Electronics - Theory and Practice

Create Electronics Schematics and PCB Layout Using DipTrace

There 2 kinds of diptrace version that are Professional version and free version.

DipTrace is a complete state-of-the-art PCB Design System. It includes:

• PCB Layout — PCB design with an easy to use manual routing tools, auto-router and auto-placer.
• Schematic — Schematic Capture and export to PCB or Spice.
• Pattern Editor — allows you to create part footprints.
• Component Editor — allows you to draw parts and make components.

Features:

1. Complete Library

2. Autorouting (automatic conversion schematics to PCB layout design)

3. Add and edit pattern

4. Print Features

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Safety Rules, Preventing the Electric Shock

While you are working on electric circuits, there is often the possibility of receiving an electric shock by touching the “live” conductors when the power is on. The shock is a sudden involuntary contraction of the muscles, with a feeling of pain, caused by current through the body. If severe enough, the shock can be fatal. Safety first, therefore, should always be the rule.

The greatest shock hazard is from high voltage circuits that can supply appreciable amounts of power. The resistance of the human body is also an important factor. If you hold a conducting wire in each hand, the resistance of the body across the conductors is about 10,000 to 50,000 ohms. Holding the conductors tighter lowers the resistance. If you hold only one conductor, your resistance is much higher. It follows that the higher the body resistance, the smaller the current that can flow through you.

A safety rule, therefore, is to work with only one hand if the power is on. Also, keep yourself insulated from earth ground when working on power-line circuits, since one side of the line is usually connected to earth. In addition, the metal chassis of radio and television receivers is often connected to the power line ground. The final and best safety rule is to work on the circuits with the power disconnected if at all possible, and make resistance tests.

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Magnetism

This article explain the complete basic theory of magneticm.

MAGNETISM AND ELECTRICITY
Any wire carrying a current of electrons is surrounded by an unseen area of force called a magnetic field. For this reason, any study of electricity or electronics must consider magnetism.

Almost everyone has had experiences with magnets or with pocket compasses at one time or another. A magnet attracts pieces of iron but has little affect on practically everything else. Why does it single out the iron? A compass, when laid on a table, swings back and forth, finally coming to rest pointing toward the North Pole of the world. Why does it always point in the same direction?

These and other questions about magnetism have puzzled scientists for hundreds of years. It is only relatively recently that theories seeming to answer many of the perplexing questions that arise when magnetism is investigated have been developed.

Radio and electronic apparatus such as relays, circuit breakers, earphones, loudspeakers, transformers, chokes, magnetron tubes, television tubes, phonograph pickups, tape and disk recorders, microphones, meters, motors, and generators depend on magnetic effects to make them function.

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Power Dissipation in Resistance

When current flows in a resistance, heat is produced because friction between the moving free electrons and the atoms obstructs the path of electron flow. The heat is evidence that power is used in producing current. This is how a fuse opens, as heat resulting from excessive current melts the metal link in the fuse.

The power is generated by the source of applied voltage and consumed in the resistance in the form of heat. As much power as the resistance dissipates in heat must be supplied by the voltage source; otherwise, it cannot maintain the potential difference required to produce the current.

Any one of the three formulas can be used to calculate the power dissipated in a resistance. The one to be used is just a matter of convenience, depending on which factors are known.

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Series-Parallel Circuits

In many circuits, some components are connected in series to have the same current, while others are in parallel for the same voltage. When analysing and doing calculations with series-parallel circuits you simply apply what you have learnt from the last two readings.

In the circuit of figure 1 below, we could work out all the voltages across all of the resistances and the current through each resistance and then total resistance. For now I am just going to walk through the simplification of this circuit to a single resistance connected across the 100 V source.

Keep in mind that any circuit (resistive) can be reduced to a single resistance. This is particularly useful when we come to do transmission lines and antennas.

For now let’s have a go at simplifying the circuit of figure 1. There are many ways to go about this problem. The method I prefer is to start at the right hand side and work my way back to the source, simplifying the circuit as I go.

Figure 1

On the right hand side we see R3 and R4 in parallel and each 12Ω. Do you remember the short cut method when parallel resistances are all the same value? Divide the value of the branch by the number of branches: 12Ω / 2 = 6Ω.

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The Battery In A Circuit

A common method of producing an emf is by the chemical action in a battery. Without going into the chemical reactions that take place inside a cell, a brief outline of the operation of a Leclanche cell is given here.

Consider a torch cell. Such a cell (two or more cells form a battery) is composed of a zinc container, a carbon rod down the middle of the cell, and a black, damp, paste-like electrolyte between them. The zinc container is the negative terminal. The carbon rod is the positive terminal. The active chemicals in such a cell are the zinc and the electrolyte.

The materials in the cell are selected substances that permit electrons to be pulled from the outer orbits of the molecules or atoms of the carbon terminal chemically by the electrolyte and be deposited onto the zinc can. This leaves the carbon positively charged and the zinc negatively charged. The number of electrons that move is dependent upon the types of chemicals used and the relative areas of the zinc and carbon electrodes. If the cell is not connected to an electric circuit, the chemicals can pull a certain number of electrons from the rod over to the zinc. The massing of these electrons on the zinc produces a backward pressure of electrons, or an electric strain, equal to the chemical energy of the cell, and no more electrons can move across the electrolyte. The cell remains in this static, or stationary, 1.5 V charged condition until it is connected to a load.

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Electric Current

What makes such a simple thing as an electric lamp glow? It is easy to pass the problem off with the statement, “The switch connects the light to the power lines and it glows” or something to that effect. But what does connecting the light to the power lines do? How does energy travel through solid copper wires? What makes a motor turn, a radio play? What is behind the dial that allows you to pick out one radio station from thousands of others operating at the same time? How fast is electricity really?

There are no simple single answers to any of these questions. Each question requires the understanding of many basic principles. By adding one basic idea to another, it is possible to answer, eventually, most of the questions that may be asked about the intriguing subjects of electricity, electronics, and radio. When the light switch is turned on at one point in a room and the light suddenly glows, energy has found a path through the switch to the light. The path used is usually along copper wires, and the tiny particles that do the moving and carry the energy are called electrons. These electrons are important to anyone studying electronics and radio, since they are usually the only particles that are considered to move in electric circuits. To explain what is meant by an electron, it will be necessary to investigate more closely the makeup of all matter.

The word “matter” means, in a general sense, anything that can be touched. It includes substances such as rubber, salt, wood, water, glass, copper, and air. The whole world is made of different kinds of matter.

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Work

Work = Power x Time

Practical Units of Power and Work. Starting with the watt, we can develop several other important units. The fundamental principle to remember is that power is the time rate of doing work, while work is power used during a period of time. The formulas are:

Power = work / time

and

Work = power x time

With the watt unit for power, one watt used during one second equals the work of one joule. To put it simply, one watt is one joule per second. Therefore, 1 W = 1 J/s. The joule is a basic practical unit of work or energy.
A unit of work that can be used with individual electrons is the electron volt. Note that the electron is charge, while the volt is potential difference. Now 1eV is the amount of work required to move an electron between two points having a potential difference of one volt.

Since 6.25 x 1018 electrons equal 1C and a joule is a volt-coulomb, there must be 6.25 x 1018 eV in 1J.

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Power

The unit of electrical power is the watt (W), named after James Watt (1736-1819). One watt of power equals the work done in one second by one volt of potential difference in moving one coulomb of charge.

Remember that one coulomb per second is an ampere. Therefore, power in watts equals the product of amperes times volts.
Power in watts = volts x amperes

P = E x I

Example: A toaster takes 5 A from the 240V power line. How much power is used?

P = E x I = 240 V x 5 A
P = 1200 Watts

Example: How much current flows in the filament of a household 75 watt light bulb connected to the normal 240 Volt supply?
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Ohm’s Law Explanation

Ohm’s Law describes the relationship between current, voltage and resistance in an electric circuit.
Ohm’s Law states:

The current in a circuit is directly proportional to voltage and inversely proportional to resistance.

Let:

I = current
E = voltage
R = resistance

Part of Ohms Law says: current is directly proportional to voltage.
Using the symbols given, we can write an equation to show a direct proportion between current and voltage.

I = E

Normally the above equation is read I ‘equals’ E. It can just as easily and more understandably be read as: I is directly proportional to E.
I know I harp on the direct proportion and inverse proportion stuff a lot. I do so because it is so important to thoroughly understand this when we come to more complex equations.

I = E

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