what are Infrared LEDs ?

Infrared LEDs are just like ordinary LEDs but the light output cannot be seen. To view an infrared LEDs, turn it on with the appropriate battery and dropper resistor and view it with a camera. You will see the illumination on the screen.

Infrared LEDs are sometimes clear and sometimes black. They operate just like a red LED with the same characteristic voltage-drop of about 1.7v.

Sometimes an infrared LED is pulsed with a high current for a very short period of time but the thing to remember is the wattage-dissipation of a 5mm LED is about 70mW. This means the constant-current should be no more than 40mA.

 Infrared LEDs are also called TRANSMITTING LEDs as they emit light. These are given the term Tx (for transmitting). An infrared LED can be connected to a 5v supply via a 220R current-limiting resistor for 15mA current.
 Infrared receivers (Rx) can look exactly like infrared LEDs, but they do not emit IR light. They detect Infrared illumination and must be connected the correct way in a circuit.
They have a very high resistance when no receiving IR illumination and the resistance decreases as the illumination increases.
This means they are connected to a 5v supply via a resistor and when the resistance of the infrared receiver decreases, current will flow thought it and the resistor. This will produce a voltage across the resistor and this voltage is fed to the rest of the circuit.

Here is a circuit to show how to connect an infrared LED and Infrared (diode) receiver:

You cannot use an IR LED as a receiver or an Infrared diode as an illuminator. They are constructed differently. An infrared LED has a characteristic voltage drop of 1.7v An Infrared receiver does not have a characteristic voltage-drop. It has a high resistance when not illuminated and a low resistance when it receives illumination.
 

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Integrated Circuit chips

Figure below shows what is often referred to as an integrated circuit (IC). The circuit is actually etched onto a tiny wafer or “chip” of silicon, embedded in a black plastic body, which is properly referred to as the “package.” Tiny wires inside the package link the circuit with the two rows of pins on either side.

                                    

 

   

                                                                                                                                                                                                                                                                                 

          

Figure 4-2. An integrated circuit chip in Plastic Dual-Inline Pin package, abbreviated PDIP, or, more often, DIP.The pins are mounted at intervals of 1/10 inch in two rows spaced 3/10 inch apart. This format is known as a Plastic Dual Inline Package, abbreviated PDIP, or, more often, just DIP. The chip in the photograph has four pins in each row; others may have many more. The first thing you need to know, when shopping for chips, is that you’ll only be using the DIP package. Figure 4-3 shows a size comparison between a 14-pin DIP package and a 14-pin surface-mount package. Many surface-mount chips are even smaller than the one shown.Just about every chip has a part number printed on it. In Figure 4-2, the part number is KA555. In Figure 4-3, the DIP chip’s part number is M74HC00B1, and the surface-mount chip is a 74LVC07AD. You can ignore the second line of numbers and/or letters on each chip, as they are not part of the part number.

Notice in Figure 4-3 that even though the chips look quite different from each other, they both have “74” in their part numbers. This is because both of them are members of the “7400” family of logic chips, which originally had part numbers from 7400 and upward (7400, 7401, 7402, 7403, and so on). Often they are now referred to as “74xx” chips, where “xx” includes all the members of the family.  The DIP chip, at the rear, has pins spaced 1/10 inch apart, suitable for insertion in a breadboard or perforated board. It can be soldered without special tools. The small-outline integrated circuit (SOIC) surface-mount chip 

(foreground) has solder tabs spaced at 1/20 inch. Other surface-mount chips have pins spaced at 1/40 inch or even less (these dimensions are often expressed in millimeters).

 Surface-mount chips are designed primarily for automated assembly and are difficult to work with manually. In this photo, the yellow lines are 1 inch apart to give you an idea of the scale.Take a look at Figure 4-4, which shows how to interpret a typical part number in a 74xx family member. The initial letters identify the manufacturer (which you can ignore, as it really makes no difference for our purposes).
Skip the letters until you get to the “74.” After that, you find two more letters, which are important. The 74xx family has evolved through many generations, and the letter(s) inserted after the “74” tell you which generation you’re dealing with. Some generations have included:

•  74L
•  74LS
•  74C
•  74HC
•  74AHC
And there are more.

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Sound , Electricity & Sound

Time to establish a clear idea of how sound is transformed into electricity and back into sound again.

Suppose someone bangs a gong with a stick. The flat metal face of the gong vibrates in and out, creating sound waves. A sound wave is a peak of higher air pressure, followed by a trough of lower air pressure.

The wavelength of the sound is the distance (usually ranging from meters to millimeters) between one peak of pressure and the next peak.
The frequency of the sound is the number of waves per second, usually ex- pressed as hertz.

Suppose we put a very sensitive little membrane of thin plastic in the path of the pressure waves. The plastic will flutter in response to the waves, like a leaf fluttering in the wind. Suppose we attach a tiny coil of very thin wire to the back of the membrane so that it moves with the membrane, and let’s posi- tion a stationary magnet inside the coil of wire. This configuration is like a tiny, ultra-sensitive loudspeaker, except that instead of electricity producing sound, it is configured so that sound produces electricity. Sound pressure waves make the membrane move to and fro along the axis of the magnet, and the magnetic field creates a fluctuating voltage in the wire.

This is known as a moving-coil microphone. There are other ways to build a microphone, but this is the configuration that is easiest to understand. Of course, the voltage that it generates is very small, but we can amplify it using a transistor, or a series of transistors. Then we can feed the output through the coil around the neck of a loudspeaker, and the loudspeaker will recreate the pressure waves in the air.

Somewhere along the way, we may want to record the sound and then replay it. But the principle remains the same. The hard part is designing the microphone, the amplifier, and the loudspeaker so that they reproduce the waveforms accurately at each step. It’s a significant challenge, which is why accurate sound reproduction can be elusive.

Time now to think about what happens inside the wire when it generates a magnetic field. Obviously, some of the power in the wire is being transformed into magnetic force. But just what exactly is going on?

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origin of LoudSpeakers

Loudspeakers utilize the fact that if you run a varying electrical current through a coil situated in a magnetic field, the coil will move in response to the current. This idea was introduced in 1874 by Ernst Siemens, a prolific German inventor. (He also built the world’s first electrically powered elevator in 1880.) Today, Siemens AG is one of the largest electronics companies in the world.

When Alexander Graham Bell patented the telephone in 1876, he used Siemen’s concept to create audible frequencies in the earpiece. From that point on, sound-reproduction devices gradually increased in quality and power, until Chester Rice and Edward Kellogg at General Electric published a paper in 1925 establishing basic principles that are still used in loudspeaker design today.

 As sound amplifiers became more powerful, speaker efficiency became less important compared with quality reproduction and low manufacturing costs. Today’s loudspeakers convert only about 1% of electrical energy into acoustical energy.

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Best Android apps for Electronic and Electrical Engineers

1.Electrodroid

ElectroDroid is a simple and powerful collection of electronics tools and references.

                           

Download Electrodroid free

2.Everycircuit

EveryCircuit is not just an eye candy. Under the hood it packs custom-built simulation engine optimized for interactive mobile use, serious numerical methods, and realistic device models. In short, Ohm's law, Kirchhoff's current and voltage laws, nonlinear semiconductor device equations, and all the good stuff is there.

Growing library of components gives you freedom to design any analog or digital circuit from a simple voltage divider to transistor-level masterpiece.

Schematic editor features automatic wire routing, and minimalistic user interface. No nonsense, less tapping, more productivity.

                               

Download Everycircuit free

3.Engineering Handbook Lite

This is an amazingly useful and handy app for every engineering student.  It provides all the concepts of engineering and formulae and can also help in length mathematical calculations.

Download Engineering handbook lite free

4.Droid Tesla

is another free app for simulating electronic circuits. This SPICE simulation tool is quiet similar to the app “EveryCircuit” mentioned above in its functionality - means you can build and simulate a circuit. But they both (EveryCircuit and DroidTesla) differ in user interface and features provided.

Download Droid tesla Free

5.Electronics Tooolkit

is another free app which is a collection of simple tools like resistor color code calculator, series and parallel calculator etc. Almost all those tools are available in ElectroDroid app too, except for a Power Triangle calculator. I have listed this app here as it is free (and I have spent some time to download and test this app in my Galaxy) and you guys can try out, if you have time.More than 10,000 users have tried this application.

Download Electronics toolkit Free

6.AllDataSheet app

This app is free version of the Datasheet website Alldatasheet.com. This app is nothing more than a book mark to alldatasheet website’s mobile version. I dont recommend you to download this app as your purpose will be served by visiting Alldatasheet.com from your mobile browser (which will get automatically redirected to mobile version) 

Download AllDataSheet app Free

7.Logic simulator

Logic Simulator is a powerful tool for simulating logic circuits and testing how different gates can be used in a circuit,

It offers a big workspace and a simple menu system. It is perfect for education on a mobile platform.

To connect nodes you simply click on an output and then click on an input to connect it to.

Download Logic simulator Free

8.Electronics Calculator

Simple electronics tools & calculators for your DIY projects.

Tools:
- Resistor Color Code (4,5 &6 band)
- Capacitor Conversion Calculator & Table
- Capacitor Code Converter (code to values - vica versa)
- Resistor in Series & Parallel
- Capacitor in Series & Parallel

Download Electronics calculator Free

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what is a Relay ?

A Relay is an electromagnetic device which is used to isolate two circuits electrically and connects them magnetically.
It is basically used in intrerfacing electronic circuit to an electric circuit. it means that a small DC voltage drives circuits working at large voltages like 230V AC (as in our homes).

A Relay consist of two parts
1. Input
2. Output

Input consist of a coil which gets energized when a voltage with appropriate magnitude is applied to it ( this voltage is known as Operating voltage). when the coil gets energized it generates a magnetic field which is responsible for the switching action of a relay.

Output consist of three contactors viz, NO,NC and COM.

NC- normally closed- In normal state or energized state the COM is connected to NC.
NO- normally open- In energized state COM gets connected to the NO.

When the DC voltage is applied at the input of relay the input coil gets energized by the applied voltage and generates magnetic field , this magnetic field switches over the COM contactor to NO
contactor. in this  way switching takes  place. and when the circuit gets denergized on the input side the COM is back to NC by a spring mechanism.

Types of relays-
1. DPDT
2.SPST
3.SPDT
4.DPST

DPDT- Double pole double throw - used to control two circuits , it has 6 pins. generally used in  robotics applications.

SPST- Single pole single throw - it is used for normal switching applications like ON/OFF.

SPDT- Single pole double throw- it is used for selecting "either" of the two power supplies. for eg. switching from 12V DC supply to 24V DC supply in a circuit.

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Soldering on a perfboard

Carefully note the position of a component on your bread- board, and then move it to the same relative position on the perfboard, poking its wires through the little holes. Turn the perfboard upside down, make sure that it’s stable, and examine the hole where the wire is poking through, as shown in Figure below.

 A copper trace surrounds this hole and links it with others. Your task is to melt solder so that it sticks to the copper and also to the wire, forming a solid, reliable connection between the two of them. Take your pencil-style soldering iron in one hand and some solder in your other hand. Hold the tip of the iron against the wire and the copper, and feed some thin solder to their intersection. After two to four seconds, the solder should start flowing.



Allow enough solder to form a rounded bump sealing the wire and the copper, as shown in Figure below :

Wait for the solder to harden thoroughly, If all is well, snip the protruding wire with your cutters. See Figure below :

 

PerfBoard Errors :

 TOO MUCH SOLDER :

If the joint is thin, the wire can break free from the solder as it cools. Even a microscopic crack is sufficient to stop the circuit from working. In extreme cases, the solder sticks to the wire, and sticks to the copper trace around the wire, yet doesn’t make a solid bridge con- necting the two, leaving the wire encircled by solder yet untouched by it, as shown in Figure below. 

You may find this undetectable unless you observe it with magnification. You can add more solder to any joint that may have insufficient solder, but be sure to reheat the joint thoroughly. 

COMPONENTS PLACED INCORRECTLY :

It’s very easy to put a component one hole away from the position where it should be. It’s also easy to forget to make a connection. I suggest that you print a copy of the schematic, and each time you make a connection on the perforated board, you eliminate that wire on your hardcopy, using a highlighter.

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All about Diodes

A diode is a very early type of semiconductor. It allows electricity to flow in one direction, but blocks it in the opposite direction. (A light-emitting diode is a much more recent invention.) Like an LED, a diode can be damaged by revers- ing the voltage and applying excessive power, but most diodes generally have a much greater tolerance for this than LEDs. The end of the diode that blocks positive voltage is always marked, usually with a circular band, while the other end remains unmarked. Diodes are especially useful in logic circuits, and can also convert alternating current (AC) into direct current (DC).

A Zener diode is a special type that  blocks current completely in one direction, and also blocks it in the other direction until a threshold voltage is reached.

Signal diodes are available for various different voltages and wattages. Like any semiconductor, they can overheat and burn out if they are subjected to mistreatment. The schematic symbol for a diode has only one significant variant: sometimes the triangle is outlined instead of filled solid black (see in Figure below).

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What are capacitors?

DC current does not flow through a capacitor, but voltage can accumulate very quickly inside it, and remains after the power supply is disconnected. Figures below may help to give you an idea of what happens inside a capacitor when it is fully charged.

In most modern electrolytic capacitors, the plates have been reduced to two strips of very thin, flexible, metallic film, often wrapped around each other, separated by an equally thin insulator. Disc ceramic capacitors typically consist of just a single disc of nonconductive material with metal painted on both sides and leads soldered on. The two most common varieties of capacitors are ceramic (capable of storing a relatively small charge) and electrolytic (which can be much larger). Ceramics are often disc-shaped and yellow in color; electrolytics are often shaped like miniature tin cans and may be just about any color.

Ceramic capacitors have no polarity, meaning that you can apply negative volt- age to either side of them. Electrolytics do have polarity, and won’t work unless you connect them the right way around. The schematic symbol for a capacitor has two significant variants: with two straight lines (symbolizing the plates inside a capacitor), or with one straight line and one curved line, as shown in below.

 

 When you see a curved line, that side of the capacitor should be more negative than the other. The schemat- ic symbol may also include a + sign. Unfortunately, some people don’t bother to draw a curved plate on a polarized capacitor, yet others draw a curved plate even on a nonpolarized capacitor.

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All about Switches

When you flip a toggle switch  it connects the center terminal with one of the outer terminals. Flip the switch back, and it connects the center terminal with the other outer terminal, as shown in Figure below:

 The center terminal is called the pole of the switch. Because you can flip, or throw, this switch to make two possible connections, it is called a double-throw switch.  Some switches are on/off, meaning that if you throw them in one direction they make a contact, but in the other direction, they make no contact at all. Most of the light switches in your house are like this. They are known as single-throw switches. A single-pole, single-throw switch is abbreviated SPST.

 Some switches have two entirely separate poles, so you can make two separate connections simultaneously when you flip the switch. These are called double-pole switches. Check the photographs below

SPARKING :

 When you make and break an electrical connection, it tends to create a spark. Sparking is bad for switch contacts. It eats them until the switch doesn’t make a reliable connection anymore. For this reason, you must use a switch that is appropriate for the voltage and amperage that you are dealing with. Electronic circuits generally are low-current, and low-voltage, so you can use almost any switch, but if you are switching a motor, it will tend to suck an initial surge of cur- rent that is at least double the rating of the motor when it is running constantly. You should probably use a 4-amp switch to turn a 2-amp motor on and off.

Checking a switch :

You can use your meter to check a switch. Doing this helps you find out which contacts are connected when you turn a switch one way or the other.
 Set your meter to measure ohms, and touch the probes to the switch terminals while you work the switch. This is a hassle, though, because you have to wait while the meter makes an accurate measurement. When you just want to know whether there is a connection, your meter has a "continuity tester" setting. It beeps if it finds a connection, and stays silent if it doesn’t.

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Exploring Potentiometers

Potentiometers come in various shapes and sizes, but they all do the same thing: they allow you to vary voltage and current by varying resistance.

Most potentiometers are held together with little metal tabs. You should be able to grab hold of the tabs with your wire cutters or pliers, and bend them up and outward. If you do this, the potentiometer should open up as shown

Depending whether you have a really cheap potentiometer or a slightly more high-class version, you may find a circular track of conductive plastic or a loop of coiled wire. Either way, the principle is the same. The wire or the plastic possesses some resistance (a total of 2K ), and as you turn the shaft of the potentiometer, a wiper rubs against the resistance, giving you a shortcut to any point from the center terminal.

To test your potentiometer, set your meter to measure resistance (ohms) and touch the probes while turning the potentiometer shaft to and fro, as shown below

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How much voltage does a wire consume?

 Normally, we can ignore the resistance in electric wires, such as the little leads of wire that stick out of resistors, because it’s trivial. However, if you try to force large amounts of current through long lengths of thin wire, the resistance of the wire can become important.

How important? we can use Ohm’s Law to find out.
Suppose that a very long piece of wire has a resistance of 0.2Ω. And we want to run 15 amps through it. How much voltage will the wire steal from the circuit, because of its resistance?
 Once again, you begin by writing down what you know:
R = 0.2
I = 15

 We want to know V, the potential difference, for the wire, so we use the version of Ohm’s Law that places V on the left side:

V = I × R

 Now plug in the values: V = 15 × 0.2 = 3 volts Three volts is not a big deal if you have a high-voltage power supply, but if you are using a 12-volt car battery, this length of wire will take one-quarter of the available voltage. Now you know why the wiring in automobiles is relatively thick—to reduce its resistance well below 0.2Ω.

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How an LDR(light dependent resistor) works!!!!

An LDR is a component that has a resistance that changes with the light intensity that falls upon it. They have a resistance that falls with an increase in the light intensity falling upon the device.   

An LDR is made of a high resistance semiconductor. In the dark, an LDR can have a resistance as high as a few megaohms (MΩ), while in the light, an LDR can have a resistance as low as a few hundred ohms. If incident light on an LDR exceeds a certain frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electrons (and their hole partners) conduct electricity, thereby lowering resistance. The resistance range and sensitivity of an LDR can substantially differ among dissimilar devices. Moreover, unique LDR may react substantially differently to photons within certain wavelength bands.

The resistance of an LDR may typically have the following resistances. 
Daylight =5000Ω  Dark =20,000,000Ω  

You can therefore see that there is a large variation between these figures. If you plot this variation on a graph you would get something similar to that shown by the graph below. 

Applications 

There are many applications for Light Dependent Resistors. These include:  

Lighting switch  The most obvious application for an LDR is to automatically turn on a light at certain light level.

 An example of this could be a street light.  

Camera shutter control LDRs can be used to control the shutter speed on a camera. The LDR would be used the measure the light intensity and the set the camera shutter speed to the appropriate level.  

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Know about Resistor color code!!

RESISTOR COLOR CODE

Some resistors have their value clearly stated on them in microscopic print that you can read with a magnifying glass. Most, however, are color-coded with stripes. The code works like this: first, ignore the color of the body of the resis- tor. Second, look for a silver or gold stripe. If you find it, turn the resistor so that the stripe is on the righthand side. Silver means that the value of the resistor is accurate within 10%, while gold means that the value is accurate within 5%. If you don’t find a silver or gold stripe, turn the resistor so that the stripes are clustered at the left end. You should now find yourself looking at three colored stripes on the left.  

Note that the color-coding is consistent, so that green, for instance, means either a value of 5 (for the first two stripes) or 5 zeros (for the third stripe). Also, the sequence of colors is the same as their sequence in a rainbow. So, a resistor colored brown-red-green would have a value of 1-2 and five zeros, making 1,200,000 ohms, or 1.2MΩ. A resistor colored orange-orange-orange would have a value of 3-3 and three zeros, making 33,000 ohms, or 33KΩ. A resistor colored brown-black-red would have a value of 1-0 and two additional zeros, or 1KΩ.

If you run across a resistor with four stripes instead of three, the first three stripes are digits and the fourth stripe is the number of zeros. The third numeric stripe allows the resistor to be calibrated to a finer tolerance. Confusing? Absolutely. That’s why it’s easier to use your meter to check the values. Just be aware that the meter reading may be slightly different from the claimed value of the resistor. This can happen because your meter isn’t absolutely accu- rate, or because the resistor is not absolutely accurate, or both. As long as you’re within 5% of the claimed value, it doesn’t matter for our purposes.

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