GsSM Based Control System Essay
Introduction of Project ?GSM based Control System? implements the emerging applications of the GSM technology. Using GSM networks, a control system has been proposed that will act as an embedded system which can monitor and contr ol appliances and other devices locally using built-in input and output peripherals. Remotely the system allows the user to effectively monitor and control the house/office appliances and equipment via the mobile phone set by sending commands in the form o f DTMF TONE.
The main concept behind the project is receiving the CALL and a fix DTMF TONE and processing it further as required to perform several operations. The type of the operation to be performed d epends on the key pressed. The principle in which the project is based is fairly simple. First ly, the DTMF TONE is sent via the mobile keypad and then it is decoded through a decoder and sent to the intermediate hardware that we have designed according to the command received in form of the DTMF TONE. The DTMF TONE is sent from the mobile set that contains commands in DTMF form which are then processed accordingly to perform the required task.
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A microcontroller based system has been proposed for our project. There are several terminologies that are used extensively throughout this project report. GSM (Global System for Mobile Communications): It is a cellular communication standard. 1. 2 Background The new age of technology has redefined communication. Most people nowadays have access to mobile phones and thus the world indeed has become a global village. At any given moment, any particular individual can be contacted with the mobile phone.
But the application of mobile phone cannot just be restricted to sending SMS or starting conversations. New innovations and ideas can be generated from it that can further enhance its capabilities. Technologies such as Infra-red, Bluetooth, etc which has developed in recent years goes to show the very fact that improvements are in fact possible and these improvements have eased our life and the way we live. Remote 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.
We have designed a control system which is based on the GSM technology that effectively allows control from a remote area to the desired location. 1 The application of our suggested system is immense in the ever changing technological world. It allows a greater degree of freedom to an individual whether it is controlling the household appliances or office equipments. The need to be physically present in order to control appliances of a certain location is eliminated with the use of our system. 1. 3 Problem Statement
Technology has advanced so much in the last decade or two that it has made life more efficient and comfortable. The comfort of being able to take control of devices from one particular location has become imperative as it saves a lot of time and effort. Therefore there arises a need to do so in a systematic manner which we have tried to implement with our system. The system we have proposed is an extended approach to automating a control system. With the advancement and breakthroughs in technology over the years, the lives of people have become more complicated and thus they have become busier than before.
With the adoption of our system, we can gain control over certain things that required constant attention. The application of our system comes in handy when people who forget to do simple things such as turn ON or OFF devices at their home or in their office, they can now do so without their presence by the trans mission of a simple call from their mobile phone. This development, we believe, will ultimately save a lot of time especially when people don‘t have to come back for simple things such as to turn ON/OFF switches at their home or at their office once they set out for their respective work.
The objective of this project is to develop a device that allows for a user to remotely control and monitor multiple home/office appliances using a cellular phone. This system will be a powerful and flexible tool that will offer this service at any time, and from anywhere with the constraints of the technologies being applied. Possible target appliances include (but are not limited to) climate control system, security systems, lights; anything with an electrical interface.
The proposed approach for designing this system is to implement a microcontroller based control module that receives its instructions and command from a cellular phone over the GSM network. The microcontroller then will carry out the issued commands and then communicate the status of a given appliance or device back to the cellular phone. 2 1. 4 Block Diagram Fig1. 1: Block Diagram The figure shown above is the simple block diagram of our project. It is a simple illustration of how we have implemented our project and the various parts involved in it.
From the above representation, the first Mobile station is used as a transmitting section from which the subscriber sends DTMF tone that contain commands and instructions to the second mobile station which is based on a specific area where our control system is located. The mobile phone as indicated in the block diagram is a mobile set. The received DTMF tone is send to the decoder via the head phone and then extracted by the microcontroller and processed accordingly to carry out specific operations. The relay driver (BUFFER ULN2003) is used to 3 drive the relay circuits which switches the different appliances connected to the interface.
The APR is used to indicate the status of the operation performed by the microcontroller and also its inclusion makes the overall system user-friendly. The input from different sensors are feed to micro -controller and processed to operate respective task semi autonomously and autonomously. 1. 5 System Operation Flow Diagram Fig1. 2: System Operation Flow Diagram Assuming that the control unit is powered and operating properly, the process of controlling a device connected to the interface will proceed through the following steps; • The remote user calls at the number designated at the control system. The remote user sends the commands in DTMF format through the keypad of cell phone. • The designated cell phone decodes the sent DTMF tone and sends the commands to the microcontroller. • Microcontroller issues commands to the appliances and the devices connected will switch ON/OFF. 4 CHAPTER 2 SYSTEM SPECIFICATION 2. 1 Scopes and Purpose of System Specification The system specification shows the description of the function and the performance of system and the user. The scope of our project ? GSM Based control system? is immense. The future implications of the project are very great considering the amount of time and resources it saves.
The project we have undertaken can be used as a reference or as a base for realizing a scheme to be implemented in other projects of greater level such as weather forecasting, temperature updates, device synchronization, etc. The project itself can be modified to achieve a complete Home Automation system which will then create a platform for the user to interface between himself and the household. 2. 2 Goals and Objectives The project ? GSM based Control System? at the title suggests is aimed to construct a control system that enables the complete control of the interface on which it is based. General objectives of the project are defined as; . To co-ordinate appliances and other devices through DTMF(Dual tone multi frequency). b. To eliminate the need of being physically present in any location for tasks involving the operation of appliances within a household/office. c. Minimize power and time wastage 2. 3 Operating Environment The control system will include two separate units: the cellular phone, and the control unit. There will therefore be two operating environments. The cellular phone will operate indoors and outdoors whereas the control unit will operate indoors within the temperature and humidity limits for proper operation of the hardware. 2. 4 Intended Users and Uses
This system is aimed toward all the average users who wish to control their household/off ice appliances remotely from their cell phones provided that the appliances are electrically controllable. Example of feasible appliances and applications under consideration include; enable/disable security systems, fans, lights, kitchen appliances, and a djusting the temperatures settings of a heating/ventilation/air conditioning system. 5 2. 5 Major Constraints Along the course of project completion we encountered various problems and obstacles. Not everything that we had planned went smoothly during the p roject development span.
Also we had a limited amount of time for its completion so we were under a certain amount of pressure as well. We had to start from the research phase at the beginning and needed to gain knowledge on all the devices and components that we had intended to use for our project. Other phases of the project included coding, debugging, testing, documentation and implementation and it needed certain time for completion so we really had to manage the limited time available to us and work accordingly to finish the project within the schedule. 2. 6 Functional Requirements The following is a list of functional requirements of the control unit/module. . The control unit will have the ability to connect to the cellular network automatically. b. The control unit will be able to receive DTMF tone and will be able to parse and interpret the tone and instructions to be sent to the microcontroller. c. The microcontroller within the control unit will issue its command to the electrical appliances through a simple control circuit. d. The control unit will control the electrical appliances. 2. 7 Constraints Considerations The following is a list of constraint Considerations a. The controlled appliances will need an electrical control interface.
This system is only capable of controlling electrical devices. b. The control module will need to be shielded against electrostatic discharges. This will increase the reliability of the system. c. Battery backup for controlling unit can be implemented in case of powe r disruption. 2. 8 Technology Considerations The considerations for this system will include a choice of networks, communication protocols and interfaces. a. Cellular Networks: The widely available networks are based on GSM. This network provides wide area coverage and can be utilized more cost -effectively for this project. . Communication Protocols: The available communication protocol that we have used is DTMF tone. 6 c. I/O interfaces between microcontroller and devices: Serial I/O is considered as options for connection between the GSM receiver and the microcontroller. Using the microcontroller, a control circuit will be implemented to control the electrical appliances. 2. 9 Limitations Our project has certain limitations and a list of such is mentioned be low; a. The receiver must reside in a location where a signal with sufficient strength can be received from a cellular phone network. b.
Only devices with electrical controlling input ports will be possible targets for control. c. Operation of the controlling unit is only possible through a cell phone. d. The Controlling unit must be able to receive and decode DTMF signals. 7 CHAPTER 3 GSM TECHNOLOGY 3. 1 GSM Technology GSM is a global system for mobile communication GSM is an interna tional digital cellular telecommunication. The GSM standard was released by ETSI (European Standard Telecommunication Standard) back in 1989. The first commercial services were launched in 1991 and after its early introduction in Europe; the standard went global in 1992.
Since then, GSM has become the most widely adopted and fastest -growing digital cellular standard, and it is positioned to become the world‘s dominant cellular standard. Today‘s second -generation GSM networks deliver high quality and secure mobile voice services with full roaming capabilities across the world. GSM platform is a hugely successful technology and as unprecedented story of global achievement. In less than ten years since the first GSM network was commercially launched, it become, the world‘s leading and fastest growing mobile standard, spanning over 173 countries.
Today, GSM technology is in use by more than one in ten of the world‘s population and growth continues to sour with the number of subscriber worldwide expected to surpass one billion by through end of 2003. Today‘s GSM platform is living, growing and evolving and already offers an expanded and feature-rich ? family‘ of voice and enabling services. The Global System for Mobile Communication (GSM) network is a cellular telecommunication network with a versatile architecture complying with the ETSI GSM 900/GSM 1800 standard.
Siemen‘s implementation is the digital cellular mobile communication system D900/1800/1900 that uses the very latest technology to meet every requirement of the standard. 3. 3 GSM Services GSM services follow ISDN guidelines and classified as either tele services or data services. Tele services may be divided into three major categories: • Telephone services, include emergency calling and facsimile. GSM also supports Videotex and Teletex, through they are not integral parts of the GSM standard. • Bearer services or Data services, which are limited to layers 1, 2 and 3 of the OSI reference model.
Data may be transmitted using either a transparent mode or non transparent mode. 8 • Supplementary ISDN services, are digital in nature, and include call diversion, closed user group, and caller identification. Supplementary services also include the short message service (SMS). Fig3. 1: GSM Architecture 3. 2 Basic Specification in GSM S. No. PARAMETER SPECIFICATIONS 1. Reverse channel frequency 890-915MHz 2. Forward Channel frequency 935-960 MHz 3. Tx/Rx Frequency Spacing 45 MHz 4. Tx/Rx Time Slot Spacing 3 Time slots 5. Modulation Data Rate 270. 833333kbps 6. Frame Period 4. 615ms 7. Users per Frame 8 . Time Slot Period 576. 9microsec 9. Bit Period 3. 692 microsecond 10. Modulation 0. 3 GMSK 11. ARFCN Number 0 to 124 & 975 to 1023 12. ARFCN Channel Spacing 200 kHz 13. Interleaving 40 ms 14. Voice Coder Bit Rate 13. 4kbps 9 CHAPTER 4 MICRO-CONTROLLER 4. 1 Introduction An embedded microcontroller is a chip, which has a computer processor with all its support function (clocking and reset), memory (both program storage and RAM), and I/O (including bus interfaces) built into the device. These built in function minimize the need for external circuits and devices to the designed in the final applications.
The improvements in micro controller technology has meant that it is often more cost effective, faster and more efficient to develop an application using a micro-controller rather than discrete logic. Creating applications for micro -controllers is completely different than any other development job in computing and electronics. In most other applications, number of subsystems and interfaces are available but this is not the case for the micro-controller where the following responsibilities have to be taken. • Power distribution • System clocking • Interface design and wiring • System Programming • Application programming Device programming There are two types of micro -controller commonly in use. Embedded micro -controller is the micro-controller, which has the entire hardware requirement to run the application, provided on the chip. External memory micro -controller is the micro -controller that allows the connection of external memory when the program memory is insufficient for an application or during the work a separate ROM (or even RAM) will make the work easier. 4. 2 ATMEL Micro-controller The AT89C52 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 80C51 and 80C52 instruction set and pin out. The on-chip Flash allows the program memory to be reprogrammed in-system or by a conventional non volatile memory programmer. By combining a versatile 8 -bit CPU with Flash on a monolithic chip, 10 the ATMEL AT89C52 is a powerful microcomputer which provides a highly-flexible and cost-effective solution to many embedded control applications. The main features of this micro -controller are as follows; Compatible with MCS-51TM \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 • Three 16-bit Timer/Counters • Eight Interrupt Sources • Programmable Serial Channel • Low-power Idle and Power-down Modes 11 CHAPTER 5 RELAY 5. 1 Inroduction NC: – Normally Connected NO: – Normally Open COM: – Common Fig5. 1: Relay Switch Connection The relay driver is used to isolate both the controlling and the controlled device.
The relay is an electromagnetic device, which consists of solenoid, moving contacts (switch) and restoring spring and consumes comparatively large amount of power. Hence it is possible for the interface IC to drive the relay satisfactorily. To enable this, a driver cir cuitry, which will act as a buffer circuit, is to be incorporated between them. The driver circuitry senses the presence of a ? high? level at the input and drives the relay from another voltage source. Hence the relay is used to switch the electrical supp ly to the appliances.
From the figure when we connect the rated voltage across the coil the back emf opposes the current flow but after the short time the supplied voltage will overcome the back emf and the current flow through the coil increase. When the current is equal to the activating current of relay the core is magnetized and it attracts the moving contacts. Now the moving contact leaves from its initial position denoted ? (N/C)? normally closed terminal which is a fixed 12 terminal. The common contact or moving contact establishes the connection with a new terminal which is indicated as a normally open terminal ? N/O)?. Whenever, the supply coil is withdrawn the magnetizing force is vanished. Now, the spring pulls the moving contact back to initial position, where it makes a connection makes with N/C terminal. However, it is also to be noted that at this time also a back emf is produced. The withdrawal time may be in microsecond, the back emf may be in the range of few kilovolts and in opposite polarity with the supplied terminals the voltage is known as surge voltage. It must be neutralized or else it may damage the system. 13 CHAPTER 6 ULN2003 IC 6. 1 Introduction
The ULN2003 is a monolithic high voltage and high current Darlington tra nsistor arrays. It consists of seven NPN Darlington pairs that feature high-voltage outputs with commoncathode clamp diode for switching inductive loads. The collector-current rating of a single Darlington pairs 500mA. The Darlington pairs may be paralleled for higher current capability. Applications include relay drivers, hammer drivers, lamp drivers, display drivers (LED gas Discharge), line drivers, and logic buffers. The ULN2003 has a 2. 7kW series base resistor for each Darlington pair for operation directly with TTL or 5V CMOS devices.
Features: • 500mA rated collector current ( Single output ) • High-voltage outputs: 50V • Inputs compatible with various types of logic. • Relay driver application. 14 6. 2 Logical Diagram Fig6. 1: ULN2003 Logical Diagram Fig6. 2: Schematic Diagram 15 CHAPTER 7 APR 9301 7. 1 Introduction APR 9301 is a single chip Voice recorder and Play back device for 20 to 30 seconds voice recording and play back. It is an ideal IC for automatic answering machine, door phones etc. This IC has data storage capacity and requires no software and microcontroller. It provides high quality voice recording and play back up to 30 seconds.
The IC requires minimum components to create a voice recorder. The IC has non volatile flash memor y technology with 100K recording cycles and 100 year message retention capacity. The IC utilizes the Invox proprietary analog / multi level flash non volatile memory cells that can store more than 256 voltage levels. It requires a single 5 volt supply and operates in 25 mA current. 7. 2 APR 9301 Voice Recorder Circuit Fig7. 1: Circuit Arrangement of APR. 16 7. 3 Mode of operation 1. RecordMode The LED glows when the IC records the voice obtained through the Mic. A single voice message up to 20 seconds can be recorded.
The IC remains in the recorded mode as long as the pin 27 is grounded. Recoding will be terminated with the last memory when 20 seconds is over. The Speaker driver will automatically mutes in the recording mode. By changing the value of the OscR resistor R1 it is possible to increase the recording period as follows A. R1 52K 20Sec. B. R1 67K 24Sec C. R1 89 K 30 Sec. 2. PlaybackMode By pressing the play back switch, the play mode starts from the beginning of the message. The input section will be muted during play back. 3. StandbyMode After completing the Record or Play back function, the IC will enters into the standby mode. . Sampling frequency A. 20 Sec 6. 4 KHz B. 24 Sec 5. 3 KHz C. 30 Sec 4 KHz 5. Recording Press ,switch S1 and speak through the Mic or record music. LED will glow in the recording mode. Open S1 after recording. Use a small condenser Mic . 6. Playback Close S2. Recorded message will be heard from the speaker. Use a 2 inch 8 Ohms speaker. 7. Power supply 5 Volt regulated supply or 6 volt battery. 17 CHAPTER 8 DTMF DECODER 8. 1 Introduction DTMF decoder is a very easy to use program to decode DTMF dial tones found on telephone lines with touch tone phones.
DTMF decoder is also used for receiving data transmissions over the air in amateur radio frequency bands. The following are the frequencies used for the DTMF (dual-tone, multi-frequency) system, which is also referred to as tone dialling. The signal is encoded as a pair of sinusoidal (sine wave) tones from the table below which are mixed with each other. DTMF is used by most PSTN (public switched telephone networks) systems for number dialling, and is also used for voice-response systems such as telephone banking and sometimes over private radio networks to provide signalling and transferring o f small amounts of data.
Detect DTMF tones from tape recorders, receivers, two -way radios, etc using the built -in microphone or direct from the phone line (via the onboard line isolation transformer). The numbers are displayed on a 16 character, single line display as they are received. Up to 32 numbers can be displayed by scrolling the display left and right. There is also a Serial Output for connection to a PC. All data written to the LCD is also sent to the serial output, including the RESET and READY messages. Data is sent as standard ASCII characters. The unit will not detect numbers dialled using pulse dialling.
Circuit uses a CM8870 DTMF receiver chip and pre-programmed microcontroller. This product is NOT a caller ID unit! 18 CHAPTER 9 CAPACITOR 9. 1 Introduction A capacitor (known as condenser) is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric (insulator); for example, one common construction consists of metal foils separated by a thin layer of insulating film. Capacitors are widely used as parts of electrical circuits in many common electrical devices.
When there is a potential difference (voltage) across the conductors, a static electric field develops across the dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in the electrostatic field. An ideal capacitor is characterized by a single constant value, capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. The capacitance is greatest when there is a narrow separation between large areas of conductor, hence capacitor conductors are often called plates, referring to an early means of construction.
In practice, the dielectric betwee n the plates passes a small amount of leakage current and also has an electric field strength limit, resulting in a breakdown voltage, while the conductors and leads introduce an undesired inductance and resistance. 9. 2 Working Principle A capacitor consists of two conductors separated by a non-conductive region. The nonconductive region is called the dielectric. In simpler terms, the dielectric is just an electrical insulator. Examples of dielectric media are glass, air, paper, vacuum, and even a semiconductor depletion region chemically identical to the co nductors.
A capacitor is assumed to be self-contained and isolated, with no net electric charge and no influence from any external electric field. The conductors thus hold eq ual and opposite charges on their facing surfaces, and the dielectric develops an electric field. In SI units, a capacitance of one farad means that one coulomb of charge on each conductor causes a voltage of one volt across the device. 19 The capacitor is a reasonably general model for electric fields within electric circuits. An ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio of charge ±Q on each conductor to the voltage V between them
Fig9. 1: Working of Capacitor Sometimes charge build-up affects the capacitor mechanically, causing its capacitance to vary. In this case, capacitance is defined in terms of incremental changes: 9. 3 Capacitance instability The capacitance of certain capacitors decreases as the component age s. In ceramic capacitors, this is caused by degradation of the dielectric. The type of dielectric, ambient operating and storage temperatures are the most significant aging factors, while the operating voltage has a smaller effect. The aging process may be reversed by heating the component above the Curie point.
Aging is fastest near the beginning of life of the component, and the device stabilizes over time. Electrolytic capacitors age as the electrolyte evaporates. In contrast with ceramic capacitors, this occurs towards the end of life of the component. Temperature dependence of capacitance is usually expressed in parts per million (ppm) per °C. It can usually be taken as a broadly linear function but can be noticeably non-linear at the 20 temperature extremes. The temperature coefficient can be either positive or negative, sometimes even amongst different samples of the same type.
In other words, the spread in the range of temperature coefficients can encompass zero. See the data sheet in the leakage current section above for an example. Capacitors, especially ceramic capacitors, and older designs such as paper capacitors, can absorb sound waves resulting in a micro phonic effect. Vibration moves the plates, causing the capacitance to vary, in turn inducing AC current. Some dielectrics also generate piezoelectricity. The resulting interference is especially problematic in audio applications, potentially causing feedback or unintended recording.
In the reverse micro phonic effect, the varying electric field between the capacitor plates exerts a physical force, moving them as a speaker. This can generate audible sound, but drains energy and stresses the dielectric and the electrolyte, if any. 9. 4 Application 1. Energy Storage A capacitor can store electric energy when disconnected from its charging circuit, so it can be used like a temporary battery. Capacitors are commonly used in electronic devices to maintain power supply while batteries are being changed. (This prevents loss of information in volatile memory. Conventional capacitors provide less than 360 joules per kilogram of energy density, whereas a conventional alkaline battery has a density of 590 kJ/kg. In car audio systems, large capacitors store energy for the amplifier to use on demand. Also for a flash tube a capacitor is used to hold the high voltage. 2. Pulsed Power and Weapons Groups of large, specially constructed, low-inductance high-voltage capacitors (capacitor banks) are used to supply huge pulses of current for many pulsed power applications. These include electromagnetic forming, Marx generators, ulsed lasers (especially TEA lasers), pulse forming networks, radar, fusion research, and particle accelerators. Large capacitor banks (reservoir) are used as energy sources for the exploding-bridgewir e detonators or slapper detonators in nuclear weapons and other specialty weapons. Experimental work is under way using banks of capacitors as power sources for electromagnetic armour and electromagnetic railgunsand coil guns. 21 3. Power Conditioning Reservoir capacitors are used in power supplies where they smooth the output of a full or half wave rectifier.
They can also be used in charge pump circuits as the energy storage element in the generation of higher voltages than the input voltage. Capacitors are connected in parallel with the power circuits of most electronic devices and larger systems (such as factories) to shunt away and conceal current fluctuations from the primary power source to provide a “clean” power supply for signal or control circuits. Audio equipment, for example, uses several capacitors in this way, to shunt away power line hum before it gets into the signal circuitry.
The capacitors act as a local reserve for the DC power source, and bypass AC currents from the power supply. This is used in car audio applications, when a stiffening capacitor compensates for the inductance and resistance of the leads to the lead-acid car battery. 4. Noise Filters When an inductive circuit is opened, the current through the inductance collapses quickly, creating a large voltage across the open circuit of the switch or relay. If the inductance is large enough, the energy will generate a spark, causing the contact points to oxidize, deteriorate, or sometimes eld together, or destroying a solid -state switch. A snubber capacitor across the newly opened circuit creates a path for this impulse to bypas s the contact points, thereby preserving their life; these were commonly found in contact breaker ignition systems, for instance. Similarly, in smaller scale circuits, the spark may not be enough to damage the switch but will still radiate undesirable radio frequency interference (RFI), which a filter capacitor absorbs. Snubber capacitors are usually employed with a low-value resistor in series, to dissipate energy and minimize RFI.
Such resistor capacitor combinations are available in a single package. Capacitors are also used in parallel to interrupt units of a high-voltage circuit breaker in order to equally distribute the voltage between these units. In this case they are called grading capacitors. In schematic diagrams, a capacitor used primarily for DC charge storage is often drawn vertically in circuit diagrams with the lower, more negative, plate drawn as an arc. The straight plate indicates the positive terminal of the device, if it is polarized (see electrolytic capacitor). 2 5. Signal Processing The energy stored in a capacitor can be used to represent information, either in binary form, as in DRAMs, or in analogue form, as in analog sampled filters and CCDs. Capacitors can be used inanalog circuits as components of integrators or more complex filt ers and in negative feedback loop stabilization. Signal processing circuits also use capacitors to integrate a current signal. 5. 1 Tuned circuits Capacitors and inductors are applied together in tuned circuits to select information in particular frequency bands.
For example, radio receivers rely on variable capacitors to tune the station frequency. Speakers use passive analog crossovers, and analog equalizers use capacitors to select different audio bands. The resonant frequency f o f a tuned circuit is a function of the inductance ( L) and capacitance (C) in series, and is given by: where L is in henries and C is in farads. 5. 2 Sensing Most capacitors are designed to maintain a fixed physical structure. However, var ious factors can change the structure of the capacitor, and the resulting change in capacitance can be used to sense those factors. . 3 Changing the Dielectric: The effects of varying the characteristics of the dielectric can be used for sensing purposes. Capacitors with an exposed and porous dielectric can be used to measure humidity in air. Capacitors are used to accurately measure the fuel level in airplanes; as the fuel covers more of a pair of plates, the circuit capacitance increases. 5. 4 Changing the Distance between the Plates: Capacitors with a flexible plate can be used to measure strain or pressure.
Industrial pressure transmitters used for process control use pressure-sensing diaphragms, which form a capacitor plate of an oscillator circuit. Capacitors are used as the sensor in condenser microphones, where one plate is moved by air pressure, relative to the fixed position of the 23 other plate. Some accelerometers use MEMS capacitors etched on a chip to measure the magnitude and direction of the acceleration vector. They are used to detect chang es in acceleration, in tilt sensors, or to detect free fall, as sensors triggering airbag deployment, and in many other applications.
Some fingerprint sensors use capacitors. Additionally, a user can adjust the pitch of a musical instrument by moving his hand since this changes the effective capacitance between the user’s hand and the antenna. 24 CHAPTER 10 TRANSFORMER 10. 1 Introduction A transformer is a power converter that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer’s coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer’s core and thus a varying magnetic field through the secondary winding.
This varying magnetic field induces a varying electromotive force (EMF), or “voltage”, in the secondary winding. This effect is called inductive coupling. If a load is connected to the secondary winding, current will flow in this winding, and electrical energy will be transferred from the primary circuit through the transformer to the load. In an ideal transformer, the induced voltage in the secondary winding ( Vs) is in proportion to the primary voltage (VP) and is given by the ratio of the number of turns in the secondary (Ns) to the number of turns in the primary ( Np) as follows: 0. 2 Working Principle The transformer is based on two principles: first, that an electric current can produce a magnetic field (electromagnetism) and second that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil ( electromagnetic induction). Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil. An ideal transformer is shown in the adjacent figure. Current passing through the primary coil creates a magnetic field.
The primary and secondary coils are wrapped around a core of very high magnetic permeability, such as iron, so that most of the magnetic flux passes through both the primary and secondary coils. If a load is connected to the secondary winding, the load current and voltage will be in the directions indicated, given t he primary current and voltage. 25 CHAPTER 11 RESISTOR 11. 1 Introduction A resistor is a passive two terminal electrical component that implements electrical resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor’s terminals.
This relationship is represented by Ohm’s law: where I is the current through the conductor in units of amperes, V is the potential difference measured across the conductor in units of volts, and R is the resistance of the conductor in units of ohms. The ratio of the voltage applied across a resistor’s terminals to the intensity of current in the circuit is called its resistance, and this can be assumed to be a constant (independent of the voltage) for ordinary resistors working within their ratings. Resistors are common elements of electrical networks and electronic circuits and are ubiquitous in electronic equipment.
Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickelchrome). Resistors are also implemented within integrated circuits, particularly analog devices, and can also be integrated into hybrid and printed circuits. Unit The ohm (symbol: ? ) is the SI unit of electrical resistance, named after Georg Simon Ohm. An ohm is equivalent to a volt per ampere 11. 2 Measurement The value of a resistor can be measured with an ohmmeter, which may be one function of a millimetre. Usually, probes on the ends of test leads connect to the resistor.
A simple ohmmeter may apply a voltage from a battery across the unknown resistor (with an internal resistor of a known value in series) producing a current which drives a meter movement. The current, in accordance with Ohm’s Law, is inversely proportional to the sum of the internal resistance and the resistor being tested, resulting in an analog meter scale which is very non linear, calibrated from infinity to 0 ohms. A digital millimetre, using active electronics, may instead pass a specified current through the test resistance . The voltage generated across the 26 est resistance in that case is linearly proportional to its resistance, which is measured and displayed. In either case the low-resistance ranges of the meter pass much more current through the test leads than do high-resistance ranges, in order for the voltages present to be at reasonable levels (generally below 10 volts) but still measurable. Measuring low-value resistors, such as fractional-ohm resistors, with acceptable accuracy requires four-terminal connections. One pair of terminals applies a known, calibrated current to the resistor, while the other pair senses the vo ltage drop across the resistor.
Some laboratory quality ohmmeters, especially milli ohmmeters, and even some of the better digital millimetres sense using four input terminals for this purpose, which may be used with special test leads. Each of the two so-called Kelvin clips has a pair of jaws insulated from each other. One side of each clip applies the measuring current, while the other connections are only to sense the voltage drop. The resistance is again calculated using Ohm’s Law as the measured voltage divided by the applied current. 11. 3 Production Resistors Resistor characteristics are quantified and reported using various national standards.
In the US, MIL-STD-202 contains the relevant test methods to which other standards refer. There are various standards specifying properties of resistors for use in equipment: BS 1852 EIA-RS-279 MIL-PRF-26 MIL-PRF-39007 (Fixed Power, established reliability) MIL-PRF-55342 (Surface-mount thick and thin film) MIL-PRF-914 MIL-R-11 STANDARD CANCELED MIL-R-39017 (Fixed, General Purpose, Established Reliability) MIL-PRF-32159 (zero ohm jumpers) There are other United States military procurement MIL-R- standards. 27 CHAPTER 12 MICROPHONE 12. 1 Introduction A microphone (colloquially called a mic or mike; both pronounced /? a? k/) is an acousticto-electric transducer or sensor that converts sound into an electrical. Microphones are used in many applications such as telephones, tape recorders, karaoke systems, hearing aids, motion picture production, live and recorded audio in radio and television broadcasting and in engineering, FRS computers for radios, megaphones, recording voice, speech recognition, VoIP, and for non-acoustic purposes such as ultrasonic checking or knock sensors. 12. 2 Components The sensitive transducer element of a microphone is called its element or capsule.
A complete microphone also includes a housing, some means of bringing the signal from the element to other equipment, and often an electronic circuit to adapt the output of the capsule to the equipment being driven. A wireless microphone contains a radio transmitter. 12. 3 Variety Microphones are referred to by their transducer principle, such as condenser, dynamic, etc. , and by their directional characteristics. So metimes other characteristics such as diaphragm size, intended use or orientation of the principal sound input to the principal axis (end – or side-address) of the icrophone are used to describe the microphone. 12. 4 Condenser Microphone The condenser microphone, invented at Bell Labs in 1916 by E. C. Wente is also called a capacitor microphone or electrostatic microphone capacitors were historically called condensers. Here, the diaphragm acts as one plate of a capacitor, and the vibrations produce changes in the distance between the plates. There are two types, depending on the method of extracting the audio signal from the transducer: DC-biased microphones, and radio frequency (RF) or high frequency (HF) condenser microphones.
With a DC-biased microphone, the plates are biased with a fixed charge (Q). The voltage maintained across the capacitor plates changes with the vibrations in the air, according to the capacitance equation (C = Q? V), where Q = charge in coulombs, C = capacitance in farads and V = potential difference in volts. The capacitance of the plates is inversely proportional to the distance between them for a parallel – 28 plate capacitor. (See capacitance for details. ) The assembly of fixed and movable plates is called an “element” or “capsule”. 12. 5 Electret Condenser Microphone
An electret microphone is a type of capacitor microphone invented by Gerhard Sesser and Jim West at Bell laboratories in 1962.  The externally applied charge described above under condenser microphones is replaced by a permanent charge in an electret material. An electret is a ferro electric material that has been permanently electrically charged or polarized. The name comes from electrostatic and magnet; a static charge is embedded in an electret by alignment of the static charges in the material, much the way a magnet is made by aligning the magnetic domains in a piece of iron. 2. 6 Dynamic Microphone Dynamic microphones work via electromagnetic induction. They are robust, relatively inexpensive and resistant to moisture. This, coupled with their potentially high gain before feedback, makes them ideal for on-stage use. Moving-coil microphones use the same dynamic principle as in a loudspeaker, only reversed. A small movable induction coil, positioned in the magnetic field of a permanent magnet, is attached to the diaphragm. When sound enters through the windscreen of the microphone, the sound wave moves the diaphragm.
When the diaphragm vibrates, the coil moves in the magnetic field, producing a varying current in the coil through electromagnetic induction. A single dynamic membrane does not respond linearly to all audio frequencies. 12. 7 Ribbon Microphone Ribbon microphones use a thin, usually corrugated metal ribbon suspended in a magnetic field. The ribbon is electrically connected to the microphone’s output, and its vibration within the magnetic field generates the electrical signal. Ribbon microphones are similar to moving coil microphones in the sense that both produce sound by means of magnetic induction.
Basic ribbon microphones detect sound in a bi-directional pattern because the ribbon, which is open to sound both front and back, responds to the pressure gradient rather than the sound pressure. Though the symmetrical front and rear pickup can be a nuisance in normal stereo recording, the high side rejection can be used to advantage by positioning a ribbon microphone horizontally, for example above cymbals, so that the rear lobe picks up only sound from the cymbals. 29 12. 8 Speakers as Microphones: A loudspeaker, a transducer that turns an electrical signal into sound waves, is the functional opposite of a microphone.
Since a conventional speaker is constructed much like a dynamic microphone (with a diaphragm, coil and magnet), speakers can actua lly work “in reverse” as microphones. The result, though, is a microphone with poor quality, limited frequency response (particularly at the high end), and poor sensitivity. 30 CHAPTER 13 CRYSTAL OSCILLATOR 13. 1 Introduction A crystal oscillator is an electronic oscillator 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 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, but other piezoelectric materials including polycrystalline ceramics are used in similar circuit s. Quartz crystals are manufactured for frequencies from a few tens of kilohertz to tens of megahertz. More than two billion crystals are manufactured annually.
Most are used 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. 13. 2 Operation 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. 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). 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 mounted in a temperaturecontrolled container, called a crystal oven, and can also be mounted on shock absorbers to prevent perturbation by external mechanical vibrations. 31 13. 3 Crystal oscillator types and their abbreviations ? ATCXO — Analog temperature controlled crystal oscillator ? CDXO — Calibrated dual crystal oscillator ? DTCXO — Digital temperature compensated crystal oscillator ? EMXO — Evacuated miniature crystal oscillator ? GPSDO — Global positioning system disciplined oscillator ? MCXO — Microcomputer-compensated crystal oscillator ?
OCVCXO — oven-controlled voltage-controlled crystal oscillator ? OCXO — Oven-controlled crystal oscillator ? RbXO — Rubidium crystal oscillators (RbXO), a crystal oscillator (can be an MCXO) synchronized with a built -in rubidium standard which is run only occasionally to save power ? TCVCXO — Temperature-compensated voltage-controlled crystal oscillator ? TCXO — Temperature-compensated crystal oscillator ? TMXO – Tactical miniature crystal oscillator ? TSXO — Temperature-sensing crystal oscillator, an adaptation of the TCXO ? VCTCXO — Voltage-controlled temperature-compensated crystal oscillator ?
VCXO — Voltage-controlled crystal oscillator 32 CHAPTER 14 CIRCUIT ARRANGEMENT 14. 1 Working Fig14. 1: Circuit Diagram 33 There is a circuit contains AT89C2051 micro – controller with its all basic components. For power supply to provide 5V, the circuit consists of step down transformer o f 230/12V. This transformer steps down 230V AC from main supply to 12V AC. Then that 12V AC is converted into 12V DC with the help of bridge rectifier. After that a 1000/25V capacitor is used to filter the ripples and then it passes through voltage regula tor 7805 which regulates it to 5V. Micro- controller AT89C51 is at heart of circuit.
It is high performance, low power, 8 bit micro- controller with 4 KB of flash programmable and erasable read only memory used as on- chip program memory. An 11. 0592MHz cr ystal oscillator is used to provide basic clock frequency for micro – controller. A push to on switch connected between pin no. 9 of controller and Vcc is used for manual reset of circuit. The DTMF (Dual-tone multi-frequency) decode MT8870 is connected to port 1 of microcontroller. It is used for decoding the mobile signal. It gets DTMF tone from the mobile headphone and decodes it into 4 bit digital signal.
There are four relays connected to the ULN2003 IC to control four appliances or any load. These loa ds are connected to the relay. DTMF decoder IC gets signal to ON or OFF any appliances it process it to micro – controller and after then micro controller controls that appliance according to instruction. An APR IC is connected to the port 0 of micro – controller. It is a playback and recording IC which receives voice from a MIC connecting to it and records it. It also plays that recorded sound when get signal from micro – controller to play it. There is a speaker connected to this APR to play the sound.
This is used for voice acknowledgement. 34 CHAPTER 15 SOFTWARE DEVELOPMENT 15. 1 Software Introduction The software for our project was developed using a simple high level language tool in C. The software extracts the sent DTMF signal from the SIM location at a regular interval and processes it to control the different appliances connected within the interface. We have made use of the two cell phones along with a head phone. The DTMF signal through the keypad of remote cell phone are send to the designated cell phone at the system. Which are then send to the DTMF decoder through the head phone.
The decoder decodes the signal and then send them to the micro controller. 15. 2 Algorithm Step 1: Start Step 2: Phone initialization Step 3: Get Hardware Software Step 4: Make a call from mobile phone Step 5: If new call received go to step3 else, go to step1 Step 6: Receive DTMF signal Step 7: Check DTMF signal Step 8: Control the device based on status Step 9: Notify user via voice acknowledgement through APR IC. Step 10: Go to step1 15. 3 Coding Line I Address Code Source 1: B 00B3 RELAY1 EQU P3. 3 2: B 00B4 RELAY2 EQU P3. 4 3: B 00B5 RELAY3 EQU P3. 5 4: B 00B6 RELAY4 EQU P3. 6 : B 0080 M1 EQU P0. 0 35 6: B 0081 M2 EQU P0. 1 7: B 0082 M3 EQU P0. 2 8: B 0083 M4 EQU P0. 3 9: B 0084 M5 EQU P0. 4 10: B 0085 M6 EQU P0. 5 11: B 0086 M7 EQU P0. 6 12: B 0087 M8 EQU P0. 7 13: N 0000 ORG 00H 14: 0000 75 B0 00 MOV P3,#00H 15: 0003 80 00 SJMP CH0 16: 0005 E5 90 CH0:MOV A,P1 17: 0007 B4 F8 08 CJNE A,#0F8H,CH1 18: 000A 11 7B ACALL DELAYMS 19: 000C 11 6C ACALL DELAY 20: 000E C2 80 CLR M1 21: 0010 11 6C ACALL DELAY 22: 0012 E5 90 CH1:MOV A,P1 23: 0014 B4 F4 0C CJNE A,#0F4H,CH2 24: 0017 11 7B ACALL DELAYMS 25: 0019 D2 B4 SETB RELAY2 26: 001B 11 6C ACALL DELAY 27: 001D 11 C ACALL DELAY 28: 001F C2 81 CLR M2 29: 0021 11 6C ACALL DELAY 30: 0023 E5 90 CH2: MOV A,P1 31: 0025 B4 FC 0C CJNE A,#0FCH,CH3 32: 0028 11 7B ACALL DELAYMS 33: 002A D2 B5 SETB RELAY3 34: 002C 11 6C ACALL DELAY 35: 002E 11 6C ACALL DELAY 36: 0030 C2 82 CLR M3 37: 0032 11 6C ACALL DELAY 38: 0034 E5 90 CH3: MOV A,P1 39: 0036 B4 F2 0C CJNE A,#0F2H,CH4 36 40: 0039 11 7B ACALL DELAYMS 41: 003B D2 B6 SETB RELAY4 42: 003D 11 6C ACALL DELAY 43: 003F 11 6C ACALL DELAY 44: 0041 C2 83 CLR M4 45: 0043 11 6C ACALL DELAY 46: 0045 E5 90 CH4: MOV A,P1 47: 0047 B4 FA 0D CJNE A,#0FAH,CH5 48: 004A 11 B ACALL DELAYMS 49: 004C 75 B0 00 MOV P3,#00H 50: 004F 11 6C ACALL DELAY 51: 0051 11 6C ACALL DELAY 52: 0053 C2 84 CLR M5 53: 0055 11 6C ACALL DELAY 54: 0057 E5 90 CH5: MOV A,P1 55: 0059 B4 F6 0D CJNE A,#0F6H,CH6 56: 005C 11 7B ACALL DELAYMS 57: 005E 75 B0 FF MOV P3,#0FFH 58: 0061 11 6C ACALL DELAY 59: 0063 11 6C ACALL DELAY 60: 0065 C2 85 CLR M6 61: 0067 11 6C ACALL DELAY 62: 0069 02 00 05 CH6: LJMP CH0 63: 006C 11 01 DELAY: 64: 006C 7E 00 MOV R6, #00H 65: 006E 7D 04 MOV R5, #04H 66: 0070 13 02 LOOPB: 67: 0070 0E 0A INC R6 68: 0071 11 7B ACALL DELAYMS 69: 0073 EE B0FF MOV A, R6 70: