Punj Tips and Tricks basic electronics

On this page we are going to try and provide a very basic understanding in the knowledge of a very specialist technological field known as electronics. The understanding of electronics can be very complicated and covers a great area. We however are going to try and explain the very basics in this highly knowledgeable specialist field.

Electronics will be found every where in the modern day. At home or work you will come across devices and gadgets which rely solely on their design and production in the provision of electronics. These so called electronic devices help us in our every day needs in today's modern world.
Everyone today is exposed to electronic devices in one way or another. Everyone can benefit from the additional knowledge of electronics. Electronics in simple terms is the flow of electrical charges to circuits to accomplish specific tasks.

Basic electronics is all about electrical components and circuits consisting of those components. Common components are resistors, capacitors, inductors, transistors, and integrated circuits. These components can be interconnected with conductors, either by physical wires or printed circuits boards. Each circuit will have a specific job and task to work satisfactorily. Components are also interconnected to perform specific tasks. Below we shall take a very basic look and understanding on some of these electronic components. We hope our readers appreciate that on this page we will be covering a very small part of this very large technological subject

Resistance can be explained as the opposition to a flow of current. The unit of the resistor is often represented by the Greek letter omega The practical unit of resistance is called the ohm.. Most resistors look like the components as shown in the image below

Resistors normally determine the flow of electrical current in an electrical circuit. Where there is high resistance in a circuit the flow of the current is small, where the resistance is low the flow of the current is large. Resistance, voltage and current are connected in an electrical circuit by Ohm’s Law

Resistors are too small to have numbers printed on them and so they are marked with a number of coloured bands. Each colour stands for a number. Three colour bands shows the resistors value in ohms and the fourth shows tolerance. Resistors can never be made to a precise value and the tolerance band (the fourth band) tells us, using a percentage, how close the resistor is to its coded value.

Resistors can generally be found connected in series (end to end), or in parallel (across one another), or in a combination of series and parallel.
The value of a resistor can be written in a variety of ways. Some examples are given below:

47R means 47 ohms
5R6 means 5.6 ohms
6k8 means 6800 ohms
1M2 means 1 200 000 ohms

A common value is 'K' which means one thousand ohms. So if a resistor has a value of 7000 ohms it can also be said to have a value of 7K.

Capaciitors and Capacitance

A capacitor is a device that stores an electrical charge when a potential difference (voltage) exists between two conductors which are usually two plates separated by a dielectric material (an insulating material like air, paper, or special chemicals between two sheets of aluminum foil).

Capacitors store electric charge. They can be used as filters, AC coupling capacitors and as by-pass capacitors. They are also used in conjunction with resistors and inductors to form tuned circuits and timing circuits. A capacitors value C (in Farads) is dependent upon the ratio of the charge Q (in Coulombs) divided by the V (in volts). Common capacitors come in values of micro farads or Pico farads. Often you will have to convert between Pico farads and micro farads.

Two coils close to one another, as found in transformers, would transfer charge from one coil to the other. This is called mutual inductance.
The electrical property of an inductor is called inductance and the unit for this is the henry, symbol H. Inductors are mainly used in tuned circuits to block high frequency AC signals (they are sometimes called chokes). They pass DC easily, but block AC signals, this is the opposite of capacitors.
An inductor may be connected either way round and no special precautions are required when soldering.

When using and connecting diodes within a circuit they must be installed the correct way around. Diodes always have markings to show the correct polarity. Basic diodes are found to be used in the following ways.
Signal diodes - Signal diodes are used to process information or electrical signals in circuits, so they are only required to pass small currents of up to 100mA. General purpose signal diodes are made from silicon and have a forward voltage drop of 0.7V.
Germanium diodes have a lower forward voltage drop of 0.2V and this makes them suitable to use in radio circuits as detectors which extract the audio signal from the weak radio signal.
Rectifier diodes - Rectifier diodes are used in power supplies to convert alternating current (AC) to direct current (DC), a process called rectification. They are also used elsewhere in circuits where a large current must pass through the diode.
All rectifier diodes are made from silicon and therefore have a forward voltage drop of 0.7V. The 1N4001 is suitable for most low voltage circuits with a current of less than 1A.
Bridge rectifiers - There are several ways of connecting diodes to make a rectifier to convert AC to DC. The bridge rectifier is one of them and it is available in special packages containing the four diodes required. Bridge rectifiers are rated by their maximum current and maximum reverse voltage. They have four leads or terminals: the two DC outputs are labelled + and -, the two AC inputs are labelled ~.
Zener diodes - Zener diodes are used to maintain a fixed voltage. They are designed to 'breakdown' in a reliable and non-destructive way so that they can be used in reverse to maintain a fixed voltage across their terminals. Zener diodes can be distinguished from ordinary diodes by their code and breakdown voltage which are printed on them. Zener diode codes begin BZX... or BZY... Their breakdown voltage is printed with V in place of a decimal point, so 4V7 means 4.7V in this example.

Transistors

Transistors amplify current, they can be used to amplify the small output current from a logic IC so that it can operate a lamp, relay or other high current devices. In many circuits a resistor is used to convert the changing current to a changing voltage, so the transistor is being used to amplify voltage. A transistor may be used as a switch (either fully on with maximum current, or fully off with no current) and as an amplifier (always partly on). The amount of current amplification is called the current gain, symbol hFE.

There are two types of the standard transistor, NPN and PNP, with different circuit symbols. The letters refer to the layers of semiconductor material used to make the transistor. Most transistors used today are NPN because this is the easiest type to make from silicon. The transistor leads are normally labelled base (B), collector (C) and emitter (E).
The labelled terms refer to the internal operation of a transistor but they are not much help in understanding how a transistor is used, so just treat them as labelled A Darlington pair is two transistors connected together to give a very high current gain.
Transistors have three leads which must be connected the correct way round. Wrongly connecting a transistor will cause damage instantly when switching the device on.

IC's are very sensitive to static and can be damaged when you touch them because your body may have become charged with static electricity. IC's will normally be supplied in anti-static packaging with a warning label and they should be left in this packaging until you are ready to use them. It is usually adequate to earth your hands by touching a metal water pipe before handling the IC but for the more sensitive (and expensive!) IC's special equipment is available, including earthed wrist straps and earthed work surfaces.
Logic IC's - Process digital signals and there are many devices, including logic gates, flip-flops, shift registers, counters and display drivers. They can be split into two groups according to their pin arrangements: the 4000 series and the 74 series which consists of various families such as the 74HC, 74HCT and 74LS.
74 Series - There are several families of logic ICs numbered from 74xx00 onwards with letters (xx) in the middle of the number to indicate the type of circuitry, eg 74LS00 and 74HC00. The original family (now obsolete) had no letters, eg 7400.
The 74LS (Low-power Schottky) family (like the original) uses TTL (Transistor-Transistor Logic) circuitry which is fast but requires more power than later families. The 74HC family has High-speed CMOS circuitry, combining the speed of TTL with the very low power consumption of the 4000 series. They are CMOS IC's with the same pin arrangements as the older 74LS family. Note that 74HC inputs cannot be reliably driven by 74LS outputs because the voltage ranges used for logic 0 are not quite compatible, use 74HCT instead.
The 74HCT family is a special version of 74HC with 74LS TTL-compatible inputs so 74HCT can be safely mixed with 74LS in the same system. In fact 74HCT can be used as low-power direct replacements for the older 74LS IC's in most circuits. The minor disadvantage of 74HCT is a lower immunity to noise, but this is unlikely to be a problem in most situations. Beware that the 74 series is often still called the 'TTL series' even though the latest IC's do not use TTL.
PIC Microconroller - PIC is known as a Programmable Integrated Circuit microcontroller, or a 'computer-on-a-chip'. They have a processor and memory to run a program responding to inputs and controlling outputs, so they can easily achieve complex functions which would require several conventional ICs. Programming a PIC microcontroller may seem daunting to a beginner but there are a number of systems designed to make this easy. Programs can be written in a simple version of BASIC or using a flowchart.

Basic Electronics