COMPONENT DESCRIPTION
PRECAUTIONS WHILE ASSEMBLING THE PROJECT
Check all the components as per the circuit specification.
IC4017 and IC4013 should be mounted on IC base.
Proper attention to be paid to the collector, base, emitter of BC109 before mounting.
Take care in wiring the circuit to avoid loose connection.
Used relay of higher rating with good contacts to handle heavy loads like Air Conditioner.
Before soldering the transistor check its base, emitter and collector by multimeter.
IC should not be soldered directly on the PCB because parts can be damaged due to leakage of electric current from the soldering iron.
Take care that the tracks are not short circuited while on soldering.
The connection of LED‘S should be tight, and are in proper sequence.
All the work on printed circuited board do carefully.
TRANSFORMER
Transformer is a device that transfers electrical energy from one circuit to another through inductively coupled electrical conductors. A changing current in the first circuit (the primary) creates a changing magnetic field; in turn, this magnetic field induces a changing voltage in the second circuit (the secondary).
By adding a load to the secondary circuit, one can make current flow in the transformer, thus transferring energy from one circuit to the other.
The secondary induced voltage VS, of an ideal transformer, is scaled from the primary VP by a factor equal to the ratio of the number of turns of wire in their respective windings:
By appropriate selection of the numbers of turns, a transformer thus allows an alternating voltage to be stepped up — by making NS more than NP — or stepped down, by making it less.
Transformers are some of the most efficient electrical 'machines', with some large units able to transfer 99.75% of their input power to their output.
The transformer is based on two principles: firstly that an electric current can produce a magnetic field (electromagnetism) and secondly that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). By changing the current in the primary coil, it changes the strength of its magnetic field; since the changing magnetic field extends into the secondary coil, a voltage is induced across the secondary. The simplified description above neglects several complicating factors, in particular the primary current required to establish a magnetic field in the core, and the contribution to the field due to current in the secondary circuit.
Models of an ideal transformer typically assume a core of negligible reluctance with two windings of zero resistance.
When a voltage is applied to the primary winding, a small current flows, driving flux around the magnetic circuit of the core.
The changing magnetic field induces an electromotive force (EMF) across each winding. Since the ideal windings have no impedance, they have no associated voltage drop, and so the voltages VP and VS measured at the terminals of the transformer, are equal to the corresponding EMFs. The primary EMF, acting as it does in opposition to the primary voltage, is sometimes termed the "back EMF". This is due to Lenz's law which states that the induction of EMF would always be such that it will oppose development of any such change in magnetic field.
Autotransformer:-
An autotransformer has only a single winding with two end terminals, plus a third at an intermediate tap point. The primary voltage is applied across two of the terminals, and the secondary voltage taken from one of these and the third terminal. The primary and secondary circuits therefore have a number of windings turns in common. Since the volts-per-turn is the same in both windings, each develops a voltage in proportion to its number of turns. By exposing part of the winding coils and making the secondary connection through a sliding brush, an autotransformer with a near-continuously variable turns ratio is obtained, allowing for very fine control of voltage.
Energy losses:-
An ideal transformer would have no energy losses, and would therefore be 100% efficient. In practical transformers energy is dissipated in the windings, core, and surrounding
structures. Larger transformers are generally more efficient, and those rated for electricity distribution usually perform better than 98%.
Experimental transformers using superconducting windings achieving efficiencies of 99.85%, While the increase in efficiency is small, when applied to large heavily-loaded transformers the annual savings in energy losses is significant.
A small transformer, such as a plug-in "power brick" used for low-power consumer electronics, may be no more than 85%
efficient; although individual power loss is small, the aggregate losses from the very large number of such devices is coming under increased scrutiny.
The losses vary with load current, and may be expressed as "no-load" or "full-"no-load" loss. Winding resistance dominates load losses, whereas hysteresis and eddy currents losses contribute to over 99% of the no-load loss. The no-load loss can be significant, meaning that even an idle transformer constitutes a drain on an electrical supply, which encourages development of low-loss transformers (also see energy efficient transformer).
For three-phase supplies, a bank of three individual single-phase transformers can be used, or all three single-phases can be incorporated as a single three-phase transformer. In this case, the magnetic circuits are connected together, the core thus containing a three-phase flow of flux. A number of winding configurations are possible, giving rise to different attributes and phase shifts. One particular polyphase configuration is the zigzag transformer, used for grounding and in the suppression of harmonic currents.
RELAY
A relay is an electrical switch that opens and closes under the control of another electrical circuit. In the original form, the switch is operated by an electromagnet to open or close one or many sets of contacts. It was invented by Joseph Henry in 1835.
Because a relay is able to control an output circuit of higher power than the input circuit, it can be considered to be, in a broad sense, a form of an electrical amplifier.
When a current flows through the coil, the resulting magnetic field attracts an armature that is mechanically linked to a moving contact. The movement either makes or breaks a connection with a fixed contact. When the current to the coil is switched off, the armature is returned by a force approximately half as strong as the magnetic force to its relaxed position.
Usually this is a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing.
If the coil is energized with DC, a diode is frequently installed across the coil, to dissipate the energy from the collapsing magnetic field at deactivation, which would otherwise generate a spike of voltage and might cause damage to circuit components. Some automotive relays already include that diode inside the relay case. Alternatively a contact protection network, consisting of a capacitor and resistor in series, may absorb the surge. If the coil is designed to be energized with AC, a small copper ring can be crimped to the end of the solenoid.
Overload protection relay:-
One type of electric motor overload protection relay is operated by a heating element in series with the electric motor . The heat generated by the motor current operates a bi-metal strip
or melts solder, releasing a spring to operate contacts. Where the overload relay is exposed to the same environment as the motor, a useful though crude compensation for motor ambient typical application the overcurrent relay is used for overcurrent protection, connected to a current transformer and calibrated to operate at or above a specific current level. When the relay operates, one or more contacts will operate and energize a trip coil in a Circuit Breaker and trip (open) the Circuit Breaker.
RELAY
APPLICATION:-
to control a high-voltage circuit with a low-voltage signal, as in some types of modems.
to control a high-current circuit with a low-current signal, as in the starter solenoid of an automobile.
to detect and isolate faults on transmission and distribution lines by opening and closing circuit breakers.
to isolate the controlling circuit from the controlled circuit when the two are at different potentials.
to perform logic functions. For example, the boolean AND function is realised by connecting NO relay contacts in series, the OR function by connecting NO contacts in parallel.
Rating of contacts - small relays switch a few amperes, large contactors are rated for up to 3000 amperes, alternating or direct current
Voltage rating of contacts - typical control relays rated 300 VAC or 600 VAC, automotive types to 50 VDC, special high-voltage relays to about 15,000 V
Coil voltage - machine-tool relays usually 24 VAC or 120 VAC, relays for switchgear may have 125 V or 250 VDC coils, "sensitive" relays operate on a few milliamperes
Switching time - where high speed is required.
CAPACITOR
The capacitor's function is to store electricity, or electrical energy. The capacitor also functions as a filter, passing alternating current (AC), and blocking direct current (DC). This symbol is used to indicate a capacitor in a circuit diagram. The capacitor is constructed with two electrode plates facing each other, but separated by an insulator. When DC voltage is applied to the capacitor, an electric charge is stored on each electrode. While the capacitor is charging up, current flows. The current will stop flowing when the capacitor has fully charged.
The value of a capacitor (the capacitance), is designated in
Electrolytic Capacitors (Electrochemical type capacitors):- Aluminum is used for the electrodes by using a thin oxidization membrane. Large values of capacitance can be obtained in comparison with the size of the capacitor, because the dielectric used is very thin. The most important characteristic of electrolytic capacitors is that they have polarity. They have a positive and a negative electrode. [Polarized] This means that it is very important which way round they are connected. If the capacitor is subjected to voltage exceeding its working voltage, or if it is connected with incorrect polarity, it may burst. It is extremely dangerous, because it can quite literally explode.
Generally, in the circuit diagram, the positive side is indicated by a
"+" (plus) symbol. Electrolytic capacitors range in value from about 1µF to thousands of µF.
Mainly this type of capacitor is used as a ripple filter in a power supply circuit, or as a filter to bypass low frequency signals, etc
Variable capacitor:-
Variable capacitors are used for adjustment etc. of frequency mainly.
On the left in the photograph is a "trimmer," which uses ceramic as the dielectric. Next to it on the right is one that uses polyester film for the dielectric. The pictured components are
meant to be mounted on a printed circuit board. When adjusting the value of a variable capacitor, it is advisable to be careful.
One of the component's leads is connected to the adjustment screw of the capacitor.
This means that the value of the capacitor can be affected by the capacitance of the screwdriver in your hand. It is better to use a special screwdriver to adjust these components.
Pictured in the upper left photograph are variable capacitors with the following specifications (according to its colour):- Capacitance: 20pF (3pF - 27pF measured) [Thickness 6 mm, height 4.8 mm] their are different colors, as well.
Blue: 7pF (2 - 9) white: 10pF (3 - 15) green: 30pF (5 - 35) brown: 60pF (8 -72)
Capacitance: 30pF (5pF - 40pF measured)
[The width (long) 6.8 mm, width (short) 4.9 mm and the height 5 mm
DIFFERENT TYPES OF CAPACITORS:- 1. Tantalum Capacitors
2. Ceramic Capacitors
3. Multilayer Ceramic Capacitors 4. Polystyrene Film Capacitors
5. Electric Double Layer Capacitors (Super Capacitors) 6. Polyester Film Capacitors
7. Polypropylene Capacitors 8. Mica Capacitors
9. Metallized Polyester Film Capacitor
TRANSISTOR
The transistor's function is to amplify an electric current.
Many different kinds of transistors are used in analog circuits, for different reasons. This is not the case for digital circuits. In a digital circuit, only two values matter; on or off. The amplification ability of a transistor is not relevant in a digital circuit. In many cases, a circuit is built with integrated circuits (ICs).
Transistors are often used in digital circuits as buffers to protect ICs. For example, when powering an electromagnetic switch (called a 'relay'), or when controlling a light emitting diode.
Two different symbols are used for the transistor.
PNP type NPN type
The name (standard part number) of the transistor, as well as the type and the way it is used is shown below.
2SAXXXX PNP type high frequency
2SBXXXX PNP type low frequency
2SCXXXX NPN type high frequency
2SDXXXX NPN type low frequency
The direction of the current flow differs between the PNP and NPN type. When the power supply is the side of the positive (plus), the NPN type is easy to use.
The electrical characteristic of each is as follows:-
VCEO : The maximum voltage that can be handled across the collector(C) and emitter (E) when the base (B) is open.
(Not connected) (It may be shown as VCE).
IC : The maximum collector(C) current.
PC :
Maximum collector(C) loss that continuously can cause it consumed. At surroundings temperature (Ta)=25°C (no radiator).
hFE : The current gain to DC at the emitter (E).
(IC/IB)
Right side: Base
Center : Collector Left side : Emitter
Right side: Emitter Center: Collector
Left side : Base
THE FACTS CAN BE EXPLAINED AS
FOLLOWS:-1. 2 to 5 % of the holes are lost in recombination with the electron and base region, which results in a small base current and hence the collector current is slightly less than the emitter current.
2. The collector current increases, as the holes reaching the collector junction are attracted by negative potential applied to the collector.
3. When the emitter current increases, most holes are injected into the base region, which is attracted by the negative potential of the collector and hence results in increasing the collector current. In this way emitter is analogous to the control of plate current by small grid voltage in vacuum triode.
Hence we can say that when the emitter is forward biased and collector is negatively biased, a substantial current flows in both the circuits. Since the small emitter voltage of about 0.1 to 0.5 volts permits the flow of the appreciable emitter current the input power is very small. The collector voltage can be high as 45 volts.
RESISTANCE
The resistor's function is to reduce the flow of electric current.
This symbol is used to indicate a resistor in a circuit diagram, known as a schematic. Resistance value is designated in units called the "Ohm." A 1000 Ohm resistor is typically shown as 1K-Ohm ( kilo 1K-Ohm ), and 1000 K-1K-Ohms is written as 1M-1K-Ohm ( mega Ohm ).There are two classes of resistors; fixed resistors and the variable resistors. They are also classified according to the material from which they are made. The typical resistor is made of either carbon film or metal film. There are other types as well, but these are the most common. The resistance value of the resistor is not the only thing to consider when selecting a resistor for use in a circuit. The "tolerance" and the electric power ratings of the resistor are also important. The tolerance of a resistor denotes how close it is to the actual rated resistance value. For example, a ±5%
tolerance would indicate a resistor that is within ±5% of the specified resistance value. The power rating indicates how much power the resistor can safely tolerate. The maximum rated power of the resistor is specified in Watts. Power is calculated using the square of the current (I2) x the resistance value (R) of the resistor.
If the maximum rating of the resistor is exceeded, it will become extremely hot and even burn. Resistors in electronic circuits are typically rated 1/8W, 1/4W, and 1/2W. 1/8W is almost always used in signal circuit applications.
Generally, it's safe to choose a resistor which has a power rating of about twice the power consumption needed.
ROUGH SIZE
From the top of the photograph 1/8W
1/4W 1/2W
Variable Resistors:-
There are two general ways in which variable resistors are used. One is the variable resistor which value is easily changed, like the volume adjustment of Radio. The other is semi-fixed resistor that is not meant to be adjusted by anyone but a technician. It is used to adjust the operating condition of the circuit by the technician. Semi-fixed resistors are used to compensate for the inaccuracies of the resistors, and to fine-tune a circuit. The rotation angle of the variable resistor is usually about 300 degrees. Some variable resistors must be turned many times to use the whole range of resistance they offer. This allows for very precise adjustments of their value. These are called
"Potentiometers" or "Trimmer Potentiometers."
In variable resistors, the resistance value is adjusted by knob. It can be divided into (a) Carbon composition (b) Wire wound (c) Special type. The most common type of resistors used in our projects is carbon type.
Resistor colour code
Color Value Multiplier Tolerance (%)
Black 0 0
-Brown 1 1 ±1
Red 2 2 ±2
Orange 3 3 ±0.05
Yellow 4 4
-Green 5 5 ±0.5
Blue 6 6 ±0.25
Violet 7 7 ±0.1
Gray 8 8
-White 9 9
-Gold - -1 ±5
Silver - -2 ±10
None - - ±20
Example 1:
(Brown=1),(Black=0),(Orange=3) 10 x 103 = 10k ohm
Tolerance(Gold) = ±5%