1. INTRODUCTION. Currency Counting Machine with Fake Note Detection

Transcription

1 1. INTRODUCTION The currency counting machine or CCM is one of the miracle of the science. The CCM works on the principle on the breadth of the bundle of currency and there in an roller which has rods in an continuous pattern and the roller moves these rods with a particular speed. The speed remains constant as like in the ATM machine counting machine and these rollers moves on the bundle of the currency and just move out the single currency one by one at a constant and high speed and there is an transducers which detect that how many single currency has passed out in front of it. FIG rupees note with its various real identification mark. Different range of counting machines like Basic Note counter, Intelligent Counting cum counterfeit detection machines and Hi Speed Heavy duty cash counting machine are available to suit different type of customers. Highly dependable and ideal for Banks, Big & small business houses, Traders, retailers, jewellers and almost all types of business establishment can use them according to their suitability. IEC-CET/ Page 1

2 The machine meant for detection of fake notes as prime function invariably should be capable of not allowing any fake note to pass as genuine. It is possible only with the detectors specially developed considering the large number of intricacies concerning to Indian notes The kind of machines Indian Banks at cash counters needed are the machine which can verify not only the images but also can check the chemical and physical properties of papers, inks, resins and other materials used in production of note. The machine should be capable of not allowing any fake note to pass as genuine. It is possible only with the detectors specially developed considering the large number of intricacies concerning to Indian notes IEC-CET/ Page 2

3 2. LITERATURE REVIEW Currency Counter provides a fast, efficient and accurate way to count stacks of currency. Some models detect counterfeit bills either magnetically and/or using ultraviolet light. Ultra Violet Light Detector is used in Currency counters. Currency created by a color copier or printer produces an image that rests on the surface of paper that can easily be seen when UV light is placed over it. FIG- 2 A 500 rupees note under UV rays. Tiny particles of toner outside the image can also be easily seen with a UV light. Bill counters and counterfeit detectors have a UV light built into the machine. If a counterfeit bill is run through the machine, an alarm or light will alert you that the banknote is counterfeit. Magnetic sensors: Magnetic sensors run over each bill and are designed to search for certain components of banknotes that cannot be seen by the naked eye. Machines automatically detect and match the piece against the already-programmed components of legitimate bills. When a suspicious note is found, the operator is notified immediately. IEC-CET/ Page 3

4 FIG- 3 Noting the discrepancy. Different range of counting machines like Basic Note counter, Intelligent Counting cum counterfeit detection machines and Hi Speed Heavy duty cash counting machine Highly dependable and ideal for Banks, Big & small business houses, Traders, retailers, jewellers and almost all types of business establishment 2.1 COUNTERFEITING TECHNIQUES Counterfeiting, of whatever kind, has been occurring ever since humans grasped the concept of valuable items, and there has been an ongoing race between certifier (banks, for example) and counterfeiter ever since. IEC-CET/ Page 4

5 First-Line Inspection Methods Varied-Density Watermarks Ultraviolet Fluorescence Intaglio Printing Microtext Holograms and Kinegrams (DOVIDs/ISIS) Second-Line Inspection Methods Isocheck/Isogram Fibre-Based Certificates of Authenticity Colour and Feature Analysis First-Line Inspection Methods First-line inspection methods are used on-the-spot by vendors and retailers to determine, at best guess, the authenticity of currency being exchanged. The disadvantages of these methods are that they are generally easier to counterfeit than second-line inspection characteristics, since they re just as visible to the counterfeiter as to the verifier, and the methods used to apply them are usually inexpensive. However, the visibility of these features means that the general population is aware of the security measures and can spot many fraudulent notes quickly. Varied-Density Watermarks By varying the density of the paper a banknote is printed on in a controlled manner, thin watermarks can be applied. These are visible when a bright light shines onto the rear of banknote, and the varied paper density causes varying intensities of light to pass through, causing the watermarked image to appear on the other side of the note. Ultraviolet Fluorescence Embedding fluorescent fibers into the paper, or printing ultra-violet ink onto the paper, creates a form of optical verification easily used at counters, checkouts, etc. By exposing IEC-CET/ Page 5

6 the note to ultra-violet light, the ink or fibers fluoresce, revealing a coloured pattern not visible under natural light. Intaglio Printing This gives a more complex and reliable first-line inspection method, since it is the printing process itself that serves to vouch for the authenticity of the document. The note is subjected to a high-pressure printing process that strengthens and slightly raises the paper s surface structure. Using different alignments of lines printed in this manner, a latent image can be produced which changes appearance depending on the angle at which the note is viewed. This method can also be used with optically-variable ink to produce interference which shows different spectral colours when viewed from different angles. Micro text It is very common for banknotes to have incredibly small text printed at much higher resolutions than most commercial copiers, scanners or printers are capable of. When a copying or scanning attempt is made, the insufficient resolution causes the text to become illegibly blurred, announcing the illegitimacy of the note. This method requires specialised printing equipment but ultimately adds very little cost to the manufacture of the currency. Holograms and Kin grams (DOVIDs/ISIS) These techniques are becoming more and more regularly used in modern anticounterfeiting measures, once used mostly on credit/debit cards but now increasingly on new bank notes and cheques. In producing diffractive optically-variable image devices (DOVIDs), iridescent foils are added to the printed currency usually after printing. Kin grams and holograms used in DOVIDs are produced by embossing micro profiles with thermoplastic films. The hologram itself is applied using the interference of light from different sources in a specific pattern, and kin grams are produced with achromatic and polarisation effects. The result is a seemingly 3D full-colour image when illuminated from different angles. ISIS uses stacked quantities of thin films to create a similar effect, with each layer having different refractive properties. The refraction of light when viewed is such that a spectral IEC-CET/ Page 6

7 pattern has been extracted and a full-colour image is produced which varies under different viewing angles. Second-Line Inspection Methods A second-line inspection method is one that cannot be verified by the naked eye alone, and requires an extra device to perform a verification function. These are more secure and harder to counterfeit than visual methods, but the extra security adds extra cost at both the manufacturing and verification ends. Isocheck/Isogram Related to intaglio printing (described above), these methods rely on a specific pattern of dots and/or lines to cause a moiré pattern when printed or scanned. Hidden watermarks can also be applied in these patterns such that when a special filter is placed between the viewer and the note, the hidden verification is revealed and verifies the note as genuine. Fibre-Based Certificates of Authenticity Based on the characteristics of fibre-optic light transmission, this method makes use of unique configurations of fibres embedded in the paper. Using a scanner to illuminate one end of an embedded fibre, the other corresponding of that fibre will become illuminated. By using the position of both illuminated ends (the one deliberately illuminated, and the one illuminated as a result), the certifier has a fibre signature. This string can then be converted into a bit string and combined with any extra data that is required (e.g. value, serial number, source, etc.). This is in turn combined with a cryptographic hash of itself and is signed using a private key, with the corresponding public key made available. The final result of these steps can then be encoded onto the banknote (this method is suitable for certifying a wide range of other documents too) in the form of a barcode or verification number of some kind. Verifying the authenticity merely involves inverting the above process. The control number is verified using the public key corresponding to the private key initially used. The hash function is inverted and the original data string extracted. The note is then scanned using the same fibre illumination method described above, and if the extracted data IEC-CET/ Page 7

8 matches the scanning observations, the document is genuine. This technique can add a large cost to the manufacturing process of banknotes, but is highly secure and very difficult to illegitimately replicate. It may be excessive for smaller-value currencies, but for largevalue notes, cheques or money orders this method provides a guarantee of the authenticity of the claim. Colour and Feature Analysis Several image-processing software packages now include a secret detection algorithm to prevent banknotes from being manipulated in their applications. Possibly by searching for a specific geometric pattern five 1mm-large circles arranged like a four-pronged star is the primary candidate, visible in Euro notes, pounds sterling notes and older now-obsolete European currency they classify images of banknotes and refuse any further processing. Touch & Feel Inspection & Visual Inspection In spite of such high complications involved with the notes whether genuine or fake it has been largely observed that validity of notes has been checked by the cashiers simultaneously while manual counting. However the human aptitudes of visual & touch feel verification with or without handy tools is having large numbers of natural limitations, not enough to serve the purpose of detection at cash counters, as there have been many invisible, high end & difficult to forge security features on the valid notes which invariably are supposed to be examined accurately while verifying validity on the notes seems to have remain unchecked, requiring highly sophisticated machine to examine the intricacies of security features of the valid notes. 2.2 ESTIMATED EXPENDITURE Although estimating the total expenditure for a project of this nature is a mean task in itself, we try to present the facts in as comprehensive a manner as possible. Following is a list of the hardware and processes used in the project along with their costs. IEC-CET/ Page 8

9 S.No. Name of device Quantity Cost per unit Total cost 1 AT89c LCD DC Motor Capacitor Resistor V Battery Relay ULN2003A Switch Security Features of Indian Banknotes Watermark Security Thread Latent Image Microlettering Intaglio Identification Mark Fluorescence Optically Variable Ink See through Register IEC-CET/ Page 9

10 Watermark The Mahatma Gandhi Series of banknotes contain the Mahatma Gandhi watermark with a light and shade effect and multi-directional lines in the watermark windowthere is also the watermark of the price of currency it s visible in presence of light & glow in uv. Security Thread Rs.1000 notes introduced in October 2000 contain a readable, windowed security thread alternately visible on the obverse with the inscriptions Bharat (in Hindi), 1000 and RBI, but totally embedded on the reverse. The Rs.500 and Rs.100 notes have a security thread with similar visible features and inscription Bharat (in Hindi), and RBI. When held against the light, the security thread on Rs.1000, Rs.500 and Rs.100 can be seen as one continuous line. The Rs.5, Rs.10, Rs.20 and Rs.50 notes contain a readable, fully embedded windowed security thread with the inscription Bharat (in Hindi), and RBI. The security thread appears to the left of the Mahatma's portrait. Notes issued prior to the introduction of the Mahatma Gandhi Series have a plain, non-readable fully embedded security thread. Latent image On the obverse side of Rs.1000, Rs.500, Rs.100, Rs.50 and Rs.20 notes, a vertical band on the right side of the Mahatma Gandhi s portrait contains a latent image showing the respective denominational value in numeral. The latent image is visible only when the note is held horizontally at eye level. Microlettering This feature appears between the vertical band and Mahatma Gandhi portrait. It contains the word RBI in Rs.5 and Rs.10. The notes of Rs.20 and above also contain the denominational value of the notes in microletters. This feature can be seen better under a magnifying glass IEC-CET/ Page 10

11 Intaglio Printing The portrait of Mahatma Gandhi, the Reserve Bank seal, guarantee and promise clause, Ashoka Pillar Emblem on the left, RBI, Governor's signature are printed in intaglio i.e. in raised prints, which can be felt by touch, in Rs.20, Rs.50, Rs.100, Rs.500 and Rs.1000 notes. Identification Mark A special feature in intaglio has been introduced on the left of the watermark window on all notes except Rs.10/- note. This feature is in different shapes for various denominations (Rs. 20-Vertical Rectangle, Rs.50-Square, Rs.100-Triangle, Rs.500-Circle, Rs Diamond) and helps the visually impaired to identify the denomination. Fluorescence Number panels of the notes are printed in fluorescent ink. The notes also have optical fibers. Both can be seen when the notes are exposed to ultra-violet lamp. When there is fake note it s letter and mainly the numeric values all are irregular in shape..for a genuine currency note, the number will be regular and when scrutinized against ultra violet rays, the letter printed with fluorescent ink shine,for fake note number will be comparatively smaller as compared the original one.. Optically Variable Ink This is a new security feature incorporated in the Rs.1000 and Rs.500 notes with revised color scheme introduced in November The numeral 1000 and 500 on the obverse of Rs.1000 and Rs.500 notes respectively is printed in optically variable ink viz., a colour-shifting ink. The colour of the numeral 1000/500 appears green when the note is held flat but would change to blue when the note is held at an angle. See through Register The small floral design printed both on the front (hollow) and back (filled up) of the note in the middle of the vertical band next to the Watermark has an accurate back to back registration. The design will appear as one floral design when seen against the light. IEC-CET/ Page 11

12 2.3 RBI GUIDELINES CONCERNING TO FAKE NOTE DETECTION It has necessitated for the Banks to deploy such authenticators which can support Banks to comply RBI guidelines concerning to fake notes detection. The machine should be 100% accurate in detection of Fake Notes. No fake note should pass as genuine in all case, have been the bottom lines for any machine which functions as authenticator unless the note is of extremely bad quality. The extremely bad quality of note should be rejected by the authenticators with error codes No judgment since the TRUE validity of such notes due to bad quality can not be judged except at forensic lab. Such bad quality of notes generally reflects overlapping of features of genuine & fake note creating, uncertainty of accurate validation even though best authenticators for not permitting deep scanning of such notes. No sorter or Currency Verification Systems (CVS) possesses any separate pocket to separate fake notes except pockets for separating notes of opposite criterion. Sorters just separate the notes which are not matching with the sorting criterion set in the machine. Fit & unfit, oriented and non oriented, face up & face down. There are pockets for collecting opposite criterion notes but no separate pocket have been there for collection of fake notes; although it has been claimed that sorters are best suited for fake note detection. It is wrongly presumed that the opposite criterion pocket collect the fake notes. There is every chance that fake notes matching the various set criterion as may be set in the sorter will pass under such set criterion for many technical reasons. The functions of AUTHENTICATION & SORTING are two mutually exclusive functions carrying wide difference in their respective weight ages and money values involved in the respective operations. Imperfect quality sorting of notes does not attracts loss of value while as passing fake notes as genuine attracts direct loss of value and criminal procedures under I PC and other provisions. Authentication function needs detailed analyses of chemical & physical properties of Bank Note Paper, varied inks, resins, security threads, chemical used in the printing process. IEC-CET/ Page 12

13 It includes checking of all security features on the face of the notes images, emblems, portraits, logos, colours, designs, texts, covert and overt features etc Most accurate authenticity check only is possible if the notes are checked length wise. Authenticators must have capacity to scan the notes length wise back to back, to match with the large number of length wise prints, texts, emblems, portraits, horizontal lines; patterns etc for checking the continuity of such security features while as sorters are checking the notes width wise loosing the continuity of scanning various lengthwise security features. Most of the security features in any currency types are designed length wise and hence without lengthwise scanning of the notes scientifically difficult to obtained 100% accuracy during the detection of fake notes. Most of the note counting /sorting machines in the international market have failed to offer 100% authentication accuracy for not having facility to check notes length wise and scanning the notes width wise, as also have been dependent on light & image based technology scanning the notes width wise, which have been scientifically unfeasible. It is scientifically impossible to check highly complicated, inter related security aspects in the notes with inter related large numbers of permutations and combinations of each and every elements that constitutes a Genuine notes at the high speeds of sorters which sorts the notes with Image & light sensor based technology. Speed kills the authentication accuracy by note getting scientific time to pip into the minute differences between genuine and fabricated security features. At the most can detect very poorly fabricated notes but not skilfully fabricated fake notes being pumped in our country by other state supports that have been having total infrastructures and notes printing technology Authentication can only be carried out with high end light cum Image cum digital technology. The fastest fake note detector that is available in the international market takes minimum 3 seconds for thorough checking of notes. Such machines mostly have facility for single note manual feedings. IEC-CET/ Page 13

14 3. MATERIALS AND METHODOLOGY 3.1 METHODOLOGY The whole system is controlled by the microcontroller (AT89c51). The currency counting machine or CCM.The CCM works on the principle on the breadth of the bundle of currency and there in an roller which has rods in an continuous pattern and the roller moves these rods with a particular speed and these rollers moves on the bundle of the currency and just move out the single currency one by one at a constant and high speed and there is an transducers which detect that how many single currency has passed out in front of it. FIG- 4- Complete circuit diagram. IEC-CET/ Page 14

15 3.2 COMPONENTS/PARTS USED: AT89C51 LCD DC motors (3) Drill Motor Relays Transformer Diodes Resistors Capacitors A brief description of these components follows. AT89C51 microcontroller The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4 Kbytes of Flash Programmable and Erasable Read Only Memory (PEROM). The device is manufactured using Atmel s high density non-volatile memory technology and is compatible with the industry standard MCS-51Ô 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, the Atmel AT89C51 is a powerful microcomputer which provides a highly flexible and cost effective solution to many embedded control applications. The Intel MCS-51 (commonly referred to as 8051) is a Harvard architecture, single chip microcontroller (µc) series which was developed by Intel in 1980 for use in embedded systems. Intel's original versions were popular in the 1980s and early 1990s. While Intel no longer manufactures the MCS-51, binary compatible derivatives remain popular today. In addition to these physical devices, several companies also offer MCS-51 derivatives as IP cores for use in FPGAs or ASICs designs. IEC-CET/ Page 15

16 Intel's original MCS-51 family was developed using NMOS technology, but later versions, identified by a letter C in their name (e.g., 80C51) used CMOS technology and consumed less power than their NMOS predecessors. This made them more suitable for batterypowered devices. FIG- 5 AT89C51 microcontroller. AT89C51 Important features and applications of 8051 micro architecture. The 8051 architecture provides many functions (CPU, RAM, ROM, I/O, interrupt logic, timer, etc.) in a single package 8-bit ALU, Accumulator and 8-bit Registers; hence it is an 8-bit microcontroller 8-bit data bus It can access 8 bits of data in one operation 16-bit address bus It can access 216 memory locations 64 KB (65536 locations) each of RAM and ROM On-chip RAM 128 bytes (data memory) On-chip ROM 4 kbyte (program memory) Four byte bi-directional input/output port UART (serial port) Two 16-bit Counter/timers Two-level interrupt priority Power saving mode (on some derivatives) One particularly useful feature of the 8051 core was the inclusion of a boolean processing engine which allows bit-level boolean logic operations to be carried out directly and IEC-CET/ Page 16

17 efficiently on select internal registers and select RAM locations. This advantageous feature helped cement the 8051's popularity in industrial control applications because it reduced code size by as much as 30%. Another valued feature is the including of four bank selectable working register sets which greatly reduce the amount of time required to complete an interrupt service routine. With a single instruction the 8051 can switch register banks as opposed to the time consuming task of transferring the critical registers to the stack or designated RAM locations. These registers also allowed the 8051 to quickly perform a context switch which is essential for time sensitive real-time applications.the MCS-51 UARTs make it simple to use the chip as a serial communications interface. External pins can be configured to connect to internal shift registers in a variety of ways, and the internal timers can also be used, allowing serial communications in a number of modes, both synchronous and asynchronous. Some modes allow communications with no external components. A mode compatible with an RS-485 multi-point communications environment is achievable, but the 8051's real strength is fitting in with existing ad-hoc protocols (e.g., when controlling serial-controlled devices).once a UART, and a timer if necessary, have been configured, the programmer needs only to write a simple interrupt routine to refill the send shift register whenever the last bit is shifted out by the UART and/or empty the full receive shift register (copy the data somewhere else). The main program then performs serial reads and writes simply by reading and writing 8-bit data to stacks. MCS-51 based microcontrollers typically include one or two UARTs, two or three timers, 128 or 256 bytes of internal data RAM (16 bytes of which are bit-addressable), up to 128 bytes of I/O, 512 bytes to 64 kb of internal program memory, and sometimes a quantity of extended data RAM (ERAM) located in the external data space. The original 8051 core ran at 12 clock cycles per machine cycle, with most instructions executing in one or two machine cycles. With a 12 MHz clock frequency, the 8051 could thus execute 1 million one-cycle instructions per second or 500,000 two-cycle instructions per second. Enhanced 8051 cores are now commonly used which run at six, four, two, or even one clock per machine cycle, and have clock frequencies of up to 100 MHz, and are thus IEC-CET/ Page 17

18 capable of an even greater number of instructions per second. All SILabs, some Dallas and a few Atmel devices have single cycle cores.features of the modern 8051 include built-in reset timers with brown-out detection, on-chip oscillators, self-programmable Flash ROM program memory, built-in external RAM, extra internal program storage, bootloader code in ROM, EEPROM non-volatile data storage, I²C, SPI, and USB host interfaces, CAN or LIN bus, PWM generators, analog comparators, A/D and D/A converters, RTCs, extra counters and timers, in-circuit debugging facilities, more interrupt sources, and extra power saving modes.in many engineering schools the 8051 microcontroller is used in introductory microcontroller courses. Memory architecture The MCS-51 has four distinct types of memory internal RAM, special function registers, program memory, and external data memory. Internal RAM (IRAM) is located from address 0 to address 0xFF. IRAM from 0x00 to 0x7F can be accessed directly, and the bytes from 0x20 to 0x2F are also bit-addressable. IRAM from 0x80 to 0xFF must be accessed indirectly, using syntax, with the address to access loaded in R0 or R1. Special function registers (SFR) are located from address 0x80 to 0xFF, and are accessed directly using the same instructions as for the lower half of IRAM. Some of the SFR's are also bit-addressable. Program memory (PMEM, though less common in usage than IRAM and XRAM) is located starting at address 0. It may be on- or off-chip, depending on the particular model of chip being used. Program memory is read-only, though some variants of the 8051 use on-chip flash memory and provide a method of re-programming the memory in-system or in-application. Aside from storing code, program memory can also store tables of constants that can be accessed by MOVC using the 16-bit special function register DPTR. External data memory (XRAM) also starts at address 0. It can also be on- or off-chip; what makes it "external" is that it must be accessed using the MOVX (Move external) instruction. Many variants of the 8051 include the standard 256 bytes of IRAM plus a few KB of XRAM on the chip. If more XRAM is required by an application, the internal XRAM can be disabled, and all MOVX instructions will fetch from the external bus. IEC-CET/ Page 18

19 FIG- 6 INTEL 8051 block diagram. Relay A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays were used extensively in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protective relays". Relay is a common, simple application of electromagnetism. It uses an electromagnet made from an iron rod wound with hundreds of fine copper wire. When electricity is IEC-CET/ Page 19

20 applied to the wire, the rod becomes magnetic. A movable contact arm above the rod is then pulled toward the rod until it closes a switch contact. When the electricity is removed, a small spring pulls the contract arm away from the rod until it closes a second switch contact. By means of relay, a current circuit can be broken or closed in one circuit as a result of a current in another circuit. Basic design and operation Small "cradle" relay often used in electronics. The "cradle" term refers to the shape of the relay's armature. A simple electromagnetic relay consists of a coil of wire wrapped around a soft iron core, an iron yoke which provides a low reluctance path for magnetic flux, a movable iron armature, and one or more sets of contacts (there are two in the relay pictured). The armature is hinged to the yoke and mechanically linked to one or more sets of moving contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB. When an electric current is passed through the coil it generates a magnetic field that activates the armature, and the consequent movement of the movable contact(s) either makes or breaks (depending upon construction) a connection with a fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low-voltage application this reduces noise; in a high voltage or current application it reduces arcing. When the coil is energized with direct current, a diode is often placed across the coil to dissipate the energy from the collapsing magnetic field at deactivation, which would IEC-CET/ Page 20

21 otherwise generate a voltage spike dangerous to semiconductor circuit components. Some automotive relays include a diode inside the relay case. Alternatively, a contact protection network consisting of a capacitor and resistor in series (snubber circuit) may absorb the surge. If the coil is designed to be energized with alternating current (AC), a small copper "shading ring" can be crimped to the end of the solenoid, creating a small out-of-phase current which increases the minimum pull on the armature during the AC cycle.[1]a solid-state relay uses a thyristor or other solid-state switching device, activated by the control signal, to switch the controlled load, instead of a solenoid. An optocoupler (a light-emitting diode (LED) coupled with a photo transistor) can be used to isolate control and controlled circuits. FIG- 7 Relay switch Relay switch Crystal Oscillators 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 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 became known as "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 IEC-CET/ Page 21

22 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. 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 HF and higher frequencies without resorting to some sort of crystal control. 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. 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 IEC-CET/ Page 22

23 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 temperature-controlled container, called a crystal oven, and can also be mounted on shock absorbers to prevent perturbation by external mechanical vibrations. Crystal structures and materials The most common material for oscillator crystals is quartz. At the beginning of the technology, natural quartz crystals were used; now synthetic crystalline quartz grown by hydrothermal synthesis is predominant due to higher purity, lower cost, and more convenient handling. One of the few remaining uses of natural crystals is for pressure transducers in deep wells. During World War II and for some time afterwards, natural quartz was considered a strategic material by the USA. Large crystals were imported from Brazil. Raw "lascas", the source material quartz for hydrothermal synthesis, are imported to USA or mined locally by Coleman Quartz. The average value of as-grown synthetic quartz in 1994 was USD60/kg. Two types of quartz crystals exist: left-handed and right-handed, differing in the optical rotation but identical in other physical properties. Both left and right-handed crystals can be used for oscillators, if the cut angle is correct. In manufacture, right-handed quartz is generally used. The SiO4 tetrahedrons form parallel helixes; the direction of twist of the helix determines the left- or right-hand orientation. The helixes are aligned along the z-axis and merged together, sharing atoms. The mass of the helixes forms a mesh of small and large channels parallel to the z-axis; the large ones are large enough to allow some mobility of smaller ions and molecules through the crystal. Quartz exists in several phases. At 573 C at 1 atmosphere (and at higher temperatures and higher pressures) the α-quartz undergoes quartz inversion, transforms reversibly to β- quartz. The reverse process however is not entirely homogeneous and crystal twinning occurs. Care has to be taken during manufacture and processing to avoid the phase IEC-CET/ Page 23

24 transformation. Other phases, e.g. the higher-temperature phases tridymite and cristobalite, are not significant for oscillators. All quartz oscillator crystals are the α-quartz type. Infrared spectrophotometry is used as one of the methods for measuring the quality of the grown crystals. The wavenumbers 3585, 3500 and 3410 cm 1 are commonly used. The measured value is based on the absorption bands of the OH radical and the infrared Q value is calculated. The electronic grade crystals, grade C, have Q of 1.8 million or above; the premium grade B crystals have Q of 2.2 million, and special premium grade A crystals have Q of 3.0 million. The Q value is calculated only for the z region; crystals containing other regions can be adversely affected. Another quality indicator is the etch channel density; when the crystal is etched, tubular channels are created along linear defects. For processing involving etching, e.g. the wristwatch tuning fork crystals, low etch channel density is desirable. The etch channel density for swept quartz is about and significantly more for unswept quartz. Presence of etch channels and etch pits degrades the resonator's Q and introduces nonlinearities. Quartz crystals can be grown for specific purposes. Crystals for AT-cut are the most common in mass production of oscillator materials; the shape and dimensions are optimized for high yield of the required wafers. High-purity quartz crystals are grown with especially low content of aluminium, alkali metal and other impurities and minimal defects; the low amount of alkali metals provides increased resistance to ionizing radiation. Crystals for wrist watches, for cutting the tuning fork Hz crystals, are grown with very low etch channel density. Crystals for SAW devices are grown as flat; with large X-size seed with low etch channel density. Special high-q crystals, for use in highly stable oscillators, are grown at constant slow speed and have constant low infrared absorption along the entire Z axis. Crystals can be grown as Y-bar, with a seed crystal in bar shape and elongated along the Y axis, or as Z- plate, grown from a plate seed with Y-axis direction length and X-axis width. The region around the seed crystal contains a large number of crystal defects and should not be used for the wafers.crystals grow anisotropically; the growth along the Z axis is up to 3 times faster than along the X axis. The growth direction and rate also influences the rate of uptake of impurities. Y-bar crystals, or Z-plate crystals with long Y axis, have four growth IEC-CET/ Page 24

25 regions usually called +X, -X, Z, and S. The distribution of impurities during growth is uneven; different growth areas contain different level of contaminants. The z regions are the purest, the small occasionally present s regions are less pure, the +x region is yet less pure, and the -x region has the highest level of impurities. The impurities have negative impact on radiation hardness, susceptibility to twinning, filter loss, and long and short term stability of the crystals. Different-cut seeds in different orientations may provide other kinds of growth regions. The growth speed of the -x direction is slowest due to the effect of adsorption of water molecules on the crystal surface; aluminium impurities suppress growth in two other directions. The content of aluminium is lowest in z region, higher in +x, yet higher in -x, and highest in s; the size of s regions also grows with increased amount of aluminium present. The content of hydrogen is lowest in z region, higher in +x region, yet higher in s region, and highest in -x. Aluminium inclusions transform to colour centres with a gamma ray irradiation, causing darkening of the crystal proportional to the dose and level of impurities; presence of regions with different darkness reveals the different growth regions. The dominant type of defect of concern in quartz crystals is the substitution of Al(III) for Si(IV) atom in the crystal lattice. The aluminium ion has an associated interstitial charge compensator present nearby, which can be a H+ ion (attached to the nearby oxygen and forming a hydroxyl group, called Al-OH defect), Li+ ion, Na+ ion, K+ ion (less common), or an electron hole trapped in a nearby oxygen atom orbital. The composition of the growth solution, whether it is based on lithium or sodium alkali compounds, determines the charge compensating ions for the aluminium defects. The ion impurities are of concern as they are not firmly bound and can migrate through the crystal, altering the local lattice elasticity and the resonant frequency of the crystal. Other common impurities of concern are e.g. iron(iii) (interstitial), fluorine, boron(iii), phosphorus(v) (substitution), titanium(iv) (substitution, universally present in magmatic quartz, less common in hydrothermal quartz), and germanium(iv) (substitution). Sodium and iron ions can cause inclusions of aconite and elemeusite crystals. Inclusions of water may be present in fast-grown crystals; interstitial water molecules are abundant near the crystal seed. Another defect of importance is the hydrogen containing growth defect, IEC-CET/ Page 25

26 when instead of a Si-O-Si structure a pair of Si-OH HO-Si groups is formed; essentially a hydrolyzed bond. Fast-grown crystals contain more hydrogen defects than slow-grown ones. These growth defects source as supply of hydrogen ions for radiation-induced processes and forming Al-OH defects. Germanium impurities tend to trap electrons created during irradiation; the alkali metal cations then migrate towards the negatively charged center and form a stabilizing complex. Matrix defects can be also present; oxygen vacancies, silicon vacancies (usually compensated by 4 hydrogens or 3 hydrogens and a hole), peroxy groups, etc. Some of the defects produce localized levels in the forbidden band, serving as charge traps; Al(III) and B(III) typically serve as hole traps while electron vacancies, titanium, germanium, and phosphorus atoms serve as electron traps. The trapped charge carriers can be released by heating; their recombination is the cause of thermoluminescence. The mobility of interstitial ions depends strongly on temperature. Hydrogen ions are mobile down to 10 K, but alkali metal ions become mobile only at temperatures around and above 200 K. The hydroxyl defects can be measured by near-infrared spectroscopy. The trapped holes can be measured by electron spin resonance. The Al-Na+ defects show as an acoustic loss peak due to their stress-induced motion; the Al-Li+ defects do not form a potential well so are not detectable this way. Some of the radiation induced defects during their thermal annealing produce thermo luminescence; defects related to aluminium, titanium, and germanium can be distinguished. Swept crystals are crystals that have undergone a solid-state electro diffusion purification process. Sweeping involves heating the crystal above 500 C in a hydrogen-free atmosphere, and the voltage gradient of at least 1 kilovolt/cm, for several (usually over 12) hours. The migration of impurities and the gradual replacement of alkali metal ions with hydrogen (when swept in air) or electron holes (when swept in vacuum) causes a weak electric current through the crystal; decay of this current to a constant value signals end of the process. The crystal is then left to cool, while the electric field is maintained. The impurities are concentrated at the cathode region of the crystal, which is cut off afterwards and discarded. Swept crystals have increased resistance to radiation, as the dose effects are dependent on the level of alkali metal impurities; they are suitable for use in devices exposed to ionizing radiation, e.g. for nuclear and space technology. Sweeping under IEC-CET/ Page 26

27 vacuum at higher temperatures and higher field strengths yields yet more radiation-hard crystals. The level and character of impurities can be measured by infrared spectroscopy. Quartz can be swept in both α and β phase; sweeping in β phase is faster, but the phase transition may induce twinning. Twinning can be mitigated by subjecting the crystal to compression stress in the X direction, or an AC or DC electric field along the X axis while the crystal cools through the phase transformation temperature region. Sweeping can be also used to introduce one kind of an impurity into the crystal. Lithium, sodium, and hydrogen swept crystals are used for e.g. studying quartz behavior.very small crystals for high fundamental mode frequencies can be manufactured by photolithography. Crystals can be adjusted to exact frequency by laser trimming. A technique used in the world of amateur radio for slight decrease of the crystal frequency may be achieved by exposing crystals with silver electrodes to vapours of iodine, which causes a slight mass increase on the surface by forming a thin layer of silver iodide; such crystals however had problematic long-term stability. Another method commonly used is electrochemical increase or decrease of silver electrode thickness by submerging resonator in lapis solved in water, citric acid in water, or water with salt, and using resonator as one electrode, and small silver electrode as another. By choosing direction of current, one can either increase or decrease mass of electrodes. Details were published in "Radio" magazine (3/1978) by UB5LEV.Raising frequency by scratching off parts of the electrodes is advised against, as this may damage the crystal and lower its Q factor. Capacitor trimmers can be also used for frequency adjustment of the oscillator circuit. Some other piezoelectric materials than quartz can be employed; e.g. single crystals of lithium tantalite, lithium niobate, lithium borate, berlinite, gallium arsenide, lithium tetraborate, aluminium phosphate, bismuth germanium oxide, polycrystalline zirconium titanate ceramics, high-alumina ceramics, silicon-zinc oxide composite, or dipotassium tartrate; some materials may be more suitable for specific applications. An oscillator crystal can be also manufactured by depositing the resonator material on the silicon chip surface. Crystals of gallium phosphate, langasite, langanite and langanate are about 10 IEC-CET/ Page 27

28 times more pullable than the corresponding quartz crystals, and are used in some VCXO oscillators. Resistors Resistors (R), are the most commonly used of all electronic components, to the point where they are almost taken for granted. There are many different resistor types available with their principal job being to "resist" the flow of current through an electrical circuit, or to act as voltage droppers or voltage dividers. They are "Passive Devices", that is they contain no source of power or amplification but only attenuate or reduce the voltage signal passing through them. When used in DC circuits the voltage drop produced is measured across their terminals as the circuit current flows through them while in AC circuits the voltage and current are both in-phase producing 0 o phase shift. Resistors produce a voltage drop across themselves when an electrical current flows through them because they obey Ohm's Law, and different values of resistance produces different values of current or voltage. This can be very useful in Electronic circuits by controlling or reducing either the current flow or voltage produced across them. There are many different Resistor Types and they are produced in a variety of forms because their particular characteristics and accuracy suit certain areas of application, such as High Stability, High Voltage, High Current etc., or are used as general purpose resistors where their characteristics are less of a problem. Some of the common characteristics associated with the humble resistor are; Temperature Coefficient, Voltage Coefficient, Noise, Frequency Response, Power as well as Temperature Rating, Physical Size and Reliability. In all Electrical and Electronic circuit diagrams and schematics, the most commonly used resistor symbol is that of a "zigzag" type line with the value of its resistance given in Ohms, Ω. Capacitor Just like the Resistor, the Capacitor or sometimes referred to as a Condenser is a passive device, and one which stores energy in the form of an electrostatic field which produces a potential (Static Voltage) across its plates. In its basic form a capacitor consists of two parallel conductive plates that are not connected but are electrically separated either by air IEC-CET/ Page 28

29 or by an insulating material called the Dielectric. When a voltage is applied to these plates, a current flows charging up the plates with electrons giving one plate a positive charge and the other plate an equal and opposite negative charge. This flow of electrons to the plates is known as the Charging Current and continues to flow until the voltage across the plates (and hence the capacitor) is equal to the applied voltage Vc. At this point the capacitor is said to be fully charged and this is illustrated below. Capacitor Construction FIG- 8 :Capacitor construction The parallel plate capacitor is the simplest form of capacitor and its capacitance value is fixed by the equal area of the plates and the distance or separation between them. Altering any two of these values alters the the value of its capacitance and this forms the basis of operation of the variable capacitors. Also, because capacitors store the energy of the electrons in the form of an electrical charge on the plates the larger the plates and/or smaller their separation the greater will be the charge that the capacitor holds for any given voltage across its plates. Liquid Crystal Display A liquid crystal display (LCD) is a flat panel display, electronic visual display, or video display that uses the light modulating properties of liquid crystals (LCs). LCs do not emit light directly. IEC-CET/ Page 29

30 FIG- 9 A general purpose alphanumeric LCD, with two lines of 16 characters. LCDs are used in a wide range of applications, including computer monitors, television, instrument panels, aircraft cockpit displays, signage, etc. They are common in consumer devices such as video players, gaming devices, clocks, watches, calculators, and telephones. LCDs have replaced cathode ray tube (CRT) displays in most applications. They are available in a wider range of screen sizes than CRT and plasma displays, and since they do not use phosphors, they cannot suffer image burn-in. LCDs are, however, susceptible to image persistence. LCDs are more energy efficient and offer safer disposal than CRTs. Its low electrical power consumption enables it to be used in battery-powered electronic equipment. It is an electronically modulated optical device made up of any number of segments filled with liquid crystals and arrayed in front of a light source (backlight) or reflector to produce images in color or monochrome. The most flexible ones use an array of small pixels. The earliest discovery leading to the development of LCD technology, the discovery of liquid crystals, dates from By 2008, worldwide sales of televisions with LCD screens had surpassed the sale of CRT units. Overview IEC-CET/ Page 30

31 Each pixel of an LCD typically consists of a layer of molecules aligned between two transparent electrodes, and two polarizing filters, the axes of transmission of which are (in most of the cases) perpendicular to each other. With no actual liquid crystal between the polarizing filters, light passing through the first filter would be blocked by the second (crossed) polarizer. The surface of the electrodes that are in contact with the liquid crystal material are treated so as to align the liquid crystal molecules in a particular direction. This treatment typically consists of a thin polymer layer that is unidirectionally rubbed using, for example, a cloth. The direction of the liquid crystal alignment is then defined by the direction of rubbing. Electrodes are made of the transparent conductor Indium Tin Oxide (ITO). The Liquid Crystal Display is intrinsically a passive device, it is a simple light valve. The managing and control of the data to be displayed is performed by one or more circuits commonly denoted as LCD drivers. Before applying an electric field, the orientation of the liquid crystal molecules is determined by the alignment at the surfaces of electrodes. In a twisted nematic device (still the most common liquid crystal device), the surface alignment directions at the two electrodes are perpendicular to each other, and so the molecules arrange themselves in a helical structure, or twist. This induces the rotation of the polarization of the incident light, and the device appears grey. If the applied voltage is large enough, the liquid crystal molecules in the center of the layer are almost completely untwisted and the polarization of the incident light is not rotated as it passes through the liquid crystal layer. This light will then be mainly polarized perpendicular to the second filter, and thus be blocked and the pixel will appear black. By controlling the voltage applied across the liquid crystal layer in each pixel, light can be allowed to pass through in varying amounts thus constituting different levels of gray. The optical effect of a twisted nematic device in the voltage-on state is far less dependent on variations in the device thickness than that in the voltage-off state. Because of this, these devices are usually operated between crossed polarizers such that they appear bright with no voltage (the eye is much more sensitive to variations in the dark state than the bright state). These devices can also be operated between parallel polarizers, in which case IEC-CET/ Page 31

32 the bright and dark states are reversed. The voltage-off dark state in this configuration appears blotchy, however, because of small variations of thickness across the device. Both the liquid crystal material and the alignment layer material contain ionic compounds. If an electric field of one particular polarity is applied for a long period of time, this ionic material is attracted to the surfaces and degrades the device performance. This is avoided either by applying an alternating current or by reversing the polarity of the electric field as the device is addressed (the response of the liquid crystal layer is identical, regardless of the polarity of the applied field). Displays for a small number of individual digits and/or fixed symbols (as in digital watches, pocket calculators etc.) can be implemented with independent electrodes for each segment. In contrast full alphanumeric and/or variable graphics displays are usually implemented with pixels arranged as a matrix consisting of electrically connected rows on one side of the LC layer and columns on the other side, which makes it possible to address each pixel at the intersections. The general method of matrix addressing consists of sequentially addressing one side of the matrix, for example by selecting the rows one-byone and applying the picture information on the other side at the columns row-by-row. For details on the various matrix addressing schemes see Passive-matrix and active-matrix addressed LCDs. Voltage Regulator The 78xx (sometimes LM78xx) is a family of self-contained fixed linear voltage regulator integrated circuits. The 78xx family is commonly used in electronic circuits requiring a regulated power supply due to their ease-of-use and low cost. For ICs within the family, the xx is replaced with two digits, indicating the output voltage (for example, the 7805 has a 5 volt output, while the 7812 produces 12 volts). The 78xx line are positive voltage regulators: they produce a voltage that is positive relative to a common ground. There is a related line of 79xx devices which are complementary negative voltage regulators. 78xx and 79xx ICs can be used in combination to provide positive and negative supply voltages in the same circuit. IEC-CET/ Page 32

33 FIG-10 Voltage regulator LM 78xx 78xx ICs have three terminals and are commonly found in the TO220 form factor, although smaller surface-mount and larger TO3 packages are available. These devices support an input voltage anywhere from a couple of volts over the intended output voltage, up to a maximum of 35 or 40 volts, and typically provide 1 or 1.5 amperes of current (though smaller or larger packages may have a lower or higher current rating). Advantages 78xx series ICs do not require additional components to provide a constant, regulated source of power, making them easy to use, as well as economical and efficient uses of space. Other voltage regulators may require additional components to set the output voltage level, or to assist in the regulation process. Some other designs (such as a switched-mode power supply) may need substantial engineering expertise to implement. 78xx series ICs have built-in protection against a circuit drawing too much power. They have protection against overheating and short-circuits, making them quite robust in most applications. In some cases, the current-limiting features of the 78xx devices can provide protection not only for the 78xx itself, but also for other parts of the circuit.78xx ICs are easy to use and handle but these cannot give a altering voltage required so Lm317 series of ICs are available to obtain a voltage output from 1.25 volts to 37 volts. IEC-CET/ Page 33

34 Disadvantages The input voltage must always be higher than the output voltage by some minimum amount (typically 2 volts). This can make these devices unsuitable for powering some devices from certain types of power sources (for example, powering a circuit that requires 5 volts using 6-volt batteries will not work using a 7805). As they are based on a linear regulator design, the input current required is always the same as the output current. As the input voltage must always be higher than the output voltage, this means that the total power (voltage multiplied by current) going into the 78xx will be more than the output power provided. The extra input power is dissipated as heat. This means both that for some applications an adequate heatsink must be provided, and also that a (often substantial) portion of the input power is wasted during the process, rendering them less efficient than some other types of power supplies. When the input voltage is significantly higher than the regulated output voltage (for example, powering a 7805 using a 24 volt power source), this inefficiency can be a significant issue.even in larger packages, 78xx integrated circuits cannot supply as much power as many designs which use discrete components, and are generally inappropriate for applications requiring more than a few amperes of current. Transformer A transformer is a device 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. IEC-CET/ Page 34

35 FIG- 11. Transformer windings If a load is connected to the secondary, current will flow in the secondary 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:by appropriate selection of the ratio of turns, a transformer thus enables an alternating current (AC) voltage to be "stepped up" by making Ns greater than Np, or "stepped down" by making Ns less than Np.In the vast majority of transformers, the windings are coils wound around a ferromagnetic core, air-core transformers being a notable exception. Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate on the same basic principles, although the range of designs is wide. While new technologies have eliminated the need for transformers in some electronic circuits, transformers are still found in nearly all electronic devices designed for household ("mains") voltage. Transformers are essential for high-voltage electric power transmission, which makes long-distance transmission economically practical. A transformer is an electrical device that transfers energy from one circuit to another by magnetic coupling with no moving parts. A transformer comprises two or more coupled windings, or a single tapped winding and, in most cases, a magnetic core to concentrate magnetic flux. A changing current in one winding creates a time-varying magnetic flux in the core, which induces a voltage in the other windings. Michael Faraday built the first IEC-CET/ Page 35

36 transformer, although he used it only to demonstrate the principle of electromagnetic induction and did not foresee the use to which it would eventually be put. FIG- 12 Transformer core DC Motor A DC motor is an electric motor that runs on direct current (DC) electricity. DC motors were used to run machinery, often eliminating the need for a local steam engine or internal combustion engine. DC motors can operate directly from rechargeable batteries, providing the motive power for the first electric vehicles. Today DC motors are still found in applications as small as toys and disk drives, or in large sizes to operate steel rolling mills and paper machines. Modern DC motors are nearly always operated in conjunction with power electronic devices. Two important performance parameters of DC motors are the motor constants, Kv and Km. IEC-CET/ Page 36

37 FIG-13DC motor DC motor When a current passes through the coil wound around a soft iron core, the side of the positive pole is acted upon by an upwards force, while the other side is acted upon by a downward force. According to Fleming's left hand rule, the forces cause a turning effect on the coil, making it rotate. To make the motor rotate in a constant direction, "direct current" commutators make the current reverse in direction every half a cycle (in a two-pole motor) thus causing the motor to continue to rotate in the same direction. A problem with the motor shown above is that when the plane of the coil is parallel to the magnetic field i.e. when the rotor poles are 90 degrees from the stator poles the torque is zero. In the pictures above, this occurs when the core of the coil is horizontal the position it is just about to reach in the last picture on the right. The motor would not be able to start in this position. However, once it was started, it would continue to rotate through this position by momentum. There is a second problem with this simple pole design. At the zero-torque position, both commutator brushes are touching (bridging) both commutator plates, resulting in a shortcircuit. The power leads are shorted together through the commutator plates, and the coil is IEC-CET/ Page 37

38 also short-circuited through both brushes (the coil is shorted twice, once through each brush independently). Note that this problem is independent of the non-starting problem above; even if there were a high current in the coil at this position, there would still be zero torque. The problem here is that this short uselessly consumes power without producing any motion (nor even any coil current.) In a low-current battery-powered demonstration this short-circuiting is generally not considered harmful. However, if a two-pole motor were designed to do actual work with several hundred watts of power output, this shorting could result in severe commutator overheating, brush damage, and potential welding of the brushes if they were metallic to the commutator. Carbon brushes, which are often used, would not weld. In any case, a short like this is very wasteful, drains batteries rapidly and, at a minimum, requires power supply components to be designed to much higher standards than would be needed just to run the motor without the shorting. The inside of an electric DC motor. One simple solution is to put a gap between the commutator plates which is wider than the ends of the brushes. This increases the zero-torque range of angular positions but eliminates the shorting problem; if the motor is started spinning by an outside force it will continue spinning. With this modification, it can also be effectively turned off simply by stalling (stopping) it in a position in the zero-torque (i.e. commutator non-contacting) angle range. This design is sometimes seen in homebuilt hobby motors, e.g. for science fairs and such designs can be found in some published science project books. A clear downside of this simple solution is that the motor now coasts through a substantial arc of rotation twice per revolution and the torque is pulsed. This may work for electric fans or to keep a flywheel spinning but there are many applications, even where starting and stopping are not necessary, for which it is completely inadequate, such as driving the capstan of a tape transport, or any instance where to speed up and slow down often and quickly is a requirement. Another disadvantage is that, since the coils have a measure of self inductance, current flowing in them cannot suddenly stop. The current attempts to jump the opening gap between the commutator segment and the brush, causing arcing. Even for fans and flywheels, the clear weaknesses remaining in this design especially that it is not self-starting from all positions make it impractical for working use, especially considering the better alternatives that exist. Unlike the demonstration motor IEC-CET/ Page 38

39 above, DC motors are commonly designed with more than two poles, are able to start from any position, and do not have any position where current can flow without producing electromotive power by passing through some coil. Many common small brushed DC motors used in toys and small consumer appliances, the simplest mass-produced DC motors to be found, have three-pole armatures. The brushes can now bridge two adjacent commutator segments without causing a short circuit. These three-pole armatures also have the advantage that current from the brushes either flows through two coils in series or through just one coil. Starting with the current in an individual coil at half its nominal value (as a result of flowing through two coils in series), it rises to its nominal value and then falls to half this value. The sequence then continues with current in the reverse direction. This results in a closer step-wise approximation to the ideal sinusoidal coil current, producing a more even torque than the two-pole motor where the current in each coil is closer to a square wave. Since current changes are half those of a comparable twopole motor, arcing at the brushes is consequently less. If the shaft of a DC motor is turned by an external force, the motor will act like a generator and produce an Electromotive force (EMF). During normal operation, the spinning of the motor produces a voltage, known as the counter-emf (CEMF) or back EMF, because it opposes the applied voltage on the motor. The back EMF is the reason that the motor when free-running does not appear to have the same low electrical resistance as the wire contained in its winding. This is the same EMF that is produced when the motor is used as a generator (for example when an electrical load, such as a light bulb, is placed across the terminals of the motor and the motor shaft is driven with an external torque). Therefore, the total voltage drop across a motor consists of the CEMF voltage drop, and the parasitic voltage drop resulting from the internal resistance of the armature's windings. Speed control Generally, the rotational speed of a DC motor is proportional to the voltage applied to it, and the torque is proportional to the current. Speed control can be achieved by variable battery tappings, variable supply voltage, resistors or electronic controls. The direction of a wound field DC motor can be changed by reversing either the field or armature connections but not both. This is commonly done with a special set of contactors (direction contactors).the effective voltage can be varied by inserting a series resistor or by an IEC-CET/ Page 39

40 electronically controlled switching device made of thyristors, transistors, or, formerly, mercury arc rectifiers. In a circuit known as a chopper, the average voltage applied to the motor is varied by switching the supply voltage very rapidly. As the "on" to "off" ratio is varied to alter the average applied voltage, the speed of the motor varies. The percentage "on" time multiplied by the supply voltage gives the average voltage applied to the motor. Therefore, with a 100 V supply and a 25% "on" time, the average voltage at the motor will be 25 V. During the "off" time, the armature's inductance causes the current to continue through a diode called a "flyback diode", in parallel with the motor. At this point in the cycle, the supply current will be zero, and therefore the average motor current will always be higher than the supply current unless the percentage "on" time is 100%. At 100% "on" time, the supply and motor current are equal. The rapid switching wastes less energy than series resistors. This method is also called pulse-width modulation (PWM) and is often controlled by a microprocessor. An output filter is sometimes installed to smooth the average voltage applied to the motor and reduce motor noise. Since the series-wound DC motor develops its highest torque at low speed, it is often used in traction applications such as electric locomotives, and trams. Another application is starter motors for petrol and small diesel engines. Series motors must never be used in applications where the drive can fail (such as belt drives). As the motor accelerates, the armature (and hence field) current reduces. The reduction in field causes the motor to speed up until it destroys itself. This can also be a problem with railway motors in the event of a loss of adhesion since, unless quickly brought under control, the motors can reach speeds far higher than they would do under normal circumstances. This can not only cause problems for the motors themselves and the gears, but due to the differential speed between the rails and the wheels it can also cause serious damage to the rails and wheel treads as they heat and cool rapidly. Field weakening is used in some electronic controls to increase the top speed of an electric vehicle. The simplest form uses a contactor and field-weakening resistor; the electronic control monitors the motor current and switches the field weakening resistor into circuit when the motor current reduces below a preset value (this will be when the motor is at its full design speed). Once the resistor is in circuit, the motor will increase speed above its normal speed IEC-CET/ Page 40

41 at its rated voltage. When motor current increases, the control will disconnect the resistor and low speed torque is made available. One interesting method of speed control of a DC motor is the Ward Leonard control. It is a method of controlling a DC motor (usually a shunt or compound wound) and was developed as a method of providing a speed-controlled motor from an AC supply, though it is not without its advantages in DC schemes. The AC supply is used to drive an AC motor, usually an induction motor that drives a DC generator or dynamo. The DC output from the armature is directly connected to the armature of the DC motor (sometimes but not always of identical construction). The shunt field windings of both DC machines are independently excited through variable resistors. Extremely good speed control from standstill to full speed, and consistent torque, can be obtained by varying the generator and/or motor field current. This method of control was the de facto method from its development until it was superseded by solid state thyristor systems. It found service in almost any environment where good speed control was required, from passenger lifts through to large mine pit head winding gear and even industrial process machinery and electric cranes. Its principal disadvantage was that three machines were required to implement a scheme (five in very large installations, as the DC machines were often duplicated and controlled by a tandem variable resistor). In many applications, the motor-generator set was often left permanently running, to avoid the delays that would otherwise be caused by starting it up as required. Although electronic (thyristor) controllers have replaced most small to medium Ward-Leonard systems, some very large ones (thousands of horsepower) remain in service. The field currents are much lower than the armature currents, allowing a moderate sized thyristor unit to control a much larger motor than it could control directly. For example, in one installation, a 300 amp thyristor unit controls the field of the generator. The generator output current is in excess of 15,000 amperes, which would be prohibitively expensive (and inefficient) to control directly with thyristors. INFRARED SENSOR In this IR detector and transmitter circuit the IC 555 is working under astable mode. The pin 4 i.e. reset pin is when grounded via IR receiver the pin 3 output is low. IEC-CET/ Page 41

42 FIG-14 Infra red sensor with circuitry As soon as the IR light beam transmitted is obstructed, a momentary pulse actuates the relay output (or LED).The IR transmitter is simple series connected resistor network from battery. The timing capacitor connected to pin 2 and ground can varied as per requirement Switched-mode power supply A switched-mode power supply (switching-mode power supply, SMPS, or switcher) is an electronic power supply that incorporates a switching regulator to convert electrial power efficiently. Like other power supplies, an SMPS transfers power from a source like the electrical powergrid to a load (such as a personal computer) while converting voltage and current characteristics. An SMPS is usually employed to efficiently provide a regulated output voltage, typically at a level different from the input voltage. IEC-CET/ Page 42

43 Unlike a linear power supply, the pass transistor of a switching mode supply continually switches between low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions (which minimizes wasted energy). Ideally, a switchedmode power supply dissipates no power FIG-15 Switched mode power supply circuitry Unlike a linear power supply, the pass transistor of a switching mode supply continually switches between low-dissipation, full-on and full-off states, and spends very little time in the high dissipation transitions (which minimizes wasted energy). Ideally, a switchedmode power supply dissipates no power. Voltage regulation is achieved by varying the ratio of on-to-off time. In contrast, a linear power supply regulates the output voltage by continually dissipating power in the pass transistor. This higher power conversion efficiency is an important advantage of a switched-mode power supply. Switched-mode power supplies may also be substantially smaller and lighter than a linear supply due to the smaller transformer size and weight. Switching regulators are used as replacements for the linear regulators when higher efficiency, smaller size or lighter weight are required. They are, however, more IEC-CET/ Page 43

44 complicated, their switching currents can cause electrical noise problems if not carefully suppressed, and simple designs may have a linear regulator provides the desired output voltage by dissipating excess power in ohmic losses (e.g., in a resistor or in the collector emitter region of a pass transistor in its active mode). A linear regulator regulates either output voltage or current by dissipating the excess electric power in the form of heat, and hence its maximum power efficiency is voltage-out/voltage-in since the volt difference is wasted. In contrast, a switched-mode power supply regulates either output voltage or current by switching ideal storage elements, like inductors and capacitors, into and out of different electrical configurations. Ideal switching elements (e.g., transistors operated outside of their active mode) have no resistance when "closed" and carry no current when "open", and so the converters can theoretically operate with 100% efficiency (i.e., all input power is delivered to the load; no power is wasted as dissipated heat). For example, if a DC source, an inductor, a switch, and the corresponding electrical ground are placed in series and the switch is driven by a square wave, the peak-to-peak voltage of the waveform measured across the switch can exceed the input voltage from the DC source. This is because the inductor responds to changes in current by inducing its own voltage to counter the change in current, and this voltage adds to the source voltage while the switch is open. If a diode-and-capacitor combination is placed in parallel to the switch, the peak voltage can be stored in the capacitor, and the capacitor can be used as a DC source with an output voltage greater than the DC voltage driving the circuit. This boost converter acts like a step-up transformer for DC signals. A buck boost converter works in a similar manner, but yields an output voltage which is opposite in polarity to the input voltage. Other buck circuits exist to boost the average output current with a reduction of voltage. In an SMPS, the output current flow depends on the input power signal, the storage elements and circuit topologies used, and also on the pattern used (e.g. pulse-width modulation with an adjustable duty cycle) to drive the switching elements. Typically, the spectral density of these switching waveforms has energy concentrated at relatively high frequencies. As such, switching transients, like ripple, introduced onto the output waveforms can be filtered with small LC filters. IEC-CET/ Page 44

45 Advantages and disadvantages The main advantage of this method is greater efficiency because the switching transistor dissipates little power when it is outside of its active region (i.e., when the transistor acts like a switch and either has a negligible voltage drop across it or a negligible current through it). Other advantages include smaller size and lighter weight (from the elimination of low frequency transformers which have a high weight) and lower heat generation due to higher efficiency. Disadvantages include greater complexity, the generation of high-amplitude, highfrequency energy that the low-pass filter must block to avoid electromagnetic interference (EMI), a ripple voltage at the switching frequency and the harmonic frequencies thereof. Very low cost SMPSs may couple electrical switching noise back onto the mains power line, causing interference with A/V equipment connected to the same phase. Non-power-factor-corrected SMPSs also cause harmonic distortion Battery An electrochemical battery - or, more precisely, a "cell" - is a device in which the reaction between two substances can be made to occur in such a way that some of the chemical energy is converted to useful electricity. When the cell can only be used once, it is called a "primary" cell. When the chemical reaction can be reversed repeatedly by applying electrical energy to the cell, it is called a "secondary" cell and can be used in an accumulator or "storage" battery. Certain cells are capable of only a few charge-discharge cycles and are, therefore, technically "secondary" cells. Such is the case with certain silver oxide-zinc batteries. These batteries are not capable of the repeated cycling required of a satellite battery system, and are, therefore, considered to be "rechargeable primary" rather than storage batteries. To define a battery in another way, it is an arrangement whereby an "electrochemical" reaction can be made to take place so that the "electrical" part of the IEC-CET/ Page 45

46 reaction proceeds via the metallic path of the external circuit, while the "chemical" part of the reaction occurs via ionic conduction through electrolyte. The type of chemical reaction that can be used in an electrochemical cell is known as an "oxidation-reduction" reaction - a reaction in which one chemical species gives electrons to another. By separating the two species and controlling the flow of ions between them, battery engineers make devices in which essentially all of these electrons can be made to flow through an external circuit, thereby converting most of the chemical energy to electrical energy during the discharge of the cell. Some of the components common to all cells are: 1. The "cathode" or "positive" electrode, which consists of a mass of "electron-receptive" chemical held in intimate contact with a metallic "plate" through which the electrons arrive from the external circuit. 2. The "anode" or "negative" electrode, which consists of another chemical which readily gives up electrons - an "electron donor" - similarly held in close contact with a metallic member through which electrons can be conducted to the external circuit. 3. The "electrolyte," usually a liquid solution that permits the transfer of mass necessary to the overall reaction. This movement takes place by "migration" of "ions" - positively or negatively charged molecular fragments - from anode to cathode and from cathode FIG- 16 Battery IEC-CET/ Page 46

47 A schematic diagram of these basic cell elements is shown above. The cell is shown connected to a load - representing the discharge reaction. Charging is accomplished by connecting an electrical source in place of the load, thereby reversing the entire process. UV Detector UV detectors function on the capacity of many compounds to absorb light in the wavelength range 180 to 350 nm. The sensor cell usually consists of a cylindrical cavity about 1 mm I.D and a few mm long, having a capacity that ranges from about two microliters to eight micro-liters. FIG- 17 UV detector Light from a UV light sources passes through the sensor onto a photoelectric cell, the out put from which is electronically modified and presented on a potentiometric recorder, a computer screen, or printer. By interposing a monochrometer between the light source and the cell, light of a specific wavelength can be selected for detection and, thus, improve the detector selectivity. Alternatively a broad band light source can be used and the light after passing through the cell can be optically dispersed by prism or grating and allowed to fall onto a diode array. By monitoring a specific diode, the detector can be made specific for those substances that absorb at that particular wavelength. If the output from all the diodes is scanned then a UV absorption spectrum can be obtained to aid in solute identification. The fixed wavelength UV detector has a sensitivity of about 1 x 10-8 g per ml at a signal to noise ratio of two are the UV detector (fixed and variable wavelength) the electrical conductivity detector, the fluorescence detector and the refractive index detector. These detectors are employed in over 95% of all LC analytical applications. These four detectors will be described and for those readers requiring more information on detectors are referred to Liquid IEC-CET/ Page 47

48 Chromatography Detectors. The UV Detector The UV detector is by far the most popular and useful LC detector that is available to the analyst at this time. This is particularly true if multi-wavelength technology is included in this class of detectors. Although the UV detector has some definite limitations (particularly for the detection of non polar solutes that do not possess a UV chromaphores) it has the best CAUTIONS (1) Cautions 1. The devices are UV light LEDs. The LED during operation radiates intense UV light, which precautions must be taken to prevent looking directly at the UV light with unaided eyes. 2. Do not look directly into the UV light or look through the optical system. When there is a possibility to receive the reflection of light, protect by using the UV light protective glasses so that light should not catch one s eye directly. 3. Put the caution label on the cardboard box. (2) Lead Forming 1. When forming leads, the leads should be bent at a point at least 3mm from the base of the lead. 2. Do not use the base of the lead frame as a fulcrum during lead forming. 3. Lead forming should be done before soldering. 4. Do not apply any bending stress to the base of the lead. The stress to the base may damage the LED s characteristics or it may break the LEDs. 5. When mounting the LEDs onto a printed circuit board, the holes on the circuit board should be exactly aligned with the leads of the LEDs. If the LEDs are mounted with stress at the leads, it causes deterioration of the lead and this will degrade the LEDs. IEC-CET/ Page 48

49 (3) Storage The LEDs should be stored at 30 C or less and 70%RH or less after being shipped from Nichia and the storage life limits are 3 months. If the LEDs are stored for 3 months or more, they can be stored for a year in a sealed container with a nitrogen atmosphere and moisture absorbent material. Nichia LED leads are comprised of a gold plated Iron alloy. The gold surface may be affected by environments which contain corrosive gases and so on. Please avoid conditions which may cause the LED to corrode, tarnish or discolor. This corrosion or discoloration may cause difficulty during soldering operations. It is recommended that the LEDs be used as soon as possible. Please avoid rapid transitions in ambient temperature, especially, in high humidity environments where condensation can occur. (4) Static Electricity Static electricity or surge voltage damages the LEDs. It is recommended that a wrist band or an anti-electrostatic glove be used when handling the LEDs. All devices, equipment and machinery must be properly grounded. It is recommended that measure be taken against surge voltage to the equipment that mounts LEDs. When inspecting the final products in which LEDs were assembled, it is recommended to check whether the assembled LEDs are damaged by static electricity or not. It is easy to find static-damaged LEDs by a light-on test or a VF test at a lower current (below 1mA is recommended). The LEDs should be used the light detector etc. when testing the light-on. Do not stare into the LEDs when testing. Damaged LEDs will show some unusual characteristics such as the forward voltage becomes lower, or the LEDs do not light at the low current. Criteria : (VF > 2.0V at IF=0.5mA) (6) Heat Generation Thermal design of the end product is of paramount importance. Please consider the heat generation of the LED when making the system design. The coefficient of temperature increase per input electric power is affected by the thermal resistance of the circuit board and density of LED placement on the board, as well as other components. It is necessary to IEC-CET/ Page 49

50 avoid intense heat generation and operate within the maximum ratings given in this specification. The operating current should be decided after considering the ambient maximum temperature of LEDs. (7) Cleaning It is recommended that isopropyl alcohol be used as a solvent for cleaning the LEDs. When using other solvents, it should be confirmed beforehand whether the solvents will dissolve the glass or not. Freon solvents should not be used to clean the LEDs because of worldwide regulations. Do not clean the LEDs by the ultrasonic. When it is absolutely necessary, the influence of ultrasonic cleaning on the LEDs depends on factors such as ultrasonic power and the assembled condition. Before cleaning, a pre-test should be done to confirm whether any damage to the LEDs will occur. (8) Safety Guideline for Human Eyes In 1993, the International Electric Committee (IEC) issued a standard concerning laser product safety. Since then, this standard has been applied for diffused light sources (LEDs) as well as lasers. In 1998 IEC Edition 1.1 evaluated the magnitude of the light source. In 2001 IEC Amendment 2 converted the laser class into 7 classes for end products. Components are excluded from this system. Products which contain visible LEDs are now classified as class 1. Products containing UV LEDs are class 1M. Products containing LEDs can be classified as class 2 in cases where viewing angles are narrow, optical manipulation intensifies the light, and/or theenergy emitted is high. For these systems it is recommended to avoid long term exposure. It is also recommended to follow the IEC regulations regarding safety and labeling of products. (9) Others NSHU550B complies with RoHS Directive. This LED also emits visible light. Please take notice of visible light spectrum, in case you use this LED as light source of sensors etc. The LEDs described in this brochure are intended to be used for ordinary electronic IEC-CET/ Page 50

51 equipment (such as office equipment, communications equipment, measurement instruments and household appliances). Consult Nichia s sales staff in advance for information on the applications in which exceptional quality and reliability are required, particularly when the failure or malfunction of the LEDs may directly. Jeopardize life or health (such as for airplanes, aerospace, submersible repeaters, nuclear reactor control systems, automobiles, traffic control equipment, life support systems and safety devices).user shall not reverse engineer by disassembling or analysis of the LEDs without having the prior written consent of Nichia. When defective LEDs are found, User shall inform to Nichia directly before disassembling or analysis.the formal specifications must be exchanged and signed by both parties before large volume purchase begins. The appearance and specifications of the product may be modified for improvement without ULN2003 ULN2003 is a high voltage and high current Darlington array IC. It contains seven open collector darlington pairs with common emitters. A darlington pair is an arrangement of two bipolar transistors. ULN2003 belongs to the family of ULN200X series of ICs. Different versions of this family interface to different logic families.uln2003 are for 5V TTL, CMOS logic devices. These ICs are used when driving a wide range of loads and are used as relay drivers, display drivers, line drivers etc. ULN2003 is also commonly used while driving Stepper Motors. The ULN2003 is a monolithic high voltage and high current Darlington transistor arrays. It consists of seven NPN darlington pairs that features high voltage outputs with common-cathode clamp diode for switching inductive loads. The collector-current rating of a single darlington pair is 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 2.7kΩ series base resistor for each darlington pair for operation directly with TTL or 5V CMOS devices. IEC-CET/ Page 51

52 FIG-18 ULN2003 Darlington using high-power stepper motor.. FEATURES 500mA rated collector current(single output) High-voltage outputs: 50V Inputs compatible with various types of logic. Relay driver application IEC-CET/ Page 52