FAMILIARIZATION AND IDENTIFICATION OF ELECTRONIC COMPONENTS WITH SPECIFICATION
AIM:
To study and familiarize
1. Passive components like resistors, capacitors, inductors and transformers.
2. Active Components like diodes Transistors etc.
3. Integrated circuits.
4. Miscellaneous components like switches, fuses, relays, wires, cables, crystals, Displays, heat sink etc.
COMPONENTS REQUIRED:
Resistors, capacitors,
inductors, transformers, diodes, transistors, wires cables etc.
THEORY
Electronic components can be classified into
1. Passive Electronic Components
2. Active Electronic Components
1. PASSIVE ELECTRONIC COMPONENTS
Components like resistance, capacitance inductance are examples of passive components. These components by themselves are not capable of amplifying or processing of electric signal.
1.1 RESISTORS
Resistance is the fundamental property of a conductor to oppose the flow of current through it. Unit of resistance is ohm (Ω). Resistors are components which exhibit the property of resistance. Specification of resistors are i) Resistance value ii) Power Rating iii) Tolerance. Resistance value and tolerance are obtained from colour coding and power rating is proportional to the size of resistance.
1.1.1 FIXED RESISTORS
A fixed resistor is one whose value does not change. Fixed resistors are following types
i) Carbon composition resistors.
ii) Carbon film resistors.
iii) Metal film resistors.
iv) Wire wound resistors.
i) CARBON COMPOSITION RESISTORS
The resistors are constructed by mixing carbon powder and china clay in a proportion to produce the desired value of resistance. A rod of this mixture about 5mm length is covered with an insulating material for insulation and mechanical strength. Its two ends are joined to metal caps with leads of tinned wire. The readily available resistance value of these type resistors are 1Ω to 10MΩ with power rating 1/8W , 1/4W, 1/2W, 1W,2W and tolerance from 5-20%.
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| Carbon Composition Resistor and circuit symbols for resistors |
Resistor
Colour Code Table
Color
|
Ist-color
band
(Ist
value)
|
IInd-color
band
(IIndvalue)
|
IIIrd-color
band
(Multiplier)
|
IVth-color
band
(Tolerance)
|
Black
|
0
|
0
|
1
|
|
Brown
|
1
|
1
|
10
|
|
Red
|
2
|
2
|
102
|
|
Orange
|
3
|
3
|
103
|
|
Yellow
|
4
|
4
|
104
|
|
Green
|
5
|
5
|
105
|
|
Blue
|
6
|
6
|
106
|
|
Violet
|
7
|
7
|
107
|
|
Grey
|
8
|
8
|
108
|
|
White
|
9
|
9
|
109
|
|
Gold
|
-
|
-
|
0.1
|
+/- 5%
|
Silver
|
-
|
-
|
0.01
|
+/- 10%
|
No color
|
-
|
-
|
-
|
+/- 20%
|
ii). CARBON FILM RESISTORS
Carbon film resistors are made with a deposition process. At high temperature and under a high pressure, a ceramic carrier is held in hydrocarbon gas. The crystalline carbon is pyrolytically deposited on the ceramic substrate. The desired resistance value can be obtained by choosing the right layer thickness, and by cutting a spiral shape in the carbon layer. The helical cut in the film increases the length of the current path. By decreasing the pitch of the helix, the length of the resistive path increases, and therewith the resistance value increases.
 |
| Carbon Film Resistors |
iii). METAL FILM RESISTORS
 |
| Metal Film Resistors |
These resistors are made from small rods of ceramic coated with metal such as a nickel alloy or a metal oxide such as tin oxide. The value of resistance is controlled firstly by the thickness of the coating layer; the thicker the layer, the lower the value of resistance. Also by a fine spiral groove cut along the rod using a laser or diamond cutter to cut the carbon or metal coating effectively into a long spiral strip, which forms the resistor. Metal film resistors can be obtained in a wide range of resistance values from a few Ohms to tens of millions of Ohms with a very small TOLERANCE. For example a typical value might be 100KΩ ±1% or less i.e. for a stated value of 100KΩ the actual value will be between 99KΩ and 101KΩ. Generally 5 band colour code is adopted in metal film resistors.
iv). WIRE WOUND RESISTORS
 |
| Wire wound resistors |
The Wire wound resistors are very variable in construction and physical appearance. Their resistive elements are commonly lengths of wire, usually an alloy such as Nichrome (Nickel/Chromium) wrapped around a ceramic or glass fibre rod and coated in an insulating flameproof cement film. They are normally available in quite low values of resistance (single ohms to a few Kilo ohms) but can dissipate large amounts of power.
1.1.2 VARIABLE RESISTORS
A variable resistor is an electronic component for change the resistance according to our needs in an electronic circuit. The value of resistance can be changed by sliding a wiper terminal across a resistive material. Variable resistors are classified as carbon film and wire wound resistors. Potentiometer, preset and rheostat are examples of variable resistors.
 |
| Symbol of Variable Resistors |
a) RHEOSTAT
Rheostats are variable resistors used in high power applications. They are constructed by winding former with a Nickel Copper wire in oxidation form. Former is usually 15cm to 30cm long, round shaped, made of ceramic and coated with vitreous enamel. A movable contact can be slided through an iron rod. Threading type terminals are provided for external connections.
 |
| Rheostat |
b) POTENTIOMETER
Potentiometers are mechanical variable resistors with three connections, two fixed and one moveable. They act as voltage dividers and as such alter the voltage in a circuit.
i) WIRE WOUND POTENTIOMETERS
A resistance wire is wrapped between two fixed connections. One fixed connection is attached to the electrical supply, the other to ground. The third moveable connection is moved across the coil by a wiper in a similar fashion to a rheostat. The variable voltage output is taken from this point.
 |
| Wire wound potentiometer |
ii) CARBON FILM POTENTIOMETER
This type of potentiometers are formed by depositing carbon composition ink on an insulating body, which in most of the cases is phenolic resin. This is one of the most commonly used materials for the pots that is quite cheap and has resolution better than the wire wound potentiometers. This used for low power application below 3W
 |
| Carbon Film Potentiometer |
c) PRESET
 |
| Preset |
The presets are a type of variable resistor. They are used when a value needs to be set within a circuit. Some presets consist of a single turn adjustment. This can be rather course when an accurate setting is required.
d) LIGHT DEPENDENT RESISTORS (LDR)
The Light Dependent Resistor or Photoresistor, which is a passive electronic component, basically a resistor which has a resistance that varies depending of the light intensity. They are used as light sensors.
 |
| LDR with circuit symbol |
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