Why Diode in Arduino Reset Pin ???

                   The thing is that if you have a capacitor with 5V across it, like when the DTR is zero and the reset is pulled up to 5V and you take that end that has a zero and make it 5V, in that instant the end that was 5V now becomes 10V because the charge on the capacitor can not change instantly. This is the basis of of voltage doublers.

              The diode shorts out that 10V to the 5V rail and so quickly discharges the capacitor.

What is Ferrite Beads , Where it is Used ???

                  An effective method for filtering high frequency power supply noise and cleanly sharing similar voltage supply rails (that is, analog and digital rails for mixed-signal ICs) while preserving high frequency isolation between the shared rails is the use of ferrite beads. A ferrite bead is a passive device that filters high frequency noise energy over a broad frequency range. It becomes resistive over its intended frequency range and dissipates the noise energy in the form of heat. The ferrite bead is connected in series with the power supply rail and is often combined with capacitors to ground on either side of the bead. This forms a low-pass filter network, further reducing the high frequency power supply noise.
               You could often seen it in your Mobile Phone Data Cables,Computer Charger Cables and so and so on.
                Ferrite Beads are also used in Electronics Circuits for the effective filtration of high frequency noises. The image shown  is the smd version of Ferrite beads used for filtration in Electronics circuits.

What are the Network Bands Used in India for 2G, 3G and 4G ???

               Network frequency bands are often overlooked while purchasing any smartphone. Network bands are important related to coverage and data speed on your mobile. So, we will discuss about different network bands used in India on GSM, HSPA or UMTS and LTE.

What is a Network Band ?

             Network band is a specific range of frequencies in a spectrum. With each band defined Upper and down limit. By default Spectrum is government property and it is leased by carriers for fixed amount of time. Government agencies allocates spectrum in auctions to various network carriers.

             In India, Telecom Regularity Authority of India is responsible for spectrum allocations. Spectrum is allocated to network carriers Like Airtel, Vodafone, Jio, Idea, BSNL for interference free and unlimited usage. Before proceeding further, we must discuss some useful terms

Spectrum:

Spectrum is collection of various types of electromagnetic radiations of different wavelengths. In simplified words, Spectrum is airwaves on which signals of network carrier travels.

LTE

Full form of LTE is Long term evolution and often referred as 4G. LTE is an standard for high speed wireless communication for mobile phones and data terminals.

GSM

Full form of GSM is Global System for Mobile communications. GSM is a standard for defining 2nd Generation of digital telephony which offers internet services on mobiles but relatively very low speeds.

HSPA

Full form of HSPA is High Speed Packet Access. HSPA is combination of HSDPA (High speed downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). It is an standard defined to improve performance of 3rd generation (3G) digital telephony with relatively much higher speeds than its predecessor 2G.

Downlink

Downlink means transfer of signals from base station to mobiles.

Uplink

Uplink means transfer of signals from mobiles to base station.

Network Bands Used in India

In India, GSM telephony works on two different frequency bands GSM900 and GSM1800 in MHz(mega hertz). Lower frequency network bands offers higher coverage while higher frequency network bands offers higher data speeds.

HSPA telephony in India works on two different network bands UMTS900 and UMTS 2100 in MHz. UMTS network bands are radio frequencies used by 3G. UMTS network bands in India are commonly deployed at 2100 MHz for better speeds.

LTE Technology in India make use of 3 network bands namely 
LTE850 (Band 5), 
LTE1800(Band 3),
LTE2300 (Band 40). 

Band 3 provided great network coverage while Band 40 0ffers greater data speeds.

Band 3

Among different network bands, Band 3 is already used by various network companies in India to provide 2G services. Band 3 runs on 1800 MHz spectrum and provides an superb ecosystem in world to deploy LTE services to users. In auction of 2015, almost every cellular company leased out Band 3 spectrum to provide their services. In India, Jio, Airtel, Vodafone, Idea, Reliance, Telenor, Videocon bags out 1800 MHz band to provide their 4G services. Only BSNL and Tata Docomo were not able to lease out this frequency band.

Band 5

Band 5 is another out of another network bands that your smartphone should support. Band 5 runs on 850MHz which results into best network coverage. Reliance Jio has already launched its LTE services on Band 5 and network is available in almost every part of the country. Apart from Jio, BSNL, MTS and Docomo also hold this spectrum in their polythenes. Earlier smartphones does not included support for this band because it provides poor 4G speeds but best network reception on 4G network. But after Jio and their VoLTE smartphones, now smartphones includes support for Band 5 as well.

Band 40

Another Popular Network Bands used includes Band 40 which run on radio frequency of 2300 MHz. It is specially used by 4G networks to provide their services with great data speeds. Currently, Airtel, Jio, Aircel and Tikona uses this spectrum for its service deployments. Band 40 is also supported on almost every 4G smartphones in India. Reliance Jio holds PAN India license for 2300 MHz spectrum and already launched it throughout the country.

Note : Reliance Jio uses all of three LTE network Bands namely Band 3, Band 5, Band 40. All three bands are required for VoLTE services and superb data speeds on Jio SIMS. Choosing Band 5 will provide better network reception while choosing Band 40 will provide greater data speeds on your mobile.

Better speed:  2300Mhz > 1800Mhz > 850Mhz

Better coverage:  850Mhz > 1800Mhz > 2300 Mhz

What is the difference between Null Modem cable and Straight Through Cable...???

             The null modem cable is frequently called a Crossover cable. It is used to allow two serial Data Terminal Equipment (DTE) devices to communicate with each other without using a modem or a Data Communications Equipment (DCE) device in between. For this to happen, the Transmit (TXD) pin of one device needs to be connected to the Receive (RXD) pin of the other device.  To enable handshaking between the two devices, the Request to Send (RTS) pin of one device must be connected to the Clear to Send (CTS) pin of the other device. Because these pins are "crossed" on the two cable terminals, the name crossover cable is used.


                            DB9 - Null Modem Cable (Female - Female Connectors)

Null Modem Cable with Handshaking

               A straight-through cable is used to connect a DTE device to a DCE device. The TXD-RXD and RTS-CTS pins are not cross-connected in this case, hence the term straight through cable.

Simple Straight Through Cable

DB9 - Straight Through Cable(Male - Female Connectors)

               The built-in serial port on a PC is a DTE device. Modems and printers are examples of DCE devices.  Note that an instrument with serial interface could be either a DTE or a DCE device.  It is best to check the user manual of the instrument to find out the device type.  For more information regarding DTE and DCE devices, please see the links below. 

To tell if your cable is null modem or straight though, you can search the part number at ni.com, the product description will tell if it is null modem. Alternatively you can use a hand held DMM to test continuity on the individual pins of your serial cable. If every pin is electrically connected to the corresponding pin on the other end, i.e.: pin 1 to pin1, pin 2 to pin 2, etc. then the cable is straight through.

What is the difference between DCE and DTE ???

           DTE is the source or destination of digital data, while DCE is the equipment used to transmit or receive the data. DTE stands for Data Terminal Equipment, while DCE stands for Data Communications Equipment.

          Examples of devices that are DTEs include computers, printers and routers. They are all devices that act as the source or destination for data, but they are not concerned with the communication of data between devices. The most common usage of the word is in relation to RS-232C standard serial communications.

          DCE, on the other hand, is concerned with the communications aspect of data. This means it communicates with a DTE. So a DCE takes data from a DTE, converts it into a signal that can be transmitted, and transmits it, usually to another DTE.

         One of the most common examples of a DCE device is a modem. It communicates data from the internet to a DTE, which could be a computer, a tablet or a smartphone. Other DCE examples include ISDN adaptors,network interface cards. Also, as well as being responsible for the communication, DCE devices are often responsible for the timing over a serial link too.

Some examples of DTE and DCE devices:

1.PC - PCI Cord - DTE

2.DCE and DTE Pinout:

3.Communication Network:

Sources : www.reference.com

What are the types of Cooling methods in Transformers ???

                    No transformer is truly an 'ideal transformer' and hence each will incur some losses, most of which get converted into heat. If this heat is not dissipated properly, the excess temperature in transformer may cause serious problems like insulation failure. It is obvious that transformer needs a cooling system. Transformers can be divided in two types as (i) dry type transformers and (ii) oil immersed transformers.

Different cooling methods of transformers are - 

§  For dry type transformers

§  Air Natural (AN)

§  Air Blast

§  For oil immersed tranformers

§  Oil Natural Air Natural (ONAN)

§  Oil Natural Air Forced (ONAF)

§  Oil Forced Air Forced (OFAF)

§  Oil Forced Water Forced  (OFWF)

Cooling Methods For Dry Type Transformers:

Air Natural Or Self Air Cooled Transformer:

              This method of transformer cooling is generally used in small transformers (upto 3 MVA). In this method the transformer is allowed to cool by natural air flow surrounding it.

Air Blast:

              For transformers rated more than 3 MVA, cooling by natural air method is inadequate. In this method, air is forced on the core and windings with the help of fans or blowers. The air supply must be filtered to prevent the accumulation of dust particles in ventilation ducts. This method can be used for transformers upto 15 MVA.

Cooling Methods For Oil Immersed Transformers:

Oil Natural Air Natural (ONAN):

                This method is used for oil immersed transformers. In this method, the heat generated in the core and winding is transferred to the oil. According to the principle of convection, the heated oil flows in the upward direction and then in the radiator. The vacant place is filled up by cooled oil from the radiator. The heat from the oil will dissipate in the atmosphere due to the natural air flow around the transformer. In this way, the oil in transformer keeps circulating due to natural convection and dissipating heat in atmosphere due to natural conduction. This method can be used for transformers upto about 30 MVA.

Oil Natural Air Forced (ONAF):

 The heat dissipation can be improved further by applying forced air on the dissipating surface. Forced air provides faster heat dissipation than natural air flow. In this method, fans are mounted near the radiator and may be provided with an automatic starting arrangement, which turns on when temperature increases beyond certain value. This transformer cooling method is generally used for large transformers upto about 60 MVA.

Oil Forced Air Forced (OFAF):

               In this method, oil is circulated with the help of a pump. The oil circulation is forced through the heat exchangers. Then compressed air is forced to flow on the heat exchanger with the help of fans. The heat exchangers may be mounted separately from the transformer tank and connected through pipes at top and bottom as shown in the figure. This type of cooling is provided for higher rating transformers at substations or power stations.

Oil Forced Water Forced (OFWF):

                  This method is similar to OFAF method, but here forced water flow is used to dissipate hear from the heat exchangers. The oil is forced to flow through the heat exchanger with the help of a pump, where the heat is dissipated in the water which is also forced to flow. The heated water is taken away to cool in separate coolers. This type of cooling is used in very large transformers having rating of several hundreds MVA.

Source : Circuits Globe.

What are Random wound and Form wound Coils in Electric Motor ??? How they influence the Motor ???

                 A typical low-voltage generator is built with multi turn stator coils, ranging from one to 16 turns per coil. These coils can either be form wound (where the wire is square or rectangular and the turns are systematically arranged) or random wound (where the wire is round and the arrangement between the turns is not defi nite).With units less than 1,500 kW, the size of the stator and the minimum wire thickness usually do not allow form-wound coils. However, in some cases, either form-wound or random-wound coils can be used. Generators with random-wound coils can be made at a reduced cost, and their capability to withstand severe environmental conditions can be enhanced through the use of vacuum-pressure impregnation (VPI). Still, performance, capability and endurance to the environment make units with form-wound coils superior.

FORM WOUND COILS:

                A form winding uses square or rectangular magnet wire. The wire insulation is designed to handle operating turnto-turn voltages as well as maximum surge or impulse voltages The coil winding process begins with skeining (looping) of the magnet wire. Because of the difficulty to form wire of high width-to-thickness ratio, several wires in parallel may make one turn. Individual turns are arranged in precise location with respect to each other. That is, turn one is always next to turn two is always next to turn three, and so on.
ADVANTAGES:

               The main advantage is as there is uniform turn-to-turn voltage stress due to uniform arrangement of coils.Form  windings have uniform temperature distribution as well as resin build up, which minimize the chance of localized hot spots. Insulation systems are categorized by temperature limits of the materials. For example, a class F system is designed to withstand an overall temperature of 155° C. This temperature is made up of ambient air plus average temperature of the windings with allowance for hot spots.

             With form wound machines the hot spot is always in a predictable location at the slot portion of the laminations. The hot spot temperature can be measured and duplicated from unit to unit. However, for random windings, because of uneven resin build up, the hot spot location can vary in duplicate units. In continuous duty applications, premature winding failures of identical units having random coils is a prime example of localized excessive hot spot.

            The end windings of form coils have large openings for air circulation, which prevent contamination build up. Therefore, the likelihood of tracking-type failures is minimized. In addition, the insulating tape on the coils provides additional environmental protection. The inherent rigidness of the rectangular wire coupled with the lacing of the end turns and VPI ensures a rigid insulation system. A rigid coil structure is very important to minimize movement at the coil-lamination interface when there are high surge currents, such as motor starting loads or short circuit faults. These can exert extreme forces between the coils.
DISADVANTAGES:

              Magnet wire is rectangular or square with double dacron glass cover or mica turn tape over 200° C heavy film. The wire is more costly and inventory costs are increased because many different sized wires are used. Round wire with 200° C heavy fi lm is used. Fewer sizes need to be kept on hand, and the wire is more economically priced.
RANDOM WOUND COILS:

            When the arrangement between turns is not definite during coil skeining or insertion, the windings are called “random.” That is, for example, turn one can be touching turn four. Random windings are used on lower kW machines where it is impractical to use form coils. Random windings are made from a lower cost magnet wire that is fi lm coated and round. With random windings, the mechanization of manufacturing is also increased to add to a lower cost.
ADVANTAGES:

               The primary advantage for manufacturing generators with random windings is economics: lower cost wire and mechanized construction. However, without vacuum-pressure impregnation (VPI), the life expectancy of random windings is drastically reduced under severe environmental conditions or with applications involving nonlinear loads, such as silicon-controlled-rectifi ed (SCR)-type loads. SCR type loads induce high turn-to-turn surge voltages into the windings, as high as twice the normal operating voltage.
DISADVANTAGES:

               In the case of random windings, the ability to withstand operating turn-to-turn voltages, which can be marginal for normal operation, will cause failures within a few hours under SCR type loads. For example, a four-pole generator rated 600 kVA and 600 volts may have four turns per coil and peak turn-to-turn voltage of 38 volts. For a random-wound design if turn one and turn four are touching, this voltage can be as high as 114 volts (38 volts x a three-turn difference), and can be amplifi ed by SCR loads. That is why random coils may prematurely fail. A similar form-coil design would have a peak voltage of only 38 volts because turns one and four would never be next to each other.

How Insulation fails in Electric Motor ???

                Moisture and contaminants promote tracking and deterioration that can lead to failure of majority of motors. Tracking failures are caused by small partial discharge currents, which develop localized heating and cause chemical decomposition of any weak insulation barrier. 

                  Arcs of relatively high currents develop additional heating, which will carbonize (track) the resin surface. This is the start of most winding failures.

Why Aluminium Windings are not being used in Motors ?

(2 Min Read)

• Resistivity of Copper  is 1.68 x 10-8 Ohm
• Resistivity of Aluminium 2.65 x 10-8 Ohm
• Aluminium/Copper  = (2.65 x 10-8) / (1.68 x 10-8) = 1.6

    Aluminum’s resistivity is 1.6 times higher than copper’s resistivity. To compensate, aluminum windings cross-section must have 1.6 times larger and diameter must be 1.26 times of copper windings to offer the same conductance.This means windings wound with aluminum wire will likely have greater volume compared with an equivalent copper wire motor.

    It is possible to match the power performance of a motor wound with aluminum to a motor wound with copper.But since aluminum requires more turns and/or a larger diameter wire,the size of the motor will go bigger, this may not always be feasible in some applications. In situations where efficiency and volume are not issues such as where the motor only has to work occasionally or for very short periods of time, aluminum windings make an acceptable motor.

Cu vs Al

What is Relation between Hardness,Ductility,Malleability&Brittleness...

HARDNESS:

 Hardness is a measure of the material’s resistance to localized plastic deformation (e.g. dent or scratch).

DUCTILITY:

 Ductility measures the amount of plastic deformation that a material goes through by the time it breaks.

Ductility is said to be the property of a material to stretch without getting damaged. Metals having ductile property can be stretched into wires. An example is copper wire.

MALLEABILITY: 

Malleability is said to be the property of a material to deform under compression. The metals having malleable property can be rolled or beaten into sheets. An example is aluminium foil.In more simple words, ductility means stretching to wires and malleability means beating to sheets.

Ductility means that a metal can be changed to another form by pulling, compression or twisting.On the other hand,Malleability means that a metal can be changed into another form by beating or hitting it hard.

Ductility also refers to the ability of a metal to change its form under tensile stress. Malleability refers to the ability of a metal to change its form under compressive stress.

A metal’s ductility is measured by looking at its tensile strength. The tensile strength inspects how far a metal could stretch without breaking. A metal’s malleability is measured by looking at how much pressure it can withstand without breaking.The bend test is the commonly used test for determining the ductility of a metal.Gold and silver are the top ranking ductile and malleable metals.

The two properties of Malleability and ductility do not always correlate in metals. For example, gold is both malleable and ductile and lead is only malleable.

BRITTLENESS:

A material is Brittle if, when subjected to stress, it breaks without significant deformation (strain). Brittle materials absorb relatively little energy prior to fracture, even those of high strength. Breaking is often accompanied by a snapping sound.

TWO MEASURES OF DUCTILITY:

1) Percent Elongation (%El )

2) Percent Reduction In Area

• Highly ductile metals can exhibit significant strain before fracturing, whereas brittle materials frequently display very little strain.

• An overly simplistic way of viewing ductility is the degree to which a material is “forgiving” of local deformation without the occurrence of fracture.

Brittle materials: %EL £ 5% at fracture

Ductile materials: %EL and %RA both ³ 25%.

What is Ductile to Brittle Transition...??? How it related to Titanic Sinks...???

                At low temperatures some metals that would be ductile at room temperature become brittle. This is known as a ductile to brittle transition.

          The ductile to brittle transition temperature is strongly dependant on the composition of the

metal.Steel is the most commonly used metal that shows this behaviour.

          For some steels the transition temperature can be around 0°C, and in winter the temperature in some parts of the world can be below this. As a result, some steel structures are very likely to fail in winter.

                                    

Example of Brittle Failure:

            Ductile fracture is always a preferred mechanism of failure. Many cases have occurred through history where catastrophic failures have occurred as a result of brittle fracture. The most infamous of these is the sinking of the Titanic.

           The sinking of the titanic was caused primarily by the brittleness of the steel used to construct the hull of the ship. In the icy water of the Atlantic, the steel was below the ductile to brittle transition temperature.

           In these conditions even a small impact could have caused a large amount of damage. The impact of an iceberg on the ship's hull resulted in brittle fracture of the bolts that were holding the steel plates together.

          Nowadays engineers know more about this phenomenon and the composition of the steels used is much more controlled, resulting in a lower temperature at which the ductile to brittle transition occurs.

What is Magnet wire?

    Magnet wire or enameled wire is a copper or aluminium wire coated with a very thin layer of insulation. It is used in the construction of transformers, inductors, motors, speakers, hard disk head actuators, electromagnets, and other applications that require tight coils of insulated wire.
    The wire itself is most often fully annealed electrolytically refined copper. Aluminium magnet wire is sometimes used for large transformers and motors. The insulation is typically made of tough polymer film materials rather than enamel, as the name might suggest.
    Annealing: In metallurgy and materials science, is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material to above its recrystallization temperature, maintaining a suitable temperature, and then cooling.