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POWER LINE MONITORING &PROTECTION
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Contents
Introduction
Linear Power Supply
Rectifiers
Regulators
PIC Microcontroller Interfacing a PIC with a LCD
Relay
Conclusion
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There is a need to monitor the voltage,current & frequency to protect devices fromvariation of these parameters. Our device is
based on PIC16F877A microcontroller & itmonitors voltage, frequency & current & ifthese parameters go below or above theset limit a relay is turned ON which can be
used to cut the power till the parametersreturn back to normal
Introduction
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Block Diagram
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Linear Power Supply:
An AC powered linear power supplyusually uses a transformer to convertthe voltage from the wall outlet(mains) to a different, usually a lowervoltage.
To produce DC, a rectifier is used. A
capacitor is used to smooth thepulsating current from the rectifier.
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Rectifiers
A rectifier is an electrical device thatconverts alternating current (AC) todirect current (DC), a process knownas rectification. Rectifiers have manyuses including as components ofpower supplies and as detectors of
radio signals
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Regulators:
Regulator (automatic control) is adevice which has the function ofmaintaining a designatedcharacteristic. A voltage regulator isan electrical regulator designed toautomatically maintain a constant
voltage level.
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PIC Microcontroller
PIC16F877A is a small piece of semiconductorintegrated circuits. The package type of thisintegrated circuits is DIP package
Additional components that you need to make this ICwork are just a 5V power supply adapter, a 20MHzcrystal oscillator and 2 units of 22pF capacitors.
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Core Architecture:
The PIC architecture is distinctively minimalist. Itis characterized by the following features:
Separate code and data spaces (Harvardarchitecture)
A small number of fixed length instructions Most instructions are single cycle execution A single accumulator (W), the use of which (as
source operand) is implied (i.e. is not encodedin the opcode)
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Core Architecture:
All RAM locations function as registers as both sourceand/or destination of math and other functions.
A hardware stack for storing return addresses
A fairly small amount of addressable data space
(typically 256 bytes), extended through banking Data space mapped CPU, port, and peripheral
registers
The program counter is also mapped into the dataspace and writable (this is used to implement indirect
jumps).
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Data Space (RAM):PICs have a set of registers that function as general purposeRAM. Special purpose control registers for on-chip hardwareresources are also mapped into the data space.
Code space:
All PICs feature Harvard architecture, so the code space and thedata space are separate. PIC code space is generallyimplemented as EPROM, ROM, or flash ROM.
Word Size:The word size of PICs can be a source of confusion. All PICshandle (and address) data in 8-bit chunks, so they should becalled 8-bit microcontrollers
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Stacks:
PICs have a hardware call stack,which is used to save returnaddresses. The hardware stack is notsoftware accessible on earlierdevices, but this changed with the 18series devices.
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Instruction Set
The instruction set includesinstructions to perform a variety ofoperations on registers directly, theaccumulator and a literal constant orthe accumulator and a register, aswell as for conditional execution, and
program branching.
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In general, PIC instructions fall into 5 classes:
Operation on W with 8-bit immediate ("literal")operand (movlw)(and lw).
Operation with W and indexed register (addwfreg,w)
( addwfreg,f) Bit operations (set or clear a bit, and test and skip on
set/clear )
Control transfers (goto and call )
Zero Operand Instructions(return from subroutine,
and sleep to enter low-power mode)
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Pin Diagram
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5 sets of input and output ports (total of 33ports)
Analog-digital converter of 10 bits of
resolution and 8 channels of entry Peripheral parallel and serial
communication (USART and MSSP)
CPC Modules
3 Timers (1 to 16 bits and 2 of 8 bits) Watchdog timer
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Keypad:
A KEYPAD is a set of buttons arranged in a block whichusually bear digits and other symbols but not a complete set ofalphabetical letters.
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LCD Display
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Interfacing a PIC with a LCD
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Relay:
A relay is an electrically operated switch. Current flowingthrough the coil of the relay creates a magnetic field whichattracts a lever and changes the switch contacts. The coilcurrent can be on or off so relays have two switch positions andthey are double throw (changeover) switches.
COM = Common, always connect to this, it is the moving part ofthe switch.
NC = Normally Closed, COM is connected to this when the relaycoil is off.
NO = Normally Open, COM is connected to this when the relaycoil is on.
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Choosing a Relay
Physical size and pin arrangement
Coil voltage
Coil resistance
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MP Lab Compiler
MPLAB C Compiler is a cross-compiler thatruns on a PC and produces code that canbe executed by the Microchip PIC18XXXX
family of microcontrollers.
ATMEL ISP:ATMEL Microcontroller can programming
with ISP(In-System Programming) whicheasy to develop the applications withoutinsert/remove microcontroller.
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Conclusion:
Increasing worldwide power demands aredriving an increase in the number of powerlines and power-line substations. As moreand more automated monitoring- and fault-detection systems are required, the trendwill be towards systems with a largenumber of channels. With multiple ADCs oneach board, efficient use of board area and
power dissipation become critical as systemdesigners try to reduce cost whileincreasing performance.
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