receiver checks for valid signal duration (referred to as

character recognition- condition). This check is performed by an external RC time constant driven by ESt. A

logic high on ESt causes VC (see block diagram Fig. 3) to rise as the capacitor discharges.

Provided that signal condition is maintained (ESt remains high) for the validation period (tGTF), VC

reaches the threshold (VTSt) of the steering logic to register the tone pair, thus latching its corresponding 4-

bit code (see DC Characteristics in Data Sheet) into the output latch. At this point, the GT output is

activated and drives VC to VDD. GT continues to drive high as long as ESt remains high.

Finally, after a short delay to allow the output latch to settle, the delayed steering output flag (StD) goes

high, signaling that a received tone pair has been registered. The contents of the output latch are made

available on the 4-bit output bus by raising the three-state control input (OE) to logic high. The steering

circuit works in reverse to validate the inter digit pause between signals.

Thus, as well as rejecting signals too short to be considered valid, the receiver will tolerate signal

interruptions (dropouts) too short to be considered a valid pause. This capability, together with the ability to

select the steering time constants externally, allows the designer to tailor performance to meet a wide

Page | 4

Page 5: Final Profect Report

variety of system requirements. The internal clock circuit of 8870 is completed with addition of external

3.579545 MHz crystal oscillator.

1.1 Literature Review

1. Control of Remote Domestic System Using DTMFTuljappa M Ladwa, Sanjay M Ladwa, R Sudharshan Kaarthik, Alok Ranjan Dhara, Nayan Dalei

Author For Correspondence, Department of Electrical Engineering, NIT Rourkela, Orissa-08

Author For Correspondence, Department of Electronics and Communication Engineering, PES Institute of

Technology, Bangalore-85

Department of Electrical Engineering, NIT Rourkela, Orissa-08

OutlineThe human mind always needs information of interest to control systems of his/her choice. In the age of

electronic systems it is important to be able to control and acquire information from everywhere.

Although many methods to remotely control systems have been devised, the methods have the problems

such as the need for special devices and software to control the system.

This paper suggests a method for control using the DTMF tone generated when the user pushes mobile

phone keypad buttons or when connected to a remote mobile system.

The proposed work has been done experimentally and has been verified in real time.

2. Implementing “Green” PCB production processesSven Lamprecht, Günter Heinz, Neil Patton, Stephen Kenny, Patrick Brooks, Christoph Rickert Atotech

Deutschland GmbH, Berlin, Germany Atotech (Guangzhou) Chemicals LTD., Guangzhou, China Atotech

Deutschland GmbH, Basel, Switzerland [email protected], [email protected],

[email protected], [email protected], [email protected],

[email protected]

OutlineThe impacts of the moving to green electronics on the PCB production process are multifaceted. New

solder alloys lead to a dramatic increase of reflow temperatures and cycle times, impacting formulations of

base materials and requirements for solder able and bondable final finishes. This paper discusses the

impact to the various production processes, ranging from inner-layer processing to surface finishing. Up to

now, there has been only little work done to determine the effect of the move to green electronics on the

inner-layer manufacturing process. This paper will outline the results of comprehensive testing using

different inner-layer bonding systems. Results will be obtained with the new halogen-free materials and will

Page | 5

Page 6: Final Profect Report

be referenced with those from standard FR4 materials. In addition, the impact of the lead-free soldering

profiles will be investigated. The higher soldering temperatures for lead free assembly lead to greater

stresses on the printed circuit board, resulting in new quality requirements for interconnections and barrel

plating. Additionally, low CTE materials are introduced to cope with that situation.

The paper will discuss the impact of those changes to the electroless and electrolytic

metallization processes. The halogen-free requirement puts significant challenges to the formulation of

advanced dielectrics for PCB production. Sufficient Tg value and low water uptake are major aspects for

the development of next generation materials. The paper will discuss a new materials solution for RCF,

which can offer state-of-the-art properties with a halogen-free composition. As the final finish of the PCB is

in direct contact with the lead free assembly process, the effects need to be well understood. Additionally,

the industry is rapidly moving towards HASL alternatives as immersion tin of immersion silver. The paper

will present a summary of test results obtained over the last years, focusing on those new immersion

processes, as well as ENIG (Electro less Nickel Immersion Gold).

3. Remote Controlling Of Home Appliances Through ATelephone LineS. Sivasankar1, D.S.B.P Gunawardena1, M.L.N Perera1

1 Department of Electrical and Electronic Engineering, University of Peradeniya, Sri Lanka

OutlineIn the fast developing world today, the need to control electrical appliances from far away is becoming a

necessity. This report describes a project that was based on this need to control appliances from remote

locations. Here an existing telephone line is used to send electrical signals by which the appliances on the

other end of the telephone line will be controlled. The device is controlled by a PIC microcontroller. The use

of the PIC not only adds flexibility to the design, but also reduces the amount of hardware used. Although

the program used in the PIC is a very basic one, it can be modified to incorporate many more features. In

this project four switches are operated by dialing a code, whereas this can be further extended to control

many devices according to the requirements of the user.

4. Remote Operation of Household Gadgets Using Mobile Phone

Debapratim Sarkar, Saikat Das Adhikari, Department of Computer Science & Engineering, Department of

Electronics & Communication Engineering, Techno India College of Technology

Rajarhat, New Town, Mega City, Kolkata 700 156

Outline

Page | 6

Page 7: Final Profect Report

This document describes a scheme of remote operation of household electrical devices using mobile

phone. The block diagram and the detailed circuit diagram of the system are shown. The technique is also

useful to operate (switch on or off) the electrical equipments housed in an unmanned enclosure remotely

using the mobile phone.

5. A Cellular Phone Based Home / Office Controller & Alarm SystemH. Haldun GÖKTAŞ, Nihat DALDAL

Gazi University Technical Education Faculty, 06500, Besevler, Ankara, TURKEY

Received: 06.12.2004 Accepted: 22.08.2005

OutlineRemote management of several home and office appliances is a subject of growing interest and in recent

years we have seen many systems providing such controls. In this study, we have developed a cellular

phone based home/office remote controller equipped with power controllers, an alarm system, a voice

memory and a back-up battery unit.

In traditional PSTN based remote controllers, the user always has the possibility of line cuts due to fires or

Professional burglars cutting the wires before getting to work. Our system eliminates such disadvantages

with its unique properties.

1.2 Aim

To design and create a device that can be used to turn ON/OFF various home appliances. The control of

home appliances should be governed by any mobile phone.

Description: This project is designed for controlling four arbitrary devices through mobile phone. The

project includes a mobile phone M1 (not included with the project kit, end user has to connect his/her

mobile phone to the project) which is connected to the project via head set. As soon as call is made to M1,

the call is answered. The caller can then press the different numbers that results in turning ON/OFF

devices. The device switching is achieved by using Relays. The Device0 to Device3 indicated in block

diagram is not included in the project kit. User has to connect his/her home appliances to the relays. The

description of various blocks is as follow

Power Supply: The AC mains supply is applied to 12v step down transformer. The transformer output is

12v AC which is rectified using Diode Bridge W10M. The output of W10M is DC 12v which is further filtered

Page | 7

Page 8: Final Profect Report

by a1000uf capacitor, and then regulated using IC 7805. The output of 7805is +5v dc which is required for

microcontroller operation. Also an LED in series with 220 Ohms resistor is used for power on indication.

Microcontroller: The microcontroller AT89S52 is provided with all necessary connections

for its operations. The 11.0592 MHz crystal along with two 33pf Capacitors provides the clock circuit to

microcontroller. The power on reset circuit consists of 10uf capacitor and 8.2K Ohms resistor.

Relay Driver: The relays can’t be directly connected to the microcontroller due to their large operating

voltage/current requirement. Hence a relay driver is connected to microcontroller that provides the required

voltage/current to relays.

Relay: The four relays are connected to Port1 of Microcontroller via relay driver. The Armature, NO and NC

of each relay is connected to corresponding three pin relimate connector. The user can connect different

devices operating at different voltages to these relimate connectors

Software: The microcontroller is pre programmed to turn OFF all relays when system is started. All the

relays are then turned ON or OFF as the corresponding key is pressed from mobile phone. The relays

continue to TURN ON and OFF according to the key pressed by the caller.

Specifications: Power Supply: 5V, 100mA (Included in the kit)

Number of Devices: four

Data Transmission: DTMF via GSM

1.3 Block Diagram

Page | 8

Page 9: Final Profect Report

Fig. 1 Block Diagram

1.4 Description of Block Diagram

The block diagram is shown in figure1. The brain of the circuit is the ATMEL AT89S51 microcontroller. The

micro controller examines incoming signals through DTMF decoder and controls the outputs by relays.

Connection to the telephone network is parallel which does not restrict the telephone in any way. The

incoming signal is detected by ring detector block which uses opto-coupler for line isolation.

MCT2E opt couplers is used for this purpose. The polarity of the incoming signal is no longer

relevant. Because the ring signal is an AC voltage with the DC offset, which is passed through capacitor

and bridge rectifier. Since this voltage can be as high as 60 V, an opto-coupler is used before the input to

the microcontroller. Capacitor ensures that only the ring signal, and not the DC offset, reaches the Opto

Page | 9

Page 10: Final Profect Report

coupler. The incoming call is answered by microcontroller by picking the line using line pickup block. The

tone amplifier is configures by transistor BC 547 which amplifies the tones. The various tones are

generated by the software. These tones are used to signal the user when commands have been completed

or of any command errors.

DTMF detection and decoding is provided by DTMF decoder block. An IC MT 8870 is a complete

DTMF receiver, which is able to detect and decode all 16 DTMF tone pairs into a 4-bit code. When a valid

DTMF digit is detected the 4-bit code is available at the output pins and a VALID SIGNAL output, is set to

logic high. For its operation the integrated circuit requires a clock signal, generated in this case by the

quartz crystal of 3.579545MHz. A two-wire serial EEPROM (AT24C02) is used in the project to retain the

password, the relay status and the number of rings to which the system should respond. Data stored

remains in the memory even after power failure, as the memory ensures reading of the latest saved

settings by the micro controller. This 12C bus compatible- 2048-bit (2-kbit) EEPROM is organized as 256x8

bits. It can retain data for more than ten years. Using just two lines (SCL and SDA) of the memory, the

microcontroller can read and write the data corresponding to the data required to be stored.

A 16x2 Line LCD module is used to display the Status and Error Messages. Two supply voltages

are required for the circuit which is derived from main 230V by step down transformer, bridge rectifier, filter

and regulators. A 7805 is used which is fixed voltage 5V Regulator for 5V supply. The unregulated voltage

of approximately 12 V is required for the relay driving circuit.

1.5 Circuit Diagrams

Page | 10

Page 11: Final Profect Report

Fig. 2 Switching of Home Appliances Using DTMF Technology

Page | 11

Page 12: Final Profect Report

Fig. 3 Circuit Diagram Relay

Fig. 4 Reset Circuit Diagram

Page | 12

Page 13: Final Profect Report

Fig. 5 Micro Controller 89S52

Fig.6 Interfacing of Micro Controller With Rest of the Components In Device

1.6 List of Components

Page | 13

Page 14: Final Profect Report

Semiconductors QuantityIC1 ATMEL AT 89S52 Microcontroller 1

IC2 CM 8870PI DTMF decoder 1

T1 TBC547B n-p-n Transistor 1

T2 BC547 (203B) 3

DI IN4007S Rectifier diode 3

LEDs 5mm LED 5

VRs LM 7805, 7812 Regulator 2

XL 12 MHz, 3.58 MHz 2

ResistorsR1 4K 5

R2 100 K 2

R3 200 K 1

R4 300 K 1

CapacitorsC1 33 pF Ceramic disk 4

C2 104 pF Ceramic disk 3

C3 1000uF/25V Electrolytic 1

C4 10uF/63V Electrolytic 1

Relay JQC-3FC (T73 DC 12 V 4

Transformer 0-12 Step down 1

DTMF Compatible Phone 1

EAR Phone UNIX 1

Page | 14

Page 15: Final Profect Report

CHAPTER 2PCB Design

2.1 PCB Fabrication2.2 PCB Design2.3 Printing Design2.4 Transferring Design2.5 Developing2.6 Etching2.7 Cutting and Drilling

2.1 PCB Fabrication

“In the earliest circuits, larger components (valve holders, capacitors, etc) were built into metal chassis and

connected by a nest of colour-coded wires” (N.Braithwaite & G.Weaver, 1990). In 1920s, a method of

Page | 15

Page 16: Final Profect Report

producing an electrical path directly onto an insulation surface known as substrate was patented by Charles

Ducas, which ultimately developed into “printed circuit board”

A Printed Circuit Board (“PCB”) is widely known as a module that permits the interconnecting of various

electronic components ranging from resistors, integrated circuit (IC) chips to connectors.

“PCBs are almost a necessity, even for prototyping or one-off projects” (AI Williams, 2004). In recent years,

PCB is widely populated and an essential module found in almost every electronic device. Completed PCB

modules will not only look ‘good’, it must also achieve the physical and electrical requirements, and this

commands substantial amount of efforts, knowledge and aptitude to derive its utmost features and

performance.

First of all, before engaging into the fabrication of a PCB for an electronic device, the fundamental

principles behind its construction must be well understood. The electrical path is actually made of copper

foil, typically with the use of copper thickness of 0.5 oz to 2.0 oz, bonded on top of the substrate where the

latter is either polymers or polymer composite materials.

The most imperative property of this substrate used is probably the dielectric constant, typically between

values of 3.9 to 4.8. This property, apart from measuring the effects of electromagnetic wave on signal

travels on the electrical path, it is also used to measure how much the unwanted stray capacitances can be

reduced when adjacent electrical paths are running very close to each other (refer to fig.7). The higher the

magnitude, the better it will prevent the signals leaking from one path to another, especially on high

frequency when the capacitance reactance 1 / (2 ƒC) between them is low. A substrate with a lower

dielectric constant is mostly preferred and the standard woven epoxy glass known as FR4 is commonly use

as it is easily available in the market.

Fig.7 Designing Circuit on PCB

There is a method of mounting the components onto the substrate surface. At present, there are 2

established techniques; the through hole technique (“THT”) and the surface mount technique (“SMT”). With

THT (refer to Fig.8), each component has thin leads that are inserted into the drilled holes of the substrate

surface and soldered to the connection pads on the opposite side, which is on the

copper foil.

Page | 16

Page 17: Final Profect Report

Fig.8 through Whole Method

With SMT, short J-shaped or L-shaped legs on each component, usually smaller as compared to the THT

component, are placed directly on top of the PCB contact. A solder paste consisting of glue, flux and solder

are applied at the point of contact to hold the components in place before the solder is melted in the oven

for the final electrical connection.

Fig.9 Surface Mount Method

THT requires considerable amount of space for the connection pads and the process of drilling holes on the

PCB is time-consuming. Nevertheless, this technique provides a much stronger mechanical bonds and this

simplifies the production line as it is easier to produce. On the other hand, the main advantages of SMT,are

he smaller component dimension (refer to Fig.10),little errors in components placement and less unwanted

RF signal affecting the components due to lower lead resistance and inductance, however, at the expense

Page | 17

Page 18: Final Profect Report

of production costs as it is more c.

Fig.10 Components for Through Hole & Surface Mount Method

“…the process of designing and laying out a PCB can be a very daunting task ” (L.J. David, 2004) It is

apparent that one would need to plan and understand the necessary techniques/skills before proceeding

with the PCB design, in order to achieve an overall electrical and functional performance. Hence, for

standardization, the Institute for Interconnecting and Packaging Electronic Circuits, known as IPC, has

defined various aspect of the PCB design and are widely accepted in PCB manufacturing industry.

2.2 PCB Design Phase

The design of a PCB is mainly divided into 3 phases. The first phase is to set-up a schematic, where all the

necessary components to be used and their interconnection are defined. This will also include testing of the

schematic using bread board to ascertain its functionality. It is critical that the design formulated from the

finalized schematic has to be clearly laid, precise and logical. As such, it will set a sound platform for the

later design phase execution. The second phase defines the positioning of all components and routing the

tracks that interconnects the components. In early days, the most primitive way of laying the PCB is by

hand using adhesive tapes and pads on a clear drafting film. Noticeably, this would account for many hours

and required craftsmanship for the cutting, placing and routing detail before the whole layout can be

completed. In addition, any mistakes made during this process may cause an irreversible damage to the

PCB. The introduction of computer based PCB design has completely taken over this traditional method,

where it allows great flexibility in designing and editing with lesser hours spent.

“An old saying is the PCB design is 90% placement and 10% routing…the concept that component placement is by far the most important aspect” (L.J. David, 2004).

Indeed, bad component placement will have difficulties in routing the interconnecting track and at the worst

case will run out of routing space and produce distorted signals. The method of components placements,

that is the laying of the components and electrical tracks, taking into consideration of the width and the

electrical clearance between tracks must been clearly established. For the ease of routing, some would

Page | 18

Page 19: Final Profect Report

choose to space the components wider or having the required components evenly space out. This will

inherently end up with a larger board, which is not efficient in term of space usage and allocation. There is

no ‘clear’ rule governing the component placement. However, there are few pointers, which can be useful

for laying out a complete board. First, the electrical parameters must always take priority over a nicely lined

up components. Second, the schematic must be analyzed and explored the possibility of breaking the

components into functional blocks. An example of functional block is the voltage regulator IC having an

input and output line, combines with other components such as resistors, capacitors and LEDs to provide a

steady Direct Current (“DC”) voltage to other different functional blocks. Last but not least, the analog circuit

should not mix with digital, as well as high frequency with low frequency circuit. Each of these circuits has

their own unique set of electrical parameters. For example, digital grounds are perpetually noisier than

analog because of the switching noise produced during the digital chips state transition. If both circuits

shared the same grounds, the inherent noise of digital would impose to the analog signal paths. Where

necessary, use a different ground each of these circuits for combination. In high frequency circuit, the

effects of parasitic inductance, capacitance and impedance of the layout become dominant. When the

signal is too rapid and the track is too lengthy, the track can take on transmission line and may cause

interference signals if it is not well taken care of. However, there is no such issue when dealing with low

frequency of less than 10MHz circuit. After laying the components and routing the tracks, the next will be

finding the track width. Theoretically, the width is proportional to the maximum current that the track is

designed to carry. However, a wider track would yield a better DC resistance, a lower inductance and is

easier to inspect or rework. One should select the appropriate track width without compromising the

minimum electrical requirement.

2.3 Printing Design

The PCB design layout can be printed from a normal home printer onto paper or transparency (refer to

Fig.11), depending on the type of transferring method used. The two main methods are the tone transfer

using paper and photo exposure using transparency, which will be explained later. A laser printer is usually

preferred to catch the fine details of the design.

Page | 19

Page 20: Final Profect Report

Fig.11 Design on Transparency

2.4 Transferring Design

The main difference between the two methods is that; one uses heat and the other uses ultra-violet light.

The paper printout will be transferred onto the copper plated board using a heated iron. Once the design is

begin transferred, it can immediately send for etching process, which explains for its simplicity using this

method. To obtain better tracks quality, the latter method using photo exposure will be a better choice but

the photo-sensitive PCB is more costly, in addition, there is a step for developing process. A photo-

sensitive PCB can be purchased from the market and it usually come with a minimum size of 10 cm x 15

cm. The photo-sensitive PCB is cut into the desirable size, preferably bigger than the actual required size,

before tearing off the white. protective film (refer to Fig.12A). Next, place the transparency on top of the

PCB and position with scotch tape (refer to Fig.12B).

Page | 20

Page 21: Final Profect Report

Fig.12A – PCB with the Protective Film

Fig.12B – Printed Transparency Positioned on PCB

The PCB is then placed under a fluorescent lamp for 8 to 10 minutes with a distance of 5 cm (refer to

Fig.13). For a better result, a piece of flat glass will be used as a top layer to make a good contact between

the transparency and surface of the PCB. The distance between the light source and the PCB also play an

important role, as double the distance will tripled the exposure time.

Fig.13 Photo Developing Process

2.5 Developing

After exposed, the design printout will be transferred onto the PCB and it can be observed with a fade

yellowish colour tracks on top of the photo-sensitive layer. The PCB can now proceed to the developing

stage. A universal developer in the form of powder is mixed with 50g per litre water, in a suitable container

(refer to Fig.14A). The powder must be completely dissolved in the water before cooling down to 20ºC to

Page | 21

Page 22: Final Profect Report

25ºC, which is the most effective temperature for developing. After which, the PCB must be fully immersed

into the container with the design facing upward and agitated until the design is appears to be clear (refer to

Fig.14B). Finally, the PCB is rinsed with running water.

Fig.14A – Universal Developer with the Container

Fig.14B – Developing Process2.6 Etching

Before the PCB is ready for etching, any small breaks on the design can be still corrected by using oil-

based permanent marker. Ferric Chloride, a toxin chemical, will be used to etch away the copper foil,

leaving behind the desired design layout. As usual, the Ferric Chloride must be totally dissolved in the

water and the amount to be used is solely depending on the size of the PCB. The etching process is most

effective when the solution is kept at a temperature of about 50ºC to 60ºC. The PCB must be fully

Page | 22

Page 23: Final Profect Report

immersed into the etching solution with the design facing upward (refer to Fig.15) and agitated until the

unwanted copper foil etched away. Subsequently, a household detergent can be used to wash out the

chemical solution without removing the photo-sensitive coating.

Fig.15 Etching Process

2.7 Cutting and Drilling

Once the etching is completed, the next step is to cut or trim the PCB to the actual size required. The

photo-sensitive coating should not be removed before the hole drilling process, as it served as a protection

to the tracks. Before drilling, it is prudent to have a dot punch to mark a shallow guide hole for the drill bit

alignment while drilling (refer to Fig.16A). The nominal drill bit size should be 0.8mm, which is sufficient for

majority of the components. However, the size will need to increase to 1.0mm with input and output

connectors. Every drill action will create sharp edges along the circumference, and these edges should be

de-bur by a small file when possible.

After the drilling is completed, the photo-sensitive coating can then be removed, using a dish-washer green

sponge. The PCB (refer to Fig.16B) is now considered completed and is ready for soldering of the

components.

Page | 23

Page 24: Final Profect Report

Fig.16A – Drilling Process

Fig.16B – Completed PCB

CHAPTER 3Description of Electronics Components

Page | 24

Page 25: Final Profect Report

3.1 Microcontroller AT 89C523.2 DTMF Decoder MT8870 3.3 Voltage Regulator LM78053.4 Transistor3.5 Resistance3.6 Capacitor3.7 Diode3.8 Led3.9 Crystal Oscillator3.10 Relay3.11 Transformer

3.1 Microcontroller AT 89S52

DESCRIPTION

The AT89S52 is a low power, high performance CMOS 8-bit microcomputer with 8K bytes of Flash

programmable and erasable read only memory (PEROM). The device is manufactured using Atmel’s high

density non-volatile memory technology and is compatible with the industry-standard MCS-51 instruction

set and pin out. The on-chip flash allows the program memory to be reprogrammed in the system or by a

conventional non-volatile memory .By combining a versatile 8-bit CPU with flash on a monolithic chip, the

Atmel AT89S52 is a powerful microcomputer which provides a highly flexible and cost-effective solution to

many embedded control application.

FEATURES

Page | 25

Page 26: Final Profect Report

Compatible with MCS-52™ Products

8K Bytes of In-System Reprogrammable Flash Memory

Endurance: 1,000 Write/Erase Cycles

Fully Static Operation: 0 Hz to 24 MHz

Three-level Program Memory Lock

256 x 8-bit Internal RAM

32 Programmable I/O Lines

Two 16-bit Timer/Counters

Six Interrupt Sources

Programmable Serial Channel

Low-power Idle and Power-down Modes

PIN CONFIGURATION

Page | 26

Page 27: Final Profect Report

Fig. 17 Pin Configuration

The AT89S52 provides the following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines,

two 16-bit timer/counters, five vector two-level interrupt architecture, a full duplex serial port, and on-chip

oscillator and clock circuitry. In addition, the AT89s52 is designed with static logic for operation down to

zero frequency and supports two software selectable power saving modes. The Idle Mode stops the CPU

while allowing the RAM, timer/counters, serial port and interrupt system to continue functioning. The Power-

down Mode saves the RAM contents but freezes the oscillator disabling all other chip functions until the

next hardware reset.

PIN DESCRIPTION

VCC Supply voltage

GND Ground

Port 0:

Port 0 is as 8-bit open-drain bi-directional I/O port. As an output port, each pin can sink eight TTL inputs.

When 1s are written to port 0 pins, the pins can be used as high impedance inputs. Port0 may also be

configured to be the multiplexed low order address/data bus during accesses to external program and data

memory. In this mode P 0 has internal pull-ups. Port 0 also receives the code bytes during program

verification. External Pull-ups are required during program verification.

Port 1:

Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 1 output buffers can sink/source four

TTL inputs. When 1s are written to Port 1 pins they are pulled high by the internal pull-ups and can be used

as inputs. As inputs, Port 1 pins that are externally being pulled low will source current (IIL) because of the

internal pull-ups. Port 1 also receives the low-order address bytes during Flash programming and

verification.

Port 2:

Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2 output buffers can sink/source four

TTL inputs. When 1s are written to Port 2 pins they are pulled high by the internal pull-ups and can be used

as inputs. As inputs, Port 2 pins that are externally being pulled low will source current (IIL) because of the

internal pull-ups. Port 2 emits the high-order address byte during fetches from external program memory

Page | 27

Page 28: Final Profect Report

and during accesses to external data memory that use 16-bitaddresses (MOVX @DPTR). In this

application, it uses strong internal pull-ups when emitting 1s. During accesses to external data memory that

use 8-bitaddresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function Register. Port 2

also receives the high-order address bits and some control signals during Flash programming and

verification.

Port 3:

Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 3 output buffers can sink/source four

TTL inputs. When 1s are written to Port 3 pins they are pulled high by the internal pull-ups and can be used

as inputs. As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the

pull-ups.

Port 3 also serves the functions of various special features of the AT89S52 as listed below.

RST:

Reset input. A high on this pin for two machine cycles while the oscillator is running resets the device.

ALE/PROG:

Address Latch Enable output pulse for latching the low byte of the address during accesses to external

memory. This pin is also the program pulse input (PROG) during Flash programming. In normal operation

ALE is emitted at a constant rate of 1/6 the oscillator frequency, and may be used for external timing or

clocking purposes. Note, however, that one ALE pulse is skipped during each access to external Data

Memory. If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set,

Page | 28

Page 29: Final Profect Report

ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting

the ALE-disable bit has no effect if the microcontroller is in external execution mode.

PSEN:

Program Store Enable is the read strobe to external program memory. When the AT89S52 is executing

code from external program memory, PSEN is activated twice each machine cycle, except that two PSEN

activations are skipped during each access to external data memory.

EA/VPP:

External Access Enable. EA must be strapped to GND in order to enable the device to fetch code from

external program memory locations starting at 0000H up to FFFFH. Note, however, that if lock bit 1 is

programmed, EA will be internally latched on reset. EA should be strapped to VCC for internal program

executions.

This pin also receives the 12-volt programming enable voltage (VPP) during Flash programming, for parts

that require 12-volt VPP.

XTAL1:

Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2:

Output from the inverting oscillator amplifier.

PROGRAMMING THE FLASH

The AT89S52 is normally shipped with the on-chip Flash memory array in the erased state (that is,

contents = FFH) and ready to be programmed. The programming interface accepts either a high-voltage

(12-volt) or a low-voltage (VCC) program enable signal. The low-voltage programming mode provides a

convenient way to program the AT89S52 inside the user’s system, while the high-voltage programming

mode is compatible with conventional third party Flash or EPROM programmers. The AT89S52 code

memory array is programmed byte-by-byte in either programming mode. To program any nonblank byte in the on-chip Flash Memory, the entire memory must be erased using the Chip Erase Mode.

PROGRAMMING ALGORITHM

Page | 29

Page 30: Final Profect Report

Before programming the AT89S52, the address, data and control signals should be set up according to the

Flash programming mode table and Figure 3 and Figure 4. To program the AT89S52, take the following

steps.

1. Input the desired memory location on the address lines.

2. Input the appropriate data byte on the data lines.

3. Activate the correct combination of control signals.

4. Raise EA/VPP to 12V for the high-voltage programming mode.

5. Pulse ALE/PROG once to program a byte in the

Flash array or the lock bits. The byte-write cycle is self-timed and typically takes no more than 1.5 ms.

Repeat steps 1 through 5, changing the address and data for the entire array or until the end of the object

file is reached.

DATA POLLING

The AT89S52 features Data Polling to indicate the end of a write cycle. During a write cycle, an attempted

read of the last byte written will result in the complement of the written datum on PO.7. Once the write cycle

has been completed, true data are valid on all outputs, and the next cycle may begin. Data Polling may

begin any time after a write cycle has been initiated.

READY/BUSY

The progress of byte programming can also be monitored by the RDY/BSY output signal. P3.4 is pulled low

after ALE goes high during programming to indicate BUSY. P3.4 is pulled high again when programming is

done to indicate READY.

PROGRAM VERIFY

If lock bits LB1 and LB2 have not been programmed, the programmed code data can be read back via the

address and data lines for verification. The lock bits cannot be verified directly. Verification of the lock bits is

achieved by observing that their features are enabled.

CHIP ERASE

Page | 30

Page 31: Final Profect Report

The entire Flash array is erased electrically by using the proper combination of control signals and by

holding ALE/PROG low for 10 ms. The code array is written with all “1”s. The chip erase operation must be

executed before the code memory can be re-programmed.

READING THE SIGNATURE BYTES

The signature bytes are read by the same procedure as a normal verification of locations 030H, 031H, and

032H, except that P3.6 and P3.7 must be pulled to a logic low. The values returned are as follows.

(030H) = 1EH indicates manufactured by Atmel

(031H) = 51H indicates 89S52

(032H) = FFH indicates 12V programming

(032H) = 05H indicates 5V programming

PROGRAMMING INTERFACE

Every code byte in the Flash array can be written and the entire array can be erased by using the

appropriate combination of control signals. The write operation cycle is self timed and once initiated, will

automatically time itself to completion. All major programming vendors offer worldwide support for the

Atmel microcontroller series. Please contact your local programming vendor for the appropriate software

revision.

PROGRAMMING THE FLASH

Page | 31

Page 32: Final Profect Report

Fig. 18 Flash Programmer IC

VERIFYING THE FLASH

Page | 32

Page 33: Final Profect Report

Fig.19 Flash Programmer Wave Forms

3.2 DTMF Decoder MT8870

Page | 33

Page 34: Final Profect Report

Dual tone multiple frequency signaling (DTMF).

Multiple-frequency signaling consists of a combination of two tones with frequencies within the

speech band.

Each combination of two frequencies representing a single digit.

The tones are in two groups: 1 Low Band (2) High Band.

Table - 3 DTMF keypad frequencies

SPECIAL TONE FREQUENCIES

National telephone systems define additional tones to indicate the status of lines, equipment, or the result

of calls with special tones. Such tones are standardized in each country and may consist of single or

multiple frequencies. Most European countries use a single frequency, where the United States uses a dual

frequency system, presented in the following table.

Table – 4 Special Tone Frequencies

Event Low frequency High frequency

Busy 480 Hz 620 Hz

Ring back tone

(US)440 Hz 480 Hz

Dial tone 350 Hz 440 Hz

Page | 34

Page 35: Final Profect Report

Fig.20 Frequency Spectrum of a DTMF Tone

The tone frequencies, as defined by the Precise Tone Plan, are selected such that harmonics and inter

modulation products will not cause an unreliable signal. No frequency is a multiple of another, the

difference between any two frequencies does not equal any of the frequencies, and the sum of any two

frequencies does not equal any of the frequencies. The frequencies were initially designed with a ratio of

21/19, which is slightly less than a whole tone. The frequencies may not vary more than ±1.8% from their

nominal frequency, or the switching center will ignore the signal. The high frequencies may be the same

volume or louder as the low frequencies when sent across the line. The loudness difference between the

high and low frequencies can be as large as 3 decibels (dB) and is referred to as "twist." The minimum

duration of the tone should be at least 70 ms, although in some countries and applications DTMF receivers

must be able to reliably detect DTMF tones as short as 45ms.

As with other multi-frequency receivers, DTMF was originally decoded by tuned filter banks. Late in the

20th century most were replaced with digital signal processors. DTMF can be decoded using the Goertzel

algorithm.

Synonyms include multifrequency pulsing and multifrequency signaling.

Fig. 21 Waveform for Key ‘1’ Press

Page | 35

Page 36: Final Profect Report

The M-8870 is a full DTMF Receiver that integrates both band split filter and decoder functions into a single

18-pin DIP or SOIC package. Manufactured using CMOS process technology, the M-8870 offers low power

consumption (35 mW max) and precise data handling. Its filter section uses switched capacitor technology

for both the high and low group filters and for dial tone rejection. Its decoder uses digital counting

techniques to detect and decode all 16 DTMF tone pairs into a 4-bit code. External component count is

minimized by provision of an on-chip differential input amplifier, clock generator, and latched tri-state

interface bus. Minimal external components required include a low-cost 3.579545 MHz color burst crystal, a

timing resistor, and a timing capacitor.

BLOCK DIAGRAM

FUNCTIONAL DESCRIPTION

MT-8870 operating functions include a band split filter that separates the high and low tones of the received

pair, and a digital decoder that verifies both the frequency and duration of the received tones before

passing the resulting 4-bit code to the output bus.

FILTER

Page | 36

Page 37: Final Profect Report

The low and high group tones are separated by applying the dual-tone signal to the inputs of two 6th order

switched capacitor band pass filters with bandwidths that correspond to the bands enclosing the low and

high group tones. The filter also incorporates notches at 350 and 440 Hz, providing excellent dial tone

rejection. Each filter output is followed by a single-order switched capacitor section that smoothes the

signals prior to limiting. Signal limiting is performed by high gain comparators provided with hysteresis to

prevent detection of unwanted low-level signals and noise.

The comparator outputs provide full-rail logic swings at the frequencies of the incoming tones.

DECODER

The MT-8870 decoder uses a digital counting technique to determine the frequencies of the limited tones

and to verify that they correspond to standard DTMF frequencies. A complex averaging algorithm is used to

protect against tone simulation by extraneous signals (such as voice) while tolerating small frequency

variations.

The algorithm ensures an optimum combination of immunity to talk off and tolerance to interfering signals

(third tones) and noise. When the detector recognizes the simultaneous presence of two valid tones (known

as signal condition), it raises the Early Steering flag (ESt). Any subsequent loss of signal condition will

cause ESt. to fall.

STEERING CIRCUIT

Before a decoded tone pair is registered, the receiver

checks for a valid signal duration (referred to as

character- recognition-condition). This check is

performed by an external RC time constant driven by

ESt. A logic high on ESt causes VC (see block diagram

on page 1) to rise as the capacitor discharges.

Provided that signal condition is maintained (ESt

remains high) for the validation period (tGTF), VC

reaches the threshold (VTSt) of the steering logic to

register the tone pair, thus latching its corresponding 4-

bit code (see DC Characteristics on page 2) into the

output latch. At this point, the GT output is activated and drives VC to VDD.

Page | 37

Page 38: Final Profect Report

GT continues to drive high as long as ESt remains high. Finally, after a short delay to allow the output latch

to settle, the delayed steering output flag (StD) goes high, signaling that a received tone pair has been

registered. The contents of the output latch are made available on the 4-bit output bus by raising the three

state control input (OE) to logic high. The steering circuit works in reverse to validate the inter digit pause

between signals. Thus, as well as rejecting signals too short to be considered valid, the receiver will

tolerate signal interruptions (dropouts) too short to be considered a valid pause. This capability, together

with the ability to select the steering time constants externally, allows the designer to tailor performance to

meet a wide variety of system requirements.

PIN CONFIGURATION

Fig. 22

PIN FUNCTIONS

Pin Name Description

1 IN+ Non-inverting input

2 IN- Inverting input

3 GS Gain select. Gives access to output of front-end amplifier for connection of feedback resistor.

4 VREF Reference voltage output (nominally VDD/2). May be used to bias the inputs at mid-rail.

Page | 38

Page 39: Final Profect Report

5 INH Inhibits detection of tones representing keys A, B, C, and D.

6 PD Power down. Logic high powers down the device and inhibits the oscillator. Internal pull down.

7 OSC1 Clock input -- 3.579545 MHz crystal connected between these pins completes the internal oscillator.

8 OSC2 Clock output

9 VSS Negative power supply (normally connected to 0 V).

10 OE Tri-stat able output enables (input).

Logic high enables the outputs Q1 - Q4. Internal pull-up.

11-14 Q1, Q2, Q3, Q4

Tri-stat able data outputs. When enabled by OE, provides the code corresponding to the last valid tone pair received (see Tone Decoding table on page 5).

15 StD Delayed steering output. Presents logic high when a received tone pair has been registered and the output latch is updated. Returns to logic low when the voltage on St/GT falls below VTSt.

16 ESt Early steering output. Presents logic high immediately when the digital algorithm detects a recognizable tone pair (signal condition). Any momentary loss of signal condition will cause ESt to return to a logic low.

17 St/GT Steering input/guard time output (bidirectional). A voltage greater than VTSt detected at St causes the device to register the detected tone pair and update the output latch. A voltage less than VTSt free the device to accept a new tone pair. The GT output acts to reset the external steering time constant, and its state is a function of ESt and the voltage on St

18 VDD Positive power supply. (Normally connected to +5V.)

GUARD TIME ADJUSTMENT

Where independent selection of signal duration and inter digit pause are not required, the simple steering

circuit of Basic Steering Circuit is applicable. Component values are chosen according to the formula:

tREC = tDP + tgtp tGTP @ 0.67 RC

Page | 39

Page 40: Final Profect Report

The value of tDP is a parameter of the device and tREC is the minimum signal duration to be recognized by

the receiver. A value for C of 0.1 μF is recommended for most applications, leaving R to be selected by the

designer. For example, a suitable value of R for a tREC of 40 ms would be 300 k. A typical circuit using

this steering configuration is shown in the Single - Ended Input Configuration on page 4. The timing

requirements for most telecommunication applications are satisfied with this circuit. Different steering

arrangements may be used to select independently the guard times for tone-present (tGTP) and tone-

absent (tGTA).

This may be necessary to meet system specifications

that place both accept and reject limits on both tone

duration and inter digit pause. Guard time adjustment

also allows the designer to tailor system parameters

such as talk off and noise immunity. Increasing tREC

improves talk off performance, since it reduces the

probability that tones simulated by speech will

maintain signal condition long enough to be

registered. On the other hand, a relatively short tREC

with a long tDO would be appropriate for extremely

noisy environments where fast acquisition time and

immunity to dropouts would be required. Design

information for guard time adjustment is shown in the

Guard Time Adjustment figure.

FEATURES

Low Power Consumption

Adjustable Acquisition and Release Times

Central Office Quality and Performance

Power-down and Inhibit Modes (-02 only)

Inexpensive 3.58 MHz Time Base

Single 5 Volt Power Supply

Dial Tone Suppression

APPLICATIONS

Page | 40

Page 41: Final Profect Report

Telephone switch equipment

Remote data entry

Paging systems

Personal computers

Credit card systems

3.3 Voltage Regulator

A voltage regulator is an electrical regulator designed to automatically maintain a constant voltage level.

It may use an electromechanical mechanism, or passive or active electronic components. Depending on

the design, it may be used to regulate one or more AC or DC voltages. With the exception of passive shunt

regulators, all modern electronic voltage regulators operate by comparing the actual output voltage to some

internal fixed reference voltage. Any difference is amplified and used to control the regulation element in

such a way as to reduce the voltage error. This forms a negative feedback control loop; increasing the

open-loop gain tends to increase regulation accuracy but reduce stability (avoidance of oscillation, or

ringing during step changes). There will also be a trade-off between stability and the speed of the response

to changes. If the output voltage is too low (perhaps due to input voltage reducing or load current

increasing), the regulation element is commanded, up to a point, to produce a higher output voltage - by

dropping less of the input voltage (for linear series regulators and buck switching regulators), or to draw

input current for longer periods (boost-type switching regulators); if the output voltage is too high, the

regulation element will normally be commanded to produce a lower voltage. However, many regulators

have over-current protection, so that they will entirely stop sourcing current (or limit the current in some

way) if the output current is too high, and some regulators may also shut down if the input voltage is outside

a given range (see also: crowbar circuits).

Page | 41

Page 42: Final Profect Report

Fig. 23 Voltage Regulator 7805

MEASURES OF REGULATOR QUALITY

The output voltage can only be held roughly constant; the regulation is specified by two measurements:

load regulation is the change in output voltage for a given change in load current (for example: "typically

15mV, maximum 100mV for load currents between 5mA and 1.4A, at some specified temperature and input

voltage

line regulation or input regulation is the degree to which output voltage changes with input (supply)

voltage changes - as a ratio of output to input change (for example "typically 13mV/V"), or the output

voltage change over the entire specified input voltage range (for example "plus or minus 2% for input

voltages between 90V and 260V, 50-60Hz").

OTHER IMPORTANT PARAMETERS ARE

Temperature coefficient of the output voltage is the change in output voltage with temperature

(perhaps averaged over a given temperature range), while...

Initial accuracy of a voltage regulator (or simply "the voltage accuracy") reflects the error in output

voltage for a fixed regulator without taking into account temperature or aging effects on output

accuracy.

Page | 42

Page 43: Final Profect Report

Dropout voltage - the minimum difference between input voltage and output voltage for which the

regulator can still supply the specified current. A Low Drop-Out (LDO) regulator is designed to work

well even with an input supply only a Volt or so above the output voltage.

Absolute Maximum Ratings are defined for regulator components, specifying the continuous and

peak output currents that may be used (sometimes internally limited), the maximum input voltage,

maximum power dissipation at a given temperature, etc.

Output noise (thermal white noise) and output dynamic impedance may be specified as graphs

versus frequency, while output ripple noise (mains "hum" or switch-mode "hash" noise) may be

given as peak-to-peak or RMS voltages, or in terms of their spectra.

Quiescent current in a regulator circuit is the current drawn internally, not available to the load,

normally measured as the input current while no load is connected (and hence a source of

inefficiency; some linear regulators are, surprisingly, more efficient at very low current loads than

switch-mode designs because of this).

ELECTROMECHANICAL REGULATORS

Fig. 24 Circuit Design for a Simple Electromechanical Voltage Regulator.

Page | 43

Page 44: Final Profect Report

Fig. 25 Graph of Voltage Output on a Time Scale.

In older electromechanical regulators, voltage regulation is easily accomplished by coiling the sensing wire

to make an electromagnet. The magnetic field produced by the current attracts a moving ferrous core held

back under spring tension or gravitational pull. As voltage increases, so does the current, strengthening the

magnetic field produced by the coil and pulling the core towards the field. The magnet is physically

connected to a mechanical power switch, which opens as the magnet moves into the field. As voltage

decreases, so does the current, releasing spring tension or the weight of the core and causing it to retract.

This closes the switch and allows the power to flow once more. If the mechanical regulator design is

sensitive to small voltage fluctuations, the motion of the solenoid core can be used to move a selector

switch across a range of resistances or transformer windings to gradually step the output voltage up or

down, or to rotate the position of a moving-coil AC regulator. Early automobile generators and alternators

had a mechanical voltage regulator using one, two, or three relays and various resistors to stabilize the

generator's output at slightly more than 6 or 12 V, independent of the engine's rpm or the varying load on

the vehicle's electrical system. Essentially, the relay(s) employed pulse width modulation to regulate the

output of the generator, controlling the field current reaching the generator (or alternator) and in this way

controlling the output voltage produced.The regulators used for generators (but not alternators) also

disconnect the generator when it was not producing electricity, thereby preventing the battery from

discharging back into the generator and attempting to run it as a motor. The rectifier diodes in an alternator

automatically perform this function so that a specific relay is not required; this appreciably simplified the

regulator design.More modern designs now use solid state technology (transistors) to perform the same

function that the relays perform in electromechanical regulators.

MAINS REGULATORS

Page | 44

Page 45: Final Profect Report

Fig. 26 Magnetic Mains Regulator

Electromechanical regulators have also been used to regulate the voltage on AC power distribution lines.

These regulators generally operate by selecting the appropriate tap on a transformer with multiple taps. If

the output voltage is too low, the tap changer switches connections to produce a higher voltage. If the

output voltage is too high, the tap changer switches connections to produce a lower voltage. The controls

provide a dead band wherein the controller will not act, preventing the controller from constantly hunting (constantly adjusting the voltage) to reach the desired target voltage

COIL-ROTATION AC VOLTAGE REGULATOR

Fig. 27 Circuit Diagram for the Rotating-Coil AC Voltage Regulator.

This is an older type of regulator used in the 1920s that uses the principle of a fixed-position field coil and a

second field coil that can be rotated on an axis in parallel with the fixed coil. When the movable coil is

positioned perpendicular to the fixed coil, the magnetic forces acting on the movable coil balance each

other out and voltage output is unchanged. Rotating the coil in one direction or the other away from the

center position will increase or decrease voltage in the secondary movable coil. This type of regulator can

be automated via a servo control mechanism to advance the movable coil position in order to provide

voltage increase or decrease. A braking mechanism or high ratio gearing is used to hold the rotating coil in

place against the powerful magnetic forces acting on the moving coil.

AC VOLTAGE STABILIZERS

A voltage stabilizer is a type of household mains regulator which uses a continuously variable

autotransformer to maintain an AC output that is as close to the standard or normal mains voltage as

possible, under conditions of fluctuation. It uses a servomechanism (or negative feedback) to control the

position of the tap (or wiper) of the autotransformer, usually with a motor. An increase in the mains voltage

causes the output to increase, which in turn causes the tap (or wiper) to move in the direction that reduces

Page | 45

Page 46: Final Profect Report

the output towards the nominal voltage. An alternative method is the use of a type of saturating transformer

called a ferroresonant transformer or constant-voltage transformer. These transformers use a tank

circuit composed of a high-voltage resonant winding and a capacitor to produce a nearly constant average

output with a varying input. The ferroresonant approach is attractive due to its lack of active components,

relying on the square loop saturation characteristics of the tank circuit to absorb variations in average input

voltage. Older designs of ferroresonant transformers had an output with high harmonic content, leading to a

distorted output waveform. Modern devices are used to construct a perfect sine wave. The ferroresonant

action is a flux limiter rather than a voltage regulator, but with a fixed supply frequency it can maintain an

almost constant average output voltage even as the input voltage varies widely. The ferroresonant

transformers, which are also known as Constant Voltage Transformers (CVTs) or ferros, are also good

surge suppressors, as they provide high isolation and inherent short-circuit protections. A ferroresonant

transformer can operate with an input voltage range ±40% or more of the nominal voltage. Output power

factor remains in the range of 0.96 or higher from half to full load Because it regenerates an output voltage

waveform, output distortion, which is typically less than 4%, is independent of any input voltage distortion,

including notching. Efficiency at full load is typically in the range of 89% to 93%. However, at low loads,

efficiency can drop below 60% and no load losses can be as high as 20%. The current-limiting capability

also becomes a handicap when a CVT is used in an application with moderate to high inrush current like

motors, transformers or magnets. In this case, the CVT has to be sized to accommodate the peak current,

thus forcing it to run at low loads and poor efficiency. Minimum maintenance is required. Transformers and

capacitors can be very reliable. Some units have included redundant capacitors to allow several capacitors

to fail between inspections without any noticeable effect on the device's performance. Output voltage varies

about 1.2% for every 1% change in supply frequency. For example, a 2-Hz change in generator frequency,

which is very large, results in an output voltage change of only 4%, which has little effect for most, loads. It

accepts 100% single-phase switch-mode power supply loading without any requirement for derating,

including all neutral components. Input current distortion remains less than 8% THD even when supplying

nonlinear loads with more than 100% current THD.Drawbacks of CVTs (constant voltage transformers) are

their larger size, audible humming sound, and high heat generation.

DC VOLTAGE STABILIZERS

Page | 46

Page 47: Final Profect Report

Fig. 28 KPEH8A Stabilizers

Many simple DC power supplies regulate the voltage using a shunt regulator such as a zener diode,

avalanche breakdown diode, or voltage regulator tube. Each of these devices begins conducting at a

specified voltage and will conduct as much current as required to hold its terminal voltage to that specified

voltage. The power supply is designed to only supply a maximum amount of current that is within the safe

operating capability of the shunt regulating device (commonly, by using a series resistor). In shunt

regulators, the voltage reference is also the regulating device. If the stabilizer must provide more power, the

shunt regulator output is only used to provide the standard voltage reference for the electronic device,

known as the voltage stabilizer. The voltage stabilizer is the electronic device, able to deliver much larger

currents on demand.

ACTIVE REGULATORS

Active regulators employ at least one active (amplifying) component such as a transistor or operational

amplifier. Shunt regulators are often (but not always) passive and simple, but always inefficient because

they (essentially) dump the excess current not needed by the load. When more power must be supplied,

more sophisticated circuits are used. In general, these active regulators can be divided into several

classes:

Linear series regulators

Switching regulators

SCR regulators

LINEAR REGULATORS

Linear regulators are based on devices that operate in their linear region (in contrast, a switching regulator

is based on a device forced to act as an on/off switch). In the past, one or more vacuum tubes were

commonly used as the variable resistance. Modern designs use one or more transistors instead, perhaps

within an Integrated Circuit. Linear designs have the advantage of very "clean" output with little noise

introduced into their DC output, but are most often much less efficient and unable to step-up or invert the

input voltage like switched supplies. Entire linear regulators are available as integrated circuits. These chips

come in either fixed or adjustable voltage types.

Page | 47

Page 48: Final Profect Report

Fig. 29 Linear Voltage Regulator

SWITCHING REGULATORS

Switching regulators rapidly switch a series device on and off. The duty cycle of the switch sets how much

charge is transferred to the load. This is controlled by a similar feedback mechanism as in a linear

regulator. Because the series element is either fully conducting, or switched off, it dissipates almost no

power; this is what gives the switching design its efficiency. Switching regulators are also able to generate

output voltages which are higher than the input, or of opposite polarity — something not possible with a

linear design. Like linear regulators, nearly-complete switching regulators are also available as integrated

circuits. Unlike linear regulators, these usually require one external component: an inductor that acts as the

energy storage element. (Large-valued inductors tend to be physically large relative to almost all other

kinds of component, so they are rarely fabricated within integrated circuits and IC regulators — with some

exceptions.

COMPARING LINEAR AND SWITCHING REGULATORS

The two types of regulators have their different advantages:

Linear regulators are best when low output noise (and low RFI radiated noise) is required

Linear regulators are best when a fast response to input and output disturbances is required.

At low levels of power, linear regulators are cheaper and occupy less printed circuit board space.

Switching regulators are best when power efficiency is critical (such as in portable computers),

except linear regulators are more efficient in a small number of cases (such as a 5V

microprocessor often in "sleep" mode fed from a 6V battery, if the complexity of the switching

circuit and the junction capacitance charging current means a high quiescent current in the

switching regulator).

Page | 48

Page 49: Final Profect Report

Switching regulators are required when the only power supply is a DC voltage, and a higher output

voltage is required.

At high levels of power (above a few watts), switching regulators are cheaper (for example, the

cost of removing heat generated is less).

SCR REGULATORS

Regulators powered from AC power circuits can use silicon controlled rectifiers (SCRs) as the series

device. Whenever the output voltage is below the desired value, the SCR is triggered, allowing electricity to

flow into the load until the AC mains voltage passes through zero (ending the half cycle). SCR regulators

have the advantages of being both very efficient and very simple, but because they cannot terminate an on-

going half cycle of conduction, they are not capable of very accurate voltage regulation in response to

rapidly-changing loads.

COMBINATION (HYBRID) REGULATORS

Many power supplies use more than one regulating method in series. For example, the output from a

switching regulator can be further regulated by a linear regulator. The switching regulator accepts a wide

range of input voltages and efficiently generates a (somewhat noisy) voltage slightly above the ultimately

desired output. That is followed by a linear regulator that generates exactly the desired voltage and

eliminates nearly all the noise generated by the switching regulator. Other designs may use an SCR

regulator as the "pre-regulator", followed by another type of regulator. An efficient way of creating a

variable-voltage, accurate output power supply is to combine a multi-tapped transformer with an adjustable

linear post-regulator.

VOLTAGE STABILIZER

A voltage stabilizer is an electronic device able to deliver relatively constant output voltage while input

voltage and load current changes over time. The voltage stabilizer is the shunt regulator such as a Zener

diode or avalanche diode. Each of these devices begins conducting at a specified voltage and will conduct

as much current as required to hold its terminal voltage to that specified voltage. Hence the shunt regulator

can be viewed as the limited power parallel stabilizer. The shunt regulator output is used as a voltage

reference. The Zener diode and avalanche diode have opposite threshold voltage dependence on

temperature. By connecting these two devices sequentially, it is possible to construct a voltage reference

Page | 49

Page 50: Final Profect Report

with improved thermal stability. Sometimes (mostly for the voltages around 5.6 V) both effects are

combined in the same diode.

SIMPLE VOLTAGE STABILIZER

Fig. 30 Simple Voltage Stabilizer

In the simplest case emitter follower is used, the base of the regulating transistor is directly connected to

the voltage reference: The stabilizer uses the power source, having voltage U in that may vary over time. It

delivers the relatively constant voltage Vout. The output load RL can also vary over time. For such a device

to work properly the input voltage must be larger than the output voltage and Voltage drop must not exceed

the limits of the transistor used. The output voltage of the stabilizer is equal to U Z - UBE where UBE is about

0.7v and depends on the load current. If the output voltage drops below that limit, this increases the voltage

difference between the base and emitter (Ube), opening the transistor and delivering more current.

Delivering more current through the same output resistor RL increases the voltage again.

VOLTAGE STABILIZER WITH AN OPERATIONAL AMPLIFIER

The stability of the output voltage can be significantly increased by using the operational amplifier:

Page | 50

Page 51: Final Profect Report

Fig. 31 Voltage Stabilizer with an Operational Amplifier

In this case, the operational amplifier opens the transistor more if the voltage at its inverting input drops

significantly below the output of the voltage reference at the non-inverting input. Using the voltage divider

(R1, R2 and R3) allows choice of the arbitrary output voltage between Uz and Uin.

3.4 Transistor

FUNCTIONS

Transistors amplify current, for example they can be used to amplify the small output

current from a logic IC so that it can operate a lamp, relay or other high current device.

In many circuits a resistor is used to convert the changing current to a changing

voltage, so the transistor is being used to amplify voltage.

A transistor may be used as a switch (either fully on with maximum current, or fully off with no current) and

as an amplifier (always partly on). The amount of current amplification is called the current gain, symbol

hFE.

TYPES OF TRANSISTOR

1. JUNCTION TRANSISTORS

There are two types of standard transistors, NPN

and PNP, with different circuit symbols. A junction

transistor consists of a thin piece of one type of

semiconductor material between two thicker layers of the

opposite type. For example, if the middle layer is p-type,

Page | 51

Page 52: Final Profect Report

the outside layers must be n-type. Such a transistor is an NPN transistor. One of the outside layers is called

the emitter, and the other is known as the collector. The middle layer is the base.

Fig.32 Transistor Circuit Symbols

The places where the emitter joins the base and the base joins the collector are called junctions.

The layers of an NPN transistor must have the proper voltage connected across them. The voltage of the

base must be more positive than that of the emitter. The voltage of the collector, in turn, must be more

positive than that of the base. The voltages are supplied by a battery or some other source of direct current.

The emitter supplies electrons. The base pulls these electrons from the emitter because it has a more

positive voltage than does the emitter. This movement of electrons creates a flow of electricity through the

transistor the letters refer to the layers of semiconductor material used to make the transistor. Most

transistors used today are NPN because this is the easiest type to make from silicon.

2. FIELD EFFECT TRANSISTORS

A field effect transistor has only two layers of semiconductor

material, one on top of the other. Electricity flows through one of

the layers, called the channel. A voltage connected to the other

layer, called the gate, interferes with the current flowing in the

channel. Thus, the voltage connected to the gate controls the

strength of the current in the channel. There are two basic varieties

of field effect transistors-the junction field effect transistor (JFET)

and the metal oxide semiconductor field effect transistor

(MOSFET). Most of the transistors contained in today's integrated

circuits are MOSFETS's.

Fig.33 N-Channel FET

DARLINGTON PAIR

A Darlington pair is two transistors connected together to give a very high current gain . This is two

transistors connected together so that the current amplified by the first is amplified further by the second

transistor. The overall current gain is equal to the two individual gains multiplied together:

Darlington pair current gain, hFE = hFE1 × hFE2

(hFE1 and hFE2 are the gains of the individual transistors)

Page | 52

Page 53: Final Profect Report

This gives the Darlington pair a very high current gain, such as 10000, so that only a tiny base current is

required to make the pair switch on.

A Darlington pair behaves like a single transistor with a very high current gain. It has three leads

(B, C and E) which are equivalent to the leads of a standard individual transistor. To turn on there must be

0.7V across both the base-emitter junctions which are connected in series inside the Darlington pair,

therefore it requires 1.4V to turn on

Fig.34 Darlington Pair

USING A TRANSISTOR AS A SWITCH

When a transistor is used as a switch it must be either OFF or fully ON. In the fully ON state the voltage VCE across the transistor is

almost zero and the transistor is said to be saturated because it

cannot pass any more collector current Ic. The output device

switched by the transistor is usually called the 'load'.

Fig. 35 Transistor As A Switch

The power developed in a switching transistor is very small:

In the OFF state: power = Ic × VCE, but Ic = 0, so the power is zero.

In the full ON state: power = Ic × VCE, but VCE = 0 (almost), so the power is very small.

WHEN TO USE A RELAYTransistors cannot switch AC or high voltages (such as mains electricity) and they are not usually a good

choice for switching large currents (> 5A). In these cases a relay will be needed, but note that a low power

transistor may still be needed to switch the current for the relay's coil!

A TRANSISTOR INVERTER (NOT GATE)

Page | 53

Page 54: Final Profect Report

Inverters (NOT gates) are available on logic ICs but if you only require one

inverter it is usually better to use this circuit. The output signal (voltage) is the

inverse of the input signal:

When the input is high (+Vs) the output is low (0V).When the input is low (0V)

the output is high (+Vs). Fig. 36 A Transistor Inverter

3.5 Resistance

FUNCTION

Resistors restrict the flow of electric current, for example a resistor is placed in series

with a light-emitting diode (LED) to limit the current passing through the LED.

A resistor is a two-terminal electronic component that produces a voltage across its

terminals that is proportional to the electric current passing through it in accordance

with Ohm's law: V = IR

RESISTOR VALUES - THE RESISTOR COLOUR CODE

Resistance is measured in ohms, the symbol for ohm is an omega .

1 is quite small so resistor values are often given in k and M .

1 k = 1000 1 M = 1000000 .

Resistor values are normally shown using coloured bands.

Each colour represents a number as shown in the table.

Most resistors have 4 bands:

The first band gives the first digit. The second band gives the second digit. The third band indicates the number of zeros.

The fourth band is used to shows the tolerance (precision) of the resistor, this may be ignored for

almost all circuits but further details are given below.

Page | 54

The ResistorColour Code

Colour Number

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9

Page 55: Final Profect Report

This resistor has red (2), violet (7), yellow (4 zeros) and gold bands.

So its value is 270000 = 270 k .

On circuit diagrams the is usually omitted and the value is written 270K.

Small value resistors (less than 10 ohm)The standard colour code cannot show values of less than 10 . To show these small

values two special colours are used for the third band: gold which means × 0.1

and silver which means × 0.01. The first and second bands represent the digits as

normal

RESISTOR COLOUR CODE CALCULATOR

The Resistor Colour Code Calculator can be used to

identify resistors. It consists of three card discs showing

the colours and values, these are fastened together so you

can simply turn the discs to select the value or colour code

required. Simple but effective!

To make the calculator, carefully cut out the three discs and fasten them together with a

small brass paper fastener.

RESISTOR VALUES-THE RESISTOR COLOR CODE

Resistance is measured in ohms, the symbol for ohm is an omega Ω.1 Ω is quite small

so resistor values are often given in k Ω and

1kΩ=1000Ω 1MΩ=1000000Ω

Resistor values are normally shown using colored bands. Each colors represents a number as shown in the

table. Most resistors have 4 bands:

The first band gives the first digit. The second band gives the second digit. The third band gives the number of zeros

Page | 55

The ResistorColour Code

Colour Number

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9

Page 56: Final Profect Report

The fourth band is used to show the tolerance (precision) of the resistor, this may be ignored foe

almost all circuits. Other tolerance colours are:

TOLERANCE COLOUR

±1% Brown

±2% Red

±5% Gold

±10% Silver

Table-5 Other Tolerance Colours

POWER DISSIPATION

The power dissipated by a resistor (or the equivalent resistance of a resistor network) is calculated using

the following:

All three equations are equivalent. The first is derived from Joule's first law. Ohm’s Law derives the other

two from that.

The total amount of heat energy released is the integral of the power over time:

VARIABLE RESISTORS

Fig.37 Variable Resistor

Page | 56

Page 57: Final Profect Report

Variable resistors consist of a resistance track with connections at both ends and a wiper which moves

along the track as you turn the spindle. The track may be made from carbon, cermet (ceramic and metal

mixture) or a coil of wire (for low resistances). The track is usually rotary but straight track versions, usually

called sliders.

Variable resistors may be used as a rheostat with two connections (the wiper and just one end of the track)

or as a potentiometer with all three connections in use. Miniature versions called presets are made for

setting up circuits which will not require further adjustment.

Variable resistors are often called potentiometers in books and catalogues. They are specified by their

maximum resistance, linear or logarithmic track, and their physical size. The standard spindle diameter is

6mm.

Fig. 38 Resistor

Fig. 39 Resistor

Page | 57

Page 58: Final Profect Report

3.6 Capacitor

Capacitors store electric charge. They are used with resistors in timing circuits because it takes time for a

capacitor to fill with charge. They are used to smooth varying DC supplies by acting as a reservoir of

charge. They are also used in filter circuits because capacitors easily pass AC (changing) signals but they

block DC (constant) signals. This symbol is used to indicate a capacitor in a circuit diagram.

CAPACITANCE

This is a measure of a capacitor's ability to store charge. A large capacitance means that more charge can

be stored. Capacitance is measured in farads, symbol F. However 1F is very large, so prefixes are used to

show the smaller values.

Three prefixes (multipliers) are used, µ (micro), n (nano) and p (pico):

µ means 10-6 (millionth), so 1000000µF = 1F

n means 10-9 (thousand-millionth), so 1000nF = 1µF

p means 10-12 (million-millionth), so 1000pF = 1nF

There are many types of capacitor but they can be split into two groups, polarized and unpolarised.

Each group has its own circuit symbol.

POLARISED CAPACITORS (LARGE VALUES, 1µF +)

Examples: Circuit symbol:

ELECTROLYTIC CAPACITORS

Electrolytic capacitors are polarised and they must be connected the correct way round, at least one of their

leads will be marked + or -. They are not damaged by heat when soldering.There are two designs of

electrolytic capacitors; axial where the leads are attached to each end (220µF in picture) and radial where

both leads are at the same end (10µF in picture). Radial capacitors tend to be a little smaller and they stand

upright on the circuit board.

Page | 58

Page 59: Final Profect Report

It is easy to find the value of electrolytic capacitors because they are clearly printed with their capacitance

and voltage rating. The voltage rating can be quite low (6V for example) and it should always be checked

when selecting an electrolytic capacitor. If the project parts list does not specify a voltage, choose a

capacitor with a rating which is greater than the project's power supply voltage. 25V is a sensible minimum

for most battery circuits.

Fig.40 Current Progress Discharging Capacitor

TANTALUM BEAD CAPACITORS

Tantalum bead capacitors are polarized and have low voltage ratings like electrolytic capacitors. They are

expensive but very small, so they are used where a large capacitance is needed in a small size.

Modern tantalum bead capacitors are printed with their capacitance, voltage and polarity in full. However

older ones use a colour-code system which has two stripes (for the two digits) and a spot of colour for the

number of zeros to give the value in µF. The standard colour code is used, but for the spot, grey is used to

mean × 0.01 and white means × 0.1 so that values of less than 10µF can be shown. A third colour stripe

near the leads shows the voltage (yellow 6.3V, black 10V, green 16V, blue 20V, grey 25V, white 30V, pink

35V). The positive (+) lead is to the right

Page | 59

Page 60: Final Profect Report

For example: blue, grey, black spot means 68µF

For example: blue, grey, white spot means 6.8µF

For example: blue, grey, grey spot means 0.68µF

UNPOLARISED CAPACITORS (SMALL VALUES, UP TO 1µF)

Examples:

Circuit symbol:

Small value capacitors are unpolarised and may be connected either way round. They are not damaged by

heat when soldering, except for one unusual type (polystyrene). They have high voltage ratings of at least

50V, usually 250V or so. It can be difficult to find the values of these small capacitors because there are

many types of them and several different labeling systems! Many small value capacitors have their value

printed but without a multiplier, so you need to use

For example 0.1 means 0.1µF = 100nF.

Sometimes the multiplier is used in place of the decimal point:

For example: 4n7 means 4.7nF.

CAPACITOR NUMBER CODEA number code is often used on small capacitors where printing is difficult:

the 1st number is the 1st digit,

the 2nd number is the 2nd digit,

The 3rd number is the number of zeros to give the capacitance in pF.

Ignore any letters - they just indicate tolerance and voltage rating.

For example: 102 means 1000pF = 1nF (not 102pF!)

Page | 60

Page 61: Final Profect Report

For example: 472J means 4700pF = 4.7nF (J means 5% tolerance

CAPACITOR COLOR CODE

A color code was used on polyester capacitors for many years. It is now obsolete, but of

course there are many still around. The colors should be read like the resistor code, the

top three color bands giving the value in pF. Ignore the 4th band (tolerance) and 5th

band (voltage rating).

For example:

Brown, black, orange means 10000pF = 10nF = 0.01µF.

Note that there are no gaps between the color bands, so 2 identical

bands actually appear as a wide band.

For example:

Wide red, yellow means 220nF = 0.22µF.

VARIABLE CAPACITORS

Variable capacitors are mostly used in radio tuning circuits and they are sometimes called 'tuning

capacitors'. They have very small capacitance values, typically between 100pF and 500pF

(100pF = 0.0001µF). The type illustrated usually has trimmers built in (for making small adjustments - see

below) as well as the main variable capacitor. Many variable capacitors have very short spindles which are

not suitable for the standard knobs used for variable resistors and rotary switches. It would be wise to

check that a suitable knob is available before ordering a variable capacitor. Variable capacitors

are not normally used in timing circuits because their capacitance is too small to be practical and the range

of values available is very limited. Instead timing circuits use a fixed capacitor and a variable resistor if it is

necessary to vary the time period.

Page | 61

COLOR CODE

Color Number

Black 0

Brown 1

Red 2

Orange 3

Yellow 4

Green 5

Blue 6

Violet 7

Grey 8

White 9

Page 62: Final Profect Report

Variable capacitor symbol

TRIMMER CAPACITORS

Trimmer capacitors (trimmers) are miniature variable capacitors. They are designed to be mounted directly

onto the circuit board and adjusted only when the circuit is built. A small screwdriver or similar tool is

required to adjust trimmers. The process of adjusting them requires patience because the presence of your

hand and the tool will slightly change the capacitance of the circuit in the region of the trimmer! Trimmer

capacitors are only available with very small capacitances, normally less than 100pF. It is impossible to

reduce their capacitance to zero, so they are usually specified by their minimum and maximum values, for

example 2-10pF.

Trimmer Capacitor Symbol

3.7 Diode

Example:

Circuit symbol:

Page | 62

Page 63: Final Profect Report

FUNCTION

Diodes allow electricity to flow in only one direction. The arrow of the circuit symbol shows the direction in

which the current can flow. Diodes are the electrical version of a valve and early diodes were actually called

valves.

Forward Voltage DropElectricity uses up a little energy pushing its way through the diode, rather like a person pushing through a

door with a spring. This means that there is a small voltage across a conducting diode, it is called

the forward voltage drop and is about 0.7V for all normal diodes which are made from silicon. The forward

voltage drop of a diode is almost constant whatever the current passing through the diode so they have a

very steep characteristic (current-voltage graph).

Reverse VoltageWhen a reverse voltage is applied a perfect diode does not conduct, but all real diodes leak a very tiny

current of a few µA or less. This can be ignored in most circuits because it will be very much smaller than

the current flowing in the forward direction. However, all diodes have a maximum reverse voltage (usually

50V or more) and if this is exceeded the diode will fail and pass a large current in the reverse direction, this

is called breakdown.

Fig. 41 Diodes

Page | 63

Page 64: Final Profect Report

Fig. 42 I–V Characteristics of a P-N Junction Diode (not to scale)

ZENER DIODES

Example: Circuit symbol:

a = anode, k = cathode

Zener diodes are used to maintain a fixed voltage. They are designed

to 'breakdown' in a reliable and non-destructive way so that they can

be used in reverse to maintain a fixed voltage across their terminals.

The diagram shows how they are connected, with a resistor in series

to limit the current.

Zener diodes can be distinguished from ordinary diodes by their code

and breakdown voltage which are printed on them. Zener diode codes

begin BZX... or BZY... Their breakdown voltage is printed with V in place of a decimal point, so 4V7 means

4.7V for example.

Zener diodes are rated by their breakdown voltage and maximum power:

The minimum voltage available is 2.4V.

Power ratings of 400mW and 1.3W are common.

TYPES OF SEMICONDUCTOR DIODE

Page | 64

Page 65: Final Profect Report

DiodeZenerdiode

Schottkydiode

Tunneldiode

Light-emittingdiode

Photodiode Varicap Silicon controlled rectifier

Fig. 43 Types Of Semiconductor Diode

APPLICATIONS

Over-voltage protection

Diodes are frequently used to conduct damaging high voltages away from sensitive electronic devices.

They are usually reverse-biased (non-conducting) under normal circumstances. When the voltage rises

above the normal range, the diodes become forward-biased (conducting). For example, diodes are used in

(stepper motor and H-bridge) motor controller and relay circuits to de-energize coils rapidly without the

damaging voltage that would otherwise occur. (Any diode used in such an application is called a fly back

diode). Many integrated circuits also incorporate diodes on the connection pins to prevent external voltages

from damaging their sensitive transistors. Specialized diodes are used to protect from over-voltages at

higher power

3.8. Light Emitting Diodes (LED’S)

Example: Circuit symbol:

FUNCTION

LEDs emit light when an electric current passes through them.

CONNECTING AND SOLDERING

Page | 65

Page 66: Final Profect Report

LEDs must be connected the correct way round, the diagram may be labeled a or + for anode and k or - for

cathode (yes, it really is k, not c, for cathode!). The cathode is the short lead and there may be a slight flat

on the body of round LEDs. If you can see inside the LED the cathode is the larger electrode (but this is not

an official identification method).

LEDs can be damaged by heat when soldering, but the risk is small unless you are very slow. No special

precautions are needed for soldering most LEDs.

TESTING AN LED

Never connect an LED directly to a battery or power supply. It will be destroyed

almost instantly because too much current will pass through and burn it out.

LEDs must have a resistor in series to limit the current to a safe value, for quick

testing purposes a 1k resistor is suitable for most LEDs if your supply voltage is

12V or less. Remember to connect the LED the correct way round!

For an accurate value please see calculating an LED resistor value below.

COLORS OF LEDS

LEDs are available in red, orange, amber, yellow, green, blue and white. Blue and white LEDs are much

more expensive than the other colors.

The color of an LED is determined by the semiconductor material, not by the coloring of the 'package' (the

plastic body). LEDs of all colors are available in uncolored packages which may be diffused (milky) or clear

(often described as 'water clear'). The colored packages are also available as diffused (the standard type)

or transparent.

Page | 66

Page 67: Final Profect Report

TRI-COLOR LEDS

The most popular type of tri-color LED has a red and a green LED combined in one package with three

leads. They are called tri-color because mixed red and green light appears to be yellow and this is

produced when both the red and green LEDs are on.

The diagram shows the construction of a tri-color LED. Note the different lengths of the three leads. The

centre lead (k) is the common cathode for both LEDs, the outer leads (a1 and a2) are the anodes to the

LEDs allowing each one to be lit separately, or both together to give the third color.

BI-COLOR LEDS

A bi-color LED has two LEDs wired in 'inverse parallel' (one forwards, one backwards) combined in one

package with two leads. Only one of the LEDs can be lit at one time and they are less useful than the tri-

color LEDs described above.

SIZES, SHAPES AND VIEWING ANGLES OF LEDS

LEDs are available in a wide variety of sizes and shapes. The 'standard' LED has a round cross-section of

5mm diameter and this is probably the best type for general use, but 3mm round LEDs are also popular.

Round cross-section LEDs are frequently used and they are very easy to install on boxes by drilling a hole

of the LED diameter, adding a spot of glue will help to hold the LED if necessary. LED clips are also

available to secure LEDs in holes. Other cross-section shapes include square, rectangular and triangular.

As well as a variety of colors, sizes and shapes, LEDs also vary in their viewing angle. This tells you how

much the beam of light spreads out. Standard LEDs have a viewing angle of 60° but others have a narrow

beam of 30° or less. Rapid stock a wide selection of LEDs and their catalogue is a good guide to the range

available.

.

CALCULATING AN LED RESISTOR VALUE

Page | 67

Page 68: Final Profect Report

An LED must have a resistor connected in series to limit the current

through the LED; otherwise it will burn out almost instantly.

The resistor value, R is given by:

R = (VS - VL) / I

VS = supply voltage

VL = LED voltage (usually 2V, but 4V for blue and white LEDs)

I = LED current (e.g. 10mA = 0.01A, or 20mA = 0.02A)

Make sure the LED current you choose is less than the maximum permitted and convert the current to amps (A) so the calculation will give the resistor value in ohms ( ).

To convert mA to A divide the current in mA by 1000 because 1mA = 0.001A.

If the calculated value is not available choose the nearest standard resistor value which is greater, so that

the current will be a little less than you chose. In fact you may wish to choose a greater resistor value to

reduce the current (to increase battery life for example) but this will make the LED less bright.

For example

If the supply voltage VS = 9V, and you have a red LED (VL = 2V), requiring a current I = 20mA = 0.020A,

R = (9V - 2V) / 0.02A = 350 , so choose 390 (the nearest standard value which is greater).

Working out the LED resistor formula using Ohm's law

Ohm's law says that the resistance of the resistor, R = V/I, where:

V = voltage across the resistor (= VS - VL in this case)

I = the current through the resistor

So R = (VS - VL) / I

Connecting LEDs in series

If you wish to have several LEDs on at the same time it may be

possible to connect them in series. This prolongs battery life by

lighting several LEDs with the same current as just one LED.

Page | 68

Page 69: Final Profect Report

All the LEDs connected in series pass the same current so it is best if they are all the same type. The

power supply must have sufficient voltage to provide about 2V for each LED (4V for blue and white) plus at

least another 2V for the resistor. To work out a value for the resistor you must add up all the LED voltages

and use this for VL.

Avoid connecting LEDs in parallel!

Connecting several LEDs in parallel with just one resistor shared between them is

generally not a good idea.

If the LEDs require slightly different voltages only the lowest voltage LED will light

and it may be destroyed by the larger current flowing through it. Although identical

LEDs can be successfully connected in parallel with one resistor this rarely offers

any useful benefit because resistors are very cheap and the current used is the

same as connecting the LEDs individually.

3.9 Crystal Oscillator

FUNCTION

A crystal oscillator is an electronic circuit that uses the mechanical resonance of a

vibrating crystal of piezoelectric material to create an electrical signal with a very precise frequency. This

frequency is commonly used to keep track of time (as in quartz wristwatches), to provide a stable clock

signal for digital integrated circuits, and to stabilize frequencies for radio transmitters and receivers. The

most common type of piezoelectric resonator used is the quartz crystal, so oscillator circuits designed

around them were called "crystal oscillators".

Quartz crystals are manufactured for frequencies from a few tens of kilohertz to tens of megahertz. More

than two billion (2×109) crystals are manufactured annually. Most are small devices for consumer devices

such as wristwatches, clocks, radios, computers, and cell phones. Quartz crystals are also found inside test

and measurement equipment, such as counters, signal generators, and oscilloscopes.

Page | 69

Page 70: Final Profect Report

Fig.44 Basic Oscillator

OPERATION

A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a regularly ordered,

repeating pattern extending in all three spatial dimensions.

Almost any object made of an elastic material could be used like a crystal, with appropriate transducers,

since all objects have natural resonant frequencies of vibration. For example, steel is very elastic and has a

high speed of sound. It was often used in mechanical filters before quartz. The resonant frequency

depends on size, shape, elasticity, and the speed of sound in the material. High-frequency crystals are

typically cut in the shape of a simple, rectangular plate. Low-frequency crystals, such as those used in

digital watches, are typically cut in the shape of a tuning fork. For applications not needing very precise

timing, a low-cost ceramic resonator is often used in place of a quartz crystal.

When a crystal of quartz is properly cut and mounted, it can be made to distort in an electric field by

applying a voltage to an electrode near or on the crystal. This property is known as piezoelectricity. When

the field is removed, the quartz will generate an electric field as it returns to its previous shape, and this can

generate a voltage. The result is that a quartz crystal behaves like a circuit composed of

an inductor, capacitor and resistor, with a precise resonant frequency. (See RLC circuit.)

Quartz has the further advantage that its elastic constants and its size change in such a way that the

frequency dependence on temperature can be very low. The specific characteristics will depend on the

mode of vibration and the angle at which the quartz is cut (relative to its crystallographic axes). [7] Therefore,

the resonant frequency of the plate, which depends on its size, will not change much, either. This means

that a quartz clock, filter or oscillator will remain accurate. For critical applications the quartz oscillator is

Page | 70

Page 71: Final Profect Report

mounted in a temperature-controlled container, called a crystal oven, and can also be mounted on shock

absorbers to prevent perturbation by external mechanical vibrations.

ELECTRICAL MODEL

Electronic symbol Schematic symbol

A quartz crystal can be modeled as an electrical network with a low impedance (series) and a

high impedance (parallel) resonance point spaced closely together. Mathematically (using the Laplace

transform) the impedance of this network can be written as:

Or,

Where s is the complex frequency (s = jω), ωs is the series resonant frequency in radians per second

and ωp is the parallel resonant frequency in radians per second.

TEMPERATURE EFFECTS

A crystal's frequency characteristic depends on the shape or 'cut' of the crystal. A tuning fork crystal is

usually cut such that its frequency over temperature is a parabolic curve centered around 25 °C. This

means that a tuning fork crystal oscillator will resonate close to its target frequency at room temperature,

but will slow down when the temperature either increases or decreases from room temperature. A common

parabolic coefficient for a 32 kHz tuning fork crystal is −0.04 ppm/°C².

Page | 71

Page 72: Final Profect Report

In a real application, this means that a clock built using a regular 32 kHz tuning fork crystal will keep good

time at room temperature, lose 2 minutes per year at 10 degrees Celsius above (or below) room

temperature and lose 8 minutes per year at 20 degrees Celsius above (or below) room temperature due to

the quartz crystal.

COMMONLY USED CRYSTAL FREQUENCIES

Crystal oscillator circuits are often designed around relatively few standard frequencies, such as 3.58 MHz,

10 MHz, 14.318 MHz, 20 MHz, 33.33 MHz, and 40 MHz. The popularity of the 3.58 MHz and 14.318 MHz

crystals is due to low cost since they are used for television color receivers. Using frequency

dividers, frequency multipliers and phase locked loop circuits; it is practical to derive a wide range of

frequencies from one reference frequency.

Crystals can be manufactured for oscillation over a wide range of frequencies, from a few kilohertz up to

several hundred megahertz. Many applications call for a crystal oscillator frequency conveniently related to

some other desired frequency, so hundreds of standard crystal frequencies are made in large quantities

and stocked by electronics distributors

CRYSTAL STRUCTURES AND MATERIALS

The most common material for oscillator crystals is quartz. At the beginning of the technology, natural

quartz crystals were used; now synthetic crystalline quartz grown by hydrothermal synthesis is predominant

due to higher purity, lower cost, and more convenient handling. One of the few remaining uses of natural

crystals is for pressure transducers in deep wells.

Two types of quartz crystals exist: left-handed and right-handed, differing in the optical rotation but identical

in other physical properties. Both left and right-handed crystals can be used for oscillators, if the cut angle

is correct. In manufacture, right-handed quartz is generally used. The SiO 4 tetrahedrons form parallel

helixes; the direction of twist of the helix determines the left- or right-hand orientation. The helixes are

aligned along the z-axis and merged together, sharing atoms. The mass of the helixes forms a mesh of

small and large channels parallel to the z-axis; the large ones are large enough to allow some mobility of

smaller ions and molecules through the crystal.

Some other piezoelectric materials than quartz can be employed; e.g. single crystals of lithium

tantalate, lithium niobate, lithium borate, berlinite, gallium arsenide, lithium tetraborate,aluminium

phosphate, bismuth germanium oxide, polycrystalline zirconium titanate ceramics, high-alumina

ceramics, silicon-zinc oxide composite, or dipotassium tartrate; some materials may be more suitable for

specific applications. An oscillator crystal can be also manufactured by depositing the resonator material on

Page | 72

Page 73: Final Profect Report

the silicon chip surface. Crystals of gallium, langasite, langanite and langanate are about 10 times more

pullable than the corresponding quartz crystals, and are used in some VCXO oscillators.

Fig. 45 Crystal Structures

3.10 Relays

A relay is an electrically operated switch. Current flowing through the coil of the relay creates a magnetic

field which attracts a lever and changes the switch contacts. The coil current can be on or off so relays

have two switch positions and most have double throw (changeover) switch contacts as shown in the

diagram.

Relays allow one circuit to switch a second circuit which can be completely separate from the first. For

example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit. There is no

electrical connection inside the relay between the two circuits; the link is magnetic and mechanical.

Page | 73

Page 74: Final Profect Report

The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be as much as

100mA for relays designed to operate from lower voltages. Most ICs (chips) cannot provide this current and

a transistor is usually used to amplify the small IC current to the larger value required for the relay coil. The

maximum output current for the popular 555 timer IC is 200mA so these devices can supply relay coils

directly without amplification.

Relays are usually SPDT or DPDT but they can have many more sets of switch contacts, for example

relays with 4 sets of changeover contacts are readily available. For further information about switch

contacts and the terms used to describe them please see the page on switches.

Most relays are designed for PCB mounting but you can solder wires directly to the pins providing you take

care to avoid melting the plastic case of the relay.

The supplier's catalogue should show you the relay's connections. The coil will be obvious and it may be

connected either way round. Relay coils produce brief high voltage 'spikes' when they are switched off and

this can destroy transistors and ICs in the circuit. To prevent damage you must connect a protection

diode across the relay coil.

The relay's switch connections are usually labeled COM, NC and NO:

COM = Common, always connect to this, it is the moving part of the switch.

NC = Normally Closed, COM is connected to this when the relay coil is off. NO = Normally Open, COM is connected to this when the relay coil is on.

Connect to COM and NO if you want the switched circuit to be on when the relay coil is on.

Connect to COM and NC if you want the switched circuit to be on when the relay coil is off.

CHOOSING A RELAY

1. Physical size and pin arrangement If you are choosing a relay for an existing PCB you will need to ensure that its dimensions and pin

arrangement are suitable. You should find this information in the supplier's catalogue.

2. Coil voltage

The relay's coil voltage rating and resistance must suit the circuit powering the relay coil. Many

relays have a coil rated for a 12V supply but 5V and 24V relays are also readily available. Some

relays operate perfectly well with a supply voltage which is a little lower than their rated value.

Page | 74

Page 75: Final Profect Report

3. Coil resistance

The circuit must be able to supply the current required by the relay coil. You can use Ohm's law to

calculate the current:

Relay coil current = supply voltage

coil resistance

For example: A 12V supply relay with a coil resistance of 400 passes a current of 30mA. This is

OK for a 555 timer IC (maximum output current 200mA), but it is too much for most ICs and they will

require a transistor to amplify the current.

4. Switch ratings (voltage and current) The relay's switch contacts must be suitable for the circuit they are to control. You will need to check

the voltage and current ratings. Note that the voltage rating is usually higher for AC, for example:

"5A at 24V DC or 125V AC".

5. Switch contact arrangement (SPDT, DPDT etc) Most relays are SPDT or DPDT which are often described as "single pole changeover" (SPCO) or

"double pole changeover" (DPCO). For further information please see the page on switches.

PROTECTION DIODES FOR RELAYS

Transistors and ICs must be protected from the brief high voltage produced when a relay coil is switched

off. Current flowing through a relay coil creates a magnetic field which collapses suddenly when the current

is switched off. The sudden collapse of the magnetic field induces a brief high voltage across the relay coil

which is very likely to damage transistors and ICs. The protection diode allows the induced voltage to drive

a brief current through the coil (and diode) so the magnetic field dies away quickly rather than instantly.

This prevents the induced voltage becoming high enough to cause damage to transistors and ICs.

Fig.46 Protection Diodes for Relays

Page | 75

Page 76: Final Profect Report

RELAYS AND TRANSISTORS COMPARED

Like relays, transistors can be used as an electrically operated switch. For switching small DC currents (<

1A) at low voltage they are usually a better choice than a relay. However, transistors cannot switch AC

(such as mains electricity) and in simple circuits they are not usually a good choice for switching large

currents (> 5A). In these cases a relay will be needed, but note that a low power transistor may still be

needed to switch the current for the relay's coil!

ADVANTAGES OF RELAYS

Relays can switch AC and DC, transistors can only switch DC.

Relays can switch higher voltages than standard transistors.

Relays are often a better choice for switching large currents (> 5A).

Relays can switch many contacts at once.

DISADVANTAGES OF RELAYS

Relays are bulkier than transistors for switching small currents.

Relays cannot switch rapidly (except reed relays), transistors can switch many times per second.

Relays use more power due to the current flowing through their coil.

Relays require more current than many ICs can provide, so a low power transistor may be

needed to switch the current for the relay's coil.

Fig.47 Relay

Page | 76

Page 77: Final Profect Report

Fig.Fhjh

Fig.48 Simple Relay circuit

Fig.49 Switching of Relay

Fig. 50 Switching of Relay

3.11 Transformer

HISTORY

A transformer is an electrical device that transfers energy from one circuit to another by magnetic coupling,

without requiring relative motion between its parts. A transformer comprises two or more coupled windings,

and, in most cases, a magnetic core to concentrate magnetic flux. A changing voltage applied to one

winding creates a time-varying magnetic flux in the core, which induces a voltage in the other windings.

Page | 77

Page 78: Final Profect Report

The transformer is one of the simplest of electrical devices, yet transformer designs and materials continue

to be improved.

Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden inside a stage

microphone to huge giga watt units used to interconnect large portions of national power grids. All operate

with the same basic principles and with many similarities in their parts.

Michael Faraday built the first transformer in 1831, although he used it only to demonstrate the principle of

electromagnetic induction and did not foresee its practical uses.

BASIC PRINCIPLES

An analogy

A transformer can be likened to a mechanical

gearbox, which transfers mechanical energy from a

high-speed, low torque shaft to a lower-speed, higher-

torque shaft, but which is not a source of energy itself.

A transformer transfers electrical energy from a high-

current, low-voltage circuit to a lower-current, higher-

voltage circuit.

Coupling By Mutual Induction

The principles of the transformer are illustrated by consideration of a hypothetical ideal transformer. In this

case, the core requires negligible magnemotive force to sustain flux, and all flux linking the primary winding

also links the secondary winding. The hypothetical ideal transformer has no resistance in its coils. A simple

transformer consists of two electrical conductors called the primary winding and the secondary winding.

Energy is coupled between the windings by the time varying magnetic flux that passes through (links) both

primary and secondary windings. Whenever the amount of current in a coil changes, a voltage is induced in

the neighboring coil. The effect, called mutual inductance, is an example of electromagnetic induction.

Induction Law

The voltage induced across the secondary coil may be calculated from Faraday's law of induction, which

states that:

Page | 78

Page 79: Final Profect Report

Where VS is the instantaneous voltage, NS is the number of turns in the secondary coil and Φ equals

the 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 flux density 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

Taking the ratio of the two equations for VS and VP gives the basic equation for stepping up or stepping

down the voltage

Ideal Power Equation

Fig.51 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 into the secondary circuit. If this condition is

met, the incoming electric power must equal the outgoing power.

Page | 79

Page 80: Final Profect Report

P incoming = IPVP = P outgoing = ISVS

Giving the ideal transformer equation

Transformers normally have high efficiency, so this formula is a reasonable approximation.

If the voltage is increased, then the current is decreased by the same factor. The impedance in one circuit

is transformed by the square of the turns ratio. For example, if an impedance ZS is attached across the

terminals of the secondary coil, it appears to the primary circuit to have an impedance of . This

relationship is reciprocal, so that the impedance ZP of the primary circuit appears to the secondary to be

.

CLASSIFICATIONS

Transformers are adapted to numerous engineering applications and may be classified in many ways:

• By power level (from fraction of a volt-ampere(VA) to over a thousand MVA),

• By application (power supply, impedance matching, circuit isolation),

• By frequency range (power, audio, radio frequency(RF))

• By voltage class (a few volts to about 750 kilovolts)

• By cooling type (air cooled, oil filled, fan cooled, water cooled, etc.)

• By purpose (distribution, rectifier, arc furnace, amplifier output, etc.).

• By ratio of the number of turns in the coils

• Step-up

The secondary has more turns than the primary.

• Step-down

The secondary has fewer turns than the primary.

• Isolating

Intended to transform from one voltage to the same voltage. The two coils have approximately

equal numbers of turns, although often there is a slight difference in the number of turns, in order to

Page | 80

Page 81: Final Profect Report

compensate for losses (otherwise the output voltage would be a little less than, rather than the

same as, the input voltage).

• Variable The primary and secondary have an adjustable number of turns, which can be selected without

reconnecting the transformer.

STEP DOWN TRANSFORMER & STEP UP TRANSFORMER

Step down transformers are designed to reduce electrical voltage. Their primary voltage is greater than

their secondary voltage. This kind of transformer "steps down" the voltage applied to it. For instance, a step

down transformer is needed to use a 110v product in a country with a 220v supply.

Step down transformers convert electrical voltage from one level or phase configuration usually down to a

lower level. They can include features for electrical isolation, power distribution, and control and

instrumentation applications. Step down transformers typically rely on the principle of magnetic induction

between coils to convert voltage and/or current levels.

Step down transformers are made from two or more coils of insulated wire wound around a core made of

iron. When voltage is applied to one coil (frequently called the primary or input) it magnetizes the iron core,

which induces a voltage in the other coil, (frequently called the secondary or output). The turns ratio of the

two sets of windings determines the amount of voltage transformation.

An example of this would be: 100 turns on the primary and 50 turns on the secondary, a ratio of 2 to Step

down transformers can be considered nothing more than a voltage ratio device.

With step down transformers the voltage ratio between primary and secondary will mirror the "turns ratio"

(except for single phase smaller than 1 kva which have compensated secondaries). A practical application

of this 2 to 1 turns ratio would be a 480 to 240 voltage step down. Note that if the input were 440 volts then

the output would be 220 volts. The ratio between input and output voltage will stay constant. Transformers

should not be operated at voltages higher than the nameplate rating, but may be operated at lower voltages

than rated. Because of this it is possible to do some non-standard applications using standard

transformers.

Single phase step down transformers 1 kva and larger may also be reverse connected to step-down or

step-up voltages. (Note: single phase step up or step down transformers sized less than 1 KVA should not

Page | 81

Page 82: Final Profect Report

be reverse connected because the secondary windings have additional turns to overcome a voltage drop

when the load is applied. If reverse connected, the output voltage will be less than desired.

Fig. 52 Step-Down Transformer

Step-up transformer 110v 220v design is one whose secondary voltage is greater than its primary voltage.

This kind of transformer "steps up" the voltage applied to it. For instance, a step up transformer is needed

to use a 220v product in a country with a 110v supply. Step-up transformer 110v 220v depends entirely on

the products you will be using it with. Give your transformer supplier a detailed list of all the products you

will be using with it - and also their maximum outputs. From this information he/she will be able to advise

the correct step up transformer rating needed.

A step up transformer 110v 220v converts alternating current (AC) from one voltage to another voltage. It

has no moving parts and works on a magnetic induction principle; it can be designed to "step-up" or "step-

down" voltage. So a step up transformer increases the voltage and a step down transformer decreases the

voltage.

The primary components for voltage transformation are the step up transformer core and coil. The

insulation is placed between the turns of wire to prevent shorting to one another or to ground. This is

typically comprised of mylar, nomex, kraft paper, varnish, or other materials. As a transformer has no

moving parts, it will typically have a life expectancy between 20 and 25 years.

Fig.53 Step-Up Transformer

Page | 82

Page 83: Final Profect Report

Fig.54 Efficiency vs. Load Curve

USES OF TRANSFORMERS

For supplying power from an alternating current power grid to equipment which uses a

different voltage.

For regulating the secondary output of a constant voltage (or Ferro-resonant), in which a

combination of core saturation and the resonance of a tank circuit prevents changes in the

primary voltage from appearing on the secondary.

Electric power transmission over long distances.

Large, specially constructed power transformers are used for electric arc furnaces used in

steelmaking.

Rotating transformers are designed so that one winding turns while the other remains

stationary. A common use was the video head system as used in VHS and Beta video

tape players. These can pass power or radio signals from a stationary mounting to a

rotating mechanism, or radar antenna.

Other rotary transformers are precisely constructed in order to measure distances or

angles. Usually they have a single primary and two or more secondaries, and electronic

circuits measure the different amplitudes of the currents in the secondaries. See synchro

and resolver.

Sliding transformers can pass power or signals from a stationary mounting to a moving

part such as a machine tool head.

A transformer-like device is used for position measurement. See linear variable differential

transformer.

Some rotary transformers are used to couple signals between two parts which rotate in

relation to each other.

Page | 83

Page 84: Final Profect Report

Small transformers are often used internally to couple different stages of radio receivers

and audio amplifiers.

Transformers may be used as external accessories for impedance matching; for example

to match a microphone to an amplifier.

Balanced-to-unbalanced conversion. A special type of transformer called a balun is used in

radio and audio circuits to convert between balanced line circuits and unbalanced

transmission lines such as antenna down leads.

Fly back transformers are built using ferrite cores. They supply high voltage to the CRTs at

the frequency of the horizontal oscillator. In the case of television sets, this is about 15.7

kHz. It may be as high as 75 - 120 kHz for high-resolution computer monitors.

Switching power supply transformers usually operate between 30-1000 kHz. The tiny

cores found in wristwatch backlight power supplies produce audible sound (about 1 kHz).

LIMITATIONS

Transformers alone cannot do the following:

Convert DC to AC or vice versa

Change the voltage or current of DC

Change the AC supply frequency.

Page | 84

Page 85: Final Profect Report

CHAPTER 4

Programming Software and Algorithms 4.1 Source Code

4.2 Program Algorithm

4.1 Source Code

#include<reg52.h>

Void delay (int);

//////////////////////////////////////////////////////////////////////////

Void main ()

{

Page | 85

Page 86: Final Profect Report

P27=0; P26=0; P25=0; P24=0;

While (1)

{

//////////////////////////////////////////////////////////////////////////

If (P17==0 && P16==1 && P15==0 && P14==1)

{

P25=0; P24=0; delay (15);

}

If (P17==0 && P16==1 && P15==1 && P14==0)

{

P25=1; P24=1; delay (15);

}

If (P17==0 && P16==1 && P15==1 && P14==1)

{

P25=0; P24=0; delay (15);

}

If (P17==1 && P16==0 && P15==0 && P14==0)

{

P25=1; P24=1; delay (15);

}

//////////////////////////////////////////////////////////////////////////

If (P17==0 && P16==0 && P15==0 && P14==1)

Page | 86

Page 87: Final Profect Report

{

P27=0; P26=0; delay (15);

}

If (P17==0 && P16==0 && P15==1 && P14==0)

{

P27=1; P26=1; delay (15);

}

If (P17==0 && P16==0 && P15==1 && P14==1)

{

P27=0; P26=0; delay (15);

}

If (P17==0 && P16==1 && P15==0 && P14==0)

{

P27=1; P26=1; delay (15);

}

//////////////////////////////////////////////////////////////////////////

If (P17==1 && P16==0 && P15==1 && P14==1)

{

P2=0x00; delay (15);

}

If (P17==1 && P16==1 && P15==0 && P14==0)

{

Page | 87

Page 88: Final Profect Report

P2=0xff; delay (15);

}

//////////////////////////////////////////////////////////////////////////

}

}

//////////////////////////////////////////////////////////////////////////

Void delay (int x)

{

int i,j;

for (i=0;i<=x;i++)

{

for (j=0;j<=32000;j++);

}

Keil

1. Open Keil from the Start menu

2. The Figure below shows the basic names of the windows referred in this document

Page | 88

Page 89: Final Profect Report

Fig.55A Keil Window

Select New Project from the Project Menu.

Start Starting a new Assembler Project

1. Select New Project from the Project Menu

Page | 89

Page 90: Final Profect Report

Fig.55B Keil Window

2. Name the project ‘Toggle.a51’

3. Click on the Save Button

Fig.55C Keil Window

4. The device window will be displayed.

5. Select the part you will be using to test with. For now we will use the Dallas Semiconductor part

DS89C420.

6. Double Click on the Dallas Semiconductor

7. Scroll down and select the DS89C420 Part

8. Click OK

Page | 90

Page 91: Final Profect Report

Fig.55D Keil Window

4.2 Program Algorithm

Page | 91

Page 92: Final Profect Report

Flow chart of the AT89S52 program

Page | 92

Page 93: Final Profect Report

Page | 93

Page 94: Final Profect Report

Chapter 5Application and Scope

5.1 Result 5.2 Application 5.3 Conclusion5.4 Future Scope

5.1 Result

The design was implemented on a printed circuit and was successfully tested with a simple program for

switching two electrical appliances. The program is due to be modified with more options for the user.

5.2 Application

Applications

Page | 94

Page 95: Final Profect Report

The device finds extensive use in different industries, home, office wherever telephone communication is

possible. This device finds use for remote operation of electrical gadgets using mobile phone. In case of

any emergency requirement, the electrical mains of a house can be powered off.

1) Combination Lock

2) Home Security System

3) Mobile / Wireless Robot control

4) Wireless Radio Control

5) Continuous monitoring of system status

6) Remote Switches

7) Reporting during car accidents

5.3 Conclusion

A device was developed that could be used to control electrical appliances through a telephone at a remote

location. There are four outputs enabling the direct control of four equipments.

The Limitations of the device are:

• The user will be charged the fee of the phone call since the telephone switch identifies the period the

device being used as a phone call taking place.

• If the appliances that are to be controlled are far from the device, wired or wireless connections must be

made from the device to the appliance.

5.4 Future Scope

There are lots of scopes of improvement on the work. For example, the number of devices, that can be

remotely operated, might be increased. The present status of each of the devices (whether ON or OFF) can

be remotely monitored. There is a plan to remotely put off the regulator of LPG Cooking Gas and to close

the water tap.

Page | 95

Page 96: Final Profect Report

Page | 96

Page 97: Final Profect Report

APPENDICES

APPENDIX – A

DATA SHEET OF MT8870

Features• Complete DTMF Receiver Table-A1 Ordering Information

• Low power consumption

• Internal gain setting amplifier

• Adjustable guard time

• Central office quality

Page | 97

Page 98: Final Profect Report

• Power-down mode

• Inhibit mode

• Backward compatible with MT8870C/MT8870C-1

Applications• Receiver system for British Telecom (BT) or

CEPT Spec (MT8870D-1)

• Paging systems

• Repeater systems/mobile radio

• Credit card systems

• Remote control

• Personal computers

• Telephone answering machine

DescriptionThe MT8870D/MT8870D-1 is a complete DTMF receiver integrating both the band split filter and digital

decoder functions. The filter section uses switched capacitor techniques for high and low group filters;

The decoder uses digital counting techniques to detect and decode all 16 DTMF tone-pairs into a 4-bit

code.

Functional DescriptionThe MT8870D/MT8870D-1 monolithic DTMF receiver offers small size, low power consumption and high

performance. Its architecture consists of a bandsplit filter section, which separates the high and low group

tones, followed by a digital counting section which verifies the frequency and duration of the received tones

before passing the corresponding code to the output bus.

Filter SectionSeparation of the low-group and high group tones is achieved by applying the DTMF signal to the inputs of

two sixth-order switched capacitor band pass filters, the bandwidths of which correspond to the low and

high group frequencies. The filter section also incorporates notches at 350 and 440 Hz for exceptional dial

tone rejection (see Figure.A2). Each filter output is followed by a single order switched capacitor filter

section which smooths the signals prior to limiting. Limiting is performed by high-gain comparators which

are provided with hysteresis to prevent detection of unwanted low-level signals. The outputs of the

comparators provide full rail logic swings at the frequencies of the incoming DTMF signals.

Page | 98

Page 99: Final Profect Report

Fig.A1 - Filter Response

Table- A 2 - Functional Decode Table L=LOGIC LOW, H=LOGIC HIGH, Z=HIGH IMPEDANCE X = DON‘T CARE

Table-A3 Absolute Maximum Rating

Page | 99

Page 100: Final Profect Report

Table-A4 DC Electrical Characteristics

Table- A5 Operating Characteristics

Page | 100

Page 101: Final Profect Report

Table-A6 AC Electrical Characteristics

Page | 101

Page 102: Final Profect Report

Fig.A2 - Timing Diagram

APPENDIX – B

Page | 102

Page 103: Final Profect Report

DATA SHEET OF LM78XX

LM78XX/LM78XXA3-Terminal 1A Positive Voltage Regulator

Page | 103

Page 104: Final Profect Report

Fig.B1 Block Diagram

Fig.B2 Pin Assignment

Table – B2 Absolute Maximum Rating

Table-B3 Electrical Characteristics

Page | 104

Page 105: Final Profect Report

Table – B4 Electrical Characteristics

Typical Performance Characteristics

Page | 105

Page 106: Final Profect Report

Fig.B3 Quiescent Current Fig.B4 Peak Output Current

Fig.B5 Output Voltage Fig.B6 Quiescent Current

Typical Applications

Fig.B7- DC Parameters

Page | 106

Page 107: Final Profect Report

Fig.B8 - Load Regulation

Fig.B9- Ripple Rejection

Fig.B10 - Fixed Output Regulator

Page | 107

Page 108: Final Profect Report

Fig.B11 - Circuit for Increasing Output Voltage with variable load

NOTES1. To specify an output voltage, substitute voltage value for “XX.” A common ground is required between

the input and the output voltage. The input voltage must remain typically 2.0V above the output voltage

even during the low point on the input ripple voltage.

2. CI is required if regulator is located an appreciable distance from power supply filter.

3. CO improves stability and transient response.

Fig.B12 - Circuit for Increasing Output Voltage

Page | 108

Page 109: Final Profect Report

Fig.B13 - Adjustable Output Regulator (7V to 30V)

Fig.B14 - High Current Voltage Regulator

Page | 109

Page 110: Final Profect Report

Fig.B15 - High Output Current with Short Circuit Protection

Fig.B16 - Tracking Voltage Regulator

Page | 110

Page 111: Final Profect Report

APPENDIX – C

PCB PRODUCTION METHODS

Outline

Motivation• File Formats– Excellon Drill Files– Gerber• A Typical PCB Manufacturing Process• Populating and Soldering• Hobbyist Solutions• Conclusion

Motivation• Understanding underlying manufacturing processes is almost always important for an engineer:

– Allows the design to exploit capabilities; and

– Ensures that the design will be manufacturable.

• PCBs have been produced for many years; advances with technological improvements are notable.

File Formats• As discussed in a previous lecture, professional manufacture of PCBs is typically done through the use of

CAD independent

Files:

– Gerber Files – describe the copper foil layout

– Drill Files (often in the Excellon format) – describe the location and size of holes

• Both are meant for direct use with automated PCB production equipment.

File Formats: Excellon Drill File• Excellon Files provide a command sequence to a system that drills PCBs

• This equipment (or its computer driver) has an interpreter that receives and executes the commands in

sequence.

File Formats: Gerber• Gerber files are typically used to describe the copper foil patterns on the PCB

Page | 111

Page 112: Final Profect Report

• The “interpreter” idea is similar to what was described for the Excellon format

• Since pad shapes and track sizes need to specified, many new commands are used

• These commands are not covered here, but a good source of information can be found in “Gerber RS

274X Format User’s Guide”, Barco Graphics, N.V., Gent, Belgium, 1998: available at

http://members.optusnet.com.au/~eseychell/rs274xrevd_e.pdf

File Formats: Gerber• Much of the terminology originates from the manner in which PCBs are often made: through exposure of a

photo-resist layer on a board:

– Aperture: a size and shape of a pad (or, if moved while “on”, the width of a trace and the shape of its

ends).

– Aperture Wheel: the set of apertures available. This is analogous to the set of drills available in the

Excellon “Drill Rack”.

File Formats: Gerber – Dated Photoplotter

Fig.C1 Gerber Photoplotter

Page | 112

Page 113: Final Profect Report

Typical PCB Manufacturing Process

• We have already examined some of the tolerances of

modern production methods.

• In this section, we will look at some of the equipment that is

used in modern PCB production.

Each development stage is carried out by a dedicated piece of

equipment – which may form part of an assembly line.

Depending on your application, note that some stages may be

missing here. For instance, a tinning stage is often included

after etching to reduce copper layer oxidation. A multi-layer PCB, too, requires a lamination stage to join

the layers.

Fig.C2 A Multi-Stage Plate-Through Hole Setup

Fig.C3 Raster Plotter

A raster plotter from Mega Electronics serves as a replacement to the photoplotter described earlier. This plotter is capable of

creating a 5 micron spot.

Page | 113

Page 114: Final Profect Report

Fig.C4 laminator

A laminator is used to apply the photo resist layer to the PCB. This laminator is from Mega Electronics.

Fig.C5 UV Unit

UV units used to expose the photo resist on a PCB.

Fig. C6 Etching Developer & Stripping Setup

There are many different sorts of etching, developing, and stripping setups. This one is from Mega

Electronics and is a unit that sprays the chemicals over board panels, mounted inside. Different units (of

the same type) are typically used for each stage described, above.

Page | 114

Page 115: Final Profect Report

Fig. C7 Spray TankA panel that is inserted into a spray tank.

Fig. C8 Production Line

Again from Mega Electronics, units such as this “Production Line” can be used to combine the chemical stages into a convenient unit. The operator is responsible for forwarding the PCB through the stages.

Fig.C9 Silkscreen Printing Technology

Etch-resist solders masks, parts placement silkscreen legends, and even solder paste can applied to a

PCB using silkscreen printing technology.

Populating and Soldering

• Each of the two methods has advantages and disadvantages:

– Some parts cannot handle the thermal shock experienced by being passed through molten solder;

– When wave soldering is used, it is necessary to hold components in place: glue!

Page | 115

Page 116: Final Profect Report

– Wave soldering is FAST!

– Reflow soldering does not really work with through hole parts.

• Regardless of the method used, particular temperature profiles must be adhered to. Populating and

Soldering

• Once a board is created, it is still necessary to “stuff” the board with components.

• This can be done by hand, but in mass production time is an issue.

• There are two typical ways that a board has components soldered onto it:

1. The Reflow method where solder is applied to the board in a paste form, the components are added and

then soldering is performed in an oven; and

2. The Wave soldering method sees the components added, and then passed over a “standing wave” of

solder to perform the soldering.

• “Solder Paste” is solder in a very fine form suspended in flux.

• It can be placed on a PCB via a silkscreen, or using a needle applicator:

• The paste locations are dictated by the corresponding Gerber output from the CAD package.

Populating and Soldering: Pick and Place Units

• To place components on a PCB, a “Pick and Place” unit can be used.

• Again, component placement information originates from the CAD package.

• An interesting home-brewed solution that shows many of the necessary steps in this process is at:

Homebrew Surface Mount Pick and Place Taig Mill Conversion

http://www.youtube.com/watch?v=__dEMKzkLYc

Page | 116

Page 117: Final Profect Report

Fig.C10 - A reflow oven

Fig.C11 Temperature profile of the reflow soldering process.

Conclusion• You now have an idea of what the PCB production process involves

– At a professional level; and

– At a hobbyist level.

• Hopefully with this knowledge you have gained enough insight to allow the design of PCBs that are

compatible with the means by which they are created.

APPENDIX –D

USER APPLICATION GUIDE

OPERATING PROCEEDURE

Make a call to the mobile phone connected to the ’Remote Operation of Household Gadgets Using Mobile’ device.

When the mobile phone starts ringing the call will automatically received and the connection will be

established (mobile phone is set in auto receiving mode)

Page | 117

Page 118: Final Profect Report

Now the commands given by the calling party can be decoded by the called party and the desired

functioning can be obtained.

Follow the command given in the table D1 and table D2

Table-D1 Red Bulb

State of Mobile key

State of Electrical Switch

Port P26 Port P27 State of Bulb

1 1 0 0 0

2 1 1 1 1

3 0 0 0 0

4 0 1 1 1

Table-D2 Green Bulb

State of Mobile key

State of Electrical Switch

Port P24 Port P25 State of Bulb

5 1 0 0 0

6 1 1 1 1

Page | 118

Page 119: Final Profect Report

7 0 0 0 0

8 0 1 1 1

Note: Special condition

# - For Both Bulb “ON”

* - For Both Bulb “OFF”

Table- D3 BCD output of MT8870

REFERENCES

1. Proceedings of the Eighth International Conference on Machine Learning and Cybernetics,

Baoding, 12-15 July 2009 978-1-4244-3703-0/09/$25.00 ©2009 IEEE 3316 CONSTRUCTING

INTELLIGENT HOME-SECURITY SYSTEM DESIGN WITH COMBINING PHONE-NET AND

BLUETOOTH MECHANISM CHUN-LIANG HSU1, SHENG-YUAN YANG2, WEI-BIN WU3 1,3

Department of Electrical Engineering, St. John’s University, Taiwan, R.O.C. 2 Department of

Computer and Communication Engineering, St. John’s University, Taiwan, R.O.C.

Page | 119

Page 120: Final Profect Report

2. A Cellular Phone Based Home / Office Controller & Alarm System H. Haldun GÖKTAŞ, Nihat

DALDALGazi University Technical Education Faculty, 06500, Besevler, Ankara, TURKEY Received: 06.12.2004 Accepted: 22.08.2005.

3. TZS402 Open Technology: Final Report Project Title: Detecting Real-Time Movement of Flight

Control Surfaces on Unmanned Aerial Vehicle Name : Soh Chee Beng Personal ID : U7513476

Date of Submission: April 18, 2008.

4. Control of Remote Domestic System Using DTMF Tuljappa M Ladwa, Sanjay M Ladwa, R

Sudharshan Kaarthik, Alok Ranjan Dhara, Nayan Dalei Author For Correspondence, Department of

Electrical Engineering, NIT Rourkela, Orissa-08 Author For Correspondence, Department of

Electronics and Communication Engineering, PES Institute of Technology, Bangalore-85

Department of Electrical Engineering, NIT Rourkela, Orissa-08.

5. Remote Operation of Household Gadgets Using Mobile Phone Debapratim Sarkar, Saikat Das

Adhikari B. Tech (3rd Year), Department of Computer Science & Engineering B. Tech (3rd Year), Department of Electronics & Communication Engineering Techno India College of Technology Rajarhat, New Town, Mega City, Kolkata 700 156.

6. REMOTE CONTROLLING OF HOME APPLIANCES THROUGH A TELEPHONE LINE S.

Sivasankar1, D.S.B.P Gunawardena1, M.L.N Perera1 1 Department of Electrical and Electronic

Engineering, University of Peradeniya, Sri Lanka.

7. Yun Chan Cho and Jae Wook Jeon, “Remote Robot control System based on DTMF of Mobile Phone” IEEE International Conference INDIN 2008, July 2008.

8. M J. Callahan, Jr., “Integrated DTMF receiver,” ZEEE J. Solzd-State Czrcuzts, vol. Sc-14, pp. 85-90, Feb. 1979.

9. M. Callahan Jr, “Integrated DTMF Receiver,” IEEE Transactions on communications, vol. 27, pp. 343-348, February 1979.

10. R. Sharma, K. Kumar, and S. Viq, “DTMF Based Remote Control System,” IEEE International Conference ICIT 2006, pp. 2380-2383, December 2006.

11. Oppenheim, Alan V. and Schafer, Ronald W. Digital Signal Processing. Prentice-Hall of India, 1989.

12. 8870 Datasheet, http://www.clare.com/datasheets/8870-01.pdf

13. Suvad Selman, Raveendran Paramesran, “Comparative Analysis of Methods Used in the Design of DTMF Tone Detectors” IEEE International Conference on Telecommunications and Malaysia International Conference on Communications, 14-17 May 2007, Penang, Malaysia .

Page | 120

Page 121: Final Profect Report

14. R.C. Luo, T.M. Chen, and C.C. Yih, “Intelligent autonomous mobile robot control through the Internet,” IEEE International Symposium ISIE 2000, vol. 1, pp. 6- 11, December 2000.

15. LPT, http://en.wikipedia.org/wiki/parallelport ICICI-BME 2009 Proceedings 74

16. Z.Y. Zhou, “Design of Self-developed Home-security and Anti-disaster System”, Master Thesis,

Dept. of Electrical Engineering, National Cheng-Kong University, Tainan, Taiwan, 2002.

17. P.L. Lai, “Bluetooth-Resolution for Short Distance Communication”, Master Thesis, Dept. of

Electronic Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan,

2007.

18. H.Y. Liu, “The Study of Equalizer in Wireless Communication System”, Master Thesis, Dept. of

Electrical Engineering, National Cheng-Kong University, Tainan, Taiwan, 2003.

19. K.H. Tsai, “The Design of Control System for Home Information-Appliance through Power-Line ”,

Master Thesis, Dept. of Electrical Engineering, National Cheng-Kong University, Tainan, Taiwan,

2001.

20. B. Liao, “Infrared Remote Control Based on LCD Displayer and Speech Synthesizer” , M.S. Theses

of Electronic Engineering Dept., National Taiwan Technology and Science University, 2007.

21. I.G. Liu, “The Event-driving for Communication Net of Integrated Mobile Phone and Wireless Sensor Network”, Master Thesis, Dept. of Information Engineering, National Chiao-Tung

University, HsinChu, Taiwan, 2003.

22. Symantec Crop. PC Anywhere 12.1 Data-book., 2009

23. C.L. Hsu and F.S. Chen, 8051/8951 Theory and Application in Practical Projects, Chuan-Hwa

Technology Bookstore, Taipei, Taiwan, 2004.

24. S.T. Lin, “The Implementation of Hardware for Speech Enhancement System Based on Micro-wave Transferring”, Master Thesis Dept. of Electrical Engineering, National Cheng-Kong

University, Tainan, Taiwan, 2005.

25. D.H. Chang, “The Improvement for Blinking Phenomenon of Mini-scaled LCD Displayer”, Master

Thesis Dept. of Electrical Engineering, National Cheng-Kong University, Tainan, Taiwan, 2007.

26. I.C. Fang, “Serial Communication Control of RS-232 Interface with Visual Basic”, Wen-Kuei

Information Bookstore Ltd. Corp., Taipei, Taiwan, 2007.

27. S.L. Wu, “Implementing Group Robots into Home-Security System”, Master Thesis, Dept. of

Electrical Engineering, National Yun-Lin Technology University, YunLin, Taiwan, 2007.

28. I.P. Tzu, “Mastering in Visual Basic6 - Basic Design”, Ru-Lin Bookstore Ltd. Corp., Taipei, Taiwan,

2007.

Page | 121

Page 122: Final Profect Report

29. B.C. Chang, “The Study of Security & Service System in Digital Home Based on UPnP Techniques”, Dept. of Information Engineering, Shu-Te Technology University, Kaohsiung, Taiwan,

2007.

30. V. Chunduru and N. Subramanian, “Effects of Power Lines on Performance of Home Control

System Power Electronics, Drives and Energy Systems,” Proc. of International Conference on Power Electronics, Drives and Energy Systems, Delhi, India, 2006, pp. 1-6.

31. I.K. Hwang and J.W. Baek, “Wireless Access Monitoring and Control System based on Digital Door

Lock,” IEEE Transactions on Consumer Electronics, 53(4), 2007 pp. 1724-1730.

32. S.M. Tsai, P.C. Yang, S.S. Wu, and S.S. Sun, “A Proceedings of the Eighth International

Conference on Machine Learning and Cybernetics, Baoding, 12-15 July 2009 3323 Service of

Home Security System on Intelligent Network,” IEEE Transactions on Consumer Electronics, 44(4),

1998, pp. 1360-1366.

33. Y. Zhao and Z. Ye,”A Low Cost GSM/GPRS Based Wireless Home Security System,” IEEE Transactions on Consumer Electronics, 54(2), 2008, pp. 567-572.

Page | 122