Acknowledgement
Electronics Electronics is the science of how to control electric energy, energy in which the electrons have a fundamental role. Electronics deals with electrical circuits that involve active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive electrical components and interconnection technologies. Commonly, electronic devices contain circuitry consisting primarily or exclusively of active semiconductors supplemented with passive elements; such a circuit is described as an electronic circuit. The nonlinear behavior of active components and their ability to control electron flows makes amplification of weak signals possible, and electronics is widely used in information processing, telecommunication, and signal processing. The ability of electronic devices to act as switches makes digital information processing possible. Interconnection technologies such as circuit boards, electronics packaging technology, and other varied forms of communication infrastructure complete circuit functionality and transform the mixed components into a regular working system.
Electronics is distinct from electrical and electromechanical science and technology, which deal with the generation, distribution, switching, storage, and conversion of electrical energy to and from other energy forms using wires, motors, generators, batteries, switches, relays, transformers, resistors, and other passive components. !ntil "#$% this field was called &radio technology& because its principal application was the design and theory of radio transmitters, receivers, and vacuum tubes. Today, most electronic devices use semiconductor components to perform electron control. The study of semiconductor devices and related technology is considered a branch of solidstate physics, whereas the design and construction of electronic circuits to solve practical problems come under electronics engineering. This article focuses on engineering aspects of electronics.
Branches of Electronics Electronics has branches as follows' •
(igital electronics'
(igital electronics or digital )electronic* circuits are electronics that handle digital signals discrete bands of analog levels rather than by continuous ranges )as used in analogue electronics*. +ll levels within a band of values represent the same numeric value. ecause of this discreti-ation, relatively small changes to the analog signal levels due to manufacturing tolerance, signal attenuation or parasitic noise do not leave the discrete envelope, and as a result are ignored by signal state sensing circuitry. In most cases, the number of these states is two, and they are represented by two voltage bands' one near a reference value )typically termed as &ground& or -ero volts*, and the other a value near the supply voltage. These correspond to the &false& )&%&* and &true& )&"&* values of the oolean domain respectively, named after its inventor, eorge oole, yielding binary code. (igital electronic circuits are usually made from large assemblies of logic gates, simple electronic representations of oolean logic functions. •
+nalogue electronics'
+nalogue electronics are electronic systems with a continuously variable signal, in contrast to digital electronics where signals usually take only two levels. The term &analogue& describes the proportional relationship between a signal and a voltage or current that represents the signal. +n analogue signal uses some attribute of the medium to convey the signal/s information. 0or example, an aneroid barometer uses the angular position of a needle as the signal to convey the information of changes in atmospheric pressure. Electrical signals may represent information by changing their voltage, current, fre1uency, or total charge. Information is converted from some other physical form )such as sound, light, temperature, pressure, position* to an electrical signal by a transducer which converts one type of energy into another.
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2icroelectronics'
2icroelectronics is a subfield of electronics. +s the name suggests, microelectronics relates to the study and manufacture )or microfabrication* of very small electronic designs and components. !sually, but not always, this means micrometrescale or smaller. These devices are typically made from semiconductor materials. 2any components of normal electronic design are available in a microelectronic e1uivalent. These include transistors, capacitors, inductors, resistors, diodes and )naturally* insulators and conductors can all be found in microelectronic devices. •
0u--y electronics
0u--y electronics is an electronic technology that uses fu--y logic, instead of the twostate oolean logic more commonly used in digital electronics. 0u--y electronics is fu--y logic implemented on dedicated hardware. This is to be compared with fu--y logic implemented in software running on a conventional processor. 0u--y electronics has a wide range of applications, including control systems and artificial intelligence. •
Integrated circuit electronics'
+n integrated circuit or monolithic integrated circuit )also referred to as an IC, a chip, or a microchip* is a set of electronic circuits on one small plate )&chip&* of semiconductor material, normally silicon. This can be made much smaller than a discrete circuit made from independent electronic components. ICs can be made very compact, having up to several billion transistors and other electronic components in an area the si-e of a fingernail. ICs have two main advantages over discrete circuits' cost and performance. Cost is low because the compactness of the chips.
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Circuit electronics'
The process of circuit design can cover systems ranging from complex electronic systems all the way down to the individual transistors within an integrated circuit. In integrated circuit design automation, the term &circuit design& often refers to the step of the design cycle which outputs the schematics of the integrated circuit. Typically this is the step between logic design and physical design. 0ormal circuit design usually involves the following stages'
i. ii. iii. iv. v. vi. vii. •
3riting the re1uirement specification after liaising with the customer. 3riting a technical proposal to meet the re1uirements of the customer specification. 4ynthesi-ing on paper a schematic circuit diagram, an abstract electrical or electronic circuit that will meet the specifications. Calculating the component values to meet the operating specifications under specified conditions. 5erforming simulations to verify the correctness of the design. uilding a breadboard or other prototype version of the design and testing against specification. 2aking any alterations to the circuit to achieve compliance. 6ptoelectronics
6ptoelectronics is the study and application of electronic devices that source, detect and control light, usually considered a subfield of photonics. In this context, light often includes invisible forms of radiation such as gamma rays, 7rays, ultraviolet and infrared, in addition to visible light. 6ptoelectronic devices are electricaltooptical or opticaltoelectrical transducers, or instruments that use
such devices in their operation. Electrooptics is often erroneously used as a synonym, but is a wider branch of physics that concerns all interactions between light and electric fields, whether or not they form part of an electronic device. 6ptoelectronics is based on the 1uantum mechanical effects of light on electronic materials, especially semiconductors, sometimes in the presence of electric fields.
Light Dependent Resistor (LDR) What is a Light Dependent Resistor or a Photo Resistor? + Light Dependent Resistor )8(9* or a 5hoto 9esistor is a device whose resistivity is a function of the incident electromagnetic radiation. :ence, they are light sensitive devices. They are also called as photo conductors, photo conductive cells or simply photocells. They are made up of semiconductor materials having high resistance. There are many different symbols used to indicate a LDR , one of the most commonly used symbol is shown in the figure below. The arrow indicates light falling on it.
Working Principle of LDR + light dependent resistor works on the principle of photo conductivity. 5hoto conductivity is an optical phenomenon in which the materials conductivity ):ence resistivity* reduces when light is absorbed by the material. 3hen light falls i.e. when the photons fall on the device, the electrons in the valence band of the semiconductor material are excited to the conduction band. These photons in the incident light
should have energy greater than the band gap of the semiconductor material to make the electrons ump from the valence band to the conduction band. :ence when light having enough energy is incident on the device more < more electrons are excited to the conduction band which results in large number of charge carriers. The result of this process is more and more current starts flowing and hence it is said that the resistance of the device has decreased. This is the most common working principle of LDR. Characteristics of LDR 8(9=s are light dependent devices whose resistance decreases when light falls on them and increases in the dark. 3hen a light dependent resistor is kept in dark, its resistance is very high. This resistance is called as dark resistor. It can be as high as "%"> ?. +nd if the device is allowed to absorb light its resistance will decrease drastically. If a constant voltage is applied to it and intensity of light is increased the current starts increasing. 0igure below shows resistance vs illumination curve for a particular LDR . 5hotocells or 8(9=s are nonlinear devices. There sensitivity varies with the wavelength of light incident on them. 4ome photocells might not at all response to a certain range of wavelengths. ased on the material used different cells have different spectral response curves.
3hen light is incident on a photocell it usually takes about @ to ">ms for the change in resistance to take place, while it takes seconds for the resistance to rise back again to its initial value after removal of light. This phenomenon is called as resistance recovery rate. This property is used in audio compressors. +lso, LDR =s are less sensitive than photo diodes and photo transistor. )+ photodiode and a photocell )8(9* are not the same, a photodiode is a pn unction semiconductor device that converts light to electricity, whereas a photocell is a passive device, there is no pn unction in this nor it AconvertsB light to electricity*. Types of Light Dependent Resistors ' ased on the materials used they are classified as' i* Intrinsic photo resistors )!ndoped semiconductor*' These are pure semiconductor materials such as silicon or germanium. Electrons get excited from valance band to conduction band when photons of enough energy falls on it and number charge carriers increases.
ii* Extrinsic photoresistors' These are semiconductor materials doped with impurities which are called as dopants. Theses dopants create new energy bands above the valence band which are filled with electrons. :ence this reduces the band gap and less energy is re1uired in exciting them. Extrinsic photo resistors are generally used for long wavelengths.
Constr!ction of a Photodiode The structure of a light dependent resistor consists of a light sensitive material which is deposited on an insulating substrate such as ceramic. The material is deposited in -ig-ag pattern in order to obtain the desired resistance < power rating. This -ig-ag area separates the metal deposited areas into two regions. Then the ohmic contacts are made on the either sides of the area. The resistances of these contacts should be as less as possible to make sure that the resistance mainly changes due to the effect of light only. 2aterials normally used are cadmium sulphide, cadmium selenide, indium antimonide and cadmium sulphonide. The use of lead and cadmium is avoided as they are harmful to the environment.
"pplications of LDR LDR =s have low cost and simple structure. They are often used as light sensors. They are used when there is a need to detect absences or presences of light like in a camera light meter. !sed in street lamps, alarm clock, burglar alarm circuits, light intensity meters, for counting the packages moving on a conveyor belt, etc.
Experimental Study Aim:To determine the relationship between resistance 6f a photodiode and Intensity and 0re1uency of 8ight )or* radiation incident on the 8(9.
Apparatus Required:-
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4ource of (C oltage )attery* oltmeter )2ultimeter* +mmeter ariable 9esistor )9heostat* 8(9 )8ight (ependent 9esistor* Connecting wires 8ead wire for soldering Dey ulb +C source for ulb
Formula:#h$%s Law& The 5otential (ifference between the terminals or ends of a conductor is directly proportional and thus varies linearly with the Current I flowing through the conductor.
2athematically, the law can be expressed as' 9I 3here 9 is the resistance if the conductor I is the current flowing through the conductor is the 5otential (ifference across the terminals of the conductor
Circuit diagram'
Procedure 4tep "' 0orming the given circuit. •
0rom the 5ositive terminal of the battery , connect to the positive terminal of the ammeter .
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Connect the negative terminal of the ammeter to the 8(9 . Fow connect the other terminal of the 8(9 to the positive terminal of the rheostat. Connect the rheostat to the attery ) source of (C*
4tep >' +fter the circuit has been made , Connect the bulb to an +C source) preferably using an extension box*.
4tep G' 4witch on the circuit. The experiment has to be done in a dark room. Fow switch of the bulb and keep it with maximum closeness to the 8(9. Fow note the reading of the voltmeter and ammeter and record them in the 6bservation Table.
4tep H' Fow move the bulb slowly away and switch on the circuit again. 2easure the distance. Fote down the ammeter and voltmeter readings. (o the same for different distances and take H values.
4tep$. (o all the steps again using a different colored light in order to change the fre1uency of the radiation or light source used. Fote down the readings in the observation table. Observations
Result !e Resistance o" t!e #$R decreases w!en t!e %ntensity o" t!e lig!t or radiation incident on t!e #$R increases and vice versa& !us ' t!e intensity o" incident radiation varies inversely wit! t!e resistance&
(%(#%O)RA*+,
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