Project Final Report On Home Automation

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CONTENTS 1) Acknowledgement 2) Certficate 3) Abstract 4) Introduction 5) Concept 6) About Project 7) Hardware Part 8) Circuit Diagrams 9) Component Description a) Resistors b) Capacitor c) Diode d) Light emitting diode e) Transistor f) Battery g) Crystal oscillator h) Power supply i) Relay j) Transformer k) Microcontroller (8051/8052) l) Infrared remote control m) Photodiode n) Phototransistor 10) Software part a) Transmitter program b) Receiver program 11) Bibliography

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ABSTRACT The HomeAutomation is a wireless home automation system that is supposed to be implemented in existing home environments, without any changes in the infrastructure. HomeAutomation let the user to control the home from his or her computer and assign actions that should happen depending on time or other sensor readings such as light, temperature or sound from any device in the HomeAutomation network.

INTRODUCTION This report is describing our group project in the Ubiquitous Computing course. It is containing the design process of the project, starting with brainstorming we had to get the final product idea and finishing with the prototyping within home alike environment. The original problem was to design and implement a larger ubiquitous computing project into a home environment. The report is describing what kind of design process, hardware and software have been used to build up the prototype for that product design that we had chosen as our final goal.

BACKGROUND Most advanced home automation systems in existence today require a big and expensive change of infrastructure. This means that it often is not feasible to install a home automation system in an existing building. The HomeAutomation is a wireless home automation system that is supposed to be implemented in existing home environments, without any changes in the existing infrastructure. HomeAutomation lets the user to control his home from his or her computer. In the computer program the user can create actions what should happen with electrical

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devices in the network depending on the sensors sensing surrounding environment.

CONCEPT Every HomeAutomation box is a stand-alone device. It is connected to the mains and controls the power outlet of the electrical device that is plugged into it. There will be a receiver and transmitter in each of the box, so they can exchange information with the master (a computer). People can control power supply of electrical devices in order to create an interactive home environment to facilitate the control without changing any home appliance. People can enjoy the high technology and simplicity modern life style. Each device will be with standard setup and while adding it into network; it can be given an address and tasks to do. All the setting will be easily resettable to default value, so people can move the devices between different electrical devices and networks. HomeAutomation boxes will be put into different rooms at home, depending on the needed functionality. Various different sensors could be attached to the boxes. The sensors are used as triggers for actions, that user can set up in the computer program.

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ABOUT PROJECT Home automation systems, or smart home technologies, are systems and devices that can control elements of your home environment — lighting, appliances, telephones, home security and mechanical, entry and safety systems. Home automation systems can be operated by electricity or a computer chip using a range of different types of switches. A simple device, such as a light can be activated by a signal from a motion detector, or can be part of a computerized home automation system. As a very basic definition, we tend to refer to home automation as anything that gives you remote or automatic control of things around the home.

DESCRIPTION Home automation (also called domotics) may designate an emerging practice of increased automation of household appliances and features in residential dwellings, particularly through electronic means that allow for things impracticable, overly expensive or simply not possible in recent past decades. The term may be used in contrast to the more mainstream "building automation," which refers to industrial settings and the automatic or semi-automatic control of lighting, climate doors and windows, and security and surveillance systems. The techniques employed in home automation include those in building automation as well as the control of home entertainment systems, houseplant watering, pet feeding, "scenes" for different

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events (such as dinners or parties), and the use of domestic robots. Typically, it is easier to more fully outfit a house during construction due to the accessibility of the walls, outlets, and storage rooms, and the ability to make design changes specifically to accommodate certain technologies. Wireless systems are commonly installed when outfitting a pre-existing house, as they obviate the need to make major structural changes. These communicate via radio or infrared signals with a central controller.

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WHAT CAN HOME AUTOMATION DO? Home automation can:  Increase your independence and give you greater control of your home environment.  Make it easier to communicate with your family.  Save you time and effort.  Improve your personal safety.  Reduce your heating and cooling costs.  Increase your home’s energy efficiency.  Alert you audibly and visually to emergency situations.  Allow you to monitor your home while you are away.

THE PRIMARY ELEMENTS OF A HOME AUTOMATION SYSTEM The operating system (for example, a computer, security system, a telephone or electricity).  The device being operated (for example, a light or furnace)  The interface, or link, between the user and the device. An interface can be a button, a keypad, a motion sensor and so on. For example, a thermostat equipped with a computer chip can be controlled by an interface such as a push button, which sends a signal to the furnace to adjust the temperature for different times of the day and night. 

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HOW CAN WE CONTROL THEM?

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Remote control Remote control gives you the convenience of controlling lighting, appliances, security systems and consumer electronics from wherever you happen to be at the time, like your couch, car or even in your bed. There are several different "methods" of controlling devices remotely.

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Automatic control Automatic control adds even more convenience by making things happen automatically, without any effort being necessary. Examples include having your lights turn on at dusk and off at your desired time, having your whole home theater turn on and tune to the desired station after one press of a button on your remote.

Features 

     

Simple, small and handy remote control made up of IC 556 ( or two IC 555) Micro-controller(89c51) based receiving unit Multi functional, programmable receiving unit Application specific programming of micro-controller for industrial purpose It's multi functional unit so can be attached to any application It can be used in industries to control/operate any application/device remotely It can be used in homes/offices to operate any appliance remotely like fan, bulb, air cooler, table lamp etc.

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WHY WE USE MICROCONTROLLER? It is a multi channel IR remote control so you can perform not just single but many functions with this remote control. Microcontroller 89c52 is used in receiver part so its programmable remote control. You can program it to perform specific task or for specific application. Some applications that I have developed are "remote control for home appliances", "remotely operated dc motor controller", “remotely operated stepper motor controller".

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HARDWARE PART

 Remote control  Receiving circuit  Power supply  Microcontroller unit  Relay circuit  Fire alarm system

List of things control by system  Appliances • Fan • Tubes • A.C. • T.V. • Sockets • Lightings Doors and windows Blinds/Curtains  Water  Fire and life safety  

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CIRCUIT AND BLOCK DIAGRAMS

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Block diagram of home automation system

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RESISTOR 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 = I*R Resistors are elements of electrical networks and electronic circuits and are ubiquitous in most 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 nickel/chrome). The primary characteristics of a resistor are the resistance, the tolerance, maximum working voltage and the power rating. Other characteristics include temperature coefficient, noise, and inductance. Less well-known is critical resistance, the value below which power dissipation limits the maximum permitted current flow, and above which the limit is applied voltage. Critical resistance depends upon the materials constituting the resistor as well as its physical dimensions; it's determined by design. Resistors can be integrated into hybrid and printed circuits, as well as integrated circuits. Size, and position of leads (or terminals) are relevant to equipment designers; resistors must be physically large enough not to overheat when dissipating their power. Units The ohm (symbol: ω) is a si-driven unit of electrical resistance, named after George Simon Ohm. Commonly used multiples and submultiples in electrical and electronic usage are the milliohm (1x10−3), kilohm (1x103), and megohm (1x106).

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Theory of operation Ohm's law The behavior of an ideal resistor is dictated by the relationship specified in ohm's law: V = I*R Ohm's law states that the voltage (v) across a resistor is proportional to the current (i) through it where the constant of proportionality is the resistance (r). Series and parallel resistors Resistors in a parallel configuration each have the same potential difference (voltage). To find their total equivalent resistance (req):

The parallel property can be represented in equations by two vertical lines "||" (as in geometry) to simplify equations. For two resistors,

The current through resistors in series stays the same, but the voltage across each resistor can be different. The sum of the potential differences (voltage) is equal to the total voltage. To find their total resistance:

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A resistor network that is a combination of parallel and series can be broken up into smaller parts that are either one or the other. For instance,

However, many resistor networks cannot be split up in this way. Consider a cube, each edge of which has been replaced by a resistor. For example, determining the resistance between two opposite vertices requires additional transforms, such as the y-δ transform, or else matrix methods must be used for the general case. However, if all twelve resistors are equal, the corner-tocorner resistance is 5⁄6 of any one of them. The practical application to resistors is that a resistance of any non-standard value can be obtained by connecting standard values in series or in parallel.

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:

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If the average power dissipated is more than the resistor can safely dissipate, the resistor may depart from its nominal resistance and may become damaged by overheating. Excessive power dissipation may raise the temperature of the resistor to a point where it burns out, which could cause a fire in adjacent components and materials. There are flameproof resistors that fail (open circuit) before they overheat dangerously. Note that the nominal power rating of a resistor is not the same as the power that it can safely dissipate in practical use. Air circulation and proximity to a circuit board, ambient temperature, and other factors can reduce acceptable dissipation significantly. Rated power dissipation may be given for an ambient temperature of 25 °c in free air. Inside an equipment case at 60 °c, rated dissipation will be significantly less; if we are dissipating a bit less than the maximum figure given by the manufacturer we may still be outside the safe operating area, and courting premature failure.

Resistor Color Code Chart

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CAPACITOR A capacitor or condenser is a passive electronic component consisting of a pair of conductors separated by a dielectric (insulator). When a potential difference (voltage) exists across the conductors, an electric field is present in the dielectric. This field stores energy and produces a mechanical force between the conductors. The effect is greatest when there is a narrow separation between large areas of conductor; hence capacitor conductors are often called plates. An ideal capacitor is characterized by a single constant value, capacitance, which is measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them. In practice, the dielectric between the plates passes a small amount of leakage current. The conductors and leads introduce an equivalent series resistance and the dielectric has an electric field strength limit resulting in a breakdown voltage. Capacitors are widely used in electronic circuits to block the flow of direct current while allowing alternating current to pass, to filter out interference, to smooth the output of power supplies, and for many other purposes. They are used in resonant circuits in radio frequency equipment to select particular frequencies from a signal with many frequencies.

Theory of operation A capacitor consists of two conductors separated by a nonconductive region. The non-conductive substance is called the dielectric medium, although this may also mean a vacuum or a semiconductor depletion region chemically identical to the conductors. A capacitor is assumed to be self-contained and isolated, with no net electric charge and no influence from an external electric field. The conductors thus contain equal and opposite charges on their facing surfaces, and the dielectric contains an electric field. The capacitor is a reasonably general model for electric fields within electric circuits.

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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:

Sometimes charge buildup affects the mechanics of the capacitor, causing the capacitance to vary. In this case, capacitance is defined in terms of incremental changes:

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. Energy storage Work must be done by an external influence to move charge between the conductors in a capacitor. When the external influence is removed, the charge separation persists and energy is stored in the electric field. If charge is later allowed to return to its equilibrium position, the energy is released. The work done in establishing the electric field, and hence the amount of energy stored, is given by:

Current-voltage relation The current i(t) through a component in an electric circuit is defined as the rate of change of the charge q(t) that has passed through it. Physical charges cannot pass through the dielectric layer of a capacitor, but rather build up in equal and opposite quantities on the electrodes: as each electron accumulates on the negative plate, one leaves the positive plate. Thus the accumulated charge on the electrodes is equal to the integral of

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the current, as well as being proportional to the voltage (as discussed above). As with any antiderivative, a constant of integration is added to represent the initial voltage v (t0). This is the integral form of the capacitor equation,

. Taking the derivative of this, and multiplying by c, yields the derivative form, . The dual of the capacitor is the inductor, which stores energy in the magnetic field rather than the electric field. Its currentvoltage relation is obtained by exchanging current and voltage in the capacitor equations and replacing c with the inductance l. D.C. Circuits

A simple resistor-capacitor circuit demonstrates charging of a capacitor. A series circuit containing only a resistor, a capacitor, a switch and a constant dc source of voltage v0 is known as a charging circuit. If the capacitor is initially uncharged while the switch is open, and the switch is closed at t = 0, it follows from Kirchhoff’s voltage law that

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Taking the derivative and multiplying by c, gives a first-order differential equation,

At t = 0, the voltage across the capacitor is zero and the voltage across the resistor is v0. The initial current is then i(0) =v0 /r. With this assumption, the differential equation yields

Where τ0 = rc is the time constant of the system. As the capacitor reaches equilibrium with the source voltage, the voltage across the resistor and the current through the entire circuit decay exponentially. The case of discharging a charged capacitor likewise demonstrates exponential decay, but with the initial capacitor voltage replacing v0 and the final voltage being zero. A.C. circuits Impedance, the vector sum of reactance and resistance, describes the phase difference and the ratio of amplitudes between sinusoidally varying voltage and sinusoidally varying current at a given frequency. Fourier analysis allows any signal to be constructed from a spectrum of frequencies, whence the circuit's reaction to the various frequencies may be found. The reactance and impedance of a capacitor are respectively

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Where j is the imaginary unit and ω is the angular velocity of the sinusoidal signal. The - j phase indicates that the ac voltage v = z*i lags the ac current by 90°: the positive current phase corresponds to increasing voltage as the capacitor charges; zero current corresponds to instantaneous constant voltage, etc. Note that impedance decreases with increasing capacitance and increasing frequency. This implies that a higher-frequency signal or a larger capacitor results in a lower voltage amplitude per current amplitude—an ac "short circuit" or ac coupling. Conversely, for very low frequencies, the reactance will be high, so that a capacitor is nearly an open circuit in ac analysis—those frequencies have been "filtered out".

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Parallel plate model

Dielectric is placed between two conducting plates, each of area A and with a separation of d. The simplest capacitor consists of two parallel conductive plates separated by a dielectric with permittivity ε (such as air). The model may also be used to make qualitative predictions for other device geometries. The plates are considered to extend uniformly over an area A and a charge density ±ρ = ±q/A exists on their surface. Assuming that the width of the plates is much greater than their separation d, the electric field near the centre of the device will be uniform with the magnitude e = ρ/ε. The voltage is defined as the line integral of the electric field between the plates

Solving this for c = q/v reveals that capacitance increases with area and decreases with separation . The capacitance is therefore greatest in devices made from materials with a high permittivity.

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Several capacitors in parallel.

Networks For capacitors in parallel Capacitors in a parallel configuration each have the same applied voltage. Their capacitances add up. Charge is apportioned among them by size. Using the schematic diagram to visualize parallel plates, it is apparent that each capacitor contributes to the total surface area.

For capacitors in series

Several capacitors in series.

Connected in series, the schematic diagram reveals that the separation distance, not the plate area, adds up. The capacitors each store instantaneous charge build-up equal to that of every other capacitor in the series. The total voltage difference from end to end is apportioned to each capacitor according to the inverse of its capacitance. The entire series acts as a capacitor smaller than any of its components.

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Capacitors are combined in series to achieve a higher working voltage, for example for smoothing a high voltage power supply. The voltage ratings, which are based on plate separation, add up. In such an application, several series connections may in turn be connected in parallel, forming a matrix. The goal is to maximize the energy storage utility of each capacitor without overloading it. Applications Capacitors have many uses in electronic and electrical systems. They are so common that it is a rare electrical product that does not include at least one for some purpose. 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 electrostatic capacitors provide less than 360 joules per kilogram of energy density, while capacitors using developing technologies can provide more than 2.52 kilojoules per kilogram. 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. In ceiling fans, capacitors play the important role of storing electrical energy to give the fan enough torque to start spinning. Pulsed power and weapons Groups of large, specially constructed, low-inductance highvoltage capacitors (capacitor banks) are used to supply huge pulses of current for many pulsed power applications. These include electromagnetic forming, Marx generators, pulsed lasers (especially tea lasers), pulse forming networks, radar, fusion research, and particle accelerators.

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Large capacitor banks (reservoir) are used as energy sources for the explodingbridgewire 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 armor and electromagnetic railguns and coilguns.

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Power Conditioning

A 10,000 microfarad capacitor in a trm-800 amplifier 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. Power factor correction In electric power distribution, capacitors are used for power factor correction. Such capacitors often come as three capacitors connected as a three phase load. Usually, the values of these capacitors are given not in farads but rather as a reactive power in volt-amperes reactive (var). The purpose is to counteract

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inductive loading from devices like electric motors and transmission lines to make the load appear to be mostly resistive. Individual motor or lamp loads may have capacitors for power factor correction, or larger sets of capacitors (usually with automatic switching devices) may be installed at a load center within a building or in a large utility substation. Suppression and coupling Signal coupling Because capacitors pass ac but block dc signals (when charged up to the applied dc voltage), they are often used to separate the ac and dc components of a signal. This method is known as ac coupling or "capacitive coupling". Here, a large value of capacitance, whose value need not be accurately controlled, but whose reactance is small at the signal frequency, is employed. Decoupling A decoupling capacitor is a capacitor used to protect one part of a circuit from the effect of another, for instance to suppress noise or transients. Noise caused by other circuit elements is shunted through the capacitor, reducing the effect they have on the rest of the circuit. It is most commonly used between the power supply and ground. An alternative name is bypass capacitor as it is used to bypass the power supply or other high impedance component of a circuit. Noise filters and snubbers 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 weld together, or destroying a solid-state switch. A snubber capacitor across the newly opened circuit creates a path for this impulse to bypass the contact points, thereby preserving their life; these were commonly found in contact breaker ignition systems, for instance.

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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 resistorcapacitor combinations are available in a single package. Capacitors are also used in parallel to interrupt units of a highvoltage 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).

Motor Starters In single phase squirrel cage motors, the primary winding within the motor housing is not capable of starting a rotational motion on the rotor, but is capable of sustaining one. To start the motor, a secondary winding is used in series with a non-polarized starting capacitor to introduce a lag in the sinusoidal current through the starting winding. When the secondary winding is placed at an angle with respect to the primary winding, a rotating electric field is created. The force of the rotational field is not constant, but is sufficient to start the rotor spinning. When the rotor comes close to operating speed, a centrifugal switch (or current-sensitive relay in series with the main winding) disconnects the capacitor. The start capacitor is typically mounted to the side of the motor housing. These are called capacitor-start motors, which have relatively high starting torque. There are also capacitor-run induction motors which have a permanently-connected phase-shifting capacitor in series with a second winding. The motor is much like a two-phase induction motor.

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Motor-starting capacitors are typically non-polarized electrolytic types, while running capacitors are conventional paper or plastic film dielectric types.

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 in analog circuits as components of integrators or more complex filters and in negative feedback loop stabilization. Signal processing circuits also use capacitors to integrate a current signal.

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 of 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.

Sensing Most capacitors are designed to maintain a fixed physical structure. However, various factors can change the structure of the capacitor, and the resulting change in capacitance can be used to sense those factors.

Changing the dielectric:

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The effects of varying the physical and/or electrical 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.

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 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 changes in acceleration, e.g. as 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 theremin musical instrument by moving his hand since this changes the effective capacitance between the user's hand and the antenna.

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DIODE In electronics, a diode is a two-terminal electronic component that conducts electric current in only one direction. The term usually refers to a semiconductor diode, the most common type today, which is a crystal of semiconductor connected to two electrical terminals, a p-n junction. A vacuum tube diode, now little used, is a vacuum tube with two electrodes; a plate and a cathode. The most common function of a diode is to allow an electric current in one direction (called the diode's forward direction) while blocking current in the opposite direction (the reverse direction). Thus, the diode can be thought of as an electronic version of a check valve. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, and extract modulation from radio signals in radio receivers. However, diodes can have more complicated behavior than this simple on-off action, due to their complex non-linear electrical characteristics, which can be tailored by varying the construction of their p-n junction. These are exploited in special purpose diodes that perform many different functions. Diodes are used to regulate voltage (zener diodes), electronically tune radio and T.V. receivers (varactor diodes), generate radio frequency oscillations (tunnel diodes), and produce light (light emitting diodes). Diodes were the first semiconductor electronic devices. The discovery of crystals' rectifying abilities was made by German physicist Ferdinand Braun in 1874. The first semiconductor diodes, called cat's whisker diodes were made of crystals of minerals such as galena. Today most diodes are made of silicon, but other semiconductors such as germanium are sometimes used.

Semiconductor diodes A modern semiconductor diode is made of a crystal of semiconductor like silicon that has impurities added to it to create

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a region on one side that contains negative charge carriers (electrons), called n-type semiconductor, and a region on the other side that contains positive charge carriers (holes), called ptype semiconductor. The diode's terminals are attached to each of these regions. The boundary within the crystal between these two regions, called a pn junction, is where the action of the diode takes place. The crystal conducts conventional current in a direction from the p-type side (called the anode) to the n-type side (called the cathode), but not in the opposite direction. Another type of semiconductor diode, the Schottky diode, is formed from the contact between a metal and a semiconductor rather than by a p-n junction.

Current–voltage characteristic A semiconductor diode’s behavior in a circuit is given by its current–voltage characteristic, or i–v graph (see graph at right). The shape of the curve is determined by the transport of charge carriers through the so-called depletion layer or depletion region that exists at the p-n junction between differing semiconductors. When a p-n junction is first created, conduction band (mobile) electrons from the n-doped region diffuse into the p-doped region where there is a large population of holes (vacant places for electrons) with which the electrons “recombine”. When a mobile electron recombines with a hole, both hole and electron vanish, leaving behind an immobile positively charged donor (dopant) on the n-side and negatively charged acceptor (dopant) on the pside. The region around the p-n junction becomes depleted of charge carriers and thus behaves as an insulator. However, the width of the depletion region (called the depletion width) cannot grow without limit. For each electron-hole pair that recombines, a positively-charged dopant ion is left behind in the n-doped region, and a negatively charged dopant ion is left behind in the p-doped region. As recombination proceeds more ions are created, an increasing electric field develops through the depletion zone which acts to slow and then finally stop recombination. At this point, there is a “built-in” potential across the depletion zone.

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If an external voltage is placed across the diode with the same polarity as the built-in potential, the depletion zone continues to act as an insulator, preventing any significant electric current flow (unless electron/hole pairs are actively being created in the junction by, for instance, light. See photodiode). This is the reverse bias phenomenon. However, if the polarity of the external voltage opposes the built-in potential, recombination can once again proceed, resulting in substantial electric current through the p-n junction (i.e. Substantial numbers of electrons and holes recombine at the junction).. For silicon diodes, the built-in potential is approximately 0.6 v. Thus, if an external current is passed through the diode, about 0.6 v will be developed across the diode such that the p-doped region is positive with respect to the n-doped region and the diode is said to be “turned on” as it has a forward bias.

Figure: I–V characteristics of a p-n junction diode (not to scale). A diode’s I–V characteristic' can be approximated by four regions of operation (see the figure at right). At very large reverse bias, beyond the peak inverse voltage or piv, a process called reverse breakdown occurs which causes a large increase in current (i.e. a large number of electrons and holes are created at, and move away from the pn junction) that usually damages the device permanently. The avalanche diode is deliberately designed for use in the avalanche region. In the zener diode, the concept of piv is not applicable. A zener diode contains a heavily doped p-n junction allowing electrons to tunnel from the

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valence band of the p-type material to the conduction band of the n-type material, such that the reverse voltage is “clamped” to a known value (called the zener voltage), and avalanche does not occur. Both devices, however, do have a limit to the maximum current and power in the clamped reverse voltage region. Also, following the end of forward conduction in any diode, there is reverse current for a short time. The device does not attain its full blocking capability until the reverse current ceases. The second region, at reverse biases more positive than the piv, has only a very small reverse saturation current. In the reverse bias region for a normal p-n rectifier diode, the current through the device is very low (in the µa range). However, this is temperature dependent, and at sufficiently high temperatures, a substantial amount of reverse current can be observed (ma or more). The third region is forward but small bias, where only a small forward current is conducted. As the potential difference is increased above an arbitrarily defined “cut-in voltage” or “on-voltage” or “diode forward voltage drop (vd)”, the diode current becomes appreciable (the level of current considered “appreciable” and the value of cut-in voltage depends on the application), and the diode presents a very low resistance. The current–voltage curve is exponential. In a normal silicon diode at rated currents, the arbitrary “cut-in” voltage is defined as 0.6 to 0.7 volts. The value is different for other diode types — schottky diodes can be rated as low as 0.2 v and red or blue lightemitting diodes (LEDs) can have values of 1.4 v and 4.0 v respectively. At higher currents the forward voltage drop of the diode increases. A drop of 1 v to 1.5 v is typical at full rated current for power diodes.

Shockley diode equation

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

Where I is the diode current, Is is the reverse bias saturation current, Vd is the voltage across the diode, Vt is the thermal voltage, and N is the emission coefficient, also known as the ideality factor. The emission coefficient n varies from about 1 to 2 depending on the fabrication process and semiconductor material and in many cases is assumed to be approximately equal to 1 (thus the notation n is omitted). The thermal voltage vt is approximately 25.85 mv at 300 k, a temperature close to “room temperature” commonly used in device simulation software. At any temperature it is a known constant defined by:

Where k is the Boltzmann constant, t is the absolute temperature of the p-n junction, and q is the magnitude of charge on an electron (the elementary charge). The Shockley ideal diode equation or the diode law is derived with the assumption that the only processes giving rise to the current in the diode are drift (due to electrical field), diffusion, and thermal recombination-generation. It also assumes that the

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recombination-generation (r-g) current in the depletion region is insignificant. This means that the Shockley equation doesn’t account for the processes involved in reverse breakdown and photon-assisted r-g. Additionally, it doesn’t describe the “leveling off” of the i–v curve at high forward bias due to internal resistance. Under reverse bias voltages (see figure 5) the exponential in the diode equation is negligible, and the current is a constant (negative) reverse current value of −is. The reverse breakdown region is not modeled by the Shockley diode equation. For even rather small forward bias voltages (see figure 5) the exponential is very large because the thermal voltage is very small, so the subtracted ‘1’ in the diode equation is negligible and the forward diode current is often approximated as

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LIGHT-EMITTING DIODE A light-emitting diode (led) is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly used for lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but modern versions are available across the visible, ultraviolet and infrared wavelengths, with very high brightness. The led is based on the semiconductor diode. When a diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. A led is usually small in area (less than 1 mm2), and integrated optical components are used to shape its radiation pattern and assist in reflection. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. However, they are relatively expensive and require more precise current and heat management than traditional light sources. Current led products for general lighting are more expensive to buy than fluorescent lamp sources of comparable output. They also enjoy use in applications as diverse as replacements for traditional light sources in automotive lighting (particularly indicators) and in traffic signals. Airbus uses led lighting in their a320 enhanced since 2007, and Boeing plans its use in the 787. The compact size of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are useful in advanced communications technology.

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Advantages 



 



 

Efficiency: LEDs produce more light per watt than incandescent bulbs. Their efficiency is not affected by shape and size unlike fluorescent light bulbs or tubes. Color: LEDs can emit light of an intended color without the use of color filters that traditional lighting methods require. This is more efficient and can lower initial costs. Size: LEDs can be very small (smaller than 2 mm2) and are easily populated onto printed circuit boards. On/off time: LEDs light up very quickly. A typical red indicator led will achieve full brightness in microseconds. LEDs used in communications devices can have even faster response times. Cycling: LEDs are ideal for use in applications that are subject to frequent on-off cycling, unlike fluorescent lamps that burn out more quickly when cycled frequently, or hid lamps that require a long time before restarting. Dimming: LEDs can very easily be dimmed either by pulsewidth modulation or lowering the forward current. Cool light: in contrast to most light sources, LEDs radiate very little heat in the form of IR that can cause damage to sensitive objects or fabrics. Wasted energy is dispersed as heat through the base of the led.

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 







Slow failure: LEDs mostly fail by dimming over time, rather than the abrupt burn-out of incandescent bulbs. Lifetime: LEDs can have a relatively long useful life. One report estimates 35,000 to 50,000 hours of useful life, though time to complete failure may be longer. Fluorescent tubes typically are rated at about 10,000 to 15,000 hours, depending partly on the conditions of use, and incandescent light bulbs at 1,000–2,000 hours. Shock resistance: LEDs, being solid state components, are difficult to damage with external shock, unlike fluorescent and incandescent bulbs which are fragile. Focus: the solid package of the led can be designed to focus its light. Incandescent and fluorescent sources often require an external reflector to collect light and direct it in a usable manner. Toxicity: LEDs do not contain mercury, unlike fluorescent lamps.

Disadvantages  



Some fluorescent lamps can be more efficient. High initial price: LEDs are currently more expensive, price per lumen, on an initial capital cost basis, than most conventional lighting technologies. The additional expense partially stems from the relatively low lumen output and the drive circuitry and power supplies needed. Temperature dependence: led performance largely depends on the ambient temperature of the operating environment. Over-driving the led in high ambient temperatures may result in overheating of the led package, eventually leading to device failure. Adequate heat-sinking is required to maintain long life. This is especially important when considering automotive, medical, and military applications where the device must operate over a large range of temperatures, and is required to have a low failure rate.

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









Voltage sensitivity: LEDs must be supplied with the voltage above the threshold and a current below the rating. This can involve series resistors or current-regulated power supplies. Light quality: most cool-white LEDs have spectra that differ significantly from a black body radiator like the sun or an incandescent light. The spike at 460 nm and dip at 500 nm can cause the color of objects to be perceived differently under cool-white led illumination than sunlight or incandescent sources, due to metamerism, red surfaces being rendered particularly badly by typical phosphor based cool-white LEDs. However, the color rendering properties of common fluorescent lamps are often inferior to what is now available in state-of-art white LEDs. Area light source: LEDs do not approximate a “point source” of light, but rather a lambertian distribution. So LEDs are difficult to use in applications requiring a spherical light field. LEDs are not capable of providing divergence below a few degrees. This is contrasted with lasers, which can produce beams with divergences of 0.2 degrees or less. Blue hazard: there is a concern that blue LEDs and coolwhite LEDs are now capable of exceeding safe limits of the so-called blue-light hazard as defined in eye safety specifications such as ansi/iesna rp-27.1-05: recommended practice for photo biological safety for lamp and lamp systems. Blue pollution: because cool-white LEDs (i.e., LEDs with high color temperature) emit proportionally more blue light than conventional outdoor light sources such as high-pressure sodium lamps, the strong wavelength dependence of Raleigh scattering means that cool-white LEDs can cause more light pollution than other light sources. The international dark-sky association discourages the use of white light sources with correlated color temperature above 3,000 k.

LED CIRCUIT In electronics, the basic led circuit is an electric power circuit used to power a light-emitting diode or led. It consists of a voltage source powering two components connected in series: a current

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limiting resistor, and an led. Optionally, a switch may be introduced to open and close the circuit. The switch may be replaced with another component or circuit to form a continuity tester. The led used will have a voltage drop, specified at the intended operating current. Ohm's law and Kirchhoff’s circuit laws are used to calculate the resistor that is used to attain the correct current. The resistor value is computed by subtracting the led voltage drop from the supply voltage, and then dividing by the desired led operating current. If the supply voltage is equal to the LED's voltage drop, no resistor is needed.

Simple led circuit diagram

Simple resistance formula brightness of the led

for

optimum

The formula to calculate the correct resistance to use is:

Where:  

Power supply voltage (vs) is the voltage of the power supply e.g. a 9 volt battery. Led voltage drop (vf) is the voltage drop across the led (typically about 1.8 - 3.3 volts; this varies by the color of the led) 1.8 volts for red and its gets higher as the spectrum increases to 3.3 volts for blue.

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

Led current rating (if) is the manufacturer rating of the led (usually given in mill amperes such as 20 ma)

Analysis using Kirchhoff’s laws The formula can be explained considering the led as a resistance, and applying the kvl (r is the unknown quantity):

TRANSISTOR The name is transistor derived from ‘transfer resistors’ indicating a solid state semiconductor device. In addition to conductor and insulators, there is a third class of material that exhibits proportion of both. Under some conditions, it acts as an insulator, and under other conditions it’s a conductor. This phenomenon is called semi-conducting and allows a variable control over electron flow. So, the transistor is semi conductor device used in electronics for amplitude. Transistor has three terminals, one is the collector, one is the base and other is the emitter, (each lead must be connected in the circuit correctly and only then the transistor will function). Electrons are emitted via one terminal and collected on another terminal, while the third terminal acts as a control element. Each transistor has a number marked on its body. Every number has its own specifications. There are mainly two types of transistor (i) NPN & (ii) PnP

NPN transistors: When a positive voltage is applied to the base, the transistor begins to conduct by allowing current to flow through the

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collector to emitter circuit. The relatively small current flowing through the base circuit causes a much greater current to pass through the emitter / collector circuit. The phenomenon is called current gain and it is measure in beta.

Pnp transistor: It also does exactly same thing as above except that it has a negative voltage on its collector and a positive voltage on its emitter.

Transistor is a combination of semi-conductor elements allowing a controlled current flow. Germanium and silicon is the two semiconductor elements used for making it. There are two types of transistors such as point contact and junction transistors. Point contact construction is defective so is now out of use. Junction triode transistors are in many respects analogous to triode electron tube. A junction transistor can function as an amplifier or oscillator as can a triode tube, but has the additional advantage of long life, small size, ruggedness and absence of cathode heating power.

Operation of pnp transistor:A pnp transistor is made by sand witching two pn germanium or silicon diodes, placed back to back. The centre of n-type portion is extremely thin in comparison to p region. The p region of the left is connected to the positive terminal and n-region to the negative terminal i.e. pn is biased in the forward direction while p region of right is biased negatively i.e. in the reverse direction as shown in fig. The p region in the forward biased circuit is called the emitter

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and p region on the right, biased negatively is called collector. The centre is called base.

The majority carriers (holes) of p region (known as emitter) move to n region as they are repelled by the positive terminal of battery while the electrons of n region are attracted by the positive terminal. The holes overcome the barrier and cross the emitter junction into n region. As the width of base region is extremely thin, two to five percent of holes recombine with the free electrons of n-region which result in a small base current while the remaining holes (95% to 98%) reach the collector junction. The collector is biased negatively and the negative collector voltage aids in sweeping the hole into collector region. As the p region at the right is biased negatively, a very small current should flow but the following facts are observed:  

A substantial current flows through it when the emitter junction is biased in a forward direction. The current flowing across the collector is slightly less than that of the emitter, and The collector current is a function of emitter current i.e. with the decrease or increase in the emitter current a corresponding change in the collector current is observed.

The facts can be explained as follows:As already discussed that 2 to 5% of the holes are lost in recombination with the electron n base region, which result in a

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small base current and hence the collector current is slightly less than the emitter current. The collector current increases as the holes reaching the collector junction are attracted by negative potential applied to the collector. When the the base emitter is voltage in

emitter current increases , most holes are injected into region increasing the collector current. In this way analogous to the control of plate current by small grid a vacuum triode

Hence we can say that when the emitter is forward biased and collector is negatively biased, a substantial current flows in both the circuits. Since a small emitter voltage of about 0.1 to 0.5 volts permits the flow of an appreciable emitter current the input power is very small. The collector voltage can be as high as 45 volts.

The transistor as a switch When used as an ac signal amplifier, the transistors base biasing voltage is applied so that it operates within its "active" region and the linear part of the output characteristics curves are used. However, both the npn & pnp type bipolar transistors can be made to operate as an "on/off" type solid state switch for controlling high power devices such as motors, solenoids or lamps. If the circuit uses the transistor as a switch, then the biasing is arranged to operate in the output characteristics curves seen previously in the areas known as the "saturation" and "cutoff" regions as shown below. Transistor curves

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The pink shaded area at the bottom represents the "cut-off" region. Here the operating conditions of the transistor are zero input base current (ib), zero output collector current (IC) and maximum collector voltage (vce) which results in a large depletion layer and no current flows through the device. The transistor is switched "fully-off". The lighter blue area to the left represents the "saturation" region. Here the transistor will be biased so that the maximum amount of base current is applied, resulting in maximum collector current flow and minimum collector emitter voltage which results in the depletion layer being as small as possible and maximum current flows through the device. The transistor is switched "fully-on". Then we can summarize this as: 



Cut-off region - both junctions are reverse-biased, base current is zero or very small resulting in zero collector current flowing, and the device is switched fully "off". Saturation region - both junctions are forward-biased, base current is high enough to give a collector-emitter voltage of 0v resulting in maximum collector current flowing, the device is switched fully "on".

An example of an NPN transistor as a switch being used to operate a relay is given below. With inductive loads such as relays or solenoids a flywheel diode is placed across the load to dissipate the back emf generated by the inductive load when the transistor switches "off" and so protect the transistor from damage. If the load is of a very high current or voltage nature, such as motors, heaters etc, then the load current can be controlled via a suitable relay as shown.

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Transistor switching circuit

The circuit resembles that of the common emitter circuit we looked at in the previous tutorials. The difference this time is that to operate the transistor as a switch the transistor needs to be turned either fully "off" (cut-off) or fully "on" (saturated). An ideal transistor switch would have an infinite resistance when turned "off" resulting in zero current flow and zero resistance when turned "on", resulting in maximum current flow. In practice when turned "off", small leakage currents flow through the transistor and when fully "on" the device has a low resistance value causing a small saturation voltage (vce) across it. In both the cut-off and saturation regions the power dissipated by the transistor is at its minimum. To make the base current flow, the base input terminal must be made more positive than the emitter by increasing it above the 0.7 volts needed for a silicon device. By varying the base-emitter voltage vbe, the base current is altered and which in turn controls the amount of collector current flowing through the transistor as previously discussed. When maximum collector current flows the transistor is said to be saturated. The value of the base resistor determines how much input voltage is required and corresponding base current to switch the transistor fully "on". Example no. 1. For example, using the transistor values from the previous tutorials of: β = 200, IC = 4ma and ib = 20ua, find the value of

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the base resistor (rb) required to switch the load "on" when the input terminal voltage exceeds 2.5v.

Example no. 2. Again using the same values, find the minimum base current required to turn the transistor fully "on" (saturated) for a load that requires 200ma of current.

Transistor switches are used for a wide variety of applications such as interfacing large current or high voltage devices like motors, relays or lamps to low voltage digital logic IC's or gates like and gates or gates. Here, the output from a digital logic gate is only +5v but the device to be controlled may require a 12 or even 24 volts supply. Or the load such as a dc motor may need to have its speed controlled using a series of pulses (pulse width modulation) and transistor switches will allow us to do this faster and more easily than with conventional mechanical switches.

Digital logic transistor switch

limit the

The base resistor, rb is required to output current of the logic gate.

BATTERY (ELECTRICITY) How batteries work

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A battery is a device that converts chemical energy directly to electrical energy. It consists of a number of voltaic cells; each voltaic cell consists of two half cells connected in series by a conductive electrolyte containing anions and cations. One half-cell includes electrolyte and the electrode to which anions (negatively-charged ions) migrate, i.e. The anode or negative electrode; the other half-cell includes electrolyte and the electrode to which cations (positively-charged ions) migrate, i.e. The cathode or positive electrode. In the redox reaction that powers the battery, reduction (addition of electrons) occurs to cations at the cathode, while oxidation (removal of electrons) occurs to anions at the anode. The electrodes do not touch each other but are electrically connected by the electrolyte. Many cells use two half-cells with different electrolytes. In that case each half-cell is enclosed in a container, and a separator that is porous to ions but not the bulk of the electrolytes prevents mixing. Each half cell has an electromotive force (or emf), determined by its ability to drive electric current from the interior to the exterior of the cell. The net emf of the cell is the difference between the emfs of its half-cells, as first recognized by Volta. Therefore, if the electrodes have emfs and , then the net emf is ; in other words, the net emf is the difference between the reduction potentials of the half-reactions. The electrical driving force or across the terminals of a cell is known as the terminal voltage (difference) and is measured in volts. The terminal voltage of a cell that is neither charging nor discharging is called the open-circuit voltage and equals the emf of the cell. Because of internal resistance, the terminal voltage of a cell that is discharging is smaller in magnitude than the opencircuit voltage and the terminal voltage of a cell that is charging exceeds the open-circuit voltage. An ideal cell has negligible internal resistance, so it would maintain a constant terminal voltage of until exhausted, then dropping to zero. If such a cell maintained 1.5 volts and stored a charge of one coulomb then on complete discharge it would perform 1.5 joule of work. In actual cells, the internal resistance increases under discharge, and the open circuit voltage also decreases under discharge. If the

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voltage and resistance are plotted against time, the resulting graphs typically are a curve; the shape of the curve varies according to the chemistry and internal arrangement employed. As stated above, the voltage developed across a cell's terminals depends on the energy release of the chemical reactions of its electrodes and electrolyte. Alkaline and carbon-zinc cells have different chemistries but approximately the same emf of 1.5 volts; likewise nicd and nimh cells have different chemistries, but approximately the same emf of 1.2 volts. On the other hand the high electrochemical potential changes in the reactions of lithium compounds give lithium cells emfs of 3 volts or more.

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CRYSTAL OSCILLATOR What are crystal oscillators? Crystal oscillators are oscillators where the primary frequency determining element is a quartz crystal. Because of the inherent characteristics of the quartz crystal the crystal oscillator may be held to extreme accuracy of frequency stability. Temperature compensation may be applied to crystal oscillators to improve thermal stability of the crystal oscillator. Crystal oscillators are usually, fixed frequency oscillators where stability and accuracy are the primary considerations. For example it is almost impossible to design a stable and accurate LC oscillator for the upper H.F. and higher frequencies without resorting to some sort of crystal control. Hence the reason for crystal oscillators. The frequency of older ft-243 crystals can be moved upward by crystal grinding. I won't be discussing frequency synthesizers and direct digital synthesis (dds) here. They are particularly interesting topics to be covered later. 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,

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computers, and cell phones. Quartz crystals are also found inside test and measurement equipment, such as counters, signal generators, and oscilloscopes.

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

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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 temperature-controlled container, called a crystal oven, and can also be mounted on shock absorbers to prevent perturbation by external mechanical vibrations.

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Electrical model

Electronic symbol for a piezoelectric crystal resonator

Schematic symbol and equivalent circuit for a quartz crystal in an oscillator 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,

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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. Adding additional capacitance across a crystal will cause the parallel resonance to shift downward. This can be used to adjust the frequency at which a crystal oscillator oscillates. Crystal manufacturers normally cut and trim their crystals to have a specified resonance frequency with a known 'load' capacitance added to the crystal. For example, a 6 pf 32 kHz crystal has a parallel resonance frequency of 32,768 Hz when a 6.0 pf capacitor is placed across the crystal. Without this capacitance, the resonance frequency is higher than 32,768 Hz.

Resonance modes A quartz crystal provides both series and parallel resonance. The series resonance is a few kilohertz lower than the parallel one. Crystals below 30 MHz are generally operated between series and parallel resonance, which means that the crystal appears as an inductive reactance in operation. Any additional circuit capacitance will thus pull the frequency down. For a parallel resonance crystal to operate at its specified frequency, the electronic circuit has to provide a total parallel capacitance as specified by the crystal manufacturer. Crystals above 30 MHz (up to >200 MHz) are generally operated at series resonance where the impedance appears at its minimum and equal to the series resistance. For these crystals the series resistance is specified (