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Contact less load Measurement Meter
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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
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
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
CMRCET-B. Tech 2 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
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.
CMRCET-B. Tech 3 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER 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
CMRCET-B. Tech 4 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
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.
CMRCET-B. Tech 5 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
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.
CMRCET-B. Tech 6 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
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
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CONTACT LESS LOAD MEASURING METER FOR POWER LINES
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.
CMRCET-B. Tech 8 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
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.
CMRCET-B. Tech 9 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
Fig 4.3 Digital tong testers
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CONTACT LESS LOAD MEASURING METER FOR POWER LINES
5. PROTOTYPE OF CONTACT LESS LOAD MEASURING METER
Fig 5.1 Photograph of the contact less load measuring meter
CMRCET-B. Tech 11 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
5.1 Block Diagrams
Fig 5.2 Block Diagrams of Transmitting System
Fig 5.3 Block Diagrams of Receiving System
CMRCET-B. Tech 12 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
5.2 Circuit Diagrams
Fig 5.4 Transmitting System Circuit Diagram
Fig 5.5 Receiving system Circuit Diagram
CMRCET-B. Tech 13 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
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.
CMRCET-B. Tech 14 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
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
CMRCET-B. Tech 15 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
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
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CONTACT LESS LOAD MEASURING METER FOR POWER LINES
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
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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
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CONTACT LESS LOAD MEASURING METER FOR POWER LINES
Fig 5.7 AT89S52 internal block diagram
CMRCET-B. Tech 19 Department of EEE
CONTACT LESS LOAD MEASURING METER FOR POWER LINES
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 .
CMRCET-B. Tech 20 Department of EEE
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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
CMRCET-B. Tech 21 Department of EEE
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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
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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
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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.
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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
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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"
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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
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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.
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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
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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.
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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.
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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.
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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
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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+.
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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
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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
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(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.
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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.
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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.
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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.
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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
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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
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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
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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
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Table 5.5 Electrical characteristics of ST-TX01-ASK (Saw Type)
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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 %
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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
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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
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Recommended