Electronics is the science and technology of electronic phenomena .
It is a branch of physics that deals with the emission, behaviour, and effects of electrons and with electronic devices
Electronics, pronounced as elec.tron.ics

The beginnings of electronics can be traced to experiments with electricity. In the 1880s
Thomas Alva Edison and others observed the flow of current between the elements in an evacuated glass tube .
By 1920 , the development of vacuum tubes and circuits employing them had advanced to the point where their superiority over all other devices used in radio transmitters and receivers was apparent.

In 1948 William Shockley , John Bardeen , and
Walter H.
Brattain of Bell Telephone
Laboratories developed the First transistor and during the early 1950's the technology was developed to mass-produce transistors.
The invention of the transistor initiated a progressive miniaturization of electronic components . By the mid 1980s ,high-density microprocessors were developed that led to tremendous advancement in Computer technology.

During the 1970's and 1980's the size of the components of integrated circuits continued to be reduced and the number of components that could be produced on each chip grew rapidly.
With increasing miniaturization, the capabilities of the electronic circuits and the speed at which they could perform their functions greatly increased.

By 1990's , introduction of
Microelectronics led to the development of new technologies, such as digital audio recording ; to the introduction of new products, such as personal computers ; and to the reduction in the size of portable telephones and many other electronic products.

Hobby electronics combines creativity and tinkering as part of the fun process of creating devices that are born out of passion, learning, dedication, curiosity and, most importantly, play.

Before building a circuit, it is necessary to understand some basics of electronics .
Electronics involves current and voltage.
Current
Current is the flows of electrons through a wire. Current flows from points of high voltage to points of low voltage.
The unit of measurement for current is the
Ampere (Amp) and is abbreviated as A

Voltage
Voltage indicates the power level of a point and is measured in Volts .
If one point is at 5 volts and another point is at 0 volts then when a wire is connected between them, current will flow from the point at 5 volts to the point at 0 volts.

Semiconductor is a substance that releases 'free electrons' from its outermost orbit when exposed to energy such as heat or light.
The space from which electrons are released is called a 'hole.'
Semiconductors carry electrical current when they release 'free electrons.'

Typical Semiconductor materials are Silicon and Germanium . By adding impurities, it is easy to create p-type semiconductors with many 'holes' and n-type semiconductors with many 'free electrons
When these two types of semiconductors are joined, they form an element called a diode . Transistors and IC's are formed by combining large numbers of these diodes.

When P-type and N-type silicon are placed in contact with one another it forms a PN junction

Biasing of PN Junction
A basic PN junction creates a diode that allows electricity to flow in one direction but not the other
Near the PN junction the electrons diffuse into the vacant holes in the P material causing a depletion zone .
This depletion zone acts like an insulator preventing other free electrons in the N-type silicon and holes in the P-type silicon from combining

There is a simple relationship between current, voltage and resistance. This relationship is called
Ohm’s Law.
Difference in Voltage = Current x Resistance
V=Ix R
Current = Difference in Voltage / Resistance
I = V / R
Resistance = Difference in Voltage / Current
R = V / I

Resistors are components that have a predetermined resistance.
Resistance determines how much current will flow through a component. Resistors are used to control voltages and currents. Resistance is given in units of ohms

Resistor Colour code
Value of a resistor is determined using the color coded stripes on the resistor .

Let us the a Resistor.
Its colour stripes are brown, black, orange and gold.
Value of brown is 1 and that of black is 0.
Combining these two gives 10.
The third colour is orange which means x
1,000.
The value of the resistance is found as 10 x
1000 = 10,000 ohms or 10 Kilo Ohms or 10K.
The gold stripe is the tolerance that means the actual value of the resistor mar vary by 5%

Series Connection
When two resistors are connected in series, their resistance will add together
For example if R1 is 500 ohms and R2 250 ohms, then R1 + R2 = 500 + 250 = 750 ohms
Parallel Connection
When two resistors are connected in parallel, their resistance will decrease. For example if
R1 is 500 and R2 = 250 then the resistance is
500 x 250) / (500 + 250) = (125,000) / (750) =
167 ohms.

Variable Resistors
Resistance of Variable resistor can be increased or decreased. They have a dial or a knob that allows you to change the resistance .In higher resistance, less current flow and in lower resistance ,more current will flow

Capacitors store current and allow AC to pass through it. Capacitor has two electrodes and between them there is a dielectric material.
Electrolytic capacitors have value
printed on its body. Pins can be easily identified. Large pin is positive. Moreover a black / white band is printed near the negative terminal to identify the polarity.

In Disc capacitors, only a number is printed on its body. One or two numbers on the capacitor represents value in PF. E.g. 8 = 8PF
Some have 3 numbers and if the third number
is zero, then the value is in P E.g. 100 = 100PF
If the capacitor has 3 numbers and the third number is not a zero, it represents the number of zeros after the first and second digits E.g. 104 = 10 – 0000 PF
Disc capacitor is non polarized and can be connected either way round

Diodes allow current to flow in only one direction. They have a positive side leg and a negative leg . When the voltage on the positive leg is higher than on the negative leg then current flows through the diode
The negative leg of a diode is the Cathode and positive end is Anode

Types of Diodes

Light Emitting Diode

LEDs use a special material which emits light when current flows through it. A current of 0.02 Amps (20 mA) to 0.04
Amps (40 mA) is a good range for LEDs.
LED Requires a series resistor to restrict the current through it. The resistor value can be determined using Ohm’s law

Transistor act as a simple switch to turn a part of circuit on and off.
The transistor has three pins namely
Collector (C) Base (B) and Emitter (E).
The Base (B) is the On/Off switch for the transistor. If a current is flowing to the
Base, current flows from the Collector (C) to Emitter in NPN transistor and Emitter to Collector in PNP transistor

Transistor has codes to identify them. Usually the code has two letters followed by the part number
First letter
A – Germanium B – Silicon C – Gallium Arsenide
D – Indium Antimide
Second letter
C – Audio frequency Amplifier D – Audio frequency power amplifier F – Low power Radio frequency amplifier P – High power Radio frequency amplifier
E.g. BC 548 is B – Silicon C - Audio frequency amplifier

Switches are devices that create a short circuit or an open circuit depending on the position of the switch. For a switch,
ON means short circuit. When the switch is OFF, that means there is an open circuit