06 Microprocessor Based Traffic Light Control

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PROJECT REPORT

ON

“MICROCONTROLLER BASED HOME

SECURITY SYSTEM”

ABSTRACT

Engineering is not only a theoretical study but it is a implementation of all we study for creating

something new and making things more easy and useful through practical study. It is an art

which can be gained with systematic study, observation and practice. In the college curriculum

we usually get the theoretical knowledge of industries, and a little bit of implementation

knowledge that how it is works? But how can we prove our practical knowledge to increase the

productivity or efficiency of the industry?

Don t take the chance of becoming victim of burglary, which is often accompanied by violence.

Protect our family and valuables with this microcontroller based security system that will let us

rest our head knowing that should anyone trying to break into our home, an alarm will go off and

the police will be alerted immediately.



The transmitter section continuously transmits IR rays which are received by the receiver

section. The received signal is further amplified and given to the PLL section, where its

frequency is locked to the transmitted frequency.

When the IR signal is interrupted, the microcontroller starts working as per the program burnt

into the EPROM and control the siren, telephone and cassette player via the respective relays.

CONTENTS:

ChapterChapter: 1. Introduction.Chapter: 2. Circuit description.Chapter: 3. Working of the circuit.Chapter: 4. Used Components.

4.1. Microcontroller (AT89C51)4.2. NE555 IC.4.3. MCT2E Optocouploer.4.4. Regulator (7805, 7809).

Chapter: 5. Other Important Used Components.5.1. BC548 NPN Transistor.5.2. Relay (12V, 200ohm).

Chapter: 6. ApplicationsSummery.Reference.

Chapter: 1

1. Introduction:

Protect our family and valuables with this microcontroller based security system knowing that

should anyone trying to break into our home, an alarm will go ON and the police will be alerted

immediately.

The microcontroller based security system consists of transmitter, receiver, phase locked loopand processing section.




section. The received signal is further amplified and given to the PLL section, where its

frequency is locked to the transmitted frequency. The transmitter and receiver are arranged such that

the transmitted IR rays fall directly onto the phototransistor LI4GI of the receiver. The signal received by

T2 is amplified by transistor T3 and operational amplifier µA741 (IC2). Series input resistor R8 and

feedback resistor R9 determine the gain of op amplifier IC2. The amplified single so applied to pin 3 of

PLLLM567 (IC3) through capacitor C4.

ICLM567 is highly stable PLL with synchronous AM lock detection and power output circuitry it is

primarily used as frequency decoder which drives a load whenever a sustained frequency falling within itsdetection band is present in its self biased input. The centre frequency of the determined by external

components.

In the absence of any input single, the center frequency of PLL s eternal free running, current control

oscillator is determined by resistor R12 abed capacitor C8.



Preset VR2 is used for tuning IC3 to the desired center frequency in the 6-10 kHz range,

Which should match the modulating frequency of the transmitter? Capacitor C6 and C7 are used as low

pass filter. Ned out filter respectively when the received signal is locked to frequency of transmitter signal

pin 8 of IC3 goes low and LED 1 glows. Since pin 8 is connected to the base of transistor T4 through R13its collector voltage rises. As a result T5 is forward biased to energies the relay RL5 the pole and

normally closed contact of really contact of RL5 are connected to +5v.


into the EPROM and control the siren, telephone and cassette player via the respective relays.

Chapter: 2

2. Circuit Description:



Transmitter Section:

In the transmitter section, NE555(ICI) is wired as an actable multivibrator whose oscillating freq is

decided by resistors R1 and R2, preset VR1 and capacitor c1, C3 bypasses the noise to ground,

preventing any change in calculated pulse-width.

The out put of ICI is fed to the base of the transistor t1, which drives an IR LED to transmit the

modulated IR signal. R4 limits the current flowing through the IR LED. Preset VR1 is used to vary the

modulating frequency.



Receiver Section:

The transmitter and receiver are arranged such that the transmitted IR rays fall directly onto the

phototransistor LI4GI of the receiver. The signal received by t2 is amplified by transistor t3 and

operational amplifier µA741 (IC2). Series input resistor R8 and feedback resistor R9 determine the gain

of op amplifier IC2. The amplified single so applied to pin 3 of PLLLM567 (IC3) through capacitor c4.

ICLM567 is highly stable PLL with synchronous AM lock detection and power output circuitry it is pre

merely used as frequency decoder which drives a load whenever a sustained frequency falling within its

detection band is present in its self biased input. The centre frequency of the determined by external

components.

In the absence of any input single, the center frequency of PLL s eternal free running, current controloscillator is determined by resistor R12 abed capacitor C8. Preset VR2 is used for tuning IC3 to thedesired center frequency in the 6-10 kHz range, which should match the modulating frequency of the



transmitter? Capacitor C6 and C7 are used as low pass filter. Ned out filter respectively when the receivedsignal is locked to frequency of transmitter signal pin 8 of IC3 goes low and LED 1 glows. Since pin 8 isconnected to the base of transistor T4 through R13 its collector

voltage rises. As a result T5 is forward biased to energies the relay RL5 the pole and normally closed

contact of really contact of RL5 are connected to +5v.

The low order multiplex address and data lines AD0 though AD7 of IC4 are connected to the EPROM

(IC5) through the latch(IC6), while its high order address line A8 through A10 are directly connected to

the EPROM. Address lines A0 through A7. Are separated from data lines D0 through D7 by latch enable

single.

Address latch – enable pin 30 of the microcontroller is connected to latch enable pin 11 Ic6. When ale

high the latch us transparent. The output changes according the input data when ALE goes low, the low

order address is latched at the input of IC6.

Data lines D0 throughD7 of microcontroller are connected to dated lines of IC5 and IC7 each. Chip sleets

signal for IC5 is generated by RD and IO/M lines with the help of NAND gate. The inverted IO/M signal

provides CS signal through IC7.

IC AT89C51 is general purpose programmable device compatible with most microcontrollers. It has three

programmable ports, any of which can be ports and the remaining eight bits as port c.

The eight bits of ports c can be used as individual bits or grouped in two 4-bits ports namely, c (upper)

and c (lower). Ports A and C are configured as input ports and port B is configured as output port A. is

used for inter detection,portB for activating the siren, cassette player, telephone cradle switch and redial

button and port C for polarity reversal detection.



The circuit for detecting the polarity reversal detection the telephone line is built around optocoupler IC8

and IC9. Normally, TIP is positive with respect to RING lead of telephone line. With the handset in off

position a nominal loop current of 10 mA is assumed to flow through the telephone line. Resistor R23 is

selected as 120 ohms to develop the voltage of

1.2v. when the the dc lines voltage polarity reversal occurs, optocoupler IC8 s internal LED conducts and

LED3 glows to indicate polarity reversal occurs. Simultaneously, optocoupler IC9 s internal LED goes

off and its pin 5 (collector) goes high to provide line – reversal sense signal to AT89C51.

Fig.3 shows the power supply circuit. The AC mains are stepped down by transformer X1 to deliver a

secondary output of 12V AC at 300 ma. The transformer output is rectified by a full-wave bridge rectifier.

Comprising diodes D7 through D10. Capacitor C12 acts as a filter to eliminate ripples. IC10 and IC11

provide regulated 5v and 9V power supplies, respectively. Capacitors C13 and C14 bypass any ripple

present in the regulated out- us. Switch S2 acts as an „on / off switch.

Relay connections:

The cradle switch in the telephone instrument is a double pole, two-way switch. Replace this cradle

switch with the contacts of DPDT relay RL3 as shown in fig.2.Now relay RL3 is

Used to implement the action of lifting the telephone handset.

There are four pads on the PCB of the telephone instrument where cradle switch is connected. The two

pads which are shorted when the telephone handset is placed on the cradle are connected to the normally

closed (N/O) contacts of relay RL3, while the other two pads which are shorted when the handset is off-

hook are connected to to the normally o0pen (N/O) contacts of relay RL3.



Relay RL2 is connected in parallel to the redial button of the telephone instrument. When relay RL3

emerges to emulate lifting of the handset, relay RL2 is energized to switch on the redial button and the

already loaded telephone number of the police station or any other help provider is automatically dialed.

Relay RL4 activates the siren whenever the IR signal being received is interrupted iron soundscontinuously until the user presses the reset button.

Relay RL1 is used to switch on the audio cassette player, in which the user s residential address and alert

message to be conveyed to the police station are prerecorded. The speaker output of the cassette player is

connected to the telephone s microphone to convey the alert message to the police station. The player gets

switched off when the message is over.

Chapter: 3

3. Working of the Circuit:

The transmitting IR LED1 and phototransistor T2 of the receiver are fitted to the gate such the IR rays

emitted by the LED directly fall on the phototransistor.

The IR LED transmits a train of IR pulses. These pulses are received by the receiver and amplified byIC2. Output pin 8 of the PLL (IC3) is low when the PLL network is locked to the transmitter frequency

and relay RL5 energies to make PA line of IC7 low.

When someone walks through the gate to enter your home, the transmitted signal is interrupted. Output

pin 8 of the PLL network goes high and relay RL5 de-energies to make PA0 line of IC7 high. Now the

microprocessor starts working as per the program loaded in the EPROM.

Relay RL4 energies to activate the siren. At the same time, relay RL3 energizes to emulate lifting the

telephone handset off the cradle to provide the dial tone. After a few seconds, relay RL2 energies to short

the redial button contacts. After the loaded number is dialed, it switches off relay RL2. Then relay RL1

turns on the audio player.

Here we have provided the same polarity-reversal detection facility so that the audio player turns on only

when polarity-reversal is detected.



The actual-size, double-size track lay-outs for solder and component sides of the PCB for the 8085

microprocessor-based home security system are shown in figs5 and figs6 , respectively, and their

component layout in fig.7.

Software Program:

Fig. shows the flow-chart of the Assembly language program. The device interface IC (IC7) is initializedwith control word 99H. Ports A and C of IC7 act as input ports, while port B becomes the output port.



After initialization, the AT89C51 microcontroller reads the status of port A. If port A is high, siren is

activated. The telephone goes in off-hook condition and the emergency number is dialed through the

redial button. Redial button gets switched off after the number is dialed. Now the microprocessor reads

the status of port C and checks for the polarity reversal of the telephone line. When polarity reversal is

detected, the audio player turns on to play the message. Otherwise, the process repeats from activation of

the siren followed by emergency number dialing and so on. After delivering the message, the player

automatically gets turned off. The siren sounds until the reset switch is pressed.

Chapter: 4

4. Used Components:

AT89C2051

NE555

uA741 Operational Amplifier

MCT2E Optocoupler

Regulator (7805,7809) BC 548 NPN Transistor

L14G1 Photo Transistor

1N4148 Switching Diode

LED’s ( Red, IR)

Resistor’s

Capacitor’s

Relay’s

Battery’s

These are important components with is use in this projects. Other components like

resistors, capacitors, transistors, inductors used PCB’s etc are not described here.



The details of the important IC’s:

4.1. AT89C51:

Features

• Compatible with MCS- 51™ Products

• 4K Bytes of In-System Reprogrammable Flash Memory – Endurance: 1,000

Write/Erase Cycles

• Fully Static Operation: 0 Hz to 24 MHz

• Three-level Program Memory Lock

• 128 x 8-bit Internal RAM

• 32 Programmable I/O Lines

• Two 16-bit Timer/Counters

• Six Interrupt Sources

• Programmable Serial Channel

• Low-power Idle and Power-down Modes

Description:

The AT89C51 is a low-power, high-performance CMOS 8-bit microcomputer with 4Kbytes of

Flash programmable and erasable read only memory (PEROM). The devices manufactured using

Atmel shigh -density nonvolatile memory technology and incompatible with the industry



standardMCS-51 instruction set and pin out. 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-bit CPU with Flash on a monolithic chip, the Atmen AT89C51 is a

powerful microcomputer which provides a highly-flexible and cost-effective solution to many

embedded control applications .

Pin Configuration:

Block Diagram:



The AT89C51 provides the following standard features: 4K bytes of Flash, 128 bytes of RAM,32 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt architecture,

a full duplex serial port, on-chip oscillator and clock circuitry. In addition, the AT89C51 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 .

Pin Description:

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 as high impedance inputs.

Port 0 may also be configured to be the multiplexed low order address/data bus during accessesto 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.

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. As inputs, Port 1 pins that are externally being pulled

low will source current (IIL) because of the internal pull-ups. Port 1 also receives the low-order

address bytes during Flash programming and verification.



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 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 is the read strobe to external program memory. When the AT89C51 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. EA should be strapped to

VCC for internal program executions. This pin also receives the 12-volt programming enable

voltage (VPP) during Flash programming, for parts that require 12-volt VPP.

XTAL1



Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2

Output from the inverting oscillator amplifier. Unconnected while XTAL1 is driven as shown inFigure 2. There are no requirements on the duty cycle of the external clock signal, since the input

to the internal clocking circuitry is through a divide-by-two flip-flop, but minimum and

maximum voltage high and low time specifications must be observed.

Idle Mode

In idle mode, the CPU puts itself to sleep while all the on chip peripherals remain active. The

mode is invoked by software. The content of the on-chip RAM and all the special functions

registers remain unchanged during this mode. The idle mode can be terminated by any enabled

interrupt or by a hardware reset. It should be noted that when idle is terminated by a hard ware

reset, the device normally resumes program execution, from where it left off, up to two machine

cycles before

The internal reset algorithm takes control. On-chip hardware inhibits access to internal RAM in

this event, but access to the port pins is not inhibited. To eliminate the possibility of an

unexpected write to a port pin when Idle is terminated by reset, the instruction following the one

that invokes Idle should not be one that writes to a port pin or to external memory.

Programming Algorithm:

Before programming the AT89C51, the address, data and control signals should be set up

according to the Flash programming mode table and Figure 3 and Figure 4. To program the

AT89C51, take the

Following steps:

1. Input the desired memory location on the address lines.

2. Input the appropriate data byte on the data lines.



3. Activate the correct combination of control signals.

4. Raise EA/VPP to 12V for the high-voltage programming mode.

5. Pulse ALE/PROG once to program a byte in the Flash array or the lock bits. The byte-writecycle is self-timed and typically takes no more than 1.5 ms. Repeat steps 1 through 5, changing

the address and data for the entire array or until the end of the object file is reached.

Data Polling:

The AT89C51 features Data Polling to indicate the end of a write cycle. During a write cycle, an

attempted read of the last byte written will result in the complement of the written datum on

PO.7. Once the write cycle has been completed, true data are valid on all outputs, and the nextcycle may begin. Data Polling may begin any time after a write cycle has been initiated.

Ready/Busy:

The progress of byte programming can also be monitored by the RDY/BSY output signal. P3.4 is

pulled low after ALE goes high during programming to indicate BUSY. P3.4 is pulled high again

when programming is done to indicate READY.

Program Verify:

If lock bits LB1 and LB2 have not been programmed, the programmed code data can be read

back via the address and data lines for verification. The lock bits cannot be verified directly.

Verification of the lock bits is achieved by observing that their features are enabled.

Chip Erase:

The entire Flash array is erased electrically by using the proper combination of control signals

and by holding ALE/PROG low for 10 ms. The code array is written with al l “1”s. The chip

erase operation must be executed before the code memory can be re-programmed.



Reading the Signature Bytes:

The signature bytes are read by the same procedure as a normal verification of locations 030H,

031H, and 032H, except that P3.6 and P3.7 must be pulled to a logic low. The values returned

are as follows.

(030H) = 1EH indicates manufactured by Atmel

(031H) = 51H indicates 89C51

(032H) = FFH indicates 12V programming

(032H) = 05H indicates 5V programming

Programming Interface

Every code byte in the Flash array can be written and the entire array can be erased by using the

appropriate combination of control signals. The write operation cycle is self timed and once

initiated, will automatically time itself to completion. All major programming vendors offer

worldwide support for the Atmen microcontroller series. Please contact your local programming

vendor for the appropriate software revision.

4.2. NE555 IC:

Features:

• High Current Drive Capability (200mA)



• Adjustable Duty Cycle

• Temperature Stability of 0.005%/°C

• Timing from μ Sec to Hours.

• Turn off Time Less than 2μSec

Applications:

• Precision Timing

• Pulse Generation

• Time Delay Generation

• Sequential Timing

Description:

The LM555/NE555/SA555 is a highly stable controller capable of producing accurate timing

pulses. With monostable operation, the time delay is controlled by one external resistor and onecapacitor. With astable operation, the frequency and duty cycle are accurately controlled with

two external resistors and one capacitor.

Internal Block Diagram:



Monostable Operation:

Monoatable Circuit:



Waveforms of Monostable Operation

Resistance and Capacitance vs.

Time delay (td)

4.3. MCT2E Optocouploer:



FEATURES:

• UL recognized (File # E90700)

• VDE recognized (File # 94766) -Add option V for white package (e.g., MCT2V-M) –Add

Option 300 for black package (e.g., MCT2.300 )

Dimension Package (Surface Mount):



• MCT2 and MCT2E are also available in white package by specifying -M suffix, e.g. MCT2M

APPLICATIONS:

• Power supply regulators

• Digital logic inputs

• Microprocessor inputs

4.4. Voltage Regulator (7805, 7809):

Features:



• Output Current up to 1A

• Output Voltages of 5, 6, 8, 9, 10, 12, 15, 18, 24V

• Thermal Overload Protection

• Short Circuit Protection

• Output Transistor Safe Operating Area Protection

The MC78XX/LM78XX/MC78XXA series of three terminal positive regulators are available in

the TO-220/D-PAK package and with several fixed output voltages, making them useful in a



wide range of applications. Each type employs internal current limiting, thermal shut down and

safe operating area protection, making it essentially indestructible. If adequate heat sinking is

provided, they can deliver over 1A output current. Although designed primarily as fixed voltage

regulators, these devices can be used with external components to obtain adjustable voltages and

currents.

Internal Block Diagram:

Typical Applications:

DC PARAMETERS



LOAD REGULATION

Constant Current Regulator

Notes :

(1) To specify an output voltage. Substitute voltage value for "XX." A common ground isrequired between the input and the

Output voltage. The input voltage must remain typically 2.0V above the output voltage even

during the low point on the input ripple voltage.



(2) CI is required if regulator is located an appreciable distance from power Supply filter.

(3) CO improves stability and transient response

LM78XX (KA78XX, MC78XX) FIXED VOLTAGE REGULATOR(POSITIVE):

(LM7809 Voltage Regulator)

3-TERMINAL 1A POSITIVE VOLTAGE REGULATORS

The LM78XX series of three-terminal positive regulators are available in the TO-220/D-PAK

package and with several fixed output voltages, making them useful in a wide range of

applications. Each type employs internal current limiting, thermal shut-down and safe area

protection, making it essentially indestructible. If adequate heat sinking is provided, they can

Deliver over 1A output current. Although designed primarily as fixed voltage regulators, these

devices can be used with external components to obtain adjustable voltages and currents.

FEATURES:

· Output Current up to 1A

· Output Voltages of 5, 6, 8, 9, 10, 11, 12, 15, 18, 24V



· Thermal Overload Protection

· Short Circuit Protection

· Output Transistor SOA Protection

BLOCK DIAGRAM:

Chapter: 5

5. Other Used Components:

5.1. BC548 NPN Transistor:



This device is designed for use as general purpose amplifiers and switches requiring collector

currents to 300 mA. Sourced from Process 10. See PN100A for characteristics.

NOTES :

1) These ratings are based on a maximum junction temperature of 150 degrees C.

2) These are steady state limits. The factory should be consulted on applications involving pulsed

or low duty cycle operations.

Absolute Maximum Ratings

5.2. Relay (12V, 200 ohm):



A relay is an electrical switch that opens and closes under control of another electrical circuit. In

the original form, the switch is operated by an electromagnet to open or close one or many sets

of contacts. It was invented by Joseph Henry in 1835. Because a relay is able to control an output

circuit of higher power than the input circuit, it can be considered, in a broad sense, to be a form

of electrical amplifier.

Operation:

When a current flows through the coil, the resulting magnetic field attracts an

armature that is mechanically linked to a moving contact. The movement either makes

or breaks a connection with a fixed contact. When the current to the coil is switched

off, the armature is returned by a force that is half as strong as the magnetic force to

its relaxed position. Usually this is a spring, but gravity is also used commonly in

industrial motor starters. Relays are manufactured to operate quickly. In a low voltageapplication, this is to reduce noise. In a high voltage or high current application, this is

to reduce arcing.



If the coil is energized with DC, a diode is frequently installed across the coil, to

dissipate the energy from the collapsing magnetic field at deactivation, which would

otherwise generate a spike of voltage and might cause damage to circuit components.

If the coil is designed to be energized with AC, a small copper ring can be crimped tothe end of the solenoid. This "shading ring" creates a small out-of-phase current,

which increases the minimum pull on the armature during the AC cycle. [1]

The contacts can be either Normally Open (NO) , Normally Closed (NC) , or

change-over contacts.

Normally-open contacts connect the circuit when the relay is activated; the circuit is

disconnected when the relay is inactive. It is also called Form A contact or "make"

contact. Form A contact is ideal for applications that require to switch a high-current

power source from a remote device.

Normally-closed contacts disconnect the circuit when the relay is activated; the circuit is

connected when the relay is inactive. It is also called Form B contact or "break" contact. Form B

contact is ideal for applications that require the circuit to remain closed until the relay is

activated.

Change-over contacts control two circuits: one normally-open contact and one normally-closed

contact with a common terminal. It is also called Form C contact or "transfer" contact.

By analogy with the functions of the original electromagnetic device, a solid-state

relay is made with a thyristor or other solid-state switching device. To achieve

electrical isolation, a light-emitting diode (LED) is used with a photo transistor.

APPLICATION’S:

Basically this project is use as a security purpose. We are using here this

project for providing the security to our home, similarly we can use this



project to protect any restricted area like power plant security, Border

security etc.

Project can be use to operate any device automatically, in this application

the interruption of the infrared waves is use to operate the device. It can use for military purpose.

It can be use as “Power supply regulators”.

Summary:

The microcontroller based security system consists of transmitter, receiver, phase locked loop

and processing section.


section. The received signal is further amplified and given to t6he PLL section, where its

frequency is locked to the transmitted frequency. The transmitter and receiver are arranged such that

the transmitted IR rays fall directly onto the phototransistor LI4GI of the receiver. The signal received by

t2 is amplified by transistor t3 and operational amplifier µA741 (IC2). Series input resistor R8 and

feedback resistor R9 determine the gain of op amplifier IC2. The amplified single so applied to pin 3 of

PLLLM567 (IC3) through capacitor c4.

ICLM567 is highly stable PLL with synchronous AM lock detection and power output circuitry it is pre

merely used as frequency decoder which drives a load whenever a sustained frequency falling within its

detection band is present in its self biased input. The centre frequency of the determined by external

components.

In the absence of any input single, the center frequency of PLL s eternal free running, current control

oscillator is determined by resistor R12 abed capacitor C8.

Preset VR2 is used for tuning IC3 to the desired center frequency in the 6-10 kHz range,

Which should match the modulating frequency of the transmitter? Capacitor C6 and C7 are used as low

pass filter. Ned out filter respectively when the received signal is locked to frequency of transmitter signal

pin 8 of IC3 goes low and LED 1 glows. Since pin 8 is connected to the base of transistor T4 through R13



its collector voltage rises. As a result T5 is forward biased to energies the relay RL5 the pole and

normally closed contact of really contact of RL5 are connected to +5v.


into the EPROM and control the siren, telephone and cassette player via the respective

Reference:

Electronics for you ( Oct. 2004 )

http://www.atmel.com

http:/ /www.electronics4u.com

http:/ /www.ttransenergie.com.au

Microprocessors And Interfacing( Programming & Hardware)-Douglas V.

Hall

Vedam Subrahmanayam- Power Electronics.

http://www.electronics4u.com/

http://www.ttransenergie.com.au/

http://www.ttransenergie.com.au/

http://www.electronics4u.com/

06 Microprocessor Based Traffic Light Control

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