Traffic light control using RFID

7/29/2019 Traffic light control using RFID

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1. EMBEDDED SYSTEMS

Introduction:

An embedded system can be defined as a computing device that does a specific

focused job. Appliances such as the air-conditioner, VCD player, DVD player, printer,fax machines, mobile phone etc. are examples of embedded systems. Each of these

appliances will have a processor and special hardware to meet the specific requirement

of the application along with the embedded software that is executed by the processor

for meeting the specific requirement, the embedded software is also called firm

ware. The desktop/laptop computer is a general purpose computer. You can use it for

a variety of applications such as playing games, word processing, accounting, software

development and so on. In contrast, the software in the embedded systems is always

fixed listed below:

Embedded systems do a very specific task; they cannot be programmed to do

things. Embedded systems have very limited resources, particularly the memory.

Generally, they do not have secondary storage devices such as the CDROM pr the

floppy disk. Embedded systems have to work against some deadlines. A specific job

has to be completed within a specific time. In some embedded systems, called real-

time systems, the deadlines are stringent. Missing a deadline may cause a catastrophe-

loss of life or damage to property. Embedded systems are constrained for power, as

many embedded systems operate through a battery; the power consumption has to be

very low.

Some embedded systems have to operate in extreme environmental conditions

such as very high temperatures and humidity.

1.1 ARCHITECTURE

Let us see the details of the various building blocks of the hardware of an

embedded system. As shown in fig 1.2.1 the building blocks are;

Central Processing Unit (CPU)

Memory (Read-Only Memory and Random Access Memory)

Input Devices


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Output Devices

Communication Interfaces

Application-specific Circuitry

Fig 1.1.1: Block Diagram of Hardware of Embedded System

1.1.1 Central Processing Unit (CPU):

The Central Processing Unit (Processor, in short) can be any of the following;

Microcontroller, microprocessor or Digital Signal Processor (DSP). A micro-

controller is a low-cost processor. Its main attraction is that on the chip itself,

there will be many other components such as memory, serial communication

interface, analog to digital converter etc. So, for small applications, a

microcontroller is the best choice as the number of external components required

will be very less. On the other hand, microprocessors are more powerful, but you

need to use many external components with them. DSP is used mainly for

applications in which signal processing is involved such as audio and video

processing.


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1.1.2 Memory:

The memory is categorized as Random Access Memory (RAM) and Read

Only Memory (ROM), the contents of the RAM will be erased if the power is

switched off. So, the firmware is stored in the ROM. When power is switched

on, the processor reads the ROM; the program is executed.

1.1.3 Input Devices:

Unlike the desktops, the input devices to an embedded system have very

limited capability. There will be no keyboard or a mouse, and hence interacting

with the embedded system is no easy task. Many embedded systems will have a

small keypad-you press one key to give a specific command, a keypad nay be

used to input only the digits. Many embedded systems used in process control do

not have any input device for user interaction.

1.1.4 Output Devices:

The output devices of the embedded systems also have very limited

capability. Some embedded systems will have a few Light Emitting Diodes

(LEDs) to indicate the health status of the system modules, or for visual indication

of alarms. A small Liquid Crystal Display (LCD) may be used to display some

more important parameters.1.1.5 Communication Interfaces:

The embedded systems may need to interact with other embedded system

at they may have to transmit data to a desktop. To facilitate this, the embedded

systems are provided with one or a few communication interfaces such as RS232,

RS422, Rs 485, Universal Serial Bus (USB), and IEEE 1394, Ethernet etc.

1.1.6 Application-specific Circuitry:

Sensors, transducers, special processing and control circuitry may berequired for an embedded system, depending on its application. This circuitry

interacts with the processor to carry out the necessary work. The entire hardware

has to be given power supply either through the 230 volts main supply or through

a battery. The hardware ha to design in such a way that the power consumption is

minimized.


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1.2 APPLICATION AREAS

Nearly 99 percent of the processors manufactured end up in the embedded

systems. The embedded system market is one of the highest growth areas as the

systems are used in every market segment-

Consumer electronics,

Offline automation,

Industrial automation,

Biomedical engineering,

Wireless communication,

Data communication,

Telecommunications, and

Transportation,

Military.


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2. MODULES OF THE PROJECT

2.1 MICROCONTROLLERS

Microprocessors are single-chip CPUs used in microcomputers.

Microcontrollers and microprocessors are different in three main aspects: hardware

architecture, applications, and instruction set features.

Hardware architecture: A microprocessor is a single chip CPU while a microcontroller

is a single IC contains a CPU and much of remaining circuitry of a complete computer

(e.g., RAM, ROM, serial interface, parallel interface, timer, and interrupt handling

circuit).

Applications: Microprocessors are commonly used as a CPU in computers while

microcontrollers are found in small, minimum component designs performing control

oriented activities.

Microprocessor instruction sets are processing Intensive.

Their instructions operate on nibbles, bytes, words, or even double words.

Addressing modes provide access to large arrays of data using pointers and offsets.

They have instructions to set and clear individual bits and perform bit operations.

They have instructions for input/output operations, event timing, enabling and setting

priority levels for interrupts caused by external stimuli.

Processing power of a microcontroller is much less than a microprocessor.

Difference between 8051 and 8052:

The 8052 microcontroller is the 8051's "big brother." It is a slightly more

powerful microcontroller, sporting a number of additional features which the developer

may make use of:

256 bytes of Internal RAM (compared to 128 in the standard 8051) and it is

having 8k bytes of ROM.

A third 16-bit timer, capable of a number of new operation modes and 16-bit

reloads.

Additional SFRs to support the functionality offered by the third timer.


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2.1.1 AT89s52FEATURES:

Compatible with MCS-51 Products

8K Bytes of In-System Programmable (ISP) Flash Memory

Endurance: 1000 Write/Erase Cycles

4.0V to 5.5V Operating Range

Fully Static Operation: 0 Hz to 33 MHz

Three-level Program Memory Lock

256K Internal RAM

32 Programmable I/O Lines

3 16-bit Timer/Counters

Eight Interrupt Sources

Full Duplex UART Serial Channel

Low-power Idle and Power-down Modes

Interrupt Recovery from Power-down Mode

Watchdog Timer

Dual Data Pointer

Power-off Flag

2.1.2 DESCRIPTION OF MICROCONTROLLER 89S52:

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

controller with 8Kbytes of in-system programmable Flash memory. The

device is manufactured

Using Atmels high-density nonvolatile memory technology and is

compatible with the industry-standard 80C51 micro controller. The on-chip

Flash allows the program memory to be reprogrammed in-system or by a

conventional nonvolatile memory programmer. By combining a versatile 8-bitCPU with in-system programmable flash one monolithic chip; the Atmel

AT89S52 is a powerful micro controller, which provides a highly flexible and

cost-effective solution to many embedded control applications.


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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,

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 contents but freezes the

oscillator, disabling all other chip functions until the next interrupt or

hardware reset.


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2.1.3 89s52 ARCHITECTURE:

Fig 2.1.1: 89s52 Architecture


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Fig 2.1.2: Pin Diagram of 89s52

PIN DESCRIPTION OF MICROCONTROLLER 89S52:

VCC

Supply voltage.

GND

Ground

Port 0

Port 0 is an 8-bit open drain bi-directional 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 ashigh 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


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Port 1

Port 1 is an 8-bit bi-directional I/O port with internal pull-ups. 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 pull-ups and can be used as inputs. 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 2.1.1: PORT1 of 89s52

Port 2:

Port 2 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 2 output


pulled high by the internal pull-ups and can be used as inputs. Port 2 emits the high-

order address byte during fetches from external program memory and during

accesses to external data memory that uses 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

2emits 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.


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Port 3:

Port 3 is an 8-bit bi-directional I/O port with internal pull-ups. The Port 3 output


pulled high by the internal pull-ups and can be used as inputs. As inputs, Port 3 pins that

are externally being pulled low will source current (IIL) because of the pull-ups. 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 2.1.2:PORT3 of 89s52

RST

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

running resets the device.

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 of1/6 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 micro controller is in external execution mode.


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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 each machine cycle, except that two PSEN activations are skipped

during each access to external data memory.

EA/VPP:

External 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. A should be strapped to VCC for internal program executions. This

pin also receives the 12-voltProgramming enables voltage (VPP) during Flash

programming.

XTAL1:

Input to the inverting oscillator amplifier and input to the internal clock

operating circuit.

XTAL2:

Output from the inverting oscillator amplifier.

Oscillator Characteristics:

XTAL1 and XTAL2 are the input and output, respectively, of an inverting

amplifier that can be configured for use as an on-chip oscillator, a quartz crystal or

ceramic resonator may be used. To drive the device from an External clock source,

XTAL2 should be left unconnected while XTAL1 is driven.

Fig 2.1.3: Oscillator Connection


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2.2 POWER SUPPLY:

Power supply is a reference to a source of electrical power. A device or system

that supplies electrical or other types of energy to an output load or group of loads is

called a power supply unit or PSU. The term is most commonly applied to electricalenergy supplies, less often to mechanical ones, and rarely to others

This power supply section is required to convert AC signal to DC signal and also

to reduce the amplitude of the signal. The available voltage signal from the mains is

230V/50Hz which is an AC voltage, but the required is DC voltage (no frequency) with

the amplitude of +5V and +12V for various applications.

In this section we have Transformer, Bridge rectifier, are connected serially and

voltage regulators for +5V and +12V (7805 and 7812) via a capacitor (1000F) in

parallel are connected parallel as shown in the circuit diagram below.

Each voltage regulator output is again is connected to the capacitors of values

(100F, 10F, 1 F, 0.1 F) are connected parallel through which the corresponding

output (+5V or +12V) are taken into consideration.

Fig 2.2.1: Power Supply


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2.2.1 Circuit Explanation:

Transformer:

A transformer is a device that transfers electrical energy from one circuit to

another through inductively coupled electrical conductors. A changing current in the

first circuit (the primary) creates a changing magnetic field; in turn, this magnetic field

induces a changing voltage in the second circuit (the secondary). By adding a load to

the secondary circuit, one can make current flow in the transformer, thus transferring

energy from one circuit to the other.

The secondary induced voltage VS, of an ideal transformer, is scaled from the

primary VP by a factor equal to the ratio of the number of turns of wire in their respective

windings:

Basic principle

The transformer is based on two principles: firstly, that an electric current can

produce a magnetic field (electromagnetism) and secondly that a changing magnetic field

within a coil of wire induces a voltage across the ends of the coil (electromagnetic

induction). By changing the current in the primary coil, it changes the strength of itsmagnetic field; since the changing magnetic field extends into the secondary coil, a

voltage is induced across the secondary.

A simplified transformer design is shown below. A current passing through the

primary coil creates a magnetic field. The primary and secondary coils are wrapped

around a core of very high magnetic permeability, such as iron; this ensures that most of

the magnetic field lines produced by the primary current are within the iron and pass

through the secondary coil as well as the primary coil.


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Fig 2.2.2: An ideal step-down transformer showing magnetic flux in the core

Induction law

The voltage induced across the secondary coil may be calculated from Faraday's

law of induction, which states that:

Where VS is the instantaneous voltage, NS is the number of turns in the secondary

coil and equals the magnetic flux through one turn of the coil. If the turns of the coil

are oriented perpendicular to the magnetic field lines, the flux is the product of the

magnetic field strength B and the area A through which it cuts. The area is constant,

being equal to the cross-sectional area of the transformer core, whereas the magnetic field

varies with time according to the excitation of the primary. Since the same magnetic flux

passes through both the primary and secondary coils in an ideal transformer, the

instantaneous voltage across the primary winding equals

Taking the ratio of the two equations forVS and VP gives the basic equationfor

stepping up or stepping down the voltage


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Ideal power equation

If the secondary coil is attached to a load that allows current to flow, electrical

power is transmitted from the primary circuit to the secondary circuit. Ideally, the

transformer is perfectly efficient; all the incoming energy is transformed from the

primary circuit to the magnetic field and into the secondary circuit. If this condition is

met, the incoming electric power must equal the outgoing power.

Pincoming = IPVP = Poutgoing = ISVS

giving the ideal transformer equation

Pin-coming = IPVP = Pout-going = ISVS

giving the ideal transformer equation

Bridge Rectifier

A diode bridge or bridge rectifier is an arrangement of four diodes in a bridge

configuration that provides the same polarity of output voltage for any polarity of input

voltage. When used in its most common application, for conversion of alternating current

(AC) input into direct current (DC) output, it is known as a bridge rectifier. A bridge

rectifier provides full-wave rectification from a two-wire AC input, resulting in lower


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cost and weight as compared to a center-tapped transformer design, but has two diode

drops rather than one, thus exhibiting reduced efficiency over a center-tapped design for

the same output voltage.

Basic Operation

When the input connected at the left corner of the diamond is positive with

respect to the one connected at the right hand corner, current flows to the right along the

upper colored path to the output, and returns to the input supply via the lower one.

When the right hand corner is positive relative to the left hand corner, current

flows along the upper colored path and returns to the supply via the lower colored path.

In each case, the upper right output remains positive with respect to the lower

right one. Since this is true whether the input is AC or DC, this circuit not only produces

DC power when supplied with AC power: it also can provide what is sometimes called

"reverse polarity protection". That is, it permits normal functioning when batteries are

installed backwards or DC input-power supply wiring "has its wires crossed" (and


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protects the circuitry it powers against damage that might occur without this circuit in

place).

Prior to availability of integrated electronics, such a bridge rectifier was always

constructed from discrete components. Since about 1950, a single four-terminal

component containing the four diodes connected in the bridge configuration became a

standard commercial component and is now available with various voltage and current

ratings.

Output smoothing (Using Capacitor)

For many applications, especially with single phase AC where the full-wave

bridge serves to convert an AC input into a DC output, the addition of a capacitor may be

important because the bridge alone supplies an output voltage of fixed polarity but

pulsating magnitude (see diagram above).


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The function of this capacitor, known as a reservoir capacitor (aka smoothing

capacitor) is to lessen the variation in (or 'smooth') the rectified AC output voltage

waveform from the bridge. One explanation of 'smoothing' is that the capacitor provides a

low impedance path to the AC component of the output, reducing the AC voltage across,

and AC current through, the resistive load. In less technical terms, any drop in the output

voltage and current of the bridge tends to be cancelled by loss of charge in the capacitor.

This charge flows out as additional current through the load. Thus the change of

load current and voltage is reduced relative to what would occur without the capacitor.

Increases of voltage correspondingly store excess charge in the capacitor, thus

moderating the change in output voltage / current. Also see rectifier output smoothing.

The simplified circuit shown has a well deserved reputation for being dangerous,

because, in some applications, the capacitor can retain a lethalcharge after the AC power

source is removed. If supplying a dangerous voltage, a practical circuit should include a

reliable way to safely discharge the capacitor. If the normal load cannot be guaranteed to

perform this function, perhaps because it can be disconnected, the circuit should include a

bleeder resistor connected as close as practical across the capacitor. This resistor should

consume a current large enough to discharge the capacitor in a reasonable time, but smallenough to avoid unnecessary power waste.

Because a bleeder sets a minimum current drain, the regulation of the circuit,

defined as percentage voltage change from minimum to maximum load, is improved.

designs, a series resistor at the load side of the capacitor is added. The smoothing can

then be improved by adding additional stages of capacitorresistor pairs, often done only


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for sub-supplies to critical high-gain circuits that tend to be sensitive to supply voltage

noise.

The idealized waveforms shown above are seen for both voltage and current when

the load on the bridge is resistive. When the load includes a smoothing capacitor, both the

voltage and the current waveforms will be greatly changed. While the voltage is

smoothed, as described above, current will flow through the bridge only during the time

when the input voltage is greater than the capacitor voltage. For example, if the load

draws an average current of n Amps, and the diodes conduct for 10% of the time, the

average diode current during conduction must be 10n Amps. This non-sinusoidal current

leads to harmonic distortion and a poor power factor in the AC supply.

In a practical circuit, when a capacitor is directly connected to the output of a

bridge, the bridge diodes must be sized to withstand the current surge that occurs when

the power is turned on at the peak of the AC voltage and the capacitor is fully discharged.

Sometimes a small series resistor is included before the capacitor to limit this current,

though in most applications the power supply transformer's resistance is already

sufficient.

Output can also be smoothed using a choke and second capacitor. The choke

tends to keep the current (rather than the voltage) more constant. Due to the relatively

high cost of an effective choke compared to a resistor and capacitor this is not employed

in modern equipment.

Some early console radios created the speaker's constant field with the current

from the high voltage ("B +") power supply, which was then routed to the consuming

circuits, (permanent magnets were considered too weak for good performance) to create

the speaker's constant magnetic field. The speaker field coil thus performed 2 jobs in one:

it acted as a choke, filtering the power supply, and it produced the magnetic field to

operate the speaker.

Voltage Regulator

A voltage regulator is an electrical regulator designed to automatically maintain a

constant voltage level.

The 78xx (also sometimes known as LM78xx) series of devices is a family of

self-contained fixed linear voltage regulator integrated circuits. The 78xx family is a very


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popular choice for many electronic circuits which require a regulated power supply, due

to their ease of use and relative cheapness. When specifying individual ICs within this

family, the xx is replaced with a two-digit number, which indicates the output voltage the

particular device is designed to provide (for example, the 7805 has a 5 volt output, while

the 7812 produces 12 volts). The 78xx line is positive voltage regulators, meaning that

they are designed to produce a voltage that is positive relative to a common ground.

There is a related line of 79xx devices which are complementary negative voltage

regulators. 78xx and 79xx ICs can be used in combination to provide both positive and

negative supply voltages in the same circuit, if necessary.

Fig 2.2.3: Internal Block Diagram of Voltage Regulator

78xx ICs have three terminals and are most commonly found in the TO220 form

factor, although smaller surface-mount and larger TrO3 packages are also available from

some manufacturers. These devices typically support an input voltage which can be

anywhere from a couple of volts over the intended output voltage, up to a maximum of

35 or 40 volts, and can typically provide up to around 1 or 1.5 amps of current (though

smaller or larger packages may have a lower or higher current rating).


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2.3 RF MODULE:

The RF module, as the name suggests, operates at Radio Frequency. The

corresponding frequency range varies between 30 kHz & 300 GHz. In this RF system, the

digital data is represented as variations in the amplitude of carrier wave. This kind of

modulation is known as Amplitude Shift Keying (ASK). Transmission through RF is

better than IR (infrared) because of many reasons. Firstly, signals through RF can travel

through larger distances making it suitable for long range applications. Also, while IR

mostly operates in line-of-sight mode, RF signals can travel even when there is an

obstruction between transmitter & receiver. Next, RF transmission is more strong and

reliable than IR transmission. RF communication uses a specific frequency unlike IR

signals which are affected by other IR emitting sources. This RF module comprises of anRF Transmitter and an RF Receiver. The transmitter/receiver (Tx/Rx) pair operates at a

frequency of 434 MHz. An RF transmitter receives serial data and transmits it wirelessly

through RF through its antenna connected at pin4. The transmission occurs at the rate of

1Kbps - 10Kbps. The transmitted data is received by an RF receiver operating at the same

frequency as that of the transmitter. The RF module is often used along with a pair of

encoder/decoder. The encoder is used for encoding parallel data for transmission feed

while reception is decoded by a decoder. HT12E-HT12D, HT640-HT648, etc. are some

commonly used encoder/decoder pair ICs.

Fig 2.3.1: HT12E & HT12D Pin Diagram


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2.3.1 RF Transmitter:

An RF transmitter generates radio frequency waves in its circuits, and to this

'carrier signal', it adds the information part by modulating the carrier signal. This

composite signal (carrier plus information) is then fed to an antenna (aerial). The aerialinduces a corresponding signal into the atmosphere, by altering the Electric and Magnetic

fields at (obviously) the same frequency. The impedance of 'free space' is few tens of

Ohms to a few hundreds of Ohms. [Impedance may be considered analogous to

resistance, but with reactive properties as well.] The power emitted by the transmitter can

vary from a megawatt or so (for VLF signals) to a few watts for handheld devices.

Fig 2.3.2: RF transmitter image

Fig 2.3.3: Pin Diagram


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Pin Description:

Pin

No Function Name1

Ground (0V)

Ground

2 Serial data input pin Data3 Supply voltage; 5V Vcc4 Antenna output pin ANT

Table 2.3.1: Pin Description of RF Transmitter

2.3.2 RF receiver:

An RF receiver receives the signal from the atmosphere, from its own aerial.

The receiver aerial is often quite simple, and the signal level is typically of a few microvolts. This it tunes in (gets rid of unwanted signals and amplifies only the wanted ones).

The receiver circuits then strip the information part of the signal from the carrier part, and

amplify this to a useful level for audio or video. The actual signal into the loudspeaker

will be a few tens of volts. In spite of the inefficiency of loudspeakers, (often only a few

%) the signal eventually appears at a level that may be heard. A background radio will be

a few mill watts of power. Even a very loud sound is only a few watts of radiated (sound)

energy!!

Fig 2.3.4: RF Receiver Image


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Fig 2.3.5: Pin Diagram

Pin

No Function Name1 Ground (0V) Ground2 Serial data output pin Data3 Linear output pin; not connected NC4 Supply voltage; 5V Vcc5 Supply voltage; 5V Vcc6 Ground (0V) Ground7 Ground (0V) Ground8 Antenna input pin ANT

Table 2.3.2: Pin Description of RF Receiver

2.4 BUZZER:

A buzzer orbeeper is a signaling device, usually electronic, typically used in

automobiles, household appliances such as a microwave oven, or game shows.

It most commonly consists of a number of switches or sensors connected to a

control unit that determines if and which button was pushed or a preset time has lapsed,

and usually illuminates a light on the appropriate button or control panel, and sounds a

warning in the form of a continuous or intermittent buzzing or beeping sound. Initiallythis device was based on an electromechanical system which was identical to an electric

bell without the metal gong. Often these units were anchored to a wall or ceiling and used

the ceiling or wall as a sounding board. Another implementation with some AC-

connected devices was to implement a circuit to make the AC current into a noise loud

enough to drive a loudspeaker and hook this circuit up to a cheap 8-ohm speaker.


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Nowadays, it is more popular to use a ceramic-based piezoelectric sounder like a Son

alert which makes a high-pitched tone. Usually these were hooked up to "driver" circuits

which varied the pitch of the sound or pulse the sound on and off.

In game shows it is also known as a "lockout system," because when one person

signals ("buzzes in"), all others are locked out from signaling. Several game shows have

large buzzer buttons which are identified as "plungers".

The word "buzzer" comes from the rasping noise that buzzers made when they

were electromechanical devices, operated from stepped-down AC line voltage at 50 or 60

cycles. Other sounds commonly used to indicate that a button has been pressed are a ring

or a beep.

Fig 2.4.1: An Electronic Buzzer


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3. PROJECT IMPLEMENTATION:

3.1 BLOCK DIAGRAM:

Ambulance:

Traffic Post:

Fig 3.1.1: Block Diagram


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3.2 CIRCUIT DIAGRAM:

Fig 3.2.1: RF Transmitter

Fig 3.2.2: RF Receiver


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3.3 PROJECT DESCRIPTION

Traffic jams is one of the major problems most cities around the world face,

especially in developing regions. Everyday many citizens spend hours stuck in traffic in

the city to commute to their work place or school. As a result, this is beginning to become

a complex problem to most countries.

Often the ambulances get stuck at the traffic signals where all other vehicles try to

squeeze in to all the available space so as to move ahead as soon as the signal turns green.

Unlike western countries, Indian cities cannot think of having separate lanes for

emergency purpose because the roads are not broad enough in absence of any specific

guidelines the drivers of ambulance tend to steer the vehicle from whichever side they

find it convenient.

So, here we came up with a project which solves this problem. In our project we

avoid red light in the way of ambulance. Here we use RF technology to transmit an

emergency signal to the traffic post from the ambulance and there by the ambulance can

pass the signals easily without waiting.

We have a RF transmitter in the ambulance, which sends out RF signals at a

frequency of 434 MHz as a sign of emergency. These signals are received by the RF

receiver in the traffic signal post and then the microcontroller analyzes it and thereby

sends signals to glow the respective LED.


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3.4 MICROCONTROLLER CODE

#include

#include

sbit rf1=P2^0;

sbit rf2=P2^1;

sbit rf3=P2^2;

sbit rf4=P2^3;

sbit g1=P3^4;

sbit g2=P3^5;

sbit g3=P3^6;

sbit g4=P3^7;

void delay(unsigned int value);

//**********************************************************************

//**************************** MAIN PROGRAM**************************

//**********************************************************************

void main()

{

g1=g2=g3=g4=0;

g1=g2=g3=g4=1;

while(rf1==0 || rf2==0 || rf3==0 || rf4==0);

while(1)

{

if(rf1==0)

{

while(rf1==0 || rf2==0 || rf3==0 || rf4==0);

if(g2==1 && g3==1 && g4==1){

g1=~g1;

}

}

if(rf2==0)


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{

while(rf1==0 || rf2==0 || rf3==0 || rf4==0);

if(g3==1 && g1==1 && g4==1)

{

g2=~g2;

}

}

if(rf3==0)

{

while(rf1==0 || rf2==0 || rf3==0 || rf4==0);

if(g2==1 && g1==1 && g4==1)

{

g3=~g3;

}

}

if(rf4==0)

{

while(rf1==0 || rf2==0 || rf3==0 || rf4==0);

if(g2==1 && g3==1 && g1==1)

{

g4=~g4;

}

}

}

}

void delay(unsigned int value)

{

int x,y;

for(x=0;x


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3.5 ADVANTAGES:

The major advantage of this project is that it solves the traffic problem faced by the

emergency vehicles.

This is of low cost and can be easily installed. It is very useful in developing countries where separate lane is not provided for

emergency vehicles.

This doesnt require complex circuitry and not many complex changes are to be made

in the traffic system to install as it doesnt disturb the regular run of the system.

3.6 DISADAVNTAGES:

This project uses RF technology and this brings the major limitation.

Most RF modules work with a same frequency and hence only one RF module can

work in a location.

3.7 APPLICATIONS:

This is useful in:

Emergency cases to pass through the traffic.

Where automated traffic signal is used rather than manual signaling. In cities where the traffic is high.


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3.8 RESULT:

Intelligent ambulance kit when power supply is not given,

Fig 3.8.1: Intelligent ambulance kit when no power supply is given

When power supply is given the LED in the power supply circuit glows indicatingthe 5V input,

Fig 3.8.2: Intelligent ambulance kit when power supply is provided


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The power supply circuit in the kit containing components from transformer to

filter

Fig 3.8.3: Power Supply Circuit

RF remote control containing battery and encoder with an antenna,

Fig 3.8.4: RF Transmitter


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RF receiver containing receiver part with HT12D decoder,green LED indicates

availability of RF transmitter in the range of reception,

Fig 3.8.5: RF Receiver


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4. CONCLUSIONThe project Intelligent ambulance for City traffic Police has been

successfully designed and tested. Integrating the features of all the hardware components

we have developed this project. Presence of every module has been reasoned out and

placed carefully thus contributing to the best working of the unit.

Secondly, using highly advanced ICs and with the help of growing technology

the project has been successfully implemented.

Date post:	03-Apr-2018
Category:	Documents
Upload:	sampath-kumar-bejgama
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Traffic light control using RFID

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