2.Multitariff Prepaid Energy Meter

8/2/2019 2.Multitariff Prepaid Energy Meter

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MODEL ENGINEERING COLLEGE MULTITARIFF PREPAID ENERGYMETER

Chapter 1

INTRODUCTION

The recharging of the user account can be done as in conventional mobile phone

prepaid recharging. A consumer can collect the prepaid recharging card from elec-

tricity can be drawn until the amount is finished. If there is no account balance,

then the electric current supply is disconnected using a relay circuit.

The energy measurement chip AD7751 computes the instantaneous power by mul-

tiplying the inputs in current channels and voltage channels.This is fed to a

counter,thereby obtaining the effective energy consumed.The Real Time Clock

(RTC) monitors the Time Of Day and the local shops and recharge using mobile

phone in the specified format. This DTMF data will be processed in the office sec-

tion and if valid, corresponding amount is credited to the specific consumer by an

RF module section whose transmitter is in the electricity office section and receiv-

er integrated with the consumer electricity meter section. Thus, once the amount is

credited, tariff is varied.

At the office section, the database of each consumer is assigned a unique code

along with the consumer consumption balance.The monitoring of the energy con-

sumption pattern during the day can be monitored.This enables the electricity

board to keep track of malpractices of over consumption and give warnings if nec-

essary.The office section also consists of the RF transceiver for varying the con-

sumer balance.

DEPARTMENT OF ELECTRONICS ENGINEERING 1


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The current variation between the two current channels must not be greater than

12.5%. In that case, the supply is automatically cut off. The consumer account bal-

ance is decremented until it becomes les than a minimum value. Below this, a

warning is given by the beep of a buzzer. The consumer gets a unique code to

recharge his balance. The consumer authentication code followed by a code corre-

sponding to a recharge denomination is sent to the office section, which is decod-

ed and accordingly the balance is updated.



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Chapter 2

HARDWARE

2.1: Energymeter section

The energymeter section calculates the energy consumption using the energy meteringIC AD7751.

Fig 2.1:Performance curve circuit of AD7751

The AD7751 is a high accuracy fault tolerant electrical energy measurement IC intended

for use with two-wire distribution system. The AD7751 incorporates a novel fault detection

scheme that both warns of fault conditions and allows the AD7751 to continue accurate

billing.



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The AD7751 supplies average real power information on the low frequency outputs F1 and

F2. These logic outputs are used to directly drive an electromechanical counter. The CF

logic output gives instantaneous real power information. This output is intended to be used

for calibration purposes.

The ADCs digitize the voltage signals from the current and voltage transducers.

These ADCs are 16-bit second order sigma-delta with an oversampling rate of 900 kHz.

This analog input structure greatly simplifies transducer interfacing by providing a wide

dynamic range for direct connection to the transducer and also simplifying the antialiasing

filter design. A programmable gain stage in the current channel further facilitates easy

transducer interfacing. A high-pass filter in the current channel removes any dc component

from the current signal. This eliminates any inaccuracies in the real power calculation due

to offsets in the voltage or current signalssee HPF and Offset Effects section. The real

power calculation is derived from the instantaneous power signal. The instantaneous power

signal is generated by a direct multiplication of the current and voltage signals. In order to

extract the real power component (i.e., the dc component) the instantaneous power signal is

low-pass filtered.

Fig 2.2:Signal Processing block diagram



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2.2: RTC Section

This section is used to compute the peak hours and vary the tariff accordingly. A

DS1307 module was used as Real Time Clock.

The DS1307 Serial Real-Time Clock is a low-power, full binary-coded decimal

(BCD) clock/calendar plus 56 bytes of NV SRAM. Address and data are transferred

serially via a 2-wire, bi-directional bus. The clock/calendar provides seconds, minutes,

hours, day, date, month, and year information. The end of the month date is automatically

adjusted for months with fewer than 31 days, including corrections for leap year. The clock

operates in either the 24-hour or 12-hour format with AM/PM indicator. The DS1307 has a

built-in power sense circuit that detects power failures and automatically switches to the

battery supply.

Fig 2.3:Pinout diagram of DS1307



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The DS1307 operates as a slave device on the serial bus. Access is obtained by

implementing a START condition and providing a device identification code followed by a

register address. Subsequent registers can be accessed sequentially until a STOP condition

is executed.

The RTC was interfaced with the microcontroller and the time was

monitored.The peak hours were programmed to have a higher tariff.



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2.3: DTMF Section

The Dual Tone Multiple Frequency (DTMF) tones are used to update the

balance by the consumer. A unique code is sent using a mobile phone by the consumer.The

recharge can be done in multiples of a certain denomination. The DTMF signals are

received in the office section and correspondingly the database checked and balance is

updated accordingly.

The MT8870D is a complete DTMF receiver integrating both the bandsplit

filter and digital decoder functions. The filter section uses switched capacitor techniques

for high and low group filters; the decoder uses digital counting techniques to detect and

decode all 16 DTMF tone pairs into a 4-bit code.



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Fig 2.4:Pinout diagram of DTMF decoder

2.4: RF Section

The function of a radio frequency (RF) transmitter is to modulate, up convert, and amplify

signals for transmission into free space. An RF transmitter generally includes a modulator

that modulates an input signal and a radio frequency power amplifier that is coupled to the

modulator to amplify the modulated input signal which is again coupled to an antenna that

transmits the amplified modulated input signal.

The RF transceiver used is CC2500. The CC2500 is a low-cost 2.4 GHz transceiver

designed for very low-power wireless applications.

RF Performance



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High sensitivity (104 dBm at 2.4 kBaud,1% packet error rate)

Low current consumption (13.3 mA in RX,250 kBaud, input well above sensitivity

limit)

Programmable output power up to +1 dBm

Excellent receiver selectivity and blocking performance

Programmable data rate from 1.2 to 500 kBaud

Frequency range: 2400 2483.5 MHz

Fig 2.5:Pinout diagram of CC2500



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CC2500 features a low-IF receiver. The received RF signal is amplified by the low noise

amplifier (LNA) and down-converted in quadrature (I and Q) to the intermediate frequency

(IF). At IF, the I/Q signals are digitised by the ADCs. Automatic gain control (AGC), fine

channel filtering, demodulation bit/packet synchronization are performed digitally.The

transmitter part of CC2500 is based on direct synthesis of the RF frequency. The frequency

synthesizer includes a

completely on-chip LC VCO and a 90 degrees phase shifter for generating the

I and Q LO.

The energy consumption balance updation value is sent to the office section by the RF

transceiver.The balance in the database of the consumer is incremented

correspondingly.The reception side is a RF transceiver which receives the data and gives it

to the control unit microcontroller which does the updation.

2.5: LCD Module

A liquid crystal display (LCD) is an electronically-modulated optical device

shaped into a thin, flat panel made up of any number of color or monochrome pixels filled

with liquid crystals and arrayed in front of a light source (backlight) or reflector. It is often

utilized in battery-powered electronic devices because it uses very small amounts of

electric power.



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Fig 2.6:LCD pinouts

Register select: Two types of registers

* Command Code Register: When RS=0, command code register will be selected.

* Data register: When RS=1, data register is selected.

Read/Write: R/W input allows the user to write information to LCD or read information

from it. The data that is being currently displayed will be stored in a buffer memory

DDRAM.

R/W=0-Reading

R/W=1-Writing

E-Enable:

The enable pin is used by the LCD to latch information at its data pins. When data is sup-

plied to data pins, a high to low pulse must be applied to this pin in order for the LCD to

latch the data present in the data pins.



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Fig 2.7 Interfacing LCD with AtMega32

2.6: Power supply



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The ac voltage (240V), is connected to a transformer, which steps down that ac

voltage to a level of the desired dc output. A diode rectifier then provides a full-wave

rectified voltage that is initially filtered by a simple capacitor filter to produce a dc voltage.

This resulting dc voltage usually has some ripple or ac voltage variation. A regulator circuit

removes the ripples and also retains the same dc value even if the input dc voltage varies,

or the load connected to the output dc voltage changes. This voltage regulation is usually

obtained using one of the popular voltage regulator IC units.

Fig 2.8:Block diagram of power supply

Chapter 3



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CIRCUIT DESIGN

3.1 Energymeter section:

The output frequencies obtained in F1,F2 and CF can be calibrated according to the

following table.

Table 3.1:Frequency calibration table

The user can select one of four frequencies.This frequency selection determines the maxi-

mum frequency on F1 and F2. These outputs are intended to be used to drive

the energy register. Since only four different output frequencies can be selected, the avail-

able frequency selection has been optimized for a meter constant of 100 imp/kWhr with a

maximum current of between 10 A and 120 A.

The computation of power by the IC is done as:



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(1)

(2)

the real powerPcan be expressed

in terms of its fundamental real

power (P1) and harmonic real pow-er (PH).

(3)

Design of Analog inputs:



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Fig 3.1: Typical connection for Channel 1

Here the analog inputs are being used to monitor both the phase and neutral currents. Be-

cause of the large potential difference between the phase and neutral, two CTs (currenttransformers) must be used to provide the isolation. Notice both CTs are referenced to

AGND (analog ground), hence the common-mode voltage is 0 V. The CT turns ratio and

burden resistor (Rb) are selected to give a peak differential voltage of 660 mV/gain.

Fig 3.2:Typical connections for Channel 2

Here a PT(potential transformer) is used to provide complete isolation

from the mains voltage.

3.2 RF section:



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Fig 3.3: Configured CC2500 transceiver

The CC2500 transceiver is configured in both energymeter and office section to

work at a frequency of 2.400GHz and baud rate 9600.

METER SECTION CIRCUIT DIAGRAM



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Fig 3.4: Meter section circuit diagram

OFFICE SECTION CIRCUIT DIAGRAM



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Fig 3.5: Office section circuit diagram

Chapter 4

SOFTWARE



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4.1 Meter section program flowchart



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Fig 4.1: Meter section program flowchart

4.2 Office section program flowchart



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NO

YES


START

INITIALISE

SLEEP

ENABLE INTERRUPT

INITIALISE USART

IF

INTERRU

PT?

C


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NO

YES

Fig 4.2:Office section program flowchart

4.3 Programs


C

CONSUMER NUMBER= DATA(0-

CARD NUMBER= DATA(4-7)

CHECK THE CONSUMER & CARD

NO WITH DATABASE

IFMATCH?

SEND THE CORRESPONDING CODE

RETURN


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#include

#include

#include

#include

#include

#include

#include "I2C.h"

#include "lcd.h"

#include "ds1307.h"

#ifndef F_CPU //define cpu clock speed if not defined

#define F_CPU 8000000

#endif

#define BAUDRATE 9600 //set desired baud rate

#define UBRRVAL ((F_CPU/(BAUDRATE*16UL))-1) //calculate UBRR value

#define RADDR 0x44 //define receive parameters

#define eetariff1 0x1E

#define eetariff2 0x2E

#define eebalance 0x3E

#define tar1 0x05

#define tar2 0x0A

#define lowerlimit 0x05

void USART_Init(void)

{

//Set baud rate

UBRRL=(uint8_t)UBRRVAL; //low byte

UBRRH=(UBRRVAL>>8); //high byte

UCSRC=(1


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(0


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uint8_t rxdata,temp,balance;

rxdata=USART_vReceiveByte();

temp=rxdata&0xf0;//get upper nibble to get receiver address

if(temp == 0x04)

{

rxdata &= 0x0f;

balance= eeprom_read_byte(eebalance);

balance+=rxdata;

eeprom_write_byte(eebalance,balance);

}

}

void cutoff()

{

PORTD|=(1


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/*void display1(uint8_t totalkwh1,uint8_t tariff1,uint8_t balance)

{

LCDClear();

LCDGotoXY(1,1);

LCDWriteInt(totalkwh1,5);

LCDWriteString("KWH");

LCDGotoXY(10,1);

LCDWriteString("T:R");

LCDWriteInt(tariff1,2);

LCDWriteStringXY(1,2,"BAL:R");

LCDWriteInt(balance,5);

}*/

void settime()

{

uint8_t hr,min,sec,am_pm,temp;

hr=8;

min=30;

sec=44;

am_pm=0;

temp=((sec/10)


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temp=((hr/10)4);



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Time[5]=':';

DS1307Read(0x01,&data);

Time[4]=48+(data & 0b00001111);

Time[3]=48+((data & 0b01110000)>>4);

Time[2]=':';

DS1307Read(0x02,&data);

Time[1]=48+(data & 0b00001111);

Time[0]=48+((data & 0b00010000)>>4);

//LCDClear();

//LCDWriteStringXY(2,1,Time);

//AM/PM

/*if(data & 0b00100000)

{

LCDWriteStringXY(11,1,"PM");

}

else

{

LCDWriteStringXY(11,1,"AM");

}*/

//Wait Some time and keep testing key input

}



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uint8_t findtariff(char time[12],uint8_t data2)

{

uint8_t tariff;

if(data2 & 0b00100000)

{

if(time[1]>=7 & time[1]


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uint8_t temp;

DS1307Read(0x00,&temp);

temp&=(~(1


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{

cutoff();

}

else

{

gettime(Time,data);

tariff=findtariff(Time,data);

cuton(); //display1(totalkwh,tariff,balance);

count=TCNT1;

unit=count/64;

rem=count%64;

TCNT1=rem;

totalkwh+=unit;

gettime(Time,data);

tariff=findtariff(Time,data);

amt=unit*tariff;

balance-=amt;

eeprom_write_byte(eebalance,balance);

delayms(25);

}

}while(balance>lowerlimit);

}

CONCLUSION



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The project Multitariff prepaid energymeter provides a comprehensive

solution to the requirement of human labour for energy consumption billing.It also

provides flexibility for the consumers to have a pre-payement option, thereby providingconvenience. The variable tariff billing features ensures the monitoring of domestic energy

consumption at various timings and charge more for peak hour consumption.



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FUTURE ENHANCEMENTS

-The energy consumptions readings can be sent through power lines.

-The electricity board can monitor the consumptions at different timings by each consumer

and can send notifications in case of high peak hour consumption.

Date post:	05-Apr-2018
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2.Multitariff Prepaid Energy Meter

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