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A detailed report on final year project - Digital Tachometer

Text of Digital Tachometer Project Report

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

    1

    1.0 INTRODUCTION

    Digital tachometer is an optical encoder that determines the angular velocity of

    a rotating shaft or motor. Digital tachometers are used in different applications such as

    automobiles, aeroplanes, and medical and instrumentation applications.

    The word tachometer is derived from two Greek words: tachos means speed

    and metron means to measure. It works on the principle of a tachometer generator,

    which means when a motor is operated as a generator, it produces the voltage according

    to the velocity of the shaft. It is also known as revolution-counter, and its operating

    principle can be electromagnetic, electronic or optical-based. Power, accuracy, RPM

    range, measurements and display are the specifications of a tachometer. Tachometers

    can be analogue or digital indicating meters; however, this article focuses only on the

    digital tachometers.

    1.1 TYPES OF DIGITAL TACHOMETER

    Digital tachometers are classified into four types based on the data acquisition

    and measurement techniques.

    Based on the data acquisition technique, the tachometers are of the following types:

    1. Contact type

    2. Non-Contact type

    Based on the measurement technique, the tachometers are of the following types:

    1. Time measurement

    2. Frequency measurement

    Fig 1.1.A: Contact type Fig 1.1.B: Non-contact type

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    1.1.A CONTACT TYPE

    A tachometer which is in contact with the rotating shaft is known as contact type

    tachometer. This kind of tachometer is generally fixed to the machine or electric motor.

    An optical encoder or magnetic sensor can also be attached to this so that it measures

    its RPM.

    Digital Tachometers are capable of measuring low-speeds at 0.5 rpm and high

    speed at 10,000 rpm and are equipped with a storage pocket for the circumferential

    measurement. The specifications of this tachometer are LCD 5 digit display, operational

    temperature range of 0 to + 40oC, temperature storage range of 20 to + 55o C and

    rotating speed of about 0.5 to 10,000 rpm.

    1.1.B NON-CONTACT TYPE

    A tachometer that does not need any physical contact with the rotating shaft

    is called as noncontact digital tachometer. In this type, a laser or an optical disk is

    attached to the rotating shaft, and it can be read by an IR beam or laser, which is directed

    by the tachometer.

    This type of tachometer can measure from 1 to 99,999 rpm; the measurement

    angle is less than 120 degrees, and the tachometer has a five-digit LCD display. These

    types of tachometers are efficient, durable, accurate, and compact, and also visible from

    long distance

    1.1.C TIME MEASUREMENT

    A tachometer that calculates the speed by measuring the time interval between

    incoming pulses is known as time-based digital tachometer. The resolution of this

    tachometer is independent of the speed of the measurement, and it is more accurate for

    measuring low speed.

    1.1.D FREQUENCY MEASUREMENT

    A tachometer that calculates the speed by measuring the frequency of the pulses

    is called as frequency-based digital tachometer. This type of tachometer is designed by

    using a red LED, and the revolution of this tachometer depends on the rotating shaft,

    and it is more accurate for measuring high speed. These tachometers are of low-cost

    and high-efficiency, which is in between 1Hz-12 KHz.

    The basis of our project is

    Non-contact type + Frequency measurement

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    1.2 OTHER PRACTICAL TACHOMETERS

    1.2.A TACHOGENERATOR

    A micro-electric machine that is used to convert, the rotating speed and the shaft

    values of a machine into an electric signal is known as tachometer generator. The

    operation of the tachometer generator is based on the principle that the angular velocity

    of rotor is proportional to the generated EMF if the excitation flux is constant.

    These tachometers are specified with generated voltage, accuracy, maximum

    speed, ripples and operating temperature. This kind of tachometer generators are used

    as sensors in various automobile and electromechanical computer devices. The

    generators can be AC or DC types.

    Fig 1.2.A: Tachogenerator

    1.2.B ELECTRONIC TACHOMETER

    A tachometer made purely from electronic components and is used to measure

    the speed of an engine or any other moving object in revolutions per minute is known

    as an electronic tachometer. Electronic tachometers are used in the dashboard of a car

    for measuring the driving speed. These tachometers are light weight, easy to view and

    accurate under all conditions. They are usually not potable.

    Fig 1.2.B: Electronic tachogenerator

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    1.3 INTEL FAMILY 8051 MOCROCONTROLLER

    The Intel MCS-51 (commonly referred to as 8051) is a Harvard

    architecture, CISC instruction set, single chip microcontroller (C) series which was

    developed by Intel in 1980 for use in embedded systems.[1] Intel's original versions were

    popular in the 1980s and early 1990s and enhanced binary compatible derivatives

    remain popular today.

    Intel's original MCS-51 family was developed using NMOS technology, but

    later versions, identified by a letter C in their name (e.g.89C51) used CMOS technology

    and consume less power than their NMOS predecessors. This made them more suitable

    for battery-powered devices.

    Fig 1.3: The original intel 8051 (aka mcs-51) chip

    The family was continued in 1996 with the enhanced 8-bit MCS-151 and the

    8/16/32-bit MCS-251 family of binary compatible microcontrollers.[2] While Intel no

    longer manufactures the MCS-51, MCS-151 and MCS-251 family,

    enhanced compatible derivatives made by numerous vendors remain popular today.

    Some derivatives integrate a digital signal processor (DSP). In addition to these

    physical devices, several companies also offer MCS-51 derivatives as IP cores for use

    in FPGAs or ASICs designs.

    1.4 IR Transmitter Receiver

    Infrared (IR) transmitters and receivers are present in many different devices,

    though they are most commonly found in consumer electronics. The way this

    technology works is that one component flashes an infrared light in a particular pattern,

    which another component can pick up and translate into an instruction. These

    transmitters and receivers are found in remote controls and all different types of

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    devices, such as televisions and DVD players. Peripheral devices that include this

    technology can also allow a computer to control various other consumer electronics.

    Fig 1.4: Optical Transducer

    Most common consumer electronic remote controls use infrared light. They

    typically generate infrared using light emitting diodes (LEDs), and the main component

    of a receiver unit is usually a photodiode. A remote control flashes a pattern of invisible

    light, which is picked up and then turned into an instruction by the receiver module.

    The parts necessary to construct transmitter and receiver are typically inexpensive, but

    these systems are limited to line of sight operation.

    We have conceptualised this idea by replacing an IR diode with a normal LED,

    because IR gets reflected from all objects, while the requirement in our project is the

    reflection of light only from a certain surface, like a reflective one.

    1.5 COMPARATOR To use operational amplifiers in open loop as comparators is quite common.

    This especially applies when an op amp is already used in the application, giving the

    user the opportunity to use a dual channel (or quad channel) op amp which can save

    space in the application. Thesis possible even if a better alternative is to use comparators

    that are optimized for this purpose. The op amp is a device which is designed to be used

    with negative feedback. A major concern is to ensure the stability of such a

    configuration.

    Fig 1.5: comparator symbol and characteristics

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    Other parameters like slew rate and maximum bandwidth are trade-offs with

    current consumption and the architecture of an op amp. Comparators, on the other hand,

    are designed to operate in open loop configuration without any negative feedback. In

    most cases, they are not internally compensated. The speed (propagation delay) and

    slew rate (rise and fall time) are maximized. The overall gain is also usually higher. The

    use of an op amp as a comparator leads to an optimized situation, where current

    consumption versus speed ratio is low. The opposite is even worse. Normally, a

    comparator cannot be used instead of an op amp. Most probably, the comparator shows

    instability under negative feedback. Generally speaking, comparators and operational

    amplifiers cannot substitute each other except for low performance designs.

    1.6 Electronic Displays

    Electronic Displays are electronic equipment used at the final stage of a circuit

    to display the output. The major types of electronic displays used are described in the

    following sections.

    1.6.A LED Display

    A seven-segment display (SSD), or seven-segment indicator, is a form of

    electronic display device for displaying decimal numerals that is an alternative to the

    more complex dot matrix displays.

    Seven-segment displays are widely used in digital clocks, electronic meters,

    basic calculators, and other electronic devices that display numerical information.

    The seven elements of the display can be lit in different combinations to

    represent the Arabic numerals. Often the seven segments are arranged in

    an oblique (slanted) arrangement, which aids readability. In most applications, the

    seven segments are of nearly uniform shape and size (usually elongated hexagons,

    though trapezoids and rectangles can also be used), though in the case of adding

    machines, the vertical segments are longer and more oddly shaped at the ends in an

    effort to further enhance the readability.

    fig 1.6.A : 7 Seg LED

    Types of seven segment LED Displays

    i) Common Anode Display

    ii) Common Cathode Display

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    1.6.B LCD Displays

    A liquid crystal display is a special thin flat panel that can let light go through

    it, or can block the light. (Unlike an LED it does not produce its own light). The panel

    is made up of several blocks, and each block can be in any shape. Each block is filled

    with liquid crystals that can be made clear or solid, by changing the electric current to

    that block. Liquid crystal displays are often abbreviated LCDs.

    Fig 1.6.B : LCD Display

    Liquid crystal displays are often used in battery-powered devices, such as digital

    watches, because they use very little electricity. They are also used for flat screen TV's.

    Many LCDs work well by themselves when there is other light around (like in a lit

    room, or outside in daylight). For smartphones, computer monitor, TV's and some other

    purposes, a back-light is built into the product.

    Though LCD display could have been easily interfaced, we chose LED ahead

    for simplicity and compactness. Also LCD needs more stabilisation time while all you

    need to do is provide a delay for repeatedly showing the result due to perception of

    vision.

    1.7 HEAT SINK

    In electronic systems, a heat sink is a passive heat exchanger that cools a device by dissipating heat into the surrounding medium. In computers, heat sinks are used to

    cool central processing units or graphics processors.

    Fig 1.7: Power Transistor Heat Sink

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    A heat sink is designed to maximize its surface area in contact with the cooling

    medium surrounding it, such as the air. Air velocity, choice of material, protrusion

    design and surface treatment are factors that affect the performance of a heat sink. Heat

    sink attachment methods and thermal interface materials also affect the die temperature

    of the integrated circuit. Thermal adhesive or thermal grease improve the heat sink's

    performance by filling air gaps between the heat sink and the heat spreader on the

    device.

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    2.0 BLOCK DIAGRAM

    Fig 2.0: Block Diagram of WRDT

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    2.1 OPTOCOUPLER

    An optical coupler, also called opt-isolator, optocoupler, optocoupler, photocoupler or optical isolator, is a passive optical component that can combine or

    split transmission data (optical power) from optical fibers. It is an electronic device

    which is designed to transfer electrical signals by using light waves in order to provide

    coupling with electrical isolation between its input and output. The main purpose of an

    optocoupler is to prevent rapidly changing voltages or high voltages on one side of a

    circuit from distorting transmissions or damaging components on the other side of the

    circuit. An optocoupler contains a light source often near an LED which converts

    electrical input signal into light, a closed optical channel and a photosensor, which

    detects incoming light and either modulates electric current flowing from an external

    power supply or generates electric energy directly. The sensor can either be a

    photoresistor, a silicon-controlled rectifier, a photodiode, a phototransistor or a triac.

    Fig 2.1 : IR-Photo Diodes as Optocoupler

    This Sensor module works on the principle of Reflection of Infrared Rays from

    the incident surface. A continuous beam of IR rays is emitted by the IR LED. Whenever

    a reflecting surface (white/obstacle) comes in front of the Receiver (photo diode), these

    rays are reflected back and captured. Whenever an absorbing surface (Black/No

    Obstacle) comes in front of the Receiver, these rays are absorbed by the surface and

    thus unable to be captured.

    FEATURES:

    1) Active low on object detection

    2) Easy interface to connector

    3) Indicator LED

    4) Potentiometer for changing the range of detection

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    2.2 SIGNAL CONDITIONER CIRCUIT

    The signal conditioner circuit performs very vital role in ant electronic circuitry.

    Signal conditioning means manipulating the available analogue signal in such a way

    that it meets the requirement of the next stage of circuit for further processing. Here

    QUAD COMPARATOR DIP IC LM339 is used as a Schmitt trigger, this Schmitt

    trigger is used to convert the artery available signal into a perfect square wave to meet

    the need of the further frequency metre to further process

    The fundamental idea is as shown here-

    Fig 2.2

    [ Note: Single comparator is used. The IC is used as A to D convertor

    The comparator is used as Schmitt trigger, providing the same frequency that

    of the input.]

    2.2.A INPUT

    Input is the measuring quantity. In our project input is the reflecting surface

    which is attached to the motor. When the rotational body rotates, the reflecting surface

    will repeat equal times the rotating body rotates. This reflecting surface will provide an

    appropriate reflected light on the surface of the optical transducer.

    2.2.B OUTPUT

    Any system without output is of no worth. The output of our system is the speed

    of the rotating machine. The speed of machine is displayed in rotation per seconds. A

    4 digit 7 segment display is used to show the speed count. This display is interfaced

    with AT89S51 microcontroller. It simply shows display count of the frequency of the

    number of pulses.

    2.3 POWER UNIT

    Power is the rate of doing work. It is equivalent to an amount of energy

    consumed per unit time. In the SI system, the unit of power is the joule per second (J/s),

    known as the watt in honour of James Watt, the eighteenth-century developer of the

    steam engine.

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    The integral of power over time defines the work performed. Because this

    integral depends on the trajectory of the point of application of the force and torque,

    this calculation of work is said to be path dependent.

    Fig 2.3: Power Unit

    The same amount of work is done when carrying a load up a flight of stairs

    whether the person carrying it walks or runs, but more power is needed for running

    because the work is done in a shorter amount of time. The output power of an electric

    motor is the product of the torque that the motor generates and the angular velocity of

    its output shaft. The power involved in moving a vehicle is the product of the traction

    force of the wheels and the velocity of the vehicle. The rate at which a light bulb

    converts electrical energy into light and heat is measured in wattsthe higher the

    wattage, the more power, or equivalently the more electrical energy is used per unit

    time.

    2.4 SIGNAL PROCESSOR (Schmitt Trigger)

    As the microcontroller cannot deal with analog data (certainly the 8051), some

    way must be established in order to help the controller count the pusles. This job is done

    by the signal processor block.

    Fig 2.4: Schmitt trigger characteristics

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    The signal processor not only does the job of A-D conversion, it also smoothens

    the waveform with a Schmitt trigger employed using comparator, and also amplifies

    the signal level.

    [Note : The comparator doesnt amplify in reality, but it does the job of comparing to

    inputs (within saturation limits), assuming that input signal is quite weak after comparison it

    gives the output either high or low (or +vsat, vsat depending on the comparator used), so we

    can say that the signal is considerably amplified in other sense.]

    2.5 DISPLAY DRIVER

    Although there are advanced and complex display driver ICs available, they increase the hardware and also the cost making the circuit bulkier. Same task can be

    done with the help of a simple transistor (NPN BJT) driver.

    Here , the base drive ( base current ) is deliberately chosen much higher than

    the Ib (sat) rating (available in the datasheet ) . Due to this the collector current can no

    longer be given as Ic = * Ib , but by Vcc/ Rc . By choosing small value of Rc (rather

    appropriate), collector current can be set as required. This ultimately increases the

    driving capacity of the transistor.

    Fig 2.4: Transistor Driver

    Note: 1. For other displays like lcd, the transistor driver becomes bulkier as the number

    Pins is more.

    2.Ic should not exceed a certain value Icmax, which increases heating and may

    lead to thermal runaway and spoil the display as well as entire circuitry

    although heat sink may be present.

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    2.6 DISPLAY (7 SEGMENT LED)

    As the controller used is only 8-bit, the maximum data it can handle is FFH i.e.

    255 decimal. Thus maximum speed in RPM that could be measure is restricted to

    only 255 RPM, which is a serious drawback.

    Thus we decided to measure speed in RPS instead of in RPM. This increased

    the range of angular frequency that could be measured immensely. The equivalent

    RPM count that could be measured comes out to be around 15K RPM, a major

    drawback resulted into a major advantage.

    This is the unique feature of our project, and thus we have named it WIDE

    RANGE DIGITAL TACHOMTER (WRDT). One output of many test readings

    taken is shown below.

    Fig 2.6: Circuit functioning at high frequency

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    3.0 VITAL COMPONENTS NOT MENTIONED IN THE

    BLOCK DIAGRAM

    3.1 CRYSTAL OSCILLATOR

    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.

    Fig 3.1.A Crystal Packages

    Quartz crystals are manufactured for frequencies from a few tens of kilohertz to

    hundreds of megahertz. More than two billion crystals are manufactured annually.

    Although RC, LC or any other oscillatory circuit can be used, the crystal

    oscillator by far gives best result for Digital Sequential Circuit. . Note the 22pF

    capacitors shown in below figure.

    Circuit configuration for crystal as CLOCK

    Fig 3.1.B : Crystal internal configuration

    The optimum load capacitance for a given crystal is specified by the

    manufacturer. Printed circuit has its own stray capacitance, hence a capacitors of

    particular value used. Usually value of capacitors are same.

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    3.2 7805 Regulator IC

    7805 is a voltage regulator integrated circuit. It is a member of 78xx series of

    fixed linear voltage regulator ICs. The voltage source in a circuit may have fluctuations

    and would not give the fixed voltage output. The voltage regulator IC maintains the

    output voltage at a constant value. The xx in 78xx indicates the fixed output voltage it

    is designed to provide. 7805 provides +5V regulated power supply. Capacitors of

    suitable values can be connected at input and output pins depending upon the respective

    voltage levels.

    Fig 3.2 : 7805 Package

    Pin No Function Name

    1 Input voltage (5V-18V) Input

    2 Ground (0V) Ground

    3 Regulated output; 5V (4.8V-5.2V) Output

    IMPORTANT RATINGS:

    SPECIFICATION DESCRIPTION RATING

    IOL(MAX) MAX LOAD CURRENT 1A

    VI RANGE OF INPUT

    VOLTAGE

    5V 18V

    VDROP DROPOUT VOLTAGE 2V TYP

    RR RIPPLE REJECTION 73 dB TYP

    RO OUTPUT RESISTANCE 15m

    ISC SHORT CIRCUIT

    CURENT

    230 mA TYP

    IPK PEAK CURRENT 2.2 A TYP

    IQ QUISCENT CURRENT 8 mA TYP

    REGLINE LINE REGULATION 1.6 mV (VI= 8-12V)

    REGLOAD LOAD REGULATION 4.0 mV(IO= 250-

    750mA)

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    3.3 HEAT SINK

    In electronic systems, a heat sink is a passive heat exchanger that cools a device by dissipating heat into the surrounding medium. In computers, heat sinks are used to

    cool central processing units or graphics processors.

    Fig 3.3: Heat Sink mounted on 7805

    A heat sink is designed to maximize its surface area in contact with the cooling

    medium surrounding it, such as the air. Air velocity, choice of material, protrusion

    design and surface treatment are factors that affect the performance of a heat sink. Heat

    sink attachment methods and thermal interface materials also affect the die temperature

    of the integrated circuit. Thermal adhesive or thermal grease improve the heat sink's

    performance by filling air gaps between the heat sink and the heat spreader on the

    device.

    3.4 9V Battery and Connector

    The most common form of nine-volt battery is commonly called the transistor

    battery which was introduced for the early transistor radios. It has a rectangular prism

    shape with rounded edges and a polarized snap connector at the top. This type is

    commonly used in pocket radios, paintball guns, and small electronic devices. They are

    also used as backup power to keep the time in certain electronic clocks. This format is

    commonly available in primary carbon-zinc and alkaline chemistry, in primary lithium

    iron disulfide, and in rechargeable form in nickel-cadmium, nickel-metal hydride and

    lithium-ion. Mercury oxide batteries in this form have not been manufactured in many

    years due to their mercury content. This type is designated NEDA 1604, IEC 6F22 and

    "Ever Ready" type PP3 (zinc-carbon) or MN1604[1] 6LR61 (alkaline).

    Most nine-volt alkaline batteries are constructed of six individual 1.5V LR61

    cells enclosed in a wrapper. These cells are slightly smaller than LR8D425 AAAA cells

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    and can be used in their place for some devices, even though they are 3.5 mm shorter

    Carbon-zinc types are made with six flat cells in a stack, enclosed in a moisture-resistant

    wrapper to prevent drying.

    Fig 3.4: Standard 9V Battery and Battery Connector

    The battery has both terminals in a snap connector on one end. The smaller

    circular (male) terminal is positive, and the larger hexagonal or octagonal (female)

    terminal is the negative contact. The connectors on the battery are the same as on the

    connector itself; the smaller one connects to the larger one and vice versa.[5] The same

    snap style connector is used on other battery types in the Power Pack (PP) series.

    Battery polarization is normally obvious since mechanical connection is usually only

    possible in one configuration. A problem with this style of connector is that it is very

    easy to connect two batteries together in a short circuit, which quickly discharges both

    batteries, generating heat and possibly a fire.[6] An advantage is that several nine-volt

    batteries can be connected to each other in series to provide higher voltages.

    3.5 Light Emitting Diode

    A light-emitting diode (LED) is a two-lead semiconductor light source. It is

    a pn-junction diode, which emits light when activated.[4]When a suitable voltage is

    applied to the leads, electrons are able to recombine with electron holes within the

    device, releasing energy in the form of photons.

    Fig 3.5: A White bright 10mm LED

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    This effect is called electroluminescence, and the colour of the light

    (corresponding to the energy of the photon) is determined by the energy band gap of

    the semiconductor. Led is the very important part of our project .We have used 10mm

    bright white led in our WRDT.

    3.6 CIRCUIT BOARD

    Although General Purpose Board can be used, it only complicates the design due a huge number of wires which makes the circuit congested. However a more

    professional but difficult approach involves the use of Copper Cladded PCB for the

    design of tracks. This is done by special technique Etching to be discussed thoroughly

    in section

    Fig 3.6.A : Copper Cladded Board (Before Etching)

    Fig 3.6.B: Etched PCB

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    4.0 POWER SUPPLY UNIT

    DC Power Supplies provide direct current at varying voltage and current to a

    device under test. These devices are useful for testing designs in real world power

    situations and can act as a constant battery source when testing DC devices. Power

    supplies come in variety of configurations and can be used for constant-voltage or

    constant-current. There are also units with multiple outputs so that one source can

    supply several outputs to the device under test. Loads are used to test the internal power

    supply of a unit without risking other elements of the unit.

    4.1 CIRCUIT DIAGRAM

    Fig 4.1: Power unit

    4.2 9V BATTERY

    The most common form of nine-volt battery is commonly called the transistor

    battery which was introduced for the early transistor radios. It has a rectangular prism

    shape with rounded edges and a polarized snap connector at the top. This type is

    commonly used in pocket radios, paintball guns, and small electronic devices. They are

    also used as backup power to keep the time in certain electronic clocks. This format is

    commonly available in primary carbon-zinc and alkaline chemistry, in primary lithium

    iron disulphide, and in rechargeable form in nickel-cadmium, nickel-metal hydride and

    lithium-ion. Mercury oxide batteries in this form have not been manufactured in many

    years due to their mercury content. This type is designated NEDA 1604, IEC 6F22 and

    "Ever Ready" type PP3 (zinc-carbon) or MN1604 6LR61 (alkaline).

    Most nine-volt alkaline batteries are constructed of six individual 1.5V LR61

    cells enclosed in a wrapper.[2] These cells are slightly smaller than LR8D425 AAAA

    cells and can be used in their place for some devices, even though they are 3.5 mm

    shorter. Carbon-zinc types are made with six flat cells in a stack, enclosed in a

    moisture-resistant wrapper to prevent drying.

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    Fig 4.2: Standard 9V Battery and Battery Connector

    The battery has both terminals in a snap connector on one end. The smaller

    circular (male) terminal is positive, and the larger hexagonal or octagonal (female)

    terminal is the negative contact. The connectors on the battery are the same as on the

    connector itself; the smaller one connects to the larger one and vice versa.[5] The same

    snap style connector is used on other battery types in the Power Pack (PP) series.

    Battery polarization is normally obvious since mechanical connection is usually only

    possible in one configuration. A problem with this style of connector is that it is very

    easy to connect two batteries together in a short circuit, which quickly discharges both

    batteries, generating heat and possibly a fire. An advantage is that several nine-volt

    batteries can be connected to each other in series to provide higher voltages.

    4.3 LM7805 VOLTAGE REGULATOR IC

    Fig 4.3: 7805 with filtering components

    We have studied the LM7805 voltage regulator IC in depth in section 3.2. It is

    a member of 78xx family. Similar device 79xx can be used in case negative regulated

    power supplies are desirable. The ratings mentioned in section 3.2 are critical to

    operation of the devices and thus must be paid with massive attention.

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    4.4 FILTERING ELEMENTS

    A filter is a device that removes unwanted signal and allows only desired signal

    to pass. By looking at the definition, filter may seem to be a complex circuit, but here

    in this case it is just a mere combination of a few capacitors.

    At input side to LM7805, line frequency of AC mains must be filtered with a

    large value capacitance as input ripple is quite large. For this a 2200uF capacitor is used

    which further enhanced by connecting 2 100nF capacitors in parallel which eliminate

    supply frequency harmonics.

    At the output side to LM7805, as the Ripple Rejection Ratio of IC is good as

    shown in the data sheet, only a small ripple is present at the output which is considerably

    eliminated by a parallel combination 2 100nF capacitors.

    An LED can be connected with a suitable series resistor to indicate ON state of

    the supply to make it look more attractive.

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    5.0 SIGNAL CONDITIONER

    A signal conditioner is a circuit that conditions analogue signal in such a way

    that it can be used to drive any A to D converter or any analogue IC. Here as the pulses

    are only a few microvolts high, they must be conditioned to some extent. This is done

    with a powerful analogue amplifier called Operational Amplifier.

    In electronics, signal conditioning means manipulating an analogue signal in

    such a way that it meets the requirements of the next stage for further processing. Most

    common use is in analogue-to-digital converters.

    In control engineering applications, it is common to have a sensing stage (which

    consists of a sensor), a signal conditioning stage (where usually amplification of the

    signal is done) and a processing stage (normally carried out by an ADC and a micro-

    controller). Operational amplifiers (op-amps) are commonly employed to carry out the

    amplification of the signal in the signal conditioning stage.

    Signal conditioning can include amplification, filtering, converting, range

    matching, isolation and any other processes required to make sensor output suitable for

    processing after conditioning. We have used LM339 as a comparator based signal

    conditioner. Types of signal conditioning are listed below.

    5.1 Filtering

    Filtering is the most common signal conditioning function, as usually not all the

    signal frequency spectrum contains valid data. The common example is 60 Hz AC

    power lines, present in most environments, which will produce noise if amplified.

    5.2 Amplifying

    Signal amplification performs two important functions: increases the resolution

    of the input signal, and increases its signal-to-noise ratio.[citation needed] For example, the

    output of an electronic temperature sensor, which is probably in the millivolts range is

    probably too low for an analog-to-digital converter (ADC) to process directly. In this

    case it is necessary to bring the voltage level up to that required by the ADC.

    Commonly used amplifiers on signal on conditioning include sample and

    hold amplifiers, peak detectors, log amplifiers, antilog amplifiers, instrumentation

    amplifiers and programmable gain amplifiers.

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

    24

    5.3 Isolation

    Signal isolation must be used in order to pass the signal from the source to the

    measurement device without a physical connection: it is often used to isolate possible

    sources of signal perturbations. Also notable is that it is important to isolate the

    potentially expensive equipment used to process the signal after conditioning from the

    sensor.

    Magnetic or optic isolation can be used. Magnetic isolation transforms the

    signal from voltage to a magnetic field, allowing the signal to be transmitted without a

    physical connection (for example, using a transformer). Optic isolation takes an

    electronic signal and modulates it to a signal coded by light transmission (optical

    encoding), which is then used for input for the next stage of processing.

    Fig 5.4.A: WRDT signal conditioner

    Fig 5.4.B: LM339 Voltage Comparator

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    5.4 VOLTAGE COMPARATOR

    Perhaps the most important block in any Signal Conditioning Circuit, a voltage

    comparator also acts like an amplifier, waveform smoothers and also level detector. As

    due to reflection of light from the rotor, the photo diode undergoes continuous

    transitions, i.e. from ON to OFF and OFF to ON. Thus some transition loss or noise is

    present. This is eliminated by using a comparator which compares the photo diode OFF

    voltage will a reference standard non-inverting terminal voltage. The moment the photo

    diode conducts and sends a low pulse, comparator senses the change at the inverting

    terminal and changes the output abruptly Thus a much smoother waveform is obtained

    at the output of the comparator that is the signal conditioner of our project. The figures

    below illustrate this action.

    .

    Fig 5.4.C: Distorted Input to Signal Conditioner

    Fig 5.4.D: Clean and Sharp Digitalized Output Signal Conditioner

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    6.0 TIME DELAY USING IC 555

    Delay can be produce with both software and hardware control, but using a

    simple hardware IC 555 considerably simplifies the circuit. It is widely used in

    monostable (one shot) mode to generate time delay. We have not used the hardware

    delay as it results in increasing cost, complexity in PCB design, reduces the

    compactness of the entire machine.

    6.1 SCHEME 1 (EXTERNAL DELAY WITH 555)

    Fig 6.1.A: Time Delay Circuit

    Fig 6.1.B: Output Waveforms for Time Delay Circuit

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    monostable multivibrator (MMV) often called a one-shot multivibrator, is a

    pulse generator circuit in which the duration of the pulse is determined by the R-C

    network,connected externally to the 555 timer. In such a vibrator, one state of output is

    stable while the other is quasi-stable (unstable). For auto-triggering of output from

    quasi-stable state to stable state energy is stored by an externally connected capacitor

    C to a reference level. The time taken in storage determines the pulse width. The

    transition of output from stable state to quasi-stable state is accomplished by external

    triggering.

    Pin 1 is grounded. Trigger input is applied to pin 2. In quiescent condition of

    output this input is kept at + VCC. To obtain transition of output from stable state to

    quasi-stable state, a negative-going pulse of narrow width (a width smaller than

    expected pulse width of output waveform) and amplitude of greater than + 2/3 VCC is

    applied to pin 2. Output is taken from pin 3. Pin 4 is usually connected to + VCC to

    avoid accidental reset. Pin 5 is grounded through a 0.01 u F capacitor to avoid noise

    problem. Pin 6 (threshold) is shorted to pin 7. A resistor RA is connected between pins

    6 and 8. At pins 7 a discharge capacitor is connected while pin 8 is connected to supply

    VCC.

    6.2 SCHEME 2 (INTERNAL USING PRAGRAM)

    In an 8051 microcontroller, it requires 12 cycles of the processor clock for

    executing a single instruction cycle. For an 8051 microcontroller clocked by a 12MHz

    crystal, the time taken for executing one instruction cycle is 1S and it is according to

    the equation, Time for 1 instruction cycle= 12 /12MHz = 1S. The shortest instructions

    will execute in 1S and other instructions will take 2 or more micro seconds depending

    up on the size of the instruction. Thus a time delay of any magnitude can be generated

    by looping suitable instructions a required number of time.

    Fig 6.2.A: Delay using register parameters

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    Anyway, keep one thing in mind that software delay is not very accurate

    because we cannot exactly predict how much time it takes for executing a single

    instruction. Generally an instruction will be executed in the theoretical amount of time

    but sometimes it may advance or retard due to other reasons. Therefore it is better to

    use 8051 Timer for generating delay in time critical applications. However software

    delay routines are very easy to develop and well enough for less critical and simple

    applications.

    Fig 6.2.B: Delay is using NOP instruction

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    7.0 ATMEL AT89S51 MICROCONTOLLER

    7.1 ARCHITECTURE OVERVIEW

    Fig 7.1: AT89S51 Architecture

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    7.2 Port Structures and Operation

    All four ports in the AT89C51 and AT89C52 are bidirectional. Each consists of

    a latch (Special Function Registers P0 through P3), an output driver, and an input

    buffer. The output drivers of Ports 0 and 2, and the input buffers of Port 0, are used in

    accesses to external memory. In this application, Port 0 outputs the low byte of the

    external memory address, time-multiplexed with the byte being written or read. Port 2

    outputs the high byte of the external memory address when the address is 16 bits wide.

    Otherwise the Port 2 pins continue to emit the P2 SFR content. All the Port 3 pins, and

    two Port 1 pins (in the AT89C52) are multifunctional. The alternate functions can only

    be activated if the corresponding bit latch in the port SFR contains a 1. Otherwise the

    port pin is stuck at 0. It has less complex feature than other microprocessor.

    7.3 AT89S51 PIN DIAGRAM

    Fig 7.3: Pin Diagram of AT89S51

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    7.4 PIN DESCRIPTION AT89S51

    Fig 7.4: Pin Description of AT89S51

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    7.5 INSTRUCTION SET AND OTHER VENDORS (8051)

    Fig 7.5.A: 8051 Instruction Set

    Fig 7.5.B: Famous 8051 Vendors Worldwide

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    8.0 LM339 VOLTAGE COMPARATOR

    8.1 LM339 PIN DIAGRAM

    Fig 8.1: LM339 Pin Diagram

    8.2 LM339 DESCRIPTION

    These devices consist of four independent voltage comparators that are designed

    to operate from a single power supply over a wide range of voltages. Operation from

    dual supplies also is possible, as long as the difference between the two supplies is 2 V

    to 36 V, and VCC is at least 1.5 V more positive than the input common-mode voltage.

    Current drain is independent of the supply voltage. The outputs can be connected to

    other open-collector outputs to achieve wired-AND relationships.

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    8.3 LM339 PIN DESCRIPTION

    Fig 8.3: LM339 Pin Description

    8.4 WORKING

    A dedicated voltage comparator will generally be faster than a general-purpose

    comparator pressed into service as a comparator. A dedicated voltage comparator may

    also contain additional features such as an accurate, internal voltage reference, an

    adjustable hysteresis and a clock gated input.

    A dedicated voltage comparator chip such as LM339 is designed to interface

    with a digital logic interface (to a TTL or a CMOS). The output is a binary state often

    used to interface real world signals to digital circuitry (see analog to digital converter).

    If there is a fixed voltage source from, for example, a DC adjustable device in the signal

    path, a comparator is just the equivalent of a cascade of amplifiers. When the voltages

    are nearly equal, the output voltage will not fall into one of the logic levels, thus analog

    signals will enter the digital domain with unpredictable results. To make this range as

    small as possible, the amplifier cascade is high gain. The circuit consists of

    mainly Bipolar transistors. For very high frequencies, the input impedance of the stages

    is low. This reduces the saturation of the slow, large P-N junction bipolar transistors

    that would otherwise lead to long recovery times. Fast small Schottky diodes, like those

    found in binary logic designs, improve the performance significantly though the

    performance still lags that of circuits with amplifiers using analog signals. Slew rate

    has no meaning for these devices. For applications in flash ADCs the distributed signal

    across eight ports matches the voltage and current gain after each amplifier, and

    resistors then behave as level-shifters.

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    9.0 OVERALL CIRCUIT IN ACTION

    Fig 9.0: Overall Circuit Diagram

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

    36

    The circuit diagram, though shown divided the into 3 individual units namely

    1. Power unit

    2. Signal conditioning

    3. Microcontroller and Display,

    they are, in actuality , part of an integral unit.

    They share the same supply voltage +vcc = 5v and ground as shown by

    appropriate symbols and labels. We will see the entire system in depth now, but step by

    step.

    As the portability of tachometer is not to be sacrificed at any cost, one portable

    power unit must be provided. This is accomplished using a fixed 9v dc battery and a

    voltage regulator. But this doesn't mean that use of ac mains is of no use. Actually, one

    rectifier circuit followed by the same regulator (as used with the battery powered

    supply) and some filtering components (also used in battery powered supply). But the

    main aim of a designer is not to sacrifice compactness, but usage of ac mains powered

    supply, requires a connecting cable to be carried all the time. This is not acceptable at

    all, if the circuit is meant to be compact as well as portable. One big disadvantage of

    using battery powered supply is the frequent drainage of battery. But we have overcome

    this issue using proper program code to save battery and perfect switch positioning

    which ensure the most efficient power handling. If battery is kept properly in a dry

    environment, may never get drained, still continuous use of the tachometer for say 2-3

    hours may need the battery to be changed. This point is again explained in Test Points

    (chap 15 )

    Now comes the signal conditioner. It can be visualized of consisting of an input,

    an output and a primary signal synthesizer. The principle operation of the project is

    simple, detection of light reflected from a rotating body. A bright white LED emits light

    continuously, but how do we sense it ? It is sensed by a photodiode. The sensitivity of

    photodiode should high. But in some cases, we may need to reduce it. Whenever light

    ray reflects, it is sensed by the photo diode, which was till now turned off with collector

    voltage Vc = +5v approx., is turned on giving a low signal (Vc = 0v ). These low signals

    which are analog in nature, are used to gate the the counter of the microcontroller.

    However, these pulses cannot be applied directly, as microcontroller only deals with

    digital data, that is either 1 or 0 . This job of digitizing the analog pulses is done by a

    op amp comparator, texas instruments lm339.When there is no reflection of light, photo

    diode is off, its collector voltage is Vc = +5v or greater than the logic high threshold of

    the microcontroller.

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

    37

    Thus when diode is off, it sends a +5v signal to the comparator, which compares

    this signal at the inverting terminal with a preset signal at the non-inverting terminal,

    which is deliberately set such that its less than the OFF state diode voltage (around +5v)

    and greater than the ON state diode voltage (a few milli volts). As the comparator

    detects a +5v which greater than the non-inverting threshold it gives an output voltage

    equal to +vsat = +5v (as stated before all components share the same vcc and ground).

    This is nothing but the logic1 of the microcontroller. Whenever light gets reflected from

    the rotating body, diode conducts and the inverting terminal voltage of the comparator

    is less that the non-inverting terminal threshold, giving output voltage = either -vsat or

    0 (depends on whether -vee is grounded or not). As we need a digital signal, -vee is set

    to ground. Whenever pulse is obtained, comparator gives a logic 0.

    This is how the comparator, which is the signal conditioner, does the job of

    smoothening, digitizing and amplifying (in odd sense).

    The output of the comparator is connected to the pin number 15 of the

    microcontroller. As we have used the Timer register for external event counting (i.e.

    pulse counting in this case), these external events must occur at the external timer 1

    interrupt pin which the pin number 15 in this case. This is set automatically when we

    set a timer x register as a counter in the TMOD register.

    Note :- If timer x is set as a timer, then the event to be counted is not external, but the

    clock cycles which synchronize the microcontroller AT89S51.

    In the TMOD register only, setting the last 2 bits of each nibble with proper

    combination we can use different modes. Out of 4 modes, we have used the MODE 2,8-

    bit auto reload mode. If the counter exceeds the value of 255 (FF), we increment a

    register count so that after one roll over of the TF1, if the counted pulse is 55, it means 155H pulses are counted. But this is an error as this 8 bit controller cannot be

    used to display a number which exceeds 255 (in fact we can display the number above

    255, but it increases the complexity almost a 1000 times, and any rotating body is very

    less likely to be running at a speed greater than, say even a 200 RPS.

    One 16 bit timer is used as a counter to count the number of pulses coming out

    of the comparator. A comparator to work properly, must have a pull up resistor at the

    output pin. If you look at our circuit diagram, you will not find any. This is because port

    3 of the AT89S51 (at one pin of which comparator output is given) already has internal

    pull up resistors.

    To calculate speed in RPS, the simplest way is to count the number pulses

    reflecting back from the rotating body for duration of 1 sec. To serve this purpose, the

    other timer is used as an internal delay timer. As stated before, in the TMOD register,

    if we reset the TMOD.7 or TMOD.2 bits (timer/counter control bits for timer 1 and 0

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

    38

    respectively), we set the respective timer in the timer delay mode. In this mode, the

    counter register (so called) is incremented by every clock pulse coming from the crystal

    which synchronizes the entire operations of the microcontroller. Out of the 4 modes,

    we have used the MODE1, the 16 bit counter. The delay scheme used is identical to the

    one used in chap 6 under the software delay scheme, except that here, instead of using

    a 8 bit register, we use a 16 bit timer to produce larger delay. As we need to have a 1

    sec delay, using only 16 bit counter is not enough because maximum delay that can be

    produced with a 16 bit register with a clock of 11.0592 MHz (what we used), max delay

    is 1.085*10^6*65535 = 71msec. So we use another register with initial count 14H and

    decrement it every time TF0 rolls over, thus we get a delay of 1 sec. This is same as

    giving a 71 msec delay 14 times (0.071*14 = 1).

    Now the final and the most important task to be done is the displaying of the

    counted pulses. The conventional persistence strategy for 7 seg LED is used. Here we

    first convert the number to decimal. As this is a 8 bit controller, maximum number is 3

    digit only (255 or FFH). We first divide the number by 100, and we display the quotient.

    We first enable the MSB digit by enabling its transistor and disable all others. Then we

    find out the corresponding code for a given number depending upon whether the display

    is Common Anode type or Common Cathode type. These codes are usually pre stored

    in the program memory as look up tables and accessed using base + index addressing

    mode. Remember we do not display the number (or character) say 1 directly, but send

    its 7 seg code which nothing but a bit pattern depending on which of the a-g segments

    need logic 1 for CK display and logic 0 for CA display.

    Once MSD is sent, we again set off the MSD transistor by giving a 0 base drive,

    we then divide remainder of the first result by 10 and again find the 7 seg code for the

    quotient. We now turn the middle digit transistor driver on, keeping all others off. We

    display the 7 seg code, wait for some time and again turn of the driver. And lastly, the

    remainder of the previous result is nothing but the LSD, whose 7 seg code is searched

    for and then sent out to corresponding digit by making that transistor driver on.

    Now the important question, If only one digit is getting ON at a given time, how

    does the display look continuous to our eyes? The answer is Persistence of Vision.

    Once the display subroutine is done, we repeat the process a number of times until a

    parameter in a register becomes zero. Microcontroller performs instructions almost

    within a microsecond, but our eyes can at max catch only 120 frames per second.

    However a, the display routine time is much smaller than the time for which 120 frames

    may last. Thus out eyes can virtually sense no change in the very fast turn ON and OFF

    of the display. Thus if the display routine is repeated for a finite duration, our eyes see

    the display as if it was a continuous one, due persistence of vision.

    After completion of display, controller restarts the 1 sec time delay and counter

    and again displays the result. This process keeps on continuing as long as power is

    running. Thus very fast varying speeds, which are termed as dynamic speeds can be

    easily measured. This is a huge bonus.

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    In this way, our project, the Wide Range Digital Tachometer (WRDT) first

    converts the analog pulses into digital ones, then counts them for a perfectly set 1 sec

    duration, and immediately displays the result, ready to count for 1 sec again. The

    efficiency is in the higher 95s as will be shown in the performance graphs (chap 10).

    Fig 9.1: Real time OUTPUT

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    10. TACHOMETER CALIBRATION UNIT

    In this chapter we will see the tachometer calibration unit. To calibrate he

    tachometer a rated DC shunt motor is used which is powered with a voltage supply of

    maximum 12v. The figure shows the physical appearance of the motor.

    Fig 10.0.1: 12v DC motor (1000Rpm)

    The armature and field are shunted and connected in parallel to supply voltage.

    The voltage supply is variable 0-12V DC power supply. Here by varying the armature

    voltage the speed variation in proportion is observed.

    Fig 10.0.2: Circuit Diagram

    Va=Armature voltage

    For Va=0V: Speed of motor = 0RPM = 0RPS

    For Va=3V: Speed of motor = 250RPM = 4 OR 5 RPS

    For Va=6V: Speed of motor = 500RPM = 8 OR 9 RPS

    For Va=9V: Speed of motor = 750RPM = 12 OR 13 RPS

    Speed of motor = 1000RPM = 16 OR 17 RPS

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    10.1 CIRCUIT FOR VARIABLE OUTPUT VOLTAGE

    The circuit uses a astable multivibrator using IC555

    Fig 10.1.1: Voltage Controller Circuit

    For duty cycle = 1% For duty cycle = 25%

    For duty cycle = 75% For duty cycle = 99%

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

    42

    As the output source and sink current of IC555 is only 200mA, the output of the

    IC is given to the motor driving L293D which provides a high current and isolates the

    motor from the supply in order to prevent the supply from back EMF of the motor.

    Note: As the calibration unit is only for demonstration purpose, there are many

    specifications (like l293d, 12v DC shunt motor etc) not covered in the report.

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    11. PERFORMANCE GRAPHS

    As our WRDT measure speed in RPS, to have a comparison with speeds in

    RPM, we have to use a multiplication of 60 in our result. The following graph displays

    the linearity between the two readings-one with our WRDT and other with analog

    tachometer used for calibration test of a 1000 RPM DC motor.

    Fig 11.1: Graph with MF = 60

    Analog Tachometer Reading in

    RPM (for calibration test) X axis WRDT Readings in RPS

    Y axis

    950 16

    820 14

    800 13

    680 12

    440 7

    380 6

    Fig 11.2: Table for MF = 60

    0

    5

    10

    15

    20

    25

    30

    0 200 400 600 800 1000 1200 1400 1600

    SPP

    ED IN

    RP

    S -

    WR

    DT

    SPEED IN RPM - ANALOG TACHOMETER

    CALIBRATION TESTRELATIONSHIP BETWEEN RPM V/S RPS READINGS

    (MULTIPLICATION FACTOR 60)

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

    44

    But in case of a motor or any other rotating body, operating at lower speed, a

    multiplication factor of 60 means that, the resolution is 60.It means that a change of 60

    RPM will correspond to a change of 1 RPS. This is highly objectionable in case of such

    motors. However, this is not a big set-off, as we can reduce multiplication factor by

    increasing the number of reflecting surfaces. This increase the accuracy of low speed

    measurements greatly. One such instance where a 500 RPM motor was tested with a

    multiplication factor of 30 (two reflecting surfaces) is shown below.

    Fig 11.3: Graph for MF = 30

    Analog Tachometer Reading in

    RPM (for calibration test) X axis WRDT Readings in RPS

    Y axis

    600 20

    550 18

    500 16

    450 15

    400 13

    350 11

    300 10

    250 8

    200 6

    150 5

    100 3

    Fig 11.4: Table for MF = 30

    0

    5

    10

    15

    20

    25

    0 100 200 300 400 500 600 700

    SPP

    ED IN

    RP

    S -

    WR

    DT

    SPEED IN RPM - ANALOG TACHOMETER

    CALIBRATION TESTRELATIONSHIP BETWEEN RPM V/S RPS READINGS

    (MULTIPLICATION FACTOR 30)

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    12.0 PROGRAME CODING

    ORG 000H

    MOV DPTR,#LUT // moves the addres of LUT to DPTR

    MOV P1,#00000000B // Sets P1 as an output port

    MOV P0,#00000000B // Sets P0 as an output port

    MAIN: MOV R6,#14D

    SETB P3.5

    MOV TMOD,#01100001B // Sets Timer1 as Mode2 counter & Timer0 as

    Mode timer

    MOV TL1,#00000000B //loads initial value to TL1

    MOV TH1,#00000000B //loads initial value to TH1

    SETB TR1 // starts timer(counter) 1

    BACK: MOV TH0,#00000000B //loads initial value to TH0

    MOV TL0,#00000000B //loads initial value to TL0

    SETB TR0 //starts timer 0

    HERE: JNB TF0,HERE // checks for Timer 0 roll over

    CLR TR0 // stops Timer0

    CLR TF0 // clears Timer Flag 0

    DJNZ R6,BACK

    CLR TR1 // stops Timer(counter)1

    CLR TF0 // clears Timer Flag 0

    CLR TF1 // clears Timer Flag 1

    ACALL DLOOP // Calls subroutine DLOOP for displaying the count

    SJMP MAIN // jumps back to the main loop

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    DLOOP: MOV R5,#100D

    BACK1: MOV A,TL1 // loads the current count to the accumulator

    MOV B,#100D

    DIV AB // isolates the first digit of the count

    SETB P1.0

    ACALL DISPLAY // converts the 1st digit to 7 seg pattern

    MOV P0,A // puts the pattern to Port 0

    ACALL DELAY // 1mS delay

    ACALL DELAY

    MOV A,B

    MOV B,#10D

    DIV AB // isolates the secong digit of the count

    CLR P1.0

    SETB P1.1

    ACALL DISPLAY // converts the 2nd digit to 7 seg pattern

    MOV P0,A

    ACALL DELAY

    ACALL DELAY

    MOV A,B // moves the last digit of the count to accumulator

    CLR P1.1

    SETB P1.2

    ACALL DISPLAY // converts the 3rd digit to 7 seg pattern

    MOV P0,A

    ACALL DELAY

    ACALL DELAY

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    CLR P1.2

    DJNZ R5,BACK1 // repeats the subroutine DLOOP 100 times

    RET

    DELAY: MOV R7,#250D // 1mS delay

    DEL1: DJNZ R7,DEL1

    RET

    DISPLAY: MOVC A,@A+DPTR // gets 7 seg digit drive pattern for current value

    In A

    RET

    LUT: DB 40H // Look up table (LUT) starts here

    DB 79H

    DB 24H

    DB 30H

    DB 19H

    DB 12H

    DB 03H

    DB 78H

    DB 00H

    DB 10H

    END

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    13.0 BURNING THE HEX CODE

    In order to store the software code into the controller memory, which is nothing

    but a flash ROM, it must be flashed with some hardware tools accompanied by some

    software called IDE.

    The software platform we used was Keil Microvision V5 and the hardware used

    to flash the ROM was USBASP which is a USB programmer.

    13.1 BUILDING HEX FILE

    The following steps are involved in building the hex file:

    1. Create a new Microvision Project in the project menu. Save the file with proper name.

    2. Select your target microcontroller (AT89S51 in this case) and add startup files if needed.

    3. Open text editor and save yourfile.asm. 4. Write down your code. 5. Add the existing file yourfile.asm to source group one in target. 6. Build target. 7. You will see hex file in the destination folder. Burn the code using USBASP.

    Fig 13.1.A: Steps 1 to 4

  • WIDE RANGE DIGITAL TACHOMETER (WRDT)

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    Fig 13.1.B: Steps 5 to 7

    Fig 13.1.C: PRPGISP program windows Fig 13.1.D: USBASP

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    50

    14.0 MAJOR PROCESSES INVOLVED IN

    FABRICATING CIRCUIT

    The major process involved in the fabrication of circuit are as follows:-

    1 ) Etching PCB

    2 ) Soldering

    14.1 Etching PCB

    A printed circuit board mechanically supports and electrically connects

    electronic components using conductive tracks, pads, and other features etched from

    copper sheets laminated on to a nonconductive substrate. PCB can be single sided (one

    copper layer) , Double sided ( two copper layers ) or multi-layer conductors on different

    layers are connected with plated through holes called vias . Advance PCB may contain

    components like capacitors, resistors or active devices embedded in the substrate.

    Printed circuit board are used in all the simplest electronic product. Alternatives

    to PCBs include wire wrap and point to point construction. PCBs required the additional

    design effort to lay out the circuit but manufacturing circuits with PCB is cheaper and

    faster than with other wiring methods as components are mounted and wired with one

    single part.

    The materials required for etching PCB are as follows:-

    1 ) Copper Cladded Board.

    2 ) LASER Printer.

    3 ) fine sand paper or Kitchen scrubber.

    4 ) Chemicals

    a ) Hydrochloric Acid (HCL)

    b ) Ferrous chloride (Fecl3)

    c ) Thinner or Acetone

    5 ) Electronic or Hand drill with Fine Drill Bits (0.5mm-1.2mm)

    6 ) Hacksaw

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    The process of PCB etching involves :-

    14.2.1 DESIGN

    After analysing the circuit diagram , The very first step for etching PCB

    involves designing of layout for components and there connections on the board.this is

    done by various softweres like ExpressPCB, Egal, etc.

    Fig 14.2.1 : PCB track design using EXPRESS PCB

    14.2.2 PRINT THE DESIGN

    A ) Selection of Paper - Selecting an appropriate paper is your first step in

    making a right selection. Glossy photo quality paper or even a glossy thick magazine

    sheet would do wonders.

    B ) Selection of Printer - We have used a printer to transfer the circuit diagram

    onto the copper board. If you are using a sharpie or a marker, go ahead with it. Set your

    printer to output maximum toner and printer your circuit on the glossy paper.

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    Fig 14.2.2 : Laser Print (PART A)

    14.3 PREPARE BOARD AND TONER TRANSFER

    14.3.A Prepare the Copper board

    Normal Copper board availabe at your radio shop would be good enough. Use

    a kitchen scrub or a fine sand paper and rub surface until you feel it is clean. DO NOT

    over do it. Once done, clean it with water and a clean cloth and avoid touching the

    surface.

    14.3.B Transfer Tonner on board

    This step is not as complicated as the title says. Switch on your cloths iron and

    turn it to its highest setting. Place the printed paper over the board and start moving the

    iron over it for 10-15 minutes. Now drop the board into a mug of water and peel off the

    glossy paper.

    14.3.C Etching the Board

    Mix Hydrochloric acid to Ferric chloride in a ratio of 2:3 and drop your copper

    board into it. Within 2-3 minutes you can see the copper removed from the board and

    tracks clearly visible.

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    14.3.D Remove Tonner

    Wash the etched board thoroughly in water and then use acetone or a nail polish

    remover and clean the surface so that the toner is removed and copper tracks are clearly

    visible.

    14.3.E Drilling holes and Soldering

    Once the toner is completely removed, use a hand driller or an electronic drill

    and drill holes into the board to mount the components. Place the components and

    solder them across.

    You are ready with a complete professionally (almost) looking circuit board. If you

    have all the tools and parts in hand, the entire process takes less than an hour.

    Cautions:-

    Muriatic Acid is dangerous. Hydrogen peroxide, although not dangerous,

    still gives your skin a burnt effect. Be careful with these solutions.

    14.4 SOLDERING

    Soldering is a process in which two or more metal items are joined together

    by melting and flowing a filler metal (solder) into the joint, the filler metal having a

    lower melting point than the adjoining metal. Soldering differs from welding in that

    soldering does not involve melting the work pieces. In brazing, the filler metal melts

    at a higher temperature, but the work piece metal does not melt. For the efficient

    soldering flux is used.

    Fig 14.4 : Needle type Soldering Tip

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    The purpose of flux is to facilitate the soldering process. One of the obstacles

    to a successful solder joint is an impurity at the site of the joint, for example, dirt, oil

    or oxidation. The impurities can be removed by mechanical cleaning or by chemical

    means, but the elevated temperatures required to melt the filler metal (the solder)

    encourages the work piece (and the solder) to re-oxidize. This effect is accelerated as

    the soldering temperatures increase and can completely prevent the solder from

    joining to the work piece.

    Soldering irons have a ton of different tips, and each of them is better suited for

    different tasks. However, we have preferred to use a 1 mm needle tip soldering iron for

    efficient soldering. The fig shows the appearance of the iron tip.

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    15.0 KEY SPECIFICATIONS OF USED ICS

    15.1 AT89S51 SPECIFICATIONS

    SPECIFICATION DESCRIPTION RATING

    VIL Input Low Voltage 0.2 VCC-0.1V

    VIL Input High Voltage VCC+0.5V

    IS Power Supply Current 6.5mA

    1/t clcl Oscillator Frequency 33MHz

    Vcc Power supply 4.0V to 5.5V

    Rpd Reset Pull-down Resistor 0.3Mohm

    ILI Input Leakage Current +10uA

    CIO Pin Capacitance 10pF

    VOH Output High Voltage 0.75Vcc

    15.2 LM339 SPECIFICATIONS

    SPECIFICATION DESCRIPTION RATING

    VCC Power Supply Voltage 36V

    VIO Input Offset Voltage 5mVdc

    IBIAS Input Bias Current 250Na

    IIO Input Offset Current 5nA

    ICC Supply Current 2.5mA

    GV Voltage Gain 200V/mV

    ISINK Output Sink Current 16mA

    VSAT Saturation Voltage 400mV

    15.3 LM7805 SPECIFICATIONS

    SPECIFICATION DESCRIPTION RATING

    IOL(MAX) Max Load Current 1A

    VI Range of Input Voltages 5V 18V

    VDROP Dropout Voltage 2V TYP

    RR Ripple Rejection 73 dB TYP

    RO Output Resistance 15m

    ISC Short Circuit Current 230 mA TYP

    IPK Peak Current 2.2 A TYP

    IQ Quiescent Current 8 mA TYP

    REGLINE Line Regulation 1.6 mV (VI= 8-12V)

    REGLOAD Load Regulation 4.0 mV(IO= 250-

    750mA)

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    16. TEST POINTS

    After few years it may observe that the circuitry may malfunction or

    may not work, so if one would like to find the errors in the circuit than one can

    go for following testing points:

    1. The very basic and first test point of the circuit is power unit. The battery

    which is used in power unit needs to be checked whether it is providing a

    appropriate voltage above 8V. If the battery fails to give the voltage equal/above

    8V, replace the battery for powering the circuit properly.

    2. At the output of the power unit, check whether the voltage is approximately

    equal to 5V.

    3. To check the working of the sensor, connect the DSO across photo diode

    check whether the photo diode is in working state.

    4. To check the working of the signal conditioning circuit, connect the DSO

    across the output of IC LM339 and VCC and check whether a perfect square

    wave is achieved.

    5. To check the 7 segment display, connect the DMM across any select line (D0,

    D1, D2) and segments (a, b, c, d, e, f, g, decimal)

    6. If all above parameters are alright, then if EPROM is used to store the

    programme code the technician may need to check the bit values are as per the

    HEX codes, in case if they are showing errors then re-program the controller as

    there are chances of alteration of bit values in the case of microcontroller

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    17.0 COST ESTIMATION

    SR.NO. COMPONENT Cost

    (Rs) 1 Circuit board

    ( Cu cladded )

    15

    2 Microcontroller

    ( AT89S51 )

    40

    Sockets

    a. Microcontroller b. Comparator

    3

    3

    3 7 Seg common anode 4 Digit display 45

    4 Comparator

    (LM339)

    12

    5 Tx = LED

    Rx = Photo Diode

    10

    7

    6 Resisters

    (