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A Project Report on
DESIGN AND IMPLEMENTATION OF DIGITAL SPEEDOMETER
A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE
REQUIREMENTS FOR THE AMIETE
IN
ELECTRONICS AND TELECOMMUNICATION ENGINEERING
Submitted By :AMIT THAPASG - 190479
Under the Guidance ofMR. RAJEEV PURI
INSTITUTE OF ELECTRONICS & TELECOMMUNICATION ENGINEERSNEW DELHI
CERTIFICATE
This is certified that AMIT THAPA has carried out project work
presented in this thesis entitled “Design And Implementation Of
Digital Speedometer” for the award of IETE, under my
supervision. The report embodies result of original work and
studies carried out by students himself and the contents of the
thesis do not form the basis for the award of any other degree or
diploma to the candidate or to anybody else.
Signature of the project Guide
MR. RAJEEV PURI
Place:-
Date :-
ACKNOWLEDGEMENT
I am very much thankful from the core of my heart for the precious
contribution of my guide who provided his possible help the
successful completion of this project has been possible due to
sincere co operation guidance, inspiration moral support and
timely advice of my guide who devoted his utmost co-operation in
this project work. I also give special thanks to my colleagues for
that endless flow of ideas and all those who helped in this project
in some way or the other.
AMIT THAPA
SG - 190479
DECLARATION BY THE CANDIDATE
I, AMIT THAPA, hereby declares that the project work entitled
“Design And Implementation Of Digital Speedometer” under the partial
fulfillment and award of the diploma or degree and this has been submitted
anywhere else for the award of any other degree
I have not submitted the matter embodied in this project for the award of any
other degree or diploma. and all the content given in this project and can be
believed.
Signature of the student
AMIT THAPA
SG - 190479
CONTENTS
Introduction
Aim
Area of Project
Motivation
Detailed Discussion
Block Diagram
Input Section
Timer Section
Output Section
Component Details
Principle and Working
Design and Implementation
Design
Implementation
Main Circuitry
Input Section
Mechanical Section
PCB Layout
Cost of Production
Hurdles Faced
Application
Conclusion
Bibliography
ABSTRACT
The aim of our project is to develop prototype of a product “Digital
Speedometer”. It's used to measure speed up to 999 kmph with a
resolution of 1 kmph. It's a hardware project done in the field of Digital
Electronics and Instrumentation. It can replace ordinary analog
speedometer which has low range and resolution. It's rather inexpensive
and can be used in almost all vehicles. It can also be used for measuring
speed on industrial machinery and modified version of circuitry can be used
as an rpm counter.
This Digital Speedometer is provided for use in an automotive vehicle and
includes a transducer for connection to a conventional speedometer cable
driver. Transducer is equipped with an IR LED and a photo transistor,that
produces pulses in response to the rotational motion of the speedometer
cable driver. Pulses are transmitted to a counting circuit which is reset by
multivibrator circuits. The number of pulses from the transducer is
indicative of speed of the vehicle. It is tabulated by the counting circuits
during intervals between reset pulses. The number of counts tabulated
during each period is passed to a visual display.
INTRODUCTION
AIM
The present invention relates to a Digital Speedometer for use with
vehicles having internal electrical power supply. In particular, the invention
relates to a digital speedometer for automotive vehicles such as auto
mobiles, trucks and motor cycles. The Digital Speedometer designed is
highly efficient , low cost and can measure speed up to 999 kmph with a
resolution of 1kmph.
AREA OF PROJECT
It.s dealing with Digital Electronics Circuits and Instrumentation. The main
sections of the circuitry are IR section, Comparator, Timer, Counter,
Latching section and LED display.
MOTIVATION
The aim of our experiment is to create an efficient low cost Digital
Speedometer. It was inspired by the fact that most of the modern-day
vehicles use analog speedometers which have resolution of about 5kmph
and the range is also limited.
Historically auto motive vehicles have been provided with mechanical
speedometers in which rotation of wheel of the vehicle or of a drive
component of the transmission is transmitted as a torsional impulse the
torsional force applied to the cable is typically transmitted to needle in the
instrument panel which is deflected across a scale to indicate speed at
which vehicle is travelling. The Principal dis advantage with such systems
has been the requirement for a signal
generating system independent of the conventional mechanical
speedometer system associated with the auto mobile. It increases the cost
of the vehicle.
The Digital Speedometer we have designed can measure up to a speed of
999kmph with a resolution of 1kmph. It.s rather inexpensive and can be
used in almost all vehicles.
BLOCK DIAGRAM
INPUT SECTION
Input Section consists of IR LED, photo transistor, a comparator and a
mechanical section. An opaque disc is mounted on the spindle attached to
the front wheel of the vehicle. This disk has ten equidistant holes on its
periphery. On one side of the disc an Infrared LED is fixed and on opposite
side of the disc, in line with the IR LED, a phototransistor is mounted. IC
LM324 is wired as a comparator.
TIMER SECTION
Timer section consists of astable and monostable multivibrator circuits. So
we use IC 556 for his purpose. Astable section is used to trigger the
monostable multivibrator. IC 7400(AND gate) is used to set the gating
period.
OUTPUT SECTION
Output section consists of counter and latching sections along with LED
display. IC 7490 is used to implement the counter section. The number of
pulses counted during the gating period is he
speed N in kmph. IC 74175(Quad D flip-flop) is used as the latching circuit.
It helps in keeping the LED display constant for a particular period of time
so that displayed value could be read. IC 7447 is used as BCD to seven
segment decoder. Common anode LEDs are used in the output section to
view the speed measured.
COMPONENT DETAILS
IC 74175
IC 74175 is a quad, edge-triggered D-type flip-flop with individual D inputs
and both Q and Q out puts. The common buffered clock (CP) and Master
Reset (MR) inputs load and reset (clear) all flip flops simultaneously.
IC 7490
IC 7490 is a monolithic counter contain four maser-slave flip flops and
additional gating to provide a divide by two counter and a three stage
binary counter for which the count cycle length is divided byfive. It has
gated zero reset.
IC 7447
It.s a decoder driver IC used to drive a seven segment indicator. There are
two types of decoder
drivers suitable to two types of seven segmented displays. Logic circuit
inside the 7447 convert
the 4 bit BCD input to seven bit output which are active low.
IC 7400
It.s output will be „low. if all the inputs are in „high. state. IC 7400 is a Quad
2 input NAND gate.
It.s logic diagram and functional table are shown below.
IC 556
This device provide two independent timing circuits of the NA555, NE555,
SA555 or SE555
type each package. These circuits can be operated in the astable or
monostable mode with the
external resistor capacitor timing control .
IC LM 324
These devices consists of four independent high gain frequency
compensated op-amps that are
designed specifically to operate from a single supply over a wide range of
voltages.
Applications include transducer amplifiers, dc amplification block and all the
conventionasl
operational amplifier circuits that can be more easily impemented in single
supply voltage
systems.
PHOTO TRANSISTOR
IR LED
COMPONENT DESCRIPTION
RESISTORS: -
A Resistor is a heat-dissipating element and in the electronic circuits
it is mostly used for either controlling the current in the circuit or developing
a voltage drop across it, which could be utilized for many applications.
There are various types of resistors, which can be classified according to a
number of factors depending upon:
(I) Material used for fabrication
(II)Wattage and physical size
(III) Intended application
(IV) Ambient temperature rating
(V) Cost
Basically the resistor can be split in to the following four parts from
the construction viewpoint.
(1) Base
(2) Resistance element
(3) Terminals
(4) Protective means.
The following characteristics are inherent in all resistors and may be
controlled by design considerations and choice of material i.e. Temperature
co–efficient of resistance, Voltage co–efficient of resistance, high frequency
characteristics, power rating, tolerance & voltage rating of resistors.
Resistors may be classified as
(1)Fixed
(2)Semi variable
(3)Variable resistor.
In our project carbon resistors are being used.
CAPACITORS
The fundamental relation for the capacitance between two flat plates
separated by a dielectric material is given by:-
C=0.08854KA/D
Where: -
C= capacitance in pf.
K= dielectric constant
A=Area per plate in square cm.
D=Distance between two plates in cm
Design of capacitor depends on the proper dielectric material with
particular type of application. The dielectric material used for capacitors
may be grouped in various classes like Mica, Glass, air, ceramic, paper,
Aluminum, electrolyte etc. The value of capacitance never remains
constant. It changes with temperature, frequency and aging. The
capacitance value marked on the capacitor strictly applies only at specified
temperature and at low frequencies.
LED (Light Emitting Diodes)
As its name implies it is a diode, which emits light when forward biased.
Charge carrier recombination takes place when electrons from the N-side
cross the junction and recombine with the holes on the P side. Electrons
are in the higher conduction band on the N side whereas holes are in the
lower valence band on the P side. During recombination, some of the
energy is given up in the form of heat and light. In the case of
semiconductor materials like Gallium arsenide (GaAs), Gallium phoshide
(Gap) and Gallium arsenide phoshide (GaAsP) a greater percentage of
energy is released during recombination and is given out in the form of
light. LED emits no light when junction is reverse biased.
TRANSISTOR: -
A transistor consists of two junctions formed by sandwiching either p-
type or n-type semiconductor between a pair of opposite types.
Accordingly, there are two types of transistors namely: -
(1) n-p-n transistor (2) p-n-p transistor
(NPN) (PNP)
An n-p-n transistor is composed of two n-type semiconductors separated
by a thin section of p type. However a p-n-p transistor is formed by two p
sections separated by a thin section of n-type. In each type of transistor the
following points may be noted.
1. There are two p-n junctions, therefore a transistor may be regarded
as combination of two diodes connected back to back.
2. There are three terminals taken from each type of semiconductor.
3. The middle section is a very thin layer, which is the most important
factor in the functioning of a transistor.
4. Transistor can be used as an Amplifier also.
A transistor raises the strength of a weak signal and thus acts as an
amplifier. The weak signal is applied between emitter base junction and
output is taken across the load Rc connected in the collector circuit (in
common emitter configuration). In order to achieve faithful amplification, the
input circuit should always remain forward biased. To do so, a dc voltage is
applied in the input in addition to the signal. This dc Voltage is known as
biasing voltage and its magnitude and polarity should be such that it always
keeps the input circuit forward biased regardless of the polarity to the signal
to be amplified.
As the input circuit has low resistance a small change in signal
voltage causes an appreciable change in emitter current. This causes
change in collector current (by a factor called current gain of transistor) due
to transistor action. The collector current flowing through a high load
resistance Rc produces a large voltage across it. Thus a weak signal
applied to the input circuit appears in the amplified form in the collector
circuit. This is how a transistor acts as an amplifier.
Transistor may be used in different configuration like CB (common base) &
CC (common collector) according to requirements of amplifier (impedance
matching, buffer amplifier etc.).
TRANSFORMER
Definition: -
The transformer is a static electro-magnetic device that transforms
one alternating voltage (current) into another voltage (current). However,
power remains the some during the transformation. Transformers play a
major role in the transmission and distribution of ac power.
Principle: -
Transformer works on the principle of mutual induction. A transformer
consists of laminated magnetic core forming the magnetic frame. Primary
and secondary coils are wound upon the two cores of the magnetic frame,
linked by the common magnetic flux. When an alternating voltage is applied
across the primary coil, a current flows in the primary coil producing
magnetic flux in the transformer core. This flux induces voltage in
secondary coil.
Transformers are classified as: -
(a) Based on position of the windings with respect to core i.e.
(1) Core type transformer
(2) Shell type transformer
(b) Transformation ratio:
(1) Step up transformer
(2) Step down transformer
(a) Core & shell types: Transformer is simplest electrical machine, which
consists of windings on the laminated magnetic core. There are two
possibilities of putting up the windings on the core.
(1) Winding encircle the core in the case of core type transformer
(2) Cores encircle the windings on shell type transformer.
(b) Step up and Step down: In these Voltage transformation takes place
according to whether the
Primary is high voltage coil or a low voltage coil.
(1) Lower to higher-> Step up
(2) Higher to lower-> Step down
DIODES
- +
It is a two terminal device consisting of a P-N junction formed either
of Ge or Si crystal. The P and N type regions are referred to as anode and
cathode respectively. Commercially available diodes usually have some
means to indicate which lead is P and which lead is N.
RELAY
In this circuit a 12V magnetic relay is used. In magnetic relay,
insulated copper wire coil is used to magnetize and attract the plunger .The
plunger is normally connected to N/C terminal. A spring is connected to
attract the plunger upper side. When output is received by relay, the
plunger is attracted and the bulb glows.
P.C.B. MANUFACTURING PROCESS
It is an important process in the fabrication of electronic
equipment. The design of PCBs (Printed Circuit Boards) depends on circuit
requirements like noise immunity, working frequency and voltage levels etc.
High power PCBs require a special design strategy.
The fabrication process to the printed circuit board will determine to a
large extent the price and reliability of the equipment. A common target
aimed is the fabrication of small series of highly reliable professional quality
PCBs with low investment. The target becomes especially important for
customer tailored equipments in the area of industrial electronics.
The layout of a PCB has to incorporate all the information of the board
before one can go on the artwork preparation. This means that a concept
which clearly defines all the details of the circuit and partly defines the final
equipment, is prerequisite before the actual lay out can start. The detailed
circuit diagram is very important for the layout designer but he must also be
familiar with the design concept and with the philosophy behind the
equipment.
BOARD TYPES:
The two most popular PCB types are:
1. Single Sided Boards
The single sided PCBs are mostly used in entertainment electronics
where manufacturing costs have to be kept at a minimum. However
in industrial electronics cost factors cannot be neglected and single
sided boards should be used wherever a particular circuit can be
accommodated on such boards.
2. Double Sided Boards
Double-sided PCBs can be made with or without plated through
holes. The production of boards with plated through holes is fairly
expensive. Therefore plated through hole boards are only chosen
where the circuit complexities and density of components does not
leave any other choice.
CHRONOLOGY
The following steps have been followed in carrying out the project.
1. Study the books on the relevant topic.
2. Understand the working of the circuit.
3. Prepare the circuit diagram.
4. Prepare the list of components along with their specification. Estimate
the cost and procure them after carrying out market survey.
5. Plan and prepare PCB for mounting all the components.
6. Fix the components on the PCB and solder them.
7. Test the circuit for the desired performance.
8. Trace and rectify faults if any.
9. Give good finish to the unit.
10. Prepare the project report.
DESIGN SPECIFICATION
(I) STEPS TAKEN WHILE PREPARING CIRCUIT
(A) PCB DESIGNING
The main purpose of printed circuit is in the routing of electric currents
and signal through a thin copper layer that is bounded firmly to an
insulating base material sometimes called the substrate. This base is
manufactured with an integrally bounded layers of thin copper foil which
has to be partly etched or removed to arrive at a pre-designed pattern to
suit the circuit connections or other applications as required.
The term printed circuit board is derived from the original method
where a printed pattern is used as the mask over wanted areas of copper.
The PCB provides an ideal baseboard upon which to assemble and hold
firmly most of the small components.
From the constructor’s point of view, the main attraction of using PCB
is its role as the mechanical support for small components. There is less
need for complicated and time consuming metal work of chassis
contraception except perhaps in providing the final enclosure. Most straight
forward circuit designs can be easily converted in to printed wiring layer the
thought required to carry out the inversion cab footed high light an possible
error that would otherwise be missed in conventional point to point
wiring .The finished project is usually neater and truly a work of art.
Actual size PCB layout for the circuit shown is drawn on the copper
board. The board is then immersed in FeCl3 solution for 12 hours. In this
process only the exposed copper portion is etched out by the solution.
Now the petrol washes out the paint and the copper layout on PCB is
rubbed with a smooth sand paper slowly and lightly such that only the oxide
layers over the Cu are removed. Now the holes are drilled at the respective
places according to component layout as shown in figure.
(B) LAYOUT DESIGN:
When designing the layout one should observe the minimum size
(component body length and weight). Before starting to design the layout
we need all the required components in hand so that an accurate
assessment of space can be made. Other space considerations might also
be included from case to case of mounted components over the printed
circuit board or to access path of present components.
It might be necessary to turn some components around to a different
angular position so that terminals are closer to the connections of the
components. The scale can be checked by positioning the components on
the squared paper. If any connection crosses, then one can reroute to
avoid such condition.
All common or earth lines should ideally be connected to a common line
routed around the perimeter of the layout. This will act as the ground plane.
If possible try to route the outer supply line to the ground plane. If possible
try to route the other supply lines around the opposite edge of the layout
through the center. The first set is tearing the circuit to eliminate the
crossover without altering the circuit detail in any way.
Plan the layout looking at the topside to this board. First this should
be translated inversely, later for the etching pattern large areas are
recommended to maintain good copper adhesion. It is important to bear in
mind always that copper track width must be according to the
recommended minimum dimensions and allowance must be made for
increased width where termination holes are needed. From this aspect, it
can become little tricky to negotiate the route to connect small transistors.
There are basically two ways of copper interconnection patterns
under side the board. The first is the removal of only the amount of copper
necessary to isolate the junctions of the components to oneanother. The
second is to make the interconnection pattern looking more like
conventional point wiring by routing uniform width of copper from
component to component.
(C) ETCHING PROCESS:
Etching process requires the use of chemicals. acid resistant dishes
and running water supply. Ferric chloride is mostly used solution but other
etching materials such as ammonium per sulphate can be used. Nitric acid
can be used but in general it is not used due to poisonous fumes.
The pattern prepared is glued to the copper surface of the board
using a latex type of adhesive that can be cubed after use. The pattern is
laid firmly on the copper using a very sharp knife to cut round the pattern
carefully to remove the paper corresponding to the required copper pattern
areas. Then apply the resistant solution, which can be a kind of ink solution
for the purpose of maintaining smooth clean outlines as far as possible.
While the board is drying, test all the components.
Before going to next stage, check the whole pattern and cross
check
with the circuit diagram. Check for any free metal on the copper. The
etching bath should be in a glass or enamel disc. If using crystal of ferric-
chloride these should be thoroughly dissolved in water to the proportion
suggested. There should be 0.5 lt. of water for 125 gm of crystal.
To prevent particles of copper hindering further etching, agitate the
solutions carefully by gently twisting or rocking the tray.
The board should not be left in the bath a moment longer than is
needed to remove just the right amount of copper. Inspite of there being a
resistive coating there is no protection against etching away through
exposed copper edges. This leads to over etching. Have running water
ready so that etched board can be removed properly and rinsed. This will
halt etching immediately.
Drilling is one of those operations that calls for great care. For most
purposes a 0.5mm drill is used. Drill all holes with this size first those that
need to be larger can be easily drilled again with the appropriate larger
size.
(D) COMPONENT ASSEMBLY: -
From the greatest variety of electronic components available, which
runs into thousands of different types it is often a perplexing task to know
which is right for a given job.
There could be damage such as hairline crack on PCB. If there are,
then they can be repaired by soldering a short link of bare copper wire over
the affected part.
The most popular method of holding all the items is to bring the wires
far apart after they have been inserted in the appropriate holes. This will
hold the component in position ready for soldering.
Some components will be considerably larger .So it is best to start
mounting the smallest first and progressing through to the largest. Before
starting, be certain that no further drilling is likely to be necessary because
access may be impossible later.
Next will probably be the resistor, small signal diodes or other similar
size components. Some capacitors are also very small but it would be best
to fit these afterwards. When fitting each group of components mark off
each one on the circuit as it is fitted so that if we have to leave the job we
know where to recommence.
Although transistors and integrated circuits are small items there are
good reasons for leaving the soldering of these until the last step. The main
point is that these components are very sensitive to heat and if subjected to
prolonged application of the soldering iron, they could be internally
damaged.
All the components before mounting are rubbed with sand paper so
that oxide layer is removed from the tips. Now they are mounted according
to the component layout.
(E) SOLDERING: -
This is the operation of joining the components with PCB after this
operation the circuit will be ready to use to avoid any damage or fault
during this operation following care must be taken.
1.A longer duration contact between soldering iron bit & components lead
can exceed the temperature rating of device & cause partial or total
damage of the device. Hence before soldering we must carefully read the
maximum soldering temperature & soldering time for device.
2.The wattage of soldering iron should be selected as minimum as
permissible for that soldering place.
3.To protect the devices by leakage current of iron its bit should be earthed
properly.
4.We should select the soldering wire with proper ratio of Pb & Tn to
provide the suitable melting temperature.
5.Proper amount of good quality flux must be applied on the soldering point
to avoid dry soldering.
PRINCIPLE AND WORKING
This instrument displays the speed of the vehicle in kmph. An opaque disc
is mounted on the spindle attached to the front wheel of the vehicle. This
disk has ten equidistant holes on its periphery. On one side of the disc an
Infrared LED is fixed and on opposite side of the disc, in line with the IR
LED, a phototransistor is mounted. IC LM324 is wired as a comparator.
When a hole appears between the IR LED and phototransistor, the
phototransistor conducts. Hence the voltage at collector of phototransistor
and inverting input of LM324 go „low., and thus output of LM324 becomes
logic „high.. So rotation of the speedometer cable results in a pulse at the
output of LM324, The frequency of this waveform is proportional to the
speed.
Let „N. be the number of pulses in time „t. seconds and numerically equal
to the number of kilometer per hour (kmph).
For vehicle with a wheel circumference of 1.38 meters, and number of
pulses equal to 10 per revolution, we get the relationship:
(N pulses)/t = N kmph
= (N×1000)/(3600×1.38) m/s
= (N×1000×10)/(3600×1.38) pulse per second.
Therefore, time „t.= 0.4968.
As shown in timing diagram, at t=0, output of astable flip-flop IC1(a) goes
low and triggers monostable multivibrator IC1(b). Pulse width of
monostable multivibrator IC1 (a), ton =0.513 and toff = 0.01 sec. The
outputs of IC1 (a) and IC1(b) and the signal from the transducer section are
ANDed. The number of pulses counted during the gating period is the
speed N is kmph. At the end of gating period, output „B. of monostable
IC1(b) goes low and B goes high. The rising edge of B is used to enable
the quad „D. flip-flops 74175. At this instant, ie at t=0.5068, the number
(speed) „N. will be latched corresponding to the „D. flip-flops and displayed.
At t= 0.510, output of astable flip-flop IC1(a) goes low and remains low for
0.01 sec. This waveform is invented and applied to the reset terminals of
the all counters (active-high).
Waveforms as shown below,
Thus the counters are rest and counting begins afresh at t=0.520. up to the
time t=0.520 + 0.5068 sec. However the „D. flip-flops are not enabled and
the previous speed is displayed. The new speed is displayed at t=
0.520+0.5068 sec. In this way speed will be updated every 0.520 sec. This
speedometer can measure up to 999kmph with a resolution of 1kmph.
3 DESIGN AND IMPLEMENTATION
3.1 DESIGN
Gating Period:
Let „N. be the number of pulses in time „t. seconds and numerically equal
to the number of
kilometer per hour (kmph).
For vehicle with a wheel circumference of 1.38 meters, and number of
pulses equal to 10 per
revolution, we get the relationship:
(N pulses)/t = N kmph
= (N×1000)/(3600×1.38) m/s
= (N×1000×10)/(3600×1.38) pulse per second.
Therefore, time „t.= 0.4968.
Input Comparator Section:
For the comparator, resistance values are determined by the voltage
divide rule. Equal voltage
(2.5V) are assumed across the + and – terminal. Thus we use 56K at the
positive terminal. In
order to obtain perfect output we used a 1M potentiometer at the collector
of phototransistor.
Astable and Monostable Multivibrator Section:
For astable multivibrator, ton = 0.693.(R1+R2).C = 0.51 Sec
Let R2= 1K and C= 10µF.
Thus we get, R1= 72.9 K. So we use 100 K potentiometer.
For monostable multivibrator, T= 1.1RC = 0.4968
Let C= 0.47µF.
Thus we get, R=960.9K. So we use 1M potentiometer.
3.2 IMPLEMENTATION
3.2.1 MAIN CIRCUITRY
3.2.2 INPUT SECTION
3.2.3 MECHANICAL ARRANGEMENT
3.2.4 PCB LAYOUT
COMPONENTS USED
APPLICATION
It can be used in almost all vehicles.
It can be used for industrial machinery speed measurement.
By modification in the circuitry can also be used as rpm counter and
odometer.
6. CONCLUSION
An efficient low cost digital speedometer which can measure speed up to
999kmph with a
resolution of 1kmph has been designed.
Resolution can be improved by using additional displays.
Circuit can be modified using microcontroller and LCD display.
PROJECT VIEW
BIBLIOGRAPHY
1) Mano M M, Digital Design, PHI
2) David A Bell, Electronic Instrumentation and measurements, PHI
3) Sedra and Smith, Microelectronic Circuits, Oxford University Press
4) Electronics For You magazine
5) www.efymagazine.com
6) www.elektor.com
