Electrosparx

Series And Parallel Resistors

2011-04-23T19:29:00.000+05:30

Electrical components can be connected together in two basic ways: parallel and series. When resistors are connected in series (figure 2.3) a fraction of the supply voltage is dropped across each resistor and each resistor dissipates some of the total energy from each coulomb of charge.
The total resistance (RT) of the circuit (ignoring the resistance of the wires) is the sum of the resistances and the same current flows through each resistor.

Temperature And Resistance

2011-04-23T19:15:00.001+05:30

When a 2V supply is connected to a 60W, 240V bulb it draws a current of 25mA, its resistance is

Thus R=U/I = 2/0.025 =80ohms

When the same bulb is connected to the correct 240V supply it glows white hot and draws a current of 250mA and its resistance is:

R=U/I = 240/0.250 = 9600ohms

Thus we can see that a larger current has caused the bulb to get very hot and its resistance has increased by 12 times. To take account of the change in resistance with temperature the temperature coefficient of resistance (α) is used.
α for a material at 0°C is the change in resistance of a 1Ω sample of that material when the temperature increases from 0°C to 1°C. Matters are complicated furtherer because it is not easy to measure the resistance of a conductor at 0°C hence, a value for α is often quoted for a temperature increase of 20°C to 21°C.
Table 2.2 contains the temperature coefficient of some metals.

We can see from the above table that when the temperature increases from 20°C to 21°C the resistance of a 1Ω copper resistance will increase to 1.00396Ω. Thus: 

Rt=Ro(1+αT)
where:
Rt = total conductor resistance at T (Ω)
R0 = resistance of a conductor at 0°C (Ω)
α = temperature coefficient of resistance
T = temperature (°C)
And: Rt=R20(1+αT)
where:
R20 = resistance of a conductor at 20°C (Ω)
If the resistance of a conductor is not known at the temperature for which α is known the following method can be used:
R1 = the conductor resistance at temperature T1
R2 = the conductor resistance at temperature T2
R1=Ro(1+αT1) and R2=Ro(1+αT2)
Dividing: R1/R2 = (Ro(1+αT1))/(Ro(1+αT2)) = (1+αT1)/(1+αT2)

Hence:
R2=(R11+αT2)/(1+αT1)
Therefore the value of R0 has been eliminated from the equation.

Resistivity (also known as specific resistance)

2011-04-23T18:58:00.000+05:30

When electrons flow through a wire they experience resistance and lose energy, the furtherer along the wire they flow the more energy they lose, therefore, we can say that the total resistance of a wire is proportional to its length.
Since the electrons are evenly distributed throughout the wire and since the current is the rate at which a charge passes any point on that wire, we can see that to provide any specific current the electrons in a wider wire will have to flow a shorter distance than electrons in a narrower wire (figure 2.2).
We can therefore say that resistance is inversely proportional to the conductor's cross-sectional area.
Therefore thicker wires have less resistance per meter and will cause less energy to be lost as heat.

Putting the previous two concepts together given us:

R~1/a (*proportional)

where l is the length of wire, a is the cross-sectional area and α means proportional to. The resistivity (ρ) of a material is defined as the resistance between opposite faces of a cube of that material with a given side length.
ρ is very small for most conductors and is usually quoted in micro-ohms (μΩ) for a 1 meter cube expressed as μΩm. For example aluminium has a resistivity of 0.0285μΩm.
Thus the resistivity of a wire is proportional to the resistivity of the material from which it is made. We can combine resistivity with the previous equation to give:

R=ρl / a

Note that the resistance calculated from this equation will be given in the same units of resistance used for the resistivity (i.e. μΩ). Also l and a must be in the same length units as ρ so that if ρ is in μΩm l must be in m and a must be in m2. Table 2.1 contains the resistivities of some metals.

Example:
Calculate the resistance of 1000m of 16mm2 single annealed copper wire.
From the table: ρ = 17.2μΩmm (since the cross sectional area is given in mm2)
l = 1000m = 10^6m
R=ρl / a = (17.2*10^6)/16 =1075000μΩ=1.075Ω

All wires and cables have some resistance, therefore there will always be some energy lost and a voltage drop within. Thin wires will get very hot and may burn out if they carry too much current, they may also cause such a large voltage drop that equipment may not function properly.
Thick wires will reduce these phenomena however, because they contain more copper they will be considerably more expensive than thin wires. Voltage drops in cables are normally recommended to be no more than 4% of the supply voltage.
That means a 9.6V drop for a 240V supply or a 4V drop for a 110V supply. Note that you can only measure a voltage drop across a length of cable when a current is flowing in it.

Resistance And Ohm's Law

2011-04-23T18:33:00.001+05:30

Electrical resistance is a little like friction and electrons flowing in wires lose energy overcoming it.
All conductors have some resistance and the larger the resistance, the larger the amount of energy dissipated within it as electrons flow, and therefore, the greater the energy needed to move electrons around a circuit.
Hence, if a fixed voltage supply is connected to a circuit with a low overall resistance more current (i.e. coulombs of charge per second) will flow than if the same supply is connected to a higher resistance circuit.
Some electrical components, such as water heaters, are designed to have a large resistance so that a lot of electrical energy is converted into heat as current flows through them.
Wires and cables on the other hand should have a low resistance so that not much energy is lost when electricity is supplied from one place to the other.
The unit of resistance (R) is the ohm (Ω) and one ohm is the resistance that causes a drop of one volt when a current of one ampere flows.
For a metallic conductor which remains at a Constance temperature Ohm's law applies:

R=U/I I=U/R U=I*R
Components in circuits that are designed to have a fixed resistance are usually shown as a simple
box, as depicted in figure 2.1.

Example
An electrical heater is used on a 240V supply draws a current of 12A. Its resistance is:
R=U/I=240/12=20ohms.

Electrical Circuits, Voltmeters And Ammeters

2011-04-22T18:24:00.004+05:30

Figure 1.2: (a) a closed circuit where current (I) can flow; (b) an open circuit where no current can flow.

The path around a circuit must be unbroken for an EMF to push electrons around it, such a circuit is said to be closed. If a switch is included in the circuit it can be used to break the path and produce an open circuit where no electrons can flow (figure 1.2a and 1.2b).
In a high voltage circuit, current may arc across a small gap causing considerable damage. Most switches will arc briefly when opened however, as long as the current doesn't jump the gap for too long, it is not a problem.
Voltmeters measure a potential difference between two points and so must be connected in parallel. If you take a voltage reading across a supply in a open circuit you will be measuring the supply's EMF, you can only measure voltage drops across a load (e.g. a piece of equipment) if a current is flowing. Figure 1.3 shows the placement of voltmeters in a circuit.
Ammeters measure the current flowing through a point in a circuit, therefore they are connected in series. Figure 1.4 shows the placement of a voltmeter in series.

Electromotive Force, Potential Difference And Voltage

2011-04-22T18:08:00.000+05:30

Moving electrons through a conductor as an electrical current requires energy because, as the electrons move they constantly dissipates energy (as heat).
This energy can be supplied by many means including batteries or generators. In the case of a battery chemical energy is converted into electrical energy, whereas a generator converts chemical energy to mechanical energy (through combustion) before turning it into electrical energy.
For historical reasons the amount of energy needed to move one coulomb of charge around a circuit is called the electromotive force or EMF (E).
The unit of EMF is the volt (V) and one volt is one joule per coulomb, thus:

EMF (V) = Energy (J)/Charge (C)
E = W/Q
Example:

A battery with an EMF of 6V can supply a current of 5A round a circuit for five minutes. How much energy is provided?

The total charge transferred in 5 minutes: Q = It = 5 * 5 * 60 = 1500C
The total energy supplied to do this: energy = E * Q = 6 * 1500 = 9000J

When you lift a ball to a height of two meters above the ground you give it potential energy. When the ball is dropped this potential energy is converted to kinetic energy until, at the point when it hits the ground, there is no potential energy left.
A coulomb of charge travelling around a circuit behaves in a similar way. Each coulomb of charge leaving from a battery with an EMF of 6V has six joules of potential energy.
By the time the charge reaches the battery again, having travelled around the circuit, it will have dissipated all six joules and posses no potential energy.
The amount of energy expended by one coulomb of charge when travelling between any two points in a circuit is known as the potential difference (PD) between those points. Since the potential difference is a number of joules per coulomb the unit of PD is the volt (i.e. the same unit used for EMF).
The PD between two points is thus called the voltage drop and has the symbol U (the symbol V used to be used). Therefore, from the previous equation we can say:

U = W/Q
Example:

How much electrical energy is converted into heat each minute by an immersion heater which takes 13A from a 240V supply?

                       Energy = lost by each coulomb = 24J
                      Quantity of charge flowing per minute: Q = It = 13 * 60 = 780C
                      Energy converted in one minute = U * Q = 240 * 780 = 187 200 = 187.5kJ

Energy, Work and Power.

2011-04-22T17:44:00.000+05:30

Generally speaking energy can either be useful or wasted. For example energy can be used to lift a weight but energy can be lost as heat because of friction.
The useful bit of energy is called work and if we lift a weight we are said to have 'done work'. Work is linked to force by the following equation:

work done (J) = distance moved (m) * force for movement (N)

In this equation force is measured in newtons (N), distance is measured in meters (m) and the work done is measured in joules (J), which is the unit normally used for any energy.
To lift an object you need to over come the force of gravity with an equal force acting is in the opposite direction. For this reason the 'force for movement' will be equal but opposite to the force opposing the movement.
It is important to note the difference between mass and weight. An object's mass is due to the amount of matter it contains and has the units of kilograms (kg). Weight is the force that an object exerts downwards towards the ground and is measured in newtons (N).
The weight of an object can be calculated by multiplying its mass by the acceleration due to gravity which is 9.8 meters per second per second (often rounded up to 10 m/s2).

Example:

How much energy (or how much work) is needed to lift a 70kg man off the floor to a height of 3m (using the acceleration due to gravity = 10 m/s2).

mass weight = 70 * 10 = 700N work done = distance moved * opposing force = 3 * 700 = 2100J

Power is the rate of using energy or doing work. Lifting the man in the previous example to 3m will always require the same amount of work but the quicker you do it, the more power is needed.

power = work or energy /time = joules/seconds
P = W/t

The unit of power is the watt (W, not to be confused with the symbol for work).
One watt is the power used supplying one joule per second. The symbol W is also used for energy used or work done, so be careful not to get confused with W used as the units of power.

Unit Of Charge And Current.

2011-04-22T17:34:00.001+05:30

Each electron carries the same amount of negative charge and we could use the charge on a single electron as the unit of charge.
However, the charge on an electron is tiny and electric currents contain many electrons flowing through a wire.
The unit of charge is thus the coulomb (C) and one coulomb is approximately equal to the total charge of six million million million electrons (to be more exact the charge on one electron is 1.6x10-19, therefore 1C comprises the charge of 6.25x1018 electrons).
If electrons flow past a point on a wire so that 1 coulomb of charge passes every second, a current of one ampere (A) is said to flow.
Therefore, electrical current is the rate at which charge passes through a wire. Mathematically we can say:

Where:
Q = the charge transferred in coulombs (C)
I = the current in amperes (A)
t = time during which the current flows in seconds (s)

The Atom And Electrical Current.

2011-04-22T17:25:00.000+05:30

All matter is made of atoms. Atoms are very small and when placed in a straight line about 8 million will fit into 1mm.
Atoms themselves are made up from three particles: electron, proton and neutrons. Electrons and protons have equal but opposite charges; the electron has a negative charge and the proton has a positive charge.
The neutron has no charge. Charges behave like magnetic poles in that alike charges repel and unalike charges attract.
The protons and neutrons make up the nucleus which is at the centre of the atom and the electrons reside around the outside (figure 1.1).
Normally an atom will have equal numbers of electrons and protons so that as a whole the atom has no overall charge.

In solid materials that are conductors the electrons are free to move between atoms. The movement may be random in all directions throughout the conductor however, if the electrons move predominantly in one direction an electric current flows.
Since the protons are at the centre of the atom they can not break free, therefore electricity is the flow of negative charge and not the flow of positive charge.
Because of these phenomena any region of negative charge is formed by an excess of electrons gathering and a region of positive charge is due to electrons moving away, leaving a deficit.
Solid materials, where the electrons are not able to move are insulators and such materials do not conduct electricity.
Materials that conduct electricity under certain conditions are called semiconductors. In a piece of metal, a wire for instance, electrons are free to move in any direction.
However, as soon as a battery is connected to both ends of the wire the electrons will move towards the positive battery terminal. For every electron that leaves the wire through this terminal, another enters the other end of the wire from the negative terminal; thus the total number of electrons in the wire remains the constant.
This flow of electrons from a negative terminal, through the wire, to the positive terminal is called an electric current. For historic reasons, in most circuits electricity is considered to flow from the positive terminal to the negative terminal; in fact for most circuits it does not matter which direction you consider the electricity to flow.
When a current flows in a conductor two important things happen:

heat is generated,
a magnetic field is set up around the conductor.

555 timer

2010-07-20T02:01:00.000+05:30

The 555 has three operating modes:

Monostable mode: in this mode, the 555 functions as a "one-shot". Applications include timers, missing pulse detection, bouncefree switches, touch switches, frequency divider, capacitance measurement, pulse-width modulation (PWM) etc

Astable - free running mode: the 555 can operate as an oscillator. Uses include LED and lamp flashers, pulse generation, logic clocks, tone generation, security alarms, pulse position modulation, etc.

Bistable mode or Schmitt trigger: the 555 can operate as a flip-flop, if the DIS pin is not connected and no capacitor is used. Uses include bounce free latched switches, etc.

The connection of the pins is as follows:

The 555 Timer IC is an integrated circuit (chip) implementing a variety of timer and multivibrator applications. The IC was designed by Hans R. Camenzind in 1970 and brought to market in 1971 by Signetics (later acquired by Philips). The original name was the SE555 (metal can)/NE555 (plastic DIP) and the part was described as "The IC Time Machine". It has been claimed that the 555 gets its name from the three 5 kΩ resistors used in typical early implementations, but Hans Camenzind has stated that the number was arbitrary. The part is still in wide use, thanks to its ease of use, low price and good stability. As of 2003, it is estimated that 1 billion units are manufactured every year.

     Depending on the manufacturer, the standard 555 package includes over 20 transistors, 2 diodes and 15 resistors on a silicon chip installed in an 8-pin mini dual-in-line package (DIP-8). Variants available include the 556 (a 14-pin DIP combining two 555s on one chip), and the 558 (a 16-pin DIP combining four slightly modified 555s with DIS & THR connected internally, and TR falling edge sensitive instead of level sensitive).

       Ultra-low power versions of the 555 are also available, such as the 7555 and TLC555. The 7555 requires slightly different wiring using fewer external components and less power.

JK flip flop

2010-07-20T01:38:00.002+05:30

In digital circuits, a flip-flop is a term referring to an electronic circuit (a bistable multivibrator) that has two stable states and thereby is capable of serving as one bit of memory. Today, the term flip-flop has come to mostly denote non-transparent (clocked or edge-triggered) devices, while the simpler transparent ones are often referred to as latches; however, as this distinction is quite new, the two words are sometimes used interchangeably .

A flip-flop is usually controlled by one or two control signals and/or a gate or clock signal. The output often includes the complement as well as the normal output.

The JK flip-flop (Jump-Key flip-flop) augments the behaviour of the SR flip-flop (J=Set, K=Reset) by interpreting the S = R = 1 condition as a "flip" or toggle command. Specifically, the combination J = 1, K = 0 is a command to set the flip-flop; the combination J = 0, K = 1 is a command to reset the flip-flop; and the combination J = K = 1 is a command to toggle the flip-flop, i.e., change its output to the logical complement of its current value. Setting J = K = 0 does NOT result in a D flip-flop, but rather, will hold the current state. To synthesize a D flip-flop, simply set K equal to the complement of J. The JK flip-flop is therefore a universal flip-flop, because it can be configured to work as an SR flip-flop, a D flip-flop, or a T flip-flop.

NOTE: The flip-flop is positive-edge triggered (rising clock pulse) as seen in the timing diagram.
A circuit symbol for a Positive edge triggered JK flip-flop, where > is the clock input, J and K are data inputs, Q is the stored data output, and Q' is the inverse of Q.

The characteristic equation of the JK flip-flop is: Qnext = JQ+KQ (-- indicates bar)

And the corresponding truth table is:

Optocouplers

2010-07-20T01:09:00.001+05:30

In electronics, an opto-isolator (or optical isolator, optical coupling device, optocoupler, photocoupler, or photoMOS) is a device that uses a short optical transmission path to transfer an electronic signal between elements of a circuit, typically a transmitter and a receiver, while keeping them electrically isolated—since the electrical signal is converted to a light beam, transferred, then converted back to an electrical signal, there is no need for electrical connection between the source and destination circuits. Isolation between input and output is rated at 7500 Volt peak for 1 second for a typical component costing less than 1 US$ in small quantities.

    The opto-isolator is simply a package that contains both an infrared light-emitting diode (LED) and a photo detector such as a photosensitive silicon diode, transistor Darlington pair, or silicon controlled rectifier (SCR).
The wave-length responses of the two devices are tailored to be as identical as possible to permit the highest measure of coupling possible. Other circuitry—for example an output amplifier—may be integrated into the package. An opto-isolator is usually thought of as a single integrated package, but opto-isolation can also be achieved by using separate devices.
    Digital opto-isolators change the state of their output when the input state changes; analog isolators produce an analog signal which reproduces the input. A common implementation is a LED and a phototransistor in a light-tight housing to exclude ambient light and without common electrical connection, positioned so that light from the LED will impinge on the photodetector. When an electrical signal is applied to the input of the opto-isolator, its LED lights and illuminates the photodetector, producing a corresponding electrical signal in the output circuit. Unlike a transformer the opto-isolator allows DC coupling and can provide any desired degree of electrical isolation and protection from serious over voltage conditions in one circuit affecting the other. A higher transmission ratio can be obtained by using a Darlington instead of a simple phototransistor, at the cost of reduced noise immunity and higher delay.
    With a photodiode as the detector, the output current is proportional to the intensity of incident light supplied by the emitter. The diode can be used in a photovoltaic mode or a photoconductive mode. In photovoltaic mode, the diode acts as a current source in parallel with a forward-biased diode. The output current and voltage are dependent on the load impedance and light intensity. In photoconductive mode, the diode is connected to a supply voltage, and the magnitude of the current conducted is directly proportional to the intensity of light. This optocoupler type is significantly faster than photo transistor type, but the transmission ratio is very low; it is common to integrate an output amplifier circuit into the same package.
    The optical path may be air or a dielectric waveguide. When high noise immunity is required an optical conductive shield can be integrated into the optical path. The transmitting and receiving elements of an optical isolator may be contained within a single compact module, for mounting, for example, on a circuit board; in this case, the module is often called an optoisolator or opto-isolator. The photosensor may be a photocell, phototransistor, or an optically triggered SCR or TRIAC. This device may in turn operate a power relay or contactor. Analog optoisolators often have two independent, closely matched output phototransistors, one of which is used to linearize the response using negative feedback.

IGBT ( Insulated gate bipolar transistor )

2010-07-20T00:41:00.000+05:30

The insulated gate bipolar transistor or IGBT is a three-terminal power semiconductor device, noted for high efficiency and fast switching. It switches electric power in many modern appliances: electric cars, variable speed refrigerators, air-conditioners, and even stereo systems with switching amplifiers. Since it is designed to rapidly turn on and off, amplifiers that use it often synthesize complex waveforms with pulse width modulation and low-pass filters.

          The IGBT combines the simple gate-drive characteristics of the MOSFETs with the high-current and low–saturation-voltage capability of bipolar transistors by combining an isolated gate FET for the control input, and a bipolar power transistor as a switch, in a single device.
The IGBT is used in medium- to high-power applications such as switched-mode power supply, traction motor control and induction heating. Large IGBT modules typically consist of many devices in parallel and can have very high current handling capabilities in the order of hundreds of amperes with blocking voltages of 6000 V. The IGBT is a fairly recent invention. The first-generation devices of the 1980s and early 1990s were relatively slow in switching, and prone to failure through such modes as latchup and secondary breakdown. Second-generation devices were much improved, and the current third-generation ones are even better, with speed rivaling MOSFETs, and excellent ruggedness and tolerance of overloads.

          The extremely high pulse ratings of second- and third-generation devices also make them useful for generating large power pulses in areas like particle and plasma physics, where they are starting to supersede older devices like thyratrons and triggered spark gaps.

          Their high pulse ratings, and low prices on the surplus market, also make them attractive to the high-voltage hobbyist for controlling large amounts of power to drive devices such as solid-state Tesla coils and coil guns.

          Availability of affordable, reliable IGBTs is a key enabler for electric vehicles and hybrid cars. Toyota's second generation hybrid Prius has a 50 kW IGBT inverter controlling two AC motor/generators connected to the DC battery pack.

Mars Exploration Rover (MER), project done by RAJKUMAR

2010-07-19T20:22:00.040+05:30

This project is a prototype model of actual "MER".
and it is focused on
-->opening of petals,
-->controlling solar panels,-->controlling Rover
-->controlling camera,
-->and receiving video signal from rover to computer.

Actual Rover:-
The Mars Exploration Rovers, launched toward Mars on June 10 and July 7, 2003.A Mars rover is an automated motor vehicle which propels itself across the surface of the planet Mars after landing...but my mars rover is controlled by computer... mainly "MER" project is 2 know abt weather conditions and to take some pictures on mars planet.

Prototype:-
Rajkumar--> “This prototype model consists of spycam 1.3MP,solar panels of each 1.5V/150mA , micro servomotors for controlling camera arm and controlling solar pannels, RX-TX 433 module, encoders(HT12E), decoders(HT12D), motor driver IC(L233d).”

Complete Video of the Project (working):

Project by,

A.Rajkumar
B.tech (EEE), SREC.
contact : 9959025437
rajkumar.a13@gmail.com

electrosparx site info

2010-03-13T18:41:00.031+05:30

Electrosparx'10

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