2modified Main Project Contactless Load Measuring

CONTACT LESS LOAD MEASURING METER FOR POWER LINES

1. INTRODUCTION

The power lines have today an important role in the electric power grid transport

lines energy in the best condition is a good of all electricity companies in the world. The

premise of this work is to develop an innovative power system for use in systems with

nominal power of 800W the main purpose of this systems. The contact less load

measuring meter is the system in which we can measure load directly without any physical

contact the load we can measure directly in the L.C.D without any physical contact

The system consist of the two kits one is the transmitter and other one is the

receiver and other one is the transmitter which is the individual kit. We can measure the

loads of these between the 10mts apart the supply consist of the 5V which is given to the

kit. The bridge rectifier converts the ac supply to the dc supply given to the micro

controller in the circuit.

The micro controllers are placed in the system to control the output of the system. The

load of the system which is measuring without any contact in the induction coil is present

by measuring the load in particular circuit we can get the how much of the power in the

circuit flowing and by using the we can measure the load.

The receiver system also consisting micro controller and the load and also the bridge

rectifier which is displayed on the 16*2LCD

The contact less load measuring meter is the advanced system in which we can

measure load in the particular pole, fan, fluorescent lamp etc and this system is the various

application in the present which is applicable for the 230V household purpose. The

microcontroller is used for interface with fm receiver and stepper motor and it gives proper

stepping pulses for vehicle movements by receiving serial data from fm receiver. It consists

of serial ports and CPU, MU and CU. The LCD added a lot your applications in terms of

providing an useful interface for the user debugging or just giving a professional look. The

CMRCET-B. Tech 1 Department of EEE


microcontroller sends the signal to ADC converter, the ADC is used to displayed in the

screen. In that ADC consist of the multiplexer and the convert and timer circuits. The

timers are used in the circuit.

The operational amplifier is used multi terminal device which internally is quite complex.

By using operational amplifier we can complex integral circuits.

The objective of our project is to see how much of current flowing through the particular

power line and if higher currents flows in the circuit then there is detect the circuit. The

contact less load measuring meter is the advanced system in which we can measure the

load in the particular pole, fan, fluorescent lamp etc and this system can be used for various

applications in the present which is applicable for 230V house hold purpose. It consists of

two kits one is the transmitter and other is receiver and the kits are having feed loads to

each other. The distance between the kits we can measure is 10m apart. The supply given to

the transformer and it step down to 5v it converts the ac supply to the dc supply by using

bridge rectifier



2. POWERLINES

High-voltage power lines cause low frequency electric and magnetic fields around

them. Exposure is concentrated close to the lines. Thus, only a very small percentage of the

Finnish population is exposed to fields generated by power lines.

In main power grid there are three main types of high-voltage power lines. Large

400 and 220 kilovolts power lines, suspended high above, and the most important 110

kilovolt power lines, are the basis of Finland’s main power grid. Other 110 kilovolt power

lines make up the so-called regional network. Smaller, 20 kilovolt, medium voltage power

lines are used in a distribution network. Electric fields can be significant when it comes to

exposure directly below 400 kilovolt power lines and can even exceed exposure limits for

the general public. This, however, does not restrict occasional visits to these locations for

activities such as picking berries or farming and forestry work. The electric field generated

by other types of power lines does not cause significant exposure.

Magnetic fields caused by power lines are only found in the direct vicinity of the

lines themselves. The magnetic fields are proportionate to the current flowing through the

power lines, which is at its highest in the 400 kV main power grid. Exposure limits to the

general public are not exceeded even directly beneath the power lines, where, at its

strongest, the field is one-fourth of the limit values. When 60-70 meters away from the 400

kilovolt power lines, and 20-40 meters away from the 110 kilovolt power lines, the

exposure is less than one-hundredth of the 100 µT limit value for the general public.

Beneath 20 kilovolt power lines, exposure is always less than one-hundredth of the limit

value. Underground cables, used in densely populated urban areas, do not generate electric

fields outside the cable. Magnetic fields, however, do extend a few meters from cables at

ground level. Only people living in the direct vicinity of power lines are exposed to

magnetic fields caused by the lines.



Fig 2.1 power lines

In the picture above one can see the strongest magnetic fields found in the direct vicinity of

400 kilovolt power lines. When over 65 meters away from the line, the exposure is less

than 1 µT.

2.1 Overhead lines

This article is about power lines for general transmission of electrical power. For

overhead lines used to power road and rail vehicles, see Overhead lines.

Fig 2.2 Transmission lines in Lund, Sweden Fig 2.3 High and medium voltage power lines in Łomża,

An overhead power line is an electric power transmission line suspended by towers or

utility poles. Since most of the insulation is provided by air, overhead power lines are

generally the lowest-cost method of transmission for large quantities of electric energy.

Towers for support of the lines are made of wood (as-grown or laminated), steel (either


http://en.wikipedia.org/wiki/Electric_power_transmission

http://en.wikipedia.org/wiki/Electrical_insulation

http://en.wikipedia.org/wiki/Utility_pole

http://en.wikipedia.org/wiki/Transmission_tower

http://en.wikipedia.org/wiki/%C5%81om%C5%BCa

http://en.wikipedia.org/wiki/Sweden

http://en.wikipedia.org/wiki/Lund

http://en.wikipedia.org/wiki/Overhead_lines

http://en.wikipedia.org/wiki/File:Electric_transmission_lines.jpg

http://en.wikipedia.org/wiki/File:%C5%81om%C5%BCa_linia_elektroenergetyczna_napowietrzna.jpg


lattice structures or tubular poles), concrete, aluminum, and occasionally reinforced

plastics. The bare wire conductors on the line are generally made of aluminum (either plain

or reinforced with steel, or sometimes composite materials), though some copper wires are

used in medium-voltage distribution and low-voltage connections to customer premises. A

major goal of overhead power line design is to maintain adequate clearance between

energized conductors and the ground so as to prevent dangerous contact with the line. [1]

Today overhead lines are routinely operated at voltages exceeding 765,000 volts between

conductors, with even higher voltages possible in some cases.

2.2 Classifications by operating voltages

Overhead power transmission lines are classified in the electrical power industry by the

range of voltages:

Low voltage – less than 1000 volts, used for connection between a residential or small

commercial customer and the utility.

Medium Voltage (Distribution) – between 1000 volts (1 kV) and to about 33 kV, used

for distribution in urban and rural areas.

High Voltage (sub transmission less than 100 kV; sub transmission or transmission at

voltage such as 115 kV and 138 kV), used for sub-transmission and transmission of

bulk quantities of electric power and connection to very large consumers.

Extra High Voltage (transmission) – over 230 kV, up to about 800 kV, used for long

distance, very high power transmission.

Ultra High Voltage – higher than 800 kV.



3. TYPES POWER LINES

Power lines are a necessary part of life in most communities. Without power lines, there

would be no electricity running to homes and businesses. It takes a lot of voltage running

through those lines to power a community, but not all power lines are the same.

3.1EHV Transmission Power Lines

Power plants create electrical energy and move that power through extra high

voltage (EHV) power lines. Many times the electrical energy travels long distances to reach

its destination. EHV lines work like an interstate. Cars move along interstates to reach

specific destinations, and extra high voltage energy moves along the EHV lines to reach

specific destinations. EHV lines can run from 345 kilovolts to 765 kilovolts.

3.2 High-voltage Lines

A substation directs electricity's flow and changes the voltage to different levels. The

substation decreases EHV voltage down to a high-voltage level. High-voltage lines move

electrical power a shorter distance than EHV lines. These lines usually run around 138

kilovolts. A high-voltage line is similar to a four-lane road that has limited access. These

power lines generally run to different areas of a city or county.

3.3 Distribution Lines

A substation is also used to decrease voltage from 138 kilovolts (or a high-voltage line) to

distribution levels. A distribution power line can run anywhere from 34.5 kilovolts to 7.2

kilovolts. Distribution lines can be compared to a two-lane road that connects the

community. There are primary distribution lines (which are the main lines) that connect the

larger parts of the community to a substation. Lateral distribution lines are the power lines

that connect a neighborhood to electricity. Smaller distribution lines connect the individual

residence to electricity.



4. METERS

4.1. Clamp Meter

A multi meter with built-in clamp pushing the large button at the bottom opens the

lower jaw of the clamp, allowing the clamp to be placed around a conductor. An electrical

meter with integral AC current clamp is known as a clamp meter, clamp-on ammeter

Fig 4.1 Clamp Meter

In order to use a clamp meter, only one conductor is normally passed through the

probe if more than one conductor is passed through then the measurement would be the

vector sum of the currents flowing in the conductors and would depend on the phase

relationship of the currents. In particular if the clamp is closed around a two-conductor

cable carrying power to equipment the same current flows down one conductor and up the

other, with a net current of zero. Clamp meters are often sold with a device that is plugged

in between the power outlet and the device to be tested. The device is essentially a short

extension cord with the two conductors separated, so that the clamp can be placed around

only one conductor. The reading produced by a conductor carrying a very low current can

be increased by winding the conductor around the clamp several times; the meter reading

divided by the number of turns is the current, with some loss of accuracy due to inductive


http://en.wikipedia.org/wiki/File:Tongtester.jpg


effects. Clamp meters are used by electricians, sometimes with the clamp incorporated into

a general purpose multi meter. It is simple to measure very high currents (hundreds of

amperes) with the appropriate current transformer. Accurate measurement of low currents

(a few milli amperes) with a current transformer clamp is more difficult.

An iron vane type clamp-on ammeter:

Less-expensive clamp meters use a rectifier circuit which actually reads mean

current, but is calibrated to display the RMS current corresponding to the measured mean,

giving a correct RMS reading only if the current is a sine wave. For other waveforms

readings will be incorrect; when these simpler meters are used with non-sinusoidal loads

such as the ballasts used with fluorescent lamps or high-intensity discharge lamps or most

modern computer and electronic equipment, readings can be quite inaccurate. Meters which

respond to true RMS rather than mean current are described as "true RMS". Typical hand-

held Hall effect units can read currents as low as 200 mA, and units that can read down to

1 mA are available. The Columbia tong test ammeter, manufactured by Weschler

Instruments, is an example of the iron vane type, used for measuring large AC currents up

to 1000 amperes.

The iron jaws of the meter direct the magnetic field surrounding the conductor to an iron

vane that is attached to the needle of the meter.



Fig 4.2 Iron vane type clamp-on ammeter

The iron vane moves in proportion to the strength to the magnetic field and thus

produces a meter indication proportional to the current. This type of ammeter can measure

both AC and DC currents and provides a true RMS current measurement of non-sinusoidal

or distorted AC waveforms. Interchangeable meter movements can be installed in the

clamping assembly to provide various full-scale current values up to 1000 amperes. The

iron vane is in a small cylinder that is inserted in a space at the hinged end of the clamp-on

jaws. Several jaw sizes are available for clamping around large conductors and bus bars up

to 41⁄2 inches (110 mm) wide.

4.2 Digital tong tester

Digital Tong Tester is an electric tester used to measure current in a circuit. These Digital

Tong Testers are available in various sizes with different technical specifications. These

Digital Tong Testers can be customized to cater to the diverse needs of our customers.


http://www.tradeindia.com/fp768533/Digital-Tong-Tester.html

http://en.wikipedia.org/wiki/File:Columbia_Ammeter_02.jpg


Fig 4.3 Digital tong testers



5. PROTOTYPE OF CONTACT LESS LOAD MEASURING METER

Fig 5.1 Photograph of the contact less load measuring meter



5.1 Block Diagrams

Fig 5.2 Block Diagrams of Transmitting System

Fig 5.3 Block Diagrams of Receiving System



5.2 Circuit Diagrams

Fig 5.4 Transmitting System Circuit Diagram

Fig 5.5 Receiving system Circuit Diagram



5.3 Principle of operation

The power lines have today an important role in the electric power grid transport lines

energy in the best condition is a good of all electricity companies in the world. The premise

of this work is to develop an innovative power system for use in systems with nominal

power of 800W the main purpose of this systems. The contact less load measuring meter

is the system in which we can measure load directly without any physical contact the load

we can measure directly in the L.C.D without any physical contact

The system consist of the two kits one is the transmitter and other one is the

receiver and other one is the transmitter which is the individual kit. We can measure the

loads of these between the 30mts apart the supply consist of the 5V which is given to the

kit. The bridge rectifier converts the ac supply to the dc supply given to the micro

controller in the circuit.

The micro controllers and the loads of placed in the system the micro controllers are

placed in the system to control the output of the system. The load of the system which is

measuring without any contact in the induction coil is present by measuring the load in

particular circuit we can get the how much of the power in the circuit flowing and by using

the we can measure the load.

The receiver system consisting of micro controller, load and also the bridge rectifier

which is displayed on the 16*2LCD. The contact less load measuring meter is the advanced

system in which we can measure load in the particular pole, fan, fluorescent lamp etc and

this system is the various application in the present which is applicable for the 230V

household purpose.



5.4 Power Supply:

Fig 5.6 Power Supply

Power supply unit provides 5V regulates power supply to the systems. It consists of

two parts namely,

1. Rectifier

2. Monolithic voltage regulator

5.4.1 Rectifier

Here the step down transformer 230-0v/9-0-9 and gives the secondary current up to

500mA, to the Rectifier. The Transformer secondary is provided with a center tap. Hence

the voltage V1 and V2 are equal and are having a phase difference of 1800. So it is anode

of Diode D1 is positive with respect to the center tap, the anode of the other diode d2 will

be negative with respect to the center tap. During the positive half cycle of the supply D1

conduct’s and current flows through the center tap D1 and load. During this period D2 will

not conduct as its anode is at a negative potential. During the negative half cycle of the

supply voltage, the voltage on the diode D2 will be positive and hence D2 conducts. The



current flows through the transformer winding, Diode D2 and load. It is to be noted that

the current i1 and i2 are flowing in the same direction in load.

The average of the two current i1 and i2 flows through the load producing a voltage drop,

which is the D.C. output voltage of the rectifier. Using capacitor filters the ripple in the out

waveform can be minimized. The voltage can be regulated by using monolithic IC voltage

regulators.

5.4.2 Monolithic IC voltage regulator:

A voltage regulator is a circuit that supplies a constant voltage regardless of

changes in load currents. Although voltage regulators can be designed using op-amps, it is

quicker and easier to use IC voltage regulators. Furthermore, IC voltage regulators are

versatile and relatively inexpensive and are available with features such as programmable

output, current/voltage boosting, internal short-circuit current limiting, thermal shutdown

and floating operation for high voltage applications

Here we are using 7800 series voltage regulators. The 7800 series consists of 3-

terminal +ve voltage regulators with seven voltage options. These ICs are designed as fixed

voltage regulators and with adequate heat sinking can deliver output currents in excess of

1A. Although these devices do not require external components, such components can be

used to obtain adjustable voltages and currents. For proper operation a common ground

between input and output voltages is required. In addition, the difference between input and

output voltages (Vi – Vo) called drop out voltage, must be typically 1.5V even during the

low point as the input ripple voltage. Furthermore, the capacitor Ci is required if the

regulator is located an appreciable distance from a power supply filter. Even though Co is

not needed, it may be used to improve the transient response of the regulator.

Typical performance parameters for voltage regulators are line regulation, load

regulation, temperature stability and ripple rejection. Line regulation is defined as the

change in output voltage for a change in the input voltage and is usually expressed in milli



volts or as a percentage of Vo. Temperature stability or average temperature coefficient of

output voltage (TC Vo) is the change in output voltage per unit change in temperature and

is expressed in either mV/ºC or parts per million (PPM/ºC). Ripple rejection is the measure

of a regulator’s ability to reject ripple voltage. It is usually expressed in decibels. The

smaller the values of line regulation, load regulation and temperature stability the better the

regulation.

5.5 Bit micro controller

The Micro controller is used for interface with FM receiver and 16*2 LCD and it

gives proper stepping pulses for displaying, by receiving serial data from FM receiver.

5.5.1 Introduction

Looking back into the history of microcomputers, one would at first come across

the development of microprocessor i.e. the processing element, and later on the peripheral

devices. The three basic elements-the CPU, I/O devices and memory-have developed in

distinct directions. While the CPU has been the proprietary item, the memory devices fall

into general-purpose category and the I/O devices may be grouped somewhere in-between.

The AT89S52 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 Atmel’s high-density nonvolatile memory technology and is

compatible with the industry-standard MCS-51 instruction set and pin out. The on-chip

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

nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a

monolithic chip, the Atmel AT89S52 is a powerful microcomputer, which provides a

highly flexible and cost-effective solution to many embedded control applications.

The AT89S52 provides for 8k EPROM/ROM, 256 bytes RAM and 32 I/O lines. It

also includes a universal asynchronous receive-transmit (UART) device, two 16-bit



Timer /counters and elaborate interrupt logic. Lack of multiply and divide instructions

which had been always felt in 8-bit microprocessors/micro controllers, has also been taken

care of in the AT89S52.Thus the AT89S52 may be called nearly equivalent of the

following devices on a single chip: 8085 + 8255 + 8251 + 8253 + 2764 + 6116.

In short, the AT89S52 has the following on-chip facilities:

8k ROM (EPROM on 8751)

256 byte RAM

UART

32 input-output port lines

Two, 16-bit timer/counters

Six interrupt sources and

On-chip clock oscillator and power on reset circuitry



Fig 5.7 AT89S52 internal block diagram



5.5.2 Special salient features

The 89S52 can be configured to bypass the internal 8 k ROM and run solely with

external program memory. For this its external access (EA) pin has to be grounded, which

makes it equivalent to 8031. The program store enable (PSEN) signal acts as read pulse for

program memory. The data memory is external only and a separate RD* signal is available

for reading its contents. Use of external memory requires that three of its 8-bit ports (out of

four) are configured to provide data/address multiplexed bus. Hi address bus and control

signals related to external memory use. The RXD and TXD ports of UART also appear on

pins 10 and 11 of 8051 and 8031, respectively. One 8-bit port, which is bit addressable and

extremely useful for control applications.

The UART utilizes one of the internal timers for generation of baud rate. The

crystal used for generation of CPU clock has therefore to be chosen carefully. The 11.0596

MHz crystals; available abundantly, can provide a baud rate of 9600. The 256-byte address

space is utilized by the internal RAM and special function registers (SFRs) array which is

separate from external data RAM space of 64k. The 00-7F space is occupied by the RAM

and the 80 - FF space by the SFRs. The 256 byte internal RAM has been utilized in the

following fashion:

00-IF: Used for four banks of eight registers of 8-bit each. The four banks may be selected

by software any time during the program.

20-2F: The 16 bytes may be used as 128 bits of individually addressable

locations. These are extremely useful for bit oriented programs.

30- 7F: This area is used for temporary storage, pointers and stack. On reset, the

stack starts at 08 and gets incremented during use.

The list of special function registers along with their hex addresses is given .



Adder. Port/Register

80 P0 (Port 0)

81 SP (stack pointer)

82 DPH (data pointer High)

83 DPL (data pointer Low)

88 TCON (timer control)

89 TMOD (timer mode)

8A TLO (timer 0 low byte)

8B TL1 (timer 1 low byte)

8C TH0 (timer 0 high byte)

8D TH1 (timer 1 high byte)

90 P1 (port 1)

98 SCON (serial control)

99 SBUF (serial buffer)

A0 P2 (port 2)

A8 Interrupt enable (IE)

B0 P3 (port 3)

B8 Interrupt priority (IP)

D0 Processor status word (PSW)

E0 Accumulator (ACC)

F0 B register

Table 5.1 AT89S52 Address registers



5.5.3 Hardware details

The on chip oscillator of 89S52 can be used to generate system clock. Depending

upon version of the device, crystals from 3.5 to 12 MHz may be used for this purpose. The

system clock is internally divided by 6 and the resultant time period becomes one processor

cycle. The instructions take mostly one or two processor cycles to execute, and very

occasionally three processor cycles. The ALE (address latch enable) pulse rate is 16th of

the system clock, except during access of internal program memory, and thus can be used

for timing purposes.

AT89S52 Serial port pins

PIN ALTERNATE USE SFR

P3.ORXD Serial data input SBUF

P3.ITXD Serial data output SBUF

P3.2INTO External interrupt 0 TCON-1

P3.3INT1 External interrupt 1 TCON- 2

P3.4TO External timer 0 input TMOD

P3.5T1 External timer 1 input TMOD

P3.6WR External memory write pulse ---------

P3.7RD External memory read pulse ----

Table 5.2 AT89S52 serial port pins

The two internal timers are wired to the system clock and pre scaling factor is

decided by the software, apart from the count stored in the two bytes of the timer control

registers. One of the counters, as mentioned earlier, is used for generation of baud rate

clock for the UART. It would be of interest to know that the 8052 have a third timer, which



is usually used for generation of baud rate. The reset input is normally low and taking it

high resets the micro controller, in the present hardware, a separate CMOS circuit has been

used for generation of reset signal so that it could be used to drive external devices as well.

Writing the software:

The 89S52 has been specifically developed for control applications. As mentioned

earlier, out of the 256 bytes of internal RAM, 16 bytes have been organized in such a way

that all the 256 bits associated with this group may be accessed bit wise to facilitate their

use for bit set/reset/test applications. These are therefore extremely useful for programs

involving individual logical operations. One can easily give example of lift for one such

application where each one of the floors, door condition, etc may be depicted by a single

hit.

The 89S52 has instructions for bit manipulation and testing. Apart from these, it has

8-bit multiply and divide instructions, which may be used with advantage. The 89S52 has

short branch instructions for 'within page' and conditional jumps, short jumps and calls

within 2k memory space which are very convenient, and as such the controller seems to

favor programs which are less than 2k byte long. Some versions of 8751 EPROM devices

have a security bit which can be programmed to lock the device and then the contents of

internal program EPROM cannot be read. The device has to be erased in full for further

alteration, and thus it can only be reused but not copied. EEPROM and FLASH memory

versions of the device are also available now. The terms used in micro controller are

Memory unit:

Memory is part of the micro controller whose function is to store data. The easiest

way to explain it is to describe it as one big closet with lots of drawers. If we suppose that

we marked the drawers in such a way that they cannot be confused, any of their contents

will then be easily accessible. It is enough to know the designation of the drawer and so its

contents will be known to us for sure.

Memory components are exactly like that. For a certain input we get the contents of

a certain addressed memory location and that’s all. Two new concepts are brought to us



addressing and memory location. Memory consists of all memory locations, and addressing

is nothing but selecting one of them. This means that we need to select the desired memory

location on one hand, and on the other hand we need to wait for the contents of that

location. Besides reading from a memory location, memory must also provide for writing

onto it. This is done by supplying an additional line, called control line. We will designate

this line as R/W (read/write). Control line is used in the following way: if r/w=1, reading is

done, and if opposite is true then writing is done on the memory location. Memory is the

first element, and we need a few operation of our micro controller.

Central Processing Unit:

Let add 3 more memory locations to a specific block that will have a built in

capability to multiply, divide, subtract, and move its contents from one memory location

onto another. The part we just added in is called “central processing unit” (CPU). Its

memory locations are called registers. Registers are therefore memory locations whose role

is to help with performing various mathematical operations or any other operations with

data wherever data can be found. Look at the current situation. We have two independent

entities (memory and CPU), which are interconnected, and thus any exchange of data is

hindered, as well as its functionality. If, for example, we wish to add the contents of two

memory locations and return the result again back to memory, we would need a connection

between memory and CPU. Simply stated, we must have some “way” through data goes

from one block to another.

Bus:

The system which connects the data between two units is called “bus”. Physically, it

represents a group of 8, 16, or more wires. There are two types of buses: address and data

bus. The first one consists of as many lines as the amount of memory we wish to address

and the other one is as wide as data, in our case 8 bits or the connection line. First one

serves to transmit address from CPU memory, and the second to connect all blocks inside

the micro controller.



Input-output unit:

Those locations we’ve just added are called “ports”. There are several types of

ports: input, output or bi-directional ports. When working with ports, first of all it is

necessary to choose which port we need to work with, and then to send data to, or take it

from the port. When working with it the port acts like a memory location. Something is

simply being written into or read from it, and it could be noticed on the pins of the micro-

controller.

5.6 CURRENT TRANSFORMER

A current transformer is defined as "as an instrument transformer in which the secondary

current is substantially proportional to the primary current (under normal conditions of

operation) and differs in phase from it by an angle which is approximately zero for an

appropriate direction of the connections." This highlights the accuracy requirement of the

current transformer but also important is the isolating function, which means no matter

what the system voltage the secondary circuit need be insulated only for a low voltage.

The current transformer works on the principle of variable flux. In the "ideal" current

transformer, secondary current would be exactly equal (when multiplied by the turn’s ratio)

and opposite of the primary current. But, as in the voltage transformer, some of the primary

current or the primary ampere-turns are utilized for magnetizing the core, thus leaving less

than the actual primary ampere turns to be "transformed" into the secondary ampere-turns.

This naturally introduces an error in the transformation. The error is classified into two-the

current or ratio error and the phase error.

Following are the salient features

1. Smaller Dimensions

2. Light weight

3. Low Stray magnetic fields

4. Compact



Fig 5.8 Current Transformer and its Schematic diagram

Ratings - Primary is wounded with 19 SWG copper enameled wire, similarly secondary is

wounded with 30 SWG copper enameled wire

Ratio = 1 : 50 Primary No. of Turns = 1

Secondary No. or Turns = 250 Primary Current = 50A

Secondary Current = 5A SWG = Standard wire guage

Core type = Toroidal 17

5.7 LCD display

LCDs can add a lot to your application in terms of providing an useful interface for the

user, debugging an application or just giving it a "professional" look. The most common

type of LCD controller is the Hitachi 44780, which provides a relatively simple interface

between a processor and an LCD. Inexperienced designers do often not attempt using this

interface and programmers because it is difficult to find good documentation on the

interface, initializing the interface can be a problem and the displays themselves are

expensive.

As you would probably guess from this description, the interface is a parallel bus, allowing

simple and fast reading/writing of data to and from the LCD. This waveform will write an

ASCII Byte out to the LCD's screen. The ASCII code to be displayed is eight bits long and

is sent to the LCD either four or eight bits at a time. If four bit mode is used, two "nybbles"



of data (Sent high four bits and then low four bits with an "E" Clock pulse with each

nybble) are sent to make up a full eight bit transfer. The "E" Clock is used to initiate the

data transfer within the LCD.

Pins Description

1 Ground

2 Vcc

3 Contrast Voltage

4 "R/S" _Instruction/Register Select

5 "R/W" _Read/Write LCD Registers

6 "E" Clock

7 – 14 Data I/O Pins

Table 5.3 LCD Description Table

Fig 5.9 LCD write waveform Fig 5.10 LCD screen



Sending parallel data as either four or eight bits are the two primary modes of

operation. While there are secondary considerations and modes, deciding how to send the

data to the LCD is most critical decision to be made for an LCD interface application.

Eight bit mode is best used when speed is required in an application and at least ten

I/O pins are available. Four bit mode requires a minimum of six bits. To wire a

microcontroller to an LCD in four bit mode, just the top four bits (DB4-7) are written to.

The "R/S" bit is used to select whether data or an instruction is being transferred

between the microcontroller and the LCD. If the Bit is set, then the byte at the current LCD

"Cursor" Position can be read or written. When the Bit is reset, either an instruction is

being sent to the LCD or the execution status of the last instruction is read back (whether or

not it has completed).

Reading Data back is best used in applications which required data to be moved

back and forth on the LCD (such as in applications which scroll data between lines). The

"Busy Flag" can be polled to determine when the last instruction that has been sent has

completed processing. In most applications, I just tie the "R/W" line to ground because I

don't read anything back. This simplifies the application because when data is read back,

the micro controller I/O pins have to be alternated between input and output modes.

For most applications, there really is no reason to read from the LCD. I usually tie

"R/W" to ground and just wait the maximum amount of time for each instruction (4.1

msecs for clearing the display or moving the cursor/display to the "home position", 160

usecs for all other commands). As well as making my application software simpler, it also

frees up a micro controller pin for other uses. Different LCDs execute instructions at

different rates and to avoid problems later on (such as if the LCD is changed to a slower

unit), I recommend just using the maximum delays given above.



The different instructions available for use with the 44780 are shown in the table below:

R/S R/W D7 D6 D5 D4 D3 D2 D1 D0 Instruction/Description

4 5 14 13 12 11 10 9 8 7 Pins

0 0 0 0 0 0 0 0 0 1 Clear Display

0 0 0 0 0 0 0 0 1 * Return Cursor and LCD to Home Position

0 0 0 0 0 0 0 1 ID S Set Cursor Move Direction

0 0 0 0 0 0 1 D C B Enable Display/Cursor

0 0 0 0 0 1 SC RL * * Move Cursor/Shift Display

0 0 0 0 1 DL N F * * Set Interface Length

0 0 0 1 A A A A A A Move Cursor into CGRAM

0 0 1 A A A A A A A Move Cursor to Display

0 1 BF * * * * * * * Poll the "Busy Flag"

1 0 D D D D D D D DWrite a Character to the Display at the Current Cursor

Position

1 1 D D D D D D D DRead the Character on the Display at the Current Cursor

Position

Table 5.4 Different instructions of 44780

The LCD can be thought of as a "Teletype" display because in normal operation,

after a character has been sent to the LCD, the internal "Cursor" is moved one character to



the right. The "Clear Display" and "Return Cursor and LCD to Home Position" instructions

are used to reset the Cursor's position to the top right character on the display. To move the

Cursor, the "Move Cursor to Display" instruction is used. For this instruction, bit 7 of the

instruction byte is set with the remaining seven bits used as the address of the character on

the LCD the cursor is to move to. These seven bits provide 128 addresses, which matches

the maximum number of LCD character addresses available. The table above should be

used to determine the address of a character offset on a particular line of an LCD display.

Fig 5.11 LCD cursor

The last aspect of the LCD to discuss is how to specify a contrast voltage to the

Display. I typically use a potentiometer wired as a voltage divider. This will provide an

easily variable voltage between Ground and Vcc, which will be used to specify the contrast

(or "darkness") of the characters on the LCD screen. You may find that different LCDs

work differently with lower voltages providing darker characters in some and higher

voltages do the same thing in others.



There are a variety of different ways of wiring up an LCD. Above, I noted that the

44780 can interface with four or eight bits. To simplify the demands in microcontrollers, a

shift register is often used (as is shown in the diagram below) to reduce the number of I/O

pins to three.

Fig 5.12 Shift Register Led data write Fig 5.13 LCD contrast circuit

In the diagram to the right, I have shown how the shift register is written to for this

circuit to work. Before data can be written to it, the shift register is cleared by loading

every latch with zeros. Next, a "1" (to provide the "E" Gate) is written followed by the

"R/S" bit and the four data bits. Once the is loaded in correctly, the "Data" line is pulsed to

Strobe the "E" bit. The biggest difference between the three wire and two wire interface is

that the shift register has to be cleared before it can be loaded and the two wire operation

requires more than twice the number of clock cycles to load four bits into the LCD.

5.8 Analog to Digital Converter

The ADC0808 and ADC0809 each consists of an analog signal multiplexer, an 8-bit

successive-approximation converter, and related control and output circuitry.

5.8.1 Multiplexer

The analog multiplexer selects 1 of 8 single-ended input channels as determined by

the address decoder. Address load control loads the address code into the decoder on a low-

to-high transition. The output latch is reset by the positive-going edge of the start pulse.



Fig 5.14 Functional block diagram of ADC

Fig 5.15 Functional Table of ADC

Sampling also starts with the positive-going edge of the start pulse and lasts for 32

clock periods. The conversion process may be interrupted by a new start pulse before the

end of 64 clock periods. The previous data will be lost if a new start of conversion occurs

before the 64thclock pulse. Continuous conversion may be accomplished by connecting the

end-of-conversion output to the start input. If used in this mode, an external pulse should be

applied after power up to assure start up.



5.8.2 Converter

The CMOS threshold detector in the successive-approximation conversion system

determines each bit by examining the charge on a series of binary-weighted capacitors

(Figure 5.16). In the first phase of the conversion process, the analog input is sampled by

closing switch SC and all ST switches, and by simultaneously charging all the capacitors to

the input voltage. In the next phase of the conversion process, all ST and SC switches are

opened and the threshold detector begins identifying bits by identifying the charge

(voltage) on each capacitor relative to the reference voltage. In the switching sequence, all

eight capacitors are examined separately until all 8 bits are identified, and then the charge-

convert sequence is repeated. in the first step of the conversion phase, the threshold

detector looks at the first capacitor (weight = 128). Node 128 of this capacitor is switched

to the reference voltage, and the equivalent nodes of all the other capacitors on the ladder

are switched to REF–. If the voltage at the summing node is greater than the trip-point of

the threshold detector (approximately one-half the VCC voltage), a bit is placed in the

output register, and the 128-weight capacitor is switched to REF–. If the voltage at the

summing node is less than the trip point of the threshold detector, this 128-weight capacitor

remains connected to REF+ through the remainder of the capacitor-sampling (bit-counting)

process. The process is repeated for the 64-weight capacitor, the 32-weight capacitor, and

so forth down the line, until all bits are counted. With each step of the capacitor-sampling

process, the initial charge is redistributed among the capacitors.

Fig 5.16 Simplified Model of the Successive-Approximation System



5.8.3 555 timer

The 555 timer is one of the most remarkable integrated circuits ever developed. It

comes in a single or dual package and even low power CMOS versions exist - ICM7555.

Common part numbers are LM555, NE555, LM556, NE556. The 555 timer consists of two

voltage comparators, a bi-stable flip flop, a discharge transistor, and a resistor divider

network.

The 555 monolithic timing circuits as a "highly stable controller capable of

producing accurate time delays, or oscillation. In the time delay mode of operation, the

time is precisely controlled by one external resistor and capacitor. For a stable operation as

an oscillator, the free running frequency and the duty cycle are both accurately controlled

with two external resistors and one capacitor. The circuit may be triggered and reset on

falling waveforms, and the output structure can source or sink up to 200mA."

Applications:

Applications include precision timing, pulse generation, sequential timing, time

delay generation and pulse width modulation (PWM).

5.8.4. Pin Functions - 8 pin package

Ground (Pin 1) - Not surprising this pin is connected directly to ground.

Trigger (Pin 2) - This pin is the input to the lower comparator and is used to set the latch,

which in turn causes the output to go high.

Output (Pin 3) - Output high is about 1.7V less than supply. Output high is capable of

Isource up to 200mA while output low is capable of Isink up to 200mA.

Reset (Pin 4) - This is used to reset the latch and return the output to a low state. The reset

is an overriding function. When not used connect to V+.



Control (Pin 5) - Allows access to the 2/3V+ voltage divider point when the 555 timer is

used in voltage control mode. When not used connect to ground through a 0.01 uF

capacitor.

Threshold (Pin 6) - This is an input to the upper comparator. See data sheet for

comprehensive explanation.

Discharge (Pin 7) - This is the open collector to Q14 in figure 4 below. See data sheet for

comprehensive explanation.

V+ (Pin 8) - This connects to Vcc and the Philips data book states the ICM7555 cmos

version operates 3V - 16V DC while the NE555 version is 3V - 16V DC. Note comments

about effective supply filtering and bypassing this pin below under "General considerations

with using a 555 timer"

5.8.5 555 Timer in Astable operation

When configured as an oscillator the 555 timer is configured as in figure 3.5 below.

This is the free running mode and the trigger is tied to the threshold pin. At power-up, the

capacitor is discharged, holding the trigger low. This triggers the timer, which establishes

the capacitor charge path through Ra and Rb. When the capacitor reaches the threshold

level of 2/3 Vcc, the output drops low and the discharge transistor turns on. The timing

capacitor now discharges through Rb. When the capacitor voltage drops to 1/3 Vcc, the

trigger comparator trips, automatically retriggering the timer, creating an oscillator whose

frequency is determined by the formula in figure 5.17



Fig 5.17 555 timer in Astable operation

There are difficulties with duty cycle here and I will deal with them below. It should

also be noted that a minimum value of 3K should be used for Rb.

Fig 5.18 Modified Duty Cycle in Astable Operation

Here two signal diodes (1N914 types) have been added. This circuit is best used at Vcc =

15V.

General considerations with using a 555 timer:

Most devices will operate down to as low as 3V DC supply voltage. However

correct supply filtering and bypassing is critical, a capacitor between .01uF to 10uF



(depending upon the application) should be placed as close as possible to the 555 timer

supply pin. Owing to internal design considerations the 555 timer can generate large

current spikes on the supply line.

While the 555 timer will operate up to about 1 MHz it is generally recommended it

not be used beyond 500 KHz owing to temperature stability considerations.

Owing to low leakage capacitor considerations limit maximum timing periods to no

more than 30 minutes.

5.8.6 External components when using a 555 timer

Care should be taken in selecting stable resistors and capacitors for timing

components in the 555 timer. Also the data sheet should be consulted to determine

maximum and minimum component values which will affect accuracy. Capacitors must be

low leakage types with very low Dielectric Absorption properties. Electrolytics and

Ceramics are not especially suited to precision timing applications.

This analog to digital converter (ADC) converts a continuous analog input signal,

into an n-bit binary number, which is easily acceptable to a computer.

As the input increases from zero to full scale, the output code stair steps. The width

of an ideal step represents the size of the least significant Bit (LSB) of the converter and

corresponds to an input voltage of VES/2n for an n-bit converter. Obviously for an input

voltage range of one LSB, the output code is constant. For a given output code, the input

voltage can be anywhere within a one LSB quantization interval. An actual converter has

integral linearity and differential linearity errors. Differential linearity error is the

difference between the actual code-step width and one LSB. Integral linearity error is a

measure of the deviation of the code transition points from the fitted line.



Fig 5.19 Equivalent Schematic of 555 timer

The errors of the converter are determined by the fitting of a line through the code

transition points, using least square fit, the terminal point method, or the zero base

technique to provide the reference line. A good converter will have less than 0.5 LSB

linearity error and no missing codes over its full temperature range. In the basic conversion

scheme of ADC, the un-known input voltage VX is connected to one input of an analog

signal comparator, and a time dependant reference voltage VR is connected to the other

input of the comparator. In this project work ADC 0809 (8 Bit A/D converter) is used to

convert an analog voltage of Instrumentation amplifier output in to an output binary word

that can be used by a computer. The following is the block diagram of A/D converter along

with associated buffers and latches.



Fig 5.20 A/D converter associated buffers and latches

5.9 Clock generator

The clock generator circuit is designed using 555 Timer IC. This IC is configured

in Astable Mode of operation (free running oscillator). The frequency can be adjusted

using external resistor and capacitor. The required frequency is more than 100 KHz. The

output of this IC is fed to the A - D converter.

5.9.1 Application of Clock Generator

*Wireless security systems

*Car Alarm systems

*Remote controls.

*Sensor reporting

*Automation systems

5.10 ASK Hybrid transmitter module

5.10.1 General Description

The ST-TX01-ASK is an ASK Hybrid transmitter module. ST-TX01-ASK is designed by

the Saw Resonator, with an effective low cost, small size, and simple-to-use for designing.



Frequency Range: 315 / 433.92 MHZ.

Supply Voltage: 3~12V.

Gain: 4~16dBm

5.10.2 Absolute Maximum Rating Specifications

Unit Min. Typical. Max.

Operation Voltage (V) 3 5V 12V

Frequency (MHz) 315 434

Gain (dB) 4 10 16

Supply current (mA) 11 20 57

DATA 5V

Data Rate 1Kbps

Tune on Time Ton Data start out by Vcc turn on 10- 20 ms

Data Rate (bps) 200 1k 3k

InputVcc=5V;

Outputduty=40-60%

Temperature= -10 to +60ºC.



Fig 5.21 315/434MHz Transmitter Module Fig 5.22 Pin Description

Fig 5.23 315/434MHz Receiver Module Fig 5.24 Pin Description of Receiver Module

Fig 5.25 RF receiver interface with micro controller unit



RF transmitters are electronic devices that create continuously varying electric

current, encode sine waves, and broadcast radio waves. RF transmitters use oscillators to

create sine waves, the simplest and smoothest form of continuously varying waves, which

contain information such as audio and video. Modulators encode these sign waves and

antennas broadcast them as radio signals. There are several ways to encode or modulate

this information, including amplitude modulation (AM) and frequency modulation (FM).

Radio techniques limit localized interference and noise. With direct sequence

spread spectrum, signals are spread over a large band by multiplexing the signal with a

code or signature that modulates each bit. With frequency hopping spread spectrum, signals

move through a narrow set of channels in a sequential, cyclical, and predetermined pattern.

Selecting RF transmitters requires an understanding of modulation methods such as AM

and FM. On-off key (OOK), the simplest form of modulation, consists of turning the signal

on or off. Amplitude modulation (AM) causes the baseband signal to vary the amplitude or

height of the carrier wave to create the desired information content. Frequency modulation

(FM) causes the instantaneous frequency of a sine wave carrier to depart from the center

frequency by an amount proportional to the instantaneous value of the modulating signal.

Amplitude shift key (ASK) transmits data by varying the amplitude of the transmitted

signal. Frequency shift key (FSK) is a digital modulation scheme using two or more output

frequencies. Phase shift key (PSK) is a digital modulation scheme in which the phase of the

transmitted signal is varied in accordance with the baseband data signal.

Additional considerations when selecting RF transmitters include supply voltage, supply

current, RF connectors, special features, and packaging. Some RF transmitters include

visual or audible alarms or LED indicators that signal operating modes such as power on or

reception. Other devices attach to coaxial cables or include a connector or port to which an

antenna can be attached. Typically, RF transmitters that are rated for outdoor use feature a

heavy-duty waterproof design. Devices with internal calibration and a frequency range

switch are also available. RF transmitters are used in a variety of applications and

industries. Often, devices that are used with integrated circuits (ICs) incorporate surface



mount technology (SMT), through hole technology (THT), and flat pack. In the

telecommunications industry, RF transmitters are designed to fit in a metal rack that can be

installed in a cabinet. RF transmitters are also used in radios and in electronic article

surveillance systems (EAS) found in retail stores. Inventory management systems use RF

transmitters as an alternative to barcodes.

5.10.3 ST-TX01-ASK (Saw Type)

General Description:

The ST-TX01-ASK is an ASK Hybrid transmitter module.

ST-TX01-ASK is designed by the Saw Resonator, with an effective low cost, small size,

and simple-to-use for designing.

Fig 5.26 Transmitter circuit

Frequency range: 315/433.92MHZ

315/434 MHz ASK Transmitter

Supply Voltage: 3~12V.

Gain : 4~16dB.

Circuit Shape: Saw



5.10.4 Features

Extremely low power operation

Low external part count

Receiver input frequency: 290 – 460 MHz

On-chip VCO with integrated PLL using crystal oscillator reference

PLL power down feature

Integrated IF and data filters

SSOP-24 package (0.64 mm pitch)

5.10.5 Applications

Mouse

Video sender remote controller

Car alarm and home security systems



Table 5.5 Electrical characteristics of ST-TX01-ASK (Saw Type)


Characteristics Min type max unit

Vcc Supply voltage 5 VDC

Is Supply current 2.3 3 Ma

FR RECIVER FREQUENCY 315/434 MHZ

RF SENSITEY(vcc=5v 1kbps data rate)

-105 dBm

Max data rate 300 1 3 Kbit/s

VOH HIGH LEVEL OUTPUT(I=30uA)

0.7Vcc VDC

VOL LOW LEVEL OUTPUT(I=30Ua)

0.3Vcc VDC

TURN ON TIME(VCC OFF-TURN ON)

53 30 ms

TOP OPERATURE TEMPRATURE RATING

-10 60 C

OUTPUY DUTY 40 60 %


6. CONCLUSION

This contact less load measuring meter is successfully constructed and tested .The

current we can measure in the circuit is up to 50A the rating of the current transformer is

50/5A the voltage we can apply in the circuit up to 230volts for the house hold purpose. In

these we can measure the load in the transmitter and it is send to the receiver .Which can be

used up to the distance 10mts apart.

Here in this prototype we have the current transformer, microcontrollers and ADC

converter this is the best real time application to measure the load. However it is used to

measure the current in the particular line or pole.

The load measuring range of this prototype is greater than or equal to 60watts



7. REFERENCES

1. "Atmel’s Self-Programming Flash Microcontrollers" by Odd Jostein Svendsli 2003.

2. Allen, Phillip .E; Holberg, Douglas R., CMOS Analog Circuit Design

3. Kester, Walt, ed. (2005), The Data Conversion Handbook, Elsevier: Newnes.

4. Huang, Han-Way (2009). The HCS12 / 9S12: An Introduction to Software and Hardware

Interfacing (2nd ed.), Delmar Cengage Learning.

5. K. Kondo, H. Terao, H. Abe, M. Ohta, K. Suzuki, T. Sasaki, G. Kawachi, J. Ohwada,

Liquid crystal display device, filed Sept. 18, 1992 and Jan. 20, 1993.

6. Basic Operational Amplifiers and Linear Integrated Circuits; 2nd Ed; Thomas L Floyd;

David Buchla, 1998.

7. Op-Amps and Linear Integrated Circuits; 4th Ed; Ram Gayakwad; 543 pages; 1999.

8. Jung, Walter G. (1983) "IC Timer Cookbook, Second Edition", pp. 40–41. Sams

Technical Publishing, 2nd edition.

9. Cyril W. Lander, Power Electronics third edition, McGraw Hill, 1993.

10. http://www.rason.org/Projects/swregdes/swregdes.htm

11. Datasheet of L78xx Showing a model that can output 1.5 Amps


http://www.rason.org/Projects/swregdes/swregdes.htm

http://www.analog.com/library/analogDialogue/archives/39-06/data_conversion_handbook.html

http://www.atmel.com/dyn/resources/prod_documents/doc2464.pdf

Documents

2modified Main Project Contactless Load Measuring