Ohm's Law

3D View of PN Junction

P Type and N Type Materials- Before forming the Junction

P and N type Materials Brought together

Recombination Started (Gold Balls- Recombination)

Depletion Region Formed

Courtesy: www.ineer.org
(From the article: 'Education in Three Dimensions: Using Virtual Reality in Education for Illustrating Spatial Relationships' by ALLPORT, Christopher, SINES, Paul, SCHREINER, Brandon & DAS, Biswajit)

THE PIEZOELECTRIC ACCELEROMETER (VIBRATION SENSOR) (Compression Type)

Accelerometers for the measurement of acceleration, shock or vibration come in many types using different principles of operation.

 

Inside a piezoelectric version, the sensing element is a crystal which has the property of emitting a charge when subjected to a compressive force.
In the accelerometer, this crystal is bonded to a mass such that when the accelerometer is subjected to a 'g' force, the mass compresses the crystal which emits a signal. This signal value can be related to the imposed 'g' force.

The sensing element is housed in a suitable sensor body to withstand the environmental conditions of the particular application. Body are usually made in stainless steel with welding of the various parts to prevent the ingress of dust, water, etc.
Electrical connection can be via a sealed cable or a plug/socket arrangement.
Many present accelerometers have internal electronic circuitry to give outputs which can be directed used by the associated acquisition or control systems.

Mechanical fixing of the sensor is important in order to achieve true transfer of the vibration or acceleration. Many fixing methods are used including beeswax, hard glues, threaded stud (male or female), magnetic mounts.
Accelerometers are used in many scientific and industrial applications such as predictive maintenance, aerospace, automotive, medical, process control, etc.

Square wave Vs Sine Wave

In the older instruments, all the generators outputs only radio frequency or 'RF'. Basically higher frequency range creates a wave form that is naturally rounded at the top and bottom.It is much more difficult to produce a very sharp signals at this high rate of oscillation.

With the advent of the new designs, then rate at which the signals are emitted dropped down which is called audio frequency.with the low frequency,the signal can be very sharp during turned on and off.This square wave design is used generally when running the lower audio frequencies. 

By Conclusion,
The signal with high frequency produces sine wave and the signal with low audio frequency produces square wave.

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A quick tour on breadboard

Bread Board is a great tool to design and test your circuits. You do not need to solder wires and components to make a circuit while using a bread board. It is easier to mount components & reuse them. Since, components are not soldered you can change your circuit design at any point without any hassle.

Structure of a Bread Board: Basically, a bread board is an array of conductive metal clips encased in a box made of white ABS plastic, where each clip is insulated with another clips. There are a number of holes on the plastic box, arranged in a particular fashion. A typical bread board layout consists of two types of region also called strips. Bus strips and socket strips. Bus strips are usually used to provide power supply to the circuit. It consists of two columns, one for power voltage and other for ground.

Socket strips are used to hold most of the components in a circuit. Generally it consists of two sections each with 5 rows and 64 columns. Every column is electrically connected from inside

The breadboard above is a single panel with two attached "bus strips." The second picture gives a little more detail. The green lines represent the internal connections of the breadboard. The bus strips on this breadboard are labeled + and - and are used for power. They run the length of the breadboard. Also, notice that the way that they are arranged, the inside edges of each bus strip is opposite polarity. This really helps when working with standard logic and most other ICs.The middle area is the component area, and this is where you will work your electronic magic.

Inside the Breadboard :

On some breaboards, the bus strips may be broken at the middle (Usually between row 31 and 33.) This splits your bus strips into 4 separate strips. This is useful if you are working with more than one voltage on your breadboard. If you need only one supply voltage on your circuit, then you should add a jumper across this gap to reconnect the bus strips.

 

Types of Breadboard :

1.Most commonly used one.

2.Breadboard with built-in power supply.

 This particular breadboard is no longer made. It has a +5V fixed supply capable of 1A, and a +- 15V supply. It also has two digital switches and two momentary switches connected to flip-flops. Lastly, it has two LEDs with current limiting resistors. If you are interested in getting a breadboard like this (or maybe something more modern) check eBay or google for "Powered Breadboard" or "Powered Protoboard." 

Courtesy:robocommunity.com

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Sound Waves

SOUND:

Sound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing.Sound also travels through plasma.

Sound is a sequence of waves of pressure that propagates through compressible media such as air or water. Sound that is perceptible by humans has frequencies from about 20 Hz to 20,000 Hz.

The behavior of sound propagation is generally affected by three things:

• A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within the medium.
• The propagation is also affected by the motion of the medium itself. For example, sound moving through wind. Independent of the motion of sound through the medium, if the medium is moving, the sound is further transported.
• The viscosity of the medium also affects the motion of sound waves. It determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.

simple simulation of sound waves traveling in air

Longitudinal Waves and Tuning Forks

Sound waves are produced by vibrating objects. Whether it be the sound of a person's voice, the sound of a piano, the sound of a trombone or the sound of a physics book slamming to the floor, the source of the sound is always a vibrating object.

A tuning fork serves as a useful illustration of how a vibrating object can produce sound. The fork consists of a handle and two tines. When the tuning fork is hit with a rubber hammer, the tines begin to vibrate. The back and forth vibration of the tines produce disturbances of surrounding air molecules. As a tine stretches outward from its usual position, it compresses surrounding air molecules into a small region of space, this creates a high pressure region next to the tine.

As the tine then moves inward from its usual position, air surrounding the tine expands; this produces a low pressure region next to the tine. The high pressure regions are known as compressions and the low pressure regions are known as rarefactions. As the tines continue to vibrate, an alternating pattern of high and low pressure regions are created. These regions are transported through the surrounding air, carrying the sound signal from one location to another.




Sound waves of Tuning Fork

Here is the link shows the animation on the sound waves.....

Animations of Sound Waves

Introduction to electrons in crystals

A meaningful discussion of semi­conductors requires some background on how electrons move through solids. The free-electron gas model simply assumes that the electrons move through an empty periodic box. But of course, to describe a real solid the box should really be filled with the countless atoms around which the conduction electrons move. 

Click below to view the animation
electrons animation



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Measuring and Testing Devices-Electrical and Electronics

Electrical Measuring Devices-Analog

Electrical measuring devices are more commonly referred to as meters. Analog meters can either measure one circuit value (current, voltage, and resistance), or they can measure all of these. Meters that measure multiple types of characteristics are called multimeters. An analog meter has a needle that swings one way or another to indicate the value being measured. A resistance meter reads in reverse. What this means is that no needle swing indicates an open circuit, or infinite resistance. Typically, an analog resistance meter must be calibrated to zero ohms resistance every time it is used to obtain optimal accuracy. Older analog meters will usually only have three settings, one for each value they measure. Newer meters will have multiple scales from which to choose, since an analog meter’s measurements are more accurate when the needle is in the middle of the scale.

Electrical Measuring Devices- Digital

Like analog meters, digital meters can test one value, or they can test a combination of values. Also, some of these only have three settings- current, voltage, and resistance- while more advanced meters have different scales for each of the three types of values. Some meters (usually lower cost handheld units) are accurate to within two or three decimal places, while others, usually expensive desktop or bench-top meters, can measure out to as many as ten decimal places. Some have rotary dials to select type of value and range, while others are pushbutton operated. There are also meters that combine these two features, with the dial selecting the reading type and the buttons selecting the range. More expensive meters also have settings to audibly test for continuity, capacitance, and inductance, and some specialty meters also have the ability to test transistor junctions. There are also meters that have special settings for testing alkaline batteries.

Clamp-Type Meters

This type of meter is designed for measuring higher currents without putting either you or your meter at risk of shock. Some of these meters only measure current, while others measure voltage and resistance as well. Voltage and resistance are measured the same way as with any other type of meter. The difference is that current is measured by clamping the meter’s clamps over the power cable with the meter switch(es) set to current. Some meters of this type are capable of reading from zero to a few thousand amps, while most clamp-type meters will read as high as 100 amps.

Solenoid Voltage Meter

This type of meter only reads voltage, both for alternating and direct current. However, the ranges this type of meter is able to read are from 120 to 600 volts. When voltage is detected, a solenoid moves an indicator up or down a graduated scale, which indicates the amount of voltage present in the circuit. It’s used in exactly the same way as an analog or digital meter is used when measuring voltage. This is an indispensable part of an electrician’s toolkit, and we call them wiggies.

Network Cable Testing Tools

Network technicians have need of a completely different set of electrical testing tools.
The first of these is the toner and probe combination. The toner is a tone generator and it creates a 1 kilohertz signal, which can be injected onto a wire, either by a telephone jack or with alligator clips. The probe will pick up this tone by induction. Network technicians usually use this tool set to identify a particular network cable in a cable bundle.
Another type of test tool that a network technician uses is called a modtaps. This is used to test an installed network cable and make sure that it’s properly terminated and is a two-piece test set. The two portions of the tool are plugged into the wire at either end, a button is pressed, and lights on the master unit light up to indicate continuity and proper wiring.

Courtesy:.brighthubengineering.com

 

 

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Battery Arrangement and Power

Based on the applications,the arrangement of cells taking place.They are two ways.
1. serial arrangement-To increase the voltage
2. parallel arrangement-To increase the current

1.Parallel Arrangement

The four batteries in parallel in the upper diagram produces the voltage in one cell and they will supply the current four times of it.Current is the rate at which electric charge passes through a circuit, and is measured in amperes. Batteries are rated in amp-hours, or, in the case of smaller household batteries, milliamp-hours (mAH). A typical household cell rated at 500 milliamp-hours should be able to supply 500 milliamps of current to the load for one hour. You can slice and dice the milliamp-hour rating in lots of different ways. A 500 milliamp-hour battery could also produce 5 milliamps for 100 hours, 10 milliamps for 50 hours, or, theoretically, 1,000 milliamps for 30 minutes. Generally speaking, batteries with higher amp-hour ratings have greater capacities.

2.Serial Arrangement

The four batteries in series in the upper diagram produces the current in one cell and they will supply the voltage four times of it.Voltage is a measure of energy per unit charge and is measured in volts. In a battery, voltage determines how strongly electrons are pushed through a circuit, much like pressure determines how strongly water is pushed through a hose. Most AAA, AA, C and D batteries are around 1.5 volts.

Imagine the batteries shown in the diagram are rated at 1.5 volts and 500 milliamp-hours. The four batteries in parallel arrangement will produce 1.5 volts at 2,000 milliamp-hours. The four batteries arranged in a series will produce 6 volts at 500 milliamp-hours.



Courtesy: entertainment.howstuffworks.com



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Resistors

Resistor

what is a resistor?

A resistor is anything that electricity can not travel through easily. When electricity is forced through a resistor, often the energy in the electricity is changed into another form of energy, such as light or heat. The reason a light bulb glows is that electricity is forced through tungsten, which is a resistor. The energy is released as light and heat.
A conductor is the opposite of a resistor. Electricity travels easily and efficiently through a conductor, with almost no other energy released as it passes.

A resistor placed at the exterior of a spacecraft can release extra electrical energy into space as heat.

Types of resistors

1. CARBON FILM

    The most popular resistor type. This resistor made by depositing a carbon film onto a small ceramic cylinder. A small spiral groove cut into the film controls the amount of carbon between the leads, hence setting the resistance. Such resistors show excellent reliability, excellent solderability, noise stability, moisture stability, and heat stability. Typical power ratings range from 1/4 to 2 W. Resistances range from about 10 Ohm to 1 MOhm, with tolerances around 5 percent.

Typically yellow or tan jacket, peanut shape , 4 band code

CARBON COMPOSITION

This type is also popular. Its made from a mixture of carbon powder and glue like binder. To increase the resistance, less carbon is added. These resistors show predictable performance, low inductance, and low capacitance. Power ratings range from about 1/4 to 2 W. Resistances range from 1 Ohm to about 100 MOhm, with tolerances around +/- 5 percent.

Typically brown jacket, straight cylinder shape, 5 band code

METAL OXIDE FILM

This type is general purpose resistor. It uses a ceramic core coated with a metal oxide film. These resistors are mechanically and electrically stable and readable during high temperature operation. They contain a special paint on their outer surfaces making them resistant to flames, solvents, heat, and humidity. Typical resistances range from 1 Ohm to 200 kOhm, with typical tolerances of +/- 5 percent. 

Usually blue or grey color, 4 band code

PRECISION METAL FILM

 This type is very accurate, ultra low noise resistor. It uses a ceramic substrate coated with a metal film, all encased in an epoxy shell. These resistors are used in precision devices, such as test instruments, digital and analog devices, and audio and video devices. Resistances range from about 10 Ohm to 2 MOhm, with power rating from 1/4 to about 1/2 W, and tolerances of +/- 1 percent.

Typical blue color, 5 band code

PRECISION WIRE WOUND

The precision wire wound resistor is a highly accurate resistor (within 0.005%) with a very low TCR. A TCR of as little as 3ppm/^o C can be achieved. However these components are too expensive for general use and are normally used in highly accurate dc applications.

HIGH POWER WIRE WOUND

These resistors are used for high power applications. Types include vitreous enamel coated, cement, and aluminum housed wire wound resistors. Resistive elements are made from a resistive wire that is coiled around a ceramic cylinder. These are the most durable of the resistors, with high heat dissipation and high temperature stability. Resistances range from 0.1 Ohm to  about 150 kOhm, with power ratings from around 2 W to as high as 500 W, or more.

VARIABLE RESISTORS

Variable resistors provide varying degrees of resistance that can be set with the turn of a knob. Special kinds of variable resistors include potensiometers, rheostats, and trimmers. Potensiometers and rheostats are essentially the same thing, but rheostats are used specially for high power AC electricity, whereas potensiometers typically are used with lower level DC electricity. Both potensiometers and rheostats are designed for frequent adjustment. Trimmers, on the other hand, are miniature potensiometers that are adjusted infrequently and usually come with pins that can be inserted into pcb. They are used for fine tuning circuits (eg. : fine tuning a circuit that goes astray as it ages), and they are usually hidden within a circuits enclosure box. Variable resistors come with 2 or 3 terminals. There are 2 kinds of taper, ie. : linear tapered and nonlinear tapered (logarithmic). The 'taper' describes the way in which the resistance changes as the control knob is twisted. Linear taper usually has coded as 'A' while nonlinear tapes has coded as 'B'.

Color coding

Black Brown Red Orange Yellow Green Blue Violet Grey White  

How to remember?

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