professor's corner

Brain Tumor

2011-06-24T07:53:00.000-07:00

BrainTumor

Brain Tumor

The symptoms of brain tumors depend on their size and location in the brain.
Symptoms often are caused by damage to vital tissue and pressure on the brain as the tumor grows within the limited space in the skull. They may be caused by swelling and a buildup of fluid around the tumor, a condition called edema. Symptoms also may be due to hydrocephalus, which occurs when the tumor blocks the flow of cerebrospinal fluid and causes a build-up in the ventricles.

If a brain tumor grows very slowly, its symptoms may not appear for some time. The most frequent symptoms of brain tumors include:

Headaches that tend to be worse in the morning and ease during the day
Seizures or convulsions
Nausea or vomiting
Weakness or loss of feeling in the arms or legs
Stumbling or lack of coordination in walking
Abnormal eye movements or changes in vision
Drowsiness
Changes in personality or memory
Changes in speech

Brain Diagnosis

To find the cause of your symptoms, your doctor will ask about your personal and family medical history and perform a complete physical examination. In addition to checking general signs of health, your doctor will perform a neurologic exam. This includes checks for alertness, muscle strength, coordination, reflexes and response to pain. Your doctor also examines the eyes to look for swelling caused by a tumor pressing on the nerve that connects the eye and the brain.

Depending on the results of the physical and neurologic examinations, your doctor may request one or both of the following:

Computerized Tomography (CT) Scan — Computerized tomography (CT) or computerized axial tomography (CAT) scan is a series of detailed pictures of the brain, created by a computer linked to an X-ray machine. In some cases, a special dye is injected into a vein before the scan. The dye helps to show differences in the tissues of the brain.
Magnetic Resonance Imaging (MRI) — Magnetic resonance imaging (MRI) provides pictures of the brain, using a powerful magnet linked to a computer. MRI is especially useful in diagnosing brain tumors because it can "see" through the bones of the skull to the tissue underneath. A special dye may be used to enhance the likelihood of detecting a brain tumor.

The doctor may also request other tests such as:

Angiogram or Arteriogram — These tests are a series of X-rays taken after a special dye is injected into an artery, usually in the area where the abdomen joins the top of the leg. The dye, which flows through the blood vessels of the brain, can be seen on X-rays. These X-rays can show the tumor and connecting blood vessels.
Brain Scan — A brain scan reveals areas of abnormal growth in the brain and records them on special film. A small amount of a radioactive material is injected into a vein. This dye is absorbed by the tumor and the growth shows up on the film. The radiation leaves the body within six hours and is not dangerous.
Functional Imaging — This test utilizes MRI or magnetic source imaging to identify functional pathways in the brain (motor, visual, language) and alerts the surgeon to potential injury to these pathways during surgery before damage could occur.
Myelogram — A myelogram, sometimes called a lumbosacral spine X-ray, is an X-ray or computerized tomography (CT) scan of the spine. A special dye is injected into the cerebrospinal fluid in the spine and the patient is tilted to allow the dye to mix with the fluid. This test may be done when the doctor suspects a tumor in the spinal cord.
MR Spectroscopy — This is a modified MRI scan that shows metabolic activity within a brain tumor. This has largely replaced positron emission tomography (PET) scanning due to its superior resolution and accuracy.

Reviewed by health care specialists at UCSF Medical Center.

Brain Tumor
Treatment

Treatment for brain tumors depends on a number of factors including the type, location and size of the tumor as well as the patient's age and general health. Treatment methods and schedules differ for children and adults.
Brain tumors are treated with surgery, radiation therapy and chemotherapy. Our doctors also are studying a vaccine for treating a recurrent cancer of the central nervous system that occurs primarily in the brain, known as glioma.
Depending on your needs, several methods may be used. Our team includes neurosurgeons, medical oncologists, radiation oncologists, nurses, a dietitian and a social worker, who work together to provide the best possible care.
Before treatment begins, most patients are given steroids, drugs that relieve swelling or edema. Your may receive anticonvulsant medicine to prevent or control seizures.
If hydrocephalus is present, you may need a shunt to drain cerebrospinal fluid. A shunt is a long, thin tube placed in a ventricle of the brain and then threaded under the skin to another part of the body, usually the abdomen. It works like a drainpipe. Excess fluid is carried away from the brain and is absorbed in the abdomen. In some cases, the fluid is drained into the heart.

Surgery

Surgery is the usual treatment for most brain tumors. To remove a brain tumor, a neurosurgeon makes an opening in the skull. This operation is called a craniotomy. Whenever possible, the surgeon attempts to remove the entire tumor. If the tumor cannot be completely removed without damaging vital brain tissue, your doctor may remove as much of the tumor as possible. Partial removal helps to relieve symptoms by reducing pressure on the brain and reduces the amount of tumor to be treated by radiation therapy or chemotherapy.
Some tumors cannot be removed. In such cases, your doctor may do only a biopsy. A small piece of the tumor is removed so that a pathologist can examine it under a microscope to determine the type of cells it contains. This helps your doctor decide which treatment to use.
Sometimes, a biopsy is done with a needle. Doctors use a special head frame (like a halo) and CT scans or MRI to pinpoint the exact location of the tumor. The surgeon makes a small hole in the skull and then guides a needle to the tumor. Using this technique to do a biopsy or for treatment is called stereotaxis.
Other advanced techniques during surgery include brain mapping to find functional pathways near tumors, endoscopy to perform biopsies and open spinal fluid pathways through a small scope and advanced frameless stereotaxic computer assisted tumor resections. Intraoperative MRI also is available to help maximize tumor removal.

Thelsemia

2011-06-24T07:43:00.000-07:00

Thelsemia

thelesemia

The thalassemias are a diverse group of genetic blood diseases. Thalassemia is the most common inherited single gene disorder in the world. Scientists and public health officials predict that thalassemia will become a worldwide issue in the next century. With global improvements in childhood disease prevention and treatment, more focus will be given to diagnosing disorders. It is our hope that by providing education about the disease we can raise awareness, encourage people to get tested for the trait, and spread knowledge about comprehensive treatment.
The thalassemias are a diverse group of genetic blood diseases characterized by absent or decreased production of normal hemoglobin, resulting in a microcytic anemia of varying degree. The thalassemias have a distribution concomitant with areas were malaria is common. People with Thalassemia Minor are able to fight malaria better than those who do not have it - therefore, in parts of the world where malaria existed Thalassemia Minor increased. This was of great value in the past since malaria was rampant and deadly. However, malaria is no longer a problem in many areas of the world, and Thalassemia Minor has no advantage to people in these areas. The alpha thalassemias are concentrated in Southeast Asia, Malaysia and southern China. The beta thalassemias are seen primarily in the Mediterranean Sea area, Africa and Southeast Asia. Due to global migration patterns, there has been an increase in the incidence of thalassemia in North America in the last ten years.
In the thalassemia patient, a mutation or deletion of the genes that control globin production occurs. This leads to a decreased production of the corresponding globin chains and an abnormal hemoglobin ratio. This abnormal ratio leads to decreased synthesis of hemoglobin and the expression of thalassemia. The globin that is produced in normal amounts winds up in excess and forms red cell aggregates or inclusions. These aggregates become oxidized and damage the cell membrane, leading to hemolysis, ineffective erythropoiesis, or both. The quantity and properties of these globin chain aggregates determine the characteristics and severity of the thalassemia.

amorphous silicon solar thin film vs crytalline silicon solar panel

2011-05-22T02:29:00.000-07:00

5″ monocrystalline Silicon 5 inch 125 Series Solar Cell
6″ Polycrystalline Silicon 6 inch 156 Series Solar Cell

1. Difference between crystal and amorphous? Daily to see the solid is divided into two major categories of non-crystalline and crystalline, non-crystalline arrangement of atoms within the material is not necessarily the law of the fracture when the fracture is random, such as plastic and glass, and called the crystal material, represent the natural shape of a regular polyhedron, with obvious edges and corners with the plane, the atom is in accordance with its internal law must line up neatly, so when they break off the plane according to certain, such as salt, crystal and so on.

2. Difference between single crystal and polycrystalline? Some of the crystal is composed of many small grains, if the arrangement between the grains are no rules, this is called polycrystalline crystal, such as copper and iron. But there are also the crystal itself is a complete large grains, the crystal is called single crystal, crystal and crystal diamond.

3. Monocrystalline silicon and polycrystalline silicon photovoltaic cells compare? Monocrystalline silicon cells with a cell conversion efficiency, good stability, but the cost is high. Low-cost polycrystalline silicon cells, the conversion efficiency slightly lower than the Czochralski silicon solar cells and materials in a variety of defects such as grain boundaries, dislocations, micro-defects, and material impurities carbon and oxygen, as well as the stained process transition metals.

The first is the advent of solar cell silicon solar cells. Silicon is very abundant on the earth, an element almost everywhere have the presence of silicon can be said to be used without silicon to make solar cells, indeed no shortage of raw materials. But it is not easy to extract, so people in the production of monocrystalline silicon solar cells, they also studied the polycrystalline silicon solar cells and amorphous silicon solar cells, has commercial-scale production of solar cells, also did not jump out of silicon series. In fact, the semiconductor materials for manufacture of solar cells a lot, along with the development of industrial materials, solar cells will be more and more varieties. Research and trial production has been the solar cell, in addition to silicon series, there are cadmium sulfide, gallium arsenide, copper indium selenium and many other types of solar cells, too numerous to mention, the following are a few of the more common solar cells.

Monocrystalline silicon solar cells

Monocrystalline silicon solar cells is currently the fastest developing a solar cell, its composition and production technology has been finalized, the products have been widely used for space and ground facilities. The high purity single crystal silicon solar cells as the raw material rod, 99.999% purity. In order to reduce production costs, and now solar terrestrial applications such as the use of solar-grade silicon rods, material performance has been relaxed. Some semiconductor devices can also be used for processing materials and discard ends of silicon materials, solar cells made by re-drawing a dedicated silicon rods. The slice of silicon rods, generally 0.3 mm thick slices. Wafer after forming, polishing, cleaning and other processes, made of silicon raw material to be processed. Solar cell processing chip, the first doping and diffusion in silicon, usually for the small amount of boron dopant, phosphorus, antimony and so on. Diffusion is the control into the quartz furnace for high temperature diffusion. And then using screen printing will be printed with a good paste made of silicon gate line, after sintering, also made of the back electrode and a gate line in the face of anti-reflection coating source, to prevent a large number of photons reflected from a smooth silicon surface, thus, single-chip silicon solar cells are produced. After single-chip random testing, according to the required specifications can be assembled into solar modules (solar panels), the method used in series and parallel to a certain output voltage and current, and finally with the framework and package materials package. According to the system user can design different size solar module solar cell composed of a variety of square, also known as the solar array. Current silicon photoelectric conversion efficiency of solar cells is about 15%, laboratory results have more than 20%. Also for the space station up to 50% or more solar panels.

Polycrystalline silicon solar cells

Monocrystalline silicon solar cell production requires large amounts of high-purity silicon material, the production of these materials, process complexity, power consumption drastically, the total cost of solar cell production has been over half, combined with the silicon rod was drawn cylindrical, sliced wafer production solar cells is to form a solar module surface low utilization rate. Thus, 80 years, some European and American countries, the development into a polycrystalline silicon solar cells. Polycrystalline silicon solar cells using current materials, mostly a collection contains a lot of single crystal particles, or silicon materials from waste materials and metallurgical grade silicon melt molded. The process is to select a resistivity of 100 to 300 ohms? Cm block of material or a polycrystalline silicon material end to end, after crushing, with the 1:5 mixture of hydrofluoric acid and nitric acid corrosion appropriate, and then spent neutral-ionized water rinse and drying. Quartz crucible installed polysilicon materials, the addition of appropriate amount of boron in silicon, release the casting furnace, heating and melting in a vacuum state. Melted insulation should be about 20 minutes, and then injected into the graphite mold, to be cooled slowly solidified, that have polysilicon ingot. The ingots can be cast cubes to be processed into square slices film solar cells can improve material utilization and easy assembly. Polycrystalline silicon solar cells and solar cell production process is similar to the photoelectric conversion efficiency of about 12%, slightly lower than the silicon solar cells, but the material is simple, to save power consumption, the total production costs low, so get a lot of development. As the technology was improved, the current conversion efficiency of polycrystalline silicon can also be reached around 14%.

Amorphous silicon solar cells

Amorphous silicon solar cells appeared in 1976 with a new thin film solar cells, monocrystalline and polycrystalline silicon solar cells it with the production method is completely different, very little silicon material consumption, lower power consumption, very attractive. Method of manufacturing a variety of amorphous silicon solar cells, the most common is the glow discharge method, as well as reactive sputtering, chemical vapor deposition, electron beam evaporation and thermal decomposition of silane method. Glow discharge method is a Dan Yingrong device pumped into vacuum, hydrogen or argon gas filled diluted silane, with the RF power heating, ionization of silane to form a plasma. Deposition of amorphous silicon film on the substrate being heated. If the silane were mixed in the amount of hydrogenated or hydrogenated boron phosphate can be N-or P-type amorphous silicon film. Substrate materials are generally made of glass or stainless steel. Preparation of amorphous silicon thin film technology which depends mainly on the strict control of pressure, flow rate and RF power, the temperature of the substrate is also very important. The structure of amorphous silicon solar cells there are different, which has a structure called the PiN better battery, it is first deposited on the substrate N-type layer of amorphous silicon doped with phosphorus, and then deposited a layer of undoped i layer, and then deposited a layer of P-type boron-doped amorphous silicon, and finally a layer of electron beam evaporation of antireflection coatings, and deposition of silver electrodes. This production process, a series of deposition chamber can be used in production form a continuous process to achieve mass production. Meanwhile, the thin amorphous silicon solar cells can be made into laminated type, or use to manufacture integrated circuits in a plane, with the appropriate mask technology, a production of multiple batteries in series to obtain higher voltage . Because the average crystalline silicon solar cells around a single voltage of 0.5 volts, and now the production of amorphous silicon tandem solar cells in Japan up to 2.4 volts. The current problem is that of amorphous silicon solar cell conversion efficiency is low, the international advanced level of about 10%, and is not stable enough, often decline down conversion efficiency of the phenomenon, so not a lot of use for large-scale solar power, but mostly with in low light power, such as pocket electronic calculators, electronic watches and clocks and copier and so on. Failure to overcome the drop in efficiency issues, the amorphous silicon solar cells will promote the great development of solar energy, because its low cost, light weight, easier application, it can be combined with the housing of the roof form independent power of households.

In the fierce sun, single crystal solar panels can be transformed more and more non-crystal-type solar energy to electricity more than doubled, but unfortunately, the price of single crystal type of non-crystal-like than the two or three times more expensive, and in the case of non-cloudy Instead, the crystal-type transistor can be almost as much to collect solar energy.

SOLAR OFFICIAL WEBSITE:

2011-05-21T02:23:00.001-07:00

Chapter 1-What is solar energy.

Chapter 2-Types of solar electric panels.

Chapter 3-Solar panel system components.

Chapter 4-Types of Solar panel systems.

Chapter 5-Solar Electric VS. Solar hot water.

Chapter 6-Sizing your solar electric system.

Chapter 7-Costing your solar electric system.

Chapter 8-Choosing a solar installer.

Chapter 9-Payback of your solar electric system.

Chapter 10-Rebates Available.

Chapter 11-Solar panel maintenance.

Chapter 12-Solar buyer checklist.

Solar System Pakistan

2011-05-21T02:10:00.001-07:00

Solar System Pakistan

In solar system the things you need is depend on what you want to do. If you want to turn on just lights, bulbs or lamps. So then what you need is listed under here.

1. Solar Panel
2. Solar Charge Controller
3. Battery
4. DC Lights

These are things that you must have to turn your lights on. Without them it is difficult to power up lights. Solar system works in this order. Solar Panel is giving current to charge controller. Charge controller charges a battery. And lights are powered up by a battery. In this case it is DC lights.

How to connect solar system?

Yes we will tell you about how to connect solar power system together to get it to work. First what you have to do is take a closer look at charge controller.

Charge Controller We can easily see on charge controller that it have been marked with solar panel, battery and lights. Now the thing is to connect correct wires of solar panel, battery and lights to plus to plus and negative to negative.

Solar Energy System We are selling solar panels, charge controllers, batteries, inverters, dc energy saving lights and other equipment for solar energy. If you want to install this system at your home in Pakistan so please contact us by email or call us. We will help you with installation of solar energy system in Pakistan.

Different Types Of Solar Panels

2011-05-20T11:00:00.000-07:00

Different Types Of Solar Panels

Monocrystal solar panels

Monocrystalline panels use crystalline silicon produced in a large sheet which has been cut to the size of the panel, thus making one large single cell. Metal strips are laid over the entire cell and act as a conductor that captures electrons.

Mono panels are slightly more efficient than Polycrystalline panels but the don't usually cost more than Poly Panels.

Polycrystal panels

Polycrystalline panels use a bunch of small cells put together instead of one large cell. Poly panels are slightly less efficient than mono panels. They are also claimed to be cheaper to manufacturer than mono panels although we have noticed them to be very similarly priced.

There are a couple different ways a polycrystalline silicon cell can be made:
Cast Polysilicon:

In this process, molten silicon is cast in a large block which, when cooled, can be cut into thin wafers to be used in photovoltaic cells. These cells are then assembled in a panel. Conducting metal strips are then laid over the cells, connecting them to each other and forming a continuous electrical current throughout the panel.
String Ribbon Silicon

String ribbon uses a variation of the polycrystalline production process, using the same molten silicon but slowly drawing a thin strip of crystalline silicon out of the molten form. These strips of photovoltaic material are then assembled in a panel with the same metal conductor strips attaching each strip to the electrical current.

It is also said that string ribbon solar panels are even cheaper to manufacturer than the cast polysilicon method. If this were the case then why are String Ribbon Panels the most costly? This technology saves on costs over standard polycrystalline panels as it eliminates the sawing process for producing wafers. Some string ribbon technologies also have higher efficiency levels than other polycrystalline technologies.

Thin Film Panels

Thin film panels are produced very differently from crystalline panels. Instead of molding, drawing or slicing crystalline silicon, the silicon material in these panels have no crystalline structure and can be applied as a film directly on various materials. Variations on this technology use other semiconductor materials like copper indium diselenide (CIS) and cadmium telluride (CdTe). These materials are then connected to the same metal conductor strips used in the other processes, but do not necessarily use the other components typical in photovoltaic panels as they do not require the same level of protection needed for more fragile crystalline cells.

The primary advantages of thin film panels lie in their low manufacturing costs and versatility. Because amorphous silicon and similar semiconductors do not depend on the long, expensive process of creating silicon crystals, they can be produced much more quickly. Because they can be applied in thin layers to different materials, it is also possible to make flexible solar cells.

thin film panels do have several significant drawbacks. They are the least efficient type of solar panel currently available. Thin-film technology also uses silicon with high levels of impurities. This can cause a drop in efficiency within a short period of time.

Conclusion

The best choice for powering your home are going to be Mono or Polycrstal panels. Their higher efficiency and greater durability make them the best option.
If prices are real close, and they should be, monocrystal panels would be our first choice. However, they both are going to get the job done, and do it well!

dcactuators

2011-05-20T10:45:00.000-07:00

http://dcactuators.com/

What is a Thin-film Solar Cell?

2011-05-20T06:47:00.000-07:00

What is a Thin-film Solar Cell?

A copper indium gallium deselenide solar cell using glass

If you've used a solar-powered calculator, you've seen a solar cell based on thin-film technology. Clearly, the small cell in a calculator is not big and bulky. Most are about an inch (2.5 cm) long, a quarter-inch (0.6 cm) wide and wafer-thin. The thinness of the cell is the defining characteristic of the technology. Unlike silicon-wafer cells, which have light-absorbing layers that are traditionally 350 microns thick, thin-film solar cells have light-absorbing layers that are just one micron thick. A micron, for reference, is one-millionth of a meter (1/1,000,000 m or 1 µm).

Thin-film solar cell manufacturers begin building their solar cells by depositing several layers of a light-absorbing material, a semiconductor onto a substrate -- coated glass, metal or plastic. The materials used as semiconductors don't have to be thick because they absorb energy from the sun very efficiently. As a result, thin-film solar cells are lightweight, durable and easy to use.

There are three main types of thin-film solar cells, depending on the type of semiconductor used: amorphous silicon (a-Si), cadmium telluride (CdTe) and copper indium gallium deselenide (CIGS). Amorphous silicon is basically a trimmed-down version of the traditional silicon-wafer cell. As such, a-Si is well understood and is commonly used in solar-powered electronics. It does, however, have some drawbacks.
One of the biggest problems with a-Si solar cells is the material used for its semiconductor. Silicon is not always easy to find on the market, where demand often exceeds supply. But the a-Si cells themselves are not particularly efficient. They suffer significant degradation in power output when they're exposed to the sun. Thinner a-Si cells overcome this problem, but thinner layers also absorb sunlight less efficiently. Taken together, these qualities make a-Si cells great for smaller-scale applications, such as calculators, but less than ideal for larger-scale applications, such as solar-powered buildings.

Promising advances in non-silicon thin-film PV technologies are beginning to overcome the issues associated with amorphous silicon. On the next page, we'll take a look at CdTe and CIGS thin-film solar cells to see how they compare.

employement

2011-05-19T06:30:00.000-07:00

Airblue - a quality airline venture in Pakistan - offers exciting and challenging opportunities for talented and innovative people looking to exploit their full potential and grow with us. We offer excellent working conditions and competitive salary and benefits package including travel privileges. Applications are only accepted online.
Airblue is pleased to offer the following job openings:

Department:	Position:	Location:	# of Openings:
Administration	CFO	ISB - Corporate HQT	1
Commercial	Call Center Counselor	ISB - Call Center	6
	Travel Counselor	KHI - Airport	4
Corporate Affairs	Medical Coordinator	KHI - Airport	1
Corporate Safety	Executive	KHI - Airport	1
Flight Operations Control	Flight Operations Officer	KHI - Airport	1
Flight Services	Cabin Crew - Trainee	ISB - Airport	1
	Cabin Crew - Trainee	KHI - Airport	1
	Performance Executive	KHI - Airport	1
MIS	Network Engineer	ISB - Airport	1

Please Note:
• Airblue does not have any Employment Offices or Agents.
• All Applications for Employment are processed free of cost.
• No Personal Contact or Phone Calls - Please.
• Applicants who are pre-qualified will be called for an interview via email.

2011-05-18T23:09:00.000-07:00

Embedded System:

Embedded systems refer to devices, instruments or large engineering structures/systems that are built to handle one or a few pre-established tasks. The computer controlling the whole thing is built into or ‘embedded’ within the device.

Cellphones and personal digital assistants (PDAs) are examples of devices with embedded systems. They both perform a specific number of tasks which are controlled by a built-in computer system. Inertial guidance systems used for aerial navigation or as part of the guidance package of smart bombs and missiles are examples of instruments with embedded systems. A traffic control system (which remotely controls traffic lights without the need for human intervention) is an example of a large engineering structure with an embedded system.

is an example of a large engineering structure with an embedded system.

In truth, the line between ‘embedded’ systems and general purpose systems (which may or may not contain an embedded system) is becoming blurred as technology progresses.

Characteristics of Embedded Systems

The key characteristic of an embedded system is that it is supposed to handle a few simple tasks, although the steps involved in handling or accomplishing that task may be as complex as any computer program. A videogame controller, for example, may be said to have simple tasks – load the game and allow the player to control it through commands entered through the handset. In truth, however, a game controller (especially the newer games built for the X-box or PS3) goes through a series of steps and actions that require as much processing power as a standalone computer. Among the characteristics of modern embedded systems are:

User Interfaces

Originally, an embedded system had no user interface – information and programs were already incorporated into the system (e.g., the guidance system for an Intercontinental Ballistic Missile or ICBM) and there was no need for human interaction or intervention except to install the device and test it.

Many modern embedded systems however, have full-scale user interfaces although these are only inputs for data but are not supposed to provide additional functionality for the system, e.g. QWERTY keyboards for PDAs used to enter names, addresses, phone numbers and notes and even full sized documents. The moment PDAs achieve full desktop computer functionalities, however, they may no longer be considered embedded systems.

Simple Systems which Stem from Limited Functionality

Originally, this referred to basic systems such as switches, small character- or digit-only displays and LEDs intended to show the ‘health’ of the embedded system, but this has also achieved some level of complexity. A cash register or an ATM with touch screen technology is considered an embedded system since it has limited uses, even if the user interface (the touch screen) is a complex system.

CPU Platforms with Microprocessors or Microcontrollers

Again, limited functionality is the key in defining these as embedded systems. In a sense, the Bios chip is considered an embedded system since it has limited functions, and works automatically (when the computer is booted up). Peripherals like the USB can also be considered as embedded systems.

embedded object

2011-05-18T23:05:00.001-07:00

embedded object

An object created with one application and embedded into a document created by another application. Embedding the object, rather than simply inserting or pasting it, ensures that the object retains its original format. In fact, you can modify the embedded object with the original program. In Windows environments, embedding objects is made possible by a technology called OLE.

FPGA-based Form Factor Serves Radar ADC Needs

2011-05-18T22:57:00.000-07:00

SPECIAL FEATURE

FPGA-based Form Factor Serves Radar ADC Needs

Advances in ADCs, combined with larger, more powerful FPGAs and the new open standard FMC format, are fueling improvements in radar systems.

JEREMY BANKS, CURTISS-WRIGHT CONTROLS EMBEDDED COMPUTING

DIGITAL EDITION

INDUSTRY NEWS

WHITEPAPERS

COMPANY	PRICE (USD)	CHANGE
Adlink	2.01	1.222%
Advantech	3.30	2.256%
Concurrent Comp	6.11	2.689%
Elma	490.45	2.005%
- Enea	7.33	0.000%
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Kontron	11.49	2.230%
Mercury Comp	18.10	-0.110%
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Article Media

In Electronic Warfare (EW) the difference between life and death can come down to just a few radar pulses. There’s a matter of milliseconds in which a ship’s countermeasure system can sense an oncoming missile threat. Radar signals from that threat won’t even show up until it’s as near as 10 km from target. Once identified the ship’s fire control system can send out a deceptive signal about its position before the enemy weapon has a chance to lock onto the ship’s radar, safely diverting the course of the speeding missile. This makes it critical to improve the speed and resolution at which embedded signal intelligence systems can take incoming analog sensor data and digitally convert it so that it can be processed in a useful way. An example system along those lines is Raytheon’s Phalanx Close-In Weapon System (Figure 1).

Figure 1
Raytheon’s Phalanx Close-In Weapon System is a rapid-fire, computer-controlled, radar-guided gun system designed to defeat anti-ship missiles and other close-in air and surface threats assessment.

The good news is that the newest generation of commercial ADCs, combined with larger, more powerful FPGAs and the new open standard FPGA Mezzanine Card (FMC), can now significantly improve these EW systems through the direct digital conversion of the analog signal, eliminating the need for an intermediary down conversion stage. The resulting performance benefits are helping to change the COTS receiver industry landscape.

Pushing the ADC Boundaries

Today’s highest end ADCs, with greater bandwidth and higher resolution than previously available, are increasingly being used in demanding military applications to provide direct digital sampling of wideband Receiver Intermediate Frequency (IF) analog sensor data. This results in improved performance and lower costs by eliminating the need for a heterodyne receiver down conversion stage in the system.

Previous generations of ADC conversion technology have not had the speed or resolution at the required frequencies to function as a true RF front end without down conversion. Today’s newer devices, however, feature multi-Gigasample per second (Gsample/s) converters in both directions with the high resolution needed to directly connect to the RF front end in close proximity to the antenna system. This new capability is fueling increased direct (baseband) conversion.

As recently as two or three years ago, leading off-the-shelf high-end ADCs could only achieve 1.5 to 3 Gbit/s bandwidth performance with 8-bit resolution. Since then, the performance of commercial ADC devices has increased dramatically. Today’s high-end ADCs are approaching 4G sample/s bandwidth with 12-bit resolution. Earlier ADC technology either wasn’t fast enough, or lacked the resolution or the combination of the two to enable direct digital conversion of analog signals. This resulted in more cost and reduced performance because a system would typically require two RF heterodyne receiver front-ends to handle the down conversion stage before the data would get to the ADCs attached to the FPGAs. Today’s FPGAs function as true processors that have large blocks of digital circuitry in which signal processing algorithms such as FFTs can be stored. FPGAs are very good at handling signal processing in the digital domain.

Today’s faster, higher resolution ADCs have the ability to take an input signal at a microwave frequency and convert it at that frequency rather than requiring the use of a costly intermediary down converter. Higher-end ADCs can sample at rates in excess of 3 to 4 Gsamples/s, which approaches the 1.5 GHz L-Band and beyond. Sampling rates that exceed 1 GHz and faster now allow bandwidths of up to 500 MHz to be processed. And the higher bit resolution of the new ADCs has increased system dynamic range, the span from the weakest to the strongest detectable signal that it can handle.

Today’s high-resolution ADCs can sample at rates near 200 Msamples/s, and soon will reach 250 Msamples/s with 16-bit resolution. They can dramatically enhance the capabilities of wideband receivers by increasing their sensitivity and selectivity, which affects the system’s ability to intercept and characterize captured signals.

FPGAs Make it Possible

The design challenge at these high data rates is how to interface these newly obtainable levels of resolution to the digital domain, a task that traditional processors can’t handle. The answer is a combination of baseboard FPGAs and FMC I/O cards. When combined with larger FPGAs and the new industry standard FMCs, the new generation of ADCs is enabling system designers to integrate open standards-based board systems in which both ADC and DAC capabilities are directly coupled to the processing element, provided by the FPGA. The result is an order of magnitude improvement in latency from input to output. Even better for Space, Weight and Power (SWaP)-constrained embedded systems, the increased bandwidth of the new ADC devices does not come at the cost of a comparable rise in power consumption. We are seeing these devices with power dissipation rated near 2W per converter, which means that a quad-channel FMC will require less than 10W.

The FMC (VITA 57) standard, recently approved by ANSI, provides a method for directly coupling FPGAs on the baseboard with I/O devices on the small mezzanine FMC board. FMCs enable the board’s bus structure to be bypassed, providing direct I/O to the FPGA processing element on the host card. This drastically improves data rates and reduces latency compared to designs where the I/O devices reside on the main PCB. Another advantage is that FMCs make it easier to tune particular I/O needs with a common processing engine and to upgrade performance as newer and better I/O devices become available without a major baseboard redesign.

Supporting High Data Rates

In comparison to FMC cards, standard I/O mezzanine cards, such as PMC and XMC, tend to support CPU-type buses such as PCI Express and PCI-X, for which data bandwidth is limited to 1 to 2 Gbytes/s. In a direct one-to-one connection, today’s FPGAs can support the very high data rates provided by the use of locating I/O on FMC cards, while eliminating the issue of latency resulting from the bus structure. Compared to XMC mezzanine cards, and depending on the devices used, FMCs can deliver an order of magnitude increase in bandwidth and similar reduction in latency. FMCs can support data throughput rates of 5 to 10 Gbytes/s, while XMC provides 500 Mbytes/s to 1 Gbyte/s. Key to the high speed of FMCs is the simplicity of their design: the FMC specification makes provision for a large number of parallel I/O connections, up to 160 single-ended (80 differential pair) signals, in addition to high-speed serial connections, directly connected to the FPGA(s) located on the base board. Figure 2 shows a side by side comparison between an XMC board and an FMC board.

Figure 2
FMCs (bottom) can support data throughput rates of 5 to 10 Gbytes/s, while XMC (top) provides 500 Mbytes/s to 1 Gbyte/s. The simple FMCs design also allows for a large number of parallel I/O connections.

Dual ADCs on FMC

An example of an FMC card designed for use with an FPGA host card such as the FPE320, is Curtiss-Wright Controls’ ADC511 Dual Channel Analog Input FMC, which features dual 400 Msample/s 14-bit Texas Instruments ADS5474 ADCs. Each of the module’s ADCs supports a sampling rate up to 400 Msamples/s, within an analog bandwidth of over 1.7 GHz, and provides 14-bits of digital output. By routing the ADC device interfaces directly to the FMC connector, the ADC511 enables an FPGA on the host board to directly control and receive data. A choice of sample clock sources is provided, including an onboard source that supports sampling rates of 300, 320 and 400 Msamples/s, as well as the ability to use an external sample clock. Input and output triggers are provided enabling the number of input channels to be increased by synchronizing multiple ADC511 modules.

Thanks to the new generations of ADC, FPGA and FMC products, we are seeing more and more applications in which direct conversion is occurring. For COTS signal processing system designers the trends are beneficial. Life-saving high-performance EW systems can be deployed faster and cheaper using commercial devices in designs that can flexibly be upgraded and modified using low-cost FMC mezzanine modules.

embedded system

2011-05-18T22:53:00.001-07:00

embedded system

A specialized computer system that is part of a larger system or machine. Typically, an embedded system is housed on a single microprocessor board with the programs stored in ROM. Virtually all appliances that have a digital interface -- watches, microwaves, VCRs, cars -- utilize embedded systems. Some embedded systems include an operating system, but many are so specialized that the entire logic can be implemented as a single program.

Software Engineer-Embedded Systems ( DO-178B )

2011-05-18T22:39:00.000-07:00

Job Information

Company:: Sierra Nevada Corporation
Location:: Reno, NV
Industries:: Aerospace and Defense
Job Type:: Full Time Employee
Years of Experience:: 7+ to 10 Years
Education Level:: Bachelor's Degree

Highly competitive total compensation package, including 401K (150% match), tuition reimbursement and relocation assistance.

Contact Information

Company:: Sierra Nevada Corporation
Job Reference Code:: 10-SPAR:091

Please Visit Our Website at www.sncorp.com

Bringing Tomorrow's Technology To Today!

Join Sierra Nevada Corporation (SNC) and help us bring tomorrow’s technology to today! SNC offers an exciting, dynamic and challenging work environment where you can expand your career opportunities and achieve professional growth. Employees are our greatest assets. Our environment encourages employees to unleash creativity, and strive for new ideas, technologies and processes.

Job Description

Software Engineer-Embedded Systems ( DO-178B )

Sierra Nevada Corporation's Communication, Navigation, Surveillance / Air Traffic Management business is continuing to grow in support of its customers and seeks qualified and highly motivated individuals to join our team in Sparks, NV.

Sparks is immediately adjacent to Reno and only 20 minutes drive from scenic Lake Tahoe in the heart of the Sierra. In addition to the night life, this area offers world class skiing, mountain biking, backpacking, hiking, kayaking – all of the outdoor adventures imaginable.

We provide capability to both military and civil aviation users supplying them with state of the art radar based technology solutions for 3 Dimensional Imaging, Sense and Avoid,, automatic landing, navigation and communications systems. We design, build, integrate, and operate these highly capable platforms around the world.

If you are ready to work alongside some of the industry’s top engineers and scientists to shape the future of this field, then now is the time to make SNC part of your future. Look over the available positions below and apply as indicated. We look forward to hearing from you.

Candidate will join a talented team of experienced software engineers in the development of a new DO-178B Level B, FAA certified Enhanced Flight Vision System. Tasks will require development of real-time, embedded software under FAA DO-178B development processes ultimately yielding FAA certification for Enhanced Flight Vision capability comprised of non-TSO airborne radar systems.

Successful execution of these tasks requires experience in developing software for embedded, real-time applications meeting program schedules and budgets.

The Software Engineer will generate detailed, measurable artifacts to evidence progress in support of key program milestones during the course of the development. This will include a basic understanding of cost and schedule reporting and measurement leveraging the Earned Value system.

In return for the above, you can expect challenging work alongside some of today’s brightest engineers and scientists, competitive salary, industry leading benefits and excellent growth opportunities.
Candidate must be a U.S. citizen and must be eligible to obtain and maintain a security clearance.
Candidate shall have 2+ years of relevant experience in real-time, embedded systems software development.
Experience developing DO-178B and/or radar software.

The ideal candidate will have a B.S. Degree, or higher, in Electrical Engineering, Computer Engineering, Computer Science or a related technical field.

*SNC is an EEO employer committed to recruiting a diverse workforce.
Apply online for immediate consideration at www.sncorp.com or send inquiries to Monique.Moultrie@SNCorp.com .

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APPLY

EMBEDDED CONTROL SYSTEM DESIGN/AVIATION

2011-05-18T22:35:00.000-07:00

The Wikibook of

Embedded Control Systems Design

This Applications chapter discusses the entire system that enables planes to fly and communicate with each other. Taking-off and landing multiple planes at major airports for instance, is a difficult task and requires a lot of subsystems. The main functionalities of the entire flight management system are navigation, flight planning and aircraft control.

There are three main levels in the full flight management system:

Air Traffic Control

ATC contains everything that enables planes to communicate directly with each other, or through a control tower. This level is essential to create a global coordinated system that transports people or equipment.

Flight Control System

FCS is the entire system that enables one plane to take-off, stay in the air, and land. A lot of an airplane's embedded control systems are linked to this functionality and are a part of the Flight Control System as a component.

Components

Each component has a specific task in an airplane. Most of them have a very straightforward functionality and are easy to describe as an embedded system. For example: door opening mechanism, engine control, inflight entertainment system, Integrated Modular Avionics (IMA), black box, ...

The goal of this applications chapter is to point out the requirements of the different system levels in aviation and their impact on the design. There are many links to other sites for detailed functionality information.

Free Ieee Format For Research Papers Downloads: Mendeley ...

2011-05-18T02:15:00.000-07:00

http://www.dogpile.com/clickserver/_iceUrlFlag=1?rawURL=http%3A%2F%2Fwww.fileguru.com%2Fapps%2Fieee_format_for_research_papers&0=&1=0&4=111.68.108.82&5=111.68.108.82&9=ed4681e79ce84f2ba2452b342915cc01&10=1&11=info.dogpl&13=search&14=239137&15=main-title&17=5&18=3&19=0&20=2&21=3&22=bsVXxmQSTz8%3D&23=0&40=y36pXPiC2d%2BpWo96yr64FQ%3D%3D&_IceUrl=true

Paper Submission

2011-05-18T02:07:00.001-07:00

Paper Submission

The paper submission deadline for the conference proceedings AND POST CONFERENCE PROCEEDINGS has passed. Thanks to all of you that have submitted to DMIN'06.

Information on CAMERA READY SUBMISSIONS are at the bottom of this page!

We welcome all contributions through theoretical research papers and industrial reports and case studies on applications in form of regular research papers of 7 pages IEEE style. In addition, we welcome student research proposals as short papers of 4 pages plus plenary presentations to receive guidance, online demonstrations of prototype software systems of 1 page and presentation in informal poster sessions. Accepted submissions include:

regular research papers (max. 7 pages IEEE style, formal presentation)
regular industry & application reports (max. 7 pages IEEE style, informal poster presentation)
short research papers (max. 4 pages IEEE style, poster presentation)
short industry & application reports (max. 4 pages IEEE style, poster presentation)
student research proposals (max. 4 pages IEEE style, formal presentation)
software demonstrations (max. 1 page IEEE style, poster presentation / online demonstration)
posters (max. 1 page IEEE style, poster presentation)

General Guidelines

Prospective authors are invited to submit their draft paper (between 1 to 7 pages, standard 2 column IEEE style) via our online submission systems by ~~Feb. 20, 2006~~ ~~extended deadline: 6 March 2006~~ (passed). Online submissions of PDF-files via the conference management system are encouraged. In selected exceptions an E-mail submission as MS Word document or Adobe PDF formats or Fax or postal submissions are also acceptable. The first page of the draft paper should include:

Paper Size: US Letter format (8.5" x 11")
Paper Length: Maximum 8 pages, including figures, tables & references
Paper formatting: double column, single spaced, 10pt font.
Margins: Left, Right, and Bottom: 0.75" (19mm). The top margin must be 0.75" in (19 mm), except for the title page where it must be 1" (25 mm).
File Size Limitation: 4.0MB.
Do not number your manuscript pages.
The first page must include:
- Title of the paper
- Name, affiliation, postal address, E-mail address, telephone number, and fax number for each author
- Underline the name of the author who will be presenting the paper (if accepted) - This will not be required for the camera ready version!
- a maximum of 5 keywords - This will not be required for the camera ready version!

Violations of any of the above paper specifications may result in rejection of your paper!!!
You may download preliminary information on the IEEE style below. Please consider, that although these files are IEEE information for submissions to the WCCI'06 conference, they are also the requirement for the DMIN'06. This information may be updated for the final camera ready submission.

For users of Microsoft Word

IEEE Formatting Template for MS Word
IEEE Formatting Example Document in MS Word
IEEE Example Document as Adobe PDF (extend author information!)

--> To create pdf files we suggest using Adobe Acrobat 7.1 or the freeware software cutepdf

For users of LATEX

IEEE Formatting Information & Files for LATEX
IEEE Example Document as Adobe PDF (extend author information!)

Online Submission

To submit your paper please visit the online conference system for DMIN'06 hosted by conference master. Please submit papers as soon as possible (from 1. January 2006) to ensure early feedback.

Review Process

Papers will be evaluated for originality, significance, clarity, and soundness. Each paper will be refereed by two researchers in the topical area. To reflect upon feedback from last year we will extend the constructive feedback given within the review. Please consult the pages for the Review Process for additional information.

We particularly encourage submissions of industrial applications and case studies from practitioners. To reflect the requirements of an application or project centric case study presentation, these will be subject to different review criteria. In particular, they will not be evaluated using predominantly theoretical research criteria of originality etc., but will take general interest and presentation stronger into consideration. The camera-ready papers will be reviewed by one person.

Final Papers

The length of the camera-ready papers (if accepted) will be limited to the pager restrictions of the paper category( e.g. 7 IEEE style pages for regular research or application papers). Papers must not have been previously published or currently submitted for publication elsewhere.

Please submit your camera ready paper (following the instructions provided below) and register by the due date. In registering, please make sure you follow the instructions: make sure to use the registration number provided WITHIN THE TEXT OF THE ACCEPTANCE EMAIL, STARTING with "DMI55xx", and not just the 1 or 2 digits used within previous correspondence. For example, use "DMI5587" instead of "#87". For single digit internal paper numbers, include a leading zero, e. "#7" becomes "DMI5507".

In submitting, please submit your paper within the correct paper category! Although DMIN paper categories may differentiate between Application and Research papers for creation of coherent sessions, WORLDCOMP submission does not differentiate this. Simply submit all "regular" papers with 7 pages as a regular research paper and all "short" papers as short research papers. We will later allocate you to research or practitioner sessions!

Accepted DMIN Categories --> submit as WORLDCOMP categories:

regular research papers (max. 7 pages IEEE style, formal presentation)
--> RRP regular research papers
regular industry & application reports (max. 7 pages IEEE style, informal poster presentation)
--> RRP regular research papers
short research papers (max. 4 pages IEEE style, poster presentation)
--> SRP short research papers
short industry & application reports (max. 4 pages IEEE style, poster presentation)
--> SRP short research papers
student research proposals (max. 4 pages IEEE style, formal presentation)
--> SRP short research papers
software demonstrations (max. 1 page IEEE style, poster presentation / online demonstration)
--> PST poster
posters (max. 1 page IEEE style, poster presentation)
--> PST poster

Conference Proceedings

The conference proceedings will be published by CSREA Press (ISBN) in hardcopy. The proceedings will be available for distribution at the conference .

Some accepted papers will also be considered for journal publication (soon after the conference). All conference proceedings published by CSREA Press are considered for inclusion in major database indexes that are designed to provide easy access to the current literature of the sciences (database examples: ISI Thomson Scientific, IEE INSPEC, DBLP, ...).

Research Paper Guidelines

2011-05-18T02:06:00.001-07:00

Research Paper Guidelines

Behrooz Parhami: 2007/06/20 || E-mail: parhami at ece.ucsb.edu || Other contact info at: Bottom of this page

Go up to: B. Parhami's course syllabi or his home page

The following is a suggested format for your course-related research or term paper. The general guidelines are followed by sample title pages.

Page 1 Title page should contain all of the following (see the sample title pages below):

Title of paper: max 20 words (make it short, yet descriptive); avoid abbreviations

Name of author

Telephone number(s) and e-mail address for quick contact in case of questions

"Research Paper for ECE x", where x is the course number (252B, 254B, etc.)

Course name

Quarter and year (e.g., "Winter 2020")

"ABSTRACT"

Body of abstract (summary of contributions and/or results; approx. 1 line per page)

"Keywords:" followed by 5 to 10 keywords and key phrases describing the content

Pages 2 – k "1. INTRODUCTION"

Give background on the topic (provide context and include references on prior work), justify your interest in the topic, prepare the readers for what they will find in later sections, and summarize (in a few sentences) your main findings and/or contributions. This section must be kept short. If it exceeds, say, 3 pages, you may wish to break it up by including an additional section that covers the necessary details for one or more of the above aspects. Use a descriptive title such as "2. REVIEW OF PRIOR WORK" or "2. NOTABLE APPLICATIONS OF ... " for this section.

Pages (k+1) – l Body of the paper (10-20 pp. is considered reasonable) should consist of sections dealing with various aspects of the investigation as appropriate; e.g., theory, applications, design issues, tradeoffs, evaluation, experiments, comparisons with other methods or approaches. Don't be afraid to compare, criticize, and generally leave your personal mark on the paper. There is no general rule, except that subdivisions must be coherent and of reasonable length. Avoid the extremes of single-paragraph and 10-page sections. For very long sections, consider dividing up or moving some details to an appendix. If you present performance or speed-up comparisons for your ECE 254B research paper, then make sure to read:

Crowl, L.A., "How to Measure, Present, and Compare Parallel Performance", IEEE Parallel & Distributed Technology (now IEEE Concurrency), Vol. 2, No. 1, pp. 9-25, Spring 1994.

Pages (l+1) – m "q. CONCLUSION"

Give a brief summary (in a few sentences) of what has been presented and/or accomplished. Emphasize the advantages and disadvantages of the proposed approach, technique, or design. Discuss possible extensions of the work and any interesting/open problem that you can envisage. Like the INTRODUCTION, this section must be fairly short.

Pages (m+1) – n "REFERENCES"

Provide complete bibliographic information for each reference (see any paper in IEEE Trans. Computers for examples). As a rule of thumb, citing 5-20 references is reasonable; review or survey-type papers tend to have much more extensive bibliographies and original contributions breaking new ground may have fewer references. However, don't take this rule too seriously.

Figures/Tables If possible, include each figure or table close to where it is first referenced in the text. Figures and tables must be numbered and have descriptive captions. Elements of figures (boxes, curves, axes) and tables (columns and/or rows) must be clearly labeled, with units shown where appropriate. Do not copy/paste figures or tables from books, journals, or conference papers.

Special Notes I will keep all submitted papers and will return to you my comments on a separate sheet or in an e-mail message. Please make a copy for yourself before submitting. Plagiarism, in any form (outright copying or failure to properly credit ideas), will not be tolerated and will result in a failing grade.

There are many good references to help you with research methodology and technical writing. The following book, which covers writing techniques, research methods, refereeing, and oral presentations is particularly recommended.

Zobel, J., Writing for Computer Science, Springer, 2nd ed., 2004. [T11.Z62 2004]

Return to: Top of this page

Sample title page #1 for a research paper:

A Procedure for Writing A-Level Research Papers

in Computer Arithmetic

A. Mark Earner

(987) 654-3210 Office

(123) 456-7890 Home

mearner@machine.dept.univ.edu

Research Paper for ECE 252B

Computer Arithmetic

Winter yyyy

ABSTRACT

The importance of earning good grades in graduate and upper-level undergraduate courses is well-recognized in academic circles. Although many instructors assign course grades in a seemingly random fashion, numerous studies have shown that the quality of a student’s work does in fact affect the final course grade. In this paper, I present a detailed procedure for submitting successful (A-level) papers in the field of computer arithmetic. The procedure starts with the important step of selecting the paper topic and continues with finding relevant references, taking notes, doing the actual research, organizing the material, writing the paper, and going through the appeals process if the final grade turns out to be unsatisfactory. Experimental results were obtained by asking 80 students to apply the procedure in producing their term papers for ECE 252B over a period of four years. Some 75% of these students earned grades of A+ or A, 15% ended up with A–, and the remaining 10% failed the course because the instructor discovered that they had copied papers published many years ago in certain obscure conferences.

Keywords: Cheating, Course grades, Grade-point average, Graduate courses, How-to guide, Research paper, Student performance evaluation, Term paper.

Return to: Top of this page

Sample title page #2 for a research paper:

The VLSI Approach to Computational Complexity*

Ann X. Student

(987) 654-3210 Office

(123) 456-7890 Home

astudent@machine.dept.univ.edu

Research Paper for ECE 254B

Advanced Computer Architecture: Parallel Processing

Spring yyyy

ABSTRACT

The rapid advances of VLSI and the trend toward the decrease of the geometrical feature size, through the submicron and the subnano to the subpico, and beyond, have dramatically reduced the cost of VLSI circuitry. As a result, many traditionally unsolvable problems can now (or will in the near future) be easily implemented using VLSI technology. In recent years, the cost of VLSI components has decreased exponentially. Hence, the application of an exponential number of processors does not cause any cost increase, and the application of only a polynomial number of processors leads to substantial cost savings. A system having an exponential number of processors will be able to solve many NP-complete problems in polynomial time. Furthermore, plotting processor costs as a function of time reveals that the cost of VLSI processors will soon become negative. Undoubtedly, this trend will create a competition for solving the same problem with more processors. We conclude that with the rapid advances of VLSI technology anything is possible and that the worth of a research paper is directly proportional to the number of processors in the system being proposed.

Keywords: Computational complexity, Concurrency, Massive parallelism, Negative-cost elements, NP-complete problems, Parallel processing, VLSI.

* Copied, with some modifications, from a piece of the same title by Danny Cohen,

in VLSI Systems and Computations, Computer Science Press, 1981, pp. 124-125.

Return to: Top of this page || Go up to: B. Parhami's course syllabi or his home page

Dr. Behrooz Parhami, Professor				Office phone: +1 805 893 3211
Dept. Electrical & Computer Eng.				Department fax: +1 805 893 3262
University of California, Santa Barbara				Office: Rm 5155 Harold Frank Hall
Santa Barbara, CA 93106-9560 USA				Deliveries: Rm 4155 Harold Frank Hall
Web: http://www.ece.ucsb.edu/~parhami				E-mail: parhami at ece.ucsb.edu

TEST/INTERVIEW FOR JOB

2011-05-07T02:41:00.000-07:00

2011-05-07T02:20:00.000-07:00

BOARD OF INTERMEDIATE EDUCATION KARACHI

2011-05-07T02:13:00.000-07:00

BOARD OF INTERMEDIATE EDUCATION KARACHI
CONSOLIDATED DATE SHEET OFpakedu.net
SCIENCE PRE-ENGINEERING, SCIENCE GENERAL, PRE-MEDICAL, HOME ECONOMICS, COMMERCE REGULAR, MEDICAL TECHNOLOGY,
IMPROVEMENT OF GRADES & ADDITIONAL SUBJECTS PART-I & II ANNUAL EXAMINATIONS 2011
S.No	Date	Day	Time	Subject		Faculty
1	16.05.11	Monday	9:30 AM to 11:30 AM	1.	Pakistan Studies (‘C) (2 Hours)	Science, Home Economics & Medical Technology
1	16.05.11	Monday	2:30 PM to 5:30 PM	2.	Principles of Commerce Paper-II (Banking)	Commerce Regular
2	17.05.11	Tuesday	9:30 AM to 12:30 PM	1.	Computer Science Paper-I	Science General
			9:30 AM to 12:30 PM	2.	Microbiology Paper-I	Medical Technology
			2:30 PM to 4:30 PM	3.	Business Mathematics Paper-I (2 Hours)	Commerce Regular
3	18.05.11	Wednesday	9:30 AM to 12:30 PM	1.	Physics Paper-I (for Failures)	Science (Pre-Eng, Sc. Gen & Pre-Med)
3	18.05.11	Wednesday	2:30 PM to 5:30 PM	2.	Principles of Commerce Paper-I (for Failures)	Commerce Regular
4	19.05.11	Thursday	9:30 AM to 12:30 PM	1.	Mathematics Paper-I	Science (Pre-Eng & Sc. General) & Additional Students
4	19.05.11	Thursday	9:30 AM to 12:30 PM	2.	Clothings & Textiles Paper-I	Home Economics
5	20.05.11	Friday	9:30 AM to 11:30 AM	1.	Botany Paper-I (2 Hours)	Science (Pre-Medical) & Additional Students
5	20.05.11	Friday	9:30 AM to 12:30 PM	2	Meal Management & Food Preservation-II	Home Economics
6	21.05.11	Saturday	9:30 AM to 12:30 PM	1.	Physics Paper-II	Science (Pre-Eng, Sc. Gen & Pre-Med)
			2:30 PM to 5:30 PM	2.	English (Normal) Paper-I	Commerce Regular
			2:30 PM to 5:30 PM	3.	English (Advanced) Paper-I	Commerce Regular
	22.05.11	Sunday	Sunday	Sunday
7	23.05.11	Monday	9:30 AM to 12:30 PM	1.	Economics Paper-II	Science General
			9:30 AM to 11:30 AM	2.	Chemistry Paper-II (2 Hours)	Home Economics
			9:30 AM to 12:30 PM	3.	Elementary Chemistry & Chemical Pathology-II	Medical Technology
			2:30PMto4:30PM	4.4.	StatisticsPaper-II(2Hours) -	CommerceRegular
8	24.05.11	Tuesday	9:30 AM to 12:30 PM	1.	Chemistry Paper-I	Science (Pre-Eng & Pre-Medical)
8	24.05.11	Tuesday	2:30 PM to 5:30 PM	2	Principles of Commerce Paper-I	Commerce Regular
9	25.05.11	Wednesday	9:30 AM to 12:30 PM	1.	Statistics Paper-I	Science General
			9:30 AM to 12:30 PM	2.	Hematology & Blood Banking-I	Medical Technology
			2:30 PM to 4:30 PM	3.	Business Mathematics Paper-I (2 Hours) (for Failures)	Commerce Regular
10	26.05.11	Thursday	9:30 AM to 12:30 PM	1.	Mathematics Paper-II	Science (Pre-Eng & Sc. Gen) & Additional
10	26.05.11	Thursday	9:30 AM to 12:30 PM	2.	Applied Arts Paper-I	Home Economics
11	27.05.11	Friday	9:30 AM to 11:30 AM	1.	Zoology Paper-II (2 Hours)	Science (Pre-Medical) & Additional
11	27.05.11	Friday	9:30 AM to 12:30 PM	2.	Home Management Paper-II	Home Economics
12	28.05.11	Saturday	9:30 AM to 12:30 PM	1.	Computer Science Paper-II (Opt-I & II)	Science General
				2.	Biology & Bacteriology Paper-I	Home Economics
				3.	Clinical Pathology & Serology-II	Medical Technology
			2:30 PM to 5:30 PM	4.	Accounting Paper-II	Commerce Regular
	29.05.11	Sunday	Sunday	Sunday
13	30.05.11	Monday	9:30 AM to 12:30 PM	1.	Physics Paper-I	Science (Pre-Eng, Sc. Gen & Pre-Med)
			2:30 PM to 5:30 PM	2.	English (Normal) Paper-I (for Failures)	Commerce Regular
			2:30 PM to 5:30 PM	3.	English (Advanced) Paper-I (for Failures)	Commerce Regular
14	31.05.11	Tuesday	9:30 AM to 12:30 PM	1.	Chemistry Paper-II	Science (Pre-Eng & Pre-Med)
14	31.05.11	Tuesday	9:30 AM to 12:30 PM	2.	Principles of Economics Paper-I	Commerce Regular
15	01.06.11	Wednesday	9:30 AM to 12:30 PM	1.	Economics Paper-I	Science General
			9:30 AM to 11:30 AM	2.	Physics -II (2 Hours)	Home Economics
			9:30 AM to 12:30 PM	3.	Elementary Anatomy & Micro Technique-I	Medical Technology
			2:30 PM to 5:30 PM	4.	Commercial Geography Paper-II	Commerce Regular
					Continued on the Next Page……………….
	Page -:2:-
16	02.06.11	Thursday	9:30 AM to 12:30 PM	1.	Mathematics Paper-I (Failures)	Science (Pre-Eng & Sc.Gen)
			2:30 PM to 5:30 PM	2.	Urdu (Normal) Paper-I	Commerce Regular
				3.	Urdu (Easy) Paper-I
				4.	Urdu (N.M.T) Paper-I
				5.	History & Culture of Pakistan Paper-I (for Foreigners Only)
17	03.06.11	Friday	9:30 AM to 11:30 AM	1.	Botany Paper-II (2 Hours)	Science (Pre-Medical) & Additional
17	03.06.11	Friday	9:30 AM to 12:30 PM	2.	Family Clothing Problems Paper-II	Home Economics
1.	Urdu (Normal) Paper-I
18	04.06.11	Saturday	9:30 AM to 12:30 PM	2.	Urdu (Easy) Paper-I	Science , Home Economics & Medical Tecnology
				3.	Urdu (N.M.T) Paper-I
				4.	History & Culture of Pakistan Paper-I (for Foreigners Only)
			2:30 PM to 5:30 PM	5.	Accounting Paper-I (for Failures)	Commerce Regular
	05.06.11	Sunday	Sunday	Sunday
19	06.06.11	Monday	9:30 AM to 12:30 PM	1.	Urdu (Normal) Paper-II	Science, Home Economics & Medical Technology
				2.	Urdu (Easy) Paper-II
				3.	Urdu (N.M.T) Paper-II
				4.	History & Culture of Pakistan Paper-II (for Foreigners Only)
				5.	Sindhi (‘C)
			2:30 PM to 5:30 PM	6.	English (Normal) Paper-II	Commerce Regular
			2:30 PM to 5:30 PM	7.	English (Advanced) Paper-II	Commerce Regular
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Fuzzy Application Library/Technical Applications/Industrial Automation

2011-05-03T07:03:00.000-07:00

Fuzzy Application Library/Technical Applications/Industrial Automation

Recent Successful Fuzzy Logic Applications in Industrial Automation

by Engr. Raja Rai M. Faheem Abid

Citation Reference: This paper was been published at the Fifth IEEE International Conference on Fuzzy Systems, held in New Orleans September 1996. The Fuzzy Logic Application Note series is published by Inform Software Corporation on its Internet server to promote the use of fuzzy logic technologies in applications.

In this paper, we review eight (8) recent applications of fuzzy logic in industrial automation. All applications used the so-called "fuzzyPLC", an innovative hardware platform that merges fuzzy logic and traditional automation techniques. Following a quick overview on the fuzzyPLC, we discuss the eight (8) applications and focus on how fuzzy logic enabled a superior solution compared to conventional techniques. Whenever possible, we quantify the benefit in cost saving or quality improvement. For detailed information on the reviewed applications, the respective papers are referenced.

1. Fuzzy Logic in Industrial Automation

In recent years, fuzzy logic has proven well its broad potential in industrial automation applications. In this application area, engineers primarily rely on proven concepts. For discrete event control, they mostly use ladder logic, a programming language resembling electrical wiring schemes and running on so called programmable logic controllers (PLC). For continuous control, either bang-bang type or PID type controllers are mostly employed.

While PID type controllers do work fine when the process under control is in a stable condition, they do not cope well in other cases:

The presence of strong disturbances (non-linearity)
Time-varying parameters of the process (non-linearity)
Presence of dead times

The reason for this is that a PID controller assumes the process to behave in a strictly linear fashion. While this simplification can be made in a stable condition, strong disturbances can push the process operation point far away from the set operating point. Here, the linear assumption usually does not work any more. The same happens if a process changes its parameters over time. In these cases, the extension or replacement of PID controllers with fuzzy controllers has been shown to be more feasible more often than using conventional but sophisticated state controllers or adaptive approaches [4]. However, this is not the only area where there is potential for fuzzy logic based solutions.

Multi-Variable Control

The real potential of fuzzy logic in industrial automation lies in the straightforward way fuzzy logic renders possible the design of multi-variable controllers. In many applications, keeping a single process variable constant can be done well using a PID or bang-bang type controller. However, set values for all these individual control loops are often still set manually by operators. The operators analyze the process condition, and tune the set values of the PID controllers to optimize the operation. This is called "supervisory control" and mostly involves multiple variables.

Figure1: Using a Fuzzy Logic Controller to Determine the Set Values for Underlying PID Control Loops (large)

Alas, both PID and bang-bang type controllers can only cope with one variable. This usually results in several independently operating control loops. These loops are not able to "talk to each other". In cases where it is desirable or necessary to exploit interdependencies of physical variables, one is forced to set up a complete mathematical model of the process and to derive differential equations from it that are necessary for the implementation of a solution. In the world of industrial automation, this is rarely feasible:

Creating a mathematical model for a real-word problem can involve years of work.
Most mathematical models involve extensive simplifications and linearizations that require "fudge" factors to optimize the resulting controller later on.
Tuning the fudge factors of a controller derived from a mathematical model is "fishing in the dark", because optimizing the system at one operating point using global factors usually degrades the performance at other operating points.

Also, many practitioners do not have the background required for rigorous mathematical modeling. Thus, the general observation in industry is that single process variables are controlled by simple control models such as PID or bang-bang, while supervisory control is done by human operators.

This is where fuzzy logic provides an elegant and highly efficient solution to the problem. Fuzzy logic lets engineers design supervisory multi-variable controllers from operator experience and experimental results rather than from mathematical models. A possible structure of a fuzzy logic based control system in industrial automation applications is exemplified by Figure 1. Each single process variable is kept constant by a PID controller, while the set values for the PID controller stem from the fuzzy logic system. This arrangement is typical for cases like control of several temperature zones of an oven or control of oxygen concentrations in different zones of a wastewater basin. In other cases, it could be reasonable to develop the complete closed loop control solution in a fuzzy system.

This illustrates why it is very desirable to integrate conventional control engineering techniques, such as ladder logic or instruction list language for digital logic and PID control blocks tightly together with fuzzy logic functionality.

2. Merging Fuzzy Logic and PLCs

In 1990, when more and more successful applications proved the potential of fuzzy logic in industrial automation, the German company Moeller GmbH and the U.S./German company Inform Software created the fuzzyPLC based on the observation that fuzzy logic needs tight integration with conventional industrial automation techniques.

The fuzzyPLC Hardware and Firmware

Figure 2: The fuzzyPLC contains fuzzy and conventional logic processing capabilities, field bus connections, and interfaces.

To make it available at a low cost, the core of the fuzzyPLC uses a highly integrated two-chip solution. An analog ASIC handles the analog/digital interfaces at industry standard 12 bit resolution. Snap-On modules can extend the periphery for large applications of up to about 100 signals. An integrated field bus connection, based on RS485, provides further expansion by networking. The conventional and the fuzzy logic computation is handled by a 16/32 bit RISC microcontroller. The operating system and communication routines, developed by Moeller, are based on a commercial real time multitasking kernel. The fuzzy inference engine, developed by Inform Software, is implemented and integrated into the operating system in a highly efficient manner, so that scan times of less than one millisecond are possible. The internal RAM of 256 KB can be expanded by memory cards using flash technology. Thus, the fuzzyPLC is capable of solving quite complex and fast industrial automation problems in spite of its compact and low price design.

The fuzzyPLC Engineering Software

The fuzzyPLC is programmed by an enhanced version of the standard fuzzy logic system development software fuzzyTECH from Inform Software. fuzzyTECH is an all-graphical, design, simulation, and optimization environment with implementation modules for most microcontrollers and industrial computers. To support the complete functionality of the fuzzyPLC, fuzzyTECH has been enhanced with editors and functions to support the conventional programming of the PLC. Thus, a user only needs one tool to program both conventional and fuzzy logic parts of the solution.

Figure 3: Both the traditional logic and the Fuzzy Logic system is programmed by fuzzyTECH 4.0 . (larger)

The fuzzyTECH software combines all necessary editors for membership functions, linguistic variables, rule tables, and system structure with analyzer functions and optimization features. The software runs on a PC and is linked to the fuzzyPLC by a standard serial cable (RS232) or the field bus (RS485). Through this link, the developer downloads the designed system to the fuzzyPLC. Because fuzzy logic systems often require optimization "on-the-fly", fuzzyTECH and the fuzzyPLC feature "online-debugging" where the system running on the fuzzyPLC is completely visualized by the graphical editors and analyzers of fuzzyTECH. Plus, in online-debugging modes, any modification of the fuzzy logic system is instantly translated to the fuzzyPLC without halting operation.

3. Application Case Studies

In this section, we review eight (8) recent highly successful applications of fuzzy logic in industrial automation using the fuzzyPLC:

Anti-Sway Control of Cranes
Fire Zone Control in Waste Incineration Plants
Dosing Control in Waste Water Treatment Plants
Control of Tunnel Inspection Robots
Positioning in Presses
Temperature Control in Plastic Molding Machines
Climate Control and Building Automation
Wind Energy Converter Control

Anti-Sway Control of Cranes

In crane control, the objective is to position a load over a target point. While the load connected to the crane head by flexible cables may well sway within certain limits during transportation, the sway must be reduced to almost zero for load release when the target position is reached. Hence, a controller must use at least two input variables, for example position and sway angle. Thus, a simple PID controller cannot be used as it is restricted to one input. Conventional solutions of the problem require highly elaborate approaches, like model based control or state variable controllers that need intensive engineering and hardware resources. These technologies tend to push system costs into regions that make anti-sway systems economically unaffordable. For these reasons, most cranes are still operated manually.

Figure 4: The 64 ton crane of Hochtief Corp. uses fuzzyPLC based anti-sway positioning control (large, Video)

In spite of the difficulties involved with automated control, human operators can control cranes quite well in most cases. Because fuzzy logic is a technology that facilitates control system design based directly on such human experiences, it has been used for crane automation for almost a decade. The types of cranes include container cranes in harbors, steel pan cranes, and cranes in a manufacturing environment. Recently, a 64 ton crane that transports concrete modules for bridges and tunnels over a distance of 500 yards has been automated with a fuzzyPLC in Germany [8]. The benefit was a capacity gain of about 20% due to the faster transportation and an increase in safety. Accidents were frequent, because the crane operators walk parallel to the crane during operation with a remote controller. Before, when they had to watch the load to concentrate on the sway angle, they frequently stumbled over parts lying on the ground. The crane was commissioned in Spring 1995 and the fuzzy logic anti-sway controller has been continuously enabled by the crane operator, showing the high degree of acceptance by the operators. This fact is of special importance since not only technological feasibility but also psychological aspects are important for the success of an industrial automation solution.

Figure 5: A software simulation of the crane controller is contained in [4] (large)

A software simulation and a simple example of an anti-sway crane controller for didactic purposes can be found in [4]. The real solution uses about 10 inputs, 2 outputs, and 4 rule blocks with a total of 75 rules.

Fire Zone Control in Waste Incineration Plants

Maintaining a stable burning temperature in waste incineration plants is important to minimize the generation of toxic gases, such as dioxin and furan, as well as to avoid corrosion in the burning chambers. There are two primary difficulties of this temperature control process:

The caloric value of the waste fluctuates strongly.
The fire position and shape cannot be measured directly.

Because the heat generated from the burning process is used to produce electrical energy, a stable incineration process is also of high commercial interest.

Figure 6: In a waste incineration plant, a crane continuously delivers waste from the bunker to the belt running through the burning zone. The exhaust gases are cooled and cleaned. (large)

In recent applications at waste incineration plants in the cities of Hamburg and Mannheim in Germany, fuzzy logic has been successfully applied. In Mannheim, where two fuzzyPLCs were used to control the burning process, the steam generation capacity of one furnace is 28 Mg/h. Using the industry standard conventional controller, steam generation fluctuated by as much as 10 Mg/h in just one hour. The fuzzy logic controller was capable of reducing this fluctuation to less than ±1 Mg/h. This dramatically improved robustness and also caused the NOx and SO2 emission to drop slightly, and the CO emission to drop to half [11, 12].

Dosing Control in Waste Water Treatment Plants

Waste water treatment processes are a combination of biological, chemical, and mechanical processes. This makes the creation of a complete mathematical model for their control intractable. However, there is a large amount of human experience that can be exploited for automated controller design. As such operator experience can be efficiently put to work by fuzzy logic, many plants already use this technique [4].

In a recent application in Bonn, dosing of liquid FeCl3 for phosphate precipitation has been successfully automated using the fuzzyPLC. Recently changes in legislation require water treatment plants in Germany to limit the total amount of phosphate in the released water to 1 milligram per liter. To extract the phosphate from the water, FeCl3 is added, which converts the phosphate into FePO4 that is sedimented with the sludge. Because a violation of the legal phosphate limit results in severe penalties, the operators tend to overdose the FeCl3.

Figure 7: By injecting FeCl3 into the sludge, dissolved phosphate precipitates from the waste water (large)

To optimize the FeCl3 dosing, a fuzzy logic controller that uses the input variables phosphate concentration, its derivative, water flow, its derivative, and dry substance contents was designed. The output of the fuzzy logic controller is the change of the set variable for the injected FeCl3. An underlying conventional PI type controller stabilizes the FeCl3 flow to this set point. The PI type controller is implemented as a function block in the fuzzyPLC as well. This is an example of the combination of fuzzy logic and conventional control engineering techniques.

Figure 8: A software simulation of a simplified precipitation controller is contained in [4] (large)

The total fuzzy logic controller uses 207 rules to express the control strategy based on the five (5) input variables of the fuzzy logic control block. The total implementation time was three (3) staff months and resulted in savings of about 50% of the FeCl3 compared to the manual control before. Taking implementation time and hardware/software costs into consideration with the savings on FeCl3 results a return in investment time of half a year.

Control of Tunnel Inspection Robots

The German Aerospace corporation DASA has developed a sewage pipe inspection system using two robot units and a support truck [7]. The objective of the robots is to detect leakage in segments of the pipe by applying air pressure to the sealed space between the two robots. Because the vertical access shafts can be quite far away from each other, the robots have to operate up to 400 yards away from the truck. The robots are connected to each other and the truck by cables that provide air pressure, electrical energy, and control signals to the robots.

Figure 9: The two robot units in the sewage pipe (right) are supplied from a specialized truck by cables (large)

When DASA developed the system, a severe control problem came up. To avoid entanglement of the cables that can result in the robots getting stuck in the pipe, cable tension must be controlled very carefully. A conventional approach using complex state variable controllers turned out to be too costly in terms of both money and design time. A control system implemented on two fuzzyPLCs using about 200 rules each showed very good results in a very short engineering time at less than 10% of the costs of a conventional solution.

Positioning of Presses

One area with big potential for fuzzy solutions is the control of drives. In this example, we discuss hydraulic axis control. One of the most complex fuzzy projects was done for a hydraulic press used to press laminates, printed circuit boards, and floor coverings. The task was the synchronized control of a 14-axis system. The position control of the axis, a superimposed pressure controller, the parallel running of the steel belt and the synchronization of all axes had to be solved.

Figure 10: Control of hydraulic systems is difficult as many non-linearities, Such as the "stick-slip" effect, are involved (large)

The automation system employed has a highly decentralized structure and consists of two large master PLCs, a number of smaller compact PLCs, a PC based supervisory system, and seven fuzzyPLCs. All units are networked using the integrated field bus interfaces. Very important for the synchronization of the entire machine is the ability of the field bus network to satisfy the real time requirements. One typical problem involved in the control of hydraulic systems is the so-called "stick slip effect". The transition of an axis from standstill to motion is highly non-linear because of the transition from stick friction to slip friction. This makes designing a good controller for hydraulic systems difficult. In the cited application, fuzzy logic rendered a good solution technique, freeing system design from the burden of the theory of non linear systems synthesis. The overall design time using fuzzy logic was only a third of what a conventional approach had required in past applications of conventional control for similar presses [9].

Temperature Control in Plastic Molding Machines

In plastic molding machines, temperature control is crucial to achieve high and consistent product quality. This requires laborious tuning of the involved control algorithms, because the dead times involved in an extrusion machine are significant and there is significant coupling between the different temperature zones [9].

Figure 11: To achieve high product quality, keeping the temperature constant is critical in molding plastic (large)

To cut down the commission time for these machines, KM corporation has developed a self-tuning controller using the fuzzyPLC. At start up time, some parameters are estimated that are used to scale the non linear fuzzy controller. In contrast to conventional tuning algorithms, this controller does not require a cooling down of the machine to room temperature before self tuning can work. Even very difficult temperature zones with big dead times can be handled by this algorithm and the result is a very robust controller. This is important because the temperature properties of an empty machine and one filled with plastic material are extremely different. Compared to conventional systems, the fuzzy logic enhanced temperature controller performs with a faster response time and a significantly smaller overshoot combined with extreme robustness.

Figure 12: The Fuzzy Logic controller in the molding machine reaches the set point faster and avoids overshoot (large)

Climate Control Using Fuzzy Logic

Climate control systems reveal a high potential for energy savings. In a recent application at a major hospital in Europe, the integration of fuzzy logic saves about 25% on electrical energy, equivalent to the amount of 50,000 per year.

Figure 13: An Application of Fuzzy Logic in the A/C system of a large hospital in Germany saved more than 25% on energy costs (large)

The fuzzy logic controller outputs the set values for the coolant valve, the water heater valve, and the humidifier water valve. The fuzzy logic control strategy uses different temperature and humidity sensors to determine how to operate the air conditioning process in a way that conserves energy. Again, the capability of processing interdependent variables results in significant advantages over conventional solutions. For example, one knows that when temperature rises, relative humidity of the air decreases.

This knowledge can be exploited by implementing a fuzzy logic control strategy that allows the temperature controller "to tell" the humidity controller that it is going to activate the heater valve. The humidity controller now can respond to this before it can detect it by its sensor. The result is an increase in control quality [4, 8].

Figure 14: Fuzzy Logic allows to increase the energy efficiency of an A/C system by evaluating several process values. (larger)

Wind Energy Converter Control

In recent years, technological advancements made the commercial use of wind energy feasible. A trend to larger plants further improved the cost/performance ratio. However, such large wind energy converters require advanced control systems both to ensure high efficiency and long life. The controller sets the angle of the rotor blades based on the wind situation (pitch control). However, wind is not a one-dimensional figure. Strength, gustiness, and fluctuation of the wind angle must be evaluated to determine the optimal rotor blade angle.

Figure 15: To maximize the efficiency of a wind energy converter, the pitch controller must consider many inputs (large)

There is a trade-off between efficiency, safety and wear of the wind energy converter. If the blade angle is set to draw the maximum amount of energy from the wind, the risk of sudden wind gusts causing excessive mechanical stress on the converter increases. For these reasons, an Aerodyn wind energy converter was enhanced with a fuzzy system based on human experience to find the best compromise to this trade-off [6]. The first implemented system is running in a field test and shows quite promising results. The quality of the controller is not only measured in constancy of the delivered power, but also in measures of mechanical stress on the tower, the nacelle and the rotor blades. The next step will be the application of the achieved results to the first 1.2 MW systems that are to be launched in the marketplace in 1996.

4. Conclusions

As a consequence of the high degree of awareness raised by a large number of publications over the past five years in Europe, a substantial number of successful applications have been generated. Of these, we have presented a selection of eight (8) recent applications in this paper. In all applications, the key to success lies in the clever combination of both conventional automation techniques and fuzzy logic. Fuzzy logic by no means replaces conventional control engineering. Rather, it compliments conventional techniques with a highly efficient methodology to implement multi-variable control strategies. Thus, the major potential for fuzzy logic lies in the implementation of supervisory control loops.

MICROPROCESSOR AND H BRIDGE CIRCUIT

2011-05-02T13:34:00.000-07:00

Lego Robots Hardware

This chapter is partly tutorial and partly technical reference: in additional to documenting the Rice Lego Robots RoboBoard hardware, it explains the design in a way that assumes minimal background in digital electronics. Additional explanatory material can be found in the Glossary (Appendix B) and in Chapter 12.
The information presented here should be considered optional, as it is not strictly necessary to know it to build a robot. Hopefully though, this chapter will satisfy most readers' curiosity about how the Lego Robots hardware works.

The Microprocessor and Memory

At the most primitive level, a computer consists of a microprocessor, which executes instructions, and a memory, for storing those instructions (as well as other data).

Figure 5.1: Diagram of Microprocessor and Memory

Figure 5.1 is a block diagram of the microprocessor and memory, showing four types of wires that connect the two:

Address Bus.: These wires are controlled by the microprocessor to select a particular location in memory for reading or writing. The RoboBoard uses a memory chip that has 15 address wires. Since each wire has two states (it can be a digital one or a zero), 2 to the 15th power locations are possible. 2¹⁵ is precisely 32,768 locations; thus, the system is said to have "32K" of memory (1K = 1024 bytes).

Data Bus.: These wires are used to pass data between the microprocessor and the memory. When data is written to the memory, the microprocessor drives the data bus; when data is read from the memory, memory drives the bus. In our example (and in the RoboBoard), there are eight data wires (or bits). These wires can transfer one of 2⁸ , or 256, different values per transaction. The data size of 8 bits is commonly referred to as a byte. (This jargon gets worse; a data size of 4 bits is frequently referred to as a nybble.)
Read/Write Control Line.: This single wire is driven by the microprocessor to control the function of the memory. If the read/write control line is asserted as a logical one, i.e., "true", then the memory performs a "read" operation. If it is asserted as a logic zero, i.e., "false" then the memory performs a "write" operation. (The relationship between logic level and voltage level can vary, depending on the implementation. For example, with the exception of some of the serial port circuitry, a logical "zero" on the RoboBoard corresponds to a voltage level near 0 volts, and a logical "one" on the RoboBoard corresponds to a voltage level near 5 volts.)

Memory Enable Control Line.: This wire, also called the E clock, connects to the enable circuitry of the memory. When the memory is enabled, it performs either a read or write operation as determined by the read/write line.

Multiplexing Data and Address Signals

Figure 5.2: Block Diagram of Microprocessor and Memory with Latch

Things are a little more complex with the particular microprocessor that is used in the RoboBoard, the Motorola 68HC11. On the 68HC11, the eight data bus wires take turns acting as address wires as well. When a memory location is accessed (for reading or writing), the data wires act first as address wires, transmitting the eight lower-order bits of the address. Then they function as data wires, either transmitting a data byte (for a write cycle) or receiving a data byte (for a read cycle). All of this happens very fast -- 2 million times per second on the RoboBoard. This kind of split-personality bus is referred to as a multiplexed address and data bus. The memory needs help to deal with a multiplexed address/data bus, provided by an 8-bit latch. This chip (the 74HC373) performs the function of latching, or storing, the 8 address values so that the memory will have the full 15-bit address available for reading or writing data. Figure 5.2 shows how the latch is wired. The upper 7 address bits are normal, and run directly from the microprocessor to the memory. The lower 8 bits are the multiplexed address and data bus. These wires connect to the inputs of the latch and also to the data inputs of the memory. An additional signal, the Address Strobe output of the microprocessor, tells the latch when to grab hold of (latch) the address values from the address/data bus. When the full 15-bit address is available to the memory (7 bits direct from the microprocessor and 8 bits from the latch), the read or write transaction can occur. Because the address/data bus is also wired directly to the memory, data can flow in either direction between the memory and the microprocessor. The entire process -- transmitting the lower address bits, latching these bits, and then the read or write transaction with the memory -- is orchestrated by the microprocessor. The E clock, the Read/Write line, and the Address Strobe line perform in tight synchronization to make sure these operations happen in the correct sequence and within the timing capacities of the actual chip hardware.

Memory Mapping

**Figure 5.3:** RoboBoard System Block Diagram

So far we have seen how a memory can be connected to the address space of a microprocessor. In a circuit like the one of the RoboBoard, the microprocessor must interact with other devices besides the memory -- for example, motors and sensors. A typical solution uses 8-bit latches for input and output. These latches are connected to the data bus of the microprocessor so that they appear like a location in memory. Then, the act of reading or writing from one of these memory locations causes data to be read from or written to a latch -- to which the external devices are connected. Figure 5.3 is a block diagram of the Lego Robots RoboBoard system. Notice that chips marked "574" are connected to the data bus. The '574s have outputs that control the motors (through other chips marked "L298N", which will be discussed later). The digital sensors are driven onto the data bus by a chip marked "245." Another '574 chip is used for eight bits of digital output. These interface chips are used in a technique called memory mapping. The chips are "mapped" to a particular address in the microprocessor's memory. The following discussion will show how both the 32K RAM memory and the digital input and output interface chips share the address space of the microprocessor.

Memory-Mapping the RAM

**Figure 5.4:** Enabling the Memory

The 68HC11 has a total of 16 address bits, yielding 65536 ("64K") bytes of addressable locations. Half of this space will be taken up by the 32K memory chip (also known as a RAM chip, for "Random Access Memory"). The 68HC11 has a bank of interrupt vectors, which are hardware-defined locations in the address space where the microprocessor expects to find pointers to driver routines. When the microprocessor is reset, it finds the reset vector to determine where it should begin running a program. These vectors are located in the upper 32K of the address space. Thus, it is logical to map the RAM into this upper block, so that the RAM may be used to store these vectors. The technique used to map the memory to the upper 32K block is fairly simple. Whenever the 68HC11's A15 (the highest-order address bit) is logic one, an address in the upper 32K is being selected. The other fifteen address bits (A0 through A14) determine the address within that 32K. A logic gate (actually a portion of a programmable logic device called a "PAL") is used to enable the memory when A15 is logic one and when the E clock is high (since the E clock must control the timing of the enable). Figure 5.4 shows a block diagram of this circuit. Memory chips are part of a class of chips that have active low (sometimes called "active false") enable inputs, meaning that they are enabled when the enable input is logic zero, not logic one. There are two methods for denoting an input that is active low. As shown in Figure 5.4, the chip enable input is shown with connecting to a circle; this circle indicates an active low input. Also, the name for the signal, CE is prefixed with a ~ symbol. The NAND gate shown in Figure 5.4 actually combines two logic functions, a NOT gate (inverter), and an AND gate. The function of the NOT gate is to convert the active-high enable produced by the AND gate into the active low signal required by the ~CE input.

Memory-Mapping with the PAL16L8 Chip

**Figure 5.5:** Typical 3-to-8 74x138 Address Decoder

Most computers use a circuit called an address decoder to demultiplex address lines and generate memory-mapped control enables for individual devices. Figure 5.5 shows the logical diagram of a 74x138 demultiplexer, which is commonly used in circuits that map devices onto an address space. This chip is a 3-to-8 decoder: a binary number of three digits (the select inputs) causes one of eight possible outputs to be selected (the control outputs). The chip also has three enable inputs, all of which must be enabled to make the chip become active. Previous versions of the RoboBoard used a 74AC138 for address decoding. Versions 3.0 and later of the RoboBoard implement this functionality using a PAL16L8 programmable logic device. The behavior of this device is controlled by "PAL code", which is shown in Figure 5.7

**Figure 5.6:** Wiring the PAL16L8 Address Decoder

**Figure 5.7:** PAL16L8 ABEL Code

Examining the PAL code (written in a language called "ABEL"), we see that the outputs of the PAL16L8 control the input and output latches shown in the system block diagram. The PAL16L8 determines when these latches are activated, either to read data from the data bus (in the case of the '574 output latch), or to write data onto the data bus (in the case of the '245 input buffer). As determined by the PAL code, the inputs of the PAL16L8 determine when the outputs will become active, and thereby turn on one, and only one, of the control outputs. This is to avoid the possibility that two devices (the RAM and perhaps the '245) would attempt to drive the data bus simultaneously, causing a problematic situation called bus contention.

System Memory Map

Figure 5.8 summarizes the memory map solution that has been implemented for the Lego Robots RoboBoard.

**Figure 5.8:** RoboBoard 68HC11 System Memory Map

The 32K RAM takes up half of the total address space of the microprocessor. As indicated in the map, it is located in the upper 32K of the microprocessor's memory, from addresses $8000 to $FFFF. The digital output and input ports are mapped at location $7800. The three motor control ports are mapped at locations $7000 (motors 1 and 2), $6800 (motors 3 and 4), and $6000 (motors 5 and 6). There is a small area of memory that is internal to the 68HC11 chip itself. This memory consists of 256 bytes located at the start of the address space, from locations $00 to $FF. The 68HC11 also has a bank of 64 internal special function registers, located at addresses $1000 to $103F. These registers control various hardware features of the 68HC11 (the analog inputs and serial communications are two examples). The remainder of this section presents details on the digital input and output circuit wiring.

Digital Inputs

**Figure 5.9:** Digital Input Circuit

Figure 5.9 shows the digital input circuitry. U7, a 74HC245 chip, is used to buffer an eight-bit word of sensor inputs and drive the 68HC11 data bus with that value when the chip is selected. The '245 is actually a bi-directional buffer or transceiver, but we connect the direction select to the enable so that the '245 can only serve as an input device. The lower two bits of the '245 are connected to the two user buttons (that have been dubbed CHOOSE and ESCAPE). The upper six bits are connected to the digital input header. The lower two bits of the input header are connected to two timer inputs of the 68HC11. These inputs can be used to precisely measure waveforms, or can simply be used for digital input. The library functions written to perform digital inputs insulate the user from the fact that the eight pins on the input header are not mapped contiguously to one location in memory. RS2, a 22K resistor pack, contains pull-up resistors for the inputs of the '245 chip, making the default value of the inputs a logical one.

One of the digital inputs (pin 8 of the Digital Input Header) is also tied to one of the 68HC11's external interrupt lines (IRQ, the maskable interrupt). This input is normally pulled high, leaving the interrupt inactive when no input is connected. The default interrupt handler routine simply returns when it is called, so no software modifications need to be made if the input is used as a digital I/O line. However, the simple act of acknowledging and returning from an interrupt takes some time, during which the processor cannot perform other functions. Therefore, frequently changing inputs should not be connected to this digital input. A user defined interrupt routine can be installed if the signal is to be used as an interrupt.

Digital Outputs

Figure 5.15 shows the complete schematic for the three '574 output latches controlling the motors. Notice that the data inputs of the '574s are connected to the 68HC11 data bus. The MOT01, MOT23, and MOT45 control signals connect to the clock inputs of the three '574s; when one of these is activated, the corresponding '574 latches the value present on the data bus. The outputs of the '574 connect to the motor driver chips, the circuitry of which is explained in the following section.

68HC11 and Memory Schematic

Figure 5.10 presents the schematic of the 68HC11, memory, address decoding, and supporting main circuitry on the Lego Robots Processor Board. By the end of this chapter, most of the circuitry depicted here will be explained.

**Figure 5.10:** 68HC11, Memory, Address Decoding and Miscellaneous Circuitry

The Motor Drivers

Motors are high-powered devices in the world of digital electronics. A typical digital output can supply about 10 to 20 milliamperes (mA) of current; a small permanent-magnet motor requires anywhere from 500 to 4000 mA of current. Special circuits are therefore required to drive motors.

The H-Bridge Circuit

**Figure 5.11:** The H-Bridge Circuit

A circuit known as the H-bridge (named for its topological similarity to the letter "H") is commonly used to drive motors. In this circuit (depicted in Figure 5.11), two of four transistors are selectively enabled to control current flow through a motor.

**Figure 5.12:** The H-Bridge with Left-to-Right Current Flow

As shown in Figure 5.12, an opposite pair of transistors (Transistor One and Transistor Three) is enabled, allowing current to flow through the motor. The other pair is disabled, and can be thought of as out of the circuit. By determining which pair of transistors is enabled, current can be made to flow in either of the two directions through the motor. Because permanent-magnet motors reverse their direction of turn when the current flow is reversed, this circuit allows bidirectional control of the motor.

The H-Bridge with Enable Circuitry

**Figure 5.13:** The H-Bridge with Enable Circuitry

It should be clear that one would never want to enable Transistors One and Two or Transistors Three and Four simultaneously. This would cause current to flow from Power + to Power - through the transistors, and not the motors, at the maximum current-handling capacity of either the power supply or the transistors. This usually results in failure of the H-Bridge. To prevent the possibility of this failure, enable circuitry as depicted in Figure 5.13 is typically used. In this circuit, the internal inverters ensure that the vertical pairs of transistors are never enabled simultaneously. The Enable input determines whether or not the whole circuit is operational. If this input is false, then none of the transistors are enabled, and the motor is free to coast to a stop. By turning on the Enable input and controlling the two Direction inputs, the motor can be made to turn in either direction. Note that if both direction inputs are the same state (either true or false) and the circuit is enabled, both terminals will be brought to the same voltage (Power + or Power - , respectively). This operation will actively brake the motor, due to a property of motors known as back emf, in which a motor that is turning generates a voltage counter to its rotation. When both terminals of the motor are brought to the same electrical potential, the back emf causes resistance to the motor's rotation.

The SGS Thompson L298N Motor Driver Chip

**Figure 5.14:** The SGS Thompson L298N Motor Driver IC

The SGS Thompson L298N 8 motor control chip incorporates two H-bridge motor-driving circuits into a single 15-pin package. Figure 5.14 shows a block diagram of this useful integrated circuit. The schematic of the motor circuit (Figure 5.15) shows how the L298N chips are controlled in the Lego Robots RoboBoard design. Six bits are used to control two motors. Four of the bits determine the direction of the motors and two bits determine when the motors are on or off. There are three such circuits on the RoboBoard, one for each pair of motors. The remaining two bits of each of the '574 chips are available as extra digital outputs, two of which are connected to transistor drivers. These transistor circuits are well-suited for powering light-load devices, such as LEDs or small lights. The other four outputs are routed to an output header. The speed of a motor may be controlled by pulsing the enable bit of its associated controller chip on and off. This technique, called pulse width modulation, is explained in the chapter on motors.

**Figure 5.15:** Motor and LED Driver Circuit

Power Considerations

Current Handling and Spike Protection

The L298N does not have significant internal protection against spike and other electrical noise. Therefore, diodes and capacitors have been added to the motor control circuitry as shown in Figure 5.15. These diodes and capacitors protect the motor chip and the rest of the circuit from electrical noise (inductive spikes) generated by the motors. The L298N can supply 2000 mA of current per motor. Since the stall current (the current drawn by the motor when the shaft is unable to turn) of the motors used in Lego Robots is less than 1500 mA, the L298N circuit is adequate for our purposes.

Power Supply Isolation

Electrical noise generated by motors can be hazardous to a microprocessor circuit even with the use of the diodes. Therefore the motors use separate power circuitry and filtering from the rest of the microprocessor electronics.

**Figure 5.16:** Power Supply and Regulating Circuit

Figure 5.16 shows the power-supply circuitry. Logic power (VCC), the supply voltage for the microprocessor circuitry, is provided by a TL750M05 low-dropout 5-Volt voltage regulator, while + Motor power for the motors is supplied directly from the battery. The control circuits of the L298N motor drivers also require a small amount of logic power; this is provided by a separate TL750L05 5-Volt regulator, as shown in Figure 5.16. The motor ground and the logic ground must be kept at the same potential so that the control signals from the '574 chip shown in Figure 5.15 can communicate with the L298N chips. These grounds are kept at the same potential by the inductor L2. Inductor L2 prevents motor current surges from upsetting the microprocessor power supply. The inductors provide reactance (frequency-dependent resistance) to trap electrical noise that might travel from the motors, through the L298N chips, and into the microprocessor circuit.

Analog Inputs

The 68HC11 has on-chip circuitry to perform an analog-to-digital signal conversion. In this operation, a voltage from 0 to 5 volts is converted into an 8-bit number (a range of 0 to 255, where zero volts corresponds with 0, and 5 volts with 255). This conversion feature is one of many that make the 68HC11 well-suited for control applications. The 68HC11 has eight of these analog inputs. In the Lego Robots RoboBoard design, six of these pins are wired to a motor current monitoring circuit, and two of them are wired to analog multiplexors, as described below.

Motor Current Monitoring Circuit

When the L298N chips drive a motor, there is a voltage drop across the transistors that form the H-bridge. The transistor connected to motor ground (0 volt potential) might drive the motor at some voltage between .2 and .8 volts; the transistor connected to the positive terminal of the battery (say it is at 12 volts) might drive the motor between 11.2 and 11.8 volts. The amount of this voltage drop is proportional to the amount of current being supplied by the motor-driving transistor. The greater the supply of current, the greater the voltage drop across the transistor. This somewhat undesirable property of the L298N transistors is exploited to give a crude measurement of the amount of current being driven through the motor. A fundamental property of motors is that, as the amount of work they are performing increases, the amount of current they draw also increases. So the current measurement yields data on how hard the motor is working -- if it is turning freely, if it is stalled, or if it is working somewhere in between. As indicated in Figure 5.15, the voltage feedback point is tapped from the indicator LEDs that are connected to the motor outputs. The voltage across the LEDs will decrease as a result of increased current draw of the motor (and the corresponding decreased performance of the L298Ns). This voltage is fed to a 68HC11 analog input and can be measured by the 68HC11 analog-to-digital conversion hardware. Each of the six motor circuits is wired in this way to a 68HC11 analog input.

Analog Input Multiplexing on the RoboBoard

**Figure 5.17:** Analog Input and Digital Output Circuitry

The RoboBoard has two eight-to-one analog multiplexor ICs. These chips (the 74HC4051) have eight inputs and one output; depending on the state of three selector inputs, one of the eight input lines is connected to the output. (Actually, the chip's signals are bidirectional, but for the purpose of this discussion, it is convenient to think of the chip as having eight inputs and one output.) The outputs of the two '4051 chips are wired into the 68HC11 analog inputs. Three signals from the 68HC11 are used to control the multiplexers and select which analog input is mapped to the 68HC11 analog input. These signals are taken from the three low order bits of the digital output port. Figure 5.17 is a schematic of the analog input circuitry on the Lego Robots RoboBoard. It is easy to see how the use of the analog multiplexor chips greatly expands the analog input capability of the Lego Robots hardware:

	The inputs of one of the '4051 chips are wired to a bank of eight analog-sensor inputs.
	The other '4051 chip is connected to the RoboKnob, a general-purpose analog input controlled by a variable resistor, four DIP switches (for user configuration input), and a voltage divider that allows the battery voltage to be directly measured.
	Two of the inputs to this second chip are available as general purpose analog inputs.

The Serial Line Circuit

**Figure 5.18:** Host and Board Communications over 3-Wire Serial Link

The Lego Robots Board communicates with a host computer over an RS-232 serial line. "RS-232" refers to a standard protocol for communications over a three-wire system, as depicted in Figure 5.18. Nearly all of today's computers have serial ports that conform to the RS-232 standard.* *The actual RS-232 standard involves quite a few more wires for conveying various status information, but the data itself is transmitted on two uni-directional wires In the RS-232 system, a "logic zero" is indicated by a + 10 volt signal with respect to ground, and a "logic one" is indicated by a - 10 volt signal. Note that this is different from standard digital logic levels in several ways. Negative voltages are used, higher voltages are used, and negative voltages connote a logic one value. The 68HC11 chip includes circuitry to generate waveforms compatible with the RS-232 systems, but requires external circuitry to convert its own signals, which obey the digital logic norms, to RS-232 signals as described.

**Figure 5.19:** Serial Line Circuit

U20, in Figure 5.19, is used to convert between the RS-232 voltage levels, and the digital logic voltage levels used everywhere else on the RoboBoard. This circuit contains two charge pumps to generate the negative voltages that are required. The first is used to double the system voltage of + 5 volts to obtain a + 10 volt supply that more closely matches the RS-232 standard. The second charge pump inverts this + 10 volts to obtain a - 10 volt supply.

High Speed Serial Peripheral Interface

The Serial Peripheral Interface (SPI) circuit is a synchronous serial data link that is standard across many Motorola microprocessors and other peripheral chips. It provides support for a high bandwidth (1 megabit) network connection between CPUs and other devices supporting the SPI. The RoboBoard's two SPI network jacks allow multiple RoboBoards or other SPI devices to be connected using a six-wire RJ-11 (telephone jack) connection. This six-wire RJ-11 interface is downward compatible with the four-wire SPI interface found on the M.I.T. "Mini Board". The RoboBoard uses a particular configuration of the SPI system that requires a minimum of external hardware support. Multiple RoboBoards may be networked with no additional components other than the cabling itself. A brief review of the SPI system follows, along with a discussion of the particular configuration of the SPI on the RoboBoard. Further details can be found in the Motorola M68HC11 Reference Manual.

Introduction to the SPI

The Serial Peripheral Interface is essentially a shift register that serially transmits data bits to other SPIs. During a data transfer, one SPI system acts as the "master" that controls the data flow, while the other system acts as the "slave" that has data shifted into and out of it by the master. Different CPUs can take turns being master, and one master may simultaneously shift data into multiple slaves. However, only one slave may drive its output to write data back to the master at any given time. The basic SPI interface consists of two data lines and two control lines:

Master Out Slave In: Abbreviated MOSI, this data line supplies the output data from the master that is shifted into the input(s) of the slave(s).
Master In Slave Out: Abbreviated MISO, this data line supplies the output data from the master that is shifted into the input(s) of the slave(s).
Serial Clock: Abbreviated SCK, this control line is driven by the master that regulates the flow of the data bits. The master may transmit data at a variety of baud rates; the SCK line cycles once for each bit that is transmitted.
Slave Select: Abbreviated SS, this control line allows slaves to be turned on and off with hardware control.

RoboBoard SPI Configuration

**Figure 5.20:** Serial Peripheral Interface Jack

The RoboBoard uses a six-wire SPI connection that carries the MOSI, MISO, SCK, signal ground, and two lines that support the Slave Select function (see Figure 5.20). Slave Select Out is a digital output that is driven by bit 5 of Port A. Slave Select In to the 68HC11 is configured by J3 on the RoboBoard. If pins 1 and 3 are connected, Slave Select In is tied low (this is the Mini Board compatible configuration), if pins 2 and 3 are connected, Slave Select In is tied high, and if no jumper is installed in J3, Slave Select In will be at whatever level is present on the RJ-11 pin. In the Mini Board compatible configuration, software protocols must be used to enable the activity of the SPI slave. In the default configuration (no jumper in J3), multiple RoboBoards can be arranged in a "ring" topology, with mastership being passed around the ring by each RoboBoard controlling the Slave Select In of the downstream board.
To connect the SPI circuits of multiple RoboBoards, each respective line of each RoboBoard can be tied together: MOSI to MOSI, MISO to MISO, etc. To make this happen, the connecting RJ-11 cables must have half-twists in them. This configuration works because of the bi-directionality of each of the control lines. When a given SPI circuit is the master, it transmits on its MOSI line while slaves receive on their MOSI lines. Likewise a slave transmits on its MISO line and the master receives on its MISO line. The SCK line also is automatically configured properly (it is an output for the master and an input for the slave).

Suggested Protocols

Two sample protocols are presented. The former, a single master protocol, would be significantly easier to implement than the latter, a multiple master protocol.

Single Master Protocol.: In this protocol, one CPU is always the master while all of the others are always slaves. One can imagine that the slave CPUs are simply input and output devices for the master. The master might desire to exchange information with a particular slave. To do this, the master would send a slave address datum in each communication packet. The selected slave would then enable its MISO line to write information back to the master. All other slaves would be required to turn their MISO lines off so as to not conflict with the selected slave. This protocol could be extended to allow the master to broadcast a message to multiple slaves, but only one slave may respond at a time (otherwise there would be hardware contention on the MISO).
Multiple Master Protocol.: This protocol allows CPUs to take turns being masters and request information from other CPUs at will. The trick here is to provide for some type of collision detection if more than one CPU decides to initiate a communication at the same time.

Non-Volatile Static RAM

The static RAM used in the Lego Robots board is a special device, manufactured by Dallas Semiconductor, that contains a 32K x 8 RAM, a small battery, and some circuitry that switches between normal and battery back-up power under controlled conditions. Having a battery-backed static memory greatly increases the usability of the Lego Robots board, since a robot can simply be turned on and operated immediately, without having to be connected to a computer first.

The Infrared Transmission Circuit

**Figure 5.21:** Square Wave Consisting of Bursts of 40 KHz Signals

The Sharp GP1U52 sensor and others like it, commonly used in TVs, VCRs, and other devices controlled by infrared, is sensitive to modulated infrared light. It detects the presence of infrared light that is blinking on and off at a particular rate. The GP1U52 sensor is tuned to 40,000 Hertz (40 KHz).
In TV remote applications, a data stream is then generated around the 40 KHz carrier frequency. The signal consists of bursts and gaps of the 40 KHz transmissions.

**Figure 5.22:** Sharp IR Sensor Decoding IR-Encoded Square Wave

For the Lego Robots application, the 40 KHz carrier is used to transmit a square wave of relatively low frequency (100 or 125 Hz), as shown in Figure 5.21. When the Sharp IR sensor decodes this signal, it removes the 40 KHz carrier, yielding a copy of the square wave that was originally transmitted (Figure 5.22).
The Lego Robots system software continuously checks the Sharp sensors for square waves of the specified frequency. The software actually locks on to the square wave when it is present and then counts the number of consecutive cycles that have been detected.

**Figure 5.23:** Block Diagram of Infrared Circuitry

A special circuit is used to generate infrared emissions modulated at the 40 KHz frequency. A block diagram of this circuit is shown in Figure 5.23.
The diagram shows that the '390 chip, wired in a divide-by-fifty configuration, is used to generate a 40 KHz signal from the 68HC11 E clock, a 2 MHz signal. In actuality, the '390 chip contains two decade counters. Each these consists of a separate divide-by-five counter and a flip-flop (a divide-by-two device). The '390 is wired in the divide-by-fifty function by ganging two of the divide-by-five counters and one of the flip-flops.
The IR control signal is wired to the clear input of the '390 chip; when this signal is true, the counters will reset and will be prevented from counting. By modulating this signal, the 68HC11 can generate the low-frequency square wave that ends up being transmitted to the Sharp sensor. Figure 5.24 shows the full circuit schematic for the IR subsystem. The 2N4401 transistor is used to drive the infrared LEDs.

**Figure 5.24:** Infrared Transmission Circuit

The IR Beacon

**Figure 5.25:** Infrared Beacon Circuit

The IR beacon is like the remote control for your TV. The IR beacon emits a modulated signal containing information which is received and interpreted by the IR sensor and the RoboBoard. This process is much like the transmission that occurs when you press a button on the remote control. The IR beacon for Lego Robots, however, has two design challenges to tackle. Figure 5.25 shows the schematic for the IR beacon.
The IR beacon must produce a signal with the maximum possible strength so that it can be easily detected, and detected at reasonable distances. Optical power output and current have a linear relationship, so in order to increase the signal strength, current must be increased. Unfortunately, increasing the current supplied to the IR board shortens the battery's life. In order to minimize the current, the IR LEDs are all wired in series.
To change channels one would point the remote at the TV and press a button. The robots, though, must broadcast their signal in every direction. Again, there is a tradeoff that must be optimized. Infrared LEDs have the property that as the viewing angle increases, the radiant intensity decreases. The Sharp GL537 LEDs used on the 2002 IR board provide the best compromise between power and viewing angle and are used in commercial remote control applications.
The IR board also has two indicator lights so that you can make sure everything is working. The red LED labeled IR XMIT on the RoboBoard lights up when the RoboBoard is attempting to transmit a signal. The red LED on the IR board lights up when all the IR LEDs are transmitting.

The LCD Display

J19 (in Figure 5.26) is a fourteen pin header designed to be compatible with a 14-pin standard LCD bus. A variety of character-based LCD devices with different screen sizes use this standard bus.
The LCD bus standard is fairly simple, consisting of the following signals:

	an 8-bit data bidirectional bus
	two mode select input signals
	a clock line
	a voltage reference for contrast adjustment
	+ 5 volt logic power
	signal ground

In fact, reading and writing data to an LCD is much like reading and writing data to latches or to memory. There is one problem, however: LCDs only work at data transfer rates up to 1 MHz. The 68HC11 on the Lego Robots RoboBoard operates at 2 MHz -- too fast for most LCDs.
One straight-forward solution to the speed problem would be to use a '574-type latch between the 68HC11 and the LCD. The '574 could be written to at the full bus rate of the 68HC11; its outputs would drive the data bus of the LCD. A separate signal could be used to toggle the LCD's clock line, causing it to latch the data that had been written to the '574. This solution assumes that one does not need to read status data back from the LCD.
An unconventional, zero-additional-hardware solution has been implemented in the Lego Robots system, which takes advantage of an obscure feature of the 68HC11 microprocessor.
The 68HC11 has two main operating modes, known as single chip mode and expanded multiplexed mode. The discussion of memory read and write cycles that has been presented in this chapter has been based on the expanded multiplexed mode, which is the 68HC11 mode that is used when external memory is part of the 68HC11 circuit.
When the 68HC11 is operated in single-chip mode, the upper-eight-bit address bus and multiplexed address/data bus become general purpose inputs and outputs of the 68HC11, controllable by system software. Thus, in single-chip mode, the 68HC11 could communicate with the LCD with a software driver, rather than the too-fast hardware communication.
There is a problem with this, however: when the 68HC11 is placed into single-chip mode, it can no longer execute a program from its external RAM. In fact, as far as the 68HC11 is concerned, there is no external memory.
Fortunately, the 68HC11 has 256 bytes of internal RAM, from which it can execute a program when in single-chip mode. Thus, a software driver could execute out of internal RAM, perform a transaction with the LCD, and then switch back to expanded-multiplexed mode and return control to the main program in external memory.
The obscure feature mentioned is not the fact that the 68HC11 has both of these modes, but the idea of dynamically switching between them. Here is the solution that has been implemented:

Start by copying a software driver from external system memory into the 256 bytes of internal 68HC11 memory.

Begin execution of the driver program located in internal memory:

	Place the 68HC11 into single-chip mode; external memory disappears.
	Execute a low-speed transaction with the LCD by directly controlling the data bus via software.
	Place the 68HC11 into expanded-multiplexed mode.
	Return to the main program in external memory.

Continue normal program execution.

The actual LCD driver routine buffers characters to be printed to the LCD; one thousand times per second, an interrupt routine calls the internal memory driver as described, writing a single character to the LCD. The whole process operates transparently to the Lego Robots system user.

**Figure 5.26:** LCD and Piezo Circuit

DC Motor-Driver H-Bridge Circuit

2011-05-02T13:23:00.000-07:00

DC Motor-Driver H-Bridge Circuit

Physical motion of some form helps differentiate a robot from a computer. It would be nice if a motor could be attached directly to a chip that controlled the movement. But, most chips can't pass enough current or voltage to spin a motor. Also, motors tend to be electrically noisy (spikes) and can slam power back into the control lines when the motor direction or speed is changed.

Specialized circuits (motor drivers) have been developed to supply motors with power and to isolate the other ICs from electrical problems. These circuits can be designed such that they can be completely separate boards, reusable from project to project.

A very popular circuit for driving DC motors (ordinary or gearhead) is called an H-bridge. It's called that because it looks like the capital letter 'H' when viewed on a discrete schematic. The great ability of an H-bridge circuit is that the motor can be driven forward or backward at any speed, optionally using a completely independent power source.

An H-bridge design can be really simple for prototyping or really extravagant for added protection and isolation. An H-bridge can be implemented with various kinds of components (common bipolar transistors, FET transistors, MOSFET transistors, power MOSFETs, or even chips).

The example provided on this page features:

TTL/CMOS compatible Microchip/Maxim 4424/4427A or IXYS IXDN404 MOSFET driver chips that protect the logic chips, isolate electrical noise, and prevent potential short-circuits inherently possible in a discrete H-bridge.
Schottky diodes to protect against overvoltage or undervoltage from the motor.
Capacitors to reduce electrical noise and provide peak power to the driver chip.
Pull-up resistors that prevent unwanted motor movement while the microcontroller powers up or powers down.

A diode-less version of this circuit successfully drove Bugdozer to mini-sumo victory. The more robust (diode protected) version is used on Sweet and Roundabout.

Resistors R1 and R2

R1 and R2 are pull-up resistors. These can be any value from 10 kilohm to 100 kilohm.

These make sure the inputs are both on unless a signal from the microcontroller tells one or the other to turn off. With both on or both off, the motor doesn't spin because there's no voltage difference between them.

Think of these as default values. Unless a different value is specified, the lines are pulled up. This means the circuit can come loose or be disconnected completely and the motor won't spin or stutter.

Technically, R1 and R2 could be eliminated, although then the motors are likely to jerk when the microcontroller powers up or powers down.

Driver Chip IC1

IC1 is a dual MOSFET transistor driver chip. Anything from the TC4424 family will do. The MAX4427 and TC4427A is the same but with a lower amperage rating. The IXDN404 has the highest amperage rating (best choice). The DIP part can be purchased at DigiKey or Mouser as part #IXDN404PI.

Warning:
Direct motor driving with this chip is only possible for motors that draw less than 100 mA (TC4427A), 150 mA (TC4424), or 340 mA (IXDN404) under load. To determine if your motors qualify, use a multimeter to measure how much current your motor uses under load (for example, when actually driving your robot around) when the motors are connected directly to the battery (not through these chips).
This chip is not really supposed to drive a motor by itself. If you find the chip gets very hot and the motor doesn't spin (or barely spins or stalls when loaded) then you need to have the chip drive some real power MOSFETs like it is supposed to. It's not that much more difficult and it really makes a huge difference in performance.

This chip provides two independent inputs that are compatible with CMOS or TTL chips. This circuit design uses IN A to vary power (on, off, or pulsed in-between) and IN B to determine direction.

OUT A follows the IN A signal but uses the full voltage from the power source, not the tiny voltage from the input signal itself. OUT B follows IN B in the same way.

For example, if IN A is turned on completely (2.4 volts or better) and IN B is turned off completely (0.8 volts or less) then OUT A turns on completely (up to 22 volts) and OUT B turns off completely (GND). The motor gets 22 volts.

This chip is constructed to protect the static sensitive MOSFETs, but also to protect the input sources from current being jammed back by the motors. Optoisolator ICs could be used at the inputs if greater protection, freedom from noise, or electrically-isolated operation is desired. However, I've never had to resort to optoisolators.

Normally four transistors are needed in an H-bridge. Each transistor forms a corner in the letter 'H', with the motor being the bar in the middle.

In this design, each output of the chip forms a complete vertical side of the letter 'H', with the motor still being in the middle. Because a side is now a single output, short-circuits can't form from the top of a side to the bottom of a side. No matter what the inputs, all power must travel from one side to the other -- through the motor.

A mechanical switch, relay, or logical gate could be used to turn the inputs on and off. It would work just fine at providing no movement (on/on or off/off), forward movement (on/off), or reverse movement (off/on). To provide power levels in between (like 50%), rapid pulses of on or off can be provided by pulse-width modulation using a chip or timer.

An important note regarding current rating: The plastic DIP package can only dissipate enough heat when the power usage is below 730 milliwatts. For example, it isn't possible to continuously run the TC4424 chip at both its absolute maximum voltage (22 V) and absolute maximum amperage (3 A) rating. That would result in 66 watts of power usage. (That's almost 100x the maximum allowed.)

From: Paul Jurczak
Sent: Monday, March 12, 2001 10:59 AM
Subject: DC Motor-Driver H-Bridge Circuit

The actual DC power losses in the H-bridge would be:
I² * (Rl + Rh)
= (3 A * 3 A) * (2.8 ohm + 2.5 ohm) = 47.7 W typical
and
= (3 A * 3 A) * (5 ohm + 5 ohm) = 90 W maximum

Which still is more than enough to melt this IC.

Paul.

I'm sincerely grateful for the feedback.

Paul is correctly pointing out that the chip only needs to dissipate the portion of power used in the chip's resistance.

For current to flow, the chip must have one gate high and one gate low. Therefore, Paul is adding the typical high and low resistance (from the 4427 datasheets) together to calculate the total amount of resistance the chip causes.

When a moving motor is added to the circuit, the motor uses up some (hopefully most) of the power. Just dive for that robot if the motors stall!

In summary, the chip can't run at maximum volts and maximum amps because most of the 66 watts (47 watts typical) would need to be dissipated by the chip. (See the temperature of a similar motor driver chip heat up and cool down.)

Thanks Paul!

Diodes D1 and D3

My original source had D1 and D3 listed as small-signal diodes. I couldn't find any at the time, so, I used 1N5817 Schottky diodes instead. It turns out that Schottky diodes are much better for motor circuts because they react more quickly.

The key factors in substitution are:

Are the diodes rated to turn on with less voltage than the TC4424's or IXDN404's internal transistor base voltage? (600 millivolts)
Are the diodes rated to handle the maximum reverse voltage? (22 volts or 35 volts)
Are the diodes rated to handle the maximum current? (3 amps or 4 amps)

In the case of the 5817s, the datasheets answers are:

Yes. (400 millivolts or less)
No. (20 volts -- so this is the circuit's new absolute voltage maximum)
Yes, peak (25 amps)

When a motor accelerates or decelerates for any reason (signal, load, or friction), there is reluctance for the electric field present in the motor coils to change. More properly, the changing field induces power. This "refunded" power can jam back into the chips.

D1 and D3 protect the chips from overvoltage by turning on when more voltage is coming from the motor than is coming from the batteries. The batteries absorb the power.

The turn-on rating of the diode must be lower than the turn-on rating of the chip, or else the diode won't turn on early enough to protect the chip.

Because the diode is installed in "reverse", the power can't flow from the batteries to the motors. If the diode was installed differently, power would immediately flow to the motors, bypassing the chip outputs (or worse, short-circuiting through the chip).

By the way, this arrangement is why the reverse or breakdown voltage of the diodes is important. If the reverse voltage rating was less than the full battery voltage, the battery would break down the reversed diode and just shoot through. In this case, the 1N5817 has a 20 V reverse breakdown voltage, so it can be used with batteries and power supplies up to this voltage.

Diodes D2 and D4

D2 and D4 are also Schottky diodes; the same as D1 and D3.

D2 and D4 protect the chips from undervoltage (less than ground) by turning on when the voltage in the motor is below GND. Once again, the batteries take care of the problem, rather than power flowing backwards from the chip.

D1 through D4 could be eliminated. In fact, Bugdozer runs without the diodes. However, parasitic voltages can and do temporarily overwhelm voltage regulators (reset!) and can even destroy the driver chips.

Actual Implementation of Motor Driver

Despite what may seem complicated at first, the photograph below includes added features such as an LP2954 5V voltage regulator, a bicolor LED, and two switches for testing.

One H-bridge drives one motor. For a common two-wheeled robot, obviously two copies of the H-bridge circuit are needed.

(Click the picture above for a movie)

Pressing the right-side button makes the motor turn counter-clockwise and lights the LED green.
Pressing the left-side button makes the motor turn clockwise and lights the LED red.
Pressing both the buttons turns on the brakes (stopping the motor) and turns off the LED.
Pressing the brakes quickly enough provides variable speed (between 0% and 100%).

Better H-bridge motor drivers

Where do you go from here?

I originally wrote this web page in December 2000. I've received a lot of email regarding this subject, especially from people seeking to drive larger motors or achieve better performance. My friend, Don Kerste, recently gave me grief for still using an IXDN404 chip in my newer robots.

If you are making a small robot or device that uses a miniature gearmotor that requires less than 100 mA continuously when running, then this motor driver with a 4424, 4427, or IXDN404 chip without diodes is perfectly adequate. If you need more current, up to a total of 340 mA, make sure to use the IXDN404 chip and go ahead and add the 1N5817 diodes.

If you need even more current, but you are locked into using this chip, then you can obtain almost 2/3 of an amp (~680 mA) continuously by stacking two chips together with copper foil in between. This allows the chips to dissipate heat.

Soldering two identical IXDN404PI motor driver DIP chips together with copper foil for a cheap heatsink.

Suppose this is still not enough current. In other words, the chip is heating up too much or the motor isn't turning. Not every motor driver is appropriate for every situation. This is a simple, low-cost, low-power motor driver.

If you have a microcontroller that can control a more complex circuit, you can build a transistor based H-bridge. Or, at the opposite end of the spectrum, if you are going to control the motor manually, consider a simple manual motor direction switch.

There are much more powerful solutions available if you need something that can electronically drive motors with multiple amps of current, can control all of the motor states (forward, reverse, brake, and coast), or if you really want to understand how motor driver circuits work. I dedicate nearly 70 pages to motor drivers in my second book, Intermediate Robot Building. The book includes many more schematics, efficiency results for other driver chips, and even a speed-controllable power MOSFET driver.

Brief H-Bridge Theory of Operation

2011-05-02T13:17:00.000-07:00

Brief H-Bridge Theory of Operation

What's all this talk about H-Bridges? How do they work? Well let's see . . .

How do we make a motor turn?
You take a battery; hook the positive side to one side of your DC motor. Then you connect the negative side of the battery to the other motor lead. The motor spins forward. If you swap the battery leads the motor spins in reverse.

Ok, that's basic. Now lets say you want a Micro Controller Unit (MCU) to control the motor, how would you do it? Well, for starters you get a device that would act like a solid state switch, a transistor, and hook it up the motor.

NOTE: If you connect up these relay circuits, remember to put a diode across the coil of the relay. This will keep the spike voltage (back EMF), coming out of the coil of the relay, from getting into the MCU and damaging it. The anode, which is the arrow side of the diode, should connect to ground. The bar, which is the Cathode side of the diode, should connect to the coil where the MCU connects to the relay.

If you connect this circuit to a small hobby motor you can control the motor with a processor (MCU, etc.) Applying a logical one, (+12 Volts in our example) to point A causes the motor to turn forward. Applying a logical zero, (ground) causes the motor to stop turning (to coast and stop).

Hook the motor up in this fashion and the circuit turns the motor in reverse when you apply a logical one (+12Volts) to point B. Apply a logical zero, which is usually a ground, causes the motor to stop spinning.

If you hook up these circuits you can only get the motor to stop or turn in one direction, forward for the first circuit or reverse for the second circuit.

Motor Speed
You can also pulse the motor control line, (A or B) on and off. This powers the motor in short burst and gets varying degrees of torque, which usually translates into variable motor speed.

But if you want to be able to control the motor in both forward and reverse with a processor, you will need more circuitry. You will need an H-Bridge. Notice the "H"-looking configuration in the next graphic. Relays configured in this fashion make an H-Bridge. The "high side drivers" are the relays that control the positive voltage to the motor. This is called sourcing current.

The "low side drivers" are the relays that control the negative voltage to sink current to the motor. "Sinking current" is the term for connecting the circuit to the negative side of the power supply, which is usually ground.

So, you turn on the upper left and lower right circuits, and power flows through the motor forward, i.e.: 1 to A, 0 to B, 0 to C, and 1 to D.

Then for reverse you turn on the upper right and lower left circuits and power flows through the motor in reverse, i.e.: 0 to A, 1 to B, 1 to C, and 0 to D.

CAUTION: You should be careful not to turn on both circuits on one side or the other, or you have a direct short which will destroy your circuit; Example: A and C or B and D both high (logical 1).

Semiconductor H-Bridges
We can better control our motor by using transistors or Field Effect Transistors (FETs).

Most of what we have discussed about the relays H-Bridge is true of these circuits. You don't need diodes that were across the relay coils now. You should use diodes across your transistors though. See the following diagram showing how they are connected.

These solid state circuits provide power and ground connections to the motor, as did the relay circuits. The high side drivers need to be current "sources" which is what PNP transistors and P-channel FETs are good at. The low side drivers need to be current "sinks" which is what NPN transistors and N-channel FETs are good at.

If you turn on the two upper circuits, the motor resists turning, so you effectively have a breaking mechanism. The same is true if you turn on both of the lower circuits. This is because the motor is a generator and when it turns it generates a voltage. If the terminals of the motor are connected (shorted), then the voltage generated counteracts the motors freedom to turn. It is as if you are applying a similar but opposite voltage to the one generated by the motor being turned. Vis-ã-vis, it acts like a brake.

To be nice to your transistors, you should add diodes to catch the back voltage that is generated by the motor's coil when the power is switched on and off. This flyback voltage can be many times higher than the supply voltage! If you don't use diodes, you could burn out your transistors.

Transistors, being a semiconductor device, will have some resistance, which causes them to get hot when conducting much current. This is called not being able to sink or source very much power, i.e.: Not able to provide much current from ground or from plus voltage.

Mosfets are much more efficient, they can provide much more current and not get as hot. They usually have the flyback diodes built in so you don't need the diodes anymore. This helps guard against flyback voltage frying your MCU.

To use Mosfets in an H-Bridge, you need P-Channel Mosfets on top because they can "source" power, and N-Channel Mosfets on the bottom because then can "sink" power. N-Channel Mosfets are much cheaper than P-Channel Mosfets, but N-Channel Mosfets used to source power require about 7 volts more than the supply voltage, to turn on. As a result, some people manage to use N-Channel Mosfets, on top of the H-Bridge, by using cleaver circuits to overcome the breakdown voltage.

It is important that the four quadrants of the H-Bridgecircuits be turned on and off properly. When there is a path between the positive and ground side of the H-Bridge, other than through the motor, a condition exists called "shoot through". This is basically a direct short of the power supply and can cause semiconductors to become ballistic, in circuits with large currents flowing. There are H-bridge chips available that are much easier, and safer, to use than designing your own H-Bridge circuit.

H-Bridge Devices
The L 293 has 2 H-Bridges, can provide about 1 amp to each and occasional peak loads to 2 amps. Motors typically controlled with this controller are near the size of a 35 mm film plastic canister.

The L298 has 2 h-bridges on board, can handle 1amp and peak current draws to about 3amps. You often see motors between the size a of 35 mm film plastic canister and a coke can, driven by this type H-Bridge. The LMD18200 has one h-bridge on board, can handle about 2 or 3 amps and can handle a peak of about 6 amps. This H-Bridge chip can usually handle an average motor about the size of a coke. There are several more commercially designed H-Bridge chips as well.

There! That's the basics about motors and H-Bridges! Hope it helps and be safe!

See also the DPRG H-Bridge Project for a do-it-yourself H-Bridge design with full schematic and PCB artwork.

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