Digital Tachometer Project Report

WIDE RANGE DIGITAL TACHOMETER (WRDT)

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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


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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.


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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


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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


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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


27

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


28

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


29

7.0 ATMEL AT89S51 MICROCONTOLLER

7.1 ARCHITECTURE OVERVIEW

Fig 7.1: AT89S51 Architecture


30

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


31

7.4 PIN DESCRIPTION AT89S51

Fig 7.4: Pin Description of AT89S51


32

7.5 INSTRUCTION SET AND OTHER VENDORS (8051)

Fig 7.5.A: 8051 Instruction Set

Fig 7.5.B: Famous 8051 Vendors Worldwide


33

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.


34

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.


35

9.0 OVERALL CIRCUIT IN ACTION

Fig 9.0: Overall Circuit Diagram


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.


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


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.


39

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


40

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



Speed of motor = 1000RPM = 16 OR 17 RPS


41

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%


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.


43

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)


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)


45

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



ACALL DLOOP // Calls subroutine DLOOP for displaying the count

SJMP MAIN // jumps back to the main loop


46

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


47

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


48

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


49

Fig 13.1.B: Steps 5 to 7

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


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


51

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.


52

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.


53

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


54

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.


55

15.0 KEY SPECIFICATIONS OF USED ICS

15.1 AT89S51 SPECIFICATIONS


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


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


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)


56

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


57

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

(

Documents

Digital Tachometer Project Report