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1.1 General
The term “computer” usually conjures up in the minds of many people the image of a mainframe, a minicomputer, a PC, a workstation or a laptop computer. However, computers have always been embedded into all sorts of everyday items from automobiles and planes to TVs, in-house entertainment centres and toasters. These are usually called embedded computers or embedded systems, and actually account for more than 90% of all the world’s manufactured processors. In general, users of embedded systems see a specialized function (such as a High-Definition TV) and do not directly think of the computer embedded within the system. Such embedded computers are gaining importance as an increasing number of systems use embedded processors, RAM, disk drives, and networks. Embedded systems range in size from simple toasters and mini-robots to large-scale systems deployed in process control, manufacturing, power generation, defence systems, telecommunication systems, automotive systems, air traffic control, avionics, video-on-demand and video-conferencing systems.
Embedded systems also differ from their conventional PC or workstation cousins in several ways. Embedded systems are typically used over long periods of time, will not (or cannot) be programmed or maintained by its end-users, and often face significantly different design constraints such as limited memory, low cost, strict performance guarantees, fail-safe operation, low power, reliability and guaranteed real-time behaviour. These embedded systems often use simple executives (OS kernels) or real-time operating systems with typically small footprints, support for real-time scheduling and no hard drives. Many embedded systems also interact with their physical environment using a variety of sensors and/or actuators. This introductory course on embedded computing focuses on these issues germane to embedded systems. . The display unit consists of any type of display that can be interfaced with microcontroller
1.2 Background
The first such system could not possibly have appeared before 1971. That was the year Intel introduced the world’s first microprocessor. This chip, the 4004, was design for use in a line of business calculation produced by the Japanese company Buissom In 1969,busicom asked Intel to design a set of custom integrated circuits one for each of their new calculator models. The 4004 was Intel’s response a general-purpose circuit that could be used throughout the entire line of calculators. This general purpose processor was designed to read and execute a set of instruction software stored in an external memory chip.
Intel’s idea was that the software would. The microprocessor was an overnight success, and its use increased steadily over the next decade. Early embedded application includes unnamed probes, computerized traffic lights, and aircraft flight, control systems. In the 1980s embedded system quietly rode the waves of the microcomputer age and brought microprocessor into every part of our personal and professional lives. Very early in their development, and certainly by the end of the 1970s, two trends were emerging for these remarkable devices. One was to scale down, in size if not computing power, the general purpose computer; this led quickly to the first desktop machine.
The other, much more revolutionary, was to place the microprocessor in products, which apparently had nothing to do with computing. They began to find their way into photocopiers, grocery scales, washing machines, and a host of other product, wherever there was a requirement to exercise some control function. While the first trend led to an inexorable demand for faster and bigger processors with increasingly power and speed. It contains everything needed to support the microcontroller and can be programmed wirelessly over the Bluetooth connection. Instructions are available for getting started with the Arduino BT.
Objective
• Knowledge and understanding of fundamental embedded systems design paradigms, architectures, possibilities and challenges, both with respect to software and hardware
• A wide competence from different areas of technology, especially from computer engineering, robotics, electronics, intelligent systems and mechatronics.
• Deep state-of-the-art theoretical knowledge in the areas of real-time systems, artificial intelligence, learning systems, sensor and measuring systems, and their interdisciplinary nature needed for integrated hardware/software development of embedded systems.
• Ability to analyze a system both as whole and in the included parts, to understand how these parts interact in the functionality and properties of the system.
• Understanding and experience of state-of-the-practice industrial embedded systems and intelligent embedded system development.
Arduino
Arduino is an open source electronics platform accompanied with a hardware and software to design, develop and test complex electronics prototypes and products. The hardware consists of a microcontroller with other electronic which can be programmed using the software to do almost any task. The simplicity of the Arduino language makes it very easy for almost everyone who has an interest in electronics to write programs without the understanding of complex algorithms or codes.
Arduino is intended for an artist, tinker, designer or anyone, interested in playing with electronics without the knowhow of complex electronics and programming skills. Arduino is an excellent designed open source platform. It has specially designed boards which can be programmed using the Ardunio Programming Language (APL).
The presence of Arduino is not only spreading between hobbyists, but it has also expanded its roots in industries and used by experts for making prototypes of commercial products. Arduino takes off the efforts required in complex coding and designing hardware.
The open source nature of Arduino has been the main reason for its rapid horizontal growth. Since it is an Open Source project, all the files related to hardware and software is available for personal or commercial use. The development cost of the hardware is very small as against the costly similar proprietary products by the industrial giants. The open source nature doesn’t require any licenses to develop, use, redistribute or even sell the product. But the Arduino name is trade mark protected (Arduino™) i.e., you are free to sell the Arduino board under any other name however in order to sell it under the name “Arduino” you need to take permission from the founders and follow their quality terms.
2.2 Embedded Design
Microcontroller can be considered a self-contained system with a processor, memory and peripherals and can be used as an embedded system. The majority of microcontrollers in use today are embedded in other machinery, such as automobiles, telephones, appliances, and peripherals for computer systems. These are called embedded systems. While some embedded systems are very sophisticated, many have minimal requirements for memory and program length, with no operating system, and low software complexity. Typical input and output devices include switches, relays, solenoids, LEDs, small or custom LCD displays, radio frequency devices, and sensors for data such as temperature, humidity, light level etc. Embedded systems usually have no keyboard, screen, disks, printers, or other recognizable I/O devices of a personal computer, and may lack human interaction devices of any kind.
2.3 Programming environments
Microcontrollers were originally programmed only in assembly language, but various high-level programming languages are now also in common use to target microcontrollers. These languages are either designed especially for the purpose, or versions of general purpose languages such as the C programming language. Compilers for general purpose languages will typically have some restrictions as well as enhancements to better support the unique characteristics of microcontrollers. Here in this project we have used embedded C.
2.4 Bluetooth module
The Arduino BT is a microcontroller board originally was based on the ATmega168, but now is supplied with the 328 and the Bluegiga WT11 Bluetooth module. It supports wireless serial communication over bluetooth (but is not compatible with Bluetooth headsets or other audio devices). It has 14 digital input/output pins (of which 6 can be used as PWM outputs and one can be used to reset the WT11 module), 6 analog inputs, a 16 MHz crystal oscillator, screw terminals for power, an ICSP header, and a reset button. It contains everything needed to support the microcontroller and can be programmed wirelessly over the Bluetooth connection. Instructions are available for getting started with the Arduino BT.
ABOUT THE PROJECT
3.1.1 Component Used
Ardiuno, male-female connectors, connecting wires, wide range of Resistors and Capacitor, Diodes, Relay, Variable Resistor or Preset, Transistor. Multicolour high power LED, LCD, Bluetooth module, buzzer etc.
3.1.2 Software Requirement
Ardiuno uno, PCB designs Software (EAGLE/ ORCAD/ DIP Press/ Express PCB), Code Editor (Keil Uvision), Simulation Software (Proteus), and Burner Software (WLPRO v2.20).
3.1.3 Working
we are supposed to design an embedded system which consists of display unit, printer and audio device using wireless technology. The display unit consists of any type of display that can be interfaced with microcontroller. Wireless printer is used for printing application. Audio device is speaker which is controlled by microcontroller through Text-To-Speech (TTS) convertor. GSM technology is specially used for SMS applications. Bluetooth is an open wireless protocol for exchanging data over short distances from fixed and mobile devices, creating Personal Area Networks (PANs). It was originally conceived as a wireless alternative to RS232 data cables. It can connect several devices, overcoming problems of synchronization. Bluetooth will receive the signal sent by the Android application device (mobile phone), and then send this signal to the microcontroller.
In order to implement this project, we need to create an Android application that is capable of performing the following Functions:
• Convert voice data to text
• Send this text over to microcontroller via
• Bluetooth for displaying on notice board
• Play the message from the audio device
The AVR controller will process that data and send it to the display unit, printer and audio device. All the transmission and reception will be done through serial communication. Further display unit will display the message, if user want print of it then print will be taken out and if that message is very much important then audio device will announce it.
3.2 SYSTEM ARCHITECTURE
3.2.1 Arduino
Arduino is an open source electronics platform accompanied with a hardware and software to design, develop and test complex electronics prototypes and products. The hardware consists of a microcontroller with other electronic components which can be programmed using the software to do almost any task. The simplicity of the Arduino language makes it very easy for almost everyone who has an interest in electronics to write programs without the understanding of complex algorithms or codes. Arduino is intended for an artist, tinker, designer or anyone, interested in playing with electronics without the knowhow of complex electronics and programming skills. Arduino is an excellent designed open source platform. It has specially designed boards which can be programmed using the Ardunio Programming Language (APL). The presence of Arduino is not only spreading between hobbyists, but it has also expanded its roots in industries and used by experts for making prototypes of commercial products. Arduino takes off the efforts required in complex coding and designing hardware.
The open source nature of Arduino has been the main reason for its rapid horizontal growth. Since it is an Open Source project, all the files related to hardware and software is available for personal or commercial use. The development cost of the hardware is very small as against the costly similar proprietary products by the industrial giants. The open source nature doesn’t require any licenses to develop, use, redistribute or even sell the product. But the Arduino name is trade mark protected (Arduino™) i.e., you are free to sell the Arduino board under any other name however in order to sell it under the name “Arduino” you need to take permission from the founders and follow their quality terms.
The Software files which includes all the source code library are also open sourced. A user can modify them to make the project more versatile and improve its capabilities.
Concept of Arduino
The root of Arduino goes deep down to the development of Processing Language by MIT researchers. Processing language is an open source language designed to introduce the software development environment for the artistic people without the need of deep knowledge of programming of algorithms. Processing is based on java. In early year of 21st century, designing an electronics gadget was nearly impossible for a common man. The requirement of specific skill set and hefty prices of software and hardware created a full stop in the path of their creativity.
In year 2003 Hernando Barragan, a programmer developed an open source electronics development platform with software IDE, where anyone with a small knowledge in electronics and programming could use his project to give wings to their creativity. His focus was to reduce the burden of complexity in designing electronics hardware and software.
The project was named as Wiring. The software IDE of the Wiring used processing language to write the codes. As the program written in C\C++ is named as Project, in the same way the code written in Wiring (even in Processing and Arduino) is termed as Sketch. The name sketch gives a familiar look for an artist. The principle idea behind Wiring is that one can make the sketch of their idea on Wiring software and implement it using specially designed Wiring board. You need to write a few lines of codes on the software IDE and then download the program to the onboard microcontroller to see the output. Wiring has predefined libraries to make the programming language easy. Arduino uses these libraries. The predefined libraries are written in C and C++. One can even write his software in C\C++ and use them on Wiring boards. The difference between writing a program in C/C++ and Wiring is that the Wiring Application Programmable Interface (API) has simplified programming style and the user doesn’t require detailed knowledge of the concepts like classes, objects, pointers, etc. While sketching hardware you need to call the predefined functions and rest will be handled by the Wiring software.
The basic difference between the Processing and the Wiring is that the Processing is use to write the program which can be used on other computers while Wiring program is used on microcontrollers.
History
Wiring is the predecessor of Arduino. Arduino was developed in lvrea, Italy by Massimo Banzi and David Cuartielles in year 2005. The Project was named after Arduin of lvrea (King of Italy). The project Arduino uses the Wiring language. The concept of Wiring Language was created by Hernando Barragan, and under his supervision Massimo Banzi and David Cuartielles developed the Project Arduino.
Open Source License
Arduino is an open source project which is probably the root cause reason for its popularity. Arduino hardware design is an Open Source Hardware, distributed under Creative Common Attribution Share-Alike license. Creative Common, a non-profitable organization has released several copyleft-licenses as free of charge, so that the creativity/ knowledge can be shared to the rest of the world while having the copyright to the authorized person. The originally designed files, like layout and schematics of Arduino products are available as Eagle CAD files.
The source code for its IDE and libraries are also available and released under GUN General Public License (known as GPL). The GPL is the first copyleft license for general use. The license is granted for the software to ensure the copyleft freedom.
Software
The Arduino hardware uses a microcontroller IC which needs to be programmed to perform any desired task. This program is written in the Arduino software using the Arduino Programming Language (APL). After compiling the program it is loaded into the memory of the microcontroller on the board using a serial or USB connection. The program can be downloaded to the memory of the microcontroller using the Arduino Software itself, thereby avoiding the need of any other external programmer. Writing codes for non professionals is a difficult task. This was the key goal of the Arduino to reduce the complexity in writing codes and allow non-professionals and creative people to foster their thinking with the help of Arduino.
The Arduino IDE provides an editor to prepare the sketch of hardware. The Arduino IDE code editor was very skillfully designed. It gives a very distinguished view (in colour and fonts) to the variables, constants, function, etc. of the source code. It includes features like syntax highlighting, brace matching and automatic code indentation. There is no need to manipulate the makefile or go on command line to dump the code into the hardware. The APL itself has a facility to burn the controller in a single click.
Sketch written in Arduino Programming Language (APL) goes under minor changes (the automatic generation of function prototype), when you press the compile button. Firstly main() function is added to the sketch and the arduino environment transforms the sketch into C or C++ code. The Arduino IDE uses GNU toolchain and AVR lib to compile the programs. Then it passes to the AVR-GCC compiler, which translate/ converts those C instructions into equivalent machine understandable instructions and creates an object file. The object file is combined with standard Arduino Libraries which provides the definitions of the inbuilt arduino functions. The result of this is a single hex (Intel hex/ .hex) file. This hex file is transferred to the microcontroller. The Arduino IDE uses avrdude to transfer the hex file on the Arduino board either by using USB or serial port of PC.
What You Need for a Working System
• Arduino Duemilanove board
• USB programming cable (A to B)
• 9V battery or external power supply (for stand-alone operation)
• Solder less breadboard for external circuits, and 22 g solid wire for connections
• Host PC running the Arduino development environment. Versions exist for Windows, Mac and Linux
3.2.2 Bluetooth module
HC‐05 module is an easy to use Bluetooth SPP (Serial Port Protocol) module, designed for transparent wireless serial connection setup. Serial port Bluetooth module is fully qualified Bluetooth V2.0+EDR (Enhanced Data Rate) 3Mbps Modulation with complete 2.4GHz radio transceiver and baseband.
It uses CSR Bluecore 04‐External single chip Bluetooth system with CMOS technology and with AFH (Adaptive Frequency Hopping Feature). It has the footprint as small as 12.7mmx27mm. Hope it will simplify your overall design/development cycle. There are some features of Bluetooth.
Hardware features
• Typical ‐80dBm sensitivity.
• Up to +4dBm RF transmit power.
• Low Power 1.8V Operation, 3.3 to 5 V I/O.
• PIO control.
• UART interface with programmable baud rate.
• With integrated antenna.
• With edge connector.
Software features
• Slave default Baud rate: 9600, Data bits:8, Stop bit:1,Parity:No parity.
• PIO9 and PIO8 can be connected to red and blue led separately. When
• master and slave are paired, red and blue led blinks 1time/2s in interval,
• while disconnected only blue led blinks 2times/s.
• Auto‐connect to the last device on power as default.
• Permit pairing device to connect as default.
• Auto‐pairing PINCODE:”1234” as default.
• Auto‐reconnect in 30 min when disconnected as a result of beyond the
• range of connection.
3.2.3 Resistor
A linear resistor is a linear, passive two-terminal electrical component that implements electrical resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's terminals to the intensity of current through the circuit is called resistance. Resistors are common 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). Resistors are also implemented within integrated circuits, particularly analog devices, and can also be integrated into hybrid and printed circuits.
The electrical functionality of a resistor is specified by its resistance: common commercial resistors are manufactured over a range of more than nine orders of magnitude. When specifying that resistance in an electronic design, the required precision of the resistance may require attention to the manufacturing tolerance of the chosen resistor, according to its specific application. The temperature coefficient of the resistance may also be of concern in some precision applications. Practical resistors are also specified as having a maximum power rating which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is mainly of concern in power electronics applications. Resistors with higher power ratings are physically larger and may require heat sinks. In a high-voltage circuit, attention must sometimes be paid to the rated maximum working voltage of the resistor.
Practical resistors have a series inductance and a small parallel capacitance; these specifications can be important in high-frequency applications. In a low-noise amplifier or pre-amp, the noise characteristics of a resistor may be an issue. The unwanted inductance, excess noise, and temperature coefficient are mainly dependent on the technology used in manufacturing the resistor. They are not normally specified individually for a particular family of resistors manufactured using a particular technology. A family of discrete resistors is also characterized according to its form factor, that is, the size of the device and the position of its leads (or terminals) which is relevant in the practical manufacturing of circuits using them.
3.2.4 Capacitors
A capacitor (formerly known as condenser) is a passive two-terminal electrical component used to store energy in an electric field. The forms of practical capacitors vary widely, but all contain at least two electrical conductors separated by a dielectric (insulator). Capacitors are used as parts of electrical systems, for example, consist ofmetal foils separated by a layer of insulating film.
When there is a potential difference (voltage) across the conductors, a static electric field develops across the dielectric, causing positive charge to collect on one plate and negative charge on the other plate. Energy is stored in the electrostatic field. An ideal capacitor is characterized by a single constant value, capacitance, measured in farads. This is the ratio of the electric charge on each conductor to the potential difference between them.
The capacitance is greatest when there is a narrow separation between large areas of conductor, hence capacitor conductors are often called "plates," referring to an early means of construction. In practice, the dielectric between the plates passes a small amount of leakage current and also has an electric field strength limit, resulting in a breakdown voltage, while the conductors and leads introduce an undesired inductance and resistance. Capacitors are widely used in electronic circuits for blocking direct current while allowing alternating current to pass, in filter networks, for smoothing the output of power supplies, in the resonant circuits that tune radios to particular frequencies and for many other purposes.
3.2.5 Transistors
A transistor is a semiconductor device used to amplify and switch electronic signals and power. It is composed of a semiconductor material with at least three terminals for connection to an external circuit. A voltage or current applied to one pair of the transistor's terminals changes the current flowing through another pair of terminals. Because the controlled (output) power can be much more than the controlling (input) power, a transistor can amplify a signal.
Today, some transistors are packaged individually, but many more are found embedded in integrated circuits. The transistor is the fundamental building block of modern electronic devices, and is ubiquitous in modern electronic systems. Following its release in the early 1950s the transistor revolutionized the field of electronics, and paved the way for smaller and cheaper radios, calculators, and computers, among other things.
3.2.6 Relays
A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), 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 were used extensively in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly control an electric motor or other loads is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device 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 "protective relays"
HARDWARE IMPLEMENTATION
3.3.1 Circuit Sections
This project is divided into following modules
A. arduino Sections
B. display and sound Sections
C. Relay Section
D. Bluetooth module
A. Arduino Sections
The Arduino hardware was very skilfully designed to reduce the complexities arising in the circuitry. It has an In System Programmer (ISP), which allows users to transfer the software inside the microcontroller without removing it from the circuit. The basic model of an Arduino board consists of an 8-bit AVR microcontroller along with some other necessary components like a 5 volt linear regulator IC, a 16 MHZ crystal, ceramic resonator, output connectors, direct adaptor input, etc. The IO ports on boards are positioned in a way that it can be easily attached with the interchangeable add-on modules, known as shields. Shields are daughter boards that can be externally attached/ plugged with the arduino boards to extent the board’s capabilities. For example an xebec shield can be attached with the arduino board to establish a wireless communication. A motor control shield can be attached on the top of Aurdino board to run the motors or to provide an ease to control the speed of motors. The Arduino Board can easily interface with external sensors, circuits or other peripherals.
Arduino hardware is available in various designs and configurations depending on the use. The different configurations use different AVR chips, Atmega8/168/328/1280/2560. Each board has its own additional feature, like Arduino UNO consists of ATmega328 which communicates to PC via USB using FTDI chip. very comfortable for attaching shields. On the other Arduino NANO uses Atmega168/328 which also uses FTDI chip but is much comfortable to use it on breadboard. Some non-ATmega Arduino boards are also available. These boards don’t contain Atmel’s ATmega controller but are compatible with arduino shield. These microcontrollers cannot be programmed by the standard Arduino IDE but manufacturers do provide some other versions of Arduino IDE which includes the necessary libraries related to the controller. For example Leaflabs Maple based on 32bit arm processor or chipKIT UNO32 based on PIC micro controllers.
The earlier version of the arduino board had controller with bootloader which communicated with the Arduino IDE mostly via a Serial port. Later a FTDI chip was introduced on the Arduino board which is a USB to serial converter to allow the communication with the USB port. And today the Arduino boards are available with Atmel’s microcontroller which have inbuilt capacity to communicate with the USB port.
B. Display and sound Sections
For display we are use LCD,LCD (Liquid Crystal Display) screen is an electronic display module and find a wide range of applications. A 16x2 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. For sound we use buzzer . The buzzer produces a same noisy sound irrespective of the voltage variation applied to it. It consists of piezo crystals between two conductors. When a potential is applied across these crystals, they push on one conductor and pull on the other. This, push and pull action, results in a sound wave. Most buzzers produce sound in the range of 2 to 4 kHz. The Red lead is connected to the Input and the Black lead is connected to Ground.
C. Relay Section
These are used to provide supply to the appliances or to disconnect them from supply so as to switch on or off them according to the signals received from the Ardiuno. Relays are used to make transition to the AC supply which is required to almost all the home appliances.
3.4 TOOLS & PLATFORM USED
Various tools are used in this project as:
3.4.1 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.
Materials Used
Conducting layers are typically made of thin copper foil. Insulating layers dielectric are typically laminated together with epoxy resin prepreg. 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 prepare 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 ball grid array (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 micrometers. One ounce per square foot is 1.344 mils or 34 micrometers.
3.4.2 Soldering Iron
A soldering iron is a hand tool most commonly used in soldering. It supplies heat to melt the solder so that it can flow into the joint between two workpieces. A soldering iron is composed of a heated metal tip and an insulated handle. Heating is often achieved electrically, by passing an electric current (supplied through an electrical cord or battery cables) through the resistive material of a heating element. Another heating method includes combustion of a suitable gas, which can either be delivered through a tank mounted on the iron (flameless), or through an external flame. Less common uses include pyrography (burning designs into wood) and plastic welding. Soldering irons are most often used for installation, repairs, and limited production work. High-volume production lines use other soldering methods
Tips while using Soldering Iron: Some soldering irons have interchangeable tips, also known as bits, that vary in size and shape for different types of work. Pyramid tips with a triangular flat face and chisel tips with a wide flat face are useful for soldering sheet metal. Fine conical or tapered chisel tips are typically used for electronics work.
Older and very cheap irons typically use a bare copper tip, which is shaped with a file or sandpaper. This dissolves gradually into the solder, suffering pitting and erosion of the shape. Copper tips are sometimes filed when worn down. Iron-plated copper tips have become increasingly popular since the 1980s. Because iron is not readily dissolved by molten solder, the plated tip is more durable than a bare copper one. This is especially important when working at the higher temperatures needed for modern lead-free solders. Solid iron and steel tips are seldom used because they store less heat, and rusting can break the heating element.
Cleaning: When burnt flux and oxidized material begin to accumulate on the tip, they can block heat transfer and contaminate joints, making soldering difficult or impossible. Therefore, the tips are periodically cleaned. Many soldering stations come with cellulose sponges which are dampened and used to wipe a hot iron's tip clean. A wire brush, preferably brass or wire wheel (mounted on a bench grinder), is sometimes carefully used to remove very severe oxidation, though this may risk damaging the tip's protective iron plating. A small amount of fresh solder is usually then applied to the clean tip in a process called tinning. The working surface of the tip is usually kept tinned (coated with wet solder) to minimize oxidation. Oxidation blocks heat transfer, corrodes the tip, and contaminates the joint
3.4.3 Soldering Wire
Solder is a fusible metal alloy used to join together metal work pieces and having a melting point below that of the work pieces. Soft solder is what is most often thought of when solder or soldering are mentioned and it typically has a melting range of 90 to 450 °C (190 to 840 °F). It is commonly used in electronics and plumbing. Alloys that melt between 180 and 190 °C (360 and 370 °F) are the most commonly used.
By definition, using alloys with melting point above 450 °C (840 °F) is called 'hard soldering', 'silver soldering' or brazing. Soft solder can contain lead and/or flux but in many applications lead free solder is used. Perhaps the most common and most familiar form of solder is as a wire or rod, though plumbers often use bars of solder while jewelers often use solder in thin sheets which they cut into snippets. Solder can also come in a paste or as a preformed foil shaped to match the work piece. The word solder comes from the Middle English word soudur, via Old French soldure and souldur, from the Latin solid are, meaning "to make solid".
Eutectic alloys melt at a single temperature. Non-eutectic alloys have markedly different solidus and liquidus temperature, and within that range they exist as a paste of solid particles in a melt of the lower-melting phase. The pasty state causes some problems during handling; it can however be exploited as it allows molding of the solder during cooling, e.g. for ensuring watertight joint of pipes, resulting in a so called 'wiped joint'. With the reduction of the size of circuit board features,the size of interconnects shrinks as well. Current densities above 104 A/cm2 are often achieved and electro migration becomes a concern. At such current densities the Sn63Pb37 solder balls form hillocks on the anode side and voids on the cathode side; the increased content of lead on the anode side suggests lead is the primary migrating species.
3.4.4 Lead solder
Tin/lead solders, also called soft solders, are commercially available with tin concentrations between 5% and 70% by weight. The greater the tin concentration, the greater the solder’s tensile and shear strengths. At the retail level, the two most common alloys are 60/40 Tin/lead (Sn/Pb) which melts at 370 °F or 188 °C and 63/37 Sn/Pb used principally in electrical/electronic work. The 63/37 ratio is notable in that it is a eutectic mixture, which means:
1) It has the lowest melting point (183 °C or 361.4 °F) of all the tin/lead alloys; and
2) The melting point is truly a point — not a range.
In plumbing, a higher proportion of lead was used, commonly 50/50. This had the advantage of making the alloy solidify more slowly, so that it could be wiped over the joint to ensure water tightness, the pipes being physically fitted together before soldering. Although lead water pipes were displaced by copper when the significance of lead poisoning began to be fully appreciated, lead solder was still used until the 1980s because it was thought that the amount of lead that could leach into water from the solder was negligible from a properly soldered joint. The electrochemical couple of copper and lead promotes corrosion of the lead and tin, however tin is protected by insoluble oxide. Since even small amounts of lead have been found detrimental to health, lead in plumbing solder was replaced by silver (food grade applications) or antimony, with copper often added, and the proportion of tin was increased (see Lead-free solder.)
The addition of tin improves wetting properties of the alloy; lead itself has poor wetting characteristics. Tin however increases the cost of the solder. High-tin tin-lead alloys have limited use as the workability range can be provided by a cheaper high-lead alloy. In electronics, printed circuit boards use solder joints to mount components and create a circuit. For miniaturized PCB joints with surface mount components, solder paste has largely replaced solid solder.