Sem

1

THE INTELLIGENT EMBEDDED CONTROL WARNING SYSTEM FOR CAR REVERSING

CHAPTER - 1

INTRODUCTION

1.1 EMBEDDED SYSTEM:

An embedded system is a special-purpose system in which the computer is

completely encapsulated by or dedicated to the device or system it controls. Unlike a general-

purpose computer, such as a personal computer, an embedded system performs one or a few

predefined tasks, usually with very specific requirements. Since the system is dedicated to

specific tasks, design engineers can optimize it, reducing the size and cost of the product.

Embedded systems are often mass-produced, benefiting from economies of scale.

Personal Digital Assistants (PDAs) or handheld computers are generally considered

embedded devices because of the nature of their hardware design, even though they are more

expandable in software terms. This line of definition continues to blur as devices expand.

With the introduction of the OQO Model 2 with the Windows XP operating system and ports

such as a USB port — both features usually belong to "general purpose computers", — the

line of nomenclature blurs even more.

Physically, embedded systems ranges from portable devices such as digital watches

and MP3 players, to large stationary installations like traffic lights, factory controllers, or the

systems controlling nuclear power plants.

In terms of complexity embedded systems can range from very simple with a single

microcontroller chip, to very complex with multiple units, peripherals and networks mounted

inside a large chassis or enclosure.

Figure 1.1: Embedded system

DEPT. OF ECE

2


1.2 EXAMPLES OF EMBEDDED SYSTEMS:

Avionics, such as inertial guidance systems, flight control hardware/software and other

integrated systems in aircraft and missiles

Cellular telephones and telephone switches

Engine controllers and antilock brake controllers for automobiles

Home automation products, such as thermostats, air conditioners, sprinklers, and security

monitoring systems

Handheld calculators

Handheld computers

Household appliances, including microwave ovens, washing machines, television sets, DVD

players and recorders

Medical equipment

Personal digital assistant

Videogame consoles

Computer peripherals such as routers and printers.

DEPT. OF ECE

3


CHAPTER - 2

BLOCK DIAGRAM

Figure 2: Block diagram

DEPT. OF ECE

AT89S52

Micro

Controller

Ultrasonic Sensor

Power supply

LDR

LCD Display

Driver Circuit

LED Lamp with

Motor

Buzzer

4


CHAPTER - 3

HARDWARE COMPONENTS

3.1 POWER SUPPLY:

All digital circuits require regulated power supply. In this article we are going to learn

how to get a regulated positive supply from the mains supply. Figure 3 shows the basic block

diagram of a fixed regulated power supply. Let us go through each block.

The input to the circuit is applied from the regulated power supply. The a.c. input i.e.,

230V from the mains supply is step down by the transformer to 12V and is fed to a rectifier.

The output obtained from the rectifier is a pulsating d.c voltage. So in order to get a pure d.c

voltage, the output voltage from the rectifier is fed to a filter to remove any a.c components

present even after rectification. Now, this voltage is given to a voltage regulator to obtain a

pure constant dc voltage.

Figure 3.1: Block Diagram Of Power Supply

DEPT. OF ECE

RegulatorBridge

Rectifier

Step down

transformer

230V AC

50HzD.C

Output

Filter

5


3.1.1 Transformer:

Usually, DC voltages are required to operate various electronic equipment and these

voltages are 5V, 9V or 12V. But these voltages cannot be obtained directly. Thus the a.c

input available at the mains supply i.e., 230V is to be brought down to the required voltage

level. This is done by a transformer. Thus, a step down transformer is employed to decrease

the voltage to a required level.

Figure 3.1.1: Transformer.

A transformer consists of two coils also called as “WINDINGS” namely PRIMARY

& SECONDARY.

They are linked together through inductively coupled electrical conductors also called

as CORE. A changing current in the primary causes a change in the Magnetic Field in the

core & this in turn induces an alternating voltage in the secondary coil. If load is applied to

the secondary then an alternating current will flow through the load. If we consider an ideal

condition then all the energy from the primary circuit will be transferred to the secondary

circuit through the magnetic field.

So,

The secondary voltage of the transformer depends on the number of turns in the Primary

as well as in the secondary.

DEPT. OF ECE

6


3.1.2 Rectifier:

A rectifier is a device that converts an AC signal into DC signal. For rectification

purpose we use a diode, a diode is a device that allows current to pass only in one direction

i.e. when the anode of the diode is positive with respect to the cathode also called as forward

biased condition & blocks current in the reversed biased condition.

Bridge Rectifier:-

As the name suggests it converts the full wave i.e. both the positive & the negative

half cycle into DC thus it is much more efficient than Half Wave Rectifier & that too without

using a center tapped transformer thus much more cost effective than Full Wave Rectifier.

Full Bridge Wave Rectifier consists of four diodes namely D1, D2, D3 and D4.

During the positive half cycle diodes D1 & D4 conduct whereas in the negative half cycle

diodes D2 & D3 conduct thus the diodes keep switching the transformer connections so we

get positive half cycles in the output.

Figure 3.1.2: Bridge rectifier

If we use a center tapped transformer for a bridge rectifier we can get both positive &

negative half cycles which can thus be used for generating fixed positive & fixed negative

voltages.

DEPT. OF ECE

7


3.1.3 Filter capacitor:

Even though half wave & full wave rectifier give DC output, none of them provides a

constant output voltage. For this we require to smoothen the waveform received from the

rectifier. This can be done by using a capacitor at the output of the rectifier this capacitor is

also called as “FILTER CAPACITOR” or “SMOOTHING CAPACITOR” or “RESERVOIR

CAPACITOR”. Even after using this capacitor a small amount of ripple will remain. We

place the Filter Capacitor at the output of the rectifier the capacitor will charge to the peak

voltage during each half cycle then will discharge its stored energy slowly through the load

while the rectified voltage drops to zero, thus trying to keep the voltage as constant as

possible.

Figure 3.1.3: Filter wave forms

If we go on increasing the value of the filter capacitor then the Ripple will decrease.

But then the costing will increase. The value of the Filter capacitor depends on the current

consumed by the circuit, the frequency of the waveform & the accepted ripple

Where,

Vr= accepted ripple voltage.( should not be more than 10% of the voltage)

I= current consumed by the circuit in Amperes.

F= frequency of the waveform. A half wave rectifier has only one peak in one cycle so F=25Hz

Where as a full wave rectifier has Two peaks in one cycle so F=100Hz.

DEPT. OF ECE

8


3.1.4 Voltage regulator:

A Voltage regulator is a device which converts varying input voltage into a constant

regulated output voltage. Voltage regulator can be of two types

1) Linear Voltage Regulator:

Also called as Resistive Voltage regulator because they dissipate the excessive

voltage resistively as heat.

2) Switching Regulators:

They regulate the output voltage by switching the Current ON/OFF very

rapidly. Since their output is either ON or OFF it dissipates very low power thus

achieving higher efficiency as compared to linear voltage regulators. But they are

more complex & generate high noise due to their switching action. For low level of

output power switching regulators tend to be costly but for higher output wattage they

are much cheaper than linear regulators.

The most commonly available Linear Positive Voltage Regulators are the 78XX

series where the XX indicates the output voltage. And 79XX series is for Negative Voltage

Regulators.

Figure 3.1.4: Voltage Regulator

After filtering the rectifier output the signal is given to a voltage regulator. The

maximum input voltage that can be applied at the input is 35V.Normally there is a 2-3 Volts

drop across the regulator so the input voltage should be at least 2-3 Volts higher than the

output voltage. If the input voltage gets below the Vmin of the regulator due to the ripple

voltage or due to any other reason the voltage regulator will not be able to produce the correct

regulated voltage.

DEPT. OF ECE

9


IC 7805:-

7805 is an integrated three-terminal positive fixed linear voltage regulator. It supports

an input voltage of 10 volts to 35 volts and output voltage of 5 volts. It has a current rating of

1 amp although lower current models are available. Its output voltage is fixed at 5.0V. The

7805 also has a built-in current limiter as a safety feature. 7805 is manufactured by many

companies, including National Semiconductors and Fairchild Semiconductors.

The 7805 will automatically reduce output current if it gets too hot. The last two digits

represent the voltage; for instance, the 7812 is a 12-volt regulator. The 78xx series of

regulators is designed to work in complement with the 79xx series of negative voltage

regulators in systems that provide both positive and negative regulated voltages, since the

78xx series can't regulate negative voltages in such a system.

The 7805 & 78 is one of the most common and well-known of the 78xx series

regulators, as it's small component count and medium-power regulated 5V make it useful for

powering TTL devices.

Table 3.1. Specifications of IC7805

DEPT. OF ECE

SPECIFICATIONS IC 7805

Vout 5V

Vein - Vout Difference 5V - 20V

Operation Ambient Temp 0 - 125°C

Output Imax 1A

10


3.2 ULTRASONIC SENSOR:

This "ECHO" Ultrasonic Distance Sensor from Rhydolabz is an amazing product that

provides very short (2CM) to long-range (4M) detection and ranging. The sensor provides

precise, stable non- contact distance measurements from 2cm to 4 meters with very high

accuracy. Its compact size, higher range and easy usability make it a handy sensor for

distance measurement and mapping. The board can easily be interfaced to microcontrollers

where the triggering and measurement can be done using one I/O pin. The sensor transmits an

ultrasonic wave and produces an output pulse that corresponds to the time required for the

burst echo to return to the sensor. By measuring the echo pulse width, the distance to target

can easily be calculated.

ECHO SENSOR FEATURES:

• Professional EMI/RFI Complaint PCB Layout Design for Noise Reduction

• Range : 2 cm to 4 m

• Accurate and Stable range data

• Data loss in Error zone eliminated

• Modulation at 40 KHz

• Mounting holes provided on the circuit board

• Triggered externally by supplying a pulse to the signal pin

• 5V DC Supply voltage

• Current - < 20mA

• Bidirectional TTL pulse interface on a single I/O pin can communicate with 5 V TTL

or 3.3V CMOS microcontrollers

• Echo pulse: positive TTL pulse, 87 ^s minimum to 30 ms maximum(PWM)

• On Board Burst LED Indicator shows measurement in progress

• 3-pin header makes it easy to connect using a servo extension cable, no soldering

required

DEPT. OF ECE

11


Table 3.2.1: Pin Description Of Ultra Sonic Sensor

PIN PIN NAME DETAILS

VCC Power Supply Power Supply Input (+5V)

GND Ground Ground Level of Power supply

SIGNAL Signal I/O This pin reads the trigger pulse from the host microcontroller and

returns the pulse based on the distance.

COMMUNICATION PROTOCOL

FINDING THE DISTANCE:

Under control of a host microcontroller (trigger pulse), the ECHO sensor emits a short

40 kHz (ultrasonic) wave. This burst travels through the air, hits an object and then bounces

back to the sensor. The ECHO sensor provides an output pulse to the host (through its signal

pin) when the echo is detected; hence the distance to the target can be measured from the

width of this pulse.

DEPT. OF ECE

Fig 3.2.1:Ultrasonic sensor waveforms

12


Table 3.2.2: Output Of UltraSonic Sensor For Different Inputs:

Host Device Input Trigger Pulse * OUT 10 us(min & typical} 100us max

ECHO Echo Holdoff HOLDOFF 700 us

Sensor Burst Frequency 'BURST 200us ® 40KHz

Echo Return Pulse Minimum !IN-HIN S7us

Echo Return Pulse Maximum 'LN-MAX 30ms

Delay before next measurement 32ms

=

Speed of ultrasonic wave is 347 m/s equivalent to 0 .0347cm/psec ( Temperature

dependent)

Timer count multiplied with 200nsec (0.2psec ), internal clock period gives the echo

time (say, Et).

As per the eqn: Speed = distance/time

=> echo distance (Ed) = echo speed(Ev)*echo time(Et)

ie, distance (Ed) = 0.0347cm per psec (Ev) * Et psec

The obtained distance will be twice the actual distance since it gives the to and fro

distance of the object as per the to and fro time equated to the equation: (ie, Et stands for

2Et). Thus the obtained distance divided by 2 gives actual distance of the obstacle.

ie, Actual distance = Ed/2

As per the above illustration your equation is,

Ed = Ev * (Et/2)

Et = 2 * Ed /Ev

Et = (2/0.0347) * Ed

Et = 58 * Ed

Ed (in cm) = Et(in psec)/58

Figure 3.2.2: Ultrasonic Sensor

PRACTICAL CONSIDERATION FOR USE

DEPT. OF ECE

13


Object Positioning:-

The ECHO sensor cannot accurately measure the distance to an object that:

• Is more than 4 meters away, Fig 3.2.3b

• That has its reflective surface at a shallow angle so that sound will not be reflected

back towards the sensor (Angle 0 < 90°), Fig 3.2.3b. or

• Is too small to reflect enough sound back to the sensor.

In addition, if your ECHO sensor is mounted low on your device, you may detect

sound reflecting off the floor.

Figure 3.2.3a: Ideal Case of Positioning Figure 3.2.3b: Error Case

Target Object Material:-

In addition, objects that absorb sound or have a soft or irregular surface, such as a

stuffed animal, may not reflect enough sound to be detected accurately. The ECHO sensor

will detect the surface of water; however it is not rated for outdoor use or continual use in a

wet environment. Condensation on its transducers may affect performance and lifespan of the

device.

Air Temperature:-

DEPT. OF ECE

14


Temperature has an effect on the speed of sound in air that is measured by the ECHO

sensor. If the temperature (degree Celsius) is known, the formula is C_air = 331.5 + (0.6 *

Tc)m/s The percent error over the sensor's operating range of 0 to 70 ° C is significant, in the

magnitude of 11 to 12 percent. The use of conversion constants to account for air temperature

may be incorporated into your program.

BOARD SPECIFICATION:

VCC -- Power supply input marked 'A'

5V supply has to be provided for its reliable performance

SIG -- Signal pin marked 'B'

This pin is used for output PWM to the host controller

GND -- Ground level of Power supply marked 'C'

The marking 'D' points to the Burst LED Indicator that shows measurement in

progress.

fi

DEPT. OF ECE

Figure 3.2.4: Ultrasonic sensor board specifications

15


3.3 LDR

A photo resistor or Light Dependent Resistor or CdS Cell is a resistor whose

resistance decreases with increasing incident light intensity. It can also be referred to as a

photoconductor. A photo resistor is made of a high resistance semiconductor. If light falling

on the device is of high enough frequency, photons absorbed by the semiconductor give

bound electrons enough energy to jump into the conduction band. The resulting free electron

(and its hole partner) conduct electricity, thereby lowering resistance.

A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor

has its own charge carriers and is not an efficient semiconductor, e.g. silicon. In intrinsic

devices the only available electrons are in the valence band, and hence the photon must have

enough energy to excite the electron across the entire band gap. Extrinsic devices have

impurities, also called dopants, added whose ground state energy is closer to the conduction

band; since the electrons don't have as far to jump, lower energy photons (i.e., longer

wavelengths and lower frequencies) are sufficient to trigger the device. If a sample of silicon

has some of its atoms replaced by phosphorus atoms (impurities), there will be extra electrons

available for conduction. This is an example of an extrinsic semiconductor.

Figure 3.3.1: LDR

A Light Dependent Resistor (LDR, photoconductor, or photocell) is a device which has a

resistance which varies according to the amount of light falling on its surface. They will be having a

resistance of 1 MOhm in total darkness, and a resistance of a 1 to 10 of kOhm in bright light. A

photoelectric device can be either intrinsic or extrinsic.

DEPT. OF ECE

http://en.wikipedia.org/wiki/Dopants

http://en.wikipedia.org/wiki/Bandgap

http://en.wikipedia.org/wiki/Valence_band

http://en.wikipedia.org/wiki/Electrical_resistance

http://en.wikipedia.org/wiki/Electron_hole

http://en.wikipedia.org/wiki/Conduction_band

http://en.wikipedia.org/wiki/Electron

http://en.wikipedia.org/wiki/Photon

http://en.wikipedia.org/wiki/Frequency

http://en.wikipedia.org/wiki/Semiconductor

http://en.wikipedia.org/wiki/Electrical_resistance

http://en.wikipedia.org/wiki/Resistor

16


Applications:-

An LDR can even be used in a simple remote control circuit using the backlight of a mobile

phone to turn on a device - call the mobile from anywhere in the world, it lights up the LDR, and

lighting can be turned on remotely!

There are two basic circuits using light dependent resistors - the first is activated by darkness,

the second is activated by light.

Figure 3.3.2: Circuit Diagram of LDR in day time

In the circuit diagram on the left, the led lights up whenever the LDR is in darkness. The 10K

variable resistor is used to fine-tune the level of darkness required before the LED lights up. The 10K

standard resistor can be changed as required to achieve the desired effect, although any replacement

must be at least 1K to protect the transistor from being damaged by excessive current.

By swapping the LDR over with the 10K and 10K variable resistors , the circuit will be

activated instead by light. Whenever sufficient light falls on the LDR (manually fine-tuned using the

10K variable resistor), the LED will light up.

Figure 3.3.3: Circuit Diagram of LDR in night time

DEPT. OF ECE

http://bp0.blogger.com/_XTElFWnvKxw/R0cNlFkDImI/AAAAAAAAAHo/JLsXCx-tCBI/s1600-h/ldr-darkness-activated-circuit.jpg

http://bp0.blogger.com/_XTElFWnvKxw/R0cOHFkDInI/AAAAAAAAAHw/IkLBsNtXijo/s1600-h/ldr-light-activated-circuit.jpg

17


The circuits shown above are not practically useful. In a real world circuit, the LED

(and resistor) between the positive voltage input (Vin) and the collector (C) of the transistor

would be replaced with the device to be powered.

Figure 3.3.4: Circuit Diagram Of Relay

Typically a relay is used - particularly when the low voltage light detecting circuit is used to

switch on (or off) a 240V mains powered device. A diagram of that part of the circuit is shown above.

When darkness falls (if the LDR circuit is configured that way around), the relay is triggered and the

240V device - for example a security light - switches on.

Measure Light Intensity using Light Dependent Resistor (LDR):

The relationship between the resistance RL and light intensity Lux for a typical LDR

is RL = 500 / Lux Kohm

With the LDR connected to 5V through a 3.3K resistor, the output voltage of the LDR

is Vo = 5*RL / (RL+3.3)

Figure 3.3.5: Measuring the intensity of LDR

Reworking the equation, we obtain the light intensity

Lux = (2500/Vo - 500)/3

DEPT. OF ECE

http://bp1.blogger.com/_XTElFWnvKxw/R0cQdVkDIoI/AAAAAAAAAH4/J0FMeIlsxdg/s1600-h/LDR_html_m5cb0e77a.gif

18


3.4 MICRO CONTROLLER

A BRIEF HISTORY OF 8051

In 1981, Intel Corporation introduced an 8 bit microcontroller called 8051. This

microcontroller had 128 bytes of RAM, 4K bytes of chip ROM, two timers, one serial port,

and four ports all on a single chip. At the time it was also referred as “A SYSTEM ON A

CHIP”

AT89S52:

The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with

8K bytes of in-system programmable Flash memory. The device is manufactured using

Atmel’s high-density nonvolatile memory technology and is compatible with the industry-

standard 80C51 instruction set and pinout. The on-chip Flash allows the program memory to

be reprogrammed in-system or by a conventional nonvolatile memory pro-grammer. By

combining a versatile 8-bit CPU with in-system programmable Flash on a monolithic chip,

the Atmel AT89S52 is a powerful microcontroller, which provides a highly flexible and cost-

effective solution to many, embedded control applications. The AT89S52 provides the

following standard features: 8K bytes of Flash, 256 bytes of RAM, 32 I/O lines, Watchdog

timer, two data pointers, three 16-bit timer/counters, a six-vector two-level interrupt

architecture, a full duplex serial port, on-chip oscillator, and clock circuitry. In addition, the

AT89S52 is designed with static logic for operation down to zero frequency and supports two

software selectable power saving modes. The Idle Mode stops the CPU while allowing the

RAM, timer/counters, serial port, and interrupt system to continue functioning. The Power-

down mode saves the RAM con-tents but freezes the oscillator, disabling all other chip

functions until the next interrupt

Figure 3.4.1: Over view of AT89S52

DEPT. OF ECE

19


Figure 3.4.2:Internal Blocks Of AT89S52

8031 has 128 bytes of RAM, two timers and 6 interrupts.

8051 has 4K ROM, 128 bytes of RAM, two timers and 6 interrupts.

8052 has 8K ROM, 256 bytes of RAM, three timers and 8 interrupts.

Of the three microcontrollers, 8051 is the most preferable. Microcontroller supports

both serial and parallel communication.

In the concerned project 8052 microcontroller is used. Here microcontroller used is

AT89S52, which is manufactured by ATMEL laboratories.

The 8051 is the name of a big family of microcontrollers. The device which we are

going to use along this tutorial is the 'AT89S52' which is a typical 8051 microcontroller

manufactured by Atmel™. Note that this part doesn't aim to explain the functioning of the

different components of a 89S52 microcontroller, but rather to give you a general idea of the

organization of the chip and the available features, which shall be explained in detail along

this tutorial.

The block diagram provided by Atmel™ in their datasheet showing the architecture

the 89S52 device can seem very complicated, and since we are going to use the C high level

language to program it, a simpler architecture can be represented as the figure 3.4.2.

This figures shows the main features and components that the designer can interact

DEPT. OF ECE

20


with. You can notice that the 89S52 has 4 different ports, each one having 8 Input/output

lines providing a total of 32 I/O lines. Those ports can be used to output DATA and orders do

other devices, or to read the state of a sensor, or a switch. Most of the ports of the 89S52 have

'dual function' meaning that they can be used for two different functions: the fist one is to

perform input/output operations and the second one is used to implement special features of

the microcontroller like counting external pulses, interrupting the execution of the program

according to external events, performing serial data transfer or connecting the chip to a

computer to update the software.

NECESSITY OF MICROCONTROLLERS:

Microprocessors brought the concept of programmable devices and made many

applications of intelligent equipment. Most applications, which do not need large amount of

data and program memory, tended to be costly.

The microprocessor system had to satisfy the data and program requirements so,

sufficient RAM and ROM are used to satisfy most applications .The peripheral control

equipment also had to be satisfied. Therefore, almost all-peripheral chips were used in the

design. Because of these additional peripherals cost will be comparatively high.

An example:

8085 chip needs:

An Address latch for separating address from multiplex address and data.32-KB

RAM and 32-KB ROM to be able to satisfy most applications. As also Timer / Counter,

Parallel programmable port, Serial port, and Interrupt controller are needed for its efficient

applications.

In comparison a typical Micro controller 8051 chip has all that the 8051 board has

except a reduced memory as follows.

4K bytes of ROM as compared to 32-KB, 128 Bytes of RAM as compared to 32-KB.

Bulky:

On comparing a board full of chips (Microprocessors) with one chip with all

components in it (Microcontroller).

Debugging:

Lots of Microprocessor circuitry and program to debug. In Micro controller there is

no Microprocessor circuitry to debug.

DEPT. OF ECE

21


Slower Development time: As we have observed Microprocessors need a lot of

debugging at board level and at program level, where as, Micro controller do not have the

excessive circuitry and the built-in peripheral chips are easier to program for operation.

So peripheral devices like Timer/Counter, Parallel programmable port, Serial

Communication Port, Interrupt controller and so on, which were most often used were

integrated with the Microprocessor to present the Micro controller .RAM and ROM also were

integrated in the same chip. The ROM size was anything from 256 bytes to 32Kb or more.

RAM was optimized to minimum of 64 bytes to 256 bytes or more.

Microprocessor has following instructions to perform:

1. Reading instructions or data from program memory ROM.

2. Interpreting the instruction and executing it.

3. Microprocessor Program is a collection of instructions stored in a Nonvolatile memory.

4. Read Data from I/O device

5. Process the input read, as per the instructions read in program memory.

6. Read or write data to Data memory.

7. Write data to I/O device and output the result of processing to O/P device.

Introduction to AT89S52

The system requirements and control specifications clearly rule out the use of 16, 32 or

64 bit micro controllers or microprocessors. Systems using these may be earlier to implement

due to large number of internal features. They are also faster and more reliable but, the above

application is satisfactorily served by 8-bit micro controller. Using an inexpensive 8-bit

Microcontroller will doom the 32-bit product failure in any competitive market place.

Coming to the question of why to use 89S52 of all the 8-bit Microcontroller available in the

market the main answer would be because it has 8kB Flash and 256 bytes of data RAM32 I/O

lines, three 16-bit timer/counters, a Eight-vector two-level interrupt architecture, a full duplex

serial port, on-chip oscillator, and clock circuitry.

DEPT. OF ECE

22


In addition, the AT89S52 is designed with static logic for operation down to zero

frequency and supports two software selectable power saving modes. The Idle Mode stops

the CPU while allowing the RAM, timer/counters, serial port, and interrupt system to

continue functioning. The Power Down Mode saves the RAM contents but freezes the

oscillator, disabling all other chip functions until the next hardware reset. The Flash program

memory supports both parallel programming and in Serial In-System Programming (ISP).

The 89S52 is also In-Application Programmable (IAP), allowing the Flash program memory

to be reconfigured even while the application is running.

By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel

AT89S52 is a powerful microcomputer which provides a highly flexible and cost effective

solution to many embedded control applications.

FEATURES:-

Compatible with MCS-51 Products

8K Bytes of In-System Reprogrammable Flash Memory

Fully Static Operation: 0 Hz to 33 MHz

Three-level Program Memory Lock

256 x 8-bit Internal RAM

32 Programmable I/O Lines

Three 16-bit Timer/Counters

Eight Interrupt Sources

Programmable Serial Channel

Low-power Idle and Power-down Modes

4.0V to 5.5V Operating Range

Full Duplex UART Serial Channel

Interrupt Recovery from Power-down Mode

Watchdog Timer

Dual Data Pointer

Power-off Flag

Fast Programming Time

Flexible ISP Programming (Byte and Page Mode)

DEPT. OF ECE

23


PIN DIAGRAM:

Figure 3.4.3: PIN DIAGRAM OF 89S52 IC

PIN DESCRIPTION:

VCC:

Supply voltage.

GND:

Ground.

Port 0:

Port 0 is an 8-bit open drain bidirectional I/O port. As an output port, each pin can

sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be used as high

impedance inputs. Port 0 can also be configured to be the multiplexed low order address/data

bus during accesses to external program and data memory. In this mode, P0 has internal pull

ups. Port 0 also receives the code bytes during Flash programming and outputs the code bytes

during program verification. External pull ups are required during program verification.

DEPT. OF ECE

24


Port 1:

Port 1 is an 8-bit bidirectional I/O port with internal pullups. The Port 1 output buffers

can sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by

the internal pullups and can be used as inputs. As inputs,Port 1 pins that are externally being

pulled low will source current (IIL) because of the internal pullups. In addition, P1.0 and P1.1

can be configured to be the timer/counter 2 external count input (P1.0/T2) and the

timer/counter 2 trigger input (P1.1/T2EX), respectively, as shown in the following table. Port

1 also receives the low-order address bytes during Flash programming and verification.

Table 3.4.1: port 1 functions

Port 2

Port 2 is an 8-bit bidirectional I/O port with internal pullups.The Port 2 output buffers

can sink/source four TTL inputs.When 1s are written to Port 2 pins, they are pulled high by

the internal pullups and can be used as inputs. As inputs, Port 2 pins that are externally being

pulled low will source current (IIL) because of the internal pullups. Port 2 emits the high-

order address byte during fetches from external program memory and during accesses to

external data memory that use 16-bit addresses (MOVX @ DPTR). In this application, Port 2

uses strong internal pull-ups when emitting 1s. During accesses to external data memory that

use 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function

Register. Port 2 also receives the high-order address bits and some control signals during

Flash programming and verification.

Port 3

Port 3 is an 8-bit bidirectional I/O port with internal pullups.The Port 3 output buffers

can sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled high by

DEPT. OF ECE

25


the internal pullups and can be used as inputs. As inputs, Port 3 pins that are externally being

pulled low will source current (IIL) because of the pullups. Port 3 also serves the functions of

various special features of the AT89S52, as shown in the following table. Port 3 also receives

some control signals for Flash programming and verification.

Table 3.4.2: functions of port 3

RST:

Reset input. A high on this pin for two machine cycles while the oscillator is running

resets the device. This pin drives High for 96 oscillator periods after the Watchdog times out.

The DISRTO bit in SFR AUXR (address 8EH) can be used to disable this feature. In the

default state of bit DISRTO, the RESET HIGH out feature is enabled. ALE/PROG Address

Latch Enable (ALE) is an output pulse for latching the low byte of the address during

accesses to external memory. This pin is also the program pulse input (PROG) during Flash

programming. In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator

frequency and may be used for external timing or clocking purposes. Note, however, that one

ALE pulse is skipped during each access to external data memory. If desired, ALE operation

can be disabled by setting bit 0 of SFR location 8EH. With the bit set, ALE is active only

during a MOVX or MOVC instruction. Otherwise, the pin is weakly pulled high. Setting the

ALE-disable bit has no effect if the microcontroller is in external execution mode.

PSEN:

Program Store Enable (PSEN) is the read strobe to external program memory. When

the AT89S52 is executing code from external program memory, PSEN is activated twice

DEPT. OF ECE

26


each machine cycle, except that two PSEN activations are skipped during each access to

external data memory.

EA/VPP:

Exsternal Access Enable. EA must be strapped to GND in order to enable the device

to fetch code from external program memory locations starting at 0000H up to FFFFH. Note,

however, that if lock bit 1 is programmed, EA will be internally latched on reset. EA should

be strapped to VCC for internal program executions. This pin also receives the 12-volt

programming enable voltage (VPP) during Flash programming.

XTAL1

Input to the inverting oscillator amplifier and input to theinternal clock operating

circuit.

XTAL2

Output from the inverting oscillator amplifier.

Figure 3.4.4: Functional block diagram of micro controller

DEPT. OF ECE

27


The 8052 Oscillator and Clock:

The heart of the 8051 circuitry that generates the clock pulses by which all the

internal all internal operations are synchronized. Pins XTAL1 And XTAL2 is provided for

connecting a resonant network to form an oscillator. Typically a quartz crystal and capacitors

are employed. The crystal frequency is the basic internal clock frequency of the

microcontroller. The manufacturers make 8051 designs that run at specific minimum and

maximum frequencies typically 1 to 16 MHz.

Figure 3.4.5: Oscillator and timing circuit

DEPT. OF ECE

28


MEMORIES

Types of memory:

The 8052 have three general types of memory. They are on-chip memory, external

Code memory and external Ram. On-Chip memory refers to physically existing memory on

the micro controller itself. External code memory is the code memory that resides off chip.

This is often in the form of an external EPROM. External RAM is the Ram that resides off

chip. This often is in the form of standard static RAM or flash RAM.

a) Code memory

Code memory is the memory that holds the actual 8052 programs that is to be run.

This memory is limited to 64K. Code memory may be found on-chip or off-chip. It is

possible to have 8K of code memory on-chip and 60K off chip memory simultaneously. If

only off-chip memory is available then there can be 64K of off chip ROM. This is controlled

by pin provided as EA

b) Internal RAM

The 8052 have a bank of 256 bytes of internal RAM. The internal RAM is found on-

chip. So it is the fastest Ram available. And also it is most flexible in terms of reading and

writing. Internal Ram is volatile, so when 8051 is reset, this memory is cleared. 256 bytes of

internal memory are subdivided. The first 32 bytes are divided into 4 register banks. Each

bank contains 8 registers. Internal RAM also contains 256 bits, which are addressed from 20h

to 2Fh. These bits are bit addressed i.e. each individual bit of a byte can be addressed by the

user. They are numbered 00h to FFh. The user may make use of these variables with

commands such as SETB and CLR.

Special Function registered memory:

DEPT. OF ECE

29


Special function registers are the areas of memory that control specific functionality

of the 8052 micro controller.

a) Accumulator (0E0h)

As its name suggests, it is used to accumulate the results of large no of instructions. It

can hold 8 bit values.

b) B registers (0F0h)

The B register is very similar to accumulator. It may hold 8-bit value. The b register is

only used by MUL AB and DIV AB instructions. In MUL AB the higher byte of the product

gets stored in B register. In div AB the quotient gets stored in B with the remainder in A.

c) Stack pointer (81h)

The stack pointer holds 8-bit value. This is used to indicate where the next value to

be removed from the stack should be taken from. When a value is to be pushed onto the

stack, the 8052 first store the value of SP and then store the value at the resulting memory

location. When a value is to be popped from the stack, the 8052 returns the value from the

memory location indicated by SP and then decrements the value of SP.

d) Data pointer

The SFRs DPL and DPH work together work together to represent a 16-bit value

called the data pointer. The data pointer is used in operations regarding external RAM and

some instructions code memory. It is a 16-bit SFR and also an addressable SFR.

e) Program counter

The program counter is a 16 bit register, which contains the 2 byte address, which

tells the 8052 where the next instruction to execute to be found in memory. When the 8052

is initialized PC starts at 0000h. And is incremented each time an instruction is executes. It is

not addressable SFR.

f) PCON (power control, 87h)

DEPT. OF ECE

30


The power control SFR is used to control the 8051’s power control modes. Certain

operation modes of the 8051 allow the 8051 to go into a type of “sleep mode” which

consumes much lee power.

g) TCON (timer control, 88h)

The timer control SFR is used to configure and modify the way in which the 8051’s

two timers operate. This SFR controls whether each of the two timers is running or stopped

and contains a flag to indicate that each timer has overflowed. Additionally, some non-timer

related bits are located in TCON SFR. These bits are used to configure the way in which the

external interrupt flags are activated, which are set when an external interrupt occurs.

h) TMOD (Timer Mode, 89h)

The timer mode SFR is used to configure the mode of operation of each of the two

timers. Using this SFR your program may configure each timer to be a 16-bit timer, or 13 bit

timer, 8-bit auto reload timer, or two separate timers. Additionally you may configure the

timers to only count when an external pin is activated or to count “events” that are indicated

on an external pin.

i) TO (Timer 0 low/high, address 8A/8C h)

DEPT. OF ECE

31


These two SFRs taken together represent timer 0. Their exact behavior depends on

how the timer is configured in the TMOD SFR; however, these timers always count up.

What is configurable is how and when they increment in value.

j) T1 (Timer 1 Low/High, address 8B/ 8D h)

These two SFRs, taken together, represent timer 1. Their exact behavior depends on

how the timer is configured in the TMOD SFR; however, these timers always count up..

k) P0 (Port 0, address 90h, bit addressable)

This is port 0 latch. Each bit of this SFR corresponds to one of the pins on a micro

controller. Any data to be outputted to port 0 is first written on P0 register. For e.g., bit 0 of

port 0 is pin P0.0, bit 7 is pin p0.7. Writing a value of 1 to a bit of this SFR will send a high

level on the corresponding I/O pin whereas a value of 0 will bring it to low level.

l) P1 (port 1, address 90h, bit addressable)

This is port latch1. Each bit of this SFR corresponds to one of the pins on a micro


port 0 is pin P1.0, bit 7 is pin P1.7. Writing a value of 1 to a bit of this SFR will send a high

level on the corresponding I/O pin whereas a value of 0 will bring it to low level

m) P2 (port 2, address 0A0h, bit addressable):

This is a port latch2. Each bit of this SFR corresponds to one of the pins on a micro




n) P3 (port 3, address B0h, bit addressable) :

This is a port latch3. Each bit of this SFR corresponds to one of the pins on a micro




o) IE (interrupt enable, 0A8h):

DEPT. OF ECE

32


The Interrupt Enable SFR is used to enable and disable specific interrupts. The low 7

bits of the SFR are used to enable/disable the specific interrupts, where the MSB bit is used to

enable or disable all the interrupts. Thus, if the high bit of IE is 0 all interrupts are disabled

regardless of whether an individual interrupt is enabled by setting a lower bit.

p) IP (Interrupt Priority, 0B8h)

The interrupt priority SFR is used to specify the relative priority of each interrupt. On

8051, an interrupt maybe either low or high priority. An interrupt may interrupt interrupts.

For e.g., if we configure all interrupts as low priority other than serial interrupt. The serial

interrupt always interrupts the system, even if another interrupt is currently executing.

However, if a serial interrupt is executing no other interrupt will be able to interrupt the serial

interrupt routine since the serial interrupt routine has the highest priority.

q) PSW (Program Status Word, 0D0h)

The program Status Word is used to store a number of important bits that are set and

cleared by 8052 instructions. The PSW SFR contains the carry flag, the auxiliary carry flag,

the parity flag and the overflow flag. Additionally, it also contains the register bank select

flags, which are used to select, which of the “R” register banks currently in use.

r) SBUF (Serial Buffer, 99h)

SBUF is used to hold data in serial communication. It is physically two registers. One

is writing only and is used to hold data to be transmitted out of 8052 via TXD. The other is

read only and holds received data from external sources via RXD. Both mutually exclusive

registers use address 99h.

DEPT. OF ECE

33


3.5 LCD MODULE

To display interactive messages we are using LCD Module. We examine an

intelligent LCD display of two lines,16 characters per line that is interfaced to the controllers.

The protocol (handshaking) for the display is as shown. Whereas D0 to D7th bit is the Data

lines, RS, RW and EN pins are the control pins and remaining pins are +5V, -5V and GND to

provide supply. Where RS is the Register Select, RW is the Read Write and EN is the Enable

pin.

The display contains two internal byte-wide registers, one for commands (RS=0) and

the second for characters to be displayed (RS=1). It also contains a user-programmed RAM

area (the character RAM) that can be programmed to generate any desired character that can

be formed using a dot matrix. To distinguish between these two data areas, the hex command

byte 80 will be used to signify that the display RAM address 00h will be chosen.Port1 is used

to furnish the command or data type, and ports 3.2 to3.4 furnish register select and read/write

levels.

The display takes varying amounts of time to accomplish the functions as listed. LCD

bit 7 is monitored for logic high (busy) to ensure the display is overwritten.

Liquid Crystal Display also called as LCD is very helpful in providing user interface

as well as for debugging purpose. The most common type of LCD controller is HITACHI

44780 which provides a simple interface between the controller & an LCD. These LCD's are

very simple to interface with the controller as well as are cost effective.

Figure 3.5.1: 2x16 Line Alphanumeric LCD DisplayThe most commonly used ALPHANUMERIC displays are 1x16 (Single Line & 16

characters), 2x16 (Double Line & 16 character per line) & 4x20 (four lines & Twenty

characters per line).

The LCD requires 3 control lines (RS, R/W & EN) & 8 (or 4) data lines. The number

on data lines depends on the mode of operation. If operated in 8-bit mode then 8 data lines +

3 control lines i.e. total 11 lines are required. And if operated in 4-bit mode then 4 data lines

DEPT. OF ECE

34


+ 3 control lines i.e. 7 lines are required. How do we decide which mode to use? It’s simple if

you have sufficient data lines you can go for 8 bit mode & if there is a time constrain i.e.

display should be faster then we have to use 8-bit mode because basically 4-bit mode takes

twice as more time as compared to 8-bit mode.

Table 3.5.1: Pin description of LCD

Pin Symbol Function

1 Vss Ground

2 Vdd Supply Voltage

3 Vo Contrast Setting

4 RS Register Select

5 R/W Read/Write Select

6 En Chip Enable Signal

7-14 DB0-DB7 Data Lines

15 A/Vee Gnd for the backlight

16 K Vcc for backlight

When RS is low (0), the data is to be treated as a command. When RS is high (1), the

data being sent is considered as text data which should be displayed on the screen.

When R/W is low (0), the information on the data bus is being written to the LCD.

When RW is high (1), the program is effectively reading from the LCD. Most of the times

there is no need to read from the LCD so this line can directly be connected to Gnd thus

saving one controller line.

The ENABLE pin is used to latch the data present on the data pins. A HIGH - LOW

signal is required to latch the data. The LCD interprets and executes our command at the

instant the EN line is brought low. If you never bring EN low, your instruction will never be

executed.

Figure 3.5.2: LCD to controller connections

Table 3.5.2: Commands Used In Lcd

DEPT. OF ECE

35


An LED lamp (LED light bulb) is a solid-state lamp that uses light-emitting

diodes (LEDs) as the source of light. The LEDs involved may be

conventional semiconductor light-emitting diodes, organic LEDs (OLED), or polymer light-

emitting diodes (PLED) devices. However, PLED technologies are not commercially

available. Diode technology improves steadily.

LED lamps can be made interchangeable with other types of lamps. Assemblies of

high power light-emitting diodes can be used to replace incandescent or fluorescent lamps.

Some LED lamps are made with identical bases so that they are directly interchangeable with

incandescent bulbs. Since the luminous efficacy (amount of visible light produced per unit of

electrical power input) varies widely between LED and incandescent lamps, lamps are

usefully marked with their lumen output to allow comparison with other types of lamps. LED

lamps are sometimes marked to show the watt rating of an incandescent lamp with

approximately the same lumen output, for consumer reference in purchasing a lamp that will

provide a similar level of illumination.

One high power LED chip used in LED lights can emit up to 7,500 lumens for an

electrical power consumption of 100 watts. LEDs do not emit light in all directions, and their

directional characteristics affect the design of lamps. The efficiency of conversion from

electric power to light is generally higher than with incandescent lamps. Since the light

outputof many types of light-emitting diodes is small compared to incandescent and compact

fluorescent lamps, in most applications multiple diodes are assembled.

LED lamps offer long service life and high energy efficiency, but initial costs are

higher than those of fluorescent and incandescent lamps. Life cycle of LED lamps is multiple

compared to incandescent lamps, however, degradation of LED chips reduces luminous flux

over life cycle as with conventional lamps.

Diodes use direct current (DC) electrical power. To use them from

standard AC power they are operated with internal or external rectifier circuits that provide a

DEPT. OF ECE

36


regulated current output at low voltage. LEDs are degraded or damaged by operating at high

temperatures, so LED lamps typically include heat dissipation elements such as heat

sinks and cooling fins.

Technology overview:-

Figure 3.5.3: DROPPED CEILING WITH LED LAMPS

General-purpose lighting needs white light. LEDs emit light in a very small band of

wavelengths, emitting light of a color characteristic of the energy bandgap of

the semiconductor material used to make the LED. To emit white light from LEDs requires

either mixing light from red, green, and blue LEDs, or using a phosphor to convert some of

the light to other colors.

The first method (RGB- or trichromatic white LEDs) uses multiple LED chips, each

emitting a different wavelength, in close proximity to generate the broad spectrum of white

light. The advantage of this method is that the intensity of each LED can be adjusted to

"tune" the character of the light emitted. The major disadvantage is high production cost. The

character of the light can be changed dynamically by adjusting the power supplied to the

different LEDs.

The color rendering of RGB LEDs, however, is worse than one would expect; the

wavelength gap between red and green is much larger than that between green and blue,

resulting in an uneven spectral density. An orange fruit, for example, does reflect some red

and it does reflect some green, but not in a ratio that the human retina interprets as orange.

Neglecting to poll the orange line makes most orange objects appear reddish. RGB LEDs are

therefore suitable for display purposes, but less so for illumination, which prompted some

manufacterers to add a fourth, amber LED, marketing the product as RGBA LED (not to be

confused with the RGBA color space) ortetrachromatic white LED. It can be expected that

the number of colors will be further increased to six or more, equally-temperedwavelengths.

DEPT. OF ECE

http://en.wikipedia.org/wiki/Equal_temperament

http://en.wikipedia.org/wiki/Tetrachromatic

http://en.wikipedia.org/wiki/RGBA_color_space

http://en.wikipedia.org/wiki/Ratio

http://en.wikipedia.org/wiki/Trichromatic

http://en.wikipedia.org/wiki/RGB

http://en.wikipedia.org/wiki/Phosphor

http://en.wikipedia.org/wiki/Semiconductor

http://en.wikipedia.org/wiki/Bandgap

http://en.wikipedia.org/wiki/File:LED_T-bar_ceiling_light.JPG

37


The second method, phosphor converted LEDs (pcLEDs) uses one short wavelength

LED (usually blue or ultraviolet) in combination with a phosphor which absorbs a portion of

the blue light and emits a broader spectrum of white light. (The mechanism is similar to the

way afluorescent lamp emits white light from a UV-illuminated phosphor.) The major

advantage is the low production cost, and high CRI (color rendering index), but the phosphor

conversion reduces the efficiency of the device, partly due to the Stokes shift effect. The

character of the light cannot be changed dynamically. The low cost and adequate

performance makes it the most widely used technology for general lighting today.

A single LED is a low-voltage solid state device and cannot be directly operated on

standard high-voltage AC power without circuitry to control the voltage applied and the

current flow through the lamp. In principle a series diode and resistor could be used to control

the voltage polarity and to limit the current, but this would be very inefficient since most of

the applied power would be dissipated by the resistor. A series string of LEDs would

minimize dropped-voltage losses, but one LED failure would extinguish the whole string.

Paralleled strings increase reliability by providing redundancy. In practice, three or more

strings are usually used. To be useful for illumination a number of LEDs must be placed

close together in a lamp to combine their illuminating effects because, as of 2011, the largest

available LEDs emit only a small fraction of the light of traditional light sources. When using

the color-mixing method a uniform color distribution can be difficult to achieve, while the

arrangement of white LEDs is not critical for color balance. Further, degradation of different

LEDs at various times in a color-mixed lamp can lead to an uneven color output. LED lamps

usually consist of clusters of LEDs in a housing with driver electronics, a heat sink, and

optics.

3.6 DC MOTOR:

DEPT. OF ECE

http://en.wikipedia.org/wiki/Heat_sink

http://en.wikipedia.org/wiki/Redundancy_(engineering)

http://en.wikipedia.org/wiki/Series_circuit

http://en.wikipedia.org/wiki/Resistor

http://en.wikipedia.org/wiki/Diode

http://en.wikipedia.org/wiki/Stokes_shift

http://en.wikipedia.org/wiki/Color_rendering_index

http://en.wikipedia.org/wiki/Fluorescent_lamp

38


Figure 3.6.1:DC Motor

DC motors are configured in many types and sizes, including brush less, servo, and

gear motor types. A motor consists of a rotor and a permanent magnetic field stator. The

magnetic field is maintained using either permanent magnets or electromagnetic windings.

DC motors are most commonly used in variable speed and torque.

Motion and controls cover a wide range of components that in some way are used to generate

and/or control motion. Areas within this category include bearings and bushings, clutches and

brakes, controls and drives, drive components, encoders and resolves, Integrated motion

control, limit switches, linear actuators, linear and rotary motion components, linear position

sensing, motors (both AC and DC motors), orientation position sensing, pneumatics and

pneumatic components, positioning stages, slides and guides, power transmission

(mechanical), seals, slip rings, solenoids, springs.

Motors are the devices that provide the actual speed and torque in a drive system.

This family includes AC motor types (single and multiphase motors, universal, servo motors,

induction, synchronous, and gear motor) and DC motors (brush less, servo motor, and gear

motor) as well as linear, stepper and air motors, and motor contactors and starters.

In any electric motor, operation is based on simple electromagnetism. A current-

carrying conductor generates a magnetic field; when this is then placed in an external

magnetic field, it will experience a force proportional to the current in the conductor, and to

the strength of the external magnetic field. As you are well aware of from playing with

magnets as a kid, opposite (North and South) polarities attract, while like polarities (North

and North, South and South) repel. The internal configuration of a DC motor is designed to

harness the magnetic interaction between a current-carrying conductor and an external

magnetic field to generate rotational motion.

DEPT. OF ECE

http://dc-motors.globalspec.com/Industrial-Directory/motors

39


Let's start by looking at a simple 2-pole DC electric motor (here red represents a

magnet or winding with a "North" polarization, while green represents a magnet or winding

with a "South" polarization).

Figure 3.6.2a: DC Motor north rotation

Every DC motor has six basic parts -- axle, rotor (a.k.a., armature), stator,

commutator, field magnet(s), and brushes. In most common DC motors (and all that Beamers

will see), the external magnetic field is produced by high-strength permanent magnets1. The

stator is the stationary part of the motor -- this includes the motor casing, as well as two or

more permanent magnet pole pieces. The rotor (together with the axle and attached

commutator) rotates with respect to the stator. The rotor consists of windings (generally on a

core), the windings being electrically connected to the commutator. The above diagram

shows a common motor layout -- with the rotor inside the stator (field) magnets.

The geometry of the brushes, commutator contacts, and rotor windings are such that when power is applied, the polarities of the energized winding and the stator magnet(s) are misaligned, and the rotor will rotate until it is almost aligned with the stator's field magnets. As the rotor reaches alignment, the brushes move to the next commutator contacts, and energize the next winding. Given our example two-pole motor, the rotation reverses the direction of current through the rotor winding, leading to a "flip" of the rotor's magnetic field, and driving it to continue rotating.

In real life, though, DC motors will always have more than two poles (three is a very

common number). In particular, this avoids "dead spots" in the commutator. You can imagine

how with our example two-pole motor, if the rotor is exactly at the middle of its rotation

(perfectly aligned with the field magnets), it will get "stuck" there. Meanwhile, with a two-

pole motor, there is a moment where the commutator shorts out the power supply (i.e., both

brushes touch both commutator contacts simultaneously). This would be bad for the power

supply, waste energy, and damage motor components as well. Yet another disadvantage of

DEPT. OF ECE

40


such a simple motor is that it would exhibit a high amount of torque” ripple" (the amount of

torque it could produce is cyclic with the position of the rotor).

Figure 3.6.2b: DC Motor rotation

So since most small DC motors are of a three-pole design, let's tinker with the

workings of one via an interactive animation (JavaScript required):

Figure 3.6.2c: DC Motor 3 pole rotation

You'll notice a few things from this -- namely, one pole is fully energized at a time

(but two others are "partially" energized). As each brush transitions from one commutator

contact to the next, one coil's field will rapidly collapse, as the next coil's field will rapidly

charge up (this occurs within a few microsecond). We'll see more about the effects of this

later, but in the meantime you can see that this is a direct result of the coil windings' series

wiring:

DEPT. OF ECE

41


Figure 3.6.3: DC Motor using wires

There's probably no better way to see how an average dc motor is put together, than by just opening one up. Unfortunately this is tedious work, as well as requiring the destruction of a perfectly good motor.

3.7 BUZZER

A buzzer or beeper is an audio signaling device, which may be mechanical, electromechanical, or electronic. Typical uses of buzzers and beepers include alarms, timers and confirmation of user input such as a mouse click or keystroke.

DEPT. OF ECE

http://en.wikipedia.org/wiki/Timer

http://en.wikipedia.org/wiki/Alarm

http://en.wikipedia.org/wiki/Electronics

http://en.wikipedia.org/wiki/Electromechanics

http://en.wikipedia.org/wiki/Machine

http://en.wikipedia.org/wiki/Sound

42


Figure 3.7.1: Buzzer

FEATURES• The PB series are high-performance buzzers with a unimorph piezoelectric ceramic element

and an integral self-excitation oscillator circuit.

• They exhibit extremely low power consumption in comparison to electromagnetic units.

• They are constructed without switching contacts to ensure long life and no electrical noise.

• Compact, yet produces high acoustic output with minimal voltage.

Mechanical

A joy buzzer is an example of a purely mechanical buzzer.

Electromechanical

Early devices were based on an electromechanical system identical to an electric bell without the metal gong. Similarly, a relay may be connected to interrupt its own actuating current, causing the contacts to buzz. Often these units were anchored to a wall or ceiling to use it as a sounding board. The word "buzzer" comes from the rasping noise that electromechanical buzzers made.

VOLTAGE BUZZER SOUND CONTROLS

When resistance is connected in series (as shown in illustrations (a) and (b)),

abnormal oscillation may occur when adjusting the sound volume.

In this case, insert a capacitor in parallel to the voltage oscillation board (as shown in

illustration (c)). By doing so, abnormal oscillation can be prevented by grounding one side.

However, the voltage VB added to the voltage oscillation board must be within the maximum

input voltage range, and as capacitance of 3.3μF or greater should be connected.

DEPT. OF ECE

43


Figure 3.7.2: Circuit Diagram of Buzzer

Electronic

Figure 3.7.3: Electronic Buzzer

A piezoelectric element may be driven by an oscillating electronic circuit or other audio signal source. Sounds commonly used to indicate that a button has been pressed are a click, a ring or a beep. Electronic buzzers find many applications in modern days.

Uses

Annunciator panels Electronic metronomes Game shows Microwave ovens and other household appliances Sporting events such as basketball games

Chapter -4

CIRCUIT DESCRIPTION

DEPT. OF ECE

http://en.wikipedia.org/wiki/File:2007-07-24_Piezoelectric_buzzer.jpg

44


CIRCUIT DIAGRAM:

Figure 4.1:Circuit Diagram

4.2 OPERATION AND WORKING:

DEPT. OF ECE

45


Accidents are occurred regularly when the vehicle is engaged in reverse direction. This is designed to detect the obstacle and displaying the distance between the vehicle and obstacle. It also provides the alert sounds when the obstacle comes near to the vehicle and stops the vehicle automatically when obstacle is very near to avoid accidents.

The ultrasonic sensor continuously transmits and receives the signals. When ever the ultrasonic sensor senses the obstacle it measures the distance by calculating the time and speed of the signal taken. The ultrasonic sensor can sense the obstacle from the distance 4cm to 3m. The distance is displayed on the LCD. When the obstacle comes very nearer then the buzzer starts alerts by a beep sound. At a distance of 40 to 75 cm from the obstacle the car stops automatically.

In night time, when the driver wants to get the vehicle reversed it makes difficult to him to know what is happening back as it will be dark.The LDR circuit is provided to glow the LED lights in night.

Chapter -6

DEPT. OF ECE

46


ADVANTAGES

Automatic vehicle control

The vehicle is automatically stops when it detects the obstacle is very nearer.

Fast response

The sensors senses the obstacle very fastly.

High reliable

System will be stable for a long time

The sensors senses the obstacle continuously and gives the distance between

the vehicle and obstacle.

Chapter -7

DEPT. OF ECE

47


APPLICATIONS

Traffic areas

Figure 7.1: Traffic Areas

Car parking facility

Figure 7.2: car parking lot

Chapter -10

FUTURE SCOPE

DEPT. OF ECE

48


In future the extention of our project is an autonomous car which is in research.

An autonomous car, also known as robotic or informally as driverless, is an

autonomous vehicle capable of fulfilling the human transportation capabilities of a traditional

car. As an autonomous vehicle, it is capable of sensing its environment and navigating on its

own. A human may choose a destination, but is not required to perform any mechanical

operation of the vehicle.

Autonomous cars are not in widespread use, but their introduction could produce several

direct advantages:

Fewer crashes, due to the autonomous system's increased reliability compared to

human drivers

Increased roadway capacity due to reduced need of safety gaps and the ability to

better manage traffic flow.

Relief of vehicle occupants from driving and navigation chores.

Removal of constraints on occupant's state - it would not matter if the occupants were

too young, too old or if their frame of mind were not suitable to drive a traditional car.

Furthermore, disabilities would no longer matter.

Elimination of redundant passengers - humans are not required to take the car

anywhere, as the robotic car can drive empty to wherever it is required.

Alleviation of parking scarcity as cars could drop off passengers, park far away where

space is not scarce, and return as needed to pick up passengers.

Indirect advantages are anticipated as well. Adoption of robotic cars could reduce the number

of vehicles worldwide, reduce the amount of space required for vehicle parking, and reduce

the need for traffic police and vehicle insurance.

Autonomous vehicles sense the world with such techniques as laser, radar, lidar, GPS and

computer vision. Advanced control systems interpret the information to identify appropriate

navigation paths, as well as obstacles and relevant signage. Autonomous vehicles typically

update their maps based on sensory input, such that they can navigate through uncharted

environments.

DEPT. OF ECE

49


Chapter -11

BIBILOGRAPHY

DEPT. OF ECE

50


http://www.technologystudent.com/elec1/ldr1.htm

http://www.parallax.com/tabid/768/ProductID/92/Default.aspx

http://www.atmel.com/devices/at89s52.aspx

http://en.wikipedia.org/wiki/Liquid_crystal_display

http://www.webopedia.com/TERM/P/power_supply.html

http://www.autonomouscar.com/

DEPT. OF ECE

http://www.autonomouscar.com/

http://www.webopedia.com/TERM/P/power_supply.html

http://en.wikipedia.org/wiki/Liquid_crystal_display

http://www.atmel.com/devices/at89s52.aspx

http://www.parallax.com/tabid/768/ProductID/92/Default.aspx

http://www.technologystudent.com/elec1/ldr1.htm

Date post:	28-Nov-2015
Category:	Documents
Upload:	poorna-devi
View:	9 times
Download:	3 times

Sem

Documents