21)EMBEDDED SYSTEMS

by engr. AFAN BAHADUR KHAN

An embedded system is a special-purpose computer system designed to perform one or a few dedicated functions,[1] often with real-time computing constraints. It is usually embedded as part of a complete device including hardware and mechanical parts. In contrast, a general-purpose computer, such as a personal computer, can do many different tasks depending on programming. Embedded systems control many of the common devices in use today.


A modern example of an embedded system. Labelled parts include a microprocessor (4), RAM (6), and flash memory 7

Since the embedded system is dedicated to specific tasks, design engineers can optimize it, reducing the size and cost of the product, or increasing 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 MP4 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.



Physically, embedded systems range from portable devices such as digital watches and MP4 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.

In general, "embedded system" is not an exactly defined term, as many systems have some element of programmability. For example, Handheld computers share some elements with embedded systems — such as the operating systems and microprocessors which power them — but are not truly embedded systems, because they allow different applications to be loaded and peripherals to be connected.


Examples of embedded systems

Embedded systems span all aspects of modern life and there are many examples of their use.

Telecommunications systems employ numerous embedded systems from telephone switches for the network to mobile phones at the end-user. Computer networking uses dedicated routers and network bridges to route data.





Consumer electronics include personal digital assistants (PDAs), mp3 players, mobile phones, videogame consoles, digital cameras, DVD players, GPS receivers, and printers. Many household appliances, such as microwave ovens, washing machines and dishwashers, are including embedded systems to provide flexibility, efficiency and features. Advanced HVAC systems use networked thermostats to more accurately and efficiently control temperature that can change by time of day and season. Home automation uses wired- and wireless-networking that can be used to control lights, climate, security, audio/visual, surveillance, etc., all of which use embedded devices for sensing and controlling.



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. This program alone reduced prices on quad nand gate ICs from $1000/each to $3/each, permitting their use in commercial products.


Characteristics

1.Embedded systems are designed to do some specific task, rather than be a general-purpose computer for multiple tasks. Some also have real-time performance constraints that must be met, for reasons such as safety and usability; others may have low or no performance requirements, allowing the system hardware to be simplified to reduce costs.



2.Embedded systems are not always standalone devices. Many embedded systems consist of small, computerized parts within a larger device that serves a more general purpose. For example, the Gibson Robot Guitar features an embedded system for tuning the strings, but the overall purpose of the Robot Guitar is, of course, to play music.[2] Similarly, an embedded system in an automobile provides a specific function as a subsystem of the car itself.


3.The program instructions written for embedded systems are referred to as firmware, and are stored in read-only memory or Flash memory chips. They run with limited computer hardware resources: little memory, small or non-existent keyboard and/or screen.

User interfaces

Embedded systems range from no user interface at all — dedicated only to one task — to complex graphical user interfaces that resemble modern computer desktop operating systems.


Simple systems


Simple embedded devices use buttons, LEDs, and small character- or digit-only displays, often with a simple menu system.

In more complex systems

A full graphical screen, with touch sensing or screen-edge buttons provides flexibility while minimising space used: the meaning of the buttons can change with the screen, and selection involves the natural behavior of pointing at what's desired.

Handheld systems often have a screen with a "joystick button" for a pointing device.

Many systems have "maintenance" or "test" interfaces that provide a menu or command system via an RS-232 interface. This avoids the cost of a display, but gives a lot of control. Most consumers cannot assemble the required cables, however.

The rise of the World Wide Web has given embedded designers another quite different option: providing a web page interface over a network connection. This avoids the cost of a sophisticated display, yet provides complex input and display capabilities when needed, on another computer. This is successful for remote, permanently installed equipment such as Pan-Tilt-Zoom cameras and network routers.


ASIC and FPGA solutions

A common configuration for very-high-volume embedded systems is the system on a chip (SoC) which contains a complete system consisting of (multiple processors, multipliers, caches and interfaces on a single chip. SoCs can be implemented as an application-specific integrated circuit (ASIC) or using a field-programmable gate array (FPGA).

Reliability

Embedded systems often reside in machines that are expected to run continuously for years without errors, and in some cases recover by themselves 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.

Specific reliability issues may include:

1.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.

2.The system must be kept running for safety reasons. "Limp modes" are less tolerable. Often backups are selected by an operator. Examples include aircraft navigation, reactor control systems, safety-critical chemical factory controls, train signals, engines on single-engine aircraft.

3.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.

Embedded software architectures

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 tasks are executed by the main loop. This method brings the system close to a multitasking kernel with discrete processes.

1) BUSINESS ELECTRONICS

by engr. AFAN BAHADUR KHAN

How Energy-efficient Electronics Work

The average American household spends $1,400 each year on energy bills [source: Forbes]. Home heating and cooling systems are responsible use about 45 percent of the energy. Lighting takes up another significant chunk, especially if you're slow to switch to efficient compact fluorescent bulbs. But some of the most energy-hungry machines making your electric bill creep higher every month are your electronic devices.



The Xbox 360 uses 187 watts of electricity


Take a look at your TV, for example. Maybe you recently splurged on one of those 40-inch (102-centimeter) plasma TVs, which requires 350 watts of energy to run. Connected to the TV is an Xbox 360 (187 watts), a PlayStation 3 (197 watts) and a digital video recorder (DVR) (33 watts) [source: CNET]. Wonder where your money's going each month? Straight into that black hole of energy consumption in your living room. Luckily, electronics manufacturers are designing equipment, appliances and gadgets that are more energy efficient.

Energy conserving electronics are not only better for our wallets, but better for the environment. More than half the electricity in the United States comes from coal-burning power plants [source: American Society of Mechanical Engineers]. Even a brand-new coal-burning power plant sends out 6 million tons (5.4 million metric tons) of carbon dioxide each year, 1,200 tons (1,089 metric tons) of sulfur dioxide and 1,600 tons (1,452 metric tons) of nitrogen oxide [source: Las Vegas Sun]. These chemicals not only deplete the ozone layer but contribute to acid rain and respiratory illness in children and the elderly.

So what can you do to cut your electric bill and clean up the air? Are there government and industry resources that can tell you which products are more efficient? And what types of TVs, computers and handheld electronics give the most bang for the energy buck? Read on to find out.


Energy Star and Other Energy-conserving Initiatives

In 1992, the U.S. Environmental Protection Agency (EPA) introduced a new program called Energy Star to show consumers how much energy the products they buy actually use. Since its inception, 12,000 electronics and appliance manufacturers have voluntarily complied with increasingly strict Energy Star standards. As a result, more than 40,000 individual products boast the highly recognizable Energy Star label [source: Energy Star].

Energy Star first began with computers and computer monitors. Over the years, the product categories and published standards have expanded to include residential heating and cooling systems, home appliances, lighting systems, and every type of office and home electronics equipment.


The Energy Star logo is a
familiar sight on the
packaging of thousands
of consumer electronics.

In 2007 alone, Americans using Energy Star products helped prevent 40 million metric tons (44.1 tons) of greenhouse gas from entering the atmosphere [source: Energy Star]. That's the equivalent of taking 27 million cars off the road for an entire year. The EPA also estimates that in 2007, Americans using Energy Star products saved $16 billion on their electric bills [source: Energy Star].


Energy Star is the most recognizable energy-conservation initiative for consumer electronics, but it's not the only one. The Electronic Product Environmental Assessment Tool (EPEAT) is a newer rating system that grades the overall environmental impact of various consumer electronics products. Among the criteria are how much of the gadget's materials can be recycled, whether any of the components are toxic and whether the product meets existing or pending Energy Star standards.


Energy Star is the most recognizable energy-conservation initiative for consumer electronics, but it's not the only one. The Electronic Product Environmental Assessment Tool (EPEAT) is a newer rating system that grades the overall environmental impact of various consumer electronics products. Among the criteria are how much of the gadget's materials can be recycled, whether any of the components are toxic and whether the product meets existing or pending Energy Star standards.


Products that meet all of EPEAT's required criteria earn a bronze label. Those that meet all required criteria plus 50 percent of optional standards get a silver label, and those that meet all required criteria plus 75 percent or more of the optional standards get a gold rating.


All computers require a power supply, a small box that converts AC power coming from the wall to the DC power that runs the device. Historically, a lot of energy was lost in this conversion process. In 2004, a new incentive program called 80 Plus was funded by American utility companies to encourage manufacturers to build more efficient power supplies for desktop and notebook computers and servers. To qualify for an 80 Plus rating, a power supply must be 80 percent efficient or greater.


Over the years, American utility companies have funded more than $5 million worth of incentives for computer makers and power supply manufacturers to improve the efficiency of their products. As a result, more than 600 power supplies that have achieved the 80 Plus rating [source: 80 Plus]. And even better, the recently published Energy Star standards for new computers requires that internal power supplies carry the 80 Plus seal of approval.

Televisions are some of the biggest energy hogs in your house. Let's look at the most and least efficient types of TVs and what's on the horizon for greening the small screen.


Energy-efficient TVs

Television screens are getting bigger, sharper and thinner every year. While the action on the screen looks better than ever, the effect on your electric bill can be downright scary. The average American still only pays around $24 a year to power his or her TV, but that average is dragged down by all of the old CRT (cathode ray tube) TVs that will be replaced as more people upgrade to power-sucking high-definition (HDTV) models [source: American Council for an Energy-efficient Economy].


According to testing by CNET labs, the most energy-efficient HDTV costs around $30 a year to power, while the most power-hungry model adds nearly $230 to the electric bill each year [source: CNET]. Larger screen size is one of the biggest contributors to this leap in the cost of watching TV. According to a study by the Natural Resource Defense Council, an HDTV with a 40-inch (102-centimeter) screen or larger consumes more energy per year than any other device or appliance in the house, including a 22.5 cubic foot (0.6 cubic meter) refrigerator [source: Energy Star].


Different television technologies also burn through different amounts of electricity. Plasma TVs are, on average, the least efficient technology. Next come LCDs, followed by projection TVs and traditional CRTs [source: CNET]. But even within these general categories, there are many factors that can make a TV either an energy sipper or a guzzler. Incredibly, both the most efficient and the least efficient TVs on CNET's list are LCDs.


In addition to the power they use while they're on, many of these large-screen TVs don't shut off completely when you press the power button. The manufacturers felt that people wouldn't want to wait so long for their sets to warm up when they press the power button, so they have the TVs go into a standby mode rather that shut off completely. Some of them require you to press a separate button or unplug the unit entirely to totally power down the equipment



The Philips 42PFL5603D, or Eco TV


As consumers become more energy conscious, TV makers are responding with innovative, energy-saving designs. One example is the Philips 42PFL5603D, also known as the Eco TV. When you activate the Eco TV's power saver mode, the television uses a trio of sensors to optimize the intensity of the LCD's backlight. The brighter the room, the harder the backlight needs to work. The Eco TV can detect the relative darkness and brightness of the room and adjust how much light it uses to illuminate the picture. In addition, the Eco TV boasts a sensor that constantly adjusts for the brightness of the scene being played on the TV. If the scene takes place at night, the backlight dims ever-so-slightly to save energy for the daytime scenes.


Another TV technology called organic light-emitting diodes (OLED) offers an even more energy efficient way to light a large TV screen. With OLED, light isn't provided by a backlight, but by individual molecules that light each pixel on the screen. The first small (30-inch, 76-cm) OLED TVs arrived in November 2007 and a consortium of Japanese electronics-makers are pushing to deliver large-screen versions within the year


TV Power Saving Tips

Even if you don't have a futuristic or "green" TV, there are still several things you can do to lower the energy impact of your TV:

•Power down the TV completely when you're not using it.
•See if your TV has some kind of power saver mode.
•Disable any "Quick Start" option that leaves the TV in standby mode as default.
•Manually dim the intensity of the backlight. The easiest way to do this is through the contrast and brightness controls.
•Watch TV in a dark room. It improves picture clarity while requiring less backlight.

Energy-saving Computers


Even the most energy-hungry home computer doesn't make much of a dent in the monthly electric bill. If you ran a desktop computer and monitor at full power for eight hours every day, it would add $30 to your annual energy costs [source: myGreenElectronics].


But imagine that you owned a business with hundreds of employees. Now imagine all of those desktop computers crowded into an office, plus the servers and storage units crammed into IT rooms. Not surprisingly, those computers eat up a lot of energy, accounting for up to 70 percent of a company's energy bill [source: Cranberry]. Computers also create heat and force the air conditioning to work even harder to keep the office cool.


Recently, several computer makers have introduced machines designed specifically to lower the energy costs of small and large businesses. One is the Earth PC and Earth Server by Tech Networks of Boston. These new PCs come with a patented power management system that keeps machines running as lightly as possible in standby mode. They also come with 80 Plus-certified power supplies which keep them cool and lower air conditioning bills by 33 percent in the process



The Cranberry SC20 smart client computer


The Cranberry SC20 is another new energy-conserving computer marketed toward businesses. The Cranberry isn't exactly a PC. Instead, it's something in between a full-fledged PC and what's known as a thin client. Thin clients are pared-down computer terminals that run all of their applications from a central server. Thin clients don't have hard drives and can't run their own native applications. The Cranberry is called a "Smart Client" because it's slim (the size of a paperback book), yet it can run its own software, be controlled locally and includes standard ports for connecting digital cameras, speakers and other devices. Because the applications reside on the Internet rather than on the machine, this is a form of cloud computing.


But the impressive thing about the Cranberry is that it uses just 10 percent of the power of a standard PC. That's because it has no moving parts (no fans or hard drive) and is powered by an extremely efficient microprocessor. The Cranberry consumes a mere 9 watts compared to a standard PC which burns through 175 watts [source: Cranberry].



The Mac Mini


The Mac Mini is another desktop computer touted for its energy efficiency. The Mini is a tiny 6.5-inch (16.5-cm)-square, white box with a built-in CD/DVD drive and the standard input/output jacks for USB and Firewire devices. But since it's stuffed with highly efficient notebook computer guts -- and has an external power supply -- it runs quiet and cool at only 25 watts. The latest Mac Mini meets Energy Star 4.0 standards and earned an Electronic Product Environmental Assessment Tool (EPEAT) Silver rating.


In terms of computer monitors, smaller LCD monitors are more energy efficient than CRT monitors of the same size -- some reports say 66 percent more efficient [source: flatpaneltv.org]. LCD monitors also give off less heat than CRTs and help save money on that air-conditioning bill.


Now let's look at some cool new handheld gadgets that keep going long after everyone else's batteries are drained.


Energy-saving Handhelds


Since handheld gadgets like cell phones, iPods and BlackBerrys run on batteries, sometimes we forget that charging and recharging adds to the electric bill. Thankfully some forward-looking companies are developing innovative ways to power the gadgets that run our lives.


The Eco Media Player is an iPod-like handheld device that can be loaded with music and video files via a standard SD memory card. What's not standard about this media player is that you can power up the battery with a hand crank that unfolds from of the back of the unit. One minute of cranking gets you 40 minutes of audio playing power [source: TreeHugger]. The technology is based on the famous hand-crank emergency radios that inventor Trevor Baylis developed for aid workers and villagers in rural Africa.


Alternative fuels are another way to get electronics off the power grid. A company called Angstrom Power recently presented a prototype cell phone at the 2008 Consumer Electronics Show that runs on a tiny hydrogen fuel cell. The company claims that its Micro Hydrogen fuel cell platform fits right into existing cell phones with no modifications and promises twice the talk time of a lithium-ion battery. The device can be fully charged in less than 10 minutes.


A simpler way to recharge a cell phone is to rig up a standard cell phone with a small, wearable solar panel. Several companies are selling small arrays of solar panels that can plug directly into cell phones or other mobile devices. A Japanese company called Strapyanext is selling a 12-cm (5-inch) solar cell phone charger that can produce and store roughly 40 minutes worth of talk time during 6 to 10 hours in the sun [source: CrunchGear].



The Nokia Eco Sensor Concept and wrist sensor unit


Solar technology isn't limited to cell phones. The Nokia Eco Sensor Concept is a futuristic personal digital assistant (PDA) prototype that comes with a separate wrist sensor unit. The wrist sensor is made out of solar cells which provide energy for the PDA. This wrist sensor can also generate electricity by capturing kinetic energy from natural arm movements, like some watches already do today. The screen of the Nokia PDA will use a highly efficient technology called electrowetting. In place of pixels on a screen, it uses tiny drops of oil that expand and contract with electrical charges [source: Nokia].

2)HOW DOES THE BODY MAKE ELECTRICITY & HOW DOES IT USE IT

by engr. AFAN BAHADUR KHAN

Without electricity, you wouldn't be reading this article right now. And it's not because your computer wouldn't work. It's because your brain wouldn't work.


Everything we do is controlled and enabled by electrical signals running through our bodies. As we learned in intro physics, everything is made up of atoms, and atoms are made up of protons, neutrons and electrons. Protons have a positive charge, neutrons have a neutral charge, and electrons have a negative charge. When these charges are out of balance, an atom becomes either positively or negatively charged. The switch between one type of charge and the other allows electrons to flow from one atom to another. This flow of electrons, or a negative charge, is what we call electricity. Since our bodies are huge masses of atoms, we can generate electricity



The electricity produced by our bodies is what allows synapses, signals and even heartbeats to occur.


When we talk about the nervous system sending "signals" to the brain, or synapses "firing," or the brain telling our hands to contract around a door handle, what we're talking about is electricity carrying messages between point A and point B. It's sort of like the digital cable signal carrying 1s and 0s that deliver "Law & Order." Except in our bodies, electrons aren't flowing along a wire; instead, an electrical charge is jumping from one cell to the next until it reaches its destination.


Electricity is a key to survival. Electrical signals are fast. They allow for a nearly instantaneous response to control messages. If our bodies relied entirely on, say, the movement of chemicals to tell our hearts to speed up when something is chasing us, we probably would've died out a long time ago.


Those crucial signals that tell our hearts to speed up when we're in danger come from a mass of cells in our heart called the sinoatrial node, or SA node. It's located in the right atrium, and it controls the rhythm of our heartbeat and the movement of blood from the heart to every other part of our body. It's our body's natural pacemaker, and it uses electrical signals to set the pace (see What determines the rhythm of your heart?). But our pulse isn't the only thing that relies on electrical impulses generated by our cells. Almost all of our cells are capable of generating electricity.


In this article, we'll look at the role of electricity in the body and find out how we generate it in the first place.


The starting point is simple: Right now, any cells in your body that aren't actively sending messages are slightly negatively charged. It gets interesting from there.


Human Voltage


Negativity is the natural resting state of your cells. It's related to a slight imbalance between potassium and sodium ions inside and outside the cell, and this imbalance sets the stage for your electrical capacity.


Your cell membranes practice a trick often referred to as the sodium-potassium gate. It's a very complex mechanism, but the simple explanation of these gates, and how they generate electrical charges, goes like this:


Getting struck by lightning is usually enough to fry your body's electrical system.


At rest, your cells have more potassium ions inside than sodium ions, and there are more sodium ions outside the cell. Potassium ions are negative, so the inside of a cell has a slightly negative charge. Sodium ions are positive, so the area immediately outside the cell membrane is positive. There isn't a strong enough charge difference to generate electricity, though, in this resting state.


When the body needs to send a message from one point to another, it opens the gate. When the membrane gate opens, sodium and potassium ions move freely into and out of the cell. Negatively charged potassium ions leave the cell, attracted to the positivity outside the membrane, and positively charged sodium ions enter it, moving toward the negative charge. The result is a switch in the concentrations of the two types of ions -- and rapid switch in charge. It's kind of like switching between a 1 and 0 -- this flip between positive and negative generates an electrical impulse. This impulse triggers the gate on the next cell to open, creating another charge, and so on. In this way, an electrical impulse moves from a nerve in your stubbed toe to the part of your brain that senses pain.


It's also how the SA node tells your heart muscles to contract, how your eyes tell your brain that what they just saw is the word "brain," and how you are comprehending this article at all.


Since everything relies on these electrical signals, any breakdown in your body's electrical system is a real problem. When you get an electric shock, it interrupts the normal operation of the system, sort of like a power surge. A shock at the lightning level can cause your body to stop. The electrical process doesn't work anymore -- it's fried. There are also less dramatic problems, like an SA node misfire that causes a heart palpitation (an extra heartbeat), or a lack of blood flow to the heart that upsets the pacemaker and causes other parts of the heart to start sending out impulses. This is sometimes what causes someone to die from coronary artery disease, or narrowing of the arteries. If the heart is constantly being told to contract, it never gets in a full contraction, and it can't get enough blood to the rest of body, leading to oxygen deprivation and a possible heart attack or stroke.


With so much electricity jumping around, it may seem like the body is a really great power source. But could human beings really power the Matrix? Probably not. A human body can only generate between 10 and 100 millivolts [source: NanoMedicine]. A cathode ray tube requires about 25,000 volts to create a picture on a TV [source: Physics Factbook]. If the machines could gather millions of electric eels, on the other hand, they'd be well juiced up. A single eel can produce in the area of 600 volts

3)HOW DID THE EAST INDIA COMPANMY CHANGE THE WORLD

by engr. AFAN BAHADUR KHAN

What comes to mind when you hear the word "corporation?" Maybe a giant, faceless conglomerate? Ruthless captains of industry? Perhaps you think of corporate scandals like Enron and WorldCom. In fact, the unscrupulous plundering done by some modern-day corporations pales in comparison to the activities carried out by one of the world's first corporations: the British East India Company (EIC).

The concept of corporations was first established under ancient Roman law [source: University of Virginia]. But it wasn't until England emerged from the Middle Ages that it created what we recognize as the modern corporate structure. It all began on Dec. 31, 1600, when Queen Elizabeth I granted a charter to the British East India Corporation, naming the corporation "The Governor and Company of Merchants of London, trading with the East Indies." The corporation conducted business in the East Indies (land that we now consider India and the Middle East) at the behest of the queen.

The East India Company established a few major precedents for modern corporations. But it also shaped the world in countless other ways. With both the financial and military support of the Crown, the EIC served as an instrument of imperialism for England. The company had its own private army and raised soldiers in the areas it subjugated. Its expansionism spurred several wars that produced at least two sovereign nations. Among its many claims to fame (and notoriety), the EIC indirectly built Yale University, helped create two nations and was the world's largest drug-dealing operation in the 18th century.

The company was ruthless in its quest for profits. Parliament even called the EIC tyrannical. However, without the EIC, England may have never developed into the nation it is today


The Creation of the East India Company

When the British East India Company (EIC) was formed in 1600, there were already other East India Companies operating on behalf of France, the Netherlands, Spain and Portugal. Thanks to the naval route that explorer Vasco da Gama discovered, riches from the Orient were pouring into Europe. With other nations importing fortunes in goods and plunder, Queen Elizabeth decided England should get some, too. So she granted the charter for the East India Company.

Queen Elizabeth used more than just royal decree and coffers (treasury funds) to help merchants and explorers establish trade on behalf of England in the East. The charter she issued created the first official joint-stock corporation. A joint-stock corporation is composed of investors who are granted shares in a company. In return for their initial investments, shareholders are given dividends, or percentages, of the company's profits based on the number of shares the investor holds.

Shares and dividends were not new concepts in England. Twenty years prior to the EIC's charter, Queen Elizabeth was already a major stakeholder in Sir Francis Drake's ship, the Golden Hind. Although it's not certain how much she made from Drake's voyages to the New World, the captain himself made a 5,000 percent return on his initial investment [source: Hartmann].

So a joint-stock corporation like the one Queen Elizabeth formed in the East India Company wasn't much of a financial leap. But it was the first of its kind, and following the establishment of the EIC, its Dutch, French and other competitors followed suit. But granting charter to the EIC wasn't the only part of the prototype for modern corporations that Queen Elizabeth devised.

Under the auspices of her royal authority, Elizabeth also limited the liability of the EIC's investors -- including hers. This made the company the world's first limited liability corporation (abbreviated as LLC in the United States and Ltd. in the United Kingdom). Under an LLC, the investors in a corporation are granted protection from losing any more money than their initial investments in the venture. If the company goes under, the investors only lose the amount of money they put into the LLC. The company's outstanding debts aren't divvied up among its investors [source: IRS].




Queen Elizabeth covered any losses or debts owed by the East India Company with the royal coffers; modern LLCs are subject to bankruptcy procedures, where creditors may be forced to take pennies on the dollar or nothing at all if a corporation goes under.

Although it took several decades for the East India Company to become truly profitable, once it did, the company rose to global domination -- both in business and in government. In a symbiotic way, as the company grew in power, so, too, did England. So it's no surprise that during its existence, the company was directly involved in major geopolitical changes: The EIC literally changed the course of history. Two nations, India and the United States, revolted against East India Company rule, which led to the establishment of their current political structures.


The East India Company and the United States

American and British schoolchildren are taught about the infamous Tea Act of 1773, which led to the rebellious Boston Tea Party. But exactly why the Boston colonists threw thousands of pounds of tea into Boston Harbor may be less clear. It's actually due to collusion between the government and the East India Company.




The Tea Act was designed by Parliament specifically to help the EIC unload the millions of pounds of unsold tea in its English warehouses. The Americas were the designated recipients (like it or not) of the surplus tea. The act was meant to enforce the EIC's monopoly on tea in the colonies. It would be like the United States government forcing all of today's Americans to purchase Apple computers only. Ultimately, the Tea Act allowed the EIC to drive its competition out of business. Colonists deemed this an unfair practice -- government was supporting one business's interests at the expense of the liberty -- and it gave rise to the famous slogan "no taxation without representation" [source: Hartmann].

Rather than agree to this corporate/government collusion, about 150 colonists dumped the EIC's new shipment of tea into Boston Harbor. The English government showed its allegiance to the East India Company when Parliament demanded that colonists reimburse the company for the nearly $1 million (in 21st-century dollars) worth of tea [source: Hartmann]. To enforce this demand, the British Navy was called in to blockade the harbor. The tension created by this situation directly led the colonists into the Revolutionary War.

The East India Company and India

Perhaps it was being stationed halfway across the world from the East India Company's home offices in London. Or maybe it was the potential for wealth afforded by India's riches. Either way, Elihu Yale (the benefactor for whom Yale University is named) was tantalized into building his own smuggling operation. His dismissal from his post as the EIC governor of Madras was a light sentence compared to the fates of others who ran afoul of the company.





Perhaps Yale got away with his life because of the work he'd done on behalf of the EIC. Thanks to factories (colonies or settlements) run by men like Yale, the East India Company was able to subjugate India and its tribal rulers. The company built forts in India to house its private army. The EIC also raised soldiers from within the native populations. With the establishment of martial rule (the government set up in a land occupied by military) profits could be garnered easily. Perhaps the most profitable export for the company's India operations was opium.

By 1750, the EIC had established control over India's most prolific sites of opium cultivation. The British exported the opium to China, which eventually resulted in two opium wars between the countries over the drug's importation. By 1793, Britain had a monopoly on opium, and no Indian grower was allowed to sell his crops to any other company [source: PBS].

The British colonialism carried out through the EIC was pretty brutal. It included the forceful seizure of land and deposing of rulers. Tribute, taxes and loyalty were extracted from average citizens through methods up to and including torture [source: Emory University]. Ultimately, the British presence proved to be unacceptable for some Indians. A number of sepoys (native Indians who joined the EIC's militia) revolted against the EIC's rule during the Sepoy Rebellion of 1857. Some historians consider this India's first war for independence, even though it was quelled by the British army. Afterward, Great Britain officially occupied the country. India would remain an English colony until 1947, when it became a constitutional republic [source: CNN].

The eventual creation of modern-day India and the United States are but two major world events that have the East India Company's fingerprints. It would be nearly impossible to trace the entire legacy -- both positive and negative impacts -- that the East India Company had on the world. With direct involvement in so many different aspects of our world, perhaps the question isn't "how did the East India Company change the world," but "how didn't it?"

4)ELECTRONIC CAR ENGINES

by engr. AFAN BAHADUR KHAN

How Car Engines Work

­­Have you ever opened the hood of your car and wondered what was going on in there? A car engine can look like a big confusing jumble of metal, tubes and wires to the uninitiated.



You might want to know what's going on simply out of curiosity. Or perhaps you are buying a new car, and you hear things like "3.0 liter V-6" and "dual overhead cams" and "tuned port fuel injection." What does all of that mean?

­­In this article, we'll discuss the basic idea behind an engine and then go into detail about how all the pieces fit together, what can go wrong and how to increase performance.

­The purpose of a gasoline car engine is to convert gasoline into motion so that your car can move. Currently the easiest way to create motion from gasoline is to burn the gasoline inside an engine. Therefore, a car engine is an internal combustion engine -- combustion takes place internally. Two things to note:

•There are different kinds of internal combustion engines. Diesel engines are one form and gas turbine engines are another. See also the articles on HEMI engines, rotary engines and two-stroke engines. Each has its own advantages and disadvantages.

•There is such a thing as an external combustion engine. A steam engine in old-fashioned trains and steam boats is the best example of an external combustion engine. The fuel (coal, wood, oil, whatever) in a steam engine burns outside the engine to create steam, and the steam creates motion inside the engine. Internal combustion is a lot more efficient (takes less fuel per mile) than external combustion, plus an internal combustion engine is a lot smaller than an equivalent external combustion engine. This explains why we don't see any cars from Ford and GM using steam engines.

Internal Combustion

The ­principle behind any reciprocating internal combustion engine: If you put a tiny amount of high-energy fuel (like gasoline) in a small, enclosed space and ignite it, an incredible amount of energy is released in the form of expanding gas. You can use that energy to propel a potato 500 feet. In this case, the energy is translated into potato motion. You can also use it for more interesting purposes. For example, if you can create a cycle that allows you to set off explosions like this hundreds of times per minute, and if you can harness that energy in a useful way, what you have is the core of a car engine!



Almost all cars currently use what is called a four-stroke combustion cycle to convert gasoline into motion. The four-stroke approach is also known as the Otto cycle, in honor of Nikolaus Otto, who invented it in 1867. The four strokes are illustrated in Figure 1. They are:

•Intake stroke
•Compression stroke
•Combustion stroke
•Exhaust stroke
You can see in the figure that a device called a piston replaces the potato in the potato cannon. The piston is connected to the crankshaft by a connecting rod. As the crankshaft revolves, it has the effect of "resetting the cannon." Here's what happens as the engine goes through its cycle:
1.The piston starts at the top, the intake valve opens, and the piston moves down to let the engine take in a cylinder-full of air and gasoline. This is the intake stroke. Only the tiniest drop of gasoline needs to be mixed into the air for this to work. (Part 1 of the figure)
2.Then the piston moves back up to compress this fuel/air mixture. Compression makes the explosion more powerful. (Part 2 of the figure)
3.When the piston reaches the top of its stroke, the spark plug emits a spark to ignite the gasoline. The gasoline charge in the cylinder explodes, driving the piston down. (Part 3 of the figure)
4.Once the piston hits the bottom of its stroke, the exhaust valve opens and the exhaust leaves the cylinder to go out the tailpipe. (Part 4 of the figure)
Now the engine is ready for the next cycle, so it intakes another charge of air and gas.
Notice that the motion that comes out of an internal combustion engine is rotational, while the motion produced by a potato cannon is linear (straight line). In an engine the linear motion of the pistons is converted into rotational motion by the crankshaft. The rotational motion is nice because we plan to turn (rotate) the car's wheels with it anyway.

Now let's look at all the parts that work together to make this happen, starting with the cylinders

Basic Engine Parts

The core of the engine is the cylinder, with the piston moving up and down inside the cylinder. The engine described above has one cylinder. That is typical of most lawn mowers, but most cars have more than one cylinder (four, six and eight cylinders are common). In a multi-cylinder engine, the cylinders usually are arranged in one of three ways: inline, V or flat (also known as horizontally opposed or boxer), as shown in the following figures.




Figure 4. Flat - The cylinders are arranged in two banks on opposite sides of the engine.




Figure 2. Inline - The cylinders are arranged in a line in a single bank.





Figure 3. V - The cylinders are arranged in two banks set at an angle to one another.


Different configurations have different advantages and disadvantages in terms of smoothness, manufacturing cost and shape characteristics. These advantages and disadvantages make them more suitable for certain vehicles.

Let's look at some key engine parts in more detail.

Spark plug

The spark plug supplies the spark that ignites the air/fuel mixture so that combustion can occur. The spark must happen at just the right moment for things to work properly.

Valves

The intake and exhaust valves open at the proper time to let in air and fuel and to let out exhaust. Note that both valves are closed during compression and combustion so that the combustion chamber is sealed.

Piston

A piston is a cylindrical piece of metal that moves up and down inside the cylinder.

Piston rings

Piston rings provide a sliding seal between the outer edge of the piston and the inner edge of the cylinder. The rings serve two purposes:

•They prevent the fuel/air mixture and exhaust in the combustion chamber from leaking into the sump during compression and combustion.
•They keep oil in the sump from leaking into the combustion area, where it would be burned and lost.
Most cars that "burn oil" and have to have a quart added every 1,000 miles are burning it because the engine is old and the rings no longer seal things properly.

Connecting rod

The connecting rod connects the piston to the crankshaft. It can rotate at both ends so that its angle can change as the piston moves and the crankshaft rotates.

Crankshaft

The crankshaft turns the piston's up and down motion into circular motion just like a crank on a jack-in-the-box does.

Sump

The sump surrounds the crankshaft. It contains some amount of oil, which collects in the bottom of the sump (the oil pan).

Next, we'll learn what can go wrong with engines.


Engine Problems

So you go out one morning and your engine will turn over but it won't start... What could be wrong? Now that you know how an engine works, you can understand the basic things that can keep an engine from running. Three fundamental things can happen: a bad fuel mix, lack of compression or lack of spark. Beyond that, thousands of minor things can create problems, but these are the "big three." Based on the simple engine we have been discussing, here is a quick rundown on how these problems affect your engine:

Bad fuel mix - A bad fuel mix can occur in several ways:

•You are out of gas, so the engine is getting air but no fuel.
•The air intake might be clogged, so there is fuel but not enough air.
•The fuel system might be supplying too much or too little fuel to the mix, meaning that combustion does not occur properly.
•There might be an impurity in the fuel (like water in your gas tank) that makes the fuel not burn.
Lack of compression - If the charge of air and fuel cannot be compressed properly, the combustion process will not work like it should. Lack of compression might occur for these reasons:

•Your piston rings are worn (allowing air/fuel to leak past the piston during compression).
•The intake or exhaust valves are not sealing properly, again allowing a leak during compression.
•There is a hole in the cylinder.
The most common "hole" in a cylinder occurs where the top of the cylinder (holding the valves and spark plug and also known as the cylinder head) attaches to the cylinder itself. Generally, the cylinder and the cylinder head bolt together with a thin gasket pressed between them to ensure a good seal. If the gasket breaks down, small holes develop between the cylinder and the cylinder head, and these holes cause leaks.





Lack of spark - The spark might be nonexistent or weak for a number of reasons:

•If your spark plug or the wire leading to it is worn out, the spark will be weak.
•If the wire is cut or missing, or if the system that sends a spark down the wire is not working properly, there will be no spark.
•If the spark occurs either too early or too late in the cycle (i.e. if the ignition timing is off), the fuel will not ignite at the right time, and this can cause all sorts of problems.
Many other things can go wrong. For example:

•If the battery is dead, you cannot turn over the engine to start it.
•If the bearings that allow the crankshaft to turn freely are worn out, the crankshaft cannot turn so the engine cannot run.
•If the valves do not open and close at the right time or at all, air cannot get in and exhaust cannot get out, so the engine cannot run.
•If someone sticks a potato up your tailpipe, exhaust cannot exit the cylinder so the engine will not run.
•If you run out of oil, the piston cannot move up and down freely in the cylinder, and the engine will seize.
In a properly running engine, all of these factors are within tolerance.

As you can see, an engine has a number of systems that help it do its job of converting fuel into motion. We'll look at the different subsystems used in engines in the next few sections.


Engine Valve Train and Ignition Systems


Most engine subsystems can be implemented using different technologies, and better technologies can improve the performance of the engine. Let's look at all of the different subsystems used in modern engines, beginning with the valve train.

The valve train consists of the valves and a mechanism that opens and closes them. The opening and closing system is called a camshaft. The camshaft has lobes on it that move the valves up and down, as shown in Figure 5.




Most modern engines have what are called overhead cams. This means that the camshaft is located above the valves, as you see in Figure 5. The cams on the shaft activate the valves directly or through a very short linkage. Older engines used a camshaft located in the sump near the crankshaft. Rods linked the cam below to valve lifters above the valves. This approach has more moving parts and also causes more lag between the cam's activation of the valve and the valve's subsequent motion. A timing belt or timing chain links the crankshaft to the camshaft so that the valves are in sync with the pistons. The camshaft is geared to turn at one-half the rate of the crankshaft. Many high-performance engines have four valves per cylinder (two for intake, two for exhaust), and this arrangement requires two camshafts per bank of cylinders, hence the phrase "dual overhead cams." See How Camshafts Work for details.

The ignition system (Figure 6) produces a high-voltage electrical charge and transmits it to the spark plugs via ignition wires. The charge first flows to a distributor, which you can easily find under the hood of most cars. The distributor has one wire going in the center and four, six, or eight wires (depending on the number of cylinders) coming out of it. These ignition wires send the charge to each spark plug. The engine is timed so that only one cylinder receives a spark from the distributor at a time. This approach provides maximum smoothness. See How Automobile Ignition Systems Work for more details.


Engine Cooling, Air-intake and Starting Systems

The cooling system in most cars consists of the radiator and water pump. Water circulates through passages around the cylinders and then travels through the radiator to cool it off. In a few cars (most notably Volkswagen Beetles), as well as most motorcycles and lawn mowers, the engine is air-cooled instead (You can tell an air-cooled engine by the fins adorning the outside of each cylinder to help dissipate heat.). Air-cooling makes the engine lighter but hotter, generally decreasing engine life and overall performance. See How Car Cooling Systems Work for details.







So now you know how and why your engine stays cool. But why is air circulation so important? Most cars are normally aspirated, which means that air flows through an air filter and directly into the cylinders. High-performance engines are either turbocharged or supercharged, which means that air coming into the engine is first pressurized (so that more air/fuel mixture can be squeezed into each cylinder) to increase performance. The amount of pressurization is called boost. A turbocharger uses a small turbine attached to the exhaust pipe to spin a compressing turbine in the incoming air stream. A supercharger is attached directly to the engine to spin the compressor.




Increasing your engine's performance is great, but what exactly happens when you turn the key to start it? The starting system consists of an electric starter motor and a starter solenoid. When you turn the ignition key, the starter motor spins the engine a few revolutions so that the combustion process can start. It takes a powerful motor to spin a cold engine. The starter motor must overcome:

•All of the internal friction caused by the piston rings
•The compression pressure of any cylinder(s) that happens to be in the compression stroke
•The energy needed to open and close valves with the camshaft
•All of the "other" things directly attached to the engine, like the water pump, oil pump, alternator, etc.
Because so much energy is needed and because a car uses a 12-volt electrical system, hundreds of amps of electricity must flow into the starter motor. The starter solenoid is essentially a large electronic switch that can handle that much current. When you turn the ignition key, it activates the solenoid to power the motor.


Engine Lubrication, Fuel, Exhaust and Electrical Systems


When it comes to day-to-day car maintenance, your first concern is probably the amount of gas in your car. How does the gas that you put in power the cylinders? The engine's fuel system pumps gas from the gas tank and mixes it with air so that the proper air/fuel mixture can flow into the cylinders. Fuel is delivered in three common ways: carburetion, port fuel injection and direct fuel injection.

•In carburetion, a device called a carburetor mixes gas into air as the air flows into the engine.
•In a fuel-injected engine, the right amount of fuel is injected individually into each cylinder either right above the intake valve (port fuel injection) or directly into the cylinder (direct fuel injection).

Oil also plays an important part. The lubrication system makes sure that every moving part in the engine gets oil so that it can move easily. The two main parts needing oil are the pistons (so they can slide easily in their cylinders) and any bearings that allow things like the crankshaft and camshafts to rotate freely. In most cars, oil is sucked out of the oil pan by the oil pump, run through the oil filter to remove any grit, and then squirted under high pressure onto bearings and the cylinder walls. The oil then trickles down into the sump, where it is collected again and the cycle repeats.




Now that you know about some of the stuff that you put in your car, let's look at some of the stuff that comes out of it. The exhaust system includes the exhaust pipe and the muffler. Without a muffler, what you would hear is the sound of thousands of small explosions coming out your tailpipe. A muffler dampens the sound. The exhaust system also includes a catalytic converter. See How Catalytic Converters Work for details.

The emission control system in modern cars consists of a catalytic converter, a collection of sensors and actuators, and a computer to monitor and adjust everything. For example, the catalytic converter uses a catalyst and oxygen to burn off any unused fuel and certain other chemicals in the exhaust. An oxygen sensor in the exhaust stream makes sure there is enough oxygen available for the catalyst to work and adjusts things if necessary.

Besides gas, what else powers your car? The electrical system consists of a battery and an alternator. The alternator is connected to the engine by a belt and generates electricity to recharge the battery. The battery makes 12-volt power available to everything in the car needing electricity (the ignition system, radio, headlights, windshield wipers, power windows and seats, computers, etc.) through the vehicle's wiring.

Now that you know all about the main engine subsystems, let's look at ways that you can boost engine performance.

5)ELECTRONIC ITEMS & THEIR PRICES

by engr. AFAN BAHADUR KHAN




Sewing Machine"Price Range : Rs. 18250 "" ""US DOLLAR 228""




window AC""Price Range : Rs. 18,490 to 22,167 "" US DOLLAR 227""






safety lockers ""Price Range : Rs. 6,950"" ""US DOLLAR 88 ""





cooler ""Price Range : Rs. 7,370"" ""US DOLLAR 91""



electric iron ""Price Range : Rs. 3,295 to 3,795 ""US DOLLAR 50""





electric fans"" Price Range : Rs. 1570* ""US DOLLAR 20""






washing machines"" Rs. 16,065 to 18,000"" ""US DOLLAR 225""




split AC "" Price Range : Rs. 30,500 to 31,500"" ""US DOLLAR 385""




DRYERS"" Rs. 13,330 to 14,700 "" ""US DOLLAR 175""




WATER COOLERS"" : Rs. 35,660 to 40,354 "" US DOLLAR 500""




WATER DISPENSERS"" Rs. 5,990 to 7,490 "" ""US DOLLAR 93""




VACUUM CLEANERS"" Rs. 899 to 1,665 "" US DOLLAR 20""




flat tvs "" Rs. 7,800 to 8,150 "" "" US DOLLAR 100""





LCD TVs "" Price Range : Rs. 36,900 to 45,000 "" US DOLLAR 562""




micro HI FI ""Price Range : Rs. 8,390 to 9,025 ""US DOLLAR 123""





VCD player "" Price Range : Rs. 4640 "" US DOLLAR 50""



DVD Players"" Price Range : Rs. 3,350 ""US DOLLAR 35""




geyser"" Price Range : Rs. 3,150 "" US DOLLAR 38""




room heater"" Rs. 2995* ( * approx. price) "" ""US DOLLAR 35"""

6)ELECTRONIC CIRCUITS BASED PROJECT

by engr. AFAN BAHADUR KHAN

MICROPOWER LINEAR PWM:

Pulse width modulators are a fundamental building block. Among other things, they are used for remote sensing, DC motor control, and switch-mode power supply controllers.

This circuit uses a rail-to-rail OpAmp to linearize the pulse width of the classic, dual 555 Pulse Width Modulator. The first timer is set to run as a 10Khz oscillator. The square wave output from this section is latched by the D Flip Flop. The Q output then triggers the second 555 timer which is acting as a one-shot. The output pulse clears the latch (which allows output pulses shorter than the trigger width) and is also integrated by the combination of R4 and C6. This integrated, or averaged signal is compared to the input voltage on the OpAmp. The OpAmp will drive the control voltage of the one-shot until the average voltage of the output is equal to the input voltage.




HOT WATER LEVEL INDICATOR



A simple device to indicate various levels of hot water in a tank.

Notes

Save fuel bills and the economy of the planet with this circuit. SW1 is a normally open press button switch which allows you to view the level of hot water in a hot water tank. When pressed the voltage difference at the junction of the thermistor and preset is compared to the fixed voltage on the op-amps non-inverting input. Depending on the heat of the water in the tank, the thermistors resistance will toggle the op-amp output to swing to almost full voltage supply and light the appropriate LED.


Construction

Masking tape was used to stick the bead thermistors to the tank. Wires were soldered and insulated at the thermistors ends. A plastic box was used to house the circuit. Battery life will probably be 4 to 5 years depending on how often you use the push switch, SW1.


Sensor Placement

Thermistors NTC1-4 should be spread evenly over the height of the tank. I placed NTC1 roughly 4 inches from the top of my tank and the others were spaced evenly across the height of the hot water tank. As hot water rises the lowest sensor indicates the fullest height of hot water and should be about 8 to 10 inches from the bottom of the tank.

Calibration

With a full tank of hot water adjust P1-4 so that all LED's are lit. As hot water rises, the sensor at the bottom of the tank will be the maximum level of hot water. "Hot" can be translated as 50C to 80C the presets P1-4 allow adjustment of this range.


Parts

I have used a quad version of the LM324 but any quad opamp can be used or even four single op-amps.
R2-R5 I used 330ohm resistors, but value is not critical. Lower values give brighter LED output.
NTC1-4 The thermistors maximum resistance must roughly equal the resistance of the fixed resistor and preset. As negative temparature coefficient (NTC) thermistors are used, then their resistance decreases for increases in temperature. I used a thermistor from theMaplin Catalogue. Cold resistance was around 300K, hot resistance 15k. Alternative thermistors may be used with different resistance ranges, but the presets P1 to P4 must also be changed as well.
R7-10 series resistance, only required if your thermistors resistance is several ohms at the hottest temperature.
P1 - P4 Chosen to match the resistance of the thermistor when cold.
R1 & R6. These resistors are equal and bias the op-amp inverting input to half the supply voltage. I used 100k.


4 DIGIT ALARM KEYPAD




This is an enhanced 4 digit keypad which may be used with the Modular Alarm System.


Notes

The Keypad must be the kind with a common terminal and a separate connection for each key. On a 12-key pad, look for 13 terminals. The matrix type with 7 terminals will NOT do. The Alarm is set by pressing a single key. Choose the key you want to use and wire it to 'E'. Choose the four keys you want to use to switch the alarm off, and connect them to 'A B C & D'. Your code can include the non-numeric symbols. With a 12-key pad, over 10 000 different codes are available. Wire the common to R1 and all the remaining keys to 'F'. When 'E' is pressed, current through D2 and R9 switches Q5 on. The relay energises, and then holds itself on by providing base current for Q5 through R10. The 12-volt output is switched from the "off " to the "set " terminal, and the LED lights. To switch the Alarm off again it is necessary to press A, B, C & D in the right order. The IC is a quad 2-input AND gate, a Cmos 4081. These gates only produce a high output when both inputs are high. Pin 1 is held high by R5. This 'enables' gate 1, so that when 'A' is pressed, the output at pin 3 will go high. This output does two jobs. It locks itself high using R2 and it enables gate 2 by taking pin 5 high. The remaining gates operate in the same way, each locking itself on through a resistor and enabling its successor. If the correct code is entered, pin 10 will switch Q4 on and so connect the base of Q5 to ground. This causes Q5 to switch off and the relay to drop out. Any keys not wired to 'A B C D or E' are connected to the base of Q3 by R7. Whenever one of these 'wrong' keys is pressed, Q3 takes pin 1 low. This removes the 'enable' from gate 1, and the code entry process fails. If 'C' or 'D' is pressed out of sequence, Q1 or Q2 will also take pin 1 low, with the same result. You can change the code by altering the keypad connections. If you need a more secure code use a bigger keypad with more 'wrong' keys wired to 'F'. A 16-key pad gives over 40 000 different codes. All components are shown lying flat on the board; but some are actually mounted upright. The links are bare copper wires on the component side. Two of the links must be fitted before the IC.