2014 in review

The WordPress.com stats helper monkeys prepared a 2014 annual report for this blog.

Here’s an excerpt:

A San Francisco cable car holds 60 people. This blog was viewed about 660 times in 2014. If it were a cable car, it would take about 11 trips to carry that many people.

Click here to see the complete report.


Automation– Potential future

The word Automation gushes into our mind a lot of thoughts ranging from small machines to  i-robot movie.Although this awakens our interest to know about it,the very next moment we feel that this topic is too tough to be understood by beginners like us.No,this is completely a misconception.This topic is not as complicated as it sounds.If learnt in a proper way suitable to our understanding,it hardly takes time to build a strong base in concept of AUTOMATION.

Automation is generally involved in areas where

  • Requirement of manpower is very high.
  • Rapid and accurate production is required.
  • Products with precision are to be manufactured.
  • Human interaction with manufacturing process is dangerous .

Automation can be defined as :

  1. Automation or automatic control, is the use of various control systems for operating equipment such as machinery, processes in factories, boilers, aircraft and other applications with minimal or reduced human intervention.
  2. The use of computers to control a particular process in order to increase reliability and efficiency, often through the replacement of employees. For a manufacturer, this could entail using robotic assembly lines to manufacture a product.
  3. The definition of automation is the use of machines and technology to make processes run on their own without manpower.

The above three are the top three definitions or meanings that you can find over net for the word Automation.

Though these are enough to understand the basic concept of automation,there is still a lot hidden from this definition.

If you observe the above three points you can realize that though there are many a situations all point out at a common platform: “Automation means making machines capable enough to perform work assigned to them with out our assistance.” There maybe other ways to define it but this can be taken as a basic or common definition to all types of automation.

Automation, now a days have become in integral part of the industry, say any production as well as process industry.Thought why?

ya because, it is progressively increasing the productivity and the profitability of most large organization by rapidly becoming more efficient and competitive by their methods of production , management and other feature it has is reducing the manpower required  for same production thus, yielding large profits.

Now lets go a bit into its working,

Ya true,Automation can be as simple as an automatic ON/OFF operation.But how and what mechanism you involve to make this operation work defines your type or class of automation.

We must a remember a few key points during selecting a mechanism that makes our process automated :

  •  It must far economical when compared to our expenditure  we usually spend on total process.
  • Maintenance cost must be as low as possible.
  • use of ingenuously developed mechanism must be preferred(future maintenance costs and service options must be kept in mind).
  • Though initial investment costs more, reliable components must be used.
  • It is advisable to study in detail the already existing industries utilizing same mechanisms.
  • Interlocks must be planned to ensure safety.

Now let us go through some theoretical aspects of Automation.


Old style H VAC systems used crude thermostats that were limited to on-off control, but some modern systems use more sophisticated sensors and digital controllers for variable speed fans or controlling other functions.

Open and closed loop:

All the elements constituting the measurement and control of a single variable are called a control loop. Control that uses a measured signal, feeds the signal back and compares it to a set point(user defined value), calculates and sends a return signal to make a correction, is called closed loop control. If the controller does not incorporate feedback to make a correction then it is open loop. Timers and sequence controllers using logic, such as those on an elevator, are open loop.

Feedback control:

Feedback control is accomplished with a controller. To function properly, a controller must provide correction in a manner that maintains stability.

Maintaining stability is a principal objective of control theory. Stability means that the system should not oscillate excessively around the set point or get into a situation where it shuts down or runs away.

As an example of feedback control, consider a steam coil air heater in which a temperature sensor measures the temperature of the heated air, which is the measured variable. This signal is constantly “fed back” to the controller, which compares it to the desired setting (set point). The controller calculates the difference (error), then calculates a correction and sends the correction signal to adjust the air pressure to a diaphragm that moves a positioner on the steam valve, opening or closing it by the calculated amount.

The complexities of this are that the quantities involved are all of different physical types; the temperature sensor signal may be electrical or pressure from an enclosed fluid, the controller may employ pneumatic, hydraulic, mechanical or electronic techniques to sense the error and send a signal to adjust the air pressure that moves the valve.

The first controllers used analog methods to perform their calculations. Analog methods were also used in solving differential equations of control theory. The electronic analog computer was developed to solve control type problems and electronic analog controllers were also developed. Analog computers were displaced by digital computers when they became widely available.

Common applications of feedback control are control of temperature, pressure, flow, and speed.

Sequential control and logical sequence or system state control:

Sequential control may be either to a fixed sequence or to a logical one that will perform different actions depending on various system states. An example of an adjustable but otherwise fixed sequence is a timer on a lawn sprinkler.

States refer to the various conditions that can occur in a use or sequence scenario of the system. An example is an elevator, which uses logic based on the system state to perform certain actions in response to its state and operator input. For example, if the operator presses the floor n button, the system will respond depending on whether the elevator is stopped or moving, going up or down, or if the door is open or closed, and other conditions.

An early development of sequential control was relay logic, by which electrical relays engage electrical contacts which either start or interrupt power to a device. Relays were first used in telegraph networks before being developed for controlling other devices, such as when starting and stopping industrial-sized electric motors or opening and closing solenoid valves. Using relays for control purposes allowed event-driven control, where actions could be triggered out of sequence, in response to external events. These were more flexible in their response than the rigid single-sequence cam timers. More complicated examples involved maintaining safe sequences for devices such as swing bridge controls, where a lock bolt needed to be disengaged before the bridge could be moved, and the lock bolt could not be released until the safety gates had already been closed.

The total number of relays, cam timers and drum sequencers can number into the hundreds or even thousands in some factories. Special computers called programmable logic controllers were later designed to replace these collections of hardware with a single, more easily re-programmed unit.

In a typical hard wired motor start and stop circuit (called a control circuit) a motor is started by pushing a “Start” or “Run” button that activates a pair of electrical relays. The “lock-in” relay locks in contacts that keep the control circuit energized when the push button is released. Another relay energizes a switch that powers the device that throws the motor starter switch (three sets of contacts for three phase industrial power) in the main power circuit. All contacts are held engaged by their respective electromagnets until a “stop” or “off” button is pressed, which de-energizes the lock in relay.

Commonly interlocks are added to a control circuit. Suppose that the motor in the example is powering machinery that has a critical need for lubrication. In this case an interlock could be added to insure that the oil pump is running before the motor starts. Timers, limit switches and electric eyes are other common elements in control circuits.

Computer control:

Computers can perform both sequential control and feedback control, and typically a single computer will do both in an industrial application.Programmable logic controllers (PLCs) are a type of special purpose microprocessor that replaced many hardware components such as timers and drum sequencers used in relay logic type systems. General purpose process control computers have increasingly replaced stand alone controllers, with a single computer able to perform the operations of hundreds of controllers. Process control computers can process data from a network of PLCs, instruments and controllers in order to implement typical (such as PID) control of many individual variables or, in some cases, to implement complex control algorithms using multiple inputs and mathematical manipulations. They can also analyze data and create real time graphical displays for operators and run reports for operators, engineers and management.

Control of an automated teller machine (ATM) is an example of an interactive process in which a computer will perform a logic derived response to a user selection based on information retrieved from a networked database. The ATM process has a lot of similarities to other online transaction processes. The different logical responses are called scenarios. Such processes are typically designed with the aid of use cases and flowcharts, which guide the writing of the software code.

Depending on our application and suitability proper mechanism must be planned and implemented.

I just wanted to introduce you with all the basic aspects and terminology dealing with Automation.If this could generate any interest in you go head and dive into depths of automation which i did not cover.

You can preferably start your hunt with different mechanisms and platforms of automation,applications,kind of industries which adapt automation,etc.,

Two sides of AUTOMATION :

Advantages commonly attributed to automation include higher production rates and increased productivity, more efficient use of materials, better product quality, improved safety  shorter workweeks for labour, and reduced factory lead times. Higher output and increased productivity have been two of the biggest reasons in justifying the use of automation. Despite the claims of high quality from good workmanship by humans, automated systems typically perform the manufacturing process with less variability than human workers, resulting in greater control and consistency of product quality. Also, increased process control makes more efficient use of materials, resulting in less scrap.

A main disadvantage often associated with automation is worker displacement.Other disadvantages of automated equipment include the high capital expenditure required to invest in automation.Also there are potential risks that automation technology will ultimately subjugate rather than serve humankind.

These dangers aside, automation technology, if used wisely and effectively, can yield substantial opportunities for the future. There is an opportunity to relieve humans from repetitive, hazardous, and unpleasant labour in all forms. And there is an opportunity for future automation technologies to provide a growing social and economic environment in which humans can enjoy a higher standard of living and a better way of life.










If you  really believe that technology today is at saturation then you are certainly have stopped imagination.Because imagination is mother of all inventions.Now,let us imagine ourselves in some situations which may give us proper reason to know about the current topic.

Imagine having a high-definition TV that is 80 inches wide and less than a quarter-inch thick, consumes less power than most TVs on the market today and can be rolled up when you’re not using it…?

What if you could have a “heads up” display in your car? How about a display monitor built into your clothing? These devices may be possible in the near future with the help of a technology called organic light-emitting diodes (OLEDs).

There are many other jaw dropping applications of OLEDs that can be possible in very near future.

More than the application,the working principle of the OLEDs is astonishing.Let us know about the OLED in detail gradually.

Let us have a look at OLED to know how it looks like instead of wasting time on wrong assumptions.

true-blue-light-emission-brightens-future-for-oled-displays         download (1)


You can have glimpse of more of them over net.

Let’s start from basics:

Principle :

OLED works on the basic principle of Electroluminescence.

Electroluminescence  is an optical phenomenon and electrical phenomenon in which a material emits light in response to the passage of an electric current or to a strong electric field.

The basic principle in simple words of OLEDs is simple: Between two electrodes a layer of OLED-material is dispensed that has a film thickness of only few nanometers.

Working :

A typical OLED is composed of a layer or a couple of organic materials(depending on application) situated between two electrodes, the anode and cathode, all deposited on a substrate(for mechanical support or strength of OLED).

The organic molecules are electrically conductive as a result of delocalization of pi electrons caused by conjugation over part or all of the molecule.



The above picture displays the various layers of an OLED :

Substrate: It is the layer usually on which OLED is laid or printed.It is usually selected transparent because the light is emitted through it.

Voltage is applied across Anode(receives holes) and Cathode(receives electrons).

These holes and electrons due to concentration gradient recombine and emit photons to give out light.The working of an OLED is same as that of normal LED.

Having known the working of an OLED let us see what it offers better than its predecessors.

  1.  OLED’s can be printed from an advanced inkjet printer or even a normal printer,So, manufacturing is much easy and fast.
  2. Better viewing angle(best thing about OLED).
  3. Faster refresh rate(1000 times greater than LCD).
  4. OLED uses or consumes no power when in shut down mode.
  5. Because the light-emitting layers of an OLED are lighter, the substrate of an OLED can be flexible instead of rigid. OLED substrates can be plastic rather than the glass used for LEDs and LCDs.
  6. OLEDs are brighter than LEDs. Because the organic layers of an OLED are much thinner than the corresponding inorganic crystal layers of an LED, the conductive and emissive layers of an OLED can be multi-layered. Also, LEDs and LCDs require glass for support, and glass absorbs some light. OLEDs do not require glass.
  7. OLEDs do not require backlighting like LCDs.

The most important and fascinating feature is that it can be used as a two way transducer i.e., it can be even used to generate electricity when light is focused.

Complications :

  1. Mass production is difficult with available techniques of production.
  2. Very costly.
  3. Lifetime is very less(While red and green OLED films have longer lifetimes (46,000 to 230,000 hours), blue organics currently have much shorter lifetimes).
  4. OLED’s can be easily damaged by water.
  5. For the best production technique available it requires vacuum  and it is an expensive process to create a vacuum in large space.
  6. Even larger displays are complicated to produce with available technology(largest in world is 77 inches display by LG).


Though it seems very advanced in technology ,this technology is still at root levels.There are much more wonder that can be made with this tool.Intense research is being carried out from a decade on this to extrude the best from this.

The main reason why a lot  of time is being taken is because of lot of hurdles faced to implement or manufacture them at large number and economical prices with available technology.There are many complications in the fields of its manufacturing,raw materials,lifetime of OLED’s etc.,

Hope these complications are solved in course of time and come to our use to deliver its best.





Surface Mount Technology (SMT)

The building blocks of any electronic circuit or chip are resistor,capacitor and inductor . The most surprising and astonishing thing regarding these are the contrast between their size and their capabilities(functions).

Many felt about a decade ago that electronic components have reached their smallest size but they were totally wrong.If they had seen today’s electronics industry they would surely take back their word.While handling electronic components like transistor,resistor,etc., they would often slip from between our fingers.We would of course get cross with them but one would surely marvel once they know it’s capabilities. I am one among them.

Electronics industry is mutating and developing from past a set of decades.This is mainly due to R&D being carried out and also due to increase in electronics market today.It is totally due to awareness in public.

The main increase in electronic goods is due to its features like, compactness,small size and flashy fabrications. Let’s concentrate on their size and compactness.They are key features of any electronic goods.

To make this feature even more strong ,rigorous R&D has been carried on it and this has yielded good.The technology used to improve compactness and decrease the size of a circuit has been constantly changing .

Process of development:

SSI   (small-scale integration)

MSI   (medium-scale integration)


VLSI   (very large-scale integration)


SOC     (system-on-a-chip)

3D-IC    (three-dimensional integrated circuit)

SMT (Surface Mounted Technology)

Let’s deal with the latest SMT technology.

Surface-mount technology (SMT) is a method for making electronic circuits in which the components are mounted or placed directly onto the surface of printed circuit boards (PCBs). An electronic device so made is called a surface-mount device (SMD). In the industry it has largely replaced the through-hole technology

Through-hole technology is nothing but construction method of fitting components with wire leads into holes in the circuit board.

Both technologies can be used on the same board for components not suited to surface mounting such as transformers and heat-sinked power semiconductors.

An SMT component is usually smaller than its through-hole counterpart because it has either smaller leads or no leads at all. It may have short pins or leads of various styles, flat contacts, a matrix of solder balls (BGAs), or terminations on the body of the component. Actually components were mechanically redesigned to have small metal tabs or end caps that could be directly soldered to the surface of the PCB. Components became much smaller and component placement on both sides of a board became far more common with surface mounting than through-hole mounting, allowing much higher circuit densities.

Much of the pioneering work in this technology was by IBM,introduced in 1960 in a small-scale computer was later applied in the Launch Vehicle Digital Computer used in the Instrument Unit that guided all Saturn IB and Saturn V vehicles.

Components became much smaller and component placement on both sides of a board became far more common with surface mounting than through-hole mounting, allowing much higher circuit densities. Often only the solder joints hold the parts to the board, although parts on the bottom or “second” side of the board may be secured with a dot of adhesive to keep components from dropping off inside reflow ovens if the part has a large size or weight. Adhesive is also used to hold SMT components on the bottom side of a board if a wave soldering process is used to solder both SMT and through-hole components simultaneously. Alternatively, SMT and throughhole components can be soldered together without adhesive if the SMT parts are first reflow-soldered, then a selective solder mask is used to prevent the solder holding the parts in place from reflowing and the parts floating away during wave soldering. Surface mounting lends itself well to a high degree of automation, reducing labor cost and greatly increasing production rates. SMDs can be one quarter to one-tenth the size and weight, and one-half to one-quarter the cost of equivalent through-hole parts.


Understanding it’s size.

Isn’t it really worthy to learn in detail?

How do they do this wonder?

Assembly Work:

Where components are to be placed, the printed circuit board normally has flat, usually tin-lead, silver, or gold plated copper pads without holes, called solder pads. Solder paste, a sticky mixture of flux and tiny solder particles, is first applied to all the solder pads with a stainless steel or nickel stencil using a screen printing process. It can also be applied by a jet-printing mechanism, similar to aninkjet printer. After pasting, the boards then proceed to the pick-and-place machines, where they are placed on a conveyor belt. The components to be placed on the boards are usually delivered to the production line in either paper/plastic tapes wound on reels or plastic tubes. Some large integrated circuits are delivered in static-free trays.

Numerical control pick-and-place machines remove the parts from the tapes, tubes or trays and place them on the PCB. The boards are then conveyed into the reflow soldering oven. They first enter a pre-heat zone, where the temperature of the board and all the components is gradually, uniformly raised. The boards then enter a zone where the temperature is high enough to melt the solder particles in the solder paste, bonding the component leads to the pads on the circuit board. The surface tension of the molten solder helps keep the components in place, and if the solder pad geometries are correctly designed, surface tension automatically aligns the components on their pads. There are a number of techniques for reflowing solder.

One is to use infrared lamps; this is called infrared reflow. Another is to use a hot gas convection. Another technology which is becoming popular again is special fluorocarbon liquids with high boiling points which use a method called vapor phase reflow. Due to environmental concerns, this method was falling out of favor until lead-free legislation was introduced which requires tighter controls on soldering. Currently, at the end of 2008, convection soldering is the most popular reflow technology using either standard air or nitrogen gas. Each method has its advantages and disadvantages. With infrared reflow, the board designer must lay the board out so that short components don’t fall into the shadows of tall components.

Component location is less restricted if the designer knows that vapor phase reflow or convection soldering will be used in production. Following reflow soldering, certain irregular or heat-sensitive components may be installed and soldered by hand, or in large-scale automation, by focused infrared beam (FIB) or localized convection equipment. If the circuit board is double-sided then this printing, placement, reflow process may be repeated using either solder paste or glue to hold the components in place. If a wave soldering process is used, then the parts must be glued to the board prior to processing to prevent them from floating off when the solder paste holding them in place is melted.

After soldering, the boards may be washed to remove flux residues and any stray solder balls that could short out closely spaced component leads. Rosin flux is removed with fluorocarbon solvents, high flash point hydrocarbon solvents, or low flash solvents e.g. limonene (derived from orange peels) which require extra rinsing or drying cycles. Water soluble fluxes are removed with deionized water and detergent, followed by an air blast to quickly remove residual water. However, most electronic assemblies are made using a “No-Clean” process where the flux residues are designed to be left on the circuit board [benign]. This saves the cost of cleaning, speeds up the manufacturing process, and reduces waste.

The major technical considerations for implementing SMT include Surface mount land pattern design, PB design for manufacturability, solder paste printing, component placement, reflow soldering, wave soldering, cleaning, and repair/rework. These areas must be studied and thoroughly understood to achieve high quality, reliable surface mount products. For more details on board assembly processing. Surface Mount Technology is latest PCB designing technique which has which has high efficiency & it is widely used in industrial production due to steadiness in its production. It further has scope for its betterment in area of reducing the soldering work i.e use of soldering material as because of this the efficiency in space management.

The added advantage of this technology is:


Defective surface-mount components can be repaired by using soldering irons (for some connections), or using a non-contact rework system. In most cases a rework system is the better choice because SMD work with a soldering iron requires considerable skill, and is not always feasible. There are essentially two non-contact soldering/ desoldering methods: infrared soldering and soldering with hot gas.


With infrared soldering, the energy for heating up the solder joint is transmitted by long- or short-wave infrared electromagnetic radiation.


  • Easy setup
  • No compressed air required
  • No requirement for different nozzles for many component shapes and sizes, reducing cost and the need to change nozzles
  • Fast reaction of infrared source (depends on system used)


  • Central areas will be heated more than peripheral areas
  • Temperature control is less precise, and there may be peaks
  • Nearby components must be shielded from heat to prevent damage, which requires additional time for every board
  • Surface temperature depends on the component’s albedo: dark surfaces will be heated more than lighter surfaces
  • The temperature additionally depends on the surface shape. Convective loss of energy will reduce the temperature of the component
  • No reflow atmosphere possible

Hot air:

During hot gas soldering, the energy for heating up the solder joint is transmitted by a hot gas. This can be air or inert gas (nitrogen).


  • Simulating reflow oven atmosphere
  • Some systems allow switching between hot air and nitrogen
  • Standard and component-specific nozzles allow high reliability and faster processing
  • Allow reproducible soldering profiles
  • Efficient heating, large amounts of heat can be transferred
  • Even heating of the affected board area
  • Temperature of the component will never exceed the adjusted gas temperature
  • Rapid cooling after reflow, resulting in small-grained solder joints (depends on system used)


  • Thermal capacity of the heat generator results in slow reaction whereby thermal profiles can be distorted (depends on system used)

Reworking usually corrects some type of error, either human- or machine-generated, and includes the following steps:

  • Melt solder and remove component (s)
  • Remove residual solder
  • Print solder paste on PCB, directly or by dispensing
  • Place new component and reflow.

Sometimes hundreds or thousands of the same part need to be repaired. Such errors, if due to assembly, are often caught during the process. However, a whole new level of rework arises when component failure is discovered too late, and perhaps unnoticed until the end user of the device being manufactured experiences it. Rework can also be used if products of sufficient value to justify it require revision or re-engineering, perhaps to change a single firmware-based component. Reworking in large volume requires an operation designed for that purpose.

Having understood then in detail,now let us see how to recognize(decode) the components:


For 5% precision SMD resistors usually are marked with their resistance values using three digits, two significant digits and a multiplier digit. These are quite often white lettering on a black background, but other colored backgrounds and lettering can be used.

The black or colored coating is usually only on one face of the device, the sides and other face simply being the uncoated, usually white ceramic substrate. The coated surface, with the resistive element beneath is normally positioned face up when the device is soldered to the board although they can rarely be seen mounted with the uncoated underside face up, whereby the resistance value code is not visible.

For 1% precision SMD resistors, the EIA-96 code is used, as three digits would otherwise not convey enough information. This code consists of two digits and a letter: the digits denote the value’s position in the E96 sequence, while the letter indicates the multiplier.

Typical examples of resistance codes
102 = 10 00 = 1,000 Ω = 1 kΩ
0R2 = 0.2 Ω
684 = 68 0000 = 680,000 Ω = 680 kΩ
68X = 499 × 0.1 = 49.9 Ω

There is an online tool to translate codes to resistance values on some websites. resistors can be found in several types of material but the most common is ceramic resistor where the substrate is ceramic. value are available in several tolerances defined in EIA Decade Values Table :

E3 50% tolerance (no longer used)

E6 20% tolerance (now seldom used)

E12 10% tolerance

E24 5% tolerance

E48 2% tolerance

E96 1% tolerance

E192 0.5, 0.25, 0.1% and higher tolerances


Non electrolytic capacitors are usually unmarked and the only reliable method of determining their value is removal from the circuit and subsequent measurement with a capacitance meter or impedance bridge. The materials used to fabricate the capacitors, such as Nickel Tantalate, possess different colours and these can give an approximate idea of the capacitance of the component.

Light grey body colour indicates a capacitance which is generally less than 100 pF.
Medium Grey colour indicates a capacitance anywhere from 10 pF to 10 nF.
Light brown colour indicates a capacitance in a range from 1 nF to 100 nF.
Medium brown colour indicates a capacitance in a range from 10 nF to 1 μF.
Dark brown colour indicates a capacitance from 100 nF to 10 μF.
Dark grey colour indicates a capacitance in the μF range, generally 0.5 to 50 μF, or the device may be an inductor and the dark grey is the color of the ferrite bead. (An inductor will measure a low resistance to a multimeter on the resistance range whereas a capacitor, out of the circuit, will measure a near infinite resistance.)

Generally physical size is proportional to capacitance and voltage^2 for the same dielectric. For example, a 100 nF 50 V capacitor may come in the same package as a 10 nF 150 V device.

SMD (non electrolytic) capacitors, which are usually monolithic ceramic capacitors, exhibit the same body color on all four faces not covered by the end caps.

SMD electrolytic capacitors, usually tantalum capacitors, and film capacitors are marked like resistors, with two significant figures and a multiplier in units of pico Farads or pF, (10−12 Farad.)

104 = 100 nF = 100,000 pF
226 = 22 μF = 22,000,000 pF

The electrolytic capacitors are usually encapsulated in black or beige epoxy resin with flat metal connecting strips bent underneath. Some film or tantalum electrolytic types are unmarked and possess red, orange or blue body colors with complete end caps, not metal strips.


Due to the small dimensions of SMDs, SMT inductors are limited to values of less than about 10 mH. Smaller inductance with moderately high current ratings are usually of the ferrite bead type. They are simply a metal conductor looped through a ferrite bead and almost the same as their through-hole versions but possess SMD end caps rather than leads. They appear dark grey and are magnetic, unlike capacitors with a similar dark grey appearance. These ferrite bead type are limited to small values in the nH (nano Henry), range and are often used as power supply rail decouplers or in high frequency parts of a circuit. Larger inductors and transformers may of course be through-hole mounted on the same board.

SMT inductors with larger inductance values often have turns of wire or flat strap around the body or embedded in clear epoxy, allowing the wire or strap to be seen. Sometimes a ferrite core is present also. These higher inductance types are often limited to small current ratings, although some of the flat strap types can handle a few amps.

As with capacitors, component values and identifiers are not usually marked on the component itself; if not documented or printed on the PCB, measurement, usually removed from the circuit, is the only way of determining them.

Discrete semiconductors:

Discrete semiconductors, such as transistors, diodes and F.E.T.s are often marked with a two- or three-symbol code in which the same code marked on different packages or on devices made by different manufacturers can translate to different devices.

Many of these codes, used because the devices are too small to be marked with more traditional numbers used on through-hole equivalent devices, correlate to more familiar traditional part numbers when a correlation list is consulted.

Some pictures that can make you understand SMT technology better:Image

Image  Image


   Overall process of SMT:







Advantages :

The main advantages of SMT over the older through-hole technique are:

  • Smaller components. As of 2012 smallest was 0.4 × 0.2 mm (0.016 × 0.008 in: 01005). Expected to sample in 2013 are 0.25 × 0.125 mm .
  • Much higher component density .
  • Lower initial cost and time of setting up for production.
  • Fewer holes need to be drilled.
  • Simpler and faster automated assembly. Some placement machines are capable of placing more than 136,000 components per hour.
  • Small errors in component placement are corrected automatically as the surface tension of molten solder pulls components into alignment with solder pads.
  • Components can be placed on both sides of the circuit board.
  • Lower resistance and inductance at the connection; consequently, fewer unwanted RF signal effects and better and more predictable high-frequency performance.
  • Better mechanical performance under shake and vibration conditions.
  • Many SMT parts cost less than equivalent through-hole parts.
  • Better EMC compatibility (lower radiated emissions) due to the smaller radiation loop area .

Disadvantages :

  • Manual prototype assembly or component-level repair is more difficult and requires skilled operators and more expensive tools, due to the small sizes and lead spacings of many SMDs.
  • SMDs cannot be used directly with plug-in breadboards .
  • SMDs’ solder connections may be damaged by potting compounds going through thermal cycling.
  • Solder joint dimensions in SMT quickly become much smaller as advances are made toward ultra-fine pitch technology. The reliability of solder joints becomes more of a concern, as less and less solder is allowed for each joint. Voiding is a fault commonly associated with solder joints, especially when reflowing a solder paste in the SMT application. The presence of voids can deteriorate the joint strength and eventually lead to joint failure.
  • SMT is unsuitable for large, high-power, or high-voltage parts, for example in power circuitry. It is common to combine SMT and through-hole construction, with transformers, heat-sinked power semiconductors, physically large capacitors, fuses, connectors, and so on mounted on one side of the PCB through holes.
  • SMT is unsuitable as the sole attachment method for components that are subject to frequent mechanical stress, such as connectors that are used to interface with external devices that are frequently attached and detached.

Zener diode

A diode is the most commonly used  passive component of electronics.Diodes are classified or rather organised based on some parameters like their working,doping levels,components it is made up of,etc., one of the well known or remembered diode is zener diode.It is that well recognized due to its wide range of advantages and applications too.

A zener diode can be simply defined as a heavily doped P-N junction diode.But if we have to define it accurately it can be defined as diode which allows current to flow in the forward direction in the same manner as an ideal diode, but also permits it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, “Zener knee voltage”, “Zener voltage”, “avalanche point”, or “peak inverse voltage”.

The device was named after Clarence Zener, who discovered this electrical property.


physical:                  Image




Regarding working there are two different effects that take place in Zener diodes …

  • Avalanche breakdown
  • Zener breakdown

Below around 5.5 Volts, the zener effect is predominant, with avalanche breakdown the primary effect at higher voltages. While I have no intention to go into specific details, there is a great deal of information on the Net  for those who want to know more. Because the two effects have opposite thermal characteristics, zener diodes at close to 5.5V usually have very stable performance with respect to temperature.

Now lets come to practical applications:

zener diodes are used in many circuits in a variety of ways.

The most common Zener diode circuit is one in which the Zener diode is used as a voltage reference element. This type of circuit uses the constant voltage as a reference in one of a variety of forms of power supply circuit.

There are other Zener diode circuits and applications. They can be used to limit voltages, preventing surges from damaging electronics circuits.

simple Zener diode circuit for voltage regulator:

When used in a regulator cirrcuit, the Zener diode must have the current entering it limited. If a perfect voltage source was placed across it, then it would draw excessive current once the breakdown voltage had been reached. To overcome this the Zener diode must be driven by a current source. This will limit the current to the chosen value.

In a practical circuit, the simplest form of current source is a resistor. This will limit the current taken by the Zener diode and ensure that the operating position of the diode remain approximately constant.


Simple circuit of a Zener diode shunt regulator
Simple circuit of a Zener diode shunt regulator


The value of the series resistor is simple to calculate. It is simply the voltage across the resistor, divided by the current required. The level of Zener current can be chosen to suit the circuit and the Zener diode used.


Resistor value (ohms)     =     (V1 – V2)   /   (Zener current + Load current)


V1 is the input voltage
V2 is the Zener diode voltage

Zener diode circuit for over voltage protection:

Another form of Zener diode circuit is an overvoltage protection circuit. While power supplies are normally reliable, the effects of the series pass transistor or FET can be catastrophic if it fails by forming a short circuit. In this case the full unregulated voltage would be placed onto the circuits using the regulated power. This could destroy all the chips being powered.

One solution is to use a crowbar circuit. When this form of circuit detects an overvoltage situation it fires an SCR. This quickly holds down the output voltage and in the instance shown, it blows a fuse that disconnects the input source power.


SCR overvoltage crowbar circuit
SCR overvoltage crowbar circuit


The circuit operates by firing the SCR when the overvoltage is detected. The Zener diode is chosen to have a voltage above the normal operating voltage – sufficient margin not to fire under normal operating conditions, but small enough to allow current to flow quickly when the fault condition is detected.

Under normal operating conditions the output voltage is below the reverse voltage of the Zener diode and no current flows though it and the gate of the SCR is not fired.

However, if the voltage rises above the allowed voltage, the Zener diode will start to conduct, the SCR will fire and the fuse will be blow.

Though the applications seem to be simple and limited, in practical there are many other applications of it

Some circuit tips:

The Zener diode is a very flexible and useful circuit component. However, like any other electronics component, there are a few hints and tips which enable the best to be made of the Zener diode. A number are listed below.

Choose correct voltage for best stability: Suppose in an application, the Zener voltage reference diode should be chosen to have a voltage of around 5.5 volts. The nearest preferred value is 5.6 volts although 5.1 volts is another popular value .The 5.6 volt Zener can be used and the surrounding electronics can be used to transfer this to the required output value.

Buffer the Zener diode circuit with an emitter or source follower: To keep the voltage from the Zener diode as stable as possible, the current flowing through the Zener diode must be kept constant. Any variations in current drawn by the load must be minimised as these will change the current through the Zener diode and cause slight voltage variations. The changes caused by the load can be minimised by using an emitter follower stage to reduce the current taken from the Zener diode circuit and hence the variations it sees. This also has the advantage that smaller Zener diodes may be used.

Drive with constant current source for best stability: Another way of improving the Zener stability is to use a good constant current source. A simple resistor is adequate for many applications, but a more effective current source can provide some improvements as the current can be maintained almost regardless of any variations in supply rail.
Ensure sufficient current for reverse breakdown: It is necessary to ensure that sufficient current is passed through the diode to ensure that it remains in reverse breakdown. For a typical 400 mW device a current of around 5 mA must be maintained. For exact values of minimum current, the datasheet for the particular device and voltage should be consulted.

Ensure maximum limits of current are not exceeded for the Zener diode: While it is necessary to ensure sufficient current is passed through the Zener diode, the maximum limits must not be exceeded. This can be a bit of a balancing act in some circuits as variations in load current will cause the Zener diode current to vary. Care should be taken not to exceed the maximum current or the maximum power dissipation (Zener voltage x Zener diode current). If this appears to be a problem, an emitter follower circuit can be used to buffer the Zener diode and increase the current capability.
When used to their best, Zener diodes can provide very high levels of performance. They often exceed the performance required, but in view of their ease of use and low cost, they provide a very effective option to use.

Zener IV characteristic:
The IV characteristic of the Zener / voltage reference diode is the key to its operation. In the forward direction, the diode performs like any other, but it is in the reverse direction where its specific performance parameters can be utilized.




Major Zener diode specifications explained !!!
When looking at the specification sheet for a Zener diode there are several parameters that will be included. Each details a different element of its performance and is required to ensure it operates correctly within any circuit.

Voltage Vz: The Zener voltage or reverse voltage specification of the diode is often designated by the letters Vz. Voltages are available over a wide range of values, often following the E24 ranges, although not all diodes are bound by this convention.

Values generally start at around 2.4 V although not all ranges extend as low as this. Values below this are not available. Ranges may extend top anywhere in the region of 47 V to 200 V, dependent upon the actual Zener diode range. Maximum voltages for SMD variants are often around 47 V.

Current : The current, IZM, of a Zener diode is the maximum current that can flow through a Zener diode at its rated voltage, VZ.

Typically there is also a minimum current required for the operation of the diode. As a rough rule of thumb, this can be around 5 to 10 mA for a typical leaded 400 mW device. Below this current level, the diode does not break down adequately to maintain its stated voltage.

Zener resistance Rz: The IV characteristic of the Zener diode is not completely vertical in the breakdown region. This means that for slight changes in current, there will be a small change in the voltage across the diode. The voltage change for a given change in current is the resistance of the diode. This value of resistance, often termed the resistance is designated Rz.
The IV characteristic of the Zener diode in the reverse direction has a gradient which indicates the resistance of the diode as shown
Zener diode resistance

The inverse of the slope shown is referred to as the dynamic resistance of the diode, and this parameter is often noted in the manufacturers’ datasheets. Typically the slope does not vary much for different current levels, provided they are between about 0.1 and 1 times the rated current Izt.

Power rating: All Zener diodes have a power rating that should not be exceeded. This defines the maximum power that can be dissipated by the package, and it is the product of the voltage across the diode multiplied by the current flowing through it.

For example many small leaded devices have a dissipation of 400mW at 20°C, but larger varieties are available with much higher dissipation levels. Surface mount varieties are also available, but generally have lower dissipation levels in view of the package size and their ability for heat removal.

Common power ratings for leaded devices include 400mW (most common), 500 mW, 1W, 5W. Values for surface mount devices may be around 200, 350, 500 mW with occasional devices extending up to 1 W.
Voltage tolerance: With diodes being marked and sorted to meet the E12 or E24 value ranges, typical tolerance specifications for the diode are ±5%. Some datasheets may specify the voltage as a typical voltage and then provide a maximum and minimum.

Temperature stability: For many applications, the temperature stability of the Zener diode is important. It is well known that the voltage of the diode varies according to temperature. In fact the two mechanisms that are used to provide breakdown within these diodes have opposite temperature coefficients, and one effect dominates below about 5 Volts and the other above. Accordingly diodes with voltages around 5 V tend to provide the best temperature stability.


Junction temperature: In order to ensure the reliability of the diode, the temperature of the diode junction is key. Even though the case may be sufficiently cool, the active area can still be very much hotter. As a result, some manufacturers specify the operating range for the junction itself. For normal design, a suitable margin is normally retained between the maximum expected temperature within the equipment and the junction. The equipment internal temperature will again be higher than the temperature external to the equipment. Carer must be taken to ensure that individual items do not become too hot despite the ambient temperature outside the equipment.

Package:  Zener diodes are specified in a variety of different packages. The main choice is between surface mount and traditional leaded devices. However the package chosen will often define the package heat dissipation.


After reading this quite whole of the above theory, you may be quite saturated and a lot confused but this is quite simple when sorted in a step by step manner.The other easier way of understanding zener is practical approach.Look for some simple circuits on the Net and  implement them and try analyzing them.You will have lot of fun !

All about LED’s

Many,actually most of us believe that we have complete knowledge regarding LED’s. Even i believed that i know almost everything about led’s until i faced a question “how to choose value of resistor?”  by my brother. So i started leaning about led’s right from the scratch to its manufacturing process. after working on it for a couple of days i realized that i actually knew nothing about it . so i thought of sharing a few things about LED’s with you all. This  is a quiet  long article and you may be knowing most of these things but be patient while reading,you may come across at least one new thing regarding this tiny astonishing component.


Who doesn’t love LED’s?

kids love them because they are bright and blinky, or soft and elegant. They’re festive! They’re colorful! They’re everywhere and they’re a lot of fun. Even professionals do because most of electronics hackery is hidden in chips, or goes very fast and we can’t see or sense it without expensive equipment. But LED’s are easy to see for everyone – this way we can visually identify what is going on inside our microcontroller.

Lets take an anatomy class first…. .Image

A really nice thing about LED’s is that they are very simple. Unlike some chips that have dozens of pins with names and special uses, LEDs have only two wires. One wire is the anode(positive) and another is the cathode (negative).

Points to keep in mind while handling led practically :

  • The longer lead is more positive terminal and shorter one is less positive terminal.
  • Current goes in one direction, from the anode (positive) to the cathode (negative).
  • LED’s that are ‘backwards’ won’t work – but they won’t break either.

It’s all a little confusing – we often have to think about which is which. So to make it easy, there’s only one thing you need to remember and that’s the LED wont light up if you put it in backwards. If you’re ever having LED problems where they are not lighting, just flip it around. Its very hard to damage an LED by putting it in backwards so don’t be scared .


Well, many of us well versed with all the theory part of an LED like definitions, principles,working etc., so i am not here to repeat them .And we have many articles on net which explain us all that stuff. now i am going to introduce how to use an led in application point of view or according to our application.



Different sizes and colors

One of the best things about modern LED’s is all the colors they come in. It used to be that LED’s were only red or maybe yellow and orange, which is why early electronics from the 70’s and 80’s only had red LED’s. The color emitted from an LED has to do with what type of material they are made of. So red, for example, is made with Gallium Arsenide. Since then, scientists have experimented with many other materials and figured out how to make other colors such as green and blue, as well as violet and white.

Here is list of materials used to bring out colors in a LED :



 LED’s come in all sorts of sizes as well. The most common among them are 3mm5mm and 10mm LED’s. the “millimeter” size refers to the diameter of the LED. For example, if you need to drill a hole in a box for your 5mm blinky LED, the hole size should be 5mm, and you’d need a 5mm drill bit to make it. 5mm are the most common size you’ll see, and they are extremely bright!


  • 5mm LEDs can be so bright, they are often used as illumination (lighting something up, like a flashlight).
  • 3mm LEDs are not as bright but are smaller, and are good for indication (like an LED that tells you something is on). They’re not as good for illumination because they have a smaller area that is lit.
  • 10mm LEDs are a little more rare, they are huge and chunky but are usually just 5mm LEDs with a bigger case so they aren’t any brighter. They can be good indicators but we rarely see them as illuminators.


The moment we hear the word LED ,the first thing that strikes our mind is brightness. We often see that among led’s we come across some are  very bright that we cant just stare at them and some are not very bright. so what makes the difference? There are actually a couple of factors making all the change…        

lets first know how the brightness is measured?    


One way to tell how bright your LED is before you buy it is to look for the milli-candela rating, sometimes shortened to mcd. Its a little tough to explain how bright something is with text or even photos . What i would like to do is instead give you some rough numbers for how bright LED’s will seem to be for most people.
MilliCandela Brightness ,
                10 “Dim” indicator, about the brightness of a tiny diffused indicator on a cheap electronic toy. Probably not visible in              daylight.  
                200 “Somewhat dim” indicator, Not visible in bright daylight.

                500 “Kinda bright”.You can look at these if you’re more than a few inches away, otherwise you’ll see spots.

                1,000 “Fairly bright”, , maybe about the brightness of those cheap LED keychain flashlights.You can look at these if you’re more than a few inches away, otherwise you’ll see spots. 
                5,000 “Bright!” – these are as bright as ultra-bright 5mm LEDs get. Expensive 5mm LED flashlights, when new, are about this bright.Looking directly at this is not pleasant.
                20,000 “Really Bright” – 5mm LEDs cant get this bright, but if you get the “1 Watt” LEDs, they’ll easily give you 20 candela of light. These are good for bicycle headlamps, big bright flashlights, and such.Don’t look straight at these, it’ll hurt your eyes.
So a ultra-bright LED may advertise itself as “5000 millicandela!”) – that’s the maximum brightness you’ll get out of it. In general, the brighter the LED the more expensive it is.
Now lets see how we can alter the brightness of a resistor manually according to our application. 


Changing the brightness with resistors:

Lets go back to our basic LED setup.one LED and one resistor connected from 5V to ground. to watch the difference this time we will duplicate it so that we have three LED’s except that each resistor is going to be different. LED #1 will have a 100 ohm resistor (Brown Black Brown), LED #2 will have 1.0K (Brown Black Red) and LED #3 will use a 10K (Brown Black Orange).Power up the circuit and examine how each LED is lit differently.

which led is brighter?(answer yourself!)

As you have seen with this experiment, the resistor we use with the LED makes a difference in how bright it is. The larger the resistor (more resistance) the dimmer the LED. A small resistor (less resistance) makes for a brighter LED.

Changing the brightness with voltage:

This time we will use only 1.0K resistors but connect the anodes to different voltages. One LED anode will go to 3.3 volts another will go to 5.0 volts and the third will go to 9.0volts .

which is brighter?(answer yourself!)

As you have seen with this experiment, the voltage we use to connect to the LED makes a difference in how bright it is. The higher the voltage the brighter the LED. A lower voltage will lead to dimmer LEDs.

now we will proceed to mathematical part of a LED to understand it to the core.

For every LED, in order to use it properly, we need to know the Forward Voltage. What is this forward voltage? Lets explain it in a photo:




In our three-piece circuit, we have the battery (which generates voltage) and the resistor+LED (which uses up the voltage). I will now tell you a very key ‘law’ of electronics:

       In any ‘loop’ of a circuit, the voltages must balance: the amount generated = the amount used

This “Voltage Loop” law was discovered by a fellow named Kirchhoff (thus it is called Kirchhoff’s Voltage Law = KVL). And we can see the loop above, where one part is made of the +9V battery. The other half must use up the +9v (making it -9V so that both halves of the loop equal out).

So what does this have to do with the Forward Voltage of an LED? Well, the Forward Voltage is the ‘negative voltage’, used by the LED when it’s on. Kinda like a ‘negative battery’! So lets modify our diagram slightly.



 Whenever the LED is on, the voltage it uses it up is somewhere between 1.85V and 2.5V. We’ll say 2.2V for average – that’s a good assumption for most red, yellow, orange and light-green LEDs. If we subtract that from 9V we get about 6.8V left. This is the voltage that must be ‘absorbed’ by the resistor.so a resistor must be chosen that way.


Ohm’s Law:

What is interesting about the law we just learned (KVL) is that in no place do we use the resistance of the resistor. It never shows up in the equation. Yet from our previous experiements we know for a fact that changing the resistance affects how bright the LED is. There must be something else going on, lets keep working on understanding the details….

Next we’re going to throw in another important law. This one is called Ohm’s Law– and it describes how resistors work.

Voltage across a resistor (volts) = Current through the resistor (amperes)* The Resistance of the resistor (ohms)


There’s a more common shorthand notation which you’ll see very often:

V = I * R

Or the two other ways of writing to solve for current or resistance:

I = V / R

R = V / I

The V is for voltage, the is for resistance and the I,  is for current. 


Solving for the current

We’ll now combine both KVL and Ohm’s Law with our diagram. Our LED is connected to a 1000 ohm resistor (you should verify this by checking the resistor color stripes!), and the voltage across that resistor must be 6.8V (the law of KVL) so the current through that resistor must be 6.8V / 1000ohm = 6.8 mA (Ohm’s law).




Our diagram is getting a little dense, but we’re pretty much done. The resistor current is 6.8mA and that current is also going through the LED, so the LED current is 6.8mA. “Big whoop,” you may be saying. “What do I care about the LED current?” The reason you should care is that:

The amount of current (I) going through an LED is directly proportional to how bright it appears.

Aha! Finally, the last piece of the puzzle. If we increase the current, the LED will be brighter. Likewise, if you decrease the current, the LED will be dimmer. By picking the correct resistor, you have full control over how the LED appears.

Most of the time, you’ll want to have a really bright LED so you’ll be calculating the smallest resistor you can get away with and not damage the LED. But note that the more current used by the LED, the quicker you’ll drain the battery. So there are good reasons for wanting to control the brightness if say you have a small battery and you want the lights to last a long time.

Since as we have seen, too much current will make the LED go poof, what is the best amount of current we should use? For some very big ‘power LEDs’, the current can be as high as 1 or 2 Amperes, but for pretty much every 3mm, 5mm or 10mm LED, the amount of current you’re expected to use is 20mA. 


You are almost done !!

Which to Adjust?

Given that you have two ways to adjust the brightness of an LED, resistor and voltage, which should you use? That is, should you increase voltage (by adding batteries) or decrease resistance, to get a brighter LED? The answer is in how power is used.



The battery (or power supply) generates power, the LED and resistor both use power, but they do so in different ways. The LED uses the power to make light (more power, more light). The resistor does not make light, it makes heat (more power, more heat).That voltage & current in the resistor is lost forever as heat and doesn’t do anything useful in our circuit. Since it’s inefficient to just pump all our battery power into the air as heat, we should make the power used by the resistor as small as possible, and the best way to do that is to keep the voltage low

.If you need to make an LED brighter, adding batteries is wasteful: you’re better off using a smaller resistor! 



IPv6 :


In december 1998 ,the internet engineering task force developed IPv6 to deal with exhaustion if IPv4 addresses .The main feature of IPv6 is it uses unique internet address of 128 bits , as opposed to 32 bits of IPv4.the 128-bit address space allows for 2^128 or 3.4*10^38 possible addresses which is quite adequate for the foreseeable future.


According to wikipedia , until IPv6 supplants IPv4, a number of transition mechanisms are needed to enable IPv6 only hosts to reach IPv4 services and to allow isolated IPv6 hosts and networks to reach the IPv6 internet over IPv4 infrastructure. A wide range of techniques have been implemented for this purpose :

  1. Dual IP stack techniques that allow IPv4 and IPv6 to coexist in the same devices and networks.
  2. Tunneling techniques that connect IPv6 domains via IPv4 clouds.
  3. Translational techniques that provide an interconnection between IPv4 and IPv4 devices and IPv6 to IPv6 devices only.

## Benefits of IPv6 over IPv4 :
1)Larger IP address space.
2)simplified and modular header structure.
3)better security for applications and networks.
4)better end-to-end connectivity.
5)better prioritized delivery.
6)better mobility features.
7)ease of administration.
8)efficient , hierarchical addressing .
A number of transitional mechanisms such as tunneling ,dual IP stack , proxy etc., have been defined that allow IPv4 and IPv6 to coexist till complete transition takes place.
The IPv6 will provide countless network addresses and will almost eliminate need for NAT. Nevertheless , this should not be considered as the only reason .Other features like network stability ,security , data integrity, auto configuration needed for new business needs have also been integrated in IPv6,which thus holds promise of achieving quality of service and simplified system management.