ELECTRONIC HAND TOOLSDEFINATION: These are mechanical equipments used to build, service, maintain and repair electronic devices (electrical appliance).
DESCRIPTION AND APPLICATIONS
1. Screw Drivers: these are hand tools used to drive in/out a screw in electrical appliances. We have Star Screw Drivers and Flat Screw drivers, depending on the kind of Screw to be driven will determine the kind of Screw driver to be used.
2. Diagonal cutters: these are scissors like pliers used in cutting of wires and trimming of electronic components terminal during circuit building.
3. Soldering Lead: this is a conductive poisonous solid substance that becomes molten substance when heated to a high temperature and changes back to its solid form when cooled. It is used to solder (join) components into circuit boards.
4. Soldering gun: this is soldering tool used to join two metallic objects together (components and vero board). It shape that looks exactly like gun earned it the name soldering gun. It is exactly a soldering iron shaped like gun.
5. Soldering paste: this is a conductive molten substance (gel) that can be used to solder components on a circuit board. It is like a tooth paste but it becomes very hard when air blows over it.
6. Soldering Iron: this is a heating device used in melting soldering lead when joining components on a circuit board.
Soldering Iron Holder
7. Soldering iron holder (stand): this is a tool used in suspending heated soldering iron to avoid this hot tool from making contact with any other object.
Soldering Iron Holder
8. Lead Sucker: this is a tool used to remove already soldered component on a circuit board. It is a vacuum pump that can suck a molten lead off a circuit board. It is therefore called a de-soldering device. It looks like a large syringe.
Lead Sucker (Vacuum pump)
9. Desoldering wick: this is also another kind of de-soldering devices that is use to remove soldered components from circuit board. It looks like wicks used in oil lamps, except that it is made of copper and very costly.
10. Pocket Knife: this is a kind of jack knife that can be used to peel off the rubber covering of insulated wires.
11. Wire Stripper: this is a hand tool used in peeling off the insulating material of coated wires.
12. Wire Crimper: this is used to crimp (join) fittings such as terminal ends or connectors onto wire instead of soldering.
12. Plier: Some are used for gripping something round like a pipe or rod, some are used for twisting wires, and others are designed to be used for a combination of tasks including cutting wire. There are also tools that are used just for cutting wires (as opposed to wire cable and rope). Use the correct pliers or wire cutters for the job.
MEANING OF ELECTRONICS AND ELECTRONIC CIRCUITDefinition of Electronics: this is a field in engineering that studies electron flow in electric circuit and suggests better means of controlling and manipulating this flow. This can be achieved by making new circuit designs, improving on existing designs or inventing new electronic components. With different capabilities of electrons controls by using different kinds of electronic components, our world today have different kinds of electronic gadgets from a simple torch light to the most complex computer system and industrial robots. Therefore, however the electrical appliance may be in simplicity or complexity it all has to do with electrons flow manipulation and this is what electronics is all about.
Definition of Electronic Circuit: this is a device composed of individual electronic components, such as resistors, transistors, capacitors, diodes and inductors, connected by conductive traces or wires which electric current can flow. An intelligent interconnection of basic electronic components to achieve a specific goal is electronic circuit.
The combination of components and wires allows various simple and complex operations to be performed.
ELEMENTS OF ELECTRONIC CIRCUITS
CONCEPT OF EMISSIONEmission is the production and discharge of particles (gases, electrons) into the air or a particular vacuum. In vacuums if this emission is intelligently controlled a very beautiful effects can be created.eg. Cathode Ray Tube (Television set).
Though, in most sense when Emission is mentioned gases comes to our mind. But in the field of electronics we are studying electronic emission.
The liberation of electrons from the surface of a metal is known as Electron Emission. If a piece of metal is investigated at room temperature, there will be random motion of electrons all about it. However, these electrons are free to the extent that they may transfer from one atom to another within the metal but cannot leave the metal surface to provide electron emission. It is because the free electrons that are at the surface of the metal found themselves being pulled inward by other atoms that are inside and no other force pulling them outwardly to entirely leave the surface of the metal. Thus at the surface of the metal, a free electron encounters forces that prevent it from leaving the metal. However, if sufficient energy is given to the free electrons, their kinetic energy increases and thus the electrons will cross over the surface barrier to leave the metal.
TYPES OF ELECTRON EMISSION
1 Thermionic emission: in this type, the metal is heated to a sufficient temperature (about 2500oC) to enable the free electrons to leave the metal’s surface. The number of electron emitted depends on the temperature. The higher the temperature, the greater is the emission of electrons. This type of emission is employed in vacuum tubes.
2 Field emission: in this type, a strong electric field (i.e. a high positive voltage) is applied at the metal because of the attraction of positive field. The strong the electric field, the greater is the electron emission.
3 Photoelectric emission: in this type, the energy of light falling upon the metal surface is transferred to the free electrons within the metal to enable them to leave the surface. The greater the intensity of light beam falling on the metal surface, the greater is the photoelectric emission. Photoelectric emission is utilized in photo tubes which form the basis of television.
4 Secondary emission:this is a phenomenon where primary incident particles of sufficient energy, when hitting a surface or passing through some materials induce emission of secondary particles. These primary particles are usually electrons or ions and the secondary particles also happen to be electrons and ions. The intensity of secondary emission depends upon the emitter material, mass and energy of bombarding particles.
APPLICATION OF EMISSION
1 Used in electric lamps.
2 Used in cathode ray tube (Television Sets).
3 Used in X-ray Tubes.
4 It is the basis of Tetrode, triode, pentode etc.
5 Used in spectroscopy.
PHOTO-ELECTRIC DEVICESDEFINATION: These are devices which give an electrical signal in response to visible, infra-red or ultraviolet radiation.
FOUR TYPES OF PHOTO-ELECTRIC DEVICES
1 Photomultiplier tube: this is an extremely sensitive detector of light. They are actually vacuum tube technology just like triode pentode etc which are no longer in use. But Photomultiplier tubes are still very much in use and the research to find a better semi-conductor to replace it has not been successful yet. But in some cases, photodiode can replace it.
2 Light dependent resistor (LDR): this device has its resistance, or opposition to passage of electric current, decrease with increasing light intensity. And this opposition to current flow increases with decrease in light intensity. They are also called photo-resistor or photo-conductors they are used in security systems, street light, camera light meter etc.
3 Photodiodes: these devices function as photo-detectors and mostly find use as smoke detectors, receivers for TV remote controls etc. They are also used to measure light intensity.
4 Photovoltaic cells: these devices convert solar light which is in the form of photons into electricity. It can also convert energy from non-solar sources like incandescent light bulbs into electric current. This particular cell is what the basis of solar electricity is.
APPLICATION OF PHOTOELECTRIC DEVICES
1 They are used in sensing objects or encoded data by a change in transmitted or reflected light.
2 Photocells are used in electrical power generation.
3 They are used in building security system.
4 They are used in TV remote controls.
5 Photoconductive cells are used in voltage regulation.
SEMICONDUCTOR DEVICESDefinition: These are the various solid crystalline substances, such as germanium or silicon, having electrical conductivity greater than insulators but less than good conductors, and used especially as a base material for computer chips and other electronic devices. Semiconductors form the heart of modern electronics. A diode is the simplest possible semiconductor device, and is therefore an excellent starting point if one really wants to understand how semiconductors work. A pure semiconductor material at 00c does not conduct electricity at all. It really starts conducting as its temperature rises or when doped (when made impure). However a semiconductor is doped or its temperature rises it can never conduct like a metal.
THE PERIODIC TABLE
Looking up from the periodic table will help us in the study of semiconductors. Semiconductors positions in the periodic table are immediately after the metals and before the non-metals. The red rectangle enclosed the semiconductor elements.
CHARACTERISTICS OF SEMICONDUCTORS
All atoms in group 4 in the periodic table are semiconductors and have four (4) valence electrons at their outermost shell. Semiconductors do not have mobile electrons in their purest state at temperature of 00celcius. They are usually pure crystal and practically non-conductor (insulator) of electricity. But, as the temperature rises, some of the covalently bonded electrons that are fixed at 00Celsius may acquire enough thermal energy that could make it break away from the parent atom; once its thermal energy becomes greater than the atomic binding energy. This leads to conductivity in semiconductors due to availability of mobile electrons. This simply means that some of the fixed electrons become librated from the bonds, and become free electrons by moving out of their fixed positions in the atoms. Because semiconductors are crystalline in nature, whenever an electron jumps off an atom it leaves a hole on that atom and also makes that atom positively charged. These newly formed positive atoms possess attractive force and tend to attract electrons in the neighbouring atoms. This overall reaction brings about the conduction in semiconductors. Therefore, availability of electrons and holes is responsible for the passage of electric current through semiconductors.
Within semiconductors, there are random movement of electrons and holes in the absence of applied voltage; just as there are random movements of electrons within conductors in the absence of applied voltage. But at the application of EMF (electromotive force) electrons move (are attracted) to the positive terminal of the voltage source (battery) while holes drift to the negative terminal. In pure semiconductors, there are equal number of electrons and holes and the removal of an electron from an atom creates electron-hole pairs.
EFFECTS OF TEMPERATURE ON SEMICONDUCTORS
At 00 Celsius all pure semiconductors do not conduct electricity. Its conductivity increases with rise in temperature. That is to say, that the resistance of a semiconductors decrease with increase in temperature and increase with decrease in temperature. Unlike conductors, the resistance of a conductor increases with increase in temperature and decreases with decrease in temperature.
NOTE: the erratic behaviours of pure semiconductors with change in temperature make them not usable as an electronic component in pure form. Semiconductors become useful when some impurities are diffused into its pure form. The act of doing so is called DOPING.
THERE ARE TWO TYPES OF SEMICONDUCTORS
1 Intrinsic semiconductor (pure semiconductors)
2 Extrinsic semiconductor (impure semiconductors)
INTRINSIC SEMICONDUCTOR MATERIAL
This is the term used in describing semiconductor in its pure state. In this state, it is a crystalline substances covalently bonded to each other by only a particular semiconductor element within group four of the periodic table. In this state it does not conduct electricity at 00 Celsius. Its conduction only begins when temperature of its surrounding rises. In fact, semiconductors have no/limited application in electronics when it is pure.
ATOMIC STRUCTURES OF SEMICONDUCTORS’ ELEMENTS
From the atomic structure of Silicon (Si) we see that it has valence electron of four (4) not only Si even Ge and all other elements within group four in the periodic table. Atoms of Silicon form crystal structure by covalently bonding together. Since each atom has four electrons for bonding, it has to pair with another atom of silicon by each one donating and sharing with each other. When this is done we have a structure as shown below.
DIAGRAM SHOWING THE STRUCTURE OF SILICON (Intrinsic semiconductor)
EXTRINSIC SEMICONDUCTOR MATERIAL
This is a term used in describing semiconductor when the pure form had been mixed with another element so as to enhance its conductivity and reduce its sensitivity to changing temperature. Some of the elements used for this purpose are those in group 3 (eg. Boron, Gallium and Indium) and group 5 (eg. Arsenic and Antimony) in the periodic table. The essence of mixing the pure semiconductor (Si and Ge) with these other elements in different group is to alter the equality in the number of holes and electrons which is usually the case in pure semiconductors.
TWO TYPES OF EXTRINSIC SEMICONDUCTORS
1. N-Type Semiconductor
2. P-Type Semiconductor
This kind of impure semiconductor is gotten when Arsenic or Antimony of group 5 is diffused into pure Germanium or Silicon. Since Germanium or Silicon has valence electron of 4, and Arsenic or Antimony has valence electron of 5; diffusing the element of Arsenic or Antimony into Germanium or Silicon Crystal leaves the new crystal structure as shown below.
From the diagram below, the excess electrons introduced into the silicon crystal as a result of doping the pure silicon with Arsenic are clearly shown. Just look for As (Arsenic atoms) and see that a free electron is attached.
DIAGRAM SHOWING SILICON THAT HAS BEEN DOPED WITH ARSENIC
From the above structure, the Arsenic atom diffused into Silicon Crystal leaves the entire substance to possess excess electrons that will be responsible for conduction. Since electrons are negatively (N) and are the carriers of electric current in this newly formed substance the crystal is said to be N-TYPE SEMICONDUCTOR. It would be good to recall that the original behaviour of pure Silicon is still retained, that is when an electron is removed a hole is left behind which is also responsible for electron conduction. But when we compare the conduction due to holes and due to electrons the difference is so much that we can correctly conclude that in N-TYPE semiconductors, electrons are the major carriers of electric current while holes are the minor carriers.
In this impure semiconductor, instead of using group 5 to diffuse into a pure semiconductor we are to use group 3 (e.g. Boron, gallium or Indium). The atoms of Boron have valence electrons of 3 remember Silicon atoms have valence electron of 4. Diffusing Boron into Silicon leaves the entire crystal as shown below. The X symbols in the structure depict the missing electrons due to Boron atoms in the structure. This represents Holes that enhances electric current conduction.
DIAGRAM SHOWING SILICON THAT HAS BEEN DOPED WITH BORON
In this Structure, the boron leaves excess holes that will improve electrical conduction. Remember the original characteristics of pure semiconductors are still maintained only that holes are now in excess when compared to electrons and is responsible for the better conductivity. These Boron atoms with holes make the overall atoms of Boron positively charged and tend to attracts electrons from the neighbouring silicon atom. Because Boron atoms leaves the crystal positively charged the new material formed is called P-TYPE SEMICONDUCTOR material.
EXPLAINING SEMICONDUCTOR USING GRAPHIC ANALYSIS
DIAGRAM SHOWING SILICON THAT HAS BEEN DOPED WITH BORONThe above diagram illustrates the true structure of Germanium or Silicon crystal in pure state. Holes are like vessels that holds electrons; the removal of electron leaves a vacant space called hole.
SHOWING EXCESS ELECTRONS AFTER DOPING
SHOWING EXCESS HOLES AFTER DOPING
PN JUNCTION DIODES
SHOWING EXCESS HOLES AFTER DOPINGOnce you have got the P-Type material and N-Type material and you successfully joined the two as shown above, you will get a rectifying diode. The Diagram above also tries to analyze what actually went on at the point of joining these two dissimilar materials together; the excess electrons in the N-type material are attracted to the excess holes in the P-type material. Both materials meet at a junction where the electrons in the N-type material occupy the holes in the P-type. This cancelling of holes by electrons continues until the junction becomes saturated that it becomes impossible for cancelling to continue since the electrons cannot meet the holes due to the fact that the neutral centre has created a barrier that makes it impossible for the reaction to continue this barrier is called the depletion region.
Transistors can be constructed just like the diode that has already been discussed above. But in this case, the junction will be two and not just one junction. Transistors are made from joining two N-materials and one P-material at the centre, or two P-materials and one N material at the centre. That is why transistors are either NPN or PNP.
SHOWING NPN TRANSISTOR CONSTRUCTION
SHOWING PNP TRANSISTOR CONSTRUCTION