final project report-parggah and gilbert (4)

7/31/2019 Final Project Report-Parggah and Gilbert (4)

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Retrofitting the electromechanical meter to make it a prepayment meter By Eric Johnson Parggah and Gilbert MensahComputer Engineering KNUST

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Contents

CHAPTER ONE-PROJECT OVERVIEW.................................................................... 4

Table1-1 Ghantt Chart for September 2007December 2007.......................................... 6

Table 1-2 Ghantt Chart for February 2008May 2008.................................................... 6

CHAPTER TWO- LITERATURE REVIEW................................................................ 8

2.1.1 Units of measurement .............................................................................................. 8

2.1.2 Types of meters ........................................................................................................ 8

2.1.3Electromechanical meters ....................................................................................... 9

2.1.4 Electronic meter ..................................................................................................... 11

2.1.4.1Solid state meter................................................................................................... 11

2.1.4.2 The prepayment meter......................................................................................... 11

2.1.4.2.1Keypad operated prepayment meters................................................................ 12

2.1.4.2.2Smart card operated prepayment meters.......................................................... 12

2.3.1 Types of relays......................................................................................................... 15

2.4.1 The I2C Protocol .................................................................................................... 18

CHAPTER 3 OVERVIEW OF MICROCONTROLLERS ..................................... 27

3.1General Architecture of microcontrollers243.1.1Memory unit 253.1.2 Types of memory.253.1.3 CPU..26

3.1.4Busses...263.1.5I/O.273.1.6ADC..273.2 PROGRAMMING.273.3 Types of Microcontrollers.283.3.1PIC Microcontrollers...283.3.2Programming of the PIC microcontrollers..31CHAPTER FOUR-DESIGN .......................................................................................... 36

4.1 Design considerations ............................................................................................... 36

4.2 Design Options .......................................................................................................... 42

4.2.2 How to deal with Please call an ECG personnel message .............................. 43

4.2.4 Warning .................................................................................................................. 44

4.3 System block diagram............................................................................................... 47

4.4 Principle of operation ............................................................................................... 47

4.5Improvement over existing system .......................................................................... 48

4.5.1 Mode of warning .................................................................................................... 48


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4.5.2 The concept of negative credit .............................................................................. 49

4.5.3Security features...................................................................................................... 49

4.6 System Design............................................................................................................ 50

4.6.2 QRB sensor module ............................................................................................... 51

4.6.2.1 QRB sensor holder .............................................................................................. 52

4.6.3 Microcontroller module......................................................................................... 53

4.6.3.1 Packaging............................................................................................................. 54

4.7 Design of the card terminal unit .............................................................................. 55

4.7.2 Packaging................................................................................................................ 57

4.8 Design of a DSP based prepayment meter.............................................................. 58

4.8.1 Circuit diagram of DSP based prepayment meter design.................................. 58

4.8.2 Comparing a DSP based system to credit based prepayment system............... 59

4.9 Printed circuit board design of microcontroller module....................................... 604.10 Programming........................................................................................................... 61

4.10.1 Flow chart for program....................................................................................... 61

4.10.2 Operation of the program ..................................................................................... 62

4.10.3 The various functions in the program................................................................ 63

CHAPTER FIVE-IMPLEMENTATION ..................................................................... 65

5.1 Design options implemented .................................................................................... 65

5.2 Calculations made ..................................................................................................... 65

5.3 Construction .............................................................................................................. 665.3.1 The power supply module ..................................................................................... 66

5.3.2 The QRB sensor module........................................................................................ 68

5.3.3 The microcontroller module ................................................................................. 69

5.3.4 The card terminal unit........................................................................................... 69

5.4 Tests performed ........................................................................................................ 70

5.4.1 The bridging problem........................................................................................ 70

5.4.2 Placement of black mark and QRB sensor.......................................................... 71

5.4.3 Test for functionality of the various modules ...................................................... 71

5.4.4 Test for the amount of power consumed by the embedded unit........................ 72

5.5 Limitation and Errors of the system ....................................................................... 73

5.6 Component list .......................................................................................................... 74

5.6.1Cost of the embedded unit..................................................................................... 75

5.6.2 Cost of the card terminal unit............................................................................... 75


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5.7 The process of retrofitting the credit energy meter with the embedded unit...... 76

CHAPTER SIX ............................................................................................................... 77

6.1 RCOMMENDATION............................................................................................... 77

6.2 Conclusions................................................................................................................ 77


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CHAPTER ONE-PROJECT OVERVIEW

1.1 Introduction

Every utility company provides service, from which revenue is generated. The Electricity

Company of Ghana (ECG) uses energy meters as the only direct revenue interface

between the company and its customers.

An energy meter is a device that measures the amount of electrical energy supplied to a

residence or business. There are several types of energy meters, one of which is the

electromechanical meter (credit meter), which is largely used by ECG for the purpose of

revenue generation. This is done by recording the value measured by the meter for the

previous month or quarter to prepare invoices for the customers.

However, the mode of revenue generation of the electromechanical meter is credit based,

where the customer uses the electricity before paying. This hinders the effective

generation of revenue.

Owing to this fact, the company introduced the prepayment metering system to provide

an almost immediate revenue generation. The company has partly achieved this by

replacing the credit meters with prepayment meters. However, the cost of changing to the

prepayment system is very high due to the following reasons


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Firstly the prepayment meters must be imported at a high cost because they are not

manufactured locally.

Secondly, upon installation of the prepayment meter, the credit meter, although in good

working condition, becomes redundant and the company incurs extra cost disposing off

them.

A very cost effective solution would be to upgrade the credit meter to the status of the

prepayment meter, which this project seeks to achieve.

1.2 Problem statement

To convert the electromechanical credit energy meter to a prepayment energy meter.

1.3 ObjectiveThis project seeks to upgrade the credit meter on site to a prepayment meter by

retrofitting it with embedded unit. This prepayment energy meter will be interactive to

use, have security features and allow the customer some amount of power on credit when

his credit finishes.


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1.4 Project plan

Table1-1 Ghantt Chart for September 2007December 2007

Table 1-2 Ghantt Chart for February 2008May 2008

Month September October November December

Week 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Activity

A

B

C

D

Month February March April May

Week 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

Activity

E

F

G

H


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A Formulation of objectives

B Research on energy meters

C Learning of microcontrollers, PIC and C programming

D Design, programming and simulation

E Building

F Testing

G Packaging and testing

H Report writing


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CHAPTER TWO- LITERATURE REVIEW

2.1 Energy meters

An energy meter is a device that measures the amount of electricity supplied to a

residence or a business.

2.1.1 Units of measurement

The most common unit of measurement on the electric meter is the kilowatt-hour, which

is the amount of electrical energy used by a load of one kilowatt over a period of one

hour.

Other units of measurement include kilovars-hour, which measures reactive power and

finally, the ampere-hour which also measures the amount of charge in coulombs used. [1]

2.1.2 Types of meters

Broadly, there are two categories of meters. These are the electromechanical meter and

the electronic meter. [1]


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2.1.3Electromechanical meters

This is the most common type of electricity meter. This meter operates by counting the

revolutions made by an aluminum disc that is made to rotate at a speed proportional to

the power consumption of the customer.

Picture of an electromechanical meter

The aluminium disc is acted upon by two coils. One coil is connected in such a way that

it produces magnetic flux in proportion to the voltage and the other coil is in proportion

to the current. The field of the voltage coil is delayed by 90 degrees using a lag coil. This

produces eddy current in the disc and the effect is such that a force is exerted on the disc

in proportion to the product of the instantaneous current and voltage.

A permanent magnet exerts an opposing force that is proportional to the speed of rotation

of the disc. This acts as a brake which prevents the disc from rotating when power stops

flowing, rather than allowing the disc to spin faster and faster. This causes the disc to

rotate at a speed proportional to the power being used.


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The meter described above is the single-phase energy meter. There are other

configurations like the three-phase.[1]

2.1.3.1 Reading

The aluminium disc is supported by a spindle that has a worm gear that drives the

register. The register is a series of dials that records the amount of energy used.

The amount of energy used represented by one revolution of the disc is denoted by the

symbol Kh, which is given in units of watt-hours per revolution. The value 7.2 is

commonly seen. Using the value ofKh, one can determine their power consumption at

any given time by timing the disc with a stopwatch. If the time in seconds taken by the

disc to complete one revolution is t, then the power in watts is P = 3600 Kh / t. For

example, ifKh = 7.2, as above, and one revolution took place in 14.4 seconds, the power

is 1800 watts. This method can be used to determine the power consumption of

household devices by switching them on one by one. [1]

Most domestic electricity meters must be read manually, whether by a representative of

the company or by the customer himself.


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2.1.4 Electronic meter

2.1.4.1Solid state meter

These are newer meters that measure the amount of power consumed and display the

result on an LCD. Aside measuring the power, the solid state meter measures other

parameters such as power factor and the reactive power used. [1]

Picture of the solid state meter

2.1.4.2 The prepayment meter

There are a number of reasons why a utility company could consider installing a prepaid

metering system. They include improved cash flow, no need for account posting or

additional billing systems (1-2% savings), elimination of bad debts (5-12% average, with

up to 40% in some developing countries), elimination of disconnection and reconnection

fees and ease of installation.


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There are also advantages to the customer, including budget management, control of

energy usage, no cost for disconnection/reconnection and no waiting for reconnection, no

deposits.

Prepaid energy meters using keypad based systems, disposable card systems (one-way)

and two-way smart card systems are in use in various parts of the world for over a

decade. [1]

2.1.4.2.1Keypad operated prepayment meters

Electronic prepaid energy meters came initially with keypad systems for inputting the

credit. Security of keypad payment system is very low. The main reason is that the

algorithm of key creation is stored inside the meter and is available to hackers. Keypad

systems were created when highly secure smart card payments did not exist.

Although keypad systems are getting obsolete, it may still be cost-effective for remote

villages, where two-way vending may not be feasible. [1]

2.1.4.2.2Smart card operated prepayment meters

With Smart Card operated systems, customers purchase a reusable power debit card for

the amount of energy they desire. These special, easy to use cards are individualized,

keyed to each customer's meter and account number. The customer simply passes the

card a few inches in front of the meter, and using an integrated card reader, the meter is

reset to the number of kilowatt-hours contained on the card. The system works very much


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like a bank debit card. Because the meter is completely sealed and has no moving parts,

maintenance is reduced and reliability is improved. Modern Smart Card operated meters

are "stand alone", requiring no separate in-house keypad or onsite programming. The

card captures transaction and power usage information, sending automatic input into the

utility's accounting system at the sales terminal each time the customer purchases

additional power. The card also captures data critical for load forecasting.

Disposable card type prepaid meters are also in use in certain utilities. The vending

infrastructure for this scheme is much simpler, but it does not offer the advantage of

capturing customer usage data.

Smart card operated meters can be used either as prepaid or postpaid. In some countries,

prepaid option is socially not acceptable. In such cases, each consumer is assigned 50-day

credit. After each month, the consumer has to recharge a card to pay off his negative

balance. After full payment, his 50-day credit is restored. Credit can be time-based or

amount-based. Mixed option like 50-day but not more than certain kWh is also possible.

[1]

Picture of the Prepayment meter


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2.2Circuit breaker

A circuit breaker is an automatically operated electrical switch that that is designed to

protect an electrical circuit from damage caused by a voltage overload or a short circuit.

Unlike the fuse which is used only once, the circuit breaker can always be reset after it

has tripped to resume normal operation. It uses the shunt trip for this purpose. When there

is a voltage overload, the live and the neutral terminals are connected together through a

shunt resistor and that causes it to trip and open the circuit as a form of protection.

Picture of the Circuit Breaker


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2.2.1 Types of circuit breakers

There are many types of circuit breakers to suit various design situations. But for the

purpose of this project, the miniature circuit breaker will be chosen. The other type of

circuit breaker is the moulded case circuit breaker both of which are for low current

applications.

For higher voltage applications, we have other circuit breaker like the vacuum circuit

breaker and the air circuit breaker.

[1]

2.3 Relays

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

operated by an electromagnet to open or close one or many sets of contacts.

Knowing the resistance of the coil, and its rated voltage, you can compute the current

requirement of the relay coil. And from that information, calculate the power needs of the

relay.

2.3.1 Types of relays

There are several types of relays. These include latching relay, reed relay, mercury-

wetted relay, polarized relay, solid state relay, among many others. The choice of relay


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depends on the design of the project. For the purpose of this project, the solid state relay

was chosen for the reason that it has no moving parts.[1]

Picture of the Solid State Relay

2.4 Memory card

Memory cards are the simplest type of smartcard. Memory cards only have some amount

of memory inside the card and this memory can be normally read and written. There is

normally nothing really intelligent inside those cards. Typically the memory inside this

kind of cards is EPROM, EEPROM or FLASH memory. This card type is very widely

used as telephone cards (telecards) and as prepayment cards where no processing is to be

done by the card. For the purpose of this project, the memory card used conforms to the

ISO 7816 standard. The standard specifies the pin outs and the communication protocols

for the card. Below is the pin out of the memory card as specified by the ISO7816

standard?


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Connector Layout of the Smart Card

Pins marked with n/c are application specific pins defined in application standards. The

standard supports two transmission modes:

Asynchronous transmission: In this type of transmission, characters aretransmitted on the I/O line in an asynchronous half duplex mode. Each character

includes an 8bit byte.

Synchronous transmission: In this type of transmission, a series of bits istransmitted on the I/O line in half duplex mode in synchronization with the clock

signal on CLK.

There is a selection of different protocols available for communicating with the card.

There is a method for selecting which communication protocol to use (one card can


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support one or more protocols).The most commonly used protocol seems to be

asynchronous half duplex character transmission protocol. In contact systems, such as

reading the data from a serial EEPROM over a two-wire (I2C) or three-wire SPI or

Microwire bus, the power, clock, and data lines are connected separately. Some wired

smartcards use RS-232 type asynchronous communications, and in this case supply

power and communication through different wires. [2] This project will consider the I2C

protocol.

2.4.1 The I2C Protocol

A brief discussion of the I2C protocol is discussed below

2.4.1.1 The physical I2C bus

This is just two wires, called SCL and SDA. SCL is the clock line. It is used to

synchronize all data transfers over the I2C bus. SDA is the data line. The SCL & SDA

lines are connected to all devices on the I2C bus. There needs to be a third wire which is

just the ground. There should be a 5volt wire from which power will be distributed to the

devices. Both SCL and SDA lines are "open drain" drivers. What this means is that the

chip can drive its output low, but it cannot drive it high. For the line to be able to go high

you must provide pull-up resistors to the 5v supply. There should be a resistor from the

SCL line to the 5v line and another from the SDA line to the 5v line. You only need one

set of pull-up resistors for the whole I2C bus, not for each device, as illustrated below:


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The value of the resistors is not critical. Anything from 1k8 (1800 ohms) to 47k (47000

ohms) can be used. 1k8, 4k7 and 10k are common values, but anything in this range

works fine. If the resistors are missing, the SCL and SDA lines will always be low -

nearly 0 volts - and the I2C bus will not work.

2.4.1.2 Masters and Slaves

The devices on the I2C bus are either masters or slaves. The master is always the device

that drives the SCL clock line. The slaves are the devices that respond to the master. A

slave cannot initiate a transfer over the I2C bus, only a master can do that. There can be,

and usually are, multiple slaves on the I2C bus, however there is normally only one

master. Slaves will never initiate a transfer. Both master and slave can transfer data over

the I2C bus, but that transfer is always controlled by the master.

2.4.1.3 The I2C Physical Protocol

When the master (the controller) wishes to talk to a slave it begins by issuing a start

sequence on the I2C bus. A start sequence is one of two special sequences defined for the

I2C bus, the other being the stop sequence. The start sequence and stop sequence are

special in that these are the only places where the SDA (data line) is allowed to change

while the SCL (clock line) is high. When data is being transferred, SDA must remain


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stable and not change whilst SCL is high. The start and stop sequences mark the

beginning and end of a transaction with the slave device.

Data is transferred in sequences of 8 bits. The bits are placed on the SDA line starting

with the MSB (Most Significant Bit). The SCL line is then pulsed high, then low. The

chip cannot really drive the line high, so it simply "lets go" of it and the resistor actually

pulls it high. For every 8 bits transferred, the device receiving the data sends back an

acknowledge bit, so there are actually 9 SCL clock pulses to transfer each 8 bit byte of

data. If the receiving device sends back a low ACK bit, then it has received the data and

is ready to accept another byte. If it sends back a high then it is indicating it cannot accept

any further data and the master should terminate the transfer by sending a stop sequence.


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2.4.1.4 Speed of the I2C bus

The standard clock (SCL) speed for I2C up to 100KHz. Philips do define faster speeds:

Fast mode, which is up to 400KHz and High Speed mode which is up to 3.4MHz. But

this needs a small delay of a few uS between each byte transferred.

2.4.1.5 I2C Device Addressing

All I2C addresses are either 7 bits or 10 bits. For 7 bits, it means that you can have up to

128 devices on the I2C bus, since a 7bit number can be from 0 to 127. When sending out

the 7 bit address, still always send 8 bits. The extra bit is used to inform the slave if the

master is writing to it or reading from it. If the bit is zero are master is writing to the

slave. If the bit is 1 the master is reading from the slave. The 7 bit address is placed in the

upper 7 bits of the byte and the Read/Write (R/W) bit is in the LSB (Least Significant

Bit).

The placement of the 7 bit address in the upper 7 bits of the byte is a source of confusion.

It means that to write to address 21, you must actually send out 42 which is 21 moved

over by 1 bit. It is probably easier to think of the I2C bus addresses as 8 bit addresses,

with even addresses as write only, and the odd addresses as the read address for the same

device.


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2.4.1.6 The I2C Software Protocol

The first thing that will happen is that the master will send out a start sequence. This will

alert all the slave devices on the bus that a transaction is starting and they should listen in

incase it is for them. Next the master will send out the device address. The slave that

matches this address will continue with the transaction, any others will ignore the rest of

this transaction and wait for the next. Having addressed the slave device the master must

now send out the internal location or register number inside the slave that it wishes to

write to or read from. This number is obviously dependant on what the slave actually is

and how many internal registers it has. Some very simple devices do not have any, but

most do, including all of our modules. Having sent the I2C address and the internal

register address the master can now send the data byte (or bytes, it doesn't have to be just

one). The master can continue to send data bytes to the slave and these will normally be

placed in the following registers because the slave will automatically increment the

internal register address after each byte. When the master has finished writing all data to

the slave, it sends a stop sequence which completes the transaction. So to write to a slave

device:

1. Send a start sequence

2. Send the I2C address of the slave with the R/W bit low (even address)

3. Send the internal register number you want to write to

4. Send the data byte

5. [Optionally, send any further data bytes]

6. Send the stop sequence.


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As an example, you have an SRF08 at the factory default address of 0xE0. To start the

SRF08 ranging you would write 0x51 to the command register at 0x00 like this:


2. Send 0xE0 (I2C address of the SRF08 with the R/W bit low (even address)

3. Send 0x00 (Internal address of the command register)

4. Send 0x51 (The command to start the SRF08 ranging)


2.4.1.7 Reading from the Slave

Before reading data from the slave device, you must tell it which of its internal addresses

you want to read. So a read of the slave actually starts off by writing to it. This is the

same as when you want to write to it: You send the start sequence, the I2C address of the

slave with the R/W bit low (even address) and the internal register number you want to

write to. Now you send another start sequence (sometimes called a restart) and the I2C

address again - this time with the read bit set. You then read as many data bytes as you

wish and terminate the transaction with a stop sequence. So to read the compass bearing

as a byte from a CMPS03 module:


2. Send 0xC0 (I2C address of the CMPS03 with the R/W bit low (even address)

3. Send 0x01 (Internal address of the bearing register)

4. Send a start sequence again (repeated start)

5. Send 0xC1 (I2C address of the CMPS03 with the R/W bit high (odd address)

6. Read data byte from CMPS03



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The bit sequence will look like this:

That's almost it for simple I2C communications, but there is one more complication.

When the master is reading from the slave, its the slave that places the data on the SDA

line, but its the master that controls the clock. What if the slave is not ready to send the

data! With devices such as EEPROMs this is not a problem, but when the slave device is

actually a microprocessor with other things to do, it can be a problem. The

microprocessor on the slave device will need to go to an interrupt routine, save its

working registers, find out what address the master wants to read from, get the data and

place it in its transmission register. This can take many uS to happen, meanwhile the

master is blissfully sending out clock pulses on the SCL line that the slave cannot

respond to. The I2C protocol provides a solution to this: the slave is allowed to hold the

SCL line low! This is called clock stretching. When the slave gets the read command

from the master it holds the clock line low. The microprocessor then gets the requested

data, places it in the transmission register and releases the clock line allowing the pull-up

resistor to finally pull it high. From the masters point of view, it will issue the first clock

pulse of the read by making SCL high and then check to see if it really has gone high. If

its still low then its the slave that holding it low and the master should wait until it goes


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high before continuing. Luckily the hardware I2C ports on most microprocessors will

handle this automatically.

Sometimes however, the master I2C is just a collection of subroutines and there are a few

implementations out there that completely ignore clock stretching. They work with things

like EEPROM's but not with microprocessor slaves that use clock stretching. The result is

that erroneous data is read from the slave. Beware!

2.5 Phototransistor reflective object sensor

Phototransistor reflective object sensor is a device consisting of an infrared emitting

diode and an NPN silicon phototransistor, mounted side by side in a black plastic

housing. The phototransistor responds to radiation from the emitter only when a

reflective object passes within its field of view. One of the many types of this sensor is

the QRB1133 with its diagram shown below. [3]


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Picture of the QRB1133 Circuit representation of the QRB113


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CHAPTER 3 OVERVIEW OF MICROCONTROLLERS

3.1 General architecture of microcontrollers

Microcontroller is an integrated circuit that incorporates a central processing unit (CPU),

a memory unit, and input/output (I/O) ports. A microcontroller is usually embedded in an

electronic device to serve as a means of controlling the functions of the particular

electronics device.

A typical microcontroller is manufactured as a single chip and has the following parts:

1. has a central processing unit2. a memory unit3. a bus system4. an input / output interface5. serial communication6. a timer unit7. a watchdog8. an analog to digital converter9. programmability


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3.1.1 The memory unit

The function of the memory unit is to store binary data in groups of bits called words.

Each word is a memory location, and it is assigned a unique address. The size of the

memory determines how much data can be stored in it. Thus, the bigger the memory size,

the greater the number words it can store. Data stored in a particular word is referenced

by a process known as addressing. Addressing refers to the act of selecting a particular

memory location.

Getting the desired data from memory is called reading, while the act of putting data

into the memory of the microcontroller is called writing. Therefore, to read or write data

to memory, the target location is first specified by addressing and the data is either read

or written to that location. A read / write (W/R) control line specifies whether a read or a

write operation is to be carried out. When this control line is high, data is read from

memory, and when it is low data is written to the selected location.

3.1.2 Types of memory

There are two types of memory, the volatile and the non-volatile memories

The volatile type of memory loses its data when there is no power supply to it. The non-

volatile memory on the other hand is able to retain its data even in the absence of power.


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RAM (Random Access Memory) is a volatile memory, while the non-volatile memories

are the ROM (Read Only Memory), PROM (Programmable Read Only Memory),

EPROM (Erasable Programmable Read Only Memory) and EEPROM (Electronically

Erasable Programmable Memory).

3.1.3 The central processing unit (CPU)

The central processing unit is that component on the microcontroller that has built-in

logic to enable it perform functions such as memory access, shift operations and the

arithmetic and logical operations. The CPU has collections memory cells called registers

that help it carry out these functions.

3.1.4 Busses

The busses are made up of a set of parallel wires that serve as a path that interconnect the

various units of the microcontroller- the memory unit, the I / O and the CPU.

There are two types of busses. These are the data bus and the address bus. The address

bus consist of as many parallel wires as needed to carry the addresses and the data bus is

responsible for carrying data to and from the memory to the CPU.


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3.1.5 The input / output (I/O)

The input/output unit of the microcontroller serves as the interface between the

microcontroller and the outside world. The I/O is connected to the bus on one side from

the microcontroller. These connections are seen as the pins from the component. These

pins are the output pins. The input connects to the inside of the microcontroller.

3.1.6

Analog-Digital converter

The microcontroller can only process digital data, and since most of the signals are

analog signals, they must first be converted into digital signals. This conversion is done

with the analog-digital converter.

There are other components that help the microcontroller to carry out its functions. These

are the timer unit and the watchdog. [4]

3.2 Programming

Instructions must be given to the microcontroller in order for it to complete any required

task. A program is a series of instructions written to give the micro controller step-by

step procedure to complete the required task. The procedure of writing a program and

loading it into the micro controller is termed programming the micro controller.


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Programs for the microcontroller can be written is several languages, of these are

Assembler and BASIC etc.

Assembler is a low level language and it is difficult to use, but programs written in

assembler take up the least memory space and have the fastest execution times and Basic

are very simple programming languages which takes a fair amount of memory space and

have good execution times.

3.3

Types of microcontrollers

There are many microcontrollers from different manufacturers. These include the PIC,

the BASIC stamp, AVR, ATMEL, and many more.

3.3.1 PIC microcontroller

The low cost and high performance of the PIC microcontroller makes it an ideal option

for use in the energy metering system. Several types of the PIC exist, but the operation of

an energy meter requires that some important information should be kept when there is

no power. This calls for the use of a PIC with a non volatile form of memory. The

PIC16F877 with 256byte of EEPROM became the obvious choice.

The PIC16F877 is made up several features. These include:


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Program memory (flash)

This is based on the flash technology and is used for storing microcontroller programs.

The flash is 8K in size. Flash can be programmed and erased several times. This makes

the PIC microcontroller suitable for device development and testing.

EEPROM

Data stored in the EEPROM is not retained even when power is removed from the unit.

This makes the PIC suitable for storing critical data like the units of electricity consumed

and the units remaining. Thus the reliability of the PIC is enhanced by this ability.

RAM

Because the RAM loses data when power supply is interrupted, it is used for storing non-

critical data during program execution.

PORTS

The ports provide the physical connections between the microcontroller and external

devices. 16F877 has ports A, B, C, D and E .The numerous number of port makes the

number of external devices that can be connected to it many.


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CPU

The function of the CPU is to execute the micro controller program and coordinate the

functions of the other blocks in carrying out the instruction

The Diagram of the PIC16F877 [5]


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3.3.2 Programming of the PIC microcontroller

The PIC16F877 microcontroller can be programmed in any of the three languages-

Assembler and Basic, but for this project, it will be programmed in C due to the

availability of development tools like the FED PIC C compiler

The FED PIC C compiler is a full integrated development environment for writing

programs for the PIC microcontroller. It has a simulator that allows

easy programming of external real devices like LCD , EEPROM, led, switches, buzzers,

keypad etc .Due to this, it becomes a convenient development tool for design problems

involving the PIC micro controller since the whole project can be simulated using the

simulator and debugged on errors. A diagram of a typical design environment using this

compiler is shown below: [6]


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Snap Shot Of The Code Simulation


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CHAPTER FOUR-DESIGN

4.1 Design considerations

The following were considered in design process of this project.

4.1.1 From customers view

A survey in the form of questionnaires was conducted at Ayiduase with 50 customers of

ECG who use the prepayment meter. The aim of this exercise was to find out what the

general public felt about the current prepayment meters.

The questionnaires were prepared with the following questions.

Comparing the prepaid meter to the credit meter, which one is better? Is there anything about the prepaid meter that you dont like? If yes please state

them

For the first question, 38 out of the 50 said they liked the prepaid meters with 12 saying

the credit meter was better because the prepaid read very fast and you have to pay before

u use it.

The second question was the focus. The following was what the response

All 50 of the customers complained about the mode of warning when their creditgot to 20. According to them, they see no reason why the meter should shut power

while they still have as many as 20 credits. Those customers who operate internet

cafs and other computer related business complained about loosing precious data

while they still had credit.


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28 0f the 50 complained of not getting credit to buy on weekends. According tothem they do not know any place where they can recharge their cards on

weekends and so pay the unfair penalty of sleeping in the dark or using the

generator, which is too expensive.

30 of the 50 said the meters were not interactive to use. It does not display anymessage when an error occurs, and they have to try and figure out what the

problem is. They also complained that the meter only displays their available

credit when it gets to 50 thus giving them no prior knowledge of how fast they

consume before being hit all of a sudden with the appearance of a deadly 50 in

red. According to them they would like to know their amount of credit all the

time.

Based on the responses obtained from the survey, the following design considerations

were developed.

Replace the mode of warning with an alarm which will sound when thecustomers credit gets to a threshold thus shutting the customer only when he has

exhausted all his credit.

Provide means for the customer to use some fixed amount of power on credit.This amount of power will be determined by the company after which the

customer will be shut if he fails to buy credit. The number of power units

consumed on credit will be deducted from the customers purchased credit as soon


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as he inserts the recharged card, and until he has paid all his debt, power will not

be restored. Also the number of power units consumed on credit will be displayed

as negative values to signify that the customer owes that amount of power. This is

to take care of those customers whose credit gets finished on weekends.

Use a liquid crystal display (LCD) to interact with the user by displayingappropriate messages that will make the use of the system very interactive. For

example, if you insert the card wrongly, a message will be displayed to warn you.

Also the LCD will be appropriate to use to display the negative credit. It will also

display credit all the time so that customers will know the amount of credit they

have so as to know and control their rate of power consumption.

4.1.2 From tests performed

From tests performed and from the experiences of the ECG technician, the following

were identified

The current prepayment meter uses only a circuit breaker to do the switching.That is the circuit breaker is used to shut off power when the customers credit

finishes and to switch power back on for the customer when he buys credit.

The problem identified was that the circuit breaker has a minimum delay of

about 8 sec to trip when a signal is sent to it from the microcontroller that the

customers credit is finished. This means that the customer will have free power

for that delay period since the system cannot record that power used. Also when


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the circuit breaker is switched on manually, the customer will enjoy free power

for about eight seconds even if he has no credit. This is due to that eight second

delay.

The current prepaid meters have minimal security in terms of card reading. Eachmeter is given a unique card from only which the meter is supposed to read. But

it has become a known fact that the operation of the meter is affected by placing

a phone card or any other card other than that unique card of the meter.

According to ECG technicians, the meter fails to shut power off while a wrong

card is inserted and the customers units are finished. The intelligent part of the

system thus loses track of all the power that the user consumes as long as the

wrong card is still inserted.

At very low voltages, it has been observed that the electronic aspect of theexisting prepayment meter goes off but the electromechanical aspect of the meter

continues to record power consumption. Since the electronic meter will store the

credit of the customer when it goes off and so the credit cannot reduce while the

electromechanical continues to record power, there will be a disparity between

power consumption displayed by the two units when normal voltage is restored

(electronic unit comes back on). The company solves this by obtaining the

difference in the two readings and billing the customer. This has led to lots of

controversies.


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From these findings, the following design considerations were made.

A double switching configuration will be used. This will involve a single pole double throw relay and the circuit breaker. The load will be connected to the

normally closed contact of the relay and the shunt trip of the circuit breaker will

be connected to the normally open contact of the relay. The relay which has no

delays will only be limited by the response time of the PIC micro controller at

power up which is 72ms.When there is no credit, the PIC energies the coil of the

relay which then moves to the normally open contact, thus disconnecting the

load.

This implies no power consumption. The normally open contact will then trip the

circuit breaker in about 8s preventing the loss of power to ECG which will be

dissipated in the circuit.

A high security feature will be implemented to detect the insertion of wrongcards. This feature will count the number of times the system has recognized the

presence of a wrong card and when that count reaches a preset value, the

customer shall be penalized by disabling further reading of any card by the

system, whether correct or wrong cards. When a card is inserted, the system will

display the message Please call an ECG personnel with a beep. Unless a

special card called Reset card is inserted by an ECG personnel to reset the

count, the meter shall not read any more cards. When the Reset card is inserted,

the system will display the message Reset card in.Security memory

cleared!With a beep. This will also serve as a source of revenue for the


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company since recalcitrant customers will have to pay a fine before the system is

reset. It will also serve as a deterrent to other customers to desist from tampering

with ECGs meters.

The electronic unit needs constant five volts supply to operate. This calls for theuse of a five volts voltage regulator (LM7805).According to the datasheet of this

regulator, an input voltage range of five to eighteen volts is required to produce a

constant five volts at the output. An input voltage less than five will not be

sufficient to turn on the voltage regulator thereby putting off the electronic unit.

After consultation with the company, it came to light that the minimum phase

voltage possible is around 120V, and the maximum phase voltage possible is

250V.thus a transformer which could produce at least 5V DC to the voltage

regulator is required.

A 220/240-12V transformer was chosen based on the following calculations

Turns ratio = 240/12 = 20

100V across the primary, secondary voltage will be 100/20 = 5V

Transformer has tolerance of 5% thus can withstand voltage up to

1.05 240 = 252V.

252V across primary, secondary voltage will be 252/20 = 12.6V

The calculations above show that the electronic unit will be up and functioning at

voltages between 100 and 252V which exceeds the minimum and maximum

voltages specified by the company.


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4.1.3 Ease of installation

The process of retrofitting the electromechanical meter with the embedded unit must be

as easy as possible. Thus, a technician must be able to mount the unit accurately and with

much ease.

4.2 Design Options

This project does not seek to impose any design on ECG. Due to this fact, all possible

design options will be discussed and the company will have the option of choosing which

designs it want to implement. The following are the various design options

4.2.1 Method of initializing the embedded unit with the credit meter ID

All credit meters installed by ECG have a nine digit id number. Due to the fact that each

credit meter should be converted to prepaid and should have a card specific to it, then

each retrofitting unit and card should be initialized with the nine digit id of the target

credit meter so that functions such as the card authentication can be done. This can be

done in two ways discussed below

The credit meter ID is hard coded as part of the retrofitting units microcontrollercode and the card also initialized using a special unit called the card terminal. For

this system to work, ECG must present the data base of the entire targeted credit

meter IDs so that they can be incorporated in the code before manufacturing. This

means that ECG will be presented with tagged retrofitting units and cards bearing

the ID of the target credit meters.


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Uninitialized retrofitting units will be presented to ECG along with a special cardcalled initialization card and the card terminal. The card terminal which has a key

pad interface will be used to program the initialization card with the credit meters

ID and when inserted into the retrofitting unit, the unit will read the credit meter

ID into its non-volatile memory (EEPROM) from which authentication can be

done. The specific card for the retrofitting unit is also initialized with the card

terminal .This flexibility give the company the option of doing the initialization

on site or on the companys premises .The card terminal unit can also be equipped

with a lot of function which have to be on demand from the company, example

will be to give it the ability to sell credit to customers.

4.2.2 How to deal with Please call an ECG personnel message

The system is equipped with a security feature which upon detecting three insertion of a

wrong card, displays the message Please call an ECG personnel and disables the

system from feather reading any card. This the system does by increasing a memory

location. To allow the system to read from a card again, then that memory location must

be cleared. This can be done in two way as follows

The customer comes to ECG to report the problem, he pays a fine and providesthe necessary information on a form so that the companys scheduled

maintenance team equipped with a Reset card would be able to locate his


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house/store .When the Reset card is inserted in the meter, the security memory is

cleared.

The customer reports to ECG with his card, he is charged a fee after which aspecial code is put on his card. Upon his insertion of his card into the system, the

security memory is cleared.

4.2.3 Power on delay

It has been observed that for the first few seconds when power is restored, there arevoltage surges. The system can be designed with a delay mechanism built into it that will

delay power supply to the house for a predetermined time within which the voltage surge

dies down.

4.2.4 Warning

An improvement of this system over the existing prepayment system is beeping when the

customers credit gets to a threshold instead of completely cutting off power. The system

beeps slowly when the credit gets to a threshold value which will be set by the company

and beeps faster when the customer has exhausted all his credit and is about to enter the

negative credit zone. The beeping can be implemented in two ways

The system can be designed in such a way that once the credit gets to a thresholdand the system starts beeping, the customer has to insert his card into the system

before the beeping will stop else the system will continuously beep until either

credit is added or the system is shut down.


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The system can be designed in such a way that when the credit gets to a threshold,the system beeps for a number of times and stops.

4.2.5 Behaviour of the retrofitted meter upon failure of electronic unit

Based on the configuration of the relay, there are two ways in which the retrofitted meter

will behave upon failure of the electronic unit:

When the load is connected to the normally closed terminal of the relay, failure ofthe electronic unit will not interrupt power supply to the household, and the

power consumed, therefore, will be measured by the electromechanical meter.

The advantage of this is that, prior to failure; the electronic unit will consume a

maximum of 0.1135W if the customer has credit and 1.0135W for 8s when the

customer runs out of credit. Thus this configuration will minimize power

consumption by the electronic unit.

The disadvantage is that when the electronic unit fails, the company reads the

power measured by the electromechanical meter to prepare a bill for the

customer. This has led to lots of controversies between the company and

customers who claim the company is trying to cheat them because the bill is too

much.

The load can be connected to the normally open contact of the relay. Upon failureof the electronic unit, power to the household will be interrupted and the

customer will have to report to the company for immediate replacement of

electronic unit. It is however advised that this option be chosen only if the


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company chooses to initialize the electronic units with the credit meter ID which

is option two of section 4.2.1 since the company will have spare uninitialized

units which can easily be initialized with the customers credit ID

Also with this configuration, the relay will have to be energized to supply power

to the customer. Thus when the customer has credit, the electronic unit will

consume 1.0135W and when the customer runs out of credit, 0.1135W will be

consumed for 8s.Thus this configuration will consume more power than the

option above.

The advantage however is that the there will be no controversy between the

company and the customer since the company will not have to prepare any bill

for the customer due to the fact that both electromechanical and electronic units

will be off in this case.


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4.3 System block diagram

The embedded unit will consist of a QRB sensor, LCD, buzzer, Pic microcontroller, card

reader socket, relay and circuit breaker. The components will be connected as shown in

the block diagram below

Shunt Trip

4.4 Principle of operation

The sensor continuously throws infrared rays onto the rotating reflective disc of the credit

meter. The reflected rays are detected until the rays hit a black non reflective mark on the

surface of the disc. The logical output of the sensor changes which then interrupts the

microcontroller to increase a count variable. When this count is equal to the number of

revolutions that make up one credit, a credit is deducted.

LCD(LIQUID CRYSTALDIODE)

ALARM(BUZZER)

SENSORQRB1133/QRB1134

RELAY

CARD READER

PIC16F877

CIRCUIT BREAKER


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When the credit is finished, the system does not shut down immediately, rather the

customer is allowed some fixed amount of power on credit, which will be deducted the

next time credit is bought. This is in view of the fact that terminals where credit is sold do

not operate on weekends and are closed from 6.00pm on working days. Thus if a

customers credit finishes, he will not be denied power supply. The microcontroller shuts

down the system through the relay when the customer exhausts the power on credit.

The system warns the customer when his credit reaches a threshold. It does this by

sounding an alarm.

Also the customer can buy credit onto his memory card, insert it into the card reader of

the unit, the microcontroller verifies the authenticity of the card by matching the ID of the

card with that of the meter. If it matches, the credit is loaded into memory and the credit

on the card is cleared. If it does not, the card is not read.

4.5Improvement over existing system

4.5.1 Mode of warning

The prepayment meter currently in use by ECG completely shuts down the customer

when the credit gets to twenty. This is to serve as a warning that the credit is getting

finished.

Even though a laudable idea, completely shutting down the customer only to remind him

of his finishing credit has led to some dissatisfaction among some users. A better


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alternative would be to sound an alarm to warn the user, and this has been incorporated

into the project.

4.5.2 The concept of negative credit

In view of the fact that terminals where credit is sold are not open on weekends, it might

the case that a users credit will get finished on the weekend or in the evening. The

current prepayment meter shuts the consumer when his credit gets finished. A better

alternative would be to allow the user a fixed amount power on credit to cater for the

special cases where credit gets finished on the weekend. The power used on credit will be

deducted the next time he buys credit.

4.5.3Security features

Each embedded unit comes with a specific card that will be given to the customer. This

card contains an identification number (ID) that corresponds to a number stored in the

memory of the unit. When the card is inserted, the unit checks its ID, if there is a match,

the card is read. If not, it increments a count variable.

If count variable gets to three, the unit refuses to read anymore cards and must be reset by

the card of an instructor.


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4.6 System Design

The system consist of three main modules

The power supply module The QRB sensor module The microcontroller module

The various modules with their circuit diagrams are presented belo

4.6.1Power supply module

The power supply module will comprise the following component connected as shown in

the circuit diagram below

220/240 9v step down transformer Bridge rectifier( 4 diodes) Smoothing capacitor Voltage regulator LM7805


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4.6.2 QRB sensor module

The QRB sensor module will comprise the following

The QRB1133/1134 sensor 220,4.7k resistors 10k variable resistor.

The circuit diagram for the module is shown below.


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4.6.2.1 QRB sensor holder

The QRB sensor must be placed under the rotating disc at a suitable distance of 5mm for

effective detection of rotation; also the sensor must be positioned such that it will always

be directly under the black mark. This necessitated the design of a holder that will keep

the sensor at the desired position. The design is shown below.


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4.6.3 Microcontroller module

The various components are connected as shown below and controlled by the PIC

microcontroller.


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4.6.3.1 Packaging

The embedded unit and the retrofitted credit meter have to be packaged. The design of

the package is show below.


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4.7 Design of the card terminal unit

The purpose of the card terminal is to write credit on the targeted meters card and also

write the reset code on a reset card. The terminal unit built for this project comes with

four push down buttons which will be used for writing either the reset code on a reset

card or for writing credit on the meters card. Two buttons are used to select the mode-

either reset code or credit code, and the other two are for writing and reading from the

card once the mode is selected. It has an LCD display for to show the values being

written to or read from the card. It has a card slot where the card is inserted.

The function and how it operates are outlined below

The four buttons are labeled as

1. Reset2. Write3. Read4. Credit

When it is desired to write or read from a reset card, then after insertion of the card, the

reset button should be pressed once since it generates an interrupt. Once the

microcontroller is interrupted, then the message Reset code will be displayed on the

LCD. At this moment if a write operation is desired, the write button should be pressed or

if it is a read, then the read button should be pressed. When finished, the reset button has

to be pressed once again to leave the reset code block.

On the other hand if it is desired to read or write credit to a card for a meter, then after

insertion of the card, the credit button should be pressed. Once pressed, the desired

operation is then selected using the write or read button.


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4.7.1 Circuit diagram of terminal unit


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4.7.2 Packaging

The package for the card terminal unit is shown below.


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4.8 Design of a DSP based prepayment meter

A DSP based prepayment system can easily be achieved by replacing the QRB sensor in

the microcontroller module shown above with a DSP chip. The DSP chip should then be

programmed to send a signal to the microcontroller when it measure one kilowatt of

power. The circuitry remains unchanged. The revise circuit diagram is shown below.

4.8.1 Circuit diagram of DSP based prepayment meter design


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4.8.2 Comparing a DSP based system to credit based prepayment system.

The DSP based prepayment meter undoubtedly is more accurate in measuringpower than the credit based prepayment meters. This is in view of the fact that the

DSP based meter takes power factor measurement into consideration which the

credit based meter totally neglects.

The credit based meter is more robust and can withstand high conditions ofvoltage and current than the DSP based system.

A test conducted at the lab and confirmation from VRA technicians revealed thatwhen the DSP based meter is bridged, the meter does not read at all and the

customer uses power free of charge but from test also conducted at the lab and

form confirmation from ECG technicians, when the credit based meter is bridged,

the meter at least reads more than half of the power used

An important advantage of the credit based prepayment meter over the DSP basedmeter is that when the DSP based meter gets damaged probably due to voltage

surge, the customer uses power for free and the company has no way of

determining how much power the customer has used but with a credit based

prepayment system, when the digital part of the meter gets damaged also due to

voltage surge, the mechanical aspect of the meter which is more robust keeps

recording the power used by the customer. Thus the company can prepare a bill

for the customer based on the readings of the mechanical part of the meter.


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4.10 Programming

4.10.1 Flow chart for program.


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4.10.2 Operation of the program

At the very first time of using the unit, initialization of the various variables isdone once in the meters operative life. The variable initialization includes

activities like clearing the EEPROM, setting counters to zero; etc. Then system

enters an infinite loop.

If an interrupt occurs,count is incremented. When count gets to N, which is themeter constant indicated by the letter N on the flow chart, then a credit is

deducted. The interrupt is the electrical pulse coming from the

QRB1133/QRB1134 sensor.

Check credit and see if it is equal to or less than five, and then sound the alarm.

If credit is finished (plus the extra credit also exhausted), then shut down power

supply to the household.

If count is not equal to N or credit is not finished, then get credit from the card

through the card reader.

Else, Check card reader for credit. If there is a card, read value on card intoEEPROM, then restart loop. If there is no card, just restart loop.


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4.10.3 The various functions in the program

Initialize ()

This function is responsible for initializing all the various components. This includes

clearing EEPROM and clearing variables.

This function is executed only once in the meters life.

Interrupt ()

This function increments the counting of the number of revolutions. It does this by

employing a sensor.

LCDNum ()

This is the LCD driver for outputting to the LCD.

Subtract ()

When the interrupt function counts to a predetermined meter constant, the main ()

function calls subtract to do the deduction of credit.

Shut ()

When subtract determines that the credit is finished, it informs main () which call shut()

to open relay. Thus shutting customer off


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getUnits ()

This function is responsible for reading credit on the card when a card is inserted.

Buzzer ()

This function is for warning. When subtract () determines that the credit is at or below

some threshold. It informs main () which then calls the buzzer () to warn the customer.


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CHAPTER FIVE-IMPLEMENTATION

5.1 Design options implemented

1. The credit meter ID is hard coded as part of the micro controller code.2. An ECG personnel has to insert a Reset card into the system to clear security

memory.

3. The system beeps for some number of times and stops.5.2 Calculations made

The credit meter used for this project has the following information from the meter

1. 240v (voltage)2. 15-60A(current)3. 200Revs/KWh

Form this information the following calculations were made.

Watt (power) = voltage current neglecting power factor

Watt = 240 60 = 14400W = 14.4KW at full load

Number of revolutions at full load = power at full load 200Rev/KWh

Number of revolutions at full load per hour = 14.4 200 = 2880revs/h

Number of revolutions at full load per second = 2880/3600 = 0.8revs/sec

Number of revolutions at full load per millisecond = 0.8/1000 = 0.0008revs/ms

From the pic16F877 data sheet, the rising time for the PIC is 72ms

Number of revolutions in 72ms = 72 0.0008 = 0.0576revs

The radius of the aluminium disc in the meter was measured and found to be 4cm

Circumference of the disc = distance moved in one revolution


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Circumference = 2 r

Circumference = 2 4 = 25.13 cm

Distance moved in 72ms

1rev = 25.13cm

0.0576rev = (0.0576 25.13) = 1.44cm 2cm

Thus it can be deduced that when a black mark of length 2cm is placed under the disc,

then there is no possibility of losing a revolution since the rising time of the circuit is

only limited by the rising time of the PIC microcontroller.

5.3 Construction

5.3.1 The power supply module

The power supply module was constructed as shown by the circuit design with the

following calculations in mind.

Transformer Rating: 9volts

Silicon diodes

Current requirement of the circuit = 22.7mA

Current that the power supply must be capable of delivering = (0.52 + 20% of 22.7) mA

AC frequency = 50Hz

Unsmoothed AC voltage = (9 - 1.4); since each of the two conducting diodes reduces the

9volts


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5.3.2 The QRB sensor module

The QRB sensor circuit was constructed as shown in the QRB sensor circuit diagram.

After the construction of the QRB sensor holder, it was fitted in the meter with the black

mark as shown below


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5.3.3 The microcontroller module

The circuit was constructed as shown in the circuit diagram. All the other modules were

added and packaged as shown below

5.3.4 The card terminal unit

The circuit was constructed and packaged as shown


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5.4 Tests performed

5.4.1 The bridging problem

A DSP (digital signal processing) based prepaid meter was obtained from a company

(source cannot be disclosed) and tested for the bridging problem

The bridging problem asserts that when the two live wires to and from the meter are

bridged, the meter is completely bypassed and does not read anything.

The meter was connected to a 200V ac supply and a load of 5A was given to it for 10min,

the dials of the meter moved signifying that the meter was measuring the power

consumed.

After connecting the two lives of the meter with a wire (bridging), it was observed that

for a time period of 30min, the dials of the meter did not move however the display was

on but dim. This signifies that the meter was truly bypassed.

The same test was performed with the credit meter obtained from ECG. Without

bridging, the dials of the meter moved 18 revolutions for a period of 5min.

However after bridging, the dials of the meter moved slow about 1 revs for the 5min

period. The dial of the meter did not show the slightest sign of movement when the

incoming live wire was disconnected and rather connected together with the outgoing live

wire.

A solution to the bridging problem is to employ sealing. Sealing is just covering all

possible holes that can be used to bridge the meter with an impenetrable substance. The


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only way to bridge the meter then will be to break the seal which can easily be detected

by the company for the culprit to pay a heavy fine.

5.4.2 Placement of black mark and QRB sensor.

The only way for the circuit to determine the amount of power used was through the

interrupt caused by the detection of a black mark placed under the disc of the meter by

the QRB sensor. But since the black mark has weight, then it was anticipated that it

would increase the weight of the disc thereby causing unacceptable reading. Even the

whole process of opening the meter and placing the black mark together with the sensor

could cause some errors to be introduced .This led to a test to find out how accurate the

meter will measure power after placing the black mark.

The meter was connected to a 200V ac supply and a load of 5A was given to it. Sixteen

revolutions were counted in a period of 5min.The meter was then opened and the black

mark and the sensor were placed and the meter was subjected to the same load and

voltage. The number of revolutions were counted and found to be exactly 16 signifying

that the placement of the black mark and sensor did not introduce any unacceptable error

in the measurement of power by the meter.

5.4.3 Test for functionality of the various modules

The various modules were tested after their construction to verify their functionality.


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The power supply module was connected to an ac source and a multi meter was

connected across its terminals, the reading of the multi meter was the expected reading of

12v

The output of the QRB sensor module was connected to an LED and the sensor was

interrupted with both a reflective aluminium plate from a tin of milk and a non reflective

black tape. It was observed that with the reflective substance, the LED was on and with

the non reflective tape, the LED was off. This verified the fact that the QRB sensor

detects non reflective objects from reflective objects.

The micro controller circuit was powered and a switch which was connected as the

interrupt was pressed five times. It was observed that the value displayed on the LCD

connected to the circuit reduced by one-a desired behavior. After the value reduced to -5,

the relay connected to the circuit was energized and after 8s tripped the circuit breaker

thus verifying the functionality of the circuit.

All modules were put together and the overall functionality of the system was tested and

found to be correct.

Also the card terminal was tested and all functionalities were verified.

5.4.4 Test for the amount of power consumed by the embedded unit

The system was

final project report-parggah and gilbert (4)

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