Automatic Power Saving Energy Meter

8/3/2019 Automatic Power Saving Energy Meter

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June 15, 2011 [AUTOMATIC POWER SAVING ENERGYMETER]

1. INTRODUCTION

The Automation of Public Service Sectors is the current trend, which

transforms the manpower oriented services to semi-automatic or full automatic

Sectors. As the country is opened to globalization, peoples income is rising. And the

Busy word is now become essential part of everybodys life. So, governments prefer

not only to give quality service but also the corrupt & error free services to its

citizens. As a result, this project proposed here is an advanced system, which sits in

consumers home and helps Electricity Boards or Electricity Corporations to handle

the Billing system smoothly. This project helps them to give quality service to its

customer without any kind of problems.

In Brief:

The present trend of tariff collection suffers from inefficient system of billing

and collection in the way of wasting of valuable man power. So our aim is to

overcome these problems with the introduction of MICRO-CONTROLLER

BASED POWER CARD- A NEW APPROACH TO TARIFF COLLECTION.

In this Power Card system the consumer purchases the pre-paid Power Card,

which is available in three designations viz., 100 units, 150 units, & 200 units, as per

his requirements. This MICRO-CONTROLLER BASED POWER CARD project is

fitted inside the consumers home, before the energy meter. When user inserts the

Power Card in his Power Card Systems Card Holder, the Card Detector takes care of

verifying the authenticity of the Power Card inserted. If it is found OK then his total

units consumed is started counting and accordingly his cards units are decremented.

At the same time his home gets power supply through Energy Meter. Simultaneously,

the Card Analyzer checks the designation of the Power Card inserted and makes the

corresponding output line high. When the total consumption reaches 80% of the

designated unit value, this project alerts consumer by beeping the buzzer. If consumer

notices it, he can buy another card of his requirement to avoid any future power-cut.

Else, after total power consumption reaches the Power Cards designation unit value

the system automatically disconnects the supply.

Dept of E.E.E. |R.Y.M.E.C Bellary. 1


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This system is efficient [as it uses Micro-controller PIC IC for monitoring

Number of Units Consumed], therefore accurate assessment of energy audit program

and also necessary to promote a goodwill and consumer relation and thereby ensuring

exact revenue collection, which is exact proportion to the generation of electrical

energy.

MICRO-CONTROLLER IN DAILY LIFE

Micro-controller has elevated electronics to a great height. It is being used in

many industrial instruments, medical equipment, microcomputers and programmable

logic controllers. Its speed of operations is amazing. Electronic equipment can be used

in efficient man-machine interface, making the communications faster.

Having helped the industry, electronics has entered the house. Transistor,

radio, tape recorders, television sets, toy and educational equipment are commonly

household items. All these products have made the life more comfortable. Personal

computers are being used in homes in many countries to keep track of accounts,

family health details and such other information.

Remote controllers for TVs and VCRs enable viewers to switch off the set or

change the channel from a distance. Bigger houses have intercoms so that a person

need not get to another room for communication. Burglar alarm is energized before

leaving the house. Whoever enters the house has to first put off the system by

resetting it. The location is known available to disable it is only 10 to 25 seconds. An

unauthorized visitor will not be able to reset the switch in that time and the alarm will

alert the neighbors. Fire sensors, gas alarm are the other gadgets, which take care of

fire mishaps. Time switches turn on and off any electrical appliance at the preset time.

Video games and electronic toys help in providing leisure and comfort at

home. However, these systems cannot generally be combined together for economical

compatibility

.



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AUTOMATION AT INDUSTRIES

Micro-controller based Industrial Automation is aimed to reduce supervision

of human and to create a comfortable & safe working environment. There are several

big companies who are engaged in this Micro-controller Based Industrial Automation

field. For example Allen Bradley, ABB, Siemens are producing Programmable Logic

Controllers [PLLs] and their related instruments, software, hardware and controlling

panels. These PLLs are capable of controlling the small, medium or big industries

with less human intervention.

Micro-controller based Industrial Automation (IA) comprises four sub-

systems to perform different functions [of course with the help of Computer]:

Industrial keeping system: -

A module called Home Terminal which comprises a telephone/intercom

master unit, master and room monitor controller, TV, door and phone controllers and

indicators is the heart of security & safety keeping system.

This sub-system controls temperature of water in furnace, keeps record of the

consumption of electricity and water gets signals from burglar alarms, gas leaks,

flame sensors etc, and gives warning. Besides, it receives the incoming phone calls,

answers or sends messages at appropriate time and turns on/off time-punch machines

for attendance purpose, lighting & vigilant cameras etc. Intercom at the main door lets

the security person know the identity of a visitor. It ensures that the employee has

enough safety and comfort by taking care of security of the industry, energy control,

equipment control etc. It has modular construction and should be installed cent rally,

mainly in new buildings as the wiring involved is to be taken care of.

INTERFACE SYSTEM

Also known as communication system, it allows the user to communicate with

others. It works with high definite TV, cable TV (CATV), direct broadcasting system

(DBS) etc. one can get the news or special announcements through video or audio or

text form.



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People in some countries now do field work sitting in the comfort of their

chamber through a personal computer connected to the office. On can also use it to

control the instruments and share the status of the instruments with another field

engineer who is far away & connected to the computer database system.



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2. BLOCK DIAGRAM & ITS DESCRIPTION

The section explains how the MICRO-CONTROLLER BASED POWER

CARD A New Approach to Tariff Collection really works.

In Brief:

This Micro-controller Based Power Card System sits in between the incoming

Mains Power Supply lines and consumers Energy Meter. When consumer inserts his

Power Card inside the Card Holder, first it is verified for authenticity. As every Power

Card has Code Generator circuit which creates unique ID for each Power Card. When

it is inserted inside the Card Holder, it gets its working voltage from this project andstarts emitting IR coded signals to Card Detector. If Card Detector finds the valid IR

coded signals from the Power Card, then it switches ON MCB [Main Circuit Breaker]

of the Home. That means as-soon consumer inserts his Power Card, if it is valid one,

then he will start getting the power supply from that instant only.

The second part of the signal coming from Card Holder goes to Card Analyzer

section for identification of Power Cards designation. This Section makes thecorresponding designations pin high, which in turn passes through Buffer & Driver

stages. This signal is further sent to Logic Stage for processing.

The Logic Stage acts as a brain of the system and receives two reference

signals for decision making. First reference signal comes from card reader section,

which reads consumers Power Card and produces unique reference signal depends

upon the Power Card rating [i.e., designation it holds-whether 100 units or 150 units

or 200 units card]. The second reference signal is taken from the Micro-controller

Chip based Energy Meter section. This signal tells the Logic Stage, how much units

are consumed by the consumer till now. If the total power consumption units equal to

80% of the Power Card designation, then it activates the Tone Generator, which in

turn beeps the buzzer. If both these reference signals equals to each other then Logic

Stage trips the MCB [Main Circuit Breaker], through which home supply is supplied.

Thus power supply will disconnected until another new Power Card is inserted. As



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consumer inserts new Power Card of any designation, the power supply to home will

be restored for the intended period the Power Card permits.

This Power Card System is divided into three sections for the clarity sake,

which is shown as dotted box in block diagram Fig 2.1. The first section, Card Reader

Section, consists of Card Holder, Card Detector, Card Analyzer, Buffer & Driver. The

Energy Meter section has four blocks: Energy Meter, Schmitt Trigger, Micro-

controller Based Consumed Unit Monitor & Buffer. The Main Section comprises of

Logic Stage, Driver, Tone Generator & Power Supply Unit blocks.

Before explaining these three sections, take a look at Power Card.

POWER CARD:

Every Power Card bears its unique IR Code number and its designation value

with it. The Code is generated by an oscillator inherited inside the Power Card. When

consumer inserts this Power Card inside the Card Holder, it receives the working

voltage from the Card Holder and starts emitting its unique card code. This Power

Cards ID code is decoded by the Card Detector and confirms that the card inserted is

authorized one or not. This Card offers unique IR code to Card Analyzer for

identification of designation of the card. This two-layer system makes this card very

robust and reliable.

Let us see the details of each block under three headings as follows:

1. Card Reader Section

2. Energy Meter Section

3. Main Section



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CARD READER SECTION

CARD HOLDER: Basically it is just a Card Holder, which holds the Power Card

inserted by the consumer and helps the system to read it. This block supplies the

working voltage to the Power Card, so that it can transmit its unique code to Card

Detector block and Card Analyzer block.

CARD DETECTOR: This block verifies the authorization of the inserted Power Card

by checking the IR packets across the IR Sensor. If it found valid IR packets or

signals then switches MCB [Main Circuit Breaker] ON. By this action, consumer gets

power supply as soon he inserts valid Power Card. This section is nothing but an IR

Receiver, which decodes Infra Red signal Packets for communication.

CARD ANALYZER: The Power Card inserted inside the Card Holder offers certain

unique Rx resistance to this Card Analyzer. This unique Rx resistance depends on the

designation of the Power Card, which it bears. Here this block makes the decision

with the help of popular Comparator IC, whether inserted Power Card is having 100

units or 150 units or 200 units designation value. According to the detected value, it

activates the respective Buffer block.

BUFFER: This stage of the system is used to isolates the driver section from the Card

Holder & its associated blocks and also to match the impedance of Input and Output

circuits. Here, hex buffer IC is used to achieve the required goal. Each designation of

Card has its own Buffer & Driver block. Any one Buffer block gets activated depends

on the Card Analyzers output. The output of that Buffer is fed to respective Driver

Block.

DRIVER: The Driver Block is used to carry the first reference signal [i.e., designation

of the Power Card]. The Darlington Transistor Pair is used in unity gain amplifier

mode, which in turn activates the relay connected across it. The relay outputs are

connected to Logic Stage for decision taking action.



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ENERGY METER SECTION

ENERGY METER: This is an Energy Meter, which shows the total units consumed

by the user in digital form. That means it produces signals whenever any units

consumption takes place. The output of this Energy Meter is fed to Schmitt Trigger

block for further processing.

SCHMITT TRIGGER: This receives the current unit consumed by Energy Meter, to

which it is connected. The information coming out of Energy Meter should be

converted into digital pulses, so that rest of the digital circuit should process it further.

So this unit consumed information of Energy Meter is converted into predefinedpulses using this Schmitt Trigger Stage. That means this stage produces a pulse for

every unit the Consumer consumes. The output of this stage is given to Consumed

Unit Monitor block.

MICRO-CONTROLLER BASED CONSUMED UNIT MONITOR: This block

counts the number of pulses coming from the Schmitt Trigger and keeps the total unit

consumption record. The output of this stage is given to Buffer stage.

BUFFER: The buffer is basically a unity gain amplifier, which is used to match the

input & output impedances. This helps us in compensating the signal disorders caused

by the improper circuit impedances. The output of this block goes to Logic Stage for

decision making purpose.



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MAIN SECTION

LOGIC STAGE: This decision making stage is built using logic ICs and receives two

inputs, one from Card Reader Section & other from Energy Meter Section. If Energy

Meter Sections output is 80% of the Card Reader Section, then it activates the Tone

Generator to beeps the buzzer. If it founds that two inputs are equal, then activates

driver block to switch OFF the MCB. This block is built around logic ICs

DRIVER: As the name of itself indicates, the driver stage is used to drive the relay.

Since the digital ICs cannot drive the heavy voltage MCB or electromagnetic relay [of

12 V], this driver circuit is used. This block actually cuts the power supply as soon isit gets coil current. This driver circuit is configured in Darlington Driver Mode.

TONE GENERATOR: This block is used to produce the alert beeps whenever total

units consumed by the user reaches the 80% of the Power Cards designation value.

POWER SUPPLY UNIT: This MICRO-CONTROLLER BASED POWER CARD

project needs three working voltages, +12Volts for driving relays, +9V for Op-amp

IC and +5 Volts for other circuits. So, special power supply is designed to generate

these triple, fixed and regulated voltages.



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Fig 2.1 BLOCK DIAGRAM OF POWER CARD [using PIC]


POWERSUPPLY

UNIT

ENERGYMETER

Card Reader Section

Buzzer

LOGIC STAGE

DRIVER

DRIVER I

DRIVER II

DRIVER III

BUFFER I

BUFFER II

BUFFER III

Energy Meter Section

BUFFER I

BUFFER II

BUFFER III

SCHMITTTRIGGER

CARDDETECTOR

CARDANALYZER

CONSUMED UNITMONITOR

[Micro-controller Chip]

CARDHOLDER

Code Generator

TONEGENERATOR

POWERSUPPLY

UNITMAIN

CIRCUITBREAKER

ID CARD

X a b Y


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3. CIRCUIT DIAGRAM & ITS DESCRIPTION

This MICRO-CONTROLLER BASED POWER CARD project generates two

reference signals and processes them intelligently so that exact designated units must be

consumed by the consumer. The Power Card is the Key Input device, which in turn

causes to generate first reference signal. The second reference signal is produced at

Energy Meter side.

Except the Power Card this MICRO-CONTROLLER BASED POWER CARD

system is divided into three parts: Card Reader Section, Energy Meter Section & Main

Section. These three parts are further divided into sub-sections, based on the circuitblocks each are constructed. The Circuit Description of each part along with Power Card

is discussed in separate headings for clarity sake.

POWER CARD

This Power Card has two layer design: one is to confirm that this Power Card is

an Authorized one [which is achieved by implementing IR Transmitter circuit]; and

second is to tell the Card Reader that how much the Power Cards designation is. ThePower Card comes in three designations 100 units, 150 units & 200 units. This

designation is set by the resistance or impedance value fitted inside this Power Card. As

this point is very clear, there is no need of any further explanation is required. Below

section explains about IR Communication & transmitter circuit and its working.



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CARD HOLDER

The function of this circuit block is to hold the Power Card, which is inserted by

the Consumer. This Card Holder block not only holds it but also provides power supplyto IR Transmitter and gives the reference resistance Rx to Card Analyzer circuit.

Circuit Description:

This circuit block is very simple. The Card Holder Slot has four active lines, X a b Y, as

shown in circuit diagram. The points X & Y offers pre-defined unique IR Coded signal to

Card Analyzer Circuit for further processing. The points a & b gives +Vcc and Gnd

connections to IR Transmitter, which are coming from Power Supply Unit.


CIRCUIT DIAGRAM OF CARD HOLDER

C1

Working VoltageFrom

Power Supply Unit

+Vcc Gnd

X a b Y

To Card Analyzer Circuit

Card Holder Slot


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CARD ANALYZER with BUFFER & DRIVER

This module analyzes the Power Card for its designation, i.e., whether it bears 100

units or 150 units or 200 units designation. Then this power card section is isolated from

the Logic stage by introducing a Buffer stage. And the output of this Buffer stage is fed to

driver circuit to drive the low impedance relay.

The heart of this card analyzer is the popular Operational Amplifier IC. Here

every Power Card offers some unique amount of resistance to the card analyzer block.

Depends upon the resistance the card offers, card reader comes to know what designation

the card holder got.

Before the detailed description of this Card Analyzer circuit, let us familiarized

with the basic terms & components used in this circuit.

Operational Amplifier: Designed originally for analogue computer and control

applications, the operational amplifier has found its way into almost every field of

electronics. Todays Integrated Circuit Op-Amps offer many advantages over their

discrete component predecessors. Circuit design is greatly simplified with the addedbonus that the characteristics of the latest generation of Op-Amps, far exceed those of

their predecessors.

An Op-amp is a direct coupled high gain amplifier, usually consisting of one or

more differential amplifiers and usually followed by a level translator and an output stage.

Output stage is generally a push-pull or push-pull complementary symmetry pair. An Op-

amp is available as single IC package. The maximum common mode voltage that can be

applied to an Op-amp without disturbing its proper function is of the order +13 V or 13

V.

THE DESIRABLE CHARACTERISTICS OF OP-AMPS ARE:

a) The open-loop voltage gain should be very high (ideally infinity).

b) The input resistance should be very high (ideally infinity).

c) The output resistance should be very low (ideally zero).

d) Full power bandwidth should be as wide as possible.



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e) Slew rate should be as large as possible.

f) Input offset should be as small as possible.

g) CMRR should be as large as possible.

ELECTRICAL PARAMETERS OF OP-AMP:

1. I/p off-set voltage (Vio) :

It is the voltage that must be applied between the two input terminals of an op-amp to

verify the output to be null.

2. I/p off-set current (Iio):

The algebraic difference between the current into the inverting and non inverting

terminal is reffered as input Off-set current.

3. I/p Bias current:

It is the average of the current that flow into inverting and non-inverting input terminalsof

the Op-amp.In the equation form:

IB= (IB1+IB2) / 2

4. Differential I/p resistance:

It is the equivalent resistance that can be measured at either terminal connected to group.

5. I/p capacitance:

It is the equivalent capacitance that can be measured at either the inverting or non-

inverting input terminal with the either terminal connected to ground .

6. CMRR (Common Mode Rejection Ratio ):

The CMRR is defined as the ratio of differential voltage gain Ad to the common

voltage gain Acm , i.e.,

CMRR = Ad / Acm .

The higher the value of CMRR ,better is the matching between two input terminals and

smaller is the output common mode voltage .

7. SVRR (Supply Voltage Rejection Ratio ):

The change in OP-amps input OFF SET voltage Vio caused by variation in supply

voltages is called the SVRR . These are expressed in v / v or in dBs



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SVRR = Vio / V .

Where ,

Vio = input offset voltage & V= supply voltage

8. Input Voltage Range:

It is the maximum common mode voltage that can be applied to an Op-amp without

disturbing its proper function. It is of the order +13 V or 13 V

9. Large Signal Voltage Gain:

Since the OP-amp amplifies difference voltage between two input terminals, the voltage

gain of the amplifier is defined as,

A= o/p Voltage / Diff. i/p Voltage = Vo / Vid.10. Gain Bandwidth Product:

It is the bandwidth of the Op-amps when the gain is unity.

11. Slew Rate :

It is defined as max. rate of change of output voltage / unit of time and is expressed in

volts / sec.

| V / sec

SR = dvo / dt |

| max.

POWER DRIVING CIRCUITS:In many applications, a relay will require some form of

interface to the circuit to which it is connected. Often such an interface need consist of

nothing more than a single transistor. Almost any n-p-n transistor with a current gain of

50 or more can be used in the circuit. However, it is important to ensure that it is operated

within its maximum collector current (IC(max)) rating. The coil resistance of relay andpreferred transistors are as follows: 50 ohm to 200 ohm - T1P31 (or equivalent), 200

Ohm to 400 Ohm - BC142 (or equivalent), 400 Ohm to 1.2 K Ohm - BC108 (or

equivalent). The circuit requires an input current of about 0.5 mA when operated from a

5V source. In some applications it may be desirable to increase the sensitivity of the

circuit, in which case a Darlington driver stage can be used. A Darlington driver based on

two (discrete) n-p-n devices requires a current of only a mere 40 A at 5V in order to

operate the relay. This circuit can be used with relays having coil resistance as low as

about 200 ohm and will also operate reliable with an input current of as little as 40 A.



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RELAY: The traditional method of switching current through a load, which requires

isolation from the controlling circuit, involves the use of an electromechanical relay. Such

devices offer a simple, low-cost solution to the problem of maintaining adequate isolation

between the controlling circuit and the potentially lethal voltages associated with an a.c.

main supply. The coils, which provide the necessary magnetic flux to operate a relay, are

available for operation on a variety of voltages between 5V and 115V d.c. and 12V to

250V a.c. at currents of between 5 mA and 100 mA.

OPTO-COUPLER IC MCT 2E: Buffers does not affect the logical state of a digital signal

(i.e. logic 1 input results into logic 1 output where as logic 0 input results into logic 0

output). Buffers are normally used to provide extra current drive at the output are used in

interfacing applications. This 6-pin DIL packaged IC MCT 2E acts as Buffer as-well-as

Isolator. The input signals may be of 2.5 to 5V digital TTL compatible or DC analogue

the IC gives 5V constant signal output. The IC acts as isolator and provides isolation to

the main circuit from varying input signals. The working voltage of IC is fed at pin-5 and

input to pin-1. The pin-2 is ground and pin-4 is output. Note that pin-3 and pin-4 are not

available pins, which must be left free. And the isolated circuit must have its own ground

connection.

The Opto-coupler IC has a photo diode which illuminates whenever input signal

appears at pin-1. A photo transistor, whose Base-lead open, receives the signal from the

blinking photo diode and passes it intact to the output pin-4. As this switching action is

very fast, in term of micro seconds, the signal transfer is successfully done without any

delay and signal loss. As there is any physical contact between photo diode and photo

transistor is observed, it is used for isolating two sections of the circuit. Especially the

delicate digital circuits or signal sensitive stages whose output is supposed to drive a

fluctuating stage or mains operated load.

Since the digital outputs of the some circuits cannot sink much current, they are

not capable of driving relays directly. So, high-voltage high-current Darlington arrays are

added to this opto-coupler IC for interfacing low-level logic circuitry and peripheral

power loads. Typical loads include relays, solenoids, stepping motors, magnetic print

hammers, multiplexed LED and incandescent displays, and heaters.



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COMPARATOR STAGE:

When consumer inserts Power Card inside the Card Holder, it measures

impedance of the Rx fitted inside the Power Card smartly by accessing X Y points and

decides what the designation it holds. The circuit diagram shows that three operational

amplifiers compare the drop across the test leads to a fixed voltage and indicate which of

the two is highest by switching their output to the positive supply level or ground [see the

accompanying table].

STATUS 100 Units 150 Units 200 UnitsComparator A1

Comparator A2

Comparator A3

Indicator LED

Relay Activated

0

0

0

D2

RLA

1

0

0

D3

RLB

1

1

0

D4

RLC

The three comparators A1, A2 & A3 of IC1 are used to compare the Power Card

input and decide, whether it got 100 Units denomination or 150 Units or 200 Units. This

circuit accepts the Unknown Resistance Rx of Power Card across the resistors R1 & R4.

Out of these two inputs one is fed to Inverting pin of comparator A1 and other input is fed

to Non-Inverting pin of comparator A2 and Inverting pin of comparator A1. Depends

upon the Unknown resistance Rx value, any one comparators output goes High.


I N P U

G N

N / C

1

2

3

6

5

4

N / C

V c

O U T P

M C 2 E O P C O U P L


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CIRCUIT DIAGRAM OF CARD READER


D4LED

D3

R19

R16

R13

D5

T5T6

T1T2

D2LED

A1

A2A2

115

12

5

21

14

13

3

R7

R10

R8

D1

D6

4

76

P1 P2

R12R11R6R4

R5 R2R1R3

A3

A2

A12

T3T4

R17

100

R18

R20

R21

Rx

R14100

RL A100 units

R15

A1 TO A3 = IC1

R9

OPTO-COUPLER IIC2

COMPARATORSTAGE OPTOCOUPLER DRIVER STAGE

RL B150units

RL C200 units

DRIVER IOUTPUT

DRIVERIIOUTPUT

DRIVER IIIOUTPUT

OPTO-COUPLERII

IC3

OPTO-COUPLERIII

IC4


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Parts List:


SEMICONDUCTORSIC1 [A1-A2-A3] LM324 Op-Amp 1

IC2 MCT 2E Opto-coupler 3

T1 TO T6 BC547 NPN Transistor 6

RESISTORSR1-R4, R13,R16,R19 1 K Ohm, Watt, Carbon Type 7

R5, R6 10 K Ohm, Watt, Carbon Type 2

R7 to R10 470 Ohm, Watt, Carbon Type 4

R11 1 Mega Ohm, Watt, Carbon Type 1

R12 2.7 Mega Ohm, Watt, Carbon Type 1

R14,R17,R20 100 Ohm, Watt, Carbon Type 3

R15,R18,R21 33 K Ohm, Watt, Carbon Type 3

P1 & P2 500 K Ohm, Preset 2

DIODES

D1& D6 1N4148 SIGNAL Diodes 2

D2 to D5 Red Indicator LEDs 4

MISCELLANEOUSRL A, RL B, RL C 12 V, 700 Ohm DPDT Reed Relays 3


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If the inserted Power Card has 100 units designation, then comparator A1s output

at pin-7 goes High. If inserted Card is of 150 Units then comparator A2s output at pin-1

goes High. Finally comparator A3s output at pin-14 goes High when 200 Units Power

Card is used.

OPTOCOUPLER:

The Comparator output is fed to Opto-coupler stage, which is used when the main

circuit is supposed to isolate itself from the relay driven stages. The output of comparator

is applied at input pin-1 and at pin-4 output is observed. Since the biasing voltage need

very high current path, two signal diodes D1 & D6 are used along the other biasing

resistors, viz., R7,R8,R9, & R10. There is one indicator LED D5, which is optional and

indicates the one more condition other than the three levels. The output at pin-4 of each

opto-coupler IC is taken out to driver stage, by supplying biasing voltage through R15,

R18, & R21.

The 100 Units High signal makes Opto-coupler I IC-IC2 to conduct and in result

transfers the signal to Driver I stage. The 150 Units High signal makes Opto-coupler II

IC-IC3 to conduct and thus drives Driver II stage. Finally 200 Units High signal makes

Opto-coupler III IC-IC4 to conduct and thus drives Driver III stage.

DRIVER STAGE:

Now the Comparator circuit is totally isolated from this relay driver circuit. But

this signal level is not strong enough to drive the low impedance relay. So, Darlington

driver is created using two NPN transistors [T1 & T2, T3 & T4, T5 & T6 transistor pairs]

and boost the signal level. The output signal from the Darlington driver stage is strong



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enough to actuate relays [RL A, RL B & RL C]. These relays N/O [Normally Open]

pins are used to give first reference signal. The red LEDs [D2, D3 & D4] indicate whether

the relay is energized or not. The resistors R13, R14 and R15 are current limiting

resistors.

The 100 Units High signal coming out of Opto-coupler I is used to drive Driver I

comprised by T1 & T2 transistor pairs. This switching circuit actuates relay RL A and

simultaneously makes Driver I output as High signal for further processing.

The 150 Units High signal coming out of Opto-coupler II is used to drive Driver II

comprised by T3 & T4 transistor pairs. This switching circuit actuates relay RL B and

simultaneously makes Driver II output as High signal for further processing.

The 200 Units High signal coming out of Opto-coupler III is used to drive Driver

III comprised by T5 & T6 transistor pairs. This switching circuit actuates relay RL C

and simultaneously makes Driver III output as High signal for further processing.

CALIBIRATION:

The ranges of indicator LEDs D1 and D2 are adjusted with presets P1 and P2.

There are two presets P1 & P2 allowing user to set the reference value. The first preset P1

is biased with R5 & R6 and its variable end goes to Non-inverting pin of Comparator A1.

The second preset P2 is biased similarly using R2 & R11 and its variable end is connected

to Inverting end of Comparator A2. Clip the test leads to a 5 resistor, and adjust P1 so

that D1 just goes out and D2 just lights. Similarly, use a 100k resistor for adjusting P2

until D3 and D4 just go out and light respectively.

NOTE: It is recommended to decouple R11 with a 22 F electrolytic capacitor when the

supply voltage is relatively low.



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4. ENERGY METER SECTION

SCHMITT TRIGGER

This Schmitt Trigger produces the pulses, which are directly proportional to the

units consumed by the consumers energy meter. That means output of Energy Meter is

fed to this stage as trigger pulse. This circuit converts the data coming out of Energy

Meter into digital pulse form for easy processing. This stage built around popular timer

IC is essential as the rest of the circuit deals with digital pulses only. The output of this

stage is given to Consumed Unit Monitor for further processing.

The basic function of the Schmitt trigger circuit is to convert / generate a chain of

square wave from any regular or irregular signal input. The triggering pulse generator

produces a series of square waves using signals produced by Energy Meter, and acts like

a clock signal generator to the further section. Here the square waves generated by the

Trigger pulse generator are fed to the Consumed Unit Monitor.

Introduction:

Digital circuits often require a source of accurately defined pulses. The

requirement is generally for a single pulse of given duration (i.e. a one shot) or for a

continuous train of pulses of given frequency and duty cycle. Rather than attempt to

produce an arrangement of standard logic gates to meet these requirements, it is usually

simpler and more cost-effective to make use of one of the range of versatile integrated

circuits known collectively as timers. The greater level of accuracy and stability with

long Monostable periods is possible only with timer IC. The 555 timer is a neat mixture

of analogue and circuitry but its applications are virtually limitless in the world of digital

pulse generation. These devices can usually be configured for wither Monostable orAstable operation and require only a few external components in order to determine their

operational parameters.



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INTERNAL ARRANGEMENT OF 555 TIMER IC

The timer comprises two operational amplifiers (used as comparators) together

with an RS Bistable element. In addition, an inverting output buffer is incorporated sothat a considerable current can be sourced or sunk to/from a load. A single transistor

switch, TR1, is also provided as a means of rapidly discharging the external timing

capacitor.

The standard 555 timer is housed in an 8-pin DIL package and operates from

supply rail voltages of between 4.5V and 15V. This encompasses the normal range for

TTL devices and thus the device is ideally suited for use in conjunction with TTL

circuitry.

PIN OUT DIAGRAM OF TIMER IC 555


RESET

OUTPUT

TRIGGER

VCC

555

8

7

6

5

2

3

1

4

DISCHARGE

THRESHOLD

GROUND

CONTROL


24/74


CIRCUIT DIAGRAM OF SCHMITT TRIGGER USING 555 TIMERIC

Parts List:


SEMICONDUCTORS

IC1 555 Timer IC 1R1 47 K Ohm Watt 1

R2 10K Ohm Watt 1

P1 100K Ohm Preset 1

CAPACITORSC1 0.001 f Ceramic Disc type 1

C2 0.01F Ceramic Disc type 1

R2

P1

C1

4 87

3

1

6

25

+Vcc

To Counter

C2

R1 47K

555

GND

Trigger pulse fromEnergy Meter


25/74



An electronic circuit that generates square waves using positive feedback is

known as a Multivibrator. This switching circuit is basically a two stage amplifier and

operates in two states (ON and OFF) controlled by external circuit conditions. There are

three types of Multivibrator: Astable or Free Running Multivibrator, Monostable or One

Shot Multivibrator and Bistable or Flip-flop Multivibrator.

An oscillator circuit which generates square wave of its own (i.e. without external

triggering) is known as Astable or Free Running Multivibrator. The outputted square

pulse is not stable in nature. It switches back and forth from one state to the other. And

the switching time is determined by the external components (i.e. RC constant). These

pulse trains are used to ON/OFF or trigger the connected external circuits. The normal

555 IC Astable Multivibrator can be used readily to drive a relay (operating current must

be less than 150mA).

The circuit diagram shows how the timer IC 555 can be used as an Astable pulse

generator. In this mode the circuit provides very constant output frequency. The

triggering pulse from Energy Meter output is fed to trigger input pin-2 which is grounded

through capacitor C1. When the circuit is first put ON, the capacitor C1 is uncharged and

the trigger input is low and that switching transistor TR1 (at pin-7) is in the non-

conducting state. Thus the output (at pin-3) is high. The capacitor C1 will begin to charge

toward +Vcc with current supplied by means of the series resistors R1, P1 and R2.

When the voltage at the threshold input (at pin-6) exceeds of Vcc, the output

of the upper comparator will change state and the Bistable will be reset, making the

output go HIGH and turning TR1 ON in the process. Due to the inverting action of the

buffer, the final output (at pin-3) will then go LOW.

The capacitor C1 will now discharge, with current flowing through R2 & P1 into

the collector of switching transistor TR1 (at pin-7). At a certain point, the voltage

appearing at the trigger input (pin-2) will have fallen back to one third of the supply

voltage at which point the lower comparator will change state and return the Bistable to

its original set condition. The Q output of the Bistable then goes low, TR1 switches

off, and the final output (pin-3) goes high. Thereafter the entire cycle is repeated

indefinitely.



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This signal going low-to-high and high-to-low makes one clock pulse and thus

increases the decade counter by one unit.

The essential characteristics of this waveform are:

Time for which output is high: Ton=0.693(R1+R2+P1) CTime for which output is low: Toff=0.693(R2+P1) C

Period of output: T=Ton+Toff=0.693(R1+P1+2R2) C

Pulse Repetitive Frequency of output: p.r.f. = 1.44 / (R1+P1+2R2) C

Pulse Period: T = 1/ p.r.f

Where T is in seconds, C is in farads, and R1 & R2 are in Ohms.

CONSUMED UNIT MONITOR & DRIVER



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This section counts the number of pulses coming out of Schmitt Trigger; if it

equals any one designation of the Power Card, then it switches the corresponding relay.

The Driver is used to enhance the Consumed Unit Monitor output signals to sufficient

level to drive the low impedance relay.

MICRO-CONTROLLER PIC:

The heart of this module is 14-pin DIL Micro-controller IC PIC, which monitors

the units consumed by Consumers Energy Meter. In this project there are only three

different value Power Cards are used viz., 100 units, 150 units, & 200 units. Hence this

section is programmed to monitor only three specific units with their 90% detection.

Depends upon the number of pulses, this Micro-controller IC makes any one output line

High. This High signal acts as one out-of-two reference signals to Logic stage. As the

received signals are not strong enough to drive the Logic stage, driver section is included.

The switching module contains relays which in turn activates respective Cards output

line High.

HEX BUFFER / CONVERTER [NON-INVERTER] IC 4050:

Buffers does not affect the logical state of a digital signal (i.e. logic 1 input results

into logic 1 output where as logic 0 input results into logic 0 output). Buffers are normally

used to provide extra current drive at the output, but can also be used to regularise the

logic present at an interface. And Inverters are used to complement the logical state (i.e.

logic 1 input results into logic 0 output and vice versa). Also Inverters are used to provide

extra current drive and, like buffers, are used in interfacing applications. This 16-pin DIL

packaged IC 4050 acts as Buffer as-well-as a Converter. The input signals may be of 2.5

to 5V digital TTL compatible or DC analogue the IC gives 5V constant signal output. The

IC acts as buffer and provides isolation to the main circuit from varying input signals. The

working voltage of IC is 4 to 16 Volts and propagation delay is 30 nanoseconds. It

consumes 0.01 mill Watt power with noise immunity of 3.7 V and toggle speed of 3

Megahertz.



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PIN DIAGRAM OF IC-4040


1

2

6

3

16

5

15

4

14

10

11

12

13

7

Vcc

Vss8 9

IC4050


29/74



This Consumed Unit Monitor Circuit is inherited with many sections: Consumed

Unit Monitor, Buffer Section, & Driver Section. Let us see all these sections in detail, in

sequential order.

Micro-Controller IC: This IC is pre-programmed to count the Consumed Units, The

working voltage +Vcc is connected to pin-1 and pin-14 is made ground. The number of

units consumed is fed as clock pulses from Schmitt Trigger section at pin-4 of Micro-

controller chip. Depends upon the number of units consumed, one out-of-six signal output

is made HIGH.

Buffer: The function of this Buffer section is to provide unit gain amplification to Micro-

controller outputted HIGH signal. And also isolates Energy Meter section from Driver

section. The Buffer IC2 has six buffers, which are carrying six outputs of Micro-

controller chip to next stage.

Working of Circuit:

For 100 Units Power Card: Whenever total units consumed reaches 90% of this

card, pin-6 goes High and is carried away as D1 to Logic Stage through Buffer IC [IC2s

input pin-3 & output pin-2]. After 100% unit consumption, pin-7 goes High and drives

the relay through Buffer IC [IC2s input pin-5 & output pin-4]. Resistors R1 & R2

provides path to the output signal.


card, pin-8 goes High and is carried away as D2 to Logic Stage through Buffer IC [IC2sinput pin-7 & output pin-6]. After 100% unit consumption, pin-9 goes High and drives

the relay through Buffer IC [IC2s input pin-9 & output pin-10]. Resistors R3 & R4

provides path to the output signal.


card, pin-10 goes High and is carried away as D3 to Logic Stage through Buffer IC [IC2s

input pin-10 & output pin-12]. After 100% unit consumption, pin-11 goes High and

Dept. of E.E.E. |R.Y.M.E.C Bellary. 29


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drives the relay through Buffer IC [IC2s input pin-14 & output pin-15]. Resistors R5 &

R6 provides path to the output signal.

This explanation is summarized in table form, as shown below:

Output is

High

at Pin

Number

Output

Notation

Power Cards

DenominationRemarks

6 D1 100 Units Indicates completion of 90%

7100u

O/P

100 Units Indicates closing of Power

Card


9150u

O/P


Card


11200u

O/P


Card

DRIVER STAGE:

Now the Energy Meter section is totally isolated from this load driver circuit. But

this signal level is not strong enough to drive the low impedance relay. So, Darlington

driver is created using two NPN transistors [T1 & T2 transistor pairs] and boost the signal

level. The output signal from the Darlington driver stage is strong enough to actuate

relays [RL I 100 Units, RL II 150 Units & RL III 200 Units]. The red LED D1 with series

resistor R7 indicate whether the relay is energized or not. The resistor R9 is current

limiting resistor and R9 resistor provides path to HIGH signal towards this driver stage.

The outputs are taken across each driver stage, viz., 100 Units High signal at RL I

as 100u O/P, 150 Units High signal at RL II as 150u O/P, and 200 Units High signal at

RL III as 200u O/P.

5. MICRO-CONTROLLER SECTION



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INTRODUCTION OF Micro-controller

The general definition of a microcontroller is a single chip computer, which

refers to the fact that they contain all of the functional sections (CPU, RAM, ROM, I/O,

ports and timers) of a traditionally defined computer on a single integrated circuit. Some

experts even describe them as special purpose computers with several qualifying

distinctions that separate them from other computers.

Microcontrollers are "embedded" inside some other device (often a consumer

product) so that they can control the features or actions of the product. Another name for

a microcontroller, therefore, is "embedded controller."

Microcontrollers are dedicated to one task and run one specific program. The

program is stored in ROM (read-only memory) and generally does not change.

Microcontrollers are often low-power devices. A desktop computer is almost

always plugged into a wall socket and might consume 50 watts of electricity. A battery-

operated microcontroller might consume 50 mill watts.

A microcontroller has a dedicated input device and often (but not always) has a

small LED or LCD display for output. A microcontroller also takes input from the device

it is controlling and controls the device by sending signals to different components in the

device.

A microcontroller is often small and low cost. The components are chosen to

minimize size and to be as inexpensive as possible.

A microcontroller is often, but not always, ruggedized in some way. The

microcontroller controlling a car's engine, for example, has to work in temperature

extremes that a normal computer generally cannot handle. A car's microcontroller in

Kashmir regions has to work fine in -30 degree F (-34 C) weather, while the same

microcontroller in Gujarat region might be operating at 120 degrees F (49 C). When you

add the heat naturally generated by the engine, the temperature can go as high as 150 or

180 degrees F (65-80 C) in the engine compartment. On the other hand, a microcontroller

embedded inside a VCR hasn't been ruggedized at all.



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Clearly, the distinction between a computer and a microcontroller is sometimes

blurred. Applying these guidelines will, in most cases, clarify the role of a particular

device.

The programmability of modern desktop PCs makes them extraordinarily

versatile. The functionality of the entire machine can be altered by merely changing its

programming. Microcontrollers share this attribute with their desktop relatives. The chips

are manufactured with powerful capabilities and the end user determines exactly how the

device will function. Often, this makes a dramatic difference in the cost and complexity

of a particular design. The true impact of this statement is best illustrated by example.

For every clock pulse, the circuit produces one of the three bit numbers in the

sequence 000, 100, 111, 010, 011. This design has been implemented with three flip-flops

and seven discrete gates as well as a significant amount of wiring.

The design of this system can be quite laborious. One must begin with a state

graph followed by a state table. Then, the flip-flop T input equations must be derived

from a set of Karnaugh maps. Next, the t input equations must be transformed into the

actual T input network. All of this circuitry must then be wired together; a task that's time

consuming and sometimes error prone. On the other hand, this can be accomplished with

a simpler, less costly microcontroller design. Notice the dramatic difference in the amount

of hardware and wiring. This simple circuit, along with about a dozen lines of code, will

perform the same task as the first circuit. There are other benefits as well. The

microcontroller implementation does not have to contend with the undetermined states

that sometimes occur with discrete designs. Also consider for a moment what would be

required to change the sequence of numbers in the first circuit. What if the output needsto be changed to eight bits instead of three? These are trivial modifications for the

microcontroller while the discrete circuit would require a complete redesign.

The example above is not an obscure case. The effects of this device are being felt

in almost every facet of digital design. A sure method of determining the popularity of an

electronic device is to note when they attain widespread use by hobbyists. It therefore

becomes essential that the electronics engineer or hobbyist learn to program these

microcontrollers to maintain a level of competence and to gain the advantages

microcontrollers provide in his or her own circuit designs.



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Introducing the Intels Microcontroller 89C51

Features

Compatible with MCS-51 Products

8K 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

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

Description

The AT89C52 is a low-power, high-performance CMOS 8-bit microcomputer

with 8K bytes of Flash programmable and erasable read only memory (PEROM). The

device is manufactured using Atmels high-density nonvolatile memory technology and is

compatible with the industry-standard 80C51 and 80C52 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 Atmel AT89C52 is a powerful microcomputer which

provides a highly-flexible and cost-effective solution to many embedded control

applications.

The AT89C52 provides the following standard features: 8K bytes of Flash, 256

bytes of RAM, 32 I/O lines, 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 AT89C52 is designed with static logic for operation down to zero

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



34/74


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.



35/74


Pin Description

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 by test 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.

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.

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

verification. Port Pin Alternate Functions P1.0 T2 (external count input to Timer/Counter

2), clock-out P1.1 T2 EX (Timer/Counter 2 capture/reload trigger and direction control)

AT89C52

Port 2




are externally being pulled low will source current (IIL) because of the internal pull ups.



36/74


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 uses 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




are externally being pulled low will source current (IIL) because of the pull ups.

Port 3 also receives some control signals for Flash programming and verification.

Port Pin Alternate Functions

P3.0 RXD (serial input port)

P3.1 TXD (serial output port)

P3.2 INT0 (external interrupt 0)

P3.3 INT1 (external interrupt 1)

P3.4 T0 (timer 0 external input)

P3.5 T1 (timer 1 external input)

P3.6 WR (external data memory write strobe)

P3.7 RD (external data memory read strobe)

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 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



37/74


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

AT89C52 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 when 12-volt programming is selected.

XTAL1

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

Special Function Registers

A map of the on-chip memory area called the Special Function Register (SFR)

space. Note that not all of the addresses are occupied, and unoccupied addresses may not

be implemented on the chip. Read accesses to these addresses will in general return

random data, and write accesses will have an indeterminate effect.



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User software should not write 1s to these unlisted locations, since they may be

used in future products to invoke AT89C52 new features. In that case, the reset or

inactive values of the new bits will always be 0.

Timer 2 Registers Control and status bits are contained in registers T2CON and

T2MOD for Timer2. The register pair (RCAP2H, RCAP2L) is the Capture/Reload

registers for Timer 2 in 16-bit capture mode or 16-bit auto-reload mode.

Interrupt Register

The individual interrupt enable bits are in the IE register. Two priorities can be set

for each of the six interrupt sources in the IP register.

Symbol FunctionTF2 Timer 2 overflow flag set by a Timer 2 overflow and must be cleared by software.

TF2 will not be set when either RCLK = 1 or TCLK = 1.

EXF2 Timer 2 external flag set when either a capture or reload is caused by a negative

transition on T2EX and EXEN2 = 1. When Timer 2 interrupt is enabled,

EXF2 = 1 will cause the CPU to vector to the Timer 2 interrupt routine.

EXF2 must be cleared by software. EXF2 does not cause an interrupt in

up/down counter mode (DCEN = 1).

RCLK Receive clock enable. When set, causes the serial port to use Timer 2 overflow

pulses for its receive clock in serial port Modes 1 and 3. RCLK = 0 causes

Timer 1 overflow to be used for the receive clock.

TCLK Transmit clock enable. When set, causes the serial port to use Timer 2 overflow

pulses for its transmit clock in serial port Modes 1 and 3. TCLK = 0 causes

Timer 1 overflows to be used for the transmit clock.

EXEN2 Timer 2 external enable. When set, allows a capture or reload to occur as a

result of a negative transition on T2EX if Timer 2 is not being used to

clock the serial port. EXEN2 = 0 causes Timer 2 to ignore events at T2EX.

TR2 Start/Stop control for Timer 2. TR2 = 1 starts the timer.

C/T2 Timer or counter select for Timer 2. C/T2 = 0 for timer function. C/T2 = 1 for

external event counter (falling edge triggered).



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CP/RL2

Capture/Reload select. CP/RL2 = 1 causes captures to occur on negative

transitions at T2EX if EXEN2 = 1. CP/RL2 = 0 causes automatic reloads to occur when

Timer 2 overflows or negative transitions occur at T2EX when EXEN2 = 1. When either

RCLK or TCLK = 1, this bit is ignored and the timer is forced to auto-reload on Timer 2

overflow.

Data Memory

The AT89C52 implements 256 bytes of on-chip RAM. The upper 128 bytes

occupy a parallel address space to the Special Function Registers. That means the upper

128 bytes have the same addresses as the SFR space but are physically separate from SFR

space.

When an instruction accesses an internal location above address 7FH, the address

mode used in the instruction specifies whether the CPU accesses the upper 128 bytes of

RAM or the SFR space. Instructions that use direct addressing access SFR space. For

example, the following direct addressing instruction accesses the SFR at location 0A0H

(which is P2).

MOV 0A0H, #data

Instructions that use indirect addressing access the upper 128 bytes of RAM. For

example, the following indirect addressing instruction, where R0 contains 0A0H,

accesses the data byte at address 0A0H, rather than P2 (whose address is 0A0H).

MOV @R0, #data

Note that stack operations are examples of indirect addressing, so the upper 128

bytes of data RAM are available as stack space.

Timer 0 and 1

Timer 0 and Timer 1 in the AT89C52 operate the same way as Timer 0 and Timer

1 in the AT89C51.

Timer 2

Timer 2 is a 16-bit Timer/Counter that can operate as either a timer or an event

counter. The type of operation is selected by bit C/T2 in the SFR T2CON. Timer 2 has

three operating modes: capture, auto-reload (up or down counting), and baud rate

generator. The modes are selected by bits in T2CON. Timer 2 consists of two 8-bit



40/74


registers, TH2 and TL2. In the Timer function, the TL2 register is incremented every

machine cycle. Since a machine cycle consists of 12 oscillator periods, the count rate is

1/12 of the oscillator frequency.

In the Counter function, the register is incremented in response to a 1-to-0

transition at its corresponding external input pin, T2. In this function, the external input is

sampled during S5P2 of every machine cycle. When the samples show a high in one cycle

and a low in the next cycle, the count is incremented. The new count value appears in the

register during S3P1 of the cycle following the one in which the transition was detected.

Since two machine cycles (24 oscillator periods) are required to recognize a 1-to-0

transition, the maximum count rate is 1/24 of the oscillator frequency. To ensure that a

given level is sampled at least once before it changes, the level should be held for at least

one full machine cycle.

Capture Mode

In the capture mode, two options are selected by bit EXEN2 in T2CON. If

EXEN2 = 0, Timer 2 is a 16-bit timer or counter which upon overflow sets bit TF2 in

T2CON.

This bit can then be used to generate an interrupt. If EXEN2 = 1, Timer 2

performs the same operation, but a 1-to-0 transition at external input T2EX also causes

the current value in TH2 and TL2 to be captured into RCAP2H and RCAP2L,

respectively. In addition, the transition at T2EX causes bit EXF2 in T2CON to be set. The

EXF2 bit, like TF2, can generate an interrupt.

Auto-reload (Up or Down Counter)

Timer 2 can be programmed to count up or down when configured in its 16-bit

auto-reload mode. This feature is invoked by the DCEN (Down Counter Enable) bit

located in the SFR T2MOD. Upon reset, the DCEN bit is set to 0 so that timer 2 will

default to count up. When DCEN is set, Timer 2 can count up or down, depending on the

value of the T2EX pin.

Baud Rate Generator



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Timer 2 is selected as the baud rate generator by setting TCLK and/or RCLK in

T2CON (Table 2). Note that the baud rates for transmit and receive can be different if

Timer 2 is used for the receiver or transmitter and Timer 1 is used for the other function.

Setting RCLK and/or TCLK puts Timer 2 into its baud rate generator mode.

The baud rate generator mode is similar to the auto-reload mode, in that a rollover

in TH2 causes the Timer 2 registers to be reloaded with the 16-bit value in registers

RCAP2H and RCAP2L, which are preset by software. The baud rates in Modes 1 and 3

are determined by Timer 2s overflow rate according to the following equation.

The Timer can be configured for either timer or counter operation. In most

applications, it is configured for timer operation (CP/T2 = 0). The timer operation is

different for Timer 2 when it is used as a baud rate generator. Normally, as a timer, it

increments every machine cycle (at 1/12 the oscillator frequency).

Note that when Timer 2 is running (TR2 = 1) as a timer in the baud rate generator mode,

TH2 or TL2 should not be read from or written to. Under these conditions, the Timer is

incremented every state time, and the results of a read or write may not be accurate. The

RCAP2 registers may be read but should not be written to, because a write might overlap

a reload and cause write and/or reload errors. The timer should be turned off (clear TR2)

before accessing the Timer 2 or RCAP2 registers.

Programmable Clock Out

A 50% duty cycle clock can be programmed to come out on P1.0. This pin,

besides being a regular I/O pin, has two alternate functions. It can be programmed to

input the external clock for Timer/Counter 2 or to output a 50% duty cycle clock ranging

from 61 Hz to 4 MHz at a 16 MHz operating frequency.

To configure the Timer/Counter 2 as a clock generator, bit C/T2 (T2CON.1) must

be cleared and bit T2OE (T2MOD.1) must be set. Bit TR2 (T2CON.2) starts and stops the

timer.

UART : The UART in the AT89C52 operates the same way as the UART in the

AT89C51.



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Interrupts

The AT89C52 has a total of six interrupt vectors: two external interrupts (INT0

and INT1), three timer interrupts (Timers 0, 1, and 2), and the serial port interrupt. Each

of these interrupt sources can be individually enabled or disabled by setting or clearing a

bit in Special Function Register IE. IE also contains a global disable bit, EA, which

disables all interrupts at once.

Note that Table shows that bit position IE.6 is unimplemented. In the A T89 C5 1,

bit position IE.5 is also unimplemented. User software should not write 1s to these bit

positions, since they may be used in future AT89 products.

Timer 2 interrupt is generated by the logical OR of bits TF2 and EXF2 in register

T2CON. Neither of these flags is cleared by hardware when the service routine is

vectored to. In fact, the service routine may have to determine whether it was TF2 or

EXF2 that generated the interrupt, and that bit will have to be cleared in software.

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, as shown in Figure 7.

Either 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.

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.

Note that when idle mode is terminated by a hardware reset, the device normally

resumes program execution from where it left off, up to two machine cycles before theinternal reset algorithm takes control. On-chip hardware inhibits access to internal RAM



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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 mode is terminated

By a reset, the instruction following the one that invokes idle mode should not write to a

port pin or to external memory.

Power-down Mode

In the power-down mode, the oscillator is stopped, and the instruction that invokes

power-down is the last instruction executed. The on-chip RAM and Special Function

Registers retain their values until the power-down mode is terminated. The only exit from

power-down is a hardware reset. Reset redefines the SFRs but does not change the on-

chip RAM. The reset should not be activated before VCC is restored to its normal

operating level and must be held active long enough to allow the oscillator to restart and

stabilize.

Programming the Flash

The AT89C52 is normally shipped with the on-chip Flash memory array in the

erased state (that is, contents = FFH) and ready to be programmed. The programming

interface accepts either a high-voltage (12-volt) or a low-voltage (VCC) program enable

signal. The Low-voltage programming mode provides a convenient way to program theAT89C52 inside the users system, while the high-voltage programming mode is

compatible with conventional third party Flash or EPROM programmers.

The AT89C52 is shipped with either the high-voltage or low-voltage

programming mode enabled. The AT89C52 code memory array is programmed byte-by-

byte in either programming mode. To program any nonblank byte in the on-chip Flash

Memory, the entire memory must be erased using the

Chip Erase Mode.

Programming Algorithm Before programming the AT89C52, the address, data

and control signals should be set up according to the Flash programming mode table and

Figure 9 and Figure 10. To program the AT89C52, 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.



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5. Pulse ALE/PROG once to program a byte in the Flash array or the lock bits. The byte-

write cycle 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 AT89C52 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 data on PO.7. Once the write cycle has been completed, true data is valid on all

outputs, and the next cycle 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

all 1s. The chip erase operation must be executed before the code memory can bereprogrammed.

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) = 52H indicates 89C52



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(032H) = FFH indicates 12V programming

(032H) = 05H indicates 5V programming

Flash Programming Modes

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.

DC Characteristics

Absolute Maximum Ratings*

Operating Temperature.................................. -55C to +125C

Storage Temperature ..................................... -65C to +150C

Voltage on Any Pin with Respect to Ground .....................................-1.0V to +7.0V

Maximum Operating Voltage............................................ 6.6V

DC Output Current...................................................... 15.0 mA



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Parts List of Power SupplyX1 12-0-12V Transformer 1

IC1 7805 Regulator IC 1

D1 & D2 1N4007 Rectifier Diode 2

D3 Red Indicator LED 1

R1 100 K Carbon Resistor 1

C1 1000MFD/25V

Electrolytic Capacitor 1

C2 & C3 0.1F Ceramic Capacitor 2

COMPLETE CIRCUIT DIAGRAM [MOTHER BOARD] OF 89C51

PORT 2PORT 3

8 x 2.2 Kport 0

port 1

89c51

ad7

ad6

ad5

ad4

ad3

ad2

ad1

ad0

a15

a14

a13

a12

a11

a10

a9

a8

230 AC

X1D1 & D2 IC1

+VCC

R1

D3

C1 C2 C3

+Vcc

P0.6

33

P0.5

34

P0.4

35

P0.3

36

P0.2

37

P0.1

38P0.0

39

P2.7

28

P2.6

27

P2.5

26

P2.4

25P2.3

24

P2.2

23

P2.1

22

P2.0

21 1

P1.7

8

P1.6

7

P1.5

6

P1.4

5

P1.3

4

P1.2

3

P1.1

2

P1.0

1 1

19 XTAL1

18 XTAL2

30 pF

12 MHz

30 pF

vss

20

40

vcc

rd

wr

t1

t0

int1

int0

txd

rxd

17

P3.7

16

P3.6

15

P3.5

14

P3.4

13

P3.3

12

P3.2

11

P3.1

10

P3.0

29

PSEN

30 ALE

31 EA

9 RST

+VCC

10 MFD/63V

20KRESET

SWITCH


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CIRCUIT DESCRIPTION

The mother board of 89C51 has following sections: Power Supply, 89C51 IC,

Oscillator, Reset Switch & I/O ports. Let us see these sections in detail.

POWER SUPPLY:

This section provides the clean and harmonic free power to IC to function

properly. The output of the full wave rectifier section, which is built using two rectifier

diodes, is given to filter capacitor. The electrolytic capacitor C1 filters the pulsating dc

into pure dc and given to Vin pin-1 of regulator IC 7805.This three terminal IC regulates

the rectified pulsating dc to constant +5 volts. C2 & C3 provides ground path to harmonic

signals present in the inputted voltage. The Vout pin-3 gives constant, regulated and

spikes free +5 volts to the mother board.

The allocation of the pins of the 89C51 follows a U-shape distribution. The top

left hand corner is Pin 1 and down to bottom left hand corner is Pin 20. And the bottom

right hand corner is Pin 21 and up to the top right hand corner is Pin 40. The Supply

Voltage pin Vcc is 40 and ground pin Vss is 20.

OSCILLATOR:

If the CPU is the brain of the system then the oscillator, or clock, is the heartbeat.

It provides the critical timing functions for the rest of the chip. The greatest timing

accuracy is achieved with a crystal or ceramic resonator. For crystals of 2.0 to 12.0 MHz,

the recommended capacitor values should be in the range of 15 to 33pf2.

Across the oscillator input pins 18 & 19 a crystal x1 of 4.7 MHz to 20 MHz value

can be connected. The two ceramic disc type capacitors of value 30pF are connected

across crystal and ground, stabilizes the oscillation frequency generated by crystal.

I/O PORTS:

There are a total of 32 i/o pins available on this chip. The amazing part about

these ports is that they can be programmed to be either input or output ports, even "on the

fly" during operation! Each pin can source 20 mA (max) so it can directly drive an LED.

They can also sink a maximum of 25 Ma current.



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Some pins for these I/O ports are multiplexed with an alternate function for the

peripheral features on the device. In general, when a peripheral is enabled, that pin may

not be used as a general purpose I/O pin. The alternate function of each pin is not

discussed here, as port accessing circuit takes care of that.

This 89C51 IC has four I/O ports and is discussed in detail:

P0.0 TO P0.7

PORT0 is an 8-bit [pins 32 to 39] open drain bi-directional I/O port. As an output

port, each pin can sink eight TTL inputs and configured to be multiplexed low order

address/data bus then has internal pull ups. External pull ups are required during program

verification.

P1.0 TO P1.7

PORT1 is an 8-bit wide [pins 1 to 8], bi-directional port with internal pull ups.

P1.0 and P1.1 can be configured to be the timer/counter 2 external count input and the

timer/counter 2 trigger input respectively.

P2.0 TO P2.7


The PORT2 output buffers can sink/source four TTL inputs. It receives the high-order

address bits and some control signals during Flash programming and verification.

P3.0 TO P3.7


The Port3 output buffers can sink/source four TTL inputs. It also receives some control

signals for Flash programming and verification.

PSEN

Program Store Enable [Pin 29] is the read strobe to external program memory.

ALE

Address Latch Enable [Pin 30] is an output pulse for latching the low byte of the

address during accesses to external memory.

EA



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External Access Enable [Pin 31] must be strapped to GND in order to enable the

device to fetch code from external program memory locations starting at 0000H upto

FFFFH.

RST

Reset input [Pin 9] must be made high for two machine cycles to resets the

devices oscillator. The potential difference is created using 10MFD/63V electrolytic

capacitor and 20KOhm resistor with a reset switch.

LOGIC STAGE WITH DRIVER

This is the decision making stage and plays vital role in taking the right decision

after comparing the two reference signals. This decision making is done with the help of

Logic gates, which are known as building blocks of Digital Electronics. This stage not

only takes the decision, also switches ON the Beeper or Tone Generator to alert the

consumer when the total power consumption cross 90% of the designation of Power Card,

he has inserted.

Before going in details of this stage, let us see the basics of the Digital

Electronics.

LOGIC GATES

The British Standard (BS) and American Standard (MIL / ANSI) symbols for

some basic logic gates are shown in fig 1. It is fair to say that, in the UK, the MIL / ANSI

standard has overwhelming support and a very few manufacturers adhere to the

recommended BS symbols. We shall now briefly consider the action of each of the basic

logic gates depicted in fig 1.

BUFFERS: Buffers do not affect the logical state of a digital signal (i.e. a logic 1 input

results in a logic 1 output whereas logic 0 input results in a logic 0 output). Buffers are

normally used to provide extra current drive at the output but can also be used to

regularize the logic present at an interface.



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INVERTERS: Inverters are used to complement the logical state (i.e. logic 1 input results

in a logic 0 output and vice versa). Inverters also provide

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