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Saturday, December 18, 2010

Memory types and its features

Memory types and its features
      In computers, Hard Disc drives, Pen Drive, RAMs are mainly used.  These memories are made of different technology. These are  Hard drive, SRAM, DRAM, Flash memory and MRAM.  Now a days, the hard disc drives are available at higher densities in the order of more than 500 GB. The flash pendrives are at higher densities of order of 16, 32 GBs and the size is also very very small. The features of these memories and its positive and negatives are given here
1. Hard drive:
High density, very low cost per byte stored, high power.
Moderate read and write speeds and bulky moving parts.

2. SRAM :
Super fast read and write speeds and low power consumption
Large memory cells take up more space, volatile

3. DRAM: High density, low cost, fast read and write speeds and low power
Volatile and require constant refreshing of data drains power

 4. Flash:
Nonvolatile, High density, fast read speed
More power consumtion, write operation is slow and limited life time

5. MRAM:
Non volatile, high density, fast read and write  speeds, low power and unlimited lifetime

Thursday, December 16, 2010

Spin transistors to keep Moore's Law and Spin Memory future memory of the world of electronics

Spin transistors to keep Moore's Law and Spin Memory future memory of the world of electronics
The transistor densities in a single chip has been increased and designed to keep the Moore's law lively. However with today's technology, the trend  has to change otherwise at one point the quantum effects will not permit and Moore's law can not be meet out. In order to overcome this problem, the spintronics technology which is spin based electronics, is going to take over the conventional chip technology.
Basics of Spin electronics Technology:
Spin is a basic unit of quantum properties of electron  and sub atomic particles. Spin can have two states relative to a magnetic field which is referred as up and down. These two states can be represented as two values of binary (0 and 1) for storing a bit. We can manipulate these states which is faster and required less energy and can take smaller scales. Hence, chips can be built with spin transistors which are so faster and more powerful than the traditional transistors. 
Spin Memory                                                 Image courtesy: IEEE Spectrum Magazine.
Spin Memories are built with the spintronics technology called as MRAM (stands for Magneto resistive RAM) . This MRAM stores the bits in a ferromagnetic substance  in which data bits are stored by making alignment of electrons in one directions or others. The spin up means 0  and spin down means 1. With this technology, we can perform erase, read and write operation. 

The features of spin memory are
High densities, 
fast read and write speeds, 
low power consumption and 
unlimited write operation possible. 
It can be used as a universal nonvolatile memory.
Dimension in the order of 150nm.
For further information, read the IEEE Spectrum Magazine.

Wednesday, December 8, 2010

Algae - A new alternative renewable bio fuel

Algae - A new alternative renewable bio fuel
   The renewable sources such as energy from solar, wind, tidal and bio fuels have been gaining momentum for replacing conventional fuels (fossil fuels) and fight against the global warming problems. Such one alternative is algae, a bio fuel to provide a renewable source for diesel, gasoline and jet fuels. 
   Algae (like plants) are micro organisms which use the photosynthesis to convert light into chemical energy and with the advantages absorbing Co2 from the surrounding atmosphere. Initial stage, algae turn carbon that it take into sugars and then into oil which can be used as fuel.The algae grow rapidly and can be reaped continuously, so high amount of oil can be generated annually.

1.Reduces carbon emissions    2. algae can be grown or cultivated anywhere

Wednesday, October 27, 2010

Online Monitoring and Control of Greenhouse Environment using Labview

Online Monitoring and Control of Greenhouse Environment using Labview
   We are in urgency of controlling the greenhouse effect on our mother earth. In order to protect our earth we have to take much care and start to do more Engineering projects on Greenhouse Environment conditions.
Appropriate environmental conditions are necessary for optimum plant growth, improved crop yields, and efficient use of water and other resources. Automating the data acquisition process of the soil conditions and various climatic parameters that govern plant growth allows information to be collected at high frequency with less labor requirements. The existing systems employ PC or SMS-based systems for keeping the user continuously informed of the conditions inside the greenhouse; but are unaffordable, bulky, difficult to maintain and less accepted by the technologically unskilled workers.

In anticipation to above A novel project can be designed with a simple, easy to install, virtual instrumentation software (LabVIEW)-based circuit to monitor and record the values of temperature, humidity, soil moisture and sunlight of the natural environment that are continuously modified and controlled in order optimize them to achieve maximum plant growth and yield. BNC card communicates with the various sensor modules to LabVIEW installed system through DAQ, in real-time in order to control the light, aeration and drainage process efficiently inside a greenhouse by actuating a cooler, fogger, dripper and lights respectively according to the necessary condition of the crops. LabVIEW front panel is also used for real time display of data acquired from the various sensors and the status of the various devices. Also, the use of easily available components reduces the manufacturing and maintenance costs. The design is quite flexible as the software can be changed any time. It can thus be tailor-made to the specific requirements of the user.
This makes the proposed system to be an economical, portable and a low maintenance solution for greenhouse applications, especially in rural areas and for small scale agriculturists.

Thursday, September 23, 2010

Basics of Programmable Logic Controller and Its Functionality

Basics of Programmable Logic Controller and Its Functionality
“PLC” means “Programmable Logic Controller”. The word “Programmable” differentiates it from the conventional hard-wired relay logic. It can be easily programmed or changed as per the application’s requirement. The PLC also surpassed the hazard of changing the wiring. The PLC as a unit consists of a processor to execute the control action on the field data provided by input and output modules. In a programming device, the PLC control logic is first developed and then transferred to the PLC.

• It can perform relay-switching tasks.
• It can conduct counting, calculation and comparison of analog process values.
• It offers flexibility to modify the control logic, whenever required, in the shortest time.
• It responds to the changes in process parameters within fractions of seconds.
• It improves the overall control system reliability.
• It is cost effective for controlling complex systems.

As shown in the Fig, the heart of the “PLC” is the center, i.e., the Processor or CPU (Central Processing Unit).
• The CPU regulates the PLC program, data storage, and data exchange with I//O modules.
• Input and output modules are the media for data exchange between field devices and CPU.
• It tells CPU the exact status of field devices and also acts as a tool to control them.
• A programming device is a computer loaded with programming software, which allows a user to create, transfer and make changes in the PLC software.
• Memory provides the storage media for the PLC program as well as for different data.

CPU or processor: The main processor (Central Processing Unit or CPU) is a microprocessor-based system that executes the control program after reading the status of field inputs and then sends commands to field outputs.
I/O section: I/O modules act as “Real Data Interface” between field and PLC CPU. The PLC reads the real status of field devices, and controls the field devices by means of the relevant I/O cards.
Programming device: A CPU card can be connected with a programming device through a communication link via a programming port on the CPU.
Operating station: An operating station is commonly used to provide an "Operating Window" to the process. It is usually a separate device (generally a PC), loaded with HMI (Human Machine Software).

Tuesday, September 14, 2010

Exposure to Labview Environment

Exposure to Labview Environment
Recently i gave lecture on LabVIEW. I observed from the audience that they are not familiar with it or no exposure to it. So i would like to share the basics and insight of LabVIEW environment compared with other simulation software in Engineering fields. There are lot more to learn about labVIEW its advantages. There are plenty of applications for Engineering students at academic level.

Basics of LabVIEW
LabVIEW short for Laboratory Virtual Instrumentation Engineering Workbench is a platform and development environment for a visual programming language from National Instruments. LabVIEW is commonly used for data acquisition and instrument control. The programming language used in LabVIEW, called G, is a dataflow language.
LabVIEW ties the creation of user interfaces (called front panels) into the development cycle. LabVIEW programs subroutines are called Virtual Instruments (VIs). Each VI has three components namely Block diagram, Front panel and Connector pane
The later may represent the VI as a sub VI in block diagrams of calling VIs. Controls and indicators on the front panel allows an operator to input data into or extract data from a running virtual instrument. However, the front panel can also serve as a programmatic interface.
The graphical approach also allows non-programmers to build programs by simply dragging and dropping virtual instrument representations of the lab equipment with which they are already familiar. The LabVIEW programming environment, with the included examples and the documentation, makes it simpler to create small applications, many libraries with a large number of functions for data acquisition, signal generation, mathematics, statistics, signal conditioning, analysis, etc., along with numerous graphical interface elements are provided in several LabVIEW package options.

LabVIEW programs are called virtual instruments or VIs, because their appearance and operation imitate physical instruments, such as oscilloscopes and multimeters. Every VI uses functions that manipulate input from the user interface or other sources and displays that information or moves it to other files or other computers.
A VI contains the following three components,
o Front panel
o Block diagram
o Icon and connector pane
The Front panel serves as the user interface. The Icon and the connector pane identify the interface to the VI so that one VI can be used in another VI. In general, a VI within another VI is called a sub VI. A sub VI corresponds to a subroutine in text based programming languages. The Block diagram contains the graphical code of VI used.
When a LabVIEW application is created, it is started at the top-level VI and inputs and outputs for the application are defined. Then a sub VI is constructed to perform the smaller tasks within the top-level VI. This modular approach is one of the strengths of LabVIEW. Hence it is possible to create complicated applications that are hierarchal in nature and reuse common elements within an application. The use of sub VI makes application easy to understand, debug and maintain.
The basic LabVIEW environment elements are the menus at the top of the front panel and block diagram windows, toolbar and free floating palettes like tools palette and controls palette.
The Tools Palette is available on the front panel and block diagram. A tool is a special operating mode of the mouse cursor. The cursor corresponds to the icon of the tool selected in the palette. The tools are used to operate and modify the front panel and block diagram objects. If automatic tool selection is enabled and the cursor is moved over the objects on the front panel or block diagram, LabVIEW automatically selects the corresponding tools from the tools palette. The tools palette can be also be used to modify the contents of the front panel or the block diagram. Each icon on the tools palette changes the behaviour of the cursor on LabVIEW so that operations like positioning, operating and editing tasks on VIs can be performed.
A Front Panel is built by placing controls and indicators from the controls palette. Each palette icon represents a sub palette, which contains control. A control is a front panel object that the user manipulates to interact with the VI.
In terms of performance, LabVIEW includes a compiler that produces native code for the CPU platform. The graphical code is translated into executable machine code by interpreting the syntax and by compilation. The LabVIEW syntax is strictly enforced during the editing process and compiled into the executable machine code when requested to run or upon saving. In the latter case, the executable and the source code are merged into a single file. The executable runs with the help of the LabVIEW run-time engine, which contains some precompiled code to perform common tasks that are defined by the G language. The run-time engine reduces compile time and also provides a consistent interface to various operating systems, graphic systems, hardware components, etc. The LabVIEW Professional Development System allows creating stand-alone executables and the resultant executable can be distributed an unlimited number of times. The run-time engine and its libraries can be provided freely along with the executable.
Simple examples of controls are buttons, slides, dials and text boxes. An indicator is also a front panel object that displays the data to the user. Examples of indicators are graphs, thermometers, gauges. When control or indicator is placed in front panel, the corresponding terminal is automatically created in block diagram.

o LabVIEW is a data flow and graphic based language, which is very suitable for designing a man-machine interface.
o The modular structure is one of the biggest advantages of the virtual instrumentation because it offers the possibility of hierarchy on the grades of complexity.
o As a user of LabVIEW one does not have to worry about configuration and control of the components within DAQ boards.
o LabVIEW identifies each board by a device number ant therefore one can have as a many devices as many as the computer can accept on their expansion slots.
o It has also reduced the complicated usage of Programming logic Controls (PLC’s) and other coding languages such as Pascal, C, FORTRAN etc…
One benefit of LabVIEW over other development environments is the extensive support for accessing instrumentation hardware. Drivers and abstraction layers for many different types of instruments and buses are included or are available for inclusion. These present themselves as graphical nodes. The abstraction layers offer standard software interfaces to communicate with hardware devices. The provided driver interfaces save program development time. The sales pitch of National Instruments is, therefore, that even people with limited coding experience can write programs and deploy test solutions in a reduced time frame when compared to more conventional or competing systems.
Another benefit of the LabVIEW environment is the platform independent nature of the G code, which is (with the exception of a few platform-specific functions) portable between the different LabVIEW systems for different operating systems (Windows, MacOSX and Linux) when compared to more conventional or competing systems.
National Instruments is increasingly focusing on the capability of deploying LabVIEW code onto an increasing number of targets including devices like Phar Lap OS based LabVIEW real-time controllers, PocketPCs, PDAs, FieldPoint modules and into FPGAs on special boards.

Friday, August 6, 2010

LM358 Dual Opamp Features, characteristics and advantages

LM358 Dual Opamp Features and applications

The LM358 series consists of two independent, high gain, internally frequency compensated operational amplifers which were designed specifically to operate from a single power supply over a wide range of voltages. Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage. Application areas include transducer amplifiers, dc gain blocks and all the conventional op amp circuits which now can be more easily implemented in single power supply systems. For example, the LM358 series can be directly operated off of the standard +5V power supply voltage which is used in digital systems and will easily provide the required interface electronics without requiring the additional ±15V power supplies.

• Internally frequency compensated for unity gain
• Large dc voltage gain: 100 dB
• Wide bandwidth (unity gain): 1 MHz (temperature compensated)
• Wide power supply range: — Single supply: 3V to 32 or dual supplies: ±1.5V to ±16V
• Very low supply current drain (500 μA) essentially independent of supply voltage
• Low input offset voltage: 2 mV
• Differential input voltage range equal to the power supply voltage
• Large output voltage swing

• In the linear mode the input common-mode voltage range includes ground and the output voltage can also swing to ground, even though operated from only a single power supply voltage.
• The unity gain cross frequency is temperature compensated.
• The input bias current is also temperature compensated.

• Two internally compensated op amps
• Eliminates need for dual supplies
• Allows direct sensing near GND and VOUT also goes to GND
• Compatible with all forms of logic
• Power drain suitable for battery operation

Friday, July 9, 2010

Solar impulse aircraft – Successful Green Flight in the History of Aviation

The non renewable energy sources have been fueling the entire transportation system such as two wheeler, four wheeler, ships and air planes since for a long period, and however going to exhaust very soon, the very promising alternate fueling system would be green energy like solar, wind systems. They development and deployment of these sources and its related technologies have already started its journey in order to overcome the energy demand. However, implementing solar energy as an alternate source of power is always a challenge because of cost and efficiency aspects which is not feasible in all the fields.
That challenge which was considered once as impossible has been achieved and successfully tested in the field of aero technologies. It is a milestone in the aircraft technologies where the aircraft run, uses only energy received from solar cells. It uses ultra efficient and light weight of about 12,000 solar panels which is fit in the wingspan of the plane.
This plane has been built by Solar Impulse engineers, with sponsors received from the electronics, engineering, aerospace, Solar energy Industries and one of Switzerland's top technical universities.
The main achievement and the recent record of this craft was that Solar Impulse takes off from western Switzerland's Payerne for a non-stop flight through day and night, for about 26 hours continuous flight with altitude of above 8500 mtrs. and piloted by Andre Borschberg. The mastermind behind this solar powered by Swiss adventurer Bertrand Piccard.
The future of aim of this team is to design an aircraft for long travel and equipping more people and payload.
Thanks for the team for successfully implementing green technology in the aviation field.

Monday, June 21, 2010

Impact factor of journals
It is a measure of reflecting the average number of citations to article published in science, engineering, social science and technology. Those who are pursuing Ph.D.s and publishing journals should know about impact factor of the particular journals. This article mainly for those who wish to publish journals of some standard and impact factor.
Most of Universities are recommending their scholars to publish journals of high impact factor.
Most of the recent journals are paid journals which have no impact factor. They do even not reviewing the articles received and publishing it in their journals for sack of earning money.
What is impact factor?
It is a qualitative measure of any journals published. Based on the impact factor, we can judge the relative importance of journals. Impact factors are calculated yearly for those indexed in Thomson Reuters.

The formula used for IM is
A = the number of times articles published in 2008 and 2009 were cited by indexed journals during 2008
B = the total number of "citable items" published in 2008 and 2009. ("Citable items" are usually articles, reviews, proceedings, or notes; not editorials or Letters-to-the-Editor.)

impact factor = A/B

The 2009 impact factors are actually published in 2010; they cannot be calculated until all of the 2009 publications have been received by the indexing agency.

The Journal Citation Reports also includes the Five year impact factor. This factor varies from year to year. The impact factors of journals are available in excel format. The can be freely downloaded from scopus site.

Thursday, June 17, 2010

A Quick review of Solar Panel working

A Quick review of Solar Panel working
I would like to share this article  "an instant solution to understand how solar panels work" which i received from  Barbara Young. 

What exactly is solar energy ?

Solar power is radiant energy that is produced by the sun. Daily the sun radiates, or sends out, an immense volume of energy. The sun radiates more energy in a second than people have used since the beginning of time!

The energy of the Sun derives from within the sun itself. Like other stars, the sun is really a big ball of gases––mostly hydrogen and helium atoms.

The hydrogen atoms in the sun’s core combine to form helium and generate energy in a process called nuclear fusion.

During nuclear fusion, the sun’s extremely high pressure and temperature cause hydrogen atoms to come apart and their nuclei (the central cores of the atoms) to fuse or combine. Four hydrogen nuclei fuse to become one helium atom. But the helium atom contains less mass than the four hydrogen atoms that fused. Some matter is lost during nuclear fusion. The lost matter is emitted into space as radiant energy.

It takes an incredible number of years for the energy in the sun’s core to make its way to the solar surface, after which somewhat over eight minutes to travel the 93 million miles to earth. The solar energy travels to the earth at a speed of 186,000 miles per second, the speed of sunshine.

Simply a small percentage of the power radiated by the sun into space strikes the earth, one part in two billion. Yet this volume of energy is enormous. Everyday enough energy strikes the united states to provide the nation’s energy needs for one and a half years!

Where does all of this energy go?

About 15 percent of the sun’s energy that hits the earth is reflected back to space. Another 30 percent is used to evaporate water, which, lifted in to the atmosphere, produces rainfall. Solar energy also is absorbed by plants, the land, and the oceans. The remaining could be employed to supply our energy needs.

Who invented solar technology ?

People have harnessed solar power for years and years. As early as the 7th century B.C., people used simple magnifying glasses to concentrate the light of the sun into beams so hot they would cause wood to catch fire. Over 100 years ago in France, a scientist used heat from a solar collector to make steam to drive a steam engine. In the beginning of this century, scientists and engineers began researching ways to use solar technology in earnest. One important development was obviously a remarkably efficient solar boiler introduced by Charles Greeley Abbott, an american astrophysicist, in 1936.

The solar water heater came into common use at this time in Florida, California, and the Southwest. The industry started in the early 1920s and was in full swing just before The second world war. This growth lasted prior to the mid-1950s when low-cost propane took over as primary fuel for heating American homes.

The public and world governments remained largely indifferent to the possibilities of solar power prior to the oil shortages of the1970s. Today, people use solar technology to heat buildings and water and to generate electricity.

How we use solar energy today ?

Solar energy is used in a number of different ways, of course. There are two very basic types of solar power:

* Solar thermal energy collects the sun's warmth through one of two means: in water or in an anti-freeze (glycol) mixture.

* Solar photovoltaic energy converts the sun's radiation to usable electricity.

Listed below are the five most practical and popular methods solar energy is used:

1. Small portable solar photovoltaic systems. We see these used everywhere, from calculators to solar garden tools. Portable units can be used for everything from RV appliances while single panel systems can be used traffic signs and remote monitoring stations.

2. Solar pool heating. Running water in direct circulation systems through a solar collector is a very practical way to heat water for your pool or spa.

3. Thermal glycol energy to heat water. In this method (indirect circulation), glycol is heated by sunshine and the heat is then transferred to water in a hot water tank. This method of collecting the sun's energy is more practical now than ever. In areas as far north as Edmonton, Alberta, solar thermal to heat water is economically sound. It can pay for itself in 3 years or less.

4. Integrating solar photovoltaic energy into your home or office power. In numerous parts on the planet, solar photovoltaics is an economically feasible method to supplement the power of your property. In Japan, photovoltaics are competitive with other kinds of power. In america alone, new incentive programs make this form of solar technology ever more viable in many states. A frequent and practical method of integrating solar energy into the power of your home or business is through the use of building integrated solar photovoltaics.

5. Large independent photovoltaic systems. For those who have enough sun power at your site, you may be able to go off grid. You may also integrate or hybridize your solar energy system with wind power or other forms of renewable energy to stay 'off the grid.'

How can Photovoltaic panels work ?

Silicon is mounted beneath non-reflective glass to create photovoltaic panels. These panels collect photons from the sun, converting them into DC electrical power. The power created then flows into an inverter. The inverter transforms the energy into basic voltage and AC electricity.

Solar cells are prepared with particular materials called semiconductors like silicon, which is presently the most generally used. When light hits the Photovoltaic cell, a particular share of it is absorbed inside the semiconductor material. This means that the energy of the absorbed light is given to the semiconductor.

The power unfastens the electrons, permitting them to run freely. Solar cells also have one or more electric fields that act to compel electrons unfastened by light absorption to flow in a specific direction. This flow of electrons is a current, and by introducing metal links on the top and bottom of the -Photovoltaic cell, the current can be drawn to use it externally.

What are the positives and negatives of solar energy ?

Solar Pro Arguments

- Heating our homes with oil or propane or using electricity from power plants running with oil and coal is a reason for climate change and climate disruption. Solar power, on the contrary, is clean and environmentally-friendly.

- Solar hot-water heaters require little maintenance, and their initial investment can be recovered in just a relatively limited time.

- Solar hot-water heaters can work in almost any climate, even in very cold ones. You just have to choose the best system for your climate: drainback, thermosyphon, batch-ICS, etc.

- Maintenance costs of solar powered systems are minimal and also the warranties large.

- Financial incentives (USA, Canada, European states…) can reduce the cost of the initial investment in solar technologies. The U.S. government, for example, offers tax credits for solar systems certified by by the SRCC (Solar Rating and Certification Corporation), which amount to 30 percent of the investment (2009-2016 period).

Solar Cons Arguments

- The first investment in Solar Hot water heaters or in Photovoltaic Electric Systems is higher than that required by conventional electric and gas heaters systems.

- The payback period of solar PV-electric systems is high, as well as those of solar space heating or solar cooling (only the solar hot water heating payback is short or relatively short).

- Solar water heating do not support a direct in conjunction with radiators (including baseboard ones).

- Some air conditioning (solar space heating and the solar cooling systems) are expensive, and rather untested technologies: solar air-con isn't, till now, a truly economical option.

- The efficiency of solar powered systems is rather influenced by sunlight resources. It's in colder climates, where heating or electricity needs are higher, that the efficiency is smaller.

About the Author - Barbara Young writes on motorhome solar battery charger in her personal hobby blog Her efforts are focused entirely on helping people save energy using solar powered energy to lower CO2 emissions and energy dependency. 

Tuesday, June 8, 2010

iPhone 4 with novel features

iPhone 4 with novel features
    Apple has unveiled  a novel i-phone with novel features. The so called 4 G technology has been a new boom to the phone era. As the taste of mobile phone user have been changing day by day, this is an another milestone in the phone era. The competition among introducing new phones have been a thrust in adding new features. According to Apple, the new phone is chemically strengthened and 30 times harder than plastic material and scratch proof.  

The features can be listed here,

• 5 megapixel camera with LED flash
• A4 processor as the iPad
• Second microphone for noise cancelling
• 720p (30 frames per second) video recording with tap to focus
• 802.11n Wi-Fi
• Quad-band HSUPA (7.2Mbps down, 5.8Mbps up)
• "FaceTime" video calls (Wi-Fi only)
• 960 x 640 "Retina" display
• 3-axis gyro in addition to the accelerometer for PS3-style 6-axis motion control
• Seven hours 3G talk time, six hours 3G web browsing, 10 hours video playback
• 9.3mm thick
• iOS 4.0 with multitasking and folders
• iMovie app for $4.99
• iBooks app (free)
• Official Apple case for $29
• $199 for the 16GB and $299 for the 32GB model
• 8GB iPhone 3GS will be available for $99

This novel phone is available:

The iPhone 4 will be available in the US, UK, France, Germany and Japan on June 24, and in Australia, Austria, Belgium, Canada, Denmark, Finland, Hong Kong, Ireland, Italy, Luxembourg, Netherlands, Norway, New Zealand, Singapore, South Korea, Spain, Sweden and Switzerland by the end of July

Wednesday, April 21, 2010

Photo Diode and its applications

Silicon photodiodes are semiconductor devices responsive to high energy particles and photons. Photodiodes operate by absorption of photons or charged particles and generate a flow of current in an external circuit, proportional to the incident power. Photodiodes can be used to detect the presence or absence of minute quantities of light and can be calibrated for extremely accurate measurements from intensities below 1 pW/cm2 to intensities above 100 mW/cm2. Silicon photodiodes are utilized in such diverse applications as spectroscopy, photography, analytical instrumentation, optical position sensors, beam alignment, surface characterization, laser range finders, optical communications, and medical imaging instruments.

Planar diffused silicon photodiodes are simply P-N junction diodes. A P-N junction can be formed by diffusing either a P-type impurity (anode), such as Boron, into a N-type bulk silicon wafer, or a N-type impurity, such as Phosphorous, into a P-type bulk silicon wafer. The diffused area defines the photodiode active area. To form an ohmic contact another impurity diffusion into the backside of the wafer is necessary. The impurity is an N-type for P-type active area and P-type for an N-type active area. The contact pads are deposited on the front active area on defined areas, and on the backside, completely covering the device. The active area is then deposited on with an anti-reflection coating to reduce the reflection of the light for a specific predefined wavelength. The non-active area on the top is covered with a thick layer of silicon oxide. By controlling the thickness of bulk substrate, the speed and responsivity of the photodiode can be controlled. Note that the photodiodes, when biased, must be operated in the reverse bias mode, i.e. a negative voltage applied to anode and positive voltage to cathode.
Silicon is a semiconductor with a band gap energy of 1.12 eV at room temperature. This is the gap between the valence band and the conduction band. At absolute zero temperature the valence band is completely filled and the conduction band is vacant. As the temperature increases, the electrons become excited and escalate from the valence band to the conduction band by thermal energy. The electrons can also be escalated to the conduction band by particles or photons with energies greater than 1.12eV, which corresponds to wavelengths shorter than 1100 nm. The resulting electrons in the conduction band are free to conduct current. Due to concentration gradient, the diffusion of electrons from the Ntype region to the P-type region and the diffusion of holes from the Ptype region to the N-type region, develops a built-in voltage across the junction. The inter-diffusion of electrons and holes between the N and P regions across the junction results in a region with no free carriers. This is the depletion region. The built-in voltage across the depletion region results in an electric field with maximum at the junction and no field outside of the depletion region. Any applied reverse bias adds to the built in voltage and results in a wider depletion region. The electron-hole pairs generated by light are swept away by drift in the depletion region and are collected by diffusion from the undepleted region. The current generated is proportional to the incident light or radiation power. The light is absorbed exponentially with distance and is proportional to the absorption coefficient. The absorption coefficient is very high for shorter wavelengths in the UV region and is small for longer wavelengths (Figure 2). Hence, short wavelength photons such as UV, are absorbed in a thin top surface layer while silicon becomes transparent to light wavelengths longer than 1200 nm. Moreover, photons with energies smaller than the band gap are not absorbed at all.

• Photodiodes are used in applications similar to photodetectors, photoconductors, charge coupled device and photo multiplier tubes
• Photodiodes are used in consumer electronic devices such as VCRs, televisions, smoke detectors and compact displays
• They are often used for fire sensing in industries and they have better linear response than photoconductors
• They are also widely used in various medical applications such as detectors for computer tomography, pulse oximeters etc

Tuesday, April 20, 2010

Relay Design and Operation

Basics of Relay:

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism, but other operating principles are also used. Relays find applications where it is necessary to control a circuit by a low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays found extensive use in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly drive an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching. Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called "protection relays".

Design and Operation:
A simple electromagnetic relay, such as the one taken from a car in the first picture, is an adaptation of an electromagnet. It consists of a coil of wire surrounding a soft iron core, an iron yoke, which provides a low reluctance path for magnetic flux, a movable iron armature, and a set, or sets, of contacts; two in the relay pictured. The armature is hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke. This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board (PCB) via the yoke, which is soldered to the PCB.
When an electric current is passed through the coil, the resulting magnetic field attracts the armature, and the consequent movement of the movable contact or contacts either makes or breaks a connection with a fixed contact. If the set of contacts was closed when the relay was De-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing.
If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a voltage spike dangerous to circuit components. Some automotive relays already include a diode inside the relay case. Alternatively a contact protection network, consisting of a capacitor and resistor in series, may absorb the surge. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid. This "shading ring" creates a small out-of-phase current, which increases the minimum pull on the armature during the AC cycle
By analogy with the functions of the original electromagnetic device, a solid-state relay is made with a thyristor or other solid-state switching device. To achieve electrical isolation an optocoupler can be used which is a light-emitting diode (LED) coupled with a photo transistor.

Relays are used to and for:
• Control a high-voltage circuit with a low-voltage signal, as in some types of modems or audio amplifiers,
• Control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile,
• Detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers (protection relays)

ARM processor and Its features

 ARM processor and Its features
Most of the Engineering Projects are in need of using advanced processors. In this scenario, ARM processor play a vital role. This article gives an over all features of ARM processor compared with conventional Micro controllers.
The LPC2148 microcontrollers are based on a 32/16 bit ARM7TDMI-S CPU with real-time emulation and embedded trace support, that combines the microcontroller with embedded high speed flash memory ranging from 32 kB to 512 kB. A 128-bit wide memory interface and unique accelerator architecture enable 32-bit code execution at the maximum clock rate. 
For critical code size applications, the alternative 16-bit Thumb mode reduces code by more than 30 % with minimal performance penalty. Due to their tiny size and low power consumption, LPC2148 are ideal for applications where miniaturization is a key requirement, such as access control and point-of-sale. A blend of serial communications interfaces ranging from a USB 2.0 Full Speed device, multiple UARTS, SPI, SSP to I2Cs and on-chip SRAM of 8 kb up to 40 kb, make these devices very well suited for communication gateways and protocol converters, soft modems, voice recognition and low end imaging, providing both large buffer size and high processing power. 
Various 32-bit timers, single or dual 10-bit ADC(s), 10-bit DAC, PWM channels and 45 fast GPIO lines with up to nine edge or level sensitive external interrupt pins make these microcontrollers particularly suitable for industrial control and medical systems.


• ARM7TDMI-S microcontroller is a 16/32-bit microcontroller.
• 8 to 40 kb of on-chip static RAM and 32 to 512 kb of on-chip flash program memory.
128 bit wide interface/accelerator enables high speed 60 MHz operation.
• In-System/In-Application Programming (ISP/IAP) via on-chip boot-loader software.
Single flash sector or full chip erase in 400 ms and programming of 256 bytes in 1 ms.
• One or two (LPC2141/2 vs. LPC2144/6/8) 10-bit A/D converters provide a total of 6/14
analog inputs, with conversion times as low as 2.44 μs per channel.
• Single 10-bit D/A converter provides variable analog output.
• Two 32-bit timers/external event counters (with four capture and four compare
channels each), PWM unit (six outputs) and watchdog.
• Low power real-time clock with independent power and dedicated 32 kHz clock input.
• Multiple serial interfaces including two UARTs (16C550), two Fast I2C-bus (400 kbit/s), SPI and SSP with buffering and variable data length capabilities.
• Vectored interrupt controller with configurable priorities and vector addresses.
• Up to 45 of 5 V tolerant fast general purpose I/O pins.
• Up to nine edge or level sensitive external interrupt pins available.
• 60 MHz maximum CPU clock available from programmable on-chip PLL with settling time of 100 μs.
• On-chip integrated oscillator operates with an external crystal in range from 1 MHz to 30 MHz and with an external oscillator up to 50 MHz.
• Power saving modes include Idle and Power-down.
• Individual enable/disable of peripheral functions as well as peripheral clock scaling for additional power optimization.
• Processor wake-up from Power-down mode via external interrupt, USB, Brown-Out Detect (BOD) or Real-Time Clock (RTC).
• Single power supply chip with Power-On Reset (POR) and BOD circuits:
– CPU operating voltage range of 3.0 V to 3.6 V (3.3 V ± 10 %) with 5 V tolerant I/O pads.

Tuesday, April 6, 2010

Grid Computing Vs Clusters

I recently attended a seminar on Grid Computing. In this seminar, a common questions was asked by the participants. The question is, what is the main difference between Grid Computing and Cluster computing?. I would like to share a glimpse of these two.
If a number of computers are used together to solve a problem over internet is called cluster of computer. On the other hand, The cooperation among the computers to solve a problem is called as cluster of computing.
In Grid computing, though the same concept as cluster computer, however it is used for solving large problems. The main difference is that cluster is homogeneous, where as grid is heterogeneous. The cluster of cluster is also called as grid computing. Homogeneous in cluster means the computers are of same hardware and OS. The computers on the part of a grid run different OS and different hardware. Grid is normally distributed over Lan or Wan.

Monday, April 5, 2010

All Built in Application – Apple’s iPad.
This device is really fantastic invention in the Modern world technology. While I watched it through a TV news, it is unbelievable to see its all the features.
The features are
Multi Touch screen capabilities
We can completely experience the world with its unique Web feature.
No keyboard, no mouse are required, however all can be done with our figures for surfing
The way of typing and sending emails is totally different
The photo viewing capabilities are really extraordinary
With its video applications, watching HD movies, TV shows, podcasts and music videos are giving us nice experience
The Youtube applications is specifically designed to view through ipad
The other features are ipod (for music) and iTunes
Though I have listed all, I watched it only on a TV news. In future would like to have such a fantastic device here with me.

Monday, February 22, 2010

Trends in Wireless Technologies Dash7 A Nnovel Wireless scheme

Trends in Wireless Technologies
The world is completely occupied with Computer networks. Wireless network in particular plays a major role. Wireless data networks includes , . Normally Bluetooth, Zigbee are intended with low power and low band width digital communications.
The Zigbee network uses airwaves to connect lamps, lighting switches, electric meters, thermostats and other electric appliances. The Zigbee network employs 868 Mhz, 915 MHz and 2.4 GHz.
We use bluetooth enabled computers, laptops and mobile phones for transferring data and files between the devices.
The recent new network scheme is Dash7 which uses less power compared with other schemes. This can be used as RFID (Radio frequency Identification) tag in order to work for years without any external power source. The actual RFID tag employ passive devices and draw energy from radio waves by their readers emit.
Dash7 tags are active and uses very small batteries. Dash7 readers do not have to transmit high power RF and cost effective compared with other devices. Dash7 can communicate with tags located with 100 m away. Dash7 works with 433 MHz which is global level. The antenna is very compact as the wavelength is 70 cm.

Courtesy : wikipedia
DASH7 features include:
* Operation at 433 MHz, globally available, unlicensed spectrum
* Based on ISO 18000-7 standard
* Multi-year battery life
* Range of up to 2 km (potentially farther)
* Penetration of concrete walls, water, and ability to "bend" around metal objects
* Low latency protocol that enables reliable tracking of moving objects
* Small, lightweight protocol stack that minimizes silicon costs
* Data transfer at up to 27.77kpbs (potentially as high as 250kpbs)
* Sensor & security support

While comparing other schemes, Dash7 is neither Wi-Fi nor Bluetooth nor Zigbee.

Friday, January 15, 2010

Full Solar Eclipse 2010 in Tamilnadu, India

Full Solar Eclipse in Tamilnadu

A full solar eclipse was seen at Kanyakumari, South of Tamilnadu, India which is called as Kanganam (Ring or Bangle shape) Solar Eclipse. This is also called as Ring of fire.
This is wonderful to see after a long gap say 108 year. This eclipse started on 15.01.2010, 11.45 am to 1.20 pm and the full eclipse lasted for about 10 minutes. The moon covered fully the sun during 1.10 to 1.20 pm.
The last time India saw this ‘Ring of Fire’ was November 22, 1965. The next longest annular solar eclipse will only be seen in 3043. I watched this amazing event only on TV.

Monday, January 4, 2010

Hummingbird Robot for rescuing humans

Hummingbird Robot for rescuing humans
Japanese researchers have unveiled a robot seems to be a Hummingbird which can fly around in mid air with rapid wing movements. This robot is equipped with a micro motor with four wings which can flutter 30 times per second. It is controlled by an infrared sensor for controlling left, right, up and down movements.

The robot weighs only 2.6 grams (0.09 ounces), However it can not stay at one point at the mid air. Their next step to do research to make it hover at one point in the mid air. They have also planned to fit a micro camera with the robot in order to help rescue humans trapped in destroyed buildings during earthquake, search criminals or to probe vehicles on other planets.

This wonderful robot cost about 2.1 million dollars for design and developed. Though this is too costly, the robot seems very amazing in the technology era.

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