THREE PHASE INDUCTION MOTOR PROTECTION FROM SINGLE PHASING & OVER HEATING A Project Report Submitted in partial fulfillment of the requirement for the award of degree of
BACHELOR OF ENGINEERING In ELECTRICAL AND ELECTRONICS ENGINEERING
By
SHAIK JUNAID
1604-12-734-014
SHAIK MOHAMMED NASER
1604-12-734-037
ALLAM SRI SAI VAJRAANG
1604-12-734-052
Under the Guidance of Mrs. NAUSHEEN BANO Associate Professor
Electrical Engineering Department
1
Muffakham Jah College of Engineering & Technology (Affiliated to Osmania University) 2015-2016
INDEX
TOPICS
1. Certificates 2. Acknowledgement CHAPTER 1: INTRODUCTION
1.1
Introduction of the project
1.2
Project overview
1.3
Thesis
CHAPTER 2: EMBEDDED SYSTEMS
2.1 Introduction to embedded systems 2.2 Need of embedded systems 2.3 Explanation of embedded systems 2.4 Applications of embedded systems
CHAPTER 3: HARDWARE DESCRIPTION
2
3.1 Introduction with block diagram 3.2 Microcontroller 3.3 Regulated power supply 3.4 LED indicator 3.5 Voltage sensor 3.6 Optocoupler 3.7 Relay 3.8 LCD
CHAPTER 4: SOFTWARE DESCRIPTION
4.1 Express PCB 4.2 PIC C Compiler 4.3 Proteus software
4.4 Procedural steps for compilation, simulation and dumping CHAPTER 5: PROJECT DESCRIPTION
CHAPTER 6: ADVANTAGES, DISADVANTAGES AND APPLICATIONS
CHAPTER 7: RESULTS, CONCLUSION, FUTURE PROSPECTS
REFERENCES
3
CHAPTER 1: INTRODUCTION
1.1Introduction: The aim of this project is to construct a three phase fault monitor and prevention system using 8-bit microcontroller. The three phasing fault analysis to prevent faults the system automatically resets are required for critical loads and circuits. These are required because the normal overload protection doesn't trip on time. For large air-conditioning compressors, irrigation pumps these are sometimes, included. The purpose of this project is to develop an intelligent system that continuously monitors all the three phase voltages (High voltage AC) and if any of these three phases is disconnected then this system takes
the
preventive
action.
The 4
preventive
action
could
be
disconnecting the power supply immediately to the load by operating an electromagnetic relay. This system also alerts the user using visual alerts on the LCD display module. This system consists of three optically isolated high voltage sensors for sensing the presence of high voltage in the respective circuits. One of the voltage sensors is connected to phase line of the supply and the other is connected to neutral line. A microcontroller based control system continuously monitors the voltage in all the three phases of the power supply circuit. In ideal conditions all the three phases gets the same voltage. The visual indicators display the health status of all three phases (Red, Yellow and Green). But, when any of the phases gets disconnected then in such situations the microcontroller-based system alerts the user using LCD module.
1.2 Project Overview: An embedded system is a combination of software and hardware to perform a dedicated task. Some of the main devices used in embedded products are Microprocessors and Microcontrollers. Microprocessors are commonly referred to as general purpose processors as they simply accept the inputs, process it and give the output. In contrast, a microcontroller not only accepts the data as inputs but also manipulates it, interfaces the data with various devices, controls the data and thus finally gives the result. 5
The Microcontroller based automatic Single Phasing Preventing System for 3-phase Industrial Motors using PIC16F72 Microcontroller is an exclusive project that can be used to design and construct a single phasing monitor and prevention system using 8-bit microcontroller. The purpose of this project is to develop an intelligent system that continuously monitors all the three phase voltages (High voltage AC) and if any of these three phases is disconnected then this system takes
the
preventive
action.
The
preventive
action
could
be
disconnecting the power supply immediately to the load by operating an electromagnetic relay. This system also alerts the user using LCD Display system.
1.3 Thesis Overview: The thesis explains the implementation of “THREE PHASE INDUCTION MOTOR PROTECTION SYSTEM” using PIC16F72 microcontroller. The organization of the thesis is explained here with: 6
Chapter 1
Presents introduction to the overall thesis and the
overview of the project. In the project overview a brief introduction of THREE PHASE INDUCTION MOTOR PROTECTION SYSTEM” and its applications are discussed. Chapter 2
Presents the topic embedded systems. It explains the
about what is embedded systems, need for embedded systems, explanation of it along with its applications. Chapter 3
Presents the hardware description. It deals with the block
diagram of the project and explains the purpose of each block. In the same chapter the explanation of microcontrollers, power supplies, relay, LCD, voltage sensor, optocoupler are considered. Chapter 4
Presents the software description. It explains the
implementation of the project using PIC C Compiler software. Chapter 5 Presents the project description along with relay, voltage sensor, LCD modules interfacing to microcontroller. Chapter 6
Presents the advantages, disadvantages and applications
of the project. Chapter 7
Presents the results, conclusion and future scope of the
project.
CHAPTER 2: EMBEDDED SYSTEMS 7
2.1 Embedded Systems: An embedded system is a computer system designed to perform one or a few dedicated functions often with real-time computing constraints. It is embedded as part of a complete device often including hardware and mechanical parts. By contrast, a general-purpose computer, such as a personal computer (PC), is designed to be flexible and to meet a wide range of end-user needs. Embedded systems control many devices in common use today. Embedded systems are controlled by one or more main processing cores that are typically either microcontrollers or digital signal processors (DSP). The key characteristic, however, is being dedicated to handle a particular task, which may require very powerful processors. For example, air traffic control systems may usefully be viewed as embedded, even though they involve mainframe computers and dedicated regional and national networks between airports and radar sites. (Each radar probably includes one or more embedded systems of its own.) Since the embedded system is dedicated to specific tasks, design engineers can optimize it to reduce the size and cost of the product and increase the reliability and performance. Some embedded systems are mass-produced, benefiting from economies of scale. Physically embedded systems range from portable devices such as digital watches and MP3 players, to large stationary installations like traffic lights, factory controllers, or the systems controlling nuclear power plants. Complexity varies from low, with a single microcontroller chip, to very high with multiple units, peripherals and networks mounted inside a large chassis or enclosure. 8
In general, "embedded system" is not a strictly definable term, as most systems have some element of extensibility or programmability. For example, handheld computers share some elements with embedded systems such as the operating systems and microprocessors
which
power
them,
but
they
allow
different
applications to be loaded and peripherals to be connected. Moreover, even systems which don't expose programmability as a primary feature generally need to support software updates. On a continuum from "general purpose" to "embedded", large application systems will have subcomponents at most points even if the system as a whole is "designed to perform one or a few dedicated functions", and is thus appropriate to call "embedded". A modern example of embedded system is shown in fig: 2.1.
Fig 2.1:A modern example of embedded system Labeled parts include microprocessor (4), RAM (6), flash memory (7).Embedded systems programming is not like normal PC programming. In many ways, programming for an embedded system is 9
like programming PC 15 years ago. The hardware for the system is usually chosen to make the device as cheap as possible. Spending an extra dollar a unit in order to make things easier to program can cost millions. Hiring a programmer for an extra month is cheap in comparison. This means the programmer must make do with slow processors and low memory, while at the same time battling a need for efficiency not seen in most PC applications. Below is a list of issues specific to the embedded field. 2.1.1 History: In the earliest years of computers in the 1930–40s, computers were sometimes dedicated to a single task, but were far too large and expensive for most kinds of tasks performed by embedded computers of today. Over time however, the concept of programmable controllers evolved from traditional electromechanical sequencers, via solid state devices, to the use of computer technology. One of the first recognizably modern embedded systems was the Apollo Guidance Computer, developed by Charles Stark Draper at the MIT Instrumentation Laboratory. At the project's inception, the Apollo guidance computer was considered the riskiest item in the Apollo project as it employed the then newly developed monolithic integrated circuits to reduce the size and weight. An early mass-produced embedded system was the Autonetics D-17 guidance computer for the Minuteman missile, released in 1961. It was built from transistor logic and had a hard disk for main memory. When the Minuteman II went into production in 1966, the D-17 was replaced with a new computer that was the first high-volume use of integrated circuits. 2.1.2 Tools: 10
Embedded development makes up a small fraction of total programming. There's also a large number of embedded architectures, unlike the PC world where 1 instruction set rules, and the UNIX world where there's only 3 or 4 major ones. This means that the tools are more expensive. It also means that they're lowering featured, and less developed. On a major embedded project, at some point you will almost always find a compiler bug of some sort.
Debugging tools are another issue. Since you can't always run general programs on your embedded processor, you can't always run a debugger on it. This makes fixing your program difficult. Special hardware such as JTAG ports can overcome this issue in part. However, if you stop on a breakpoint when your system is controlling real world hardware (such as a motor), permanent equipment damage can occur. As a result, people doing embedded programming quickly become masters at using serial IO channels and error message style debugging.
2.1.3 Resources: To save costs, embedded systems frequently have the cheapest processors that can do the job. This means your programs need to be written as efficiently as possible. When dealing with large data sets, issues like memory cache misses that never matter in PC programming can hurt you. Luckily, this won't happen too often- use reasonably efficient algorithms to start, and optimize only when necessary. Of course, normal profilers won't work well, due to the same reason debuggers don't work well.
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Memory is also an issue. For the same cost savings reasons, embedded systems usually have the least memory they can get away with. That means their algorithms must be memory efficient (unlike in PC programs, you will frequently sacrifice processor time for memory, rather than the reverse). It also means you can't afford to leak memory. Embedded applications generally use deterministic memory techniques and avoid the default "new" and "malloc" functions, so that leaks can be found and eliminated more easily. Other resources programmers expect may not even exist. For example, most embedded processors do not have hardware FPUs (Floating-Point Processing Unit). These resources either need to be emulated in software, or avoided altogether.
2.1.4 Real Time Issues: Embedded systems frequently control hardware, and must be able to respond to them in real time. Failure to do so could cause inaccuracy in measurements, or even damage hardware such as motors. This is made even more difficult by the lack of resources available. Almost all embedded systems need to be able to prioritize some tasks over others, and to be able to put off/skip low priority tasks such as UI in favor of high priority tasks like hardware control. 2.2 Need For Embedded Systems: The uses of embedded systems are virtually limitless, because every day new products are introduced to the market that utilizes embedded computers in novel ways. In recent years, hardware such as microprocessors, microcontrollers, and FPGA chips have become much cheaper. So when implementing a new form of control,
12
it's wiser to just buy the generic chip and write your own custom software for it. Producing a custom-made chip to handle a particular task or set of tasks costs far more time and money. Many embedded computers even come with extensive libraries, so that "writing your own software"
becomes
a very
trivial task indeed.
From an
implementation viewpoint, there is a major difference between a computer and an embedded system. Embedded systems are often required to provide Real-Time response. The main elements that make embedded systems unique are its reliability and ease in debugging.
2.2.1 Debugging: Embedded debugging may be performed at different levels, depending on the facilities available. From simplest to most sophisticate they can be roughly grouped into the following areas:
Interactive resident debugging, using the simple shell provided by the embedded operating system (e.g. Forth and Basic)
External debugging using logging or serial port output to trace operation using either a monitor in flash or using a debug server like the Remedy Debugger which even works for heterogeneous multi core systems.
An in-circuit debugger (ICD), a hardware device that connects to the microprocessor via a JTAG or Nexus interface. This allows the operation of the microprocessor to be controlled externally, but is typically restricted to specific debugging capabilities in the processor.
An in-circuit emulator replaces the microprocessor with a simulated equivalent, providing full control over all aspects of the microprocessor. 13
A complete emulator provides a simulation of all aspects of the hardware, allowing all of it to be controlled and modified and allowing debugging on a normal PC.
Unless restricted to external debugging, the programmer can typically load and run software through the tools, view the code running in the processor, and start or stop its operation. The view of the code may be as assembly code or source-code.
Because an embedded system is often composed of a wide variety of elements, the debugging strategy may vary. For instance, debugging a software(and microprocessor) centric embedded system is different from debugging an embedded system where most of the processing is performed by peripherals (DSP, FPGA, co-processor). An increasing number of embedded systems today use more than one single
processor
core.
A
common
problem
with
multi-core
development is the proper synchronization of software execution. In such a case, the embedded system design may wish to check the data traffic on the busses between the processor cores, which requires very low-level debugging, at signal/bus level, with a logic analyzer, for instance.
2.2.2 Reliability: Embedded systems often reside in machines that are expected to run continuously for years without errors and in some cases recover by them if an error occurs. Therefore the software is usually developed and tested more carefully than that for personal computers, and unreliable mechanical moving parts such as disk drives, switches or buttons are avoided.
14
Specific reliability issues may include:
The system cannot safely be shut down for repair, or it is too inaccessible
to
repair.
Examples
include
space
systems,
undersea cables, navigational beacons, bore-hole systems, and automobiles.
The system must be kept running for safety reasons. "Limp modes" are less tolerable. Often backup
s is selected by an
operator. Examples include aircraft navigation, reactor control systems, safety-critical chemical factory controls, train signals, engines on single-engine aircraft.
The system will lose large amounts of money when shut down: Telephone switches, factory controls, bridge and elevator controls, funds transfer and market making, automated sales and service. A variety of techniques are used, sometimes in combination, to
recover from errors—both software bugs such as memory leaks, and also soft errors in the hardware:
Watchdog timer that resets the computer unless the software periodically notifies the watchdog
Subsystems with redundant spares that can be switched over to
software "limp modes" that provide partial function
Designing with a Trusted Computing Base (TCB) architecture[6] ensures a highly secure & reliable system environment
An
Embedded
encapsulation
Hypervisor for
any
is
able
subsystem
to
provide
component,
so
secure that
a
compromised software component cannot interfere with other subsystems, encapsulation
or
privileged-level
keeps
faults 15
from
system
software.
propagating
from
This one
subsystem to another, improving reliability. This may also allow a subsystem to be automatically shut down and restarted on fault detection.
Immunity Aware Programming
2.3 Explanation of Embedded Systems: 2.3.1 Software Architecture: There are several different types of software architecture in common use.
Simple Control Loop:
In this design, the software simply has a loop. The loop calls subroutines, each of which manages a part of the hardware or software.
Interrupt Controlled System:
Some embedded systems are predominantly interrupt controlled. This means that tasks performed by the system are triggered by different kinds of events. An interrupt could be generated for example by a timer in a predefined frequency, or by a serial port controller receiving a byte. These kinds of systems are used if event handlers need low latency and the event handlers are short and simple. Usually these kinds of systems run a simple task in a main loop also, but this task is not very sensitive to unexpected delays. Sometimes the interrupt handler will add longer tasks to a queue structure. Later, after the interrupt handler has finished, these
16
tasks are executed by the main loop. This method brings the system close to a multitasking kernel with discrete processes.
Cooperative Multitasking:
A non-preemptive multitasking system is very similar to the simple control loop scheme, except that the loop is hidden in an API. The programmer defines a series of tasks, and each task gets its own environment to “run” in. When a task is idle, it calls an idle routine, usually called “pause”, “wait”, “yield”, “nop” (stands for no operation), etc.The advantages and disadvantages are very similar to the control loop, except that adding new software is easier, by simply writing a new task, or adding to the queue-interpreter.
Primitive Multitasking:
In this type of system, a low-level piece of code switches between tasks or threads based on a timer (connected to an interrupt). This is the level at which the system is generally considered to have an "operating system" kernel. Depending on how much functionality is required, it introduces more or less of the complexities of managing multiple tasks running conceptually in parallel. As any code can potentially damage the data of another task (except in larger systems using an MMU) programs must be carefully designed and tested, and access to shared data must be controlled by some synchronization strategy, such as message queues, semaphores or a non-blocking synchronization scheme. Because of these complexities, it is common for organizations to buy a real-time operating system, allowing the application programmers to concentrate on device functionality rather
17
than operating system services, at least for large systems; smaller systems often cannot afford the overhead associated with a generic real time system, due to limitations regarding memory size, performance, and/or battery life.
Microkernels And Exokernels: A microkernel is a logical step up from a real-time OS.
The usual arrangement is that the operating system kernel allocates memory and switches the CPU to different threads of execution. User mode processes implement major functions such as file systems, network interfaces, etc. In general, microkernels succeed when the task switching and inter task communication is fast, and fail when they are slow. Exokernels communicate efficiently by normal subroutine calls. The hardware and all the software in the system are available to, and extensible by application programmers. Based on performance, functionality, requirement the embedded systems are divided into three categories: 2.3.2 Stand Alone Embedded System: These systems takes the input in the form of electrical signals from transducers or commands from human beings such as pressing of a button etc.., process them and produces desired output. This entire process of taking input, processing it and giving output is done in standalone mode. Such embedded systems comes under stand alone embedded systems Eg: microwave oven, air conditioner etc.. 2.3.3 Real-time embedded systems: 18
Embedded systems which are used to perform a specific task or operation in a specific time period those systems are called as real-time embedded systems. There are two types of real-time embedded systems.
Hard Real-time embedded systems: These embedded systems follow an absolute dead line
time period i.e.., if the tasking is not done in a particular time period then there is a cause of damage to the entire equipment. Eg: consider a system in which we have to open a valve within 30 milliseconds. If this valve is not opened in 30 ms this may cause damage to the entire equipment. So in such cases we use embedded systems for doing automatic operations.
Soft Real Time embedded systems:
Eg: Consider a TV remote control system, if the remote control takes a few milliseconds delay it will not cause damage either to the TV or to the remote control. These systems which will not cause damage when they are not operated at considerable time period those systems comes under soft real-time embedded systems.
2.3.4 Network communication embedded systems: A wide range network interfacing communication is provided by using embedded systems. Eg:
Consider a web camera that is connected to the computer with internet can be used to spread communication like
19
sending pictures, images, videos etc.., to another computer with internet connection throughout anywhere in the world.
Consider a web camera that is connected at the door lock. Whenever a person comes near the door, it captures the
image of a person and sends to the desktop of your computer which is connected to internet. This gives an alerting message with image on to the desktop of your computer, and then you can open the door lock just by clicking the mouse. Fig: 2.2 show the network communications in embedded systems.
Fig 2.2: Network communication embedded systems
2.3.5 Different types of processing units: The central processing unit (c.p.u) can be any one of the following microprocessor, microcontroller, digital signal processing.
20
Among these Microcontroller is of low cost processor and one of the main advantage of microcontrollers is, the components such as memory, serial communication interfaces, analog to digital converters etc.., all these are built on a single chip. The numbers of external components that are connected to it are very less according to the application.
Microprocessors are more powerful than microcontrollers. They are used in major applications with a number of tasking requirements. But the microprocessor requires many external components like memory, serial communication, hard disk, input output ports etc.., so the power consumption is also very high when compared to microcontrollers.
Digital signal processing is used mainly for the applications that particularly involved with processing of signals
2.4 APPLICATIONS OF EMBEDDED SYSTEMS: 2.4.1 Consumer applications: At home we use a number of embedded systems which include microwave oven, remote control, vcd players, dvd players, camera etc….
Fig2.3: Automatic coffee makes equipment
21
2.4.2 Office automation: We use systems like fax machine, modem, printer etc…
Fig2.4: Fax machine
Fig2.5:Printing machine
2.4.3. Industrial automation: Today a lot of industries are using embedded systems for process control. In industries we design the embedded systems to perform a specific operation like monitoring temperature, pressure, humidity ,voltage, current etc.., and basing on these monitored levels we do control other devices, we can send information to a centralized monitoring station.
Fig2.6: Robot 22
In critical industries where human presence is avoided there we can use robots which are programmed to do a specific operation.
2.4.5 Computer networking: Embedded systems are used as bridges routers etc..
Fig2.7: Computer networking 2.4.6 Tele communications: Cell phones, web cameras etc.
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Fig2.8: Cell Phone
Fig2.9: Web camera
CHAPTER 3: HARDWARE DESCRIPTION: 3.1 Introduction: In this chapter the block diagram of the project and design aspect of independent modules are considered. Block diagram is shown in fig: 3.1:
24
FIG 3.1: Block diagram of THREE PHASE INDUCTION MOTOR PROTECTION SYSTEM”
The main blocks of this project are:
1. Micro controller (16F72) 2. Crystal oscillator 3. Reset 25
4. Regulated power supply (RPS) 5. Led indicator 6. Voltage sensor 7. Optocoupler 8. Relay 9. LCD 3.2 Micro controller:
Fig: 3.2 Microcontrollers Introduction The PIC16F72 CMOS FLASH-based 8-bit microcontroller is upward compatible with PIC16C72/72A and PIC16F872devices. It features 200 ns instruction execution, self programming, an ICD, 2 Comparators, 5 channels of 8-bit Analog-to-Digital (A/D) converter, 2 capture/compare/PWM functions, a synchronous serial port that can be configured as either 3-wire SPI or 2-wire I2C bus, a USART, and a Parallel Slave Port. High-Performance RISC CPU
26
• High performance RISC CPU • Only 35 single word instructions to learn • All single cycle instructions except for program branches which are two-cycle • Operating speed: DC - 20 MHz clock input DC - 200 ns instruction cycle • 2K x 14 words of Program Memory 128 x 8 bytes of Data Memory (RAM) • Pin out compatible to the PIC16C72/72A and PIC16F872 • Interrupt capability • Eight level deep hardware stack • Direct, Indirect and Relative Addressing modes Peripheral Features • Timer0: 8-bit timer/counter with 8-bit prescaler • Timer1: 16-bit timer/counter with prescaler, can be incremented during SLEEP via external crystal/clock • Timer2: 8-bit timer/counter with 8-bit period register, prescaler and postscaler • Capture, Compare, PWM (CCP) module - Capture is 16-bit, max resolution is 12.5 ns - Compare is 16-bit, max resolution is 200 ns 27
- PWM max resolution is 10-bit • 8-bit, 5-channel Analog-to-Digital converter • Synchronous Serial Port (SSP) with SPI (Master mode) and I2C (Slave) • Heat sink/Source Current:25 mA • Brown-out detection circuitry for Brown-out Reset (BOR) CMOS Technology: • Low power, high speed CMOS FLASH technology • Fully static design • Wide operating voltage range: 2.0V to 5.5V • Industrial temperature range • Low power consumption: - < 0.6 mA typical @ 3V, 4 MHz - 20 μA typical @ 3V, 32 kHz - < 1 μA typical standby current Following are the major blocks of PIC Microcontroller. Program memory (FLASH) is used for storing a written program. Since memory made in FLASH technology can be programmed and cleared more than once, it makes this microcontroller suitable for device development.
28
EEPROM - data memory that needs to be saved when there is no supply. It is usually used for storing important data that must not be lost if power supply suddenly stops. For instance, one such data is an assigned temperature in temperature regulators. If during a loss of power supply this data was lost, we would have to make the adjustment once again upon return of supply. Thus our device looses on self-reliance. RAM - Data memory used by a program during its execution. In RAM are stored all inter-results or temporary data during run-time. PORTS are physical connections between the microcontroller and the outside world. PIC16F72 has 22 I/O.
FREE-RUN TIMER is an 8-bit register inside a microcontroller that works independently of the program. On every fourth clock of the oscillator it increments its value until it reaches the maximum (255), and then it starts counting over again from zero. As we know the exact timing between each two increments of the timer contents, timer can be used for measuring time which is very useful with some devices. CENTRAL PROCESSING UNIT has a role of connective element between other blocks in the microcontroller. It coordinates the work of other blocks and executes the user program.
29
CISC, RISC It has already been said that PIC16F72 has RISC architecture. This term is often found in computer literature, and it needs to be explained here in more detail. Harvard architecture is a newer concept than von-Neumann. It rose out of the need to speed up the work of a microcontroller. In Harvard architecture, data bus and address bus are separate. Thus a greater flow of data is possible through the central processing unit, and of course, a greater speed of work. Separating a program from data memory makes it further possible for instructions not to have to be 8-bit words. PIC16F72 uses 14 bits for instructions, which allows for all instructions to be one-word instructions. It is also typical for Harvard architecture to have fewer instructions than von-Neumann's, and to have instructions usually executed in one cycle.
Microcontrollers with Harvard architecture are also called "RISC microcontrollers". RISC stands for Reduced Instruction Set Computer. Microcontrollers with von-Neumann's architecture are called 'CISC
30
microcontrollers'. Title CISC stands for Complex Instruction Set Computer Since PIC16F72 is a RISC microcontroller, that means that it has a reduced set of instructions, more precisely 35 instructions. (Ex. Intel's and Motorola's microcontrollers have over hundred instructions) All of these instructions are executed in one cycle except for jump and branch instructions. According to what its maker says, PIC16F72 usually reaches results of 2:1 in code compression and 4:1 in speed in relation to other 8-bit microcontrollers in its class. Crystal oscillator: The crystal oscillator speed that can be connected to the PIC microcontroller range from DC to 20Mhz. Using the CCS C compiler normally 20Mhz oscillator will be used and the price is very cheap. The 20 MHz crystal oscillator should be connected with about 22pF capacitor. Please refer to my circuit schematic. There are 5 input/output ports on PIC microcontroller namely port A, port B, port C, port D and port E. Each port has different function. Most of them can be used as I/O port. Applications PIC16F72 perfectly fits many uses, from automotive industries and controlling home appliances to industrial instruments, remote sensors, electrical door locks and safety devices. It is also ideal for smart cards as well as for battery supplied devices because of its low consumption.
31
EEPROM memory makes it easier to apply microcontrollers to devices where permanent storage of various parameters is needed (codes for transmitters, motor speed, receiver frequencies, etc.). Low cost, low consumption, easy handling and flexibility make PIC16F72 applicable even in areas where microcontrollers had not previously been considered (example: timer functions, interface replacement in larger systems, coprocessor applications, etc.). In System Programmability of this chip (along with using only two pins in data transfer) makes possible the flexibility of a product, after assembling and testing have been completed. This capability can be used to create assembly-line production, to store calibration data available only after final testing, or it can be used to improve programs on finished products. Clock / instruction cycle Clock is microcontroller's main starter, and is obtained from an external component called an "oscillator". If we want to compare a microcontroller with a time clock, our "clock" would then be a ticking sound we hear from the time clock. In that case, oscillator could be compared to a spring that is wound so time clock can run. Also, force used to wind the time clock can be compared to an electrical supply.
Clock from the oscillator enters a microcontroller via OSC1 pin where internal circuit of a microcontroller divides the clock into four even clocks Q1, Q2, Q3, and Q4 which do not overlap. These four clocks make up one instruction cycle (also called machine cycle) during which one instruction is executed.
32
Execution of instruction starts by calling an instruction that is next in string. Instruction is called from program memory on every Q1 and is written in instruction register on Q4. Decoding and execution of instruction are done between the next Q1 and Q4 cycles. On the following diagram we can see the relationship between instruction cycle and clock of the oscillator (OSC1) as well as that of internal clocks Q1-Q4. Program counter (PC) holds information about the address of the next instruction.
Pipelining Instruction cycle consists of cycles Q1, Q2, Q3 and Q4. Cycles of calling and executing instructions are connected in such a way that in order to make a call, one instruction cycle is needed, and one more is needed for decoding and execution. However, due to pipelining, each instruction is effectively executed in one cycle. If instruction causes a change on program counter, and PC doesn't point to the following but to some other address (which can be the case with jumps or with calling subprograms), two cycles are needed for executing an instruction. This is so because instruction must be processed again, but this time from the right address. Cycle of calling begins with Q1
33
clock, by writing into instruction register (IR). Decoding and executing begins with Q2, Q3 and Q4 clocks.
Pin description PIC16F72 has a total of 28 pins. It is most frequently found in a DIP28 type of case but can also be found in SMD case which is smaller from a DIP. DIP is an abbreviation for Dual In Package. SMD is an abbreviation for Surface Mount Devices suggesting that holes for pins to go through when mounting aren't necessary in soldering this type of a component.
34
Pins on PIC16F72 microcontroller have the following meaning:
There are 28 pins on PIC16F72. Most of them can be used as an IO pin. Others are already for specific functions. These are the pin functions. 1. MCLR – to reset the PIC 2. RA0 – port A pin 0 3. RA1 – port A pin 1 4. RA2 – port A pin 2 5. RA3 – port A pin 3 6. RA4 – port A pin 4 7. RA5 – port A pin 5 8. VSS – ground 9. OSC1 – connect to oscillator 10. OSC2 – connect to oscillator 35
11. RC0 – port C pin 0 VDD – power supply 12. RC1 – port C pin 1 13. RC2 – port C pin 2 14. RC3 – port C pin 3 15. RC4 - port C pin 4 16. RC5 - port C pin 5 17. RC6 - port C pin 6 18. RC7 - port C pin 7 19. VSS - ground 20. VDD – power supply 21. RB0 - port B pin 0 22. RB1 - port B pin 1 23. RB2 - port B pin 2 24. RB3 - port B pin 3 25. RB4 - port B pin 4 26. RB5 - port B pin 5 27. RB6 - port B pin 6 28. RB7 - port B pin 7
By utilizing all of this pin so many application can be done such as: 1. LCD – connect to Port B pin. 2. LED – connect to any pin declared as output. 3. Relay and Motor - connect to any pin declared as output. 4. External EEPROM – connect to I2C interface pin – RC3 and RC4 (SCL and SDA) 5. LDR, Potentiometer and sensor – connect to analogue input pin such as RA0. 6. GSM modem dial up modem – connect to RC6 and RC7 – the serial communication interface using RS232 protocol. 36
For more detail function for each specific pin please refer to the device datasheet from Microchip. Ports Term "port" refers to a group of pins on a microcontroller which can be accessed simultaneously, or on which we can set the desired combination of zeros and ones, or read from them an existing status. Physically, port is a register inside a microcontroller which is connected by wires to the pins of a microcontroller. Ports represent physical connection of Central Processing Unit with an outside world. Microcontroller uses them in order to monitor or control other components or devices. Due to functionality, some pins have twofold roles like PA4/TOCKI for instance, which is in the same time the fourth bit of port A and an external input for free-run counter. Selection of one of these two pin functions is done in one of the configuration registers. An illustration of this is the fifth bit T0CS in OPTION register. By selecting one of the functions the other one is disabled. All port pins can be designated as input or output, according to the needs of a device that's being developed. In order to define a pin as input or output pin, the right combination of zeros and ones must be written in TRIS register. If the appropriate bit of TRIS register contains logical "1", then that pin is an input pin, and if the opposite is true, it's an output pin. Every port has its proper TRIS register. Thus, port A has TRISA, and port B has TRISB. Pin direction can be changed during the course of work which is particularly fitting for one-line communication where data flow constantly changes direction. PORTA 37
and PORTB state registers are located in bank 0, while TRISA and TRISB pin direction registers are located in bank 1.
PORTB and TRISB
PORTB have adjoined 8 pins. The appropriate register for data direction is TRISB. Setting a bit in TRISB register defines the corresponding port pin as input, and resetting a bit in TRISB register defines the corresponding port pin as output.
Each PORTB pin has a weak internal pull-up resistor (resistor which defines a line to logic one) which can be activated by resetting the seventh bit RBPU in OPTION register. These 'pull-up' resistors are automatically being turned off when port pin is configured as an output. When a microcontroller is started, pull-ups are disabled.
38
Four pins PORTB, RB7:RB4 can cause an interrupt which occurs when their status changes from logical one into logical zero and opposite. Only pins configured as input can cause this interrupt to occur (if any RB7:RB4 pin is configured as an output, an interrupt won't be generated at the change of status.) This interrupt option along with internal pull-up resistors makes it easier to solve common problems we find in practice like for instance that of matrix keyboard. If rows on the keyboard are connected to these pins, each push on a key will then cause an interrupt. A microcontroller will determine which key is at hand while processing an interrupt It is not recommended to refer to port B at the same time that interrupt is being processed. PORTA and TRISA PORTA have 5 adjoining pins. The corresponding register for data direction is TRISA at address 85h. Like with port B, setting a bit in TRISA register defines also the corresponding port pin as input, and clearing a bit in TRISA register defines the corresponding port pin as output. It is important to note that PORTA pin RA4 can be input only. On that pin is also situated an external input for timer TMR0. Whether RA4 will be a standard input or an input for a counter depends on T0CS bit (TMR0 Clock Source Select bit). This pin enables the timer TMR0 to increment either from internal oscillator or via external impulses on RA4/T0CKI pin. Example shows how pins 0, 1, 2, 3, and 4 are designated input, and pins 5, 6, and 7 outputs. After this, it is possible to read the pins RA2, RA3, RA4, and to set logical zero or one to pins RA0 and RA1. 39
Memory organization PIC16F72 has two separate memory blocks, one for data and the other for program. EEPROM memory with GPR and SFR registers in RAM memory make up the data block, while FLASH memory makes up the program block. Program memory
Program memory has been carried out in FLASH technology which makes it possible to program a microcontroller many times before it's installed into a device, and even after its installment if eventual changes in program or process parameters should occur. The size of program memory is 1024 locations with 14 bits width where locations zero and four are reserved for reset and interrupt vector.
Data memory 40
Data memory consists of EEPROM and RAM memories. EEPROM memory consists of 256 eight bit locations whose contents are not lost during loosing of power supply. EEPROM is not directly addressable, but is accessed indirectly through EEADR and EEDATA registers. As EEPROM memory usually serves for storing important parameters (for example, of a given temperature in temperature regulators) , there is a strict procedure for writing in EEPROM which must be followed in order to avoid accidental writing. RAM memory for data occupies space on a memory map from location 0x0C to 0x4F which comes to 68 locations. Locations of RAM memory are also called GPR registers which is an abbreviation for General Purpose Registers. GPR registers can be accessed regardless of which bank is selected at the moment. 3.3 REGULATED POWER SUPPLY: 3.3.1 Introduction: Power supply is a supply of electrical power. A device or system that supplies electrical or other types of energy to an output load
or group of loads is called a power supply unit or PSU. The term
is most commonly applied to electrical energy supplies, less often to mechanical ones, and rarely to others. A power supply may include a power distribution system as well as primary or secondary sources of energy such as
Conversion of one form of electrical power to another desired form and voltage, typically involving converting AC line voltage to a well-regulated lower-voltage DC for electronic devices. Low voltage, low power DC power supply units are commonly integrated with 41
the devices they supply, such as computers and household electronics.
Batteries.
Chemical fuel cells and other forms of energy storage systems.
Solar power.
Generators or alternators.
3.3.2 Block Diagram:
Fig 3.3.2 Regulated Power Supply The basic circuit diagram of a regulated power supply (DC O/P) with led connected as load is shown in fig: 3.3.3.
42
Fig 3.3.3 Circuit diagram of Regulated Power Supply with Led connection The components mainly used in above figure are
230V AC MAINS
TRANSFORMER
BRIDGE RECTIFIER(DIODES)
CAPACITOR
VOLTAGE REGULATOR(IC 7805)
RESISTOR
LED(LIGHT EMITTING DIODE) The detailed explanation of each and every component
mentioned above is as follows: Step 1: Transformation: The process of transforming energy from one device to another is called transformation. For transforming energy we use transformers.
43
Transformers: A transformer is energy from
a
device
one circuit to
coupled conductors
without
varying current in
the
first
varying magnetic
flux in
the
that
transfers electrical
another changing or
through inductively its
frequency.
primary winding
transformer's
core,
creates and
thus
A a a
varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or "voltage" in the secondary winding. This effect is called mutual induction. If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load. This field is made up from lines of force and has the same shape as a bar magnet. If the current is increased, the lines of force move outwards from the coil. If the current is reduced, the lines of force move inwards. If another coil is placed adjacent to the first coil then, as the field moves out or in, the moving lines of force will "cut" the turns of the second coil. As it does this, a voltage is induced in the second coil. With the 50 Hz AC mains supply, this will happen 50 times a second. This is called MUTUAL INDUCTION and forms the basis of the transformer.
44
The input coil is called the PRIMARY WINDING; the output coil is the SECONDARY WINDING. Fig: 3.3.4 shows step-down transformer.
Fig 3.3.4: Step-Down Transformer The voltage induced in the secondary is determined by the TURNS RATIO.
For example, if the secondary has half the primary turns; the secondary will have half the primary voltage. Another example is if the primary has 5000 turns and the secondary has 500 turns, then the turn’s ratio is 10:1. If the primary voltage is 240 volts then the secondary voltage will be x 10 smaller = 24 volts. Assuming a perfect transformer, the power provided by the primary must equal the power taken by a load on the secondary. If a 24-watt lamp is connected across a 24 volt secondary, then the primary must supply 24 watts. To aid magnetic coupling between primary and secondary, the coils are wound on a metal CORE. Since the primary would
45
induce power, called EDDY CURRENTS, into this core, the core is LAMINATED. This means that it is made up from metal sheets insulated from each other. Transformers to work at higher frequencies have an iron dust core or no core at all. Note that the transformer only works on AC, which has a constantly changing current and moving field. DC has a steady current and therefore a steady field and there would be no induction. Some transformers have an electrostatic screen between primary and secondary. This is to prevent some types of interference being fed from the equipment down into the mains supply, or in the other direction. Transformers are sometimes used for IMPEDANCE MATCHING. We can use the transformers as step up or step down. Step Up transformer: In case of step up transformer, primary windings are every less compared to secondary winding. Because of having more turns secondary winding accepts more energy, and it releases more voltage at the output side. Step down transformer: Incase of step down transformer, Primary winding induces more flux than the secondary winding, and secondary winding is having less number of turns because of that it accepts less number of flux, and releases less amount of voltage. Battery power supply: 46
A battery is a type of linear power supply that offers benefits that traditional line-operated power supplies lack: mobility, portability
and
reliability.
A
battery
consists
of
multiple
electrochemical cells connected to provide the voltage desired. Fig: 3.3.5 shows Hi-Watt 9V battery
Fig 3.3.5: Hi-Watt 9V Battery The most commonly used dry-cell battery is the carbonzinc dry cell battery. Dry-cell batteries are made by stacking a carbon plate, a layer of electrolyte paste, and a zinc plate alternately until the desired total voltage is achieved. The most common dry-cell batteries have one of the following voltages: 1.5, 3, 6, 9, 22.5, 45, and 90. During the discharge of a carbon-zinc battery, the zinc metal is converted to a zinc salt in the electrolyte, and magnesium dioxide is reduced at the carbon electrode. These actions establish a voltage of approximately 1.5 V. The lead-acid storage battery may be used. This battery is rechargeable; it consists of lead and lead/dioxide electrodes which are immersed in sulfuric acid. When fully charged, this type of battery has a 2.06-2.14 V potential (A 12 volt car battery uses 6 cells in series). During discharge, the lead is converted to lead sulfate and the sulfuric acid is converted to water. When the battery is charging, the lead sulfate is converted back to lead and lead dioxide A nickel47
cadmium battery has become more popular in recent years. This battery cell is completely sealed and rechargeable. The electrolyte is not involved in the electrode reaction, making the voltage constant over the span of the batteries long service life. During the charging process, nickel oxide is oxidized to its higher oxidation state and cadmium oxide is reduced. The nickel-cadmium batteries have many benefits. They can be stored both charged and uncharged. They have a long service life, high current availabilities, constant voltage, and the ability to be recharged. Fig: 3.3.6 shows pencil battery of 1.5V.
Fig 3.3.6: Pencil Battery of 1.5V Step 2: Rectification The process of converting an alternating current to a pulsating direct current is called as rectification. For rectification purpose we use rectifiers. Rectifiers: A rectifier is an electrical device that converts alternating current (AC) to direct current (DC), a process known as rectification. Rectifiers have many uses including as components of power supplies and as detectors of radio signals. Rectifiers may be made of solid-state
48
diodes,
vacuum
tube
diodes,
mercury
arc
valves,
and
other
components. A device that it can perform the opposite function (converting DC to AC) is known as an inverter. When only one diode is used to rectify AC (by blocking the negative or positive portion of the waveform), the difference between the term diode and the term rectifier is merely one of usage, i.e., the term rectifier describes a diode that is being used to convert AC to DC. Almost all rectifiers comprise a number of diodes in a specific arrangement for more efficiently converting AC to DC than is possible with only one diode. Before the development of silicon semiconductor rectifiers, vacuum tube diodes and copper (I) oxide or selenium rectifier stacks were used. Bridge full wave rectifier: The Bridge rectifier circuit is shown in fig:3.8, which converts an ac voltage to dc voltage using both half cycles of the input ac voltage. The Bridge rectifier circuit is shown in the figure. The circuit has four diodes connected to form a bridge. The ac input voltage is applied to the diagonally opposite ends of the bridge. The load resistance is connected between the other two ends of the bridge. For the positive half cycle of the input ac voltage, diodes D1 and D3 conduct, whereas diodes D2 and D4 remain in the OFF state. The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL.
49
For the negative half cycle of the input ac voltage, diodes D2 and D4 conduct whereas, D1 and D3 remain OFF. The conducting diodes D2 and D4 will be in series with the load resistance R L and hence the current flows through RL in the same direction as in the previous half cycle. Thus a bi-directional wave is converted into a unidirectional wave. Input
Output
Fig 3.3.7: Bridge rectifier: a full-wave rectifier using 4 diodes DB107: Now -a -days Bridge rectifier is available in IC with a number of DB107. In our project we are using an IC in place of bridge rectifier. The picture of DB 107 is shown in fig: 3.9. Features:
Good for automation insertion
Surge overload rating - 30 amperes peak
50
Ideal for printed circuit board
Reliable low cost construction utilizing molded
Glass passivated device
Polarity symbols molded on body
Mounting position: Any
Weight: 1.0 gram
Fig 3.3.8: DB107 Step 3: Filtration The process of converting a pulsating direct current to a pure direct current using filters is called as filtration. Filters: Electronic filters are electronic circuits, which perform signal-processing
functions,
specifically
to
remove
unwanted
frequency components from the signal, to enhance wanted ones. Introduction to Capacitors:
51
The Capacitor or sometimes referred to as a Condenser is a passive device, and one which stores energy in the form of an electrostatic field which produces a potential (static voltage) across its plates. In its basic form a capacitor consists of two parallel conductive plates that are not connected but are electrically separated either by air or by an insulating material called the Dielectric. When a voltage is applied to these plates, a current flows charging up the plates with electrons giving one plate a positive charge and the other plate an equal and opposite negative charge this flow of electrons to the plates is known as the Charging Current and continues to flow until the voltage across the plates (and hence the capacitor) is equal to the applied voltage Vcc. At this point the capacitor is said to be fully charged and this is illustrated below. The construction of capacitor and an electrolytic capacitor are shown in figures 3.3.9 and 3.3.10 respectively.
52
Fig 3.3.9:Construction Of a Capacitor 3.3.10:Electrolytic Capaticor Units of Capacitance: Microfarad (μF) 1μF = 1/1,000,000 = 0.000001 = 10-6 F Nanofarad (nF) 1nF = 1/1,000,000,000 = 0.000000001 = 10-9 F
53
Fig
Pico farad (pF) 1pF = 1/1,000,000,000,000 = 0.000000000001 = 1012
F
Operation of Capacitor: Think of water flowing through a pipe. If we imagine a capacitor as being a storage tank with an inlet and an outlet pipe, it is possible to show approximately how an electronic capacitor works. First, let's consider the case of a "coupling capacitor" where the capacitor is used to connect a signal from one part of a circuit to another but without allowing any direct current to flow.
If the current flow is alternating between zero and a maximum, our "storage tank" capacitor will allow the current waves to pass through. However, if there is a steady current, only the initial short burst will flow until the "floating ball valve" closes and stops further flow.
So a coupling capacitor allows "alternating current" to pass through because the ball valve doesn't get a chance to close as the waves go up and down. However, a steady current quickly fills the tank so that all flow stops. A capacitor will pass alternating current but (apart from an initial surge) it will not pass d.c. 54
Where a capacitor is used to decouple a circuit, the effect is to "smooth out ripples". Any ripples, waves or pulses of current are passed to ground while d.c. Flows smoothly.
Step 4: Regulation The process of converting a varying voltage to a constant regulated voltage is called as regulation. For the process of regulation we use voltage regulators.
Voltage Regulator: A voltage regulator (also called a ‘regulator’) with only three terminals appears to be a simple device, but it is in fact a very complex integrated circuit. It converts a varying input voltage into a constant ‘regulated’ output voltage. Voltage Regulators are available in a variety of outputs like 5V, 6V, 9V, 12V and 15V. The LM78XX series of voltage regulators are designed for positive input. For applications requiring negative input, the LM79XX series is used. Using a pair of ‘voltage-divider’ resistors can increase the output voltage of a regulator circuit. It is not possible to obtain a voltage lower than the stated rating. You cannot use a 12V regulator to make a 5V power supply. Voltage regulators are very robust. These can withstand over-current 55
draw due to short circuits and also over-heating. In both cases, the regulator will cut off before any damage occurs. The only way to destroy a regulator is to apply reverse voltage to its input. Reverse polarity destroys the regulator almost instantly. Fig: 3.3.11 shows voltage regulator.
Fig 3.3.11: Voltage Regulator Resistors: A resistor is a two-terminal electronic component that produces a voltage across its terminals that is proportional to the electric current passing through it in accordance with Ohm's law: V = IR
Resistors are elements of electrical networks and electronic circuits and are ubiquitous in most electronic equipment. Practical resistors can be made of various compounds and films, as well as resistance wire (wire made of a high-resistivity alloy, such as nickel/chrome). The primary characteristics of a resistor are the resistance, the tolerance, maximum working voltage and the power rating. Other characteristics include temperature coefficient, noise, and inductance. 56
Less well-known is critical resistance, the value below which power dissipation limits the maximum permitted current flow, and above which the limit is applied voltage. Critical resistance is determined by the design, materials and dimensions of the resistor. Resistors can be made to control the flow of current, to work as Voltage dividers, to dissipate power and it can shape electrical waves when used in combination of other components. Basic unit is ohms. Theory of operation: Ohm's law: The behavior of an ideal resistor is dictated by the relationship specified in Ohm's law: V = IR Ohm's law states that the voltage (V) across a resistor is proportional to the current (I) through it where the constant of proportionality is the resistance (R). Power dissipation: The power dissipated by a resistor (or the equivalent resistance of a resistor network) is calculated using the following:
57
Fig 3.3.12: Resistor
Fig 3.3.13:
Color Bands In Resistor
3.4. LED: A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps in many devices, and are increasingly used for lighting. Introduced as a practical electronic component in 1962, early LEDs emitted low-intensity red light, but
58
modern versions are available across the visible, ultraviolet and infrared wavelengths,
with very high brightness.
The internal
structure and parts of a led are shown below.
Fig 3.4.1: Inside a LED 3.4.2: Parts of a LED
Working: 59
Fig
The structure of the LED light is completely different than that of the light bulb. Amazingly, the LED has a simple and strong structure.
The
light-emitting
semiconductor
material
is
what
determines the LED's color. The LED is based on the semiconductor diode. When a diode is forward biased (switched on), electrons are able to recombine with holes within the device, releasing energy in the form of photons. This effect is called electroluminescence and the color of the light (corresponding to the energy of the photon) is determined by the energy gap of the semiconductor. An LED is usually small in area (less than 1 mm2), and integrated optical components are used to shape its radiation pattern and assist in reflection. LEDs present many advantages over incandescent light sources including lower energy consumption, longer lifetime, improved robustness, smaller size, faster switching, and greater durability and reliability. However, they are relatively expensive and require more precise current and heat management than traditional light sources. Current LED products for general lighting are more expensive to buy than fluorescent lamp sources of comparable output. They also enjoy use in applications as diverse as replacements for traditional light sources in automotive lighting (particularly indicators) and in traffic signals. The compact size of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are useful in advanced communications technology. The electrical symbol and polarities of led are shown in fig: 3.4.3.
60
Fig 3.4.3: Electrical Symbol & Polarities of LED LED lights have a variety of advantages over other light sources:
High-levels of brightness and intensity
High-efficiency
Low-voltage and current requirements
Low radiated heat
High reliability (resistant to shock and vibration)
No UV Rays
Long source life
Can be easily controlled and programmed
Applications of LED fall into three major categories:
Visual signal application where the light goes more or less directly from the LED to the human eye, to convey a message or meaning.
61
Illumination where LED light is reflected from object to give visual response of these objects.
Generate light for measuring and interacting with processes that do not involve the human visual system.
3.5 VOLTAGE SENSOR: In practice a voltage transformer can be used as a voltage sensor. The voltage transformer must be connected across the transmission lines. The
primary
of
the
transformer
must
be
connected
to
the
transmission lines and the secondary must be given to the microcontroller. A step down voltage transformer is used. Illustration of a voltage sensor
Fig: Diagram of voltage sensor In the project we have made use of a potentiometer in place of a voltage sensor. A potentiometer (colloquially known as a "pot") is a three-terminal resistor with a sliding contact that forms an adjustable voltage divider. It is a measuring device which measures the voltage or current at the output by comparing it with the known input voltage. Varying the input voltage is a difficult process and requires advanced equipments. In the potentiometer the input is fixed at some maximum and minimum value. By turning the notch of the potentiometer the 62
output voltage is varied, whenever the output voltage exceeds the bounds it indicates the occurrence of fault. After the fault is indicated the microcontroller gives trip signals to the relay which in turn operates the circuit breaker. However in real time applications a potentiometer cannot be used, a voltage transformer should be used. 3.6 OPTOCOUPLER An optocoupler-isolated power supply is often the safest and most practical way to go when it comes to performance and protection. Here’s the basic on today’s LED/photo detector isolators and what you need to know to apply them to your system. The junior system designer often places the system’s power requirements at the end of the list, and thus overlooks the importance of an isolated, versus non-isolated AC/AC, AC/DC, DC/AC, or DC/DC converter. True isolation (transformer at the input, optoisolator in the supply’s feedback control loops) virtually removes any direct conductive path between the power supply’s input stage and its output terminals/load. That’s especially important in the high-power density applications that are becoming more the rule than the exception, and for more demanding system requirements That often place power supplies in explosive or otherwise hazardous environments. The use of an optocoupler also acts to break ground loops, and this functionality is valuable in eliminating common-mode noise, especially for systems working at the higher operating voltages. When different power supplies in a system are tied together, ground
63
loop currents tend to be induced due to slight differences in ground potential. In addition, power supplies tend to see transient noise in equipment that switches between various power states (today’s optocouplers are able to withstand up to 40 kV/microsecond transient common-mode voltage). Typical optocouplers for performing this socalled galvanic isolation function—in essence to connect intrinsically safe circuitry to circuits that pose a safety risk—comprise an LED, a photo detector, and appropriate connecting circuitry in the supply’s output-to-input feedback Loop. In general circuit operation, the optocoupler, driven by the supply’s PWM, serves as the link to maintain the supply’s desired output voltage When the output voltage deviates either due to line and/or load changes, the supply’s error amplifier attempts to compensate. It compares its input with a reference voltage, and the error signal thus controls the output of the PWM. In turn, the PWM directs the primary- side Power MOSFET's via the optocoupler.
64
The standards Regulatory agencies such as UL in the United States, CENELEC in Europe, CSA in Canada, and TIIS in Japan, set the power level needed to make circuitry intrinsically safe. In essence, the standards set the requirements for the galvanic isolation barrier between the “safe” circuitry and the outside world. For best results, choose optocouplers with additional reinforced insulation as suggested by IEC EN-60747- 5-2. Reinforced insulation ensures protection from electric shock as well as provides a failsafe mode. Fail-safe techniques terminate
system
operation
and
leaves
system
processes
and
components in a secure state when a failure occurs. The input-voltage level usually defines the insulation voltage rating, which typically ranges from 500 volts for some telecom applications to 3500 volts for universal line-voltage capability. The regulations you need to know about, and the specs you should study, include IEC60950, EN55022, and IEC 61000. IEC 61000 in particular covers electromagnetic compatibility (EMC), and part 4 of that document (IEC61000- 4-4) covers fast transient/burst Electrical Fast Transient (EFT) testing discussed in part 4.4 addresses interference simulated in inductively loaded switches. In this standard, the modules will be subjected to the following test levels, depending on the designed environment: Level 1 (Well protected); Level 2 (Protected); Level 3 (Typical Industrial Environment); and Level 4 (Severe Industrial Environment), where test voltage peaks at the power supply ports are 0.5 kV (5kHz repetition rate), 1 kV (5kHz), 2 kV (5kHz), and 4 kV (2.5kHz), respectively.
65
Simple Remote Reset Power On/Off This is a simple schematic for a remote reset/power on/off device to
use
for
controlling
up
to
4
lines
via
the
parallel
port.
Depending on the number of lines you require, the opto coupler will be PC817, PC827 or PC847.
Or you could use the following schematic to drive up to 8 lines, with the drawback that a reboot of the controlling machine will probably reboot all your attached devices...
Applications 1. Computer terminals 2. System appliances, measuring instruments 3. Registers, copiers, automatic vending machines 4. Electric home appliances, such as fan heaters, etc. 5. Signal transmission between circuits of different potentials and impedances 66
3.7 Relay: A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism, but other operating principles are also used. Relays find applications where it is necessary to control a circuit by a low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays found extensive use in telephone
exchanges
and
early
computers
to
perform
logical
operations. A type of relay that can handle the high power required to directly drive an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device triggered by light to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protection relays". 3.8.1 Basic design and operation:
67
1. Simple electromechanical relay
Small relay as used in electronics A simple electromagnetic relay, such as the one taken from a car in the first picture, is an adaptation of an electromagnet. It consists of a coil of wire surrounding a soft iron core, an iron yoke, which provides a low reluctance path for magnetic flux, a movable iron armature, and a set, or sets, of contacts; two in the relay pictured. The armature is hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in place by a spring so that when the relay is deenergized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB. When an electric current is passed through the coil, the resulting magnetic field attracts the armature and the consequent movement of the movable contact or contacts either makes or breaks a connection 68
with a fixed contact. If the set of contacts was closed when the relay was De-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing. If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation,
which
would
otherwise
generate
a
voltage
spike
dangerous to circuit components. Some automotive relays already include a diode inside the relay case. Alternatively a contact protection network, consisting of a capacitor and resistor in series, may absorb the surge. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle. By analogy with the functions of the original electromagnetic device, a solid-state relay is made with a thyristor or other solid-state switching device. To achieve electrical isolation an opt coupler can be used which is a light-emitting diode (LED) coupled with a photo transistor.
69
3.8.2 Types of Relays: 2. Latching relay
Latching relay, dust cover removed, showing pawl and ratchet mechanism. The ratchet operates a cam, which raises and lowers the moving contact arm, seen edge-on just below it. The moving and fixed contacts are visible at the left side of the image. A latching relay has two relaxed states (bi stable). These are also called "impulse", "keep", or "stay" relays. When the current is switched off, the relay remains in its last state. This is achieved with a solenoid operating a ratchet and cam mechanism, or by having two opposing coils with an over-center spring or permanent magnet to hold the armature and contacts in position while the coil is relaxed, or with a remnant core. In the ratchet and cam example, the first pulse to the coil turns the relay on and the second pulse turns it off. In the two coil example, a pulse to one coil turns the relay on and a pulse to the opposite coil turns the relay off. This type of relay has the advantage that it consumes power only for an instant, while it is being switched, and it retains its last setting across a power outage. A remnant core latching relay requires a current pulse of opposite polarity to make it change state.
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3. Reed relay A reed relay has a set of contacts inside a vacuum or inert gas filled glass tube, which protects the contacts against atmospheric corrosion. The contacts are closed by a magnetic field generated when current passes through a coil around the glass tube. Reed relays are capable of faster switching speeds than larger types of relays, but have low switch current and voltage ratings.
4. Mercury-wetted relay A mercury-wetted reed relay is a form of reed relay in which the contacts are wetted with mercury. Such relays are used to switch lowvoltage signals (one volt or less) because of their low contact resistance, or for high-speed counting and timing applications where the mercury eliminates contact bounce. Mercury wetted relays are position-sensitive and must be mounted vertically to work properly. Because of the toxicity and expense of liquid mercury, these relays are rarely specified for new equipment. See also mercury switch. 5. Polarized relay A polarized relay placed the armature between the poles of a permanent magnet to increase sensitivity. Polarized relays were used in middle 20th Century telephone exchanges to detect faint pulses and 71
correct telegraphic distortion. The poles were on screws, so a technician could first adjust them for maximum sensitivity and then apply a bias spring to set the critical current that would operate the relay. 6. Machine tool relay A machine tool relay is a type standardized for industrial control of machine tools, transfer machines, and other sequential control. They are
characterized
by
a
large
number
of
contacts
(sometimes
extendable in the field) which are easily converted from normally-open to normally-closed status, easily replaceable coils, and a form factor that allows compactly installing many relays in a control panel. Although such relays once were the backbone of automation in such industries as automobile assembly, the programmable logic controller (PLC) mostly displaced the machine tool relay from sequential control applications. 7. Contactor relay A contactor is a very heavy-duty relay used for switching electric motors and lighting loads. Continuous current ratings for common contactors range from 10 amps to several hundred amps. Highcurrent
contacts are made with alloys containing silver. The
unavoidable arcing causes the contacts to oxidize; however, silver oxide is still a good conductor. Such devices are often used for motor starters. A motor starter is a contactor with overload protection devices attached. The overload sensing devices are a form of heat operated relay where a coil heats a bi-metal strip, or where a solder pot melts, releasing a spring to operate auxiliary contacts. These 72
auxiliary contacts are in series with the coil. If the overload senses excess current in the load, the coil is de-energized. Contactor relays can be extremely loud to operate, making them unfit for use where noise is a chief concern. 8. Solid-state relay
Solid state relay, which has no moving parts
25 A or 40 A solid state contactors A solid state relay (SSR) is a solid state electronic component that provides a similar function to an electromechanical relay but does not have any moving components, increasing long-term reliability. With early SSR's, the tradeoff came from the fact that every transistor has a small voltage drop across it. This voltage drop limited the amount of current a given SSR could handle. As transistors improved, higher current SSR's, able to handle 100 to 1,200 Amperes, have become
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commercially available. Compared to electromagnetic relays, they may be falsely triggered by transients. 9. Solid state contactor relay A solid state contactor is a very heavy-duty solid state relay, including the necessary heat sink, used for switching electric heaters, small electric motors and lighting loads; where frequent on/off cycles are required. There are no moving parts to wear out and there is no contact bounce due to vibration. They are activated by AC control signals or DC control signals from Programmable logic controller (PLCs), PCs, Transistor-transistor logic (TTL) sources, or other microprocessor and microcontroller controls. 10. Buchholz relay A Buchholz relay is a safety device sensing the accumulation of gas in large oil-filled transformers; this will Display on slow accumulation of gas or shut down the transformer if gas is produced rapidly in the transformer oil. 11. Forced-guided contacts relay A
forced-guided
contacts
relay
has relay
contacts
that
are
mechanically linked together, so that when the relay coil is energized or de-energized, all of the linked contacts move together. If one set of contacts in the relay becomes immobilized, no other contact of the same relay will be able to move. The function of forced-guided contacts is to enable the safety circuit to check the status of the relay. Forcedguided contacts are also known as "positive-guided contacts", "captive contacts", "locked contacts", or "safety relays". 74
12. Overload protection relay Electric motors need over current protection to prevent damage from over-loading the motor, or to protect against short circuits in connecting cables or internal faults in the motor windings. One type of electric motor overload protection relay is operated by a heating element in series with the electric motor. The heat generated by the motor current heats a bimetallic strip or melts solder, releasing a spring to operate contacts. Where the overload relay is exposed to the same environment as the motor, a useful though crude compensation for motor ambient temperature is provided. 13. Pole and throw:
Circuit symbols of relays. "C" denotes the common terminal in SPDT and DPDT types.
The diagram on the package of a DPDT AC coil relay 75
Since relays are switches, the terminology applied to switches is also applied to relays. A relay will switch one or more poles, each of whose contacts can be thrown by energizing the coil in one of three ways:
Normally-open (NO) contacts connect the circuit when the relay is activated; the circuit is disconnected when the relay is inactive. It is also called a Form A contact or "make" contact.
Normally-closed (NC) contacts disconnect the circuit when the relay is activated; the circuit is connected when the relay is inactive. It is also called a Form B contact or "break" contact.
Change-over (CO), or double-throw (DT), contacts control two circuits: one normally-open contact and one normally-closed contact with a common terminal. It is also called a Form C contact or "transfer" contact ("break before make"). If this type of contact utilizes” make before break" functionality, then it is called a Form D contact.
The following designations are commonly encountered:
SPST – Single Pole Single Throw. These have two terminals which can be connected or disconnected. Including two for the coil, such a relay has four terminals in total. It is ambiguous whether the pole is normally open or normally closed. The terminology "SPNO" and "SPNC" is sometimes used to resolve the ambiguity.
SPDT – Single Pole Double Throw. A common terminal connects to either of two others. Including two for the coil, such a relay has five terminals in total.
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DPST – Double Pole Single Throw. These have two pairs of terminals. Equivalent to two SPST switches or relays actuated by a single coil. Including two for the coil, such a relay has six terminals in total. The poles may be Form A or Form B (or one of each).
DPDT – Double Pole Double Throw. These have two rows of change-over terminals. Equivalent to two SPDT switches or relays actuated by a single coil. Such a relay has eight terminals, including the coil.
The "S" or "D" may be replaced with a number, indicating multiple switches connected to a single actuator. For example 4PDT indicates a four pole double throw relay (with 14 terminals). 3.8.3 Applications of Relays:
Control a high-voltage circuit with a low-voltage signal, as in some types of modems or audio amplifiers,
Control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile,
Detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers (protection relays),
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A DPDT AC coil relay with "ice cube" packaging
Isolate the controlling circuit from the controlled circuit when the two are at different potentials, for example when controlling a mains-powered device from a low-voltage switch. The latter is often applied to control office lighting as the low voltage wires are easily installed in partitions, which may be often moved as needs change. They may also be controlled by room occupancy detectors in an effort to conserve energy,
Logic functions. For example, the Boolean AND function is realized by connecting normally open relay contacts in series, the OR function by connecting normally open contacts in parallel. The change-over or Form C contacts perform the XOR (exclusive or) function. Similar functions for NAND and NOR are accomplished using normally closed contacts. The Ladder programming language is often used for designing relay logic networks. o
Early computing. Before vacuum tubes and transistors, relays were used as logical elements in digital computers. See ARRA (computer), Harvard Mark II, Zuse Z2, and Zuse Z3.
o
Safety-critical logic. Because relays are much more resistant than semiconductors to nuclear radiation, they are widely used in safety-critical logic, such as the control panels of radioactive waste-handling machinery.
Time delay functions. Relays can be modified to delay opening or delay closing a set of contacts. A very short (a fraction of a second) delay would use a copper disk between the armature 78
and moving blade assembly. Current flowing in the disk maintains magnetic field for a short time, lengthening release time. For a slightly longer (up to a minute) delay, a dashpot is used. A dashpot is a piston filled with fluid that is allowed to escape slowly. The time period can be varied by increasing or decreasing the flow rate. For longer time periods, a mechanical clockwork timer is installed. Relay application considerations:
A large relay with two coils and many sets of contacts, used in an old telephone switching system
Several 30-contact relays in "Connector" circuits in mid 20th century 1XB switch and 5XB switch telephone exchanges; cover removed on one Selection of an appropriate relay for a particular application requires evaluation of many different factors:
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Number and type of contacts – normally open, normally closed, (double-throw)
Contact sequence – "Make before Break" or "Break before Make". For example, the old style telephone exchanges required Makebefore-break so that the connection didn't get dropped while dialing the number.
Rating of contacts – small relays switch a few amperes, large contactors are rated for up to 3000 amperes, alternating or direct current
Voltage rating of contacts – typical control relays rated 300 VAC or 600 VAC, automotive types to 50 VDC, special high-voltage relays to about 15 000 V
Coil voltage – machine-tool relays usually 24 VAC, 120 or 250 VAC, relays for switchgear may have 125 V or 250 VDC coils, "sensitive" relays operate on a few mill amperes
Coil current
Package/enclosure
–
open,
touch-safe,
double-voltage
for
isolation between circuits, explosion proof, outdoor, oil and splash resistant, washable for printed circuit board assembly
Assembly – Some relays feature a sticker that keeps the enclosure sealed to allow PCB post soldering cleaning, which is removed once assembly is complete.
Mounting – sockets, plug board, rail mount, panel mount, through-panel mount, enclosure for mounting on walls or equipment
Switching time – where high speed is required 80
"Dry" contacts – when switching very low level signals, special contact materials may be needed such as gold-plated contacts
Contact protection – suppress arcing in very inductive circuits
Coil protection – suppress the surge voltage produced when switching the coil current
Isolation between coil circuit and contacts
Aerospace
or
radiation-resistant
testing,
special
quality
assurance
Expected mechanical loads due to acceleration – some relays used in aerospace applications are designed to function in shock loads of 50 g or more
Accessories such as timers, auxiliary contacts, pilot lamps, test buttons
Regulatory approvals
Stray magnetic linkage between coils of adjacent relays on a printed circuit board.
Advantages of relays:
Relays can switch AC and DC, transistors can only switch DC.
Relays can switch high voltages, transistors cannot.
Relays are a better choice for switching large currents (> 5A).
Relays can switch many contacts at once.
Disadvantages of relays:
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Relays are bulkier than transistors for switching small currents.
Relays cannot switch rapidly (except reed relays), transistors can switch many times per second.
Relays use more power due to the current flowing through their coil.
Relays require more current than many ICs can provide, so a low power transistor may be needed to switch the current for the relay's coil.
3.8: LCD
3.6: LCD DISPLAY LCD Background: One of the most common devices attached to a micro controller is an LCD display. Some of the most common LCD’s connected to the many microcontrollers are 16x2 and 20x2 displays. This means 16 characters per line by 2 lines and 20 characters per line by 2 lines, respectively. Basic 16x 2 Characters LCD Figure 1: LCD Pin diagram
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Pin description:
Pin No.
Name
Description
Pin no. 1
VSS
Power supply (GND)
Pin no. 2
VCC
Power supply (+5V)
Pin no. 3
VEE
Contrast adjust
Pin no. 4
RS
0
=
Instruction
input
1 = Data input 0 = Write to LCD module
Pin no. 5
R/W
1
=
Read
from
LCD
module Pin no. 6
EN
Enable signal
Pin no. 7
D0
Data bus line 0 (LSB)
Pin no. 8
D1
Data bus line 1
Pin no. 9
D2
Data bus line 2 83
Pin no. 10
D3
Data bus line 3
Pin no. 11
D4
Data bus line 4
Pin no. 12
D5
Data bus line 5
Pin no. 13
D6
Data bus line 6
Pin no. 14
D7
Data bus line 7 (MSB)
Table 1: Character LCD pins with Microcontroller The LCD requires 3 control lines as well as either 4 or 8 I/O lines for the data bus. The user may select whether the LCD is to operate with a 4-bit data bus or an 8-bit data bus. If a 4-bit data bus is used the LCD will require a total of 7 data lines (3 control lines plus the 4 lines for the data bus). If an 8-bit data bus is used the LCD will require a total of 11 data lines (3 control lines plus the 8 lines for the data bus). The three control lines are referred to as EN, RS, and RW. The EN line is called "Enable." This control line is used to tell the LCD that we are sending it data. To send data to the LCD, our program should make sure this line is low (0) and then set the other two control lines and/or put data on the data bus. When the other lines are completely ready, bring EN high (1) and wait for the minimum amount of time required by the LCD datasheet (this varies from LCD to LCD), and end by bringing it low (0) again.
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The RS line is the "Register Select" line. When RS is low (0), the data is to be treated as a command or special instruction (such as clear screen, position cursor, etc.). When RS is high (1), the data being sent is text data which should be displayed on the screen. For example, to display the letter "T" on the screen we would set RS high. The RW line is the "Read/Write" control line. When RW is low (0), the information on the data bus is being written to the LCD. When RW is high (1), the program is effectively querying (or reading) the LCD. Only one instruction ("Get LCD status") is a read command. All others are write commands--so RW will almost always be low. Finally, the data bus consists of 4 or 8 lines (depending on the mode of operation selected by the user). In the case of an 8-bit data bus, the lines are referred to as DB0, DB1, DB2, DB3, DB4, DB5, DB6, and DB7. Schematic:
Circuit Description:
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Above is the quite simple schematic. The LCD panel's Enable and Register Select is connected to the Control Port. The Control Port is an open collector / open drain output. While most Parallel Ports have internal pull-up resistors, there is a few which don't. Therefore by incorporating the two 10K external pull up resistors, the circuit is more portable for a wider range of computers, some of which may have no internal pull up resistors. We make no effort to place the Data bus into reverse direction. Therefore we hard wire the R/W line of the LCD panel, into write mode. This will cause no bus conflicts on the data lines. As a result we cannot read back the LCD's internal Busy Flag which tells us if the LCD has accepted and finished processing the last instruction. This problem is overcome by inserting known delays into our program. The 10k Potentiometer controls the contrast of the LCD panel. Nothing fancy here. As with all the examples, I've left the power supply out. We can use a bench power supply set to 5v or use an onboard +5 regulator. Remember a few de-coupling capacitors, especially if we have trouble with the circuit working properly. SETB RW Handling the EN control line: As we mentioned above, the EN line is used to tell the LCD that we are ready for it to execute an instruction that we've prepared on the data bus and on the other control lines. Note that the EN line must be raised/ lowered before/after each instruction sent to the LCD regardless of whether that instruction is read or write text or 86
instruction.
In
short,
we
must
always
manipulate
EN
when
communicating with the LCD. EN is the LCD's way of knowing that we are talking to it. If we don't raise/lower EN, the LCD doesn't know we're talking to it on the other lines. Thus, before we interact in any way with the LCD we will always bring the EN line low with the following instruction: CLR EN And once we've finished setting up our instruction with the other control lines and data bus lines, we'll always bring this line high: SETB EN The line must be left high for the amount of time required by the LCD as specified in its datasheet. This is normally on the order of about 250 nanoseconds, but checks the datasheet. In the case of a typical microcontroller running at 12 MHz, an instruction requires 1.08 microseconds to execute so the EN line can be brought low the very next instruction. However, faster microcontrollers (such as the DS89C420 which executes an instruction in 90 nanoseconds given an 11.0592 MHz crystal) will require a number of NOPs to create a delay while EN is held high. The number of NOPs that must be inserted depends on the microcontroller we are using and the crystal we have selected. The instruction is executed by the LCD at the moment the EN line is brought low with a final CLR EN instruction. Checking the busy status of the LCD:
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As previously mentioned, it takes a certain amount of time for each instruction to be executed by the LCD. The delay varies depending on the frequency of the crystal attached to the oscillator input of the LCD as well as the instruction which is being executed. While it is possible to write code that waits for a specific amount of time to allow the LCD to execute instructions, this method of "waiting" is not very flexible. If the crystal frequency is changed, the software will need to be modified. A more robust method of programming is to use the "Get LCD Status" command to determine whether the LCD is still busy executing the last instruction received. The "Get LCD Status" command will return to us two tidbits of information; the information that is useful to us right now is found in DB7. In summary, when we issue the "Get LCD Status" command the LCD will immediately raise DB7 if it's still busy executing a command or lower DB7 to indicate that the LCD is no longer occupied. Thus our program can query the LCD until DB7 goes low, indicating the LCD is no longer busy. At that point we are free to continue and send the next command.
Applications:
Medical equipment
Electronic test equipment
Industrial machinery Interface
Serial terminal
Advertising system
EPOS 88
Restaurant ordering systems
Gaming box
Security systems
R&D Test units
Climatizing units
PLC Interface
Simulators
Environmental monitoring
Lab development
Student projects
Home automation
PC external display
HMI operator interface.
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CHAPTER 4: SOFTWARE DESCRIPTION
This project is implemented using following software’s:
Express PCB – for designing circuit
PIC C compiler - for compilation part
Proteus 7 (Embedded C) – for simulation part
4.1 Express PCB: Breadboards are great for prototyping equipment as it allows great flexibility to modify a design when needed; however the final product of a project, ideally should have a neat PCB, few cables, and survive a shake test. Not only is a proper PCB neater but it is also more durable as there are no cables which can yank loose. Express PCB is a software tool to design PCBs specifically for manufacture by the company Express PCB (no other PCB maker accepts Express PCB files). It is very easy to use, but it does have several limitations. It can be likened to more of a toy then a professional CAD program. It has a poor part library (which we can work around)
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It cannot import or export files in different formats It cannot be used to make prepare boards for DIY production Express PCB has been used to design many PCBs (some layered and with surface-mount parts. Print out PCB patterns and use the toner transfer method with an Etch Resistant Pen to make boards. However, Express PCB does not have a nice print layout. Here is the procedure to design in Express PCB and clean up the patterns so they print nicely. 4.1.1 Preparing Express PCB for First Use: Express PCB comes with a less then exciting list of parts. So before any project is started head over to Audio logic and grab the additional parts by morsel, ppl, and tangent, and extract them into your Express PCB directory. At this point start the program and get ready to setup the workspace to suit your style. Click View -> Options. In this menu, setup the units for “mm” or “in” depending on how you think, and click “see through the top copper layer” at the bottom. The standard color scheme of red and green is generally used but it is not as pleasing as red and blue. 4.1.2 The Interface: When a project is first started you will be greeted with a yellow outline. This yellow outline is the dimension of the PCB. Typically after positioning of parts and traces, move them to their final position and then crop the PCB to the correct size. However, in designing a board with a certain size constraint, crop the PCB to the correct size before starting. 91
Fig: 4.1 show the toolbar in which the each button has the following functions:
Fig 4.1: Tool bar necessary for the interface
The select tool: It is fairly obvious what this does. It allows you to move
and manipulate parts. When this tool is selected the
top toolbar will show buttons to move traces to the top / bottom copper layer, and rotate buttons.
The zoom to selection tool: does just that.
The place pad: button allows you to place small soldier pads which are useful for board connections or if a part is not in the part library but the part dimensions are available. When this tool is selected the top toolbar will give you a large selection of round holes, square holes and surface mount pads.
The place component: tool allows you to select a component from the top toolbar and then by clicking in the workspace places that component in the orientation chosen using the buttons next to the component list. The components can always be rotated afterwards with the select tool if the orientation is wrong.
The place trace: tool allows you to place a solid trace on the board of varying thicknesses. The top toolbar allows you to select the top or bottom layer to place the trace on.
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The Insert Corner in trace: button does exactly what it says. When this tool is selected, clicking on a trace will insert a corner which can be moved to route around components and other traces.
The remove a trace button is not very important since the delete key will achieve the same result.
4.1.3 Design Considerations: Before starting a project there are several ways to design a PCB and one must be chosen to suit the project’s needs. Single sided, or double sided: When making a PCB you have the option of making a single sided board, or a double sided board. Single sided boards are cheaper to produce and easier to etch, but much harder to design for large projects. If a lot of parts are being used in a small space it may be difficult to make a single sided board without jumpering over traces with a cable. While there’s technically nothing wrong with this, it should be avoided if the signal traveling over the traces is sensitive (e.g. audio signals). A double sided board is more expensive to produce professionally, more difficult to etch on a DIY board, but makes the layout of components a lot smaller and easier. It should be noted that if a trace is running on the top layer, check with the components to make sure you can get to its pins with a soldering iron.
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Large capacitors, relays, and similar parts which don’t have axial leads can NOT have traces on top unless boards are plated professionally. Ground-plane or other special purposes for one side: When using a double sided board you must consider which traces should be on what side of the board. Generally, put power traces on the top of the board, jumping only to the bottom if a part cannot be soldiered onto the top plane (like a relay), and viceversa. Some projects like power supplies or amps can benefit from having a solid plane to use for ground. In power supplies this can reduce noise, and in amps it minimizes the distance between parts and their ground connections, and keeps the ground signal as simple as possible. However, care must be taken with stubborn chips such as the TPA6120 amplifier from TI. The TPA6120 datasheet specifies not to run a ground plane under the pins or signal traces of this chip as the capacitance generated could effect performance negatively. 4.2 PIC Compiler: PIC compiler is software used where the machine language code is written and compiled. After compilation, the machine source code is converted into hex code which is to be dumped into the microcontroller for further processing. PIC compiler also supports C language code. It’s important that you know C language for microcontroller which is commonly known as Embedded C. As we are 94
going to use PIC Compiler, hence we also call it PIC C. The PCB, PCM, and PCH are separate compilers. PCB is for 12-bit opcodes, PCM is for 14-bitopcodes, and PCH is for 16-bit opcode PIC microcontrollers. Due to many similarities, all three compilers are covered in this reference manual. Features and limitations that apply to only specific microcontrollers are indicated within. These compilers are specifically designed to meet the unique needs of the PIC microcontroller. This allows developers to quickly design applications software in a more readable, high-level language. When compared to a more traditional C compiler, PCB, PCM, and PCH have some limitations. As an example of the limitations, function recursion is not allowed. This is due to the fact that the PIC has no stack to push variables onto, and also because of the way the compilers optimize the code. The compilers can efficiently implement normal C constructs, input/output operations, and bit twiddling operations. All normal C data types are supported along with pointers to constant arrays, fixed point decimal, and arrays of bits. PIC C is not much different from a normal C program. If you know assembly, writing a C program is not a crisis. In PIC, we will have a main function, in which all your application specific work will be defined. In case of embedded C, you do not have any operating system running in there. So you have to make sure that your program or main file should never exit. This can be done with the help of simple while (1) or for (;;) loop as they are going to run infinitely. We have to add header file for controller you are using, otherwise you will not be able to access registers related to peripherals.
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#include <16F72.h> // header file for PIC 16F72// 4.3 Proteus: Proteus is software which accepts only hex files. Once the machine code is converted into hex code, that hex code has to be dumped into the microcontroller and this is done by the Proteus. Proteus is a programmer which itself contains a microcontroller in it other than the one which is to be programmed. This microcontroller has a program in it written in such a way that it accepts the hex file from the pic compiler and dumps this hex file into the microcontroller which is to be programmed. As the Proteus programmer requires power supply to be operated, this power supply is given from the power supply circuit designed and connected to the microcontroller in proteus. The program which is to be dumped in to the microcontroller is edited in proteus and is compiled and executed to check any errors and hence after the successful compilation of the program the program is dumped in to the microcontroller using a dumper. 4.4 Procedural steps for compilation, simulation and dumping: 4.4.1 Compilation and simulation steps: For PIC microcontroller, PIC C compiler is used for compilation. The compilation steps are as follows:
Open PIC C compiler.
You will be prompted to choose a name for the new project, so create a separate folder where all the files of your project will be stored, choose a name and click save. 96
Fig 4.1: Picture of opening a new file using PIC C compiler
Click Project, New, and something the box named 'Text1' is where your code should be written later.
Now you have to click 'File, Save as' and choose a file name for your source code ending with the letter '.c'. You can name as 'project.c' for example and click save. Then you have to add this file to your project work.
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Fig 4.2: Picture of compiling a new file using PIC C compiler
Fig 4.3: Picture of compiling a project.c file using PIC C compiler
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You can then start to write the source code in the window titled 'project.c' then before testing your source code; you have to compile your source code, and correct eventual syntax errors.
Fig 4.4: Picture of checking errors and warnings using PIC C compiler
By
clicking
on
compile
option
automatically.
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.hex
file
is
generated
This is how we compile a program for checking errors and hence the compiled program is saved in the file where we initiated the program.
Fig 4.5: Picture of .hex file existing using PIC C compiler
After compilation, next step is simulation. Here first circuit is designed in Express PCB using Proteus 7 software and then simulation takes place followed by dumping. The simulation steps are as follows:
Open Proteus 7 and click on IS1S6.
Now
it
displays
PCB
where
circuit
is
designed
using
microcontroller. To design circuit components are required. So click on component option.
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10. Now click on letter ’p’, then under that select PIC16F72 ,other components related to the project and click OK. The PIC 16F72 will be called your “'Target device”, which is the final destination of your source code.
4.4.2 Dumping steps: The steps involved in dumping the program edited in proteus 7 to microcontroller are shown below: 1. Initially before connecting the program dumper to the microcontroller kit the window is appeared as shown below.
101
Fig 4.6: Picture of program dumper window
2. Select Tools option and click on Check Communication for establishing a connection as shown in below window
102
Fig 4.7: Picture of checking communications before dumping program into microcontroller 103
3. After connecting the dumper properly to the microcontroller kit the window is appeared as shown below.
104
Fig 4.8: Picture after connecting the dumper to microcontroller 105
4. Again by selecting the Tools option and clicking on Check Communication the microcontroller gets recognized by the dumper and hence the window is as shown below.
106
Fig 4.9: Picture of dumper recognition to microcontroller
107
5. Import the program which is ‘.hex’ file from the saved location by selecting File option and clicking on ‘Import Hex’ as shown in below window.
108
109
Fig 4.10: Picture of program importing into the microcontroller
6. After clicking on ‘Import Hex’ option we need to browse the location of our program and click the ‘prog.hex’ and click on ‘open’ for dumping the program into the microcontroller.
Fig 4.11: Picture of program browsing which is to be dumped
7. After the successful dumping of program the window is as shown below.
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Fig 4.12: Picture after program dumped into the microcontroller
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CHAPTER 5: PROJECT DESCRIPTION In this chapter, schematic diagram and interfacing of PIC16F877 microcontroller with each module is considered.
Fig 5.1: schematic diagram of THREE PHASE INDUCTION MOTOR PROTECTION SYSTEM
The above schematic diagram of THREE PHASE
INDUCTION MOTOR PROTECTION SYSTEM explains the interfacing section of each component with micro controller and current sensor module. The crystal oscillator connected to 9th and 10th pins of micro controller and regulated power supply is also connected
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to micro controller and LED’s also connected to micro controller through resistors and motor driver connected to micro controller The detailed explanation of each module interfacing with microcontroller is as follows:
5.2 Interfacing crystal oscillator with micro controller: Fig 5.2: explains crystal oscillator and reset button which are connected to micro controller. The two pins of oscillator are connected to the 9th and 10th pins of micro controller; the purpose of external crystal oscillator is to speed up the execution part of instructions per cycle and here the crystal oscillator having 20 MHz frequency. The 1st pin of the microcontroller is referred as MCLR ie.., master clear pin or reset input pin is connected to reset button or power-on-reset.
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Fig 5.2: crystal oscillator interfacing with micro controller 5.4 LED interfacing with PIC16F72: LED stands for Light Emitting Diode and these are connected to micro controller through resistors.
Fig 5.4: LED interfacing with PIC microcontroller 5.5 Relay interfacing with PIC16F72:
Fig 5.5: Relay interfacing with PIC microcontroller 114
CHAPTER 6: ADVANTAGES AND DISADVANTAGES
Advantages: 1. Faster protection of critical electrical equipment. 2. Heavy-duty irrigation water pumps. 3. Industrial drive motors. 4. Any three phase driven industrial loads. 5. Conservation of energy. 6. Efficient and low cost design. 7. Low power consumption. 8. Easy to install. 9. Fast response.
Disadvantages: Interfacing High voltage sensor to the Micro Controller is sensitive.
Applications: 1. Rural installations. 2. Heavy industrial loads. 3. Public lighting 4. Irrigation water pumps
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CHAPTER 7: RESULTS 7.1 Result:
The project “Microcontroller based automatic THREE
PHASE INDUCTION MOTOR PROTECTION SYSTEM ” was designed such that to construct a single phasing monitor and prevention system using 8-bit microcontroller. Anti-single phasing relays or single phasing preventer are required for critical loads and circuits. 7.2 Conclusion: A single phase earth fault protection is relatively easy to establish on most power systems compared to other protection schemes. Flexibility of fault analysis depends upon the complexity of power system. Hence we can conclude that the occurrence of earth fault at any point in a single phase system can be easily detected using earth fault protection scheme. By installing the earth fault protection scheme, a consumer can be aware whether he is exactly charged, or not, for his energy consumption. Integrating features of all the hardware components used have been developed in it. Presence of every module has been reasoned out and placed carefully, thus contributing to the best working of the unit. Secondly, using highly advanced IC’s with the help of growing
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technology, the project has been successfully implemented. Thus the project has been successfully designed and tested. Microcontroller based automatic Single Phasing Preventing System for 3-phase Industrial Motors
7.3 Future Scope: We can extend the project by adding GSM modem through which we can send the alerts when the fault occurred. We can add even high voltage devices with protection circuits. The system can also added using wireless modules Like PLCC, zigbee, and RF communication which can alert from distances.
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REFERENCES
The sites which were used while doing this project: 1. www.wikipedia.com 2. www.allaboutcircuits.com 3. www.microchip.com 4. www.howstuffworks.com
Books referred:
1. Raj
kamal
–Microcontrollers
Architecture,
Interfacing and System Design. 2. Mazidi and Mazidi –Embedded Systems. 3. PCB Design Tutorial –David.L.Jones. 4. PIC Microcontroller Manual – Microchip. 5. Pyroelectric Sensor Module- Murata.
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Programming,
6. Embedded C –Michael.J.Pont.
APPENDIX Program Code: The program code which is dumped in the microcontroller of our project is shown below. #include <16F72.h> #include
#include #include #fuses
HS,NOWDT,PROTECT,brownout,put
#use
delay
(clock=20000000)
void main() { int i = 0; void main() { lcd_init(); lcd_putc('\f'); // Clear LCD lcd_gotoxy(1,1); // row-1, column-1 printf(lcd_putc," AC induction "); lcd_gotoxy(1,2); // row-1, column-2 printf(lcd_putc," protection "); delay_ms(2000); //Microcontroller Health Check Start output_high(PIN_C3);
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delay_ms(1000); output_low(PIN_C3); delay_ms(1000); output_high(PIN_C3); delay_ms(1000); output_low(PIN_C3); output_high(PIN_C4); delay_ms(1000); output_low(PIN_C4); delay_ms(1000); while(1) { if(!(input(PIN_A0) && input(PIN_A2) && input(PIN_A5))) { output_low(PIN_C7); } if(!input(PIN_A0)) { lcd_putc('\f'); lcd_gotoxy(1,1); printf(lcd_putc,"R-Phase Fault"); output_high(PIN_C3); output_high(PIN_C7); delay_ms(100); } if(!input(PIN_A2)) { lcd_putc('\f'); lcd_gotoxy(1,1); printf(lcd_putc,"Y-Phase Fault"); output_high(PIN_C3); output_high(PIN_C7); output_low(PIN_C2); output_high(PIN_C1); output_high(PIN_C3); delay_ms(100); } if(!input(PIN_A5)) { lcd_putc('\f'); lcd_gotoxy(1,1); printf(lcd_putc,"B-Phase Fault"); output_high(PIN_C3); output_high(PIN_C7); output_low(PIN_C3); output_high(PIN_C2); output_high(PIN_C1); delay_ms(100);
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} } }
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