INSTRUMENTS REQUIRED:

DIGITAL MULTIMETER: A multimeter is an electronic measuring instrument that combines several measurement functions in one unit. A typical multimeter may include features such as the ability to measure voltage, current and resistance. Apart from these functions a mutimeter is also use for testing diode, transistor, and as a continuity tester.

ELECTRONICS WORKSHOP

INTRODUCTION TO ACTIVE AND PASSIVE ELECTRONIC COMPONENTS

PASSIVE COMPONENT: The passive component is a device which is basically static in operation. It is not capable of producing amplification or oscillation. It does not require power supply for its characteristics operation.

Example: resistors, capacitors, inductors, fuses, etc.

ACTIVE COMPONENT: An active component is a device capable of some dynamic function like amplification, oscillation and signal control, it require a power supply for its characteristic operation.

Example: transistors, p-n junction diode, tunnel diode, magnetic amplifier, silicon controlled rectifier.

1) Resistors : These are passive components which are used to control current to a specific value and also to provide a desired voltage drop.They are also used for setting biases, voltage division, controlling gain fixing time constant, matching and loading circuits, heat generation and related applications.

They are represented by their resistance values.it is measured in ohms.

TYPES OF RESISTORS

Resistors can be classified on the basis of nature of value of resistance, material used, wattage, lead configuration, intended applications, temperature rating and cost etc. resistors when classified on the basisn of nature of value of resistance are of two types:

1) Fixed resistors.2) Variable resistors.

1) Fixed resistors: the fixed resistors are those whose resistance is fixed and cannot be changed. They are:

i) Carbon film resistor,

ii) metal oxide film resistor,

iii) thin film resistor,

iv) wire wound resistor,

v) carbon composition resistor,

vi) fusible resistor,

vii) foil resistor,

viii) Alloy resistor.

Carbon composition resistor: They are as shown in figure below

Composition Resistors

Carbon Resistors are the most common type of Composition Resistors as they are a cheap general purpose resistor.

Carbon Resistor

Carbon Composite Resistors are low to medium power resistors with low inductance which makes them ideal for high frequency applications but they can also suffer from noise and stability when hot.

Fusible resistor: They works as a resistor for certain value of current but when current increases beyond this value they act as a fuse and gets melt.

Wire wound resistor: Another type of resistor, called a Wirewound Resistor, is made by winding a thin metal alloy wire (Nichrome) or similar wire onto an insulating ceramic former in the form of a spiral helix 

Thermistor: Thermistors are temperature sensitive resistors, increasing the temperature will decrease the resistance in most cases, when this is the case they are said to be have negative temperature coefficient or else if the resistance increases with the increase in temperature they are said to be have positive temperature coefficient.

Light dependent resistor(LDR): The resistance of LDR changes when the intensity of light falling on it changes, in most of the cases resistance decreases with the increase in amount of light falling on it.

MEASUREMENT OF RESISTOR:

1) BY USING MULTIMETER

Resistor can be measured with the help of multimeter as shown below. keep the knob of multimeter on resitor mesurement position and select the range. Now touch or hold the two pins of multimeter alongwith the two axial leads of resistors. the value of resistor will be displayed on the screen.

by this method value of any resistor can be measured provided it is in the range of multimeter resistance measurement range.

WITH THE HELP OF COLOR CODE CHART:

The resistance value, tolerance, and watt rating of the resistor are generally printed onto the body of the resistor as numbers or letters when the resistor is big enough to read the print, such as large power resistors. When resistors are small such as 1/4W Carbon and Film types, these specifications must be shown in some other manner as the print would be too small to read. So to overcome this, small resistors use coloured painted bands to indicate both their resistive value and their tolerance with the physical size of the resistor indicating its wattage rating. These coloured painted bands are generally known as aResistors Colour Code.

An International resistor colour code scheme was developed many years ago as a simple and quick way of identifying a resistors value. It consists of coloured rings (in spectral order) whose meanings are illustrated below:

The Standard Resistor Colour Code Chart.

 

The Resistor Colour Code Table.

The following table shows the colors used to identify resistor values:

COLOR DIGIT MULTIPLIER TOLERANCE

 Silver    x 0.01  ±10%

 Gold    x 0.1  ±5%

 Black 0  x 1    Brown 1  x 10  ±1%

 Red 2  x 100  ±2%

 Orange 3  x 1 k   Yellow 4  x 10 k   Green 5  x 100 k ±0.5%

 Blue 6  x 1 M ±0.25%

 Violet 7  x 10 M ±0.1%

 Grey 8  x 100 M   White 9  x 1 G  

Calculating Resistor Values

The Resistor Colour Code system is all well and good but we need to understand how to apply it in order to get the correct value of the resistor. The "left-hand" or the most significant coloured band is the band which is nearest to a connecting lead with the colour coded bands being read from left-to-right as follows;

Digit, Digit, Multiplier = Colour, Colour x 10 colour  in Ohm's (Ω's)

For example, a Resistor has the following coloured markings;

Yellow  Violet  Red =  4  7  2 =  4  7 x 10 2 = 4700Ω or 4k7.

The fourth band if used, determines the percentage tolerance of the resistor and is given as;

Brown = 1%, Red = 2%, Gold = 5%, Silver = 10 %

If resistor has no fourth tolerance band then the default tolerance would be at 20%

2) Capacitors : Two metallic surfaces with a gap between them are capable of storing electrical charge and an electrical field can be created in the gap. The gap may be filled up with air or with any other insulating material, often called the dielectric. The complete device is known as capacitor. Its unit is farad. It is used in filtering, tuning, coupling and decoupling, bypassing, buffer, motor start and run applications, etc.

The two types of most commonly used capacitors are ceramic capacitor and electrolytic capacitor:

Ceramic capacitor: Ceramic Capacitors or Disc Capacitors as they are generally called, are made by coating two sides of a small porcelain or ceramic disc with silver and are then stacked together to make a capacitor. For very low capacitance values a single ceramic disc of about 3-6mm is used. Ceramic capacitors have a high dielectric constant (High-K) and are available so that relatively high capacitances can be obtained in a small physical size.

Ceramic types of capacitors generally have a 3-digit code printed onto their body to identify their capacitance value in pico-farads. Generally the first two digits indicate the capacitors value and the third digit indicates the number of zero's to be added. For example, a ceramic disc capacitor with the markings103 would indicate 10 and 3 zero's in pico-farads which is equivalent to10,000 pF or 10nF. Likewise, the digits 104 would indicate 10 and 4 zero's in pico-farads which is equivalent to 100,000 pF or 100nF and so on. Then on the image of a ceramic capacitor above the numbers 154 indicate 15 and 4 zero's in pico-farads which is equivalent to 150,000 pF or 150nF. Letter codes are sometimes used to indicate their tolerance value such as: J = 5%, K = 10% or M = 20% etc.

Electrolytic capacitor: Electrolytic Capacitors are generally used when very large capacitance values are required. The majority of electrolytic types of capacitors are Polarised, that is the DC voltage applied to the capacitor terminals must be of the correct polarity, i.e. positive to the positive terminal and negative to the negative terminal as an incorrect polarisation will break down the

insulating oxide layer and permanent damage may result. All polarised electrolytic capacitors have their polarity clearly marked with a negative sign to indicate the negative terminal and this polarity must be followed. Electrolytic Capacitors are generally used in DC power supply circuits due to their large capacitances and small size to help reduce the ripple voltage or for coupling and decoupling applications. One main disadvantage of electrolytic capacitors is their relatively low voltage rating and due to the polarisation of electrolytic capacitors, it follows then that they must not be used on AC supplies. Electrolytic's generally come in two basic forms; Aluminum Electrolytic Capacitors and Tantalum Electrolytic Capacitors.

Capacitor Colour Codes

Sometimes, capacitors are identified with colors, similar to the 4-band system used for resistors (figure 2.2).

The first two colors (A and B) represent the first two digits, third color (C) is the multiplier, fourth color (D)

is the tolerance, and the fifth color (E) is the working voltage.

COLOR DIGIT MULTIPLIER TOLERANCE VOLTAGE

 Black 0  x 1 pF ±20%   Brown 1  x 10 pF ±1%   Red 2  x 100 pF ±2% 250V

 Orange 3  x 1 nF ±2.5%   Yellow 4  x 10 nF   400V

 Green 5  x 100 nF ±5%   Blue 6  x 1 µF     Violet 7  x 10 µF     Grey 8  x 100 µF     White 9  x 1000 µF ±10%  

A colour code was used on polyester capacitors for many years. It is now obsolete, but of course there are many still around. The colours should be read like the resistor code, the top three colour bands giving the value in pF. Ignore the 4th band (tolerance) and 5th band (voltage rating).

For example:

    brown, black, orange   means 10000pF = 10nF = 0.01µF.

Note that there are no gaps between the colour bands, so 2 identical bands actually appear as a wide band.

For example:

    wide red, yellow   means 220nF = 0.22µF. 

3) Inductor : Inductor is a coil which has the ability to produce induce voltage when the current varies. An inductor consists of an insulated coil wound around some core. The core may be iron powder or some magnetic material. It may be air or cardboard tube. An inductor is represented by its inductance value, it is expressed in Henries.

The various types of inductor are:

i) Air core inductor.

ii) Iron core inductor.

iii) Powder core inductor.

iv) Ferrite core inductor.

v) Variable inductor.

Active devices:

Diodes: A diode is one of the simplest semiconductor devices, which has the characteristic of passing current in one direction only. If a suitable positive voltage (forward bias) is applied between the two ends of the PN junction, it can supply free electrons and holes with the extra energy they require to cross the junction as the width of the depletion layer around the PN junction is decreased. By applying a negative voltage (reverse bias) results in the free charges being pulled away from the junction resulting in the depletion layer width being increased. This has the effect of increasing or decreasing the effective resistance of the junction itself allowing or blocking current flow through the diode.

Transistor: Transistors are active components and are found everywhere in electronic circuits. They are used as amplifiers and switching devices. As amplifiers, they are used in high and low frequency stages, oscillators, modulators, detectors and in any circuit needing to perform a function. In digital circuits they are used as switches. 

Types of transistorThere are two types of standard transistors, 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. If you are new to electronics it is best to start by learning how to use NPN transistors.

The leads are labelled base (B), collector (C) and emitter (E).

Transistor circuit symbols

LIST OF QUESTIONS:

1) List any two passive devices?

2) List any two active devices?

_______________________________________________________________________

3) The capacitor shown below is ceramic or electrolytic_____________________

4) What will be value of resistor a) If from left to right 1st band is brown, 2nd band is black and 3rd band is red

________________

b) If from right to left 1st band is yellow, 2nd band is black and 3rd band is brown.

________________

SCHEDULE OF DEMONSTRATION COMPLETION:

DATESignature of Instructor

Starting Finishing

ASSESMENT SCHEME:

Assessment Criteria Grade

1.Identification of electronic devices.

2.Knowledge of electronic components

3.Knowladge of tools used & operations shown

4.Knowledge of safety

Signature of Teacher with date

PRINTED CIRCUIT BOARDS WORKSHOP

THEORY:

A printed circuit board, or PCB, is used to mechanically support and electrically connect electronic components using conductive pathways, tracks or signal traces etched from copper sheets laminated onto a non-conductive substrate. It is also referred to as printed wiring board (PWB) or etched wiring board. A PCB populated with electronic components is a printed circuit assembly (PCA), also known as a printed circuit board assembly (PCBA). PCBs are inexpensive, and can be highly reliable. They require much more layout effort and higher initial cost than either wire-wrapped or point-to-point constructed circuits, but are much cheaper and faster for high-volume production.

The printed circuit boards consist of an insulating substrate material with metallic circuitry photochemically formed upon that substrate. Thus pcb provides sufficient mechanilcal support and necessary electrical connections for an electronic circuit. Inter-connections between components are achieved by means of conducting paths(metallic conductor pattern) running on or through the substrate called tracks. Tracks meet components to which they are to be connected by means of a larger conductor area called a land or pad. The electrical connection between a land and component’s terminal is achieved by means of a solder joint.

Materials required for the fabrication of printed circuit boards:

1) PCB drill with drill bits : It is used for drilling holes in the PCB after the etching process is over.

2) Solder wick : A solder wick, also known as a desoldering wick or desoldering braid, is a roll of

fine, braided 18 to 42 SWG wire typically made from oxygen free copper that has been treated with

a rosin solder flux. The processes of removing solder with a wick start by placing the wick over the

solder to be removed and then heating the portion of the wick in contact with the joint with

a soldering iron. As the the solder wick is heated and the solder reaches its melting point the solder is

sucked into the solder wick via capillary action. The solder wick is then removed along with the heat

and the solder is allowed to solidify within the wick,

apart from the workpiece. Finally, the used section of

wick is discarded.

4) Desolder pump : A desoldering pump, also known as a solder sucker, is a device which is

used to remove solder from a printed circuit board. There are two

types: the plunger style and bulb style.The plunger style is usually

a small, spring-loaded device that sucks the solder off the soldered

connection. It is applied to a heated solder connection, then the

user activates the device (usually via button) to suck the solder

away.

5) Copper clad laminate : It a sheet with insulating

substrate as a base and a thin copper foil which is bonded to it or deposited on it by some process. The layout diagram or artwork

of schematic diagrams transferred on this copper clad laminate and then it is ready for etching process.

6)

7) Soldering iron : It is used for soldering electronic components on the printed circuit board.

8) Solder flux : A flux is a chemical cleaning agent that facilitates soldering by

removing oxidation from the metals to be joined. In soldering of metals, flux serves a threefold purpose: it removes oxidation from the surfaces to be soldered, it seals out air thus preventing further oxidation, andbyfacilitating amalgamation improves wetting characteristics of the liquid solder.

Solder : Solder is a fusible metal alloy with a melting point or melting range of 90 to 450

degree Celsius (190 to 840 °F), used in a process called soldering where it is melted to join metallic surfaces. Lead solder:

1) Tin /lead solders, also called soft solders, are commercially available with tin concentrations between 5% and 70% by weight. The greater the tin concentration, the greater the solder’s tensile and shear strengths. At the retail level, the two most common alloys are 60/40 Tin/lead (Sn/Pb) which melts at 370 °F or 188 °C and 63/37 Sn/Pb used principally in electrical/electronic work

Acetone: It is used for cleaning copper clad laminate before etching and also for removing ink from pcb after etching process is over.

Permanent marker : It is used for drawing artwork or layout diagram on the copper clad laminate.

Ferric chloride powder: It is used for preparing ferric chloride solution in which PCB is dipped for etching the unwanted copper.

Hydrochloric acid: It is mixed in the ferric chloride solution to increase the etching rate of making PCB.

Safety rubber gloves: Ferric chloride solution is a toxic solution, it also attacks skin so rubber gloves are

wore to avoid contact with the solution while stirring or shaking the ferric chloride solution.

PCB preparation process:

1) Draw the schematic circuit diagram of your design.Eg; consider simple circuit of transistor as a switch as shown below:

2) Convert the schematic diagram into layout diagram or artwork by removing the components from it and leaving the terminal contacts of the components so that it can be transferred onto the copper clad laminate as shown below.

3) Take copper clad sheet of proper size clean it with acetone.4) Now transfer the artwork onto the copper clad laminate by toner transfer method or photoresist

method. Here in this case the artwork is simply transferred by drawing tracks and land on the copper sheet by permanent marker pen as shown

5) After transfer of artwork on copper sheet the copper clad sheet is ready for etching, for etching ;

i) First heat 250 ml of water.

ii) Put the warm water into plastic tray and mix 3-4 spoon of ferric chloride powder in water, stir while mixing so that powder gets completely dissolve in water, then mix 15-20 ml of HCl in this solution and stir once again. Now the solution is ready for doing etching.

6) Dip the image transferred copper clad sheet into the above solution and shake the plastic tray till the unwanted copper gets etched out leaving behind only those copper tracks which are covered with permanent marker, since the permanent marker is dye only, ferric chloride solution doesn’t attack on it.

7) Now clean the marker ink from the tracks and pad by washing the printed circuit board with acetone.

The PCB is ready for drilling holes in it.

8) Drill the holes into the pads by pcb-hand drill.

9) Place the components into circuit board properly.

10) Solder the components and cut out the extra lead extending outwards.

THE PCB IS READY WITH THE CIRCUIT DESIGNED.

LIST OF QUESTIONS:

1) Name the chemical solution used for etching of printed circuit boards?

2) List any one tools used for soldering ?

_______________________________________________________________________

3) The path which connects components on printed circuit board is called pads true or false.

If false then what it is called ____________________

4) Printed circuit boards are made from _______________ clad laminate.

SAFETY PRECAUTIONS:

1. Always wear safety rubber gloves while etching printed circuit board.

2. Always mix ferric chloride powder to water and not water to ferric chloride powder.

SCHEDULE OF DEMONSTRATION COMPLETION:

DATESignature of Instructor

Starting Finishing

ASSESMENT SCHEME:

Assessment Criteria Grade

1. Identification of electronic devices.

2.Knowledge of electronic components

3.Knowladge of tools used & operations shown

4.Knowledge of safety

Signature of Teacher with date

Soldering is a process in which two or more metal items are joined together by melting and flowing a filler metal into the joint, the filler metal having a relatively low melting point.

. The 63/37 ratio is notable in that it is a eutectic mixture, which means:

1. It has the lowest melting point (183 °C or 361.4 °F) of all the tin/lead alloys; and

2. The melting point is truly a point — not a range.

n metallurgy, a flux is a chemical cleaning agent that facilitates soldering, brazing, and welding by removing oxidation from the metals to be joined. Common fluxes are: ammonium chloride or rosin for soldering tin; hydrochloric acid and zinc chloride for soldering galvanized iron (and other zinc surfaces); and borax for brazing or braze-welding ferrous metals. Different fluxes, mostly based on sodium chloride, potassium chloride, and a fluoride such as sodium fluoride, are used in foundries for removing impurities from molten nonferrous metals such as aluminum, or for adding desirable trace elements such as titanium.

n high-temperature metal joining processes (welding, brazing and soldering), the primary purpose of flux is to prevent oxidation of the base and filler materials. Tin-lead solder, for example, attaches very well to copper, but poorly to the various oxides of copper, which form quickly at soldering temperatures. Flux is a substance which is nearly inert at room temperature, but which becomes stronglyreducing at elevated temperatures, preventing the formation of metal oxides. Secondarily, flux acts as a wetting agent in the soldering process, reducing the surface tension of the molten solder and causing it to better wet out the parts to be joined.

A soldering iron is a hand tool most commonly used in soldering. It supplies heat to melt the solder so that it can flow into the joint

between two workpieces.

A soldering iron is composed of a heated metal tip and an insulated handle. Heating is often achieved electrically, by passing an

electric current (supplied through an electrical cord or battery cables) through the resistive material of a heating element

MEASUREMENT OF AC VOLTAGE AND FREQUENCY, DC VOLTAGE

MESUREMENT OF AC VOLTAGE :

FORMULA:

PEAK TO PEAK AC VOLTAGE= VOLTS/DIVISION x NUMBERS OF DIVISIONS ON VERTICAL AXIS IN WAVE BETWEEN PEAK TO PEAK.

PROCEDURE:

1) Switch ON the CRO.2) Keep the switch of CRO on AC.3) Make the connections as shown in figure, i.e. connect the output of the function generator to the

channel no 1 of CRO.

4) Now switch on the function generator.5) Keep the waveform switch of function generator on sine wave and adjust voltage level and frequency.

6) Now sine wave will be displayed on the CRO screen.7) Now adjust the volt/division and time per division so that the waveform fits in the CRO screen.

8) Count the number of divisions, on vertical scale in wave between peak to peak(from positive peak to negative peak).

9) Note down the volts/divisions. 10) Put the value of number of divisions and volts/divs in above formula and calculate peak to peak ac

voltage.11) The peak voltage can be calculated by

VP = VP-P /2and rms voltage can be calculated byVRMS = VP/√2.

FREQUENCY MEASUREMENT:

FORMULA:

FREQUENCY= 1/ TIME PERIOD (T)

TIME PERIOD (T) = TIME/DIVISION x NUMBERS OF DIVISION ON HORIZONTAL AXIS IN WAVE FOR ONE COMPLETE CYCLE.

PROCEDURE:

1) Repeat step 1 to step 7 as given in the measurement of ac voltage measurement.2) Now, count the number of divisions, on horizontal scale covered by one complete cycle of waveform.

3) Note down the time/divisions 4) Put the value of number of divisions and time/divs in above formula and calculate time period.5) Now, put value of time period in the formula of frequency and calculate it.

MEASUREMNT OF DC VOLTAGE:

FORMULA:

DC VOLTAGE VDC= NUMBER OF DIVISIONS ON VERTICAL AXIS X VOLTS/ DIVISIONS.

PROCEDURE:1) Switch on the CRO.2) Keep the switch of CRO on DC.3) Coincide the trace with central horizontal line.

4) Connect the output of regulated dc power supply to channel 1 of CRO and switch on the dc supply, when the dc voltage is increased the trace moves up.

5) Count the number of divisions on vertical axis.6) Note down volts/divisions and determine dc voltage using formula written above.