The old days of finding a job right out of school and sticking with it until retirement are certainly in the past. In these modern times, people have become more adept at locating new job opportunities. But some of the more traditional tactics have started to fade in popularity; no longer are people looking solely at the newspaper want-ads to find their dream jobs. Job seekers are becoming more creative and utilizing new strategies in moving their careers forward.

1. Networking
It is said that the majority of job vacancies are never advertised, often referred to as the “hidden job market.” To land these jobs, seekers will need to find a way to get a foot in the door. Networking can go a long way in locating job opportunities; even if no one you know directly has knowledge of a job opening, there’s a chance they know someone who does.

Networking can be done both in person and online. You can join professional associations, attend events for graduates of your school, or aim to connect with professionals who work in your field. Various online tools also exist, such as LinkedIn, which allow you to network with other professionals and learn out about possible job openings. You may also be able to meet other professionals through social networking sites like Facebook or Twitter.

2. Referrals
Referrals also come from individuals you know,however, this method may get you an invitation to apply for a position without actually searching for a new a job. Some employers offer incentives to their employees for referring a successful candidate to their company – a win-win situation for everyone. You get a new job, and your contact gets a finder’s fee for attracting a top-notch employee.

3. Job Boards and Career Websites
Job boards were traditionally just that – boards posting vacancies and employment opportunities. Though some of these boards may still exist in a literal sense, many job boards have moved toward a virtual format. Often federal or state governments will provide job boards and job banks that job seekers can access. You can also use job search engines on the internet or the vast number of career-related websites that post job openings, such as or These websites function in a similar way to the traditional want-ads, however, they have a much quicker turnaround time and allow you to search a much larger number of jobs over a large area.

4. Job Fairs
Job fairs are typically targeted toward specific industries, though some job or recruitment fairs are more generalized. These ads will usually come with a list of the organizations that will be present. Investigate any companies that interest you, bring a number of resumes and be ready to sell yourself. Consider any conversations with recruiters as mini interviews that can set you apart from other applicants. Some organizations may even offer on-site interviews to candidates that match their requirements.

5. Company Websites
If you already have your dream employer in mind, why not go directly to the career section of their website? If you watch for openings on their site, there’s a chance you’ll find just the opportunity that you’ve been waiting for. Create a list of employers that you’d like to work for and visit their websites often. If you’re really set on working for a specific company it may take some time to find just the opportunity that fits your skill set. But if you’ve got the luxury of time, this might be the optimal method for finding your dream job.

6. Cold Calling
If you don’t see any job listings posted for a company you’re particularly interested in, you might consider making a cold call. You can use the telephone or email to contact individuals within an organization by finding their contact details on the company website or by inquiring with a receptionist. Contact individuals directly to find out if they foresee any upcoming vacancies, and be sure to attach a copy of your resume to any emails you send. You can also ask for information about types of jobs, or what kind of skills or qualities the organization looks for in a candidate. Keep in mind that this kind of contact may not always be well received, but there is always a chance it’ll give you the inside track on upcoming vacancies.

7. Head Hunters and Recruitment Agencies
If you’re looking for some professional help in your job search, head hunters and recruitment agencies can definitely lend a hand (though in some cases it may come at a price). There are a number of organizations that hire through recruitment agencies because it helps to streamline the lengthy process of locating and interviewing candidates. Head hunters locate individuals to fill a specific vacancy within an organization or find a position for a job seeker who has hired their services. Payment is often based upon commission. Keep in mind that many high schools, colleges and universities have job placement services that can help new graduates to develop their resumes and assist both current students and alumni with their job searches.

8. Temping or Intern ships
Sometimes temporary employment can lead to permanent positions. If you’re without work, finding a temporary position with a great company is a great way to get a foot in the door, or provide you with useful business contacts to call upon in the future. Many recruitment agencies can assist with locating temporary or casual positions and contract work. Intern ships are a great choice for students who are just graduating from college and many schools’ job placement services can connect students with opportunities. Volunteering can also be a great method for gaining valuable industry contacts.

9. Creative or Outlandish Tactics
In a competitive job market, some job seekers have moved toward more creative methods for drawing attention to themselves. Billboards, chain letters with a copy of your resume attached, or even pasting your resume to yourself and walking around the city as a human billboard are just some of the methods individuals have used to get noticed by potential employers. Though these methods can actually work, be cautious. You may get the attention of recruiters, but you may also be sending the wrong message. If you’re going to resort to creative techniques, be sure that it’s appropriate for the industry in which you’re attempting to find employment.

The Bottom Line
In the modern job market, finding the very best job opportunities often requires a combination of methods. Always keep in mind that there are a variety of methods available for finding job opportunities, all with their own strengths and weaknesses, so don’t be shy to experiment with a variety of techniques.






Interested in starting a career or a career change? Thinking about changing jobs? Are you wondering what qualifications are required for a job you’re interested in? Here’s information on what you need to find a job for a variety of different career fields, industries and types of job. 

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                    Logitech Bluetooth Multi-Device Keyboard


The Logitech® Bluetooth® Multi-Device Keyboard K480 is designed for use with up to three devices, regardless of computing platform. Now, you can work on a report on your computer, and with the flick of the Easy-Switch dial, respond to a message on your smartphone or type a tweet on your tablet – all from the Logitech Bluetooth Multi-Device Keyboard K480.

Cost: $49.99

                                       G-DRIVE ev SSD


With a need for speed – take the power of the G-DRIVE ev SSD with you. With extreme solid-state performance connected with USB 3.0, you’ll get transfer rates up to 400MB/s. The drive comes with 512GB of storage capacity and is compatible with Mac OS 10.6, Windows 7, 8 and Vista. It comes with a three-year warranty. Use it alone or with the G-DOCK ev with Thunderbolt and experience up to 480MB/s for the ultimate flexibility and expandability that today’s creative professionals demand.

Cost: $499.95

                                           Logitech Type-S


The Logitech Type-S is a thin and light protective keyboard case for the Samsung Galaxy Tab S 10.5 and protects both sides of your Galaxy Tab S from accidental bumps, scratches and spills. Its built-in Bluetooth® keyboard and well-spaced keys provide a fast and comfortable typing experience. The dual-view stand caters to different activities from typing to reading to chatting online, and includes an auto-wake auto-sleep feature so that the tablet wakes when you open the case. The Logitech Type-S is also now available in bright red.

Cost: $99.99

                               Livescribe Echo Smartpen


The Livescribe Echo Smartpen allows you to record audio while you’re taking notes, and then play them back later. You can save and share interactive notes to your computer, iPad or iPhone via a micro-USB connector that also allows you to recharge your pen. The memory storage holds 400 or 800 hours of recorded audio, depending on the model, and includes an OLED display that makes it easy to navigate smartpen apps.

Cost: Starting at $169.95



The SyrenPro is a wireless weather-resistant outdoor Bluetooth speaker with TrueWireless Stereo pairing, which lets you create your own stereo system wirelessly using two speakers. The speakers can be plugged into an electrical outlet or run by rechargeable battery for up to four hours, so you can enjoy your music anywhere. The speakers provide 360-degree sound, are weather/UV resistant, and work with most Bluetooth devices.

Cost: $129.99

                                       LaCie RuggedKey


The LaCie RuggedKey is built to withstand accidental drops from heights far above what you’d encounter on your way to the office. Its rubber construction is 100-meter drop-resistant. That means ultimate protection for your key – and your data – for all of life’s little stumbles. The RuggedKey has a USB 3.0 interface and file transfer speed of up to 150 MB/s, but it’s also backward compatible with USB 2.0. The USB also comes with AES 256-bit encryption for data security.

Cost: Starts at $39.99



The iFusion is an integrated communications docking station for the Apple iPhone. Combining the capabilities of many top-selling iPhone accessories into a single device, the iFusion utilizes built-in Bluetooth technology, a full duplex speaker phone and a patented ergonomic design to deliver superior voice quality that meets the requirements of today’s home and business consumer.

The cradle design of the iFusion supports the iPhone 3G, 3GS and 4, providing a means to securely dock the phone while supplying power, battery charging and data synchronization via an integrated USB cable. With support for A2DP Bluetooth streaming, users are able to enjoy their favorite iPhone music over the internal speakerphone.

Cost: $169

                             NEC VE281 Mobile Projector


NEC’s VE281 mobile projector is designed to provide high brightness for small-to-medium-sized businesses, education environments, corporate conference rooms and mobility applications where heavy ambient light is present but the space requires a small projector. This lightweight model includes 3D-ready technology, high-contrast images and a powerful 7W speaker. Its automated technologies — from Auto Power On and quick startup/shutdown to a lamp life up to 6000 hours — make it an eco-friendly choice. The VE281 offers the Intelligent Driving Scheme (IDS2) for increased lamp life and contrast.

Cost: $339

                             Photo iPad Scanning Dock


This is the scanner that saves treasured photos directly to an iPad while it docks and charges the device. Controlled by a free app, the sheet-fed scanner makes it simple to preserve and share heirloom photos and documents as digital files. In as little as 12 seconds, a photo is converted to a crisp 300- or 600-dpi color JPEG image that is displayed on screen in real time and saved to the iPad’s camera roll. The integrated dock holds the iPad upright and has a built-in Lightning connector that recharges its battery in five hours. Scans sheets up to 8 1/2″ x 14″. Plugs into AC with your iPad’s USB power adapter. For iPad 4, iPad Mini, and iPhone 5/s/c running iOS 6.0 or later. 4 1/2″ H x 13″ W x 4″ D. (1 3/4 lbs.)

Cost: $169.95

                                        WOWee One Slim


The WOWee One Slim is a compact portable speaker unit which provides a full range frequency response. It is intended for use as both a fixed and portable solution for all iPod, iPad, mp3, mp4, mobile phone and computer applications. It uses the same hybrid technology as the WOWee ONE and produces an incredible bass sound with a 40Hz – 20kHz sound range.

The unit is powered by an internal rechargeable battery and can deliver up to 10 hours of playtime per charge. It can be recharged via computer USB or a 5V USB power adapter using a plug. There is also a built in LED low battery indicator.

Cost: $39.95




                       What is Voltage drop

A voltage drop occurs whenever electrical current passes threw a point of resistance. To recap from last months article we learned Voltage is the force that makes electrons flow and Amperage is the actual flow of electrons. Resistance restricts the flow of electrons. A good analogy that can help you understand this is to compare the flow of electricity in a conductor to the flow water in a pipe. Voltage can be compared to water pressure. Amperage is measured in electrons per second where as water flow is measured in gallons per minuet. Electrical resistance restricts the flow of electrons. This can be compared to a partially clogged pipe restricting the flow of water. Imagine a 1” water pipe with a section in the middle that is reduced down to ¼” then increased back to 1”. One side of the pipe is connected to a water supply that delivers an unlimited amount of water at 50 PSI (pounds per square inch). The other end of the pipe has a valve on it. The ¼” pipe in the middle is the resistance. When the valve on the end is closed and no water is flowing the pressure will be 50 PSI on both sides of the ¼” resistance. As the valve is opened water will start flow. As long as the water supply can supply enough current the pressure on the up stream side of the ¼” restriction will stay at 50 PSI. The pressure down stream of the ¼” restriction will start to drop. The wider you open the valve the more water current will increase and the pressure after the resistance will drop. When the valve is closed and the flow of current stops the pressure will equalize. Pressure on both sides will be the same and there will be no pressure drop. What we learn from this is if there is no current flowing there will be no voltage drop. As the current increases, so does the voltage drop.


                        Where do voltage drops happen?

The fact of the matter is that all conductors have resistance. Some just have more than others. Resistance is measured in Ohms. The resistance of a wire depends on the material the wire is made of, the size or gauge and length of the wire. 12-gauge copper wire has 1.588 ohms per thousand feet. 16-gauge wire has 4.016 ohms per thousand feet At 68° F. The 12-gauge wire has less than half the resistance of the 16-gauge wire. For low current applications a small wire will do. As amperage requirements increase it is necessary to use a larger wire to keep the voltage drop within reason. Not to mention the energy lost when the voltage is dropping is turned in to heat. An excessive voltage drop can make enough heat to melt insulation and even burn up wires. The resistance of the wire should not change over time. The main source of resistance in the wiring system is at connections.  Every place there is a connection there is a place for a bad connection. This is where you should look for excessive voltage drops. The resistance of a new clean connector depends on the contact surface areas and the amount of force between the two surfaces. Over time the resistance can increase due to corrosion and possibly becoming lose. To calculate the effect of increasing resistance compared to voltage drop we can use ohms law. Ohms law states that it takes one volt to push one amp through a one-ohm resister. Using this formula, if you know two of the components you can find the third. For instance if you have 10 amps flowing through a 1 ohm resister there will be a 10 volt drop across the resister. A vary small resistance can make an unacceptable voltage drop. A derivative of ohms law states I X R=V. V is the voltage drop across the resistance. I stands for intensity, which is another term for current. R is the resistance measured in ohms. Lets look at some scenarios.

In the case of my FXR the headlight draws 5 amps.

5amps X .6 ohms = 3 Volt drop

This means the circuit had 0.6 ohm between the battery and the headlight. Some of this was between the positive terminal and the light bulb and some was between the bulb and the negative battery terminal.

In the case of an electric starter that draws 100 amps with .05 ohms in the circuit

100 amps X .05ohms = 5 volt drop

That would leave 7 volts at the starter motor, which would be unacceptable.

The average ohmmeter is not accurate enough to read tenths of an ohm. This is why it is better to use a voltmeter to find bad connections that cause unacceptable voltage drops.

                                    Voltage Drop Parameters

When a certain amount of energy is lost to the wire that’s carrying it, or voltage drop, is a normal electric function within certain parameters. Depending on the type of circuit, its amperage, its length, the type of conductor, and its load, national and local electrical codes set guidelines for the maximum voltage drop allowed in a circuit. This not only ensures efficient distribution of energy and proper operation of the equipment being powered, but it also speaks to electrical safety issues. Generally, for power efficiency, the National Electric Code (NEC) holds a recommended standard of 5% maximum voltage drop.

                            Causes of Excess Voltage Drop

When excess voltage drop occurs, it’s caused by too much resistance in the wire, which lowers the amount of power that reaches the “load,” or what’s drawing the electricity from its source. This is typically caused by a wire that doesn’t meet code standards, meaning it isn’t appropriate for that particular circuit. A high-resistance connection can also be caused by poor splicing, loose or intermittent connections, or corroded connections within the circuit.

                      Consequences of Excess Voltage Drop

When the voltage drop is too steep, it can cause the load to work harder with less voltage pushing the current. Overall, this leads to poor efficiency and wasted energy. A low voltage to the equipment being powered can also cause improper, erratic, or ceased operation, which can ultimately result in damage to the equipment. Even more alarming, heating a high-resistance voltage connection can result in a fire if it’s in contact with a combustible material or there isn’t enough air flow to dissipate the heat.

In electric design and power transmission, voltage drop needs to be taken into consideration. Electricians can always use various techniques to compensate for the effect of voltage drop, the most simple being to increase the diameter of the conductor between the source and the load, thereby lowering the overall resistance.








Strain Meter

Posted: February 4, 2014 in DIY

This strain meter shows whether the strain is compressive (reducing the length) or tensile (increasing the length) when an object such as a strut on a crane changes its shape. The strain is sensed by a strain gauge that is glued to the object being tested. The change in resistance of the strain gauge produces a change in the reading of the meter. For the purpose, an analogue or digital meter, such as a voltmeter, can be used that has full-scale deflection of 1V DC. But use of a digital multimeter would be better.

The circuit shows how a single op-amp IC 741 (IC3) amplifies the output from a network of three resistors (R1 through R3) and strain gauge SG1. Since the nominal resistance of the strain gauge recommended for this circuit is 120 ohms, each of resistors R1 through R3 should have a value of 120 ohms. The resistors should also have a tolerance of better than 0.1 per cent so that any change in the temperature doesn’t cause unwanted change in the reading of the meter.

Working of the circuit is simple. When the strain gauge is unstrained, variable resistors VR1 (coarse control) and VR2 (fine control) are set to give a zero reading on the multimeter. (This zero voltage may instead be any convenient voltage, such as 1.5V, and not necessarily a zero voltage supply for the circuit.) If the meter reading increases, it indicates that the strain gauge is undergoing an increase in length (tensile strain). If the meter reading decreases, the strain gauge is undergoing a decrease in length (compressive strain).


Using variable resistor VR2, you can adjust the sensitivity of the op-amp (IC3) and therefore enable the circuit to respond to different magnitudes of the strain. +5V and -5V supply voltages provided by voltage regulators IC1 and IC2, respectively, assure stable readings on the meter. The op-amp amplifies the output from the Wheatstone bridge.Assemble the circuit on a general-purpose PCB. Use appropriate PCB sockets to terminate the wire ends for connecting the strain meter to the multimeter, battery and strain gauge.Use Araldite to glue the strain gauge to the surface of a 150×10×1mm3 strip of plastic pad. Plug the strain gauge into the strain meter. Use a digital multimeter to measure negative voltages since this makes setting up easier.

The strain meter needs to be set up such that when the strain gauge is unstrained, the output voltage is about 0.5V. If the plastic strip is bent such that the strain gauge becomes slightly longer (tensile stress), the output voltage should increase, and if it is bent such that the strain gauge becomes slightly shorter (compressive stress), the output reading should decrease.

The setting is done by adjusting multiturn trimmers VR1 and VR2 using an adjusting tool made for the job. Proceed as follows:
1.Set the multimeter to 0V to 5V DC range.
2.Keep S1 in ‘LO’ position.
3.Adjust VR1 and VR2 until the reading on the voltmeter is about +0.5V.
4.Check whether the reading on the voltmeter changes when you bend the plastic strip.
5.Switch the multimeter to its 1V range, bend the strip again and then mark the response. If the response is not sensitive enough, flip switch S1 to ‘HI’ position. Readjust VR1 to make sure that the reading is still within the range. You may increase the gain by increasing the values of resistors R6 and R7.


Digital Soil Moisture Tester

Posted: February 4, 2014 in DIY

Here is a simple and compact digital soil moisture tester to check whether the soil is dry or wet. It can also be used to check the dryness or wetness of cotton, woolen and woven fabrics. For indication, the tester (see Fig.1) uses a number of LEDs driven by ubiquitous display driver IC LM3915 (IC1). The display panel shows the relative magnitude of conductance (reciprocal of resistance) between the two test probes when these are inserted in the soil.



The tester measures the dryness or wetness through soil resistance readings (0 to about 5 kilo-ohms) and indicates in dot mode by sequential lighting of LED1 through LED9. The first LED (LED1) lights up when the conductance is high (resistance is almost nil).

Normally, the soil resistivity varies from 0 to about 5 kilo-ohms. So for calibration, connect a 5-kilo-ohm potmeter between the two probes. Using trimpot VR1, set resistance to zero (minimum). LED1 should glow. Similarly, set resistance to 5 kilo-ohms (maximum). Now, LED9 should glow.

Assemble the circuit on a general-purpose PCB. After construction, enclose the tester (including battery) in a small plastic cabinet as shown in Fig. 2. The probes can be constructed from a pair of new injection needles. The needles should be firmly fixed about 2.5 cm apart on a piece of laminated plastic sheet. Use short length of a flat, twin wire-lead flexible cable for interconnection. After wiring the circuit, power the circuit using switch S1 and adjust zero-set trimpot (VR1) slowly such that LED1 lights up when probes are shorted. The tester is best powered by a compact 9V alkaline battery

                 OLED Display Technology

During the last two decades, organic light-emitting diodes (OLEDs) have attracted considerable interest owing to their promising applications. They have already made inroads into the displays used for mobiles, PDAs and OLED TVs are also available in the market. Soon, OLEDs will be replacing incandescent and fluorescent lamps.
 OLEDs, based on electroluminescence, are energy conversion devices. They convert electricityinto light. Electroluminescence is the emission of light from materials in an electric field. In 1960, hole injection into an organic crystal was first observed by Martin Pope and his group in anthracene. Three years later, they also observed electroluminescence (EL) from single crystal anthracene and an impurity-doped one under direct current. Despite the high quantum efieciency obtained with such organic crystals, no applications emerged due to the requirement of high working voltage(above 400 V) for visible emission. Subsequently, Helfrich and Schneider achieved double injection recombination electroluminescence in single crystal anthracene using electron and hole injecting electrodes with voltages reduced to ~60 V for observable emission.
In 1987, Van Slyke   and C. Tang from Eastman Kodak developed a novel heterostructure- double layered device containing active “small  molecules”. The two thin-film organic layers independently were responsible for hole and electron transport. The device provided good brightness (>1000 cd/m2), low operating voltages (<10V)  and respectable luminous efficiency (1.5 lm/W), research gained the momentum. Additionally, the device showed rectifier behavior, giving rise to the term OLED (organic light emitting diode). This discovery stimulated explosive development of this field.
OLED is an emissive technology; they emit light instead of diffusing or reflecting a secondary source.
OLED is an acronym for Organic Light Emitting Diode. OLED is a self light-emitting technology which consists of a number of semiconducting organic layers sandwiched between two electrodes at least one of them being transparent. Transparent electrode is composed of electric conductive transparent Indium Tin Oxide (ITO) coated glass substrate.
A simplified device structure is shown in following figure. The device on the left has one transparent electrode and emits light on one side only. The device on the right uses both the electrodes as  transparent ones and it emits light in both top and bottom direction.
OLEDs are extremely thin, practically 2- dimensional multi-layer devices. The thickness of all the active layers put together is of the order of a 100 nm. This is extremely useful in space critical applications, such as in aircrafts. Also, these devices can work in subzero temperatures and hence can be significance for military applications as well.
OLED devices have no restriction on the size and shape. Every conceivable shape, including flexible ones, can be provided.  The devices can be in form of fibers, and woven to fabrics. They can be bent, rolled into films or it can constitute the surface of spheres. For lighting applications, thin glass substrates can be used.
OLEDs are extremely thin, practically 2- dimensional multi-layer devices. The thickness of all the active layers put together is of the order of a 100 nm. This is extremely useful in space critical applications, such as in aircrafts. Also, these devices can work in subzero temperatures and hence can be significance for military applications as well.
OLED devices have no restriction on the size and shape. Every conceivable shape, including flexible ones, can be provided.  The devices can be in form of fibers, and woven to fabrics. They can be bent, rolled into films or it can constitute the surface of spheres. For lighting applications, thin glass substrates can be used.

                         MATERIALS FOR OLED

OLEDs consist of multiple layers – Cathode, Election Injection Layer(EIL), Electron Transport Layer(ETL), Emission Layer(EML), Hole Transport Layer(HTL), Hole Injection Layer(HIL) and the anode. The multi-layer structure is shown in the following figure

An extremely thin layer of indium tin oxide is used as anode; thin layer is used as it has to be optically transparent.  For cathodes, low work-function metals like Li, Mg, and their alloys with Ag or Al are used.
Various types of organic materials are used for the functional layers of OLEDs. Since all emission materials are not good for electron or hole transport, different materials for different functions are used. Also, stability of single material emission layer is not good, dye dopants are used for stabilized OLED emission and color tuning.
·         Electron Transport Materials
Most prominent OLED material is Alq. Not only is it a very good emissive material, it is also a good electron transport material. Another electron transport material used is ADN.
      ·         Hole Transport Materials
There are several established hole transport materials, but the mature ones are NPD and TPD; both are used in OLEDs.
      ·         Dyes
Main purpose of the dyes is – color tuning and color stabilization.
Rubrene is used to dope Alqfor yellow emission.  DCM II and DCJTB are used to dope Alqfor red emission. C545 is used for green color stabilization and Perlene is used for blue color stabilization.
Based on the two classes of electroluminescence materials used in organic light emitting devices, two types of OLEDs are available. Electroluminescence is similar in both types; the difference is in the deposition of the organic films
·         Polymer based LEDs(PLED)
Polymers are bigger molecules and hence cannot be thermally deposited. Polymer OLEDs are made by depositing the polymer materials on substrates through inkjet printing process or other solution processing methods(also referred to as ‘wet process’) under ambient conditions. They are used for fabrication of large size screens.
Polymeric OLED devices usually have fewer layers. The electro-active polymers may serve number of functions: some may act as electron transport as well as electon injection and even as emission layer and similarly, some polymers act as hole transport as well as light emission. Dopant emitters are often used for colour tuning. Polymer device structure is shown below. It is bi-layer structure made from solution.ll
OLED-5.jpgPolyaniline (PANI:PSS)
.    Polyethylenediooxythiophene(PDOT:PSS)
Emissive polymers are
.   Polyphenylenevinylene (R-PPV)
.   Polyfluorene(PF)
·   Small molecule materials (SM-OLED)
Small molecular OLEDs are made by vacuum evaporating (also referred to as ‘dry process’ small molecules to the substrate. Since small molecules do not exhibit any orientating property and therefore form amorphous films.
Small molecular device structure is shown below. It is a multilayer structure made all in vacuum.
Hole Transport small molecules are
.   Metal-phthalocyanines
.   Arylamines, starburst amines
Emissive small molecules are
.   Metal-chelates, distyrylbenzenes
.   Fluoroscent dyes
Transfer material, Emission Layer material and choice of electrode are the key factors that determine the quality of OLED components.

           OLEDs – HOW DO OLEDs WORK? 

As explained in previous section, OLED consists of multiple layers; each layer is responsible for a certain function. 
When forward bias is applied on the electrodes, electric fields of the order of 105 – 107  V/cm are generated in the active layers though applied voltages are low, from 2.5 to ~ 20 V.  These high electric fields force charges to be injected across the active layers interfaces. Transparent anode injects the holes while cathode injects the electrons. Sometimes, there is difficulty in injecting carriers into the organic layer from the inorganic contacts. So, to facilitate charge injection, Hole Injection Layer and Electron Injection Layer are used in the structure.
Injected holes and electrons from the anode and cathode move inside the material (typically by hopping) and then recombine in the emission layers to form excitons, after which electroluminescence occurs. Radiative relaxation of the excitons generates photons, part of which exit from the transparent side of OLEDs.
The energy level diagram is shown below
Since charge carrier transport relies on hopping process, the conductivity of organic semiconductors is several orders of magnitude lower than that of inorganic counterparts. Also concept of energetic bands is not applicable to organic electronics. Instead of valence and conduction bands, highest occupied and lowest unoccupied molecular orbital (HOMO and LUMO) levels are used.
The color of the photon is a function of the energy difference between the HOMO and LUMO levels of the electroluminescent molecule. The wavelength of the light emission can thus be controlled by the extent of the conjugation in the molecule or the polymer.
The emission color is a material property. Thus, by stacking several different emitting layers in a single device the total emission can be tuned to virtually every colour including white at any color temperature.


Displays are often classified as Active Matrix and Passive Matrix and so does the OLED

1.      Passive Matrix OLEDs (PMOLED) 

Passive Matrix OLEDs (PMOLEDs) consists of an array of strips of cathode and an array of strips of anode. Sandwitched between the two is the organic layer.  The strips of the anode are arranged at right angles to the cathode strips thereby forming a row and column matrix. Pixels are formed at the intersections of the cathode and anode; the pixels are the points where photons are emitted
To illuminate a particular pixel, external circuitry applies current to the row line of anode and column line of the cathode. Thus, the desired pixels can be turned on and off. The brightness of the pixel is governed by the amount of current through the pixel
Passive matrix OLEDs are relatively low cost and are easier to fabricate. However  they are on the higher side in terms of power consumption when compared with other types of OLEDs due to presence of external circuitry. However, power consumption of   PMOLEDs is smaller than that of LCDs.
PMOLEDs can be manufactured economically for small sizes; standard sizes for colour PMOLED are 0.95” and 1.5” and are best suited for small displays of cellphones, PDAs, MP3 players,etc.

          Active Matrix OLEDs(AMOLED)

Huge amount of current is required to achieve adequate brightness in passive matrix OLEDs. This necessitates use of large drive voltages leading to increased power dissipation, more flickering and shortened lifetiemes.
AMOLEDs uses active matrix addressing, where each pixel is defined by its own electrode and driven by circuitry comprising of thin film transistor andcapacitors. The anode is then placed on top of this active-matrix circuitry and the counter electrode, which is not patterned, acts as a ground electrode. In such a device the capacitor is aimed at retaining the information during a frame period.

                               OLED –PROS

OLEDs offer numerous advantages over both LCDs and LEDs, including:

.   Thicknes
The organic layers of an OLED are thinner as well as lighter than the crystalline layers used in LCDs and  LEDs. At present, the thickness of OLEDs is less than 2 mm whereas LCD thickness is 4-6 mm. Thickness of OLEDs is likely to go down further.
.   Flexibility
As OLEDs use plastic substrate instead of glass (used for LCD), OLEDs can be flexible/foldable.
.  Viewing angle
Viewing angles of LCDs have increased significantly to about 170 degrees but at a poor contrast ratio. As LCDs work by blocking light, they have viewing obstacles from certain directions. OLEDs are self emissive, so they have a wider viewing angle. OLEDs are in good approximation Lambertian surface emitter, which means that when viewed from any angle, they have the same apparent radiance.
.  Fast Response Time
OLEDs have very response time of the order of tens of microseconds compared to milliseconds for LCDs. This is important for high speed video.
·  Power
In LCDs, backlighting consumes lot of power. As OLEDs do not need backlighting, their power consumption is much lesser.  Low power consumption is very useful for energy critical handheld devices like cell phones.
.   Emissive technology
OLEDs do not need backlighting, they are self emissive. LCDs functions by selectively blocking areas of the backlight to display the images, while OLEDs light themselves.
.   Ease of fabrication
Fabrication of OLEDs is relatively easier. As OLEDs are essentially plastics, they can be formed into thinner and larger sizes. Liquid crystal displays are difficult to grow and lay down.
.  Photo-biological Safety
OLED emission is harmless in terms of eye safety. 
OLED is probably the perfect technology for the displays; however, they do have some issues, including: 
.  Lifetime: Red OLED and green OLED films have longer lifetimes; typically 10,000 to 40,000 hours. However, blue organics have much shorter lifetimes (around 1000 hours).
.   Manufacturing: Processes are expensive right now.
.   Water: Water can easily damage OLEDs. The organic layers have to be protected against air as they are sensitive to moisture and oxygen and decompose when exposed. Hence they need proper encapsulation
      1.      Small molecule Passive matrix display products 
OLED-14.jpg      2.      Small molecule Active matrix display products 
      3.      Polymer based Active matrix display products
      4.      Polymer based Passive matrix display products