Essay: Password based circuit breaker – A PROJECT REPORT

CHAPTER 1
INTRODUCTION
The entire project is based on Embedded Systems. In this project Microcontroller are used which controls all the operations in regarding the password system. For this process we require the components like microcontroller,control circuitry, power supply and key pad. This key pads are used for entering password for operating different load which are connected to the controller. If suppose password is wrong, then load will not be switched to the controller and then the controller checks for the precaution instruction which is provided by the developer. This includes the operations such as the number of loads to be opened, the number of threshold levels that are crossed. In this process the controller checks the number of threshold levels that are crossed and according to that the gates are being controlled.
1.1 Embedded System
The embedded systems are electronic devices which are incorporated microprocessors with in their implementations. The embedded systems designers generally have a significant grasps over hardware technologies. They use specific programming languages and software to develop embedded systems and manipulate the equipment. Embedded systems often use a slow processor and small memory size to minimize costs. An embedded system is a special-purpose system in which the computer is completely encapsulated by or dedicated to the device or system it controls. Unlike a general-purpose computer, such as a personal computer, an embedded system performs one or a few pre-defined tasks, usually with very specific requirements.
1.2 Micro controller
Microcontrollers as name suggests are small controllers. They as single chip computers that are often embedded into other systems to function as processing/controlling unit. Microcontroller – A single chip is used to controlling other devices. Any microcomputer system requires memory for storing the sequence of instructions for making up a pro-gram, parallel port or serial port for communicating with an external system, the timer for controlling purpose like generating time delays, Baud rate for the serial port, apart from the controlling unit called the Central Processing Unit.
CHAPTER 2
DESCRIPTION OF PROJECT
Hardware Introductions
2.1 Circuit Diagram
Working
The Circuit diagram of MICROCONTROLLER base circuit breaker is as shown in Fig (1.2). The Main Part of the above Circuit diagrams is the Microcontroller. The Keypad is the input device and it is connected in a matrix (4”3) format so that the numbers of ports needed are reduced ,the key pad is connected with microcontroller at port no (P1.0,1.1,1.2,1.4,1.5,1.6,1.7) .The LCD display is used as indicator which is connected with controller at port no(p3.0 TXD,p3.1 RXD,p3.7,p3.5) & another pin no 1 VSS is connected with ground & pin no 3 VCC is connected with +5v.The crystal is used for generate stable clock pulses which is connected with (P5 XTAL1&P6 XTAL2) .The BC547 is NPN type transistor which is connected with P1.3 , the collector of transistor is connected with relay. The loud speaker is connected with P3.4.The pin no 1 is RST (RESET).
When we enter the password through key pad first of all the password is load in controller ,the controller converts the password in BINARY, then controller compare the password with EPROM password , If password is match with EPROM password , then controller switch ON the relay, the relay is also connected with O\P device and we get output. But if we enter three time wrong password then buzzer is switched ON. By pressing RST button we can switched OFF the buzzer.
2.2 Power supply
The power supplies are designed to convert high voltage AC mains electricity to a suitable low voltage supply for electronic circuits and other devices. A power supply can by broken down into a series of blocks, each of which performs a particular function. A d.c power supply which maintains the output voltage constant irrespective of a.c mains fluctuations or load variations is known as ‘Regulated D.C Power Supply’.
For example a 5V regulated power supply system as shown below:
Fig 2.2 5V regulated power supply system
The regulated DC output is very smooth with no ripple. It is suitable for all electronic circuits.
2.2.1 Transformer
Transformers convert AC electricity from one voltage to another with little loss of power. Transformers work only with AC and this is one of the reasons why mains electricity is AC. Step-up transformers increase voltage, step-down transformers reduce voltage. Most power supplies use a step-down transformer to reduce the dangerously high mains voltage (230V in UK) to a safer low voltage.
Transformers waste very little power so the power out is (almost) equal to the power in. Note that as voltage is stepped down current is stepped up.
2.2.2 Rectifier
A circuit which is used to convert a.c to dc is known as ‘rectifier’. The process of conversion a.c to d.c is called ‘rectification’
Types of rectifier:
‘ Half wave Rectifier
‘ Full wave rectifier
1. Centre tap full wave rectifier.
2. Bridge type full bridge rectifier.
Bridge Rectifier: A bridge rectifier makes use of four diodes in a bridge arrangement to achieve full-wave rectification. This is a widely used configuration, both with individual diodes wired as shown and with single component bridges where the diode bridge is wired internally.
A bridge rectifier makes use of four diodes in a bridge arrangement as shown in fig below to achieve full-wave rectification. This is a widely used configuration, both with individual diodes wired as shown and with single component bridges where the diode bridge is wired internally.
Fig 2.2.2 Bridge Rectifier arrangement
2.2.3 Filter
A Filter is a device which removes the a.c component of rectifier output but allows the d.c component to reach the load.We have seen that the ripple content in the rectified output of half wave rectifier is 121% or that of full-wave or bridge rectifier or bridge rectifier is 48% such high percentages of ripples is not acceptable for most of the applications. Ripples can be removed by one of the following methods of filtering.
‘ A capacitor, in parallel to the load, provides an easier by ‘pass for the ripples voltage though it due to low impedance. At ripple frequency and leave the d.c.to appears the load.
‘ An inductor, in series with the load, prevents the passage of the ripple current (due to high impedance at ripple frequency) while allowing the d.c (due to low resistance to d.c)
2.2.4 Regulator
Voltage regulator ICs is available with fixed (typically 5, 12 and 15V) or variable output voltages. The maximum current they can pass also rates them. Negative voltage regulators are available, mainly for use in dual supplies. Most regulators include some automatic protection from excessive current (‘overload protection’) and overheating (‘thermal protection’). Many of the fixed voltage regulator ICs has 3 leads and look like power transistors, such as the 7805 +5V 1A regulator shown on the right. The LM7805 is simple to use. You simply connect the positive lead of your unregulated DC power supply (anything from 9VDC to 24VDC) to the Input pin, connect the negative lead to the Common pin and then when you turn on the power, you get a 5 volt supply from the output pin. Regulator eliminates ripple by setting DC output to a fixed voltage.
Fig 2.2.4 Regulator
2.3 Micro controller
ATmega16 is an 8-bit high performance microcontroller of Atmel’s Mega AVR family with low power consumption. Atmega16 is based on enhanced RISC (Reduced Instruction Set Computing, Know more about RISC and CISC Architecture) architecture with 131 powerful instructions. Most of the instructions execute in one machine cycle. Atmega16 can work on a maximum frequency of 16MHz
ATmega16 has 16 KB programmable flash memory, static RAM of 1 KB and EEPROM of 512 Bytes. The endurance cycle of flash memory and EEPROM is 10,000 and 100,000, respectively.
ATmega16 is a 40 pin microcontroller. There are 32 I/O (input/output) lines which are divided into four 8-bit ports designated as PORTA, PORTB, PORTC and PORTD.
ATmega16 has various in-built peripherals like USART, ADC, Analog Comparator, SPI, JTAG etc. Each I/O pin has an alternative task related to in-built peripherals. The following table shows the pin description of ATmega16.
2.3.1 Features:
‘ High-performance, Low-power Atmel” AVR” 8-bit Microcontroller
‘ Advanced RISC Architecture
o 131 Powerful Instructions ‘ Most Single-clock Cycle Execution
o 32 x 8 General Purpose Working Registers
o Fully Static Operation
o Up to 16 MIPS Throughput at 16 MHz
o On-chip 2-cycle Multiplier
‘ High Endurance Non-volatile Memory segments
o 16 Kbytes of In-System Self-programmable Flash program memory
o 512 Bytes EEPROM
o 1 Kbyte Internal SRAM
o Write/Erase Cycles: 10,000 Flash/100,000 EEPROM
o Data retention: 20 years at 85”C/100 years at 25”C(1)
o Optional Boot Code Section with Independent Lock Bits
o In-System Programming by On-chip Boot Program
o True Read-While-Write Operation
o Programming Lock for Software Security
‘ JTAG (IEEE std. 1149.1 Compliant) Interface
o Boundary-scan Capabilities According to the JTAG Standard
o Extensive On-chip Debug Support
o Programming of Flash, EEPROM, Fuses, and Lock Bits through the JTAG Interface
‘ Peripheral Features
o Two 8-bit Timer/Counters with Separate Presales and Compare Modes
o One 16-bit Timer/Counter with Separate Presale, Compare Mode, and Capture
‘ Mode
o Real Time Counter with Separate Oscillator
o Four PWM Channels
o 8-channel, 10-bit ADC
‘ 8 Single-ended Channels
‘ 7 Differential Channels in TQFP Package Only
‘ 2 Differential Channels with Programmable Gain at 1x, 10x, or 200x
o Byte-oriented Two-wire Serial Interface
o Programmable Serial USART
o Master/Slave SPI Serial Interface
o Programmable Watchdog Timer with Separate On-chip Oscillator
o On-chip Analog Comparator
‘ Special Microcontroller Features
o Power-on Reset and Programmable Brown-out Detection
o Internal Calibrated RC Oscillator
o External and Internal Interrupt Sources
o Six Sleep Modes: Idle, ADC Noise Reduction, Power-save, Power-down, Standby and Extended Standby
‘ I/O and Packages
o 32 Programmable I/O Lines
o 40-pin PDIP, 44-lead TQFP, and 44-pad QFN/MLF
‘ Operating Voltages
‘ ‘ 2.7V – 5.5V for ATmega16L
‘ ‘ 4.5V – 5.5V for ATmega16
‘ Speed Grades
o 0 – 8 MHz for ATmega16L
o 0 – 16 MHz for ATmega16
‘ Power Consumption @ 1 MHz, 3V, and 25”C for ATmega16L
o Active: 1.1 mA
o Idle Mode: 0.35 mA
o Power-down Mode: < 1 ”A
2.3.2 Pin Diagram:
2.3.3 Pin Descriptions:
Pin No. Pin name Description Alternate Function
1 (XCK/T0) PB0 I/O PORTB, Pin 0 T0: Timer0 External Counter Input.
XCK : USART External Clock I/O
2 (T1) PB1 I/O PORTB, Pin 1 T1:Timer1 External Counter Input
3 (INT2/AIN0) PB2 I/O PORTB, Pin 2 AIN0: Analog Comparator Positive I/P
INT2: External Interrupt 2 Input
4 (OC0/AIN1) PB3 I/O PORTB, Pin 3 AIN1: Analog Comparator Negative I/P
OC0 : Timer0 Output Compare Match Output
5 (SS) PB4 I/O PORTB, Pin 4 In System Programmer (ISP)
Serial Peripheral Interface (SPI)
6 (MOSI) PB5 I/O PORTB, Pin 5
7 (MISO) PB6 I/O PORTB, Pin 6
8 (SCK) PB7 I/O PORTB, Pin 7
9 RESET Reset Pin, Active Low Reset
10 Vcc Vcc = +5V
11 GND GROUND
12 XTAL2 Output to Inverting Oscillator Amplifier
13 XTAL1 Input to Inverting Oscillator Amplifier
14 (RXD) PD0 I/O PORTD, Pin 0 USART Serial Communication Interface
15 (TXD) PD1 I/O PORTD, Pin 1
16 (INT0) PD2 I/O PORTD, Pin 2 External Interrupt INT0
17 (INT1) PD3 I/O PORTD, Pin 3 External Interrupt INT1
18 (OC1B) PD4 I/O PORTD, Pin 4 PWM Channel Outputs
19 (OC1A) PD5 I/O PORTD, Pin 5
20 (ICP) PD6 I/O PORTD, Pin 6 Timer/Counter1 Input Capture Pin
21 PD7 (OC2) I/O PORTD, Pin 7 Timer/Counter2 Output Compare Match Output
22 PC0 (SCL) I/O PORTC, Pin 0 TWI Interface
23 PC1 (SDA) I/O PORTC, Pin 1
24 PC2 (TCK) I/O PORTC, Pin 2 JTAG Interface
25 PC3 (TMS) I/O PORTC, Pin 3
26 PC4 (TDO) I/O PORTC, Pin 4
27 PC5 (TDI) I/O PORTC, Pin 5
28 PC6 (TOSC1) I/O PORTC, Pin 6 Timer Oscillator Pin 1
29 PC7 (TOSC2) I/O PORTC, Pin 7 Timer Oscillator Pin 2
30 AVcc Voltage Supply = Vcc for ADC
31 GND GROUND
32 AREF Analog Reference Pin for ADC
33 PA7 (ADC7) I/O PORTA, Pin 7 ADC Channel 7
34 PA6 (ADC6) I/O PORTA, Pin 6 ADC Channel 6
35 PA5 (ADC5) I/O PORTA, Pin 5 ADC Channel 5
36 PA4 (ADC4) I/O PORTA, Pin 4 ADC Channel 4
37 PA3 (ADC3) I/O PORTA, Pin 3 ADC Channel 3
38 PA2 (ADC2) I/O PORTA, Pin 2 ADC Channel 2
39 PA1 (ADC1) I/O PORTA, Pin 1 ADC Channel 1
40 PA0 (ADC0) I/O PORTA, Pin 0 ADC Channel 0
2.3.4 Block Diagram:
2.4 LCD Display
LCD (Liquid Crystal Display) screen is an electronic display module and find a wide range of applications. A 16×2 LCD display is very basic module and is very commonly used in various devices and circuits. These modules are preferred over seven segments and other multi segment LEDs. The reasons being: LCDs are economical; easily programmable; have no limitation of displaying special & even custom characters (unlike in seven segments), animations and so on.A 16×2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in 5×7 pixel matrix. This LCD has two registers, namely, Command and Data.
The command register stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing it, clearing its screen, setting the cursor position, controlling display etc. The data register stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD. Click to learn more about internal structure of a LCD.
A 16×2 LCD means it can display 16 characters per line and there are 2 such lines. In this LCD each character is displayed in 5×7 pixel matrix. The LCD discussed in this section has 16 pins.
The function of each pin is given in Table.
2.4.1 Pin configuration:
Pin Symbol Description
1 VSS Ground 0 V
2 VCC Main power supply +5 V
3 VEE Power supply to control contrast Contrast adjustment by providing a variable resistor through VCC
4 RS Register Select
RS=0 to select Command Register
RS=1 to select Data Register
5 R/W Read/write
R/W=0 to write to the register
R/W=1 to read from the register
6 EN Enable A high to low pulse (minimum 450ns wide) is given when data is sent to data pins
7 DB0 To display letters or numbers, their ASCII codes are sent to data pins (with RS=1). Also instruction command codes are sent to these pins.
8 DB1
9 DB2
10 DB3 8-bit data pins
11 DB4
12 DB5
13 DB6
14 DB7
15 Led+ Backlight VCC +5 V
16 Led- Backlight Ground 0 V
Table 2: Pin configuration of LCD
. This LCD has two registers.
‘ Command/Instruction Register- stores the command instructions given to the LCD. A command is an instruction given to LCD to do a predefined task like initializing, clearing the screen, setting the cursor position, controlling display etc.
‘ Data Register- stores the data to be displayed on the LCD. The data is the ASCII value of the character to be displayed on the LCD.
2.4.2 Features:
‘ Built-in controller (KS 0066 or Equivalent)
‘ + 5V power supply (Also available for + 3V)
‘ B/L to be driven by pin 1, pin 2 or pin 15, pin 16 or A.K (LED)
‘ N.V. optional for + 3V power supply
‘ 61 x 15.8 mm viewing area
‘ 5 x 7 dot matrix format for 2.96 x 5.56 mm characters, plus cursor line
‘ Can display 224 different symbols
‘ Low power consumption (1 mA typical)
‘ Powerful command set and user-produced characters
‘ TTL and CMOS compatible
2.5 Relay
Relay is an electromagnetic device which is used to isolate two circuits electrically and connect them magnetically. They are very useful devices and allow one circuit to switch another one while they are completely separate. They are often used to interface an electronic circuit (working at a low voltage) to an electrical circuit which works at very high voltage. For example, a relay can make a 5V DC battery circuit to switch a 230V AC mains circuit. Thus a small sensor circuit can drive, say, a fan or an electric bulb. A relay switch can be divided into two parts: input and output. The input section has a coil which generates magnetic field when a small voltage from an electronic circuit is applied to it. This voltage is called the operating voltage. Commonly used relays are available in different configuration of operating voltages like 6V, 9V, 12V, 24V etc. The output section consists of contactors which connect or disconnect mechanically. In a basic relay there are three contactors: normally open (NO), normally closed (NC) and common (COM). At no input state, the COM is connected to NC. When the operating voltage is applied the relay coil gets energized and the COM changes contact to NO. Different relay configurations are available like SPST, SPDT, DPDTetc, which have different number of changeover contacts. By using proper combination of contactors, the electrical circuit can be switched on and off. Get inner details about structure of a relay switch.
Despite the speed of technological developments, some products prove so popular that their key parameters and design features remain virtually unchanged for years. One such product is the ‘sugar cube’ relay, shown in the figure above, which has proved useful to many designers who needed to switch up to 10A, whilst using relatively little PCB area 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 relay is inactive. It is also called form B contact or’ break’ contact
Change-Over or double-throw contacts control two circuits ; one normally open contact and one normally ‘closed contact with a commom terminal. It is also called a Form C ‘transfer’ contact.
Relay is one of the most important electromechanical devices highly used in industrial applications specifically in automation. A relay is used for electronic to electrical interfacing i.e. it is used to switch on or off electrical circuits operating at high AC voltage using a low DC control voltage. A relay generally has two parts, a coil which operates at the rated DC voltage and a mechanically movable switch. The electronic and electrical circuits are electrically isolated but magnetically connected to each other, hence any fault on either side does not affects the other side.
Relay switch shown in the image above consists of five terminals. Two terminals are used to give the input DC voltage also known as the operating voltage of the relay. Relays are available in different operating voltages like 6V, 12V, 24V etc. The rest of the three terminals are used to connect the high voltage AC circuit. The terminals are called Common, Normally Open (NO) and Normally Closed (NC). Relays are available in various types & categories and in order to identify the correct configuration of the output terminals, it is best to see the data sheet or manual. You can also identify the terminals using a multi meter and at times it is printed on the relay itself.
2.6 key pad
Many application requires large number of keys connected to a computing system.
Example includes a PC keyboard, Cell Phone keypad and Calculators. If we connect
a single key to MCU, we just connect it directly to
i/o line. But we cannot connect, say 10 or 100 keys directly MCUs i/o. Because
:-
‘ It will eat up precious i/o line.
‘ MCU to Keypad interface will contain lots of wires.
‘ As you can see in the image above C0 is made LOW while all other Columns are
in HIGH Z State. We can read the Value of R0 to R3 to get their pressed status.
If they are high the button is NOT pressed. As we have enabled internal pullups
on them, these pullups keep their value high when they are floating (that means
NOT connected to anything). But when a key is pressed it is connected to LOW
line from the column thus making it LOW.
‘ After that we make the C0 High Z again and make C1 LOW. And read R0 to R3 again.
This gives us status of the second column of keys. Similarly we scan all columns.
CHAPTER 3
SOFTWARE INTRODUCTION
Mainly following software tools are required
‘ Eagle PCB Design Soft
‘ WinAVR for Microcontroller Emulator
3.1 EAGLE PCB Design Software:
For PCB designing we used EAGLE software. EAGLE is abbreviation of EASILY APPLICABLE GRAPHICAL LAYOUT EDITOR. A number of EAGLE editions are offered. We are using CadSoft Eagle Professional v6.1.0 for Windows. You can add an AutoRoute Module and/or a Schematic diagram Module to the Layout Editor. The term module is used because EAGLE always behaves like one single program. The user interface is identical for all parts of the program.
3.1.1 features of EAGLE for PCB designing:
‘ Maximum drawing area 64 x 64 inches
‘ Resolution 1/10,000 mm (0.1 microns)
‘ Mm or inch grid
‘ Up to 255 layers, user definable colors
‘ command (script) files
‘ C-like User Language for data export and import and the realization of self-defined commands
‘ Easy library editing
‘ Composition of self-defined libraries by Drag & Drop
‘ Simple generation of new package variants from other libraries by Drag & Drop
‘ Free rotation of package variants (0.1-degree steps)
‘ Library browser and convenient component search function
‘ Technology support (e. g. 74L00, 74LS00…)
‘ Output of manufacturing data on plotter, photo plotter and drilling machine or as a graphic data format
‘ print via the operating systems’ printer devices
‘ User definable, free programmable User Language for generating data for mounting machines, in-circuit tester and milling machines
‘ Drag & Drop in the Control Panel
‘ Automatic backup function
Fig 3.1.1: the schematic editor window of EAGLE
3.2 Introduction to WinAvr:
‘ WinAvr is a suite of executable, open source software development tools for the Atmel AVR series of RISC microprocessors hosted on the Windows platform. It includes the GNU GCC compiler for C and C++.
‘ inAVR is a set of open source software development tools for C programming the AVR microcontroller family. It includes the GNU GCC compiler for C and the Programmers Notepad.
‘ Winavr is not just one tool, like many other software names. Winavr is instead a set of tools, these tools include avr-gcc (the command line compiler), avr-libc (the compiler library that is essential for avrgcc), avr-as (the assembler), avrdude (the programming interface), avarice (JTAG ICE interface), avr-gdb (the de-bugger), programmers notepad (editor) and a few others. These tools are all compiled for Microsoft Windows and put together with a nice installer program.
3.2.1Programmers Notepad
‘ The C code will be written using the Programmers Notepad, it is included in the WinAVR package.
‘ Where’s the GUI/IDE WinAVR comes with an editor/IDE called Programmers Notepad. This is an Open Source editor with some IDE capabilities. Because the compiler and associated utilities are all command-line driven, you are free to use whatever editor / IDE you want to provide it can call command-line programs. See below for more information on Programmers Notepad.
‘ Programmers Notepad (PN) is an Open Source editor with some IDE features. It is used for writing program for AVR micro controller.
3.2.2 File Template
‘ Make is a program that is widely used to build software. Make reads and executes make files, which are descriptions of how to build something. Make files typical do things such as group files together, set lists of compiler and linker flags, list rules of how to compile source code to object code, how to link object files, how to convert files from one type to another, and many other things.
‘ When you set up your project, add a makefile to control how to build your software. When you use Programmers Notepad, or other IDE, set it up to call make and have it execute your project’s make file.
‘ Three Makefile Templates are included in WinAVR, which provides a lot of functionality already written for us. There is the standard Makefile Template (Makefile) that has always been included with WinAVR. In Makefile we have to change name of AVR controller , clock frequency, add name of target file
‘ WinAVR also includes the Mfile utility. MFile is a automatic makefile generator for AVR GCC written in Tcl/Tk and can run on various platforms including Windows, FreeBSD, Linux, etc. You can use this utility to help you quickly generate a makefile for your project based on some simple menu input. MFile for the Windows platform uses the WinAVRMakefile Template for it’s template.
‘ open Mfile and select MCU target via Makefile>>MCU type
‘ specify name of file which is to be written in Program Notepad
‘ save as makefile at same folder where .c file is present.
‘ Now, open Program notepad and select new C file
‘ Save that file as XXXX.c, where .c denotes c program file
‘ Write code on that .c file
‘ Save file and compile that program
‘ To compile program TOOL>>MAKE CLEAN so that all previous file will be removed.
‘ Then press MAKEALL for compile and creating .HEX, .EEP file
‘ .Hex file used for controller to set user define logic
‘ .EEP file used for non volatile memory storage
CHAPTER 4
Proteus Simulator
4. Proteus Simulator:
Proteus 7.6 is a Virtual System Modelling (VSM) that combines circuit simulation, animated components and microprocessor models to co-simulate the complete microcontroller based designs.
This is the perfect tool for engineers to test their microcontroller designs before constructing a physical prototype in real time. This program allows users to interact with the design using on-screen indicators and/or LED and LCD displays and, if attached to the PC, switches and buttons.
One of the main components of Proteus 7.6 is the Circuit Simulation — a product that uses a SPICE3f5 analogue simulator kernel combined with an event-driven digital simulator that allow users to utilize any SPICE model by any manufacturer. Proteus VSM comes with extensive debugging features, including breakpoints, single stepping and variable display for a neat design prior to hardware prototyping.
In summary, Proteus 7.6 is the program to use when you want to simulate the interaction between software running on a microcontroller and any analog or digital electronic device connected to it.
Fig 8.2.3: Protues 7.6
CHAPTER 5
PCB Designing
5.1 Printed circuit board:
A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board (PWB) or etched wiring board. A PCB populated with electronic components is a printed circuit assembly (PCA), also known as a printed circuit board assembly (PCBA). Printed circuit boards are used in virtually all but the simplest commercially-produced electronic devices. PCBs are inexpensive, and can be highly reliable. They require much more layout effort and higher initial cost than either wire wrap or point-to-point construction, but are much cheaper and faster for high-volume production; the production and soldering of PCBs can be done by totally automated equipment. Much of the electronics industry’s PCB design, assembly, and quality control needs are set by standards that are published by the IPC organization.
5.1.1 History:
The inventor of the printed circuit was the Austrian engineer PaulEisler who, while working in England, made one circa 1936 as part of a radio set. Around 1943 the USA began to use the technology on a large scale to make rugged radios for use in World War II. After the war, in 1948, the USA released the invention for commercial use. Printed circuits did not become commonplace in consumer electronics until the mid-1950s, after the Auto-Sembly process was developed by the United States Army. Before printed circuits (and for a while after their invention), point-to-point construction was used. For prototypes, or small production runs, wire wrap or turret board can be more efficient. Predating the printed circuit invention, and similar in spirit, was John Sargrove’s 1936-1947 Electronic Circuit Making Equipment (ECME) which sprayed metal onto a Bakelite plastic board. The ECME could produce 3 radios per minute.
During World War II, the development of the anti-aircraft proximity fuse required an electronic circuit that could withstand being fired from a gun, and could be produced in quantity. The Centralab Division of Globe Union submitted a proposal which met the requirements: a ceramic plate would be screenprinted with metallic paint for conductors and carbon material for resistors, with ceramic disc capacitors and subminiature vacuum tubes soldered in place.
Originally, every electronic component had wire leads, and the PCB had holes drilled for each wire of each component. The components’ leads were then passed through the holes and soldered to the PCB trace. This method of assembly is called through-hole construction. In 1949, Moe Abramson and Stanislaus F. Danko of the United States Army Signal Corps developed the Auto-Sembly process in which component leads were inserted into a copper foil interconnection pattern and dip soldered. With the development of board lamination and etching techniques, this concept evolved into the standard printed circuit board fabrication process in use today. Soldering could be done automatically by passing the board over a ripple, or wave, of molten solder in a wave-soldering machine. However, the wires and holes are wasteful since drilling holes is expensive and the protruding wires are merely cut off.
In recent years, the use of surface mount parts has gained popularity as the demand for smaller electronics packaging and greater functionality has grown.
5.1.2 Materials used in PCB:
Conducting layers are typically made of thin copper foil. Insulating layers dielectric are typically laminated together with epoxy resinprepreg. The board is typically coated with a solder mask that is green in color. Other colors that are normally available are blue, black, white and red. There are quite a few different dielectrics that can be chosen to provide different insulating values depending on the requirements of the circuit. Some of these dielectrics are polytetrafluoroethylene (Teflon), FR-4, FR-1, CEM-1 or CEM-3. Well known prepreg materials used in the PCB industry are FR-2 (Phenolic cotton paper), FR-3 (Cotton paper and epoxy), FR-4 (Woven glass and epoxy), FR-5 (Woven glass and epoxy), FR-6 (Matte glass and polyester), G-10 (Woven glass and epoxy), CEM-1 (Cotton paper and epoxy), CEM-2 (Cotton paper and epoxy), CEM-3 (Woven glass and epoxy), CEM-4 (Woven glass and epoxy), CEM-5 (Woven glass and polyester). Thermal expansion is an important consideration especially with BGA and naked die technologies, and glass fiber offers the best dimensional stability.
FR-4 is by far the most common material used today. The board with copper on it is called “copper-clad laminate”.
Copper foil thickness can be specified in ounces per square foot or micrometres. One ounce per square foot is 1.344 mils or 34 micrometres.
5.2 Screen printing on PCB:
Screen printing is a printing technique that uses a wovenmesh to support an ink-blocking stencil. The attached stencil forms open areas of mesh that transfer ink or other printable materials which can be pressed through the mesh as a sharp-edged image onto a substrate. Aroller or squeegee is moved across the screen stencil, forcing or pumping ink past the threads of the woven mesh in the open areas.
Screen printing is also a stencil method of print making in which a design is imposed on a screen of silk or other fine mesh, with blank areas coated with an impermeable substance, and ink is forced through the mesh onto the printing surface. It is also known as silkscreen, stereography and serigraph.
There is considerable and semantic discussion about the process, and the various terms for what is essentially the same technique. Much of the current confusion is based on the popular traditional reference to the process of screen printing as silkscreen printing. Traditionally silk was used for screen-printing, hence the name silk screening. Currently, synthetic threads are commonly used in the screen printing process. The most popular mesh in general use is made of polyester. There are special-use mesh materials of nylon and stainless steel available to the screen printer.
Encyclopedia references, encyclopedias and trade publications also use an array of spellings for this process with the two most often encountered English spellings as, screen printing spelled as a single undivided word, and the more popular two word title of screen printing without hyphenation.
5.3 PCB Etching:
The developed PCB is etched with a 220 gram solution of ammonium peroxydisulfate (NH4)2S2O8 a.k.a. ammonium persulfate, 220 gram added to 1 liter of water and mix it until everything is dissolved. Theoretically it should be possible to etch slightly more than 60 grams of copper with 1 liter etching solution. Assume an 50% efficiency, about 30 grams of copper. With a thickness of 35 ”m copper on your PCB this covers a copper area of about 1000 cm2. Unfortunately the efficiency of the etching solution degrades, dissolved ammonium peroxydisulfate decomposes slowly. You better make just enough etching solution you need to etch. For an etching tray of about 20 x 25 cm a minimum practical amount is 200-250 ml solution. So you dissolve about 44 grams ammonium peroxydisulfate into 200 ml or 55 grams into 250 ml water.
Etching at ambient temperature might take over an hour, it is better to heat up the etching solvent to about 35-45 degrees Celcius. The etching solution heating up could be done in a magnetron, this takes about 40 to 60 seconds in a 850W magnetron depending on the initial temperature of the etching solution (hint: first try this with just water to determine the timer setting of the magnetron). The etching – rocking the etching tray – takes about 15-30 minutes at this temperature. If you have a heated, air-bubble circulated etching fluid tank available, this is probably the fastest way to etch. At higher temperatures the etching performance decreases. The etching process is an exothermic reaction, it generates heat. Take care, cool your etching tray when necessary! You should minimize the amount of copper to etch by creating copper area in your PCB layout as much as possible. When starting the etching process and little to etch it is difficult to keep the etching solution at 35-45 degrees Celcius. It helps to fill for example the kitchen sink with warm water and rock the etching tray in the filled kitchen sink.
When the ammonium peroxydisulfate is dissolved it is a clear liquid. After an etching procedure it gradually becomes blue and more deeper blue – the chemical reaction creates dissolved copper sulfate CuSO4. Compared to other etching chemicals like hydrated iron (III) chloride FeCl3.6H2O a.k.a. ferric chloride or the combination of hydrochloric acid HCL and hydrogen peroxide H2O2, using ammonium peroxydisulfate is a clean and safe method.
5.4 Removing the Toner:
Before you can solder the components into the board, you need to remove the toner. This may be done with steel wool or a ‘Scotch Brite’ type scrubbing pad. When you’re finished, you’ll have a shiny copper layout. Try not to touch the copper with your fingers because it will cause it to oxidize. Later you’ll apply a clear coating to protect it. You’ll notice that every little crack or pin hole in the toner mask has resuted in the copper being removed. If one of those cracks were across a trace, it would cause an open circuit and would have to be repaired. After the board is cleaned, look for areas where the copper hasn’t been completely removed (between traces, pads or anything else). If there are any short circuits, they must be removed now. If they are not and the device is powered up, there could be significant damage to the board and the electrical components. To cut them free, you can use something like an Exacto knife. Be very careful and take your time.
5.5 Drilling:
Holes through a PCB are typically drilled with tiny drill bits made of solid tungsten carbide. The drilling is performed by automateddrilling machines with placement controlled by a drill tape or drill file. These computer-generated files are also called numerically controlled drill (NCD) files or “Excellon files”. The drill file describes the location and size of each drilled hole. These holes are often filled with annular rings (hollow rivets) to create vias. Vias allow the electrical and thermal connection of conductors on opposite sides of the PCB.
Most common laminate is epoxy filled fiberglass. Drill bit wear is partly due to embedded glass, which is harder than steel. High drill speed necessary for cost effective drilling of hundreds of holes per board causes very high temperatures at the drill bit tip, and high temperatures (400-700 degrees) soften steel and decompose (oxidize) laminate filler. Copper is softer than epoxy and interior conductors may suffer damage during drilling.
The walls of the holes, for boards with 2 or more layers, are made conductive then plated with copper to form plated-through holes that electrically connect the conducting layers of the PCB. For multilayer boards, those with 4 layers or more, drilling typically produces a smear of the high temperature decomposition products of bonding agent in the laminate system. Before the holes can be plated through, this smear must be removed by a chemical de-smear process, or by plasma-etch.
5.6 Proteus Simulator:
Proteus 7.6 is a Virtual System Modelling (VSM) that combines circuit simulation, animated components and microprocessor models to co-simulate the complete microcontroller based designs.
This is the perfect tool for engineers to test their microcontroller designs before constructing a physical prototype in real time. This program allows users to interact with the design using on-screen indicators and/or LED and LCD displays and, if attached to the PC, switches and buttons.
One of the main components of Proteus 7.6 is the Circuit Simulation — a product that uses a SPICE3f5 analogue simulator kernel combined with an event-driven digital simulator that allow users to utilize any SPICE model by any manufacturer. Proteus VSM comes with extensive debugging features, including breakpoints, single stepping and variable display for a neat design prior to hardware prototyping.
In summary, Proteus 7.6 is the program to use when you want to simulate the interaction between software running on a microcontroller and any analog or digital electronic device connected to it.
Fig 8.2.3: Protues 7.6
Conclusion
This project is arranged in such a way that maintenance staff or line man has to enter the password to ON/OFF the electrical line. Now if there is any fault in electrical line then line man will switch off the power supply to the line by entering password and comfortably repair the electrical line, and after coming to the substation line man switch on the supply to the particular line by entering the password.
Bibliography
1. WWW.MITEL.DATABOOK.COM
2. WWW.ATMEL.DATABOOK.COM
3. WWW.FRANKLIN.COM
4. WWW.KEIL.COM
5. WWW.NATIONAL.COM
6. WWW.ATMEL.COM
7. WWW.MICROSOFTSEARCH.COM
8. WWW.GEOCITIES.COM
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-Mohd. Mazidi
10. The 8051 Micro controller Architecture, Programming & Applications
-Kenneth J.Ayala
11. Fundamentals of Micro processors and Micro computers
-B.Ram