Basic Electronics Book

Basic of Electronics

Hand Out

BASIC OF ELECTRONICS FOR MECHATRONICS STUDENTS

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Chapter 1: Basic Concepts Topics • • • • • •

Atoms and Electrical Charge Current. Voltage. Power Resistance Ohm's Law

1.1. Atoms and Electrical Charge - Discusses the structure of atoms.

Figure 1-1. Model of an Atom Atoms are the building blocks of all a ll matter. They are made up of protons, neutrons, and electrons. Every electron has a small negative (-) charge. The proton has the same amount of charge except that it is the opposite, positive (+) charge. Neutrons are elec trically neutral and have no charge. The protons and neutrons are located in the center of atoms forming what is called the nucleus and the electrons revolve around them. It is very important to know that particles of like ch arges will repel and unlike charges will attract. For example, two protons or two electrons will repel each other. However, a proton and a electron will attract. That is how the electrons are held inside the atom. The attraction between the electrons and protons keeps the electrons in orbit much like the gravitational attraction between the sun and its planets.

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Chapter 1: Basic Concepts Topics • • • • • •

Atoms and Electrical Charge Current. Voltage. Power Resistance Ohm's Law

1.1. Atoms and Electrical Charge - Discusses the structure of atoms.

Figure 1-1. Model of an Atom Atoms are the building blocks of all a ll matter. They are made up of protons, neutrons, and electrons. Every electron has a small negative (-) charge. The proton has the same amount of charge except that it is the opposite, positive (+) charge. Neutrons are elec trically neutral and have no charge. The protons and neutrons are located in the center of atoms forming what is called the nucleus and the electrons revolve around them. It is very important to know that particles of like ch arges will repel and unlike charges will attract. For example, two protons or two electrons will repel each other. However, a proton and a electron will attract. That is how the electrons are held inside the atom. The attraction between the electrons and protons keeps the electrons in orbit much like the gravitational attraction between the sun and its planets.

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Figure 1-2. Interaction between electrons and protons Electricity is the flow of electrons so it is necessary to measure the charge . The basic unit for measuring charge is the coulomb or the letter C. 1 coulomb is equal to the charge of 6,250,000,000,000,000,000 electrons!!! 1C = 6.25x10^18 electrons 1.2. Current - Introduces current and ampere.

Electric current is the amount of electrons, or charge, moving past a point every second. It is basically the speed of electron flow. The faster the electrons flow, the higher the current.

Figure 1-3. Electron Flow Current is represented by the letter I. The basic unit for measuring current is ampere. Ampere can be abbreviated to amp or just A. 1 amp = 1 coulomb/sec

Meaning for every amp, there are 6.25x10^18 electrons moving past a point every second. 1.3. Voltage - Potential difference and voltage

To make sense of voltage, we will need to make an analogy. Lets imagine that electrons are represented by a marble on a flat plane. At this point, the plane is level and the marble does not move. If the plane plan e is lifted at one side, the marble will roll down to the lower point.

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Figure 1-4. Analogy electron with a marble In electricity, the high point is a point with lots of electrons and the low point is a point with a lack of electrons. The high point is called the high potential and the low point is the low potential. The difference between these two points is called the potential difference. The larger the potential difference, the larger the voltage.

Figure 1-5. Energy potential

Voltage can be thought of as the measure of the pressure pushing the electrons. The higher the pressure, the higher the voltage. Voltage is represented by the letter E. The basic unit of measure is volts or the letter V. One volt will push 1 amp of current through 1 ohm of resistance. Resistance will be discussed in a later section.

1.4. Power - Discusses power or the amount of work a circuit is doing.

Power is simply the amount of energy used or the amount of "work" a circuit is doing. Power is represented by the letter P. The basic un it for measuring power is watts or the letter W. To find power, all you need nee d is a simple equation: P=EI

or Power equals voltage times current. For example, if E = 9V I = 0.5A then P = 9 * 0.5 P = 4.5W

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1.5. Resistance - Discusses electron flow, materials, and the ohm unit .

To better understand what resistance is, you must first get an idea of how electrons flow. When an electron is knocked out of an atom, it will fly off and hit h it another atom. If the electron strikes the atom with enough force, it will knock off another electron. The atom that was just knocked off will hit another atom and so forth.

Figure 1-6. Two electrons Note that every time an electron strikes another, it is transferring its energy. Some of th e energy is converted into heat every time it is transferred. The voltage will drop as the energy is transferred over long distances. Thus a long wire has a higher resistance than a short wire. Some materials - such as copper and silver - does not hold on to its electrons very tightly. Therefore it doesn't require much energy to knock off an electron. These materials are called conductors and has a very low resistance to electron flow. Materials such as clay and plastics hold on to their electrons more tightly than conductors. It takes more energy to knock off an a n electron from these materials. These materials are called insulators and has a high resistance to electron flow. Now, you must understand that this is NOT how electrons really flow; It serves only as something for you to work with. To really rea lly know how electrons flow, which we will not get into, you will need to study quantum physics. Resistance is represented by the letter R. The ba sic unit of measure is ohm or the symbol (Greek omega). In the next section (Ohm's Law), we will show you the relationship between Current, Voltage, and Resistance. Resistance will also be further discussed as we introduce the resistor.

1.6. Ohm's Law - The relationship between Current, Voltage, and Resistance.

The German physicist, George Simon Ohm, established that voltage in volt, electrical resistance in ohms, and ampereres flowing through an y circuit are all related. Ohms’s law states:

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It requires 1 volt to push 1 ampere through 1 ohm of resistance. Ohm law camn also be sated as asimple formula to calculate one value of an electrical circuit if the other two are known. I=E/R

Where: I= Current in ampere (A) E= Voltage in volt (V) R= Resistance in ohms (Ω)

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Chapter 2: Schematic Diagram A schematic diagram shows how each component connect with another. It is a simple and easy to read outline of the circuit. Each type of component has a unique symbol and a name (usually 1-2 letters). All relevant values and component specific information are usually included. Below is an example of a schematic diagram:

Figure 2-1 A simple schematic diagram As you can see, this diagram has 3 components: the thing with 4 horizontal lines, the triangle in a circle, and the thing with the wavy lines. Can you guess which is the battery? Yes, the 4 horizontal lines. The triangle in the circle represents the light emitting diode and the wavy lines represent the resistor -- both of which will be discussed in the components section. Note the "R1" next to the resistor symbol and "R1 470 ohm" below the diagram. This tells you what value to use for that component. If there was a second resistor, the second resistor will be called R2. That's all it is to schematic diagrams. It's not that tough right?

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Chapter 3: Electronics Component

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Resistors - A component that resist the flow of electrons. Capacitors - A mini recharable battery. Diodes - A "one way street" for electrons. Transistors - A component used for switching and amplifying. Integrated circuits - An overview of integrated circuits Switches - Discusses the different configurations of switches.

3.1. Resistors - A component that resist the flow of electrons.

Resistors are one of the most commonly used components in electronics. As its name implies, resistors resist the flow of electrons. They are used to add resistance to a circuit. The color bands around the resistors are color codes that tell you its resistance value. Recall that resistance is measured in ohms. The tolerance bands indicates the accuracy of the values. A 5% tolerance (gold band) for example, indicates that the resistor will be within 5% of its value. For most applications, a resistor within 5% tolerance should be sufficient. To get the value of a resistor, hold the resistor so that the tolerance band is on the right. The first two color bands from the left are the significant figures - simply write down the numbers represented by the colors. The third band is the multiplier - it tells you how many zeros to put after the significant figures. Put them all together and you have the value.

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NOTE: There are resistors with more bands and other types for specific applications. However, 4 band resistors(the ones discussed here) are the most common and should work for most projects.

One last important note about resistors is their wattage rating. You should not use a 1/4 watt resistor in a circuit that has more than 1 /4 watt of power flowing. For example, it is NOT okay to use a 1/4 watt resistor in a 1/2 watt circuit. However, it is okay to use a 1/2 watt resistor in a 1/4 watt circuit.

Figure 3-1 Schematic and Symbol of Resistor The simplest resistors are made from carbon rod with end caps and wire leads. Other types are carbon film which is a thin layer of carbon on a ceramic rod, and metal oxide and metal glaze on glass rods. Wire wound resistors are used where the resistor has to dissipate a lot of heat. Faulty resistors have gone open circuit or changed in value. They never go short circuit. Some resistors are designed to change in value when heated. They are called THERMISTORS and are used in temperature measuring circuits. Some resistors change in value when exposed to light. They are called LIGHT DEPENDANT RESISTORS. Most resistors are color coded to indicate their value and tolerance. Wire wound resistors have their value written on them. (color would change with heat). High stability resistors (marked with a fifth pink band) do not change value easily. Resistors generate heat. Resistors have a wattage rating. The higher this rating the more heat they can dissipate. To limit the range of resistor values to a manageable number a preferred range only is available. These are 1.0 1.2 1.8 2.2 2.7 3.3 3.9 4.7 5.6 6.8 8.2 This mean that 1 ohm, 12 ohm, 180 ohm, 2200 ohm resistors etc are available. 1000 ohms is 1k, 1000,000 ohms is 1M. 3,300,000 ohms is 3.3M etc. Decimal points are not used on circuit diagrams (they may be confused with fly specks). 3.3M would be written as 3M3 and 1.8k as 1K8 etc.

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On circuit diagrams tolerance is indicated by the following letters. F=1% G=2% J=5% K=10% M=20% R22M= 0.22 ohm 20% 4R7K= 4.7 ohm 10% 68RJ=68 ohm 5% Variable resistors are available. These can be operated by means of a knob on the control panel. Examples are volume and brightness controls. Preset variable resistors are internal controls which are adjusted in value by means of a screwdriver. Once adjusted, they are never touched again.

3.2. Capacitors - A mini rechargeable battery.

Capacitors are basically two parallel metal plates separated by an insulator.

Figure 3-4 a pair plate of Capacitor This insulator is called the dielectric.

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Capacitor types are named after the dielectric. Thus we have ceramic, mica, polyester, paper air capacitors etc. Capacitors can be charged up and store electricity, similar to a car battery. This can be a hazard if they are charged up to high voltages. If it is necessary, capacitors with large charges should be discharged via a resistor to limit the discharge current. Capacitors are the second most commonly used c omponent in electronics. They can be thought of as tiny rechargeable batteries -- Capacitors can be charged and discharged. The amount of charge that a capacitor can hold is measured in Farads or the letter F. However, 1F is too large for capacitors, so microfarads(µF) and picofarads(pF) are used. micro = 1/1,000,000 and pico = 1/1,000,000,000,000 So 100,000pF = 0.1µF = 0.0000001F

DC current cannot flow through a capacitor since the dielectric forms an open circuit. Capacitors come in all shapes and sizes and are usually marked with their value.

We will only be discussing two types of the most commonly used capacitors: Ceramic and Electrolytic. •

Ceramic capacitors are brown and has a disc shape. These capacitors are non polarized, meaning that you can connect them in any way. To find the value, you simply decode the 3 digit number on the surface of the capacitor. The coding is just like the resistor color codes except that they used numbers instead of colors. The first 2 digit are the significant figures and the third digit is the multiplier. These capacitors are measured in pF.

Figure 3-2 Ceramic Capacitor •

Electrolytic Capacitors has a cylinder shape. These capacitors are polarized so you must connect the negative side in the right place. The value of the resistor as well as the negative side is clearly printed on the capacitor. These capacitors are measured in µF.

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Figure 3-3 Electrolytic Capacitor They are often marked with their maximum working v oltage. The voltage across the terminals must not exceed this value. It is OK to use a voltage below the maximum value. Some capacitors such as electrolytic and tantalums are polarised. This means that they must be fitted the correct way round. They are marked to indicate polarity. Some values are indicated with a colour code similar to resistors. There can be some confusion. A 2200pf capacitor would have three red bands. These merge into one wide red band.

Figure 3-4 Color band on Capacitor

Some values are marked in picofarads using three digit numbers. The first two digits are the base number and the third digit is a multiplier. For example, 102 is 1000 pF and 104 is 100,000 pF = 100 nF = 0.1 uF. To find the total value of capacitors in parallel (that is connected across each other) their values are added. To find the total value if they are in series (that is in line with each other) then the following formula is used. 1/C total =1/C1 + 1/C2 + 1/C3 etc Variable capacitors are available in which the value can be adjusted by controlling the amount of overlap of the plates or the distance between them. There is a type of diode called the Varicap diode which similar characteristics.

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Figure 3-5 Symbol of fix and variable capacitor

3.3 Diodes

- A "one way street" for electrons. Diodes let electrons flow through them only in one direction. Diodes flow from cathode to anode. The cathode side of the diode is marked with a band around it.

Figure 3-6 Diodes and its symbol

There are basically three different types of diodes: Diodes, Zener Diodes, and Light Emitting Diodes. Zener diodes have a set voltage rating. When a voltage exceeds the voltage rating going the opposite direction (from anode to cathode), the diode allows the electrons flow. Light Emitting Diodes (LED for short) are just like the regular diodes except that it lights up when electrons are flowing through. Note: there aren't any bands to identify which pin is anode and which is cathode. However, one pin is longer then the other. The longer pin is the anode, the positive side.

Figure 3-7 Symbol of LED

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Diodes are polarised, which means that they must be inserted into the PCB the correct way round. This is because an electric current will only flow through them in one direction (like air will only flow one way through a type valve). Diodes have two connections, an anode and a cathode. The cathode is always identified by a dot, ring or some other mark.

Figure 3-8 Mark indicator in Diodes The pcb is often marked with a + sign for the cathode end. Diodes come in all shapes and sizes. They are often marked with a type number. Detailed characteristics of a diode can be found by looking up the type number in a data book. If you know how to measure resistance with a meter then test some diodes. A good one has low resistance in one direction and high in the other. There are specialised types of diode available such as the zener and light emitting diode (LED).

Figure 3-9 Some diode circuit symbols LED

The light emitting diode (LED) is commonly used as an indicator. It can show when the power is on, act as a warning indicator, or be part of trendy jewelry etc.

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Figure 3-9 LED circuit It needs to be fed from a DC supply, with the anode positive and the cathode negative, as shown in the diagram. To calculate the value of the series resistor we need to know the diode forward voltage and current and its connections. The necessary data can be obtained from a catalogue or data book. In our example it is 2 volts and 20mA (0.02 amps). The cathode lead is the one nearest a "flat" on the body. Since the voltage across the diode is 2 volts and the battery voltage is 12 volts, then the voltage across the resistor is 12-2 = 10 volts. The diode is in series with the resistor, so the current through then both is the same, 0.02 amps. We now know the voltage across, and the current through the resistor. From Ohm's Law we can now ca lculate the value of the resistor. Resistance = Volts divided by Amps = V/I = 10/0.02 =500 ohms. Since this is not a standard value we can use a 470 or 560 ohm resistor as this application is not critical of v alues. 3.4. Transistors -A component used for switching and amplifying.

The transistor is a three terminal solid state semiconductor device that can be used for amplification, switching, voltage stabilization, signal modulation and many other functions. Transistors are used as switches and amplifiers. We will discuss two types of transistors: PNP and NPN transistors. Both of these transistors has 3 pins: emitter, base, collector. There aren't any standards for where and what order the physical pins are on the transistors, so be sure to check the packaging when purchasing.

Figure 3-10 Transistors

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To allow electrons to flow through the collector and emitter of a PNP transistor, the following must apply: The emitter is more positive than the base and the collector leads to the negative.

Figure 3-11 Symbol of PNP Transistors

The NPN transistor is the opposite: The collector must be more positive than the base and the emitter leads to the negative.

Figure 3-12 Symbol of NPN Transistors

3.5. Integrated circuits (IC) - An overview of integrated circuits

Integrated circuits (IC) are usually referred to as chips. Inside them is a tiny piece of semiconductor(usually silicon) with large circuits built in. Most common are 8, 14, or 16 pin dual in line (dil) chips. IC's can be soldered directly into printed circuit boards, or may plug into sockets which have already been soldered into the board. When soldering, ensure that the IC (or the socket) is the correct way round and that no pins have been bent underneath the body. When fitting new IC's it is often necessary to bend the pins in slightly, in order to fit it into the board (or socket). Some IC's are damaged by the static electricity which most people carry on their bodies. They should be stored in conductive foam or wrapped in tin foil. When handling them, discharge yourself periodically by touching some metalwork which is earthed, such a s a radiator. Solder two diagonally opposite pins (say pin 1 and pin 5 in the diagram below) and check that the IC is flat on the board before soldering the rest. If it is not flat then reflow the solder on the two pins pushing the IC flat. When satisfied, solder the remaining pins.

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There are millions of different integrated circuits. The general types of integrated circuits include:

Figure 3-12 Symbol of IC

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Logic circuits These IC's are basically decision makers. most contain logic gate circuits. (logic gates will be discussed in a later section).

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Comparators These IC's compare inputs and gives an output.

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Operational Amplifiers These are amplifiers. Works very much like transistor amplifier circuits.

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Audio amplifiers These are used to amplify audio.

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Timers These are counting IC's used for circuits that counts or needs to keep track of time.

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Switches Switching IC's are also very much like the switching circuits of transistors.

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Other There are thousands of other types. A lot of IC's are made for a special purpose like digital sound recording. Most IC's come with pinout information and how to use it. If not, you'll need one of those large reference books that have info on most of the IC's.

3.6. Batteries

Batteries are assembled from cells, connected in series, to increase the voltage available. In a cell chemical energy is converted into electrical energy. Cells may be either PRIMARY or SECONDARY types. A primary cell is discarded when its chemical

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energy is exhausted. A secondary cell can be recharged. The most common primary cell is the zinc/carbon (Leclanche) as used in torches, portable radios etc.

Figure 3-13 Symbol of Battery

The zinc and carbon react with the ammonium chloride ELECTROLYTE to produce electricity. The manganese dioxide absorbs hydrogen gas produced around the carbon rod which would insulate it from the electrolyte and stop the cell working. The most common secondary cells are the lead/acid and nickel/cadmium (nicad). Lead acid batteries need a constant voltage charger. Nicads must be charged with a constant current charger. All cells have INTERNAL RESISTANCE. This is not an actual resistor but a characteristic of the cell. Internal resistance increases as the cell ages.

Figure 3-14 Internal Resistance of Battery

When current is taken from a battery, voltage is dropped across this internal resistance and the voltage at the battery terminals falls. The diagram shows that as the current taken increases the terminal voltage decreases.

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Figure 3-15 Voltage-Current characteristics of Battery

This is called POOR REGULATION. It occurs in any type of power supply. Battery voltages must therefore always be measured ON LOAD, i.e. with the radio etc switched on and drawing current. 3.7. Transformer

If you have read the page on ELECTROMAGNETISM then you will know that when a current is passed through a coil, the coil becomes surrounded by a magnetic field. This field is made up from lines of force and has the same shape as a bar magnet. If the current is increased, the lines of force move outwards from the coil. If the current is reduced, the lines of force move inwards. If another coil is placed adjacent to the first coil then, as the field moves out or in, the moving lines of force will "cut" the turns of the second coil. As it does this, a voltage is induced in the second coil. With the 50 Hz AC mains supply , this will happen 50 times a second. This is called MUTUAL INDUCTION and forms the basis of the transformer. The input coil is called the PRIMARY WINDING, the output coil is the SECONDARY WINDING. The voltage induced in the secondary is determined by the TURNS RATIO. Primary voltage --------------------Secondary voltage

=

Number of primary turns ----------- -----------------------Number of secondary turns

For example, if the secondary has half the primary turns, the secondary will have half the primary voltage. Another example is if the primary has 5000 turns and the secondary has 500 turns, then the turns ratio is 10:1. If the primary voltage is 240 volts then the secondary voltage will be x 10 smaller = 24 volts. Assuming a perfect transformer, the power provided by the primary must equal the power taken by a load on the secondary. If a 24 watt lamp is connected across a 24 volt secondary, then the primary must supply 24 watts. If it is a 240 volt primary then the current in it must be 0.1 amp. (Watts = volts x amps).

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To aid magnetic coupling between primary and secondary, the coils are wound on a metal CORE. Since the primary would induce power, called EDDY CURRENTS, into this core, the core is LAMINATED. This means that it is made up from metal sheets insulated from each other. Transformers to work at higher frequencies have an iron dust core, or no core at all. Note that the transformer only works on AC which has a constantly changing current and moving field. DC has a steady current and therefore a steady field and there would be no induction. Some transformers have an electrostatic screen between primary and secondary. This is to prevent some types o f interference being fed from the equipment down into the mains supply, or in the other direction. Transformers are sometimes used for IMPEDANCE MATCHING.

Figure 3-15 Diagram of Transformers

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3.8 Inductor

Inductors are coils of wire. They may be woun d on tubular FORMERS or may be self supporting. The former may contain a metallic core up its centre. Iron cores are used for frequencies below about 100 kHz. Ferrite cores are used for frequencies up to say, 10 Mhz. Above 100Mhz the core is usually air and the coil is self supporting. At low frequencies the inductor may have hundreds of turns, above 1 Mhz only a few turns. Most inductors have a low DC resistance since they are wound from copper wire. Inductor values of INDUCTANCE are measured in HENRIES. Inductors oppose the flow of ac current. This opposition is called INDUCTIVE REACTANCE. Reactance increases with frequency and as the value of the inductance increases.

Figure 3-16 Diagrams of Inductors

3.9. Switches

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Discusses the different configurations of switches.

Switches really don't need any introduction. It simply connects and disconnect a circuit. This section gives an overview of the contact configurations. There are 3 commonly used configurations: SPST, SPDT, and DPDT. SPST = Single Pole, Single Throw This is a two terminal switch that opens and closes a circuit.

SPDT = Single Pole, Double Throw This is a three terminal switch that connects one terminal to either of the other two.

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DPDT = Double Pole, Double Throw This is a six terminal switch that connects a pair of terminals to either of the other two pairs.

Fig. 1 Switches are used to open/close a circuit. Fig. 2 S1 is a "single pole on/off" switch in the off position. Fig. 3 This is a "2 pole on/off" switch which completely isolates the lamp from the supply in the off position. This may be important if it is a high voltage supply. The dotted line indicates that S1a and S1b are part of the same switch "ganged" together and operate simultaneously.

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Fig. 4 This is a "single pole changeover" switch. Either lamp 1 or lamp 2 is on. Fig. 5 This is a "2 pole changeover" switch. The unlit lamp is completely isolated from the supply. Again S1a and S1b are part of the same switch. Fig. 6 This is a "single pole 5 way" switch. It can select 1 of 5 circuits. You can have 2p 5w, 3p 4w etc. Fig. 7 This shows (1) a "normally closed, push to break". (2) a "normally open, push to make". (3) both used together to make a "changeover" switch. Fig. 8 This is a "changeover" slide switch. When operated a-b opens and b-c closes. Here are assorted switch types. Panel-Toggle-Make before break-Pneumatic-WaferProximity-Light activated-Toggle-Rotary Reed-Pull-Locking-Vane-Interlocking-RockerDimmer-Mercury-Tilt-Microswitch Thumbwheel-Key-Wafer-Slide-Float-Optical-FootThermal-Hall effect 3.10. The Fuse

The fuse is a piece of wire which can carry a stated current. If the current rises above this value it will melt. If the fuse melts (blows) then there is an open circuit and no current can then flow thus protecting the equipment by isolating it from the power supply. The fuse must be able to carry slightly more than the n ormal operating current of the equipment to allow for tolerances and small current surges. With some equipment there is a very large surge of current for a short time at switch on. If a fuse is fitted to withstand this large current there would be no protection against faults which cause the current to rise slightly above the normal value. Therefore special antisurge fuses are fitted. These can stand 10 times the rated current for 10 milliseconds. If the surge lasts longer than this the fuse will blow. Always find out why the fuse b lew before replacing it. Occasionly they grow tired and fail. If the fuse is black and silvery then it is likely that there is a dead short (very low resistance) somewhere.

Figure 3-17 Fuse Configuration in circuit

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3.11. Gates

Gates are logic circuits. They take binary inputs and and gives out a binary result. 1(one) is represented by a positive electrical value and 0(zero) is represented by no electricity at all. Logic IC's contain these and other types of gates. This section describes the different types of gates and their symbols: •

AND gate To get an output of 1, both inputs must be at a value of 1.

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OR gate To get an output of 1, one or more inputs must be at a value of 1.

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NOT gate To get an output of 1, its input must be at a value of 0. This gate only has one input. It is also known as an inverter circuit.

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NAND gate To get an output of 1, one or more of its inputs must be at a value of 0.

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NOR gate To get an output of 1, all inputs must be at a value of 0.

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3.11. Loudspeaker

The most common type of loudspeaker is the MOVING COIL speaker, where a coil of wire is suspended in the magnetic field of a circular magnet. When a speech current is passed through the coil a varying magnetic field is generated by the coil.

Figure 3-18 Diagrams of Speaker

The two magnetic fields interact causing movement of the coil. The movement of the coil causes a cone, which is attached to the coil, to move back and forth. This compresses and decompresses the air thereby generating sound waves. The loudspeaker is a TRANSDUCER converting one form of energy to another. Loudspeakers have Impedance, typically 4 or 8 ohms. This must be matched to the output impedance of the amplifier (see the page on REACTANCE and IMPEDANCE). Loudspeakers are mounted in enclosures (boxes). The design of enclosures is very complicated. Large speakers cannot reproduce high frequencies and small ones cannot reproduce low frequencies. Therefore two speakers are used, a large one (a Woofer) for low frequencies, and a small one (a Tweeter) for high frequencies. To ensure that the correct frequencies go to the desired speaker, a Crossover Unit is used. In the diagram, C1 and L1 are a low pass filter. C2 and L2 are a high pass filter. (there is a page on FILTERS). When using two speakers together, as in stereo systems, they must be in phase. This means that they move out and in together. This happens if the speaker leads are connected correctly. Speakers can be connected in series and parallel but the total impedance must match the amplifier impedance. Using a lower impedance than the correct one can blow up your amplifier.

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Figure 3-19 Woofer and Tweeter configuration 3.12. Electromagnetic relay

The electromagnetic relay consists of a multi-turn coil, wound on a n iron core, to form an electromagnet. When the coil is energised, by passing current through it, the core becomes temporarily magnetised.

Figure 3-20 Electromagnetic Relay

The magnetised core attracts the iron armature. The armature is pivoted which causes it to operate one or more sets of contacts. When the coil is de-energised the armature and contacts are released.

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The coil can be energised from a low power source such as a transistor while the contacts can switch high powers such as the mains supply. The relay can also be situated remotely from the control source. Relays can generate a very high voltage across the coil when switched off. This can damage other components in the circuit. To prevent this a diode is connected across the coil. The cathode of the diode is connected to the most positive end of the coil.

Figure 3-20 Relay position

The springsets (contacts) can be a mixture of n.o n.c and c.o. Various coil operating voltages (ac and dc) are available. The actual contact points on the springsets are available for high current and low current operation. The REED RELAY has a much faster operation than the relays described above.

3.13. Value Multiplier

In Electronics we use some very large and some very small values. To make them easier to deal with we use MULTIPLIERS. For example 1000,000,000,000 Hertz can be labelled 1 Terahertz. and 0.000,000,000,001 Ohms is the same as 1 picohm PREFIX SYMBOL MULTIPLICATION FACTOR -----------------------------------------------------------------------------------------------------tera T 1,000,000,000,000 giga G 1,000,000,000 mega M 1,000,000 kilo K 1,000 milli m 0.001 micro u 0.000,001 nano n 0.000,000,001 pico p 0.000,000,000,001 See that 1 microfarad is 1000 nanofarad. There are 1,000 picofarad in 1 nanofarad. Practice converting one to another.

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CIRCUIT SYMBOLS

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Chapter 4 Circuit Concepts •

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Resistors in Series - Discusses series circuits and the result of putting resistors in series. Resistors in Parallel - Discusses Parallel circuits and the result of putting resistors in parallel. Capacitors in Series - Discusses the result of putting capacitors in series. Capacitors in Parallel - Discusses the result of putting capacitors in parallel

4.1. Resistors in Series - Discusses series circuits and the result of putting resistors in series. So what is a series circuit? A series circuit means connecting components one after the other. So when we say "Resistors in series", we mean c onnecting one resistor after the other:

To find the TOTAL resistance, simply add up the resistance of the resistors in the series circuit. 4.2. Resistors in Parallel - Discusses Parallel circuits and the result of putting resistors in parallel.

What happens when resistors are placed side by side -- in other words, in a parallel circuit?

The result is the total resistance being lower than the lowest resistor. To calculate what the total resistance is, you must use this equation: Rt = (R1 * R2) / (R1 + R2) 4.3. Capacitors in Series

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- Discusses the result of putting capacitors in series. Unlike resistors in series, capacitors in series lowers the total capacitance. The total capacitance in a capacitor series circuit is less than the lowest capacitor in the circuit. To find the total capacitance, use the following equation: Ct = (C1 * C2) / (C1 + C2) Notice that it's the same equation as resistors in parallel

Capacitors in Parallel - Discusses the result of putting capacitors in parallel Now if capacitors in series uses the same equation as resistors in parallel, how do you find the total capacitance of capactors in parallel? Right! You just add it up! So if there are 4 capacitors in parallel and their values are: 2pF, 3pF, 4pF, and 5pF The total value is 2pF + 3pF + 4pF + 5pF = 14pF

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Chapter 5 Skills in Electronics 5.1. Using Breadboards - Introduces the breadboard.

Breadboards are used for testing and experimenting with electronic circuits. They are very convenient since all you have to do is plug in the components. Oh the surface of a breadboard, there are many holes for plugging in components:

The bread board has many strips of metal which run underneath the board that connects the component. The metal strips are laid out as shown below:

Each strip is a connection. So whichever components connected to a certain strip are connected to eachother. The blue strips shown in the illustration are usually used for connecting the batteries and the green strips are for the components.

5.2. Soldering - Discusses how to solder

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First a few safety precautions: Never touch the element or tip of the soldering iron. They are very hot (about 400°C) and will give you a nasty burn. Take great care to avoid touching the mains flex with the tip of the iron. The iron should have a heatproof flex for extra protection. An ordinary plastic flex will melt immediately if touched by a hot iron and there is a serious risk of burns and electric shock. Always return the soldering iron to its stand when not in use. Never put it down on your workbench, even for a moment! Work in a well-ventilated area. The smoke formed as you melt solder is mostly from the flux and quite irritating. Avoid breathing it by keeping you head to the side of, not above, your work. Wash your hands after using solder. Solder contains lead which is a poisonous metal.

Now that you have your circuit boards, you can start soldering. what you need: • • •

Soldering iron (around 25W) 60/40 solder and optionally a soldering iron holder. Note that you'll probably want one unless you're the careful type and you're sure you won't burn up anything.

Before you solder, you must tin the tip. Simply wait for the soldering iron to heat up, apply a coat of solder on the tip, and wipe it with a wet sponge. Now, to solder the components onto the board, cut the leads at the proper length. Stick the component's leads through the proper holes and bend it so that it'll stay still. Put the soldering iron tip so that it's touching the lead and the copper at the same time. Then apply the solder on the lead (not on the tip of the soldering iron). Let the joint cool by itself.

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Cleaning the bit with a damp sponge. Tinning the bit. Heating the joint and applying the solder Use a damp sponge, frequently, to keep the bit clean. Tin the bit for good heat conduction.(This means putting a small blob of solder on the tip of the bit). Hold the iron like a pen. Rest your hands on the workbench to steady them. Take precautions against the work moving. (use a small vice or sticky tape). Heat the biggest part of the joint for 2-3 seconds. Apply solder to the joint not to the iron. Allow the solder to run over the joint without moving the iron. Remove the solder. Remove the iron. Avoid overheating.The process should take only 2-3 seconds. A dry joint is a poorly soldered one. A good joint is smooth and shiny. If the joint has moved during soldering it will be dull and crinkly. If you have taken too long it will have have solder spikes. The shape of the wire should be visible through the solder. All soldered joints should be easily removable.This means a minimum of lea d wrapping. When using printed circuit boards avoid bending wires flat on the board. It makes them difficult to remove. Spring component leads out just slightly, to prevent them falling out during soldering. Mount components so that value markings are visible. Do not carry solder on the bit to the joint. The smoke you see is evaporating flux, which should normally clean the joint. Reflow soldering is tinning two pieces of wire separately and then reheating to join them together. PRACTICE MAKES PERFECT !!!

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Don't allow the blobs to run into each other. Make the blobs all the same size and shape. A good joint is smooth and shiny. See (a). The solder must run along the copper track, not stand on it like a bead. (b) A bad joint is unevenly shaped, dull and crinkly in appearance.(c) If there are spikes on the joint, then you are taking too long to make the joint. When you can produce good results proceed to the next part of the exercise.

Some components require special care when soldering. Many must be placed the correct way round and a few are easily damaged by the heat from soldering. Appropriate warnings are given in the table below, together with other advice which may be useful when soldering. Components

1

Pictures

Reminders and Warnings Connect the correct way round by making sure the notch is at the correct end. Do NOT put the ICs (chips) in yet.

Chip Holders (DIL sockets)

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No special precautions are needed with resistors.

2 Resistors

Small value capacitors (usually less than 1µF)

These may be connected either way round. Take care with polystyrene capacitors because they are easily damaged by heat.

Electrolytic capacitors 4 (1µF and greater)

Connect the correct way round. They will be marked with a + or - near one lead.

5 Diodes

Connect the correct way round. Take care with germanium diodes (e.g. OA91) because they are easily damaged by heat.

6 LEDs

Connect the correct way round. The diagram may be labelled a or + for anode and k or - for cathode; yes, it really is k, not c, for cathode! The cathode is the short lead and there may be a slight flat on the body of round LEDs.

7 Transistors

Connect the correct way round. Transistors have 3 'legs' (leads) so extra care is needed to ensure the connections are correct. Easily damaged by heat.

Wire Links between 8 points on the circuit board.

Use single core wire, this is one solid wire which is plastic-coated. If there is no danger of touching other parts you can use tinned copper wire, this has no plastic coating and looks just like solder but it is stiffer.

3

single core wire

Battery clips, buzzers 9 and other parts with their own wires

Connect the correct way round.

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Wires to parts off the circuit board, including 10 switches, relays, variable resistors and loudspeakers.

stranded wire

You should use stranded wire which is flexible and plasticcoated. Do not use single core wire because this will break when it is repeatedly flexed. Connect the correct way round. Many ICs are static sensitive. Leave ICs in their antistatic packaging until you need them, then earth your hands by touching a metal water pipe or window frame before touching the ICs. Carefully insert ICs in their holders: make sure all the pins are lined up with the socket then push down firmly with your thumb.

11 ICs (chips)

DESOLDERING COMPONENTS

Tools required - pliers, cutters, soldering iron and solder sucker (desoldering tool). Take great care to avoid damage. Components cost a few pence, an assembled printed circuit board may be worth several hundred pounds. Ensure the iron bit is well tinned. Heat up the joint to be desoldered until the solder runs. Apply the solder sucker and remove the solder. This should only take two or three seconds. If the operation is unsuccessful resolder the joint and then try again. Ensure the joint is completely desoldered by wriggling the wire with a pair of pliers to check for freeness.Check that all pins are loose on an integrated circuit. Working on a double-sided PCB (where copper tracks are on both sides of the PCB) is more difficult and requires more care. It is often safer to cut the component leads and discard the component, then desolder the leads individually. In some cases desoldering braid is useful. Ensure the iron is tinned. Place the braid on top of the joint. Place the iron on top of the braid and allow the solder from the joint to run up the braid. At some stage you will probably need to desolder a joint to remove or re-position a wire or component. There are two ways to remove the solder:

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1. With a desoldering pump (solder sucker)

Set the pump by pushing the spring-loaded plunger down until it locks. Apply both the pump nozzle and the tip of your soldering iron to the joint. Wait a second or two for the solder to melt. Then press the button on the pump to release the plunger and suck the molten solder into the tool. Repeat if necessary to remove as much solder as possible. The pump will need emptying occasionally by unscrewing the nozzle.

2. With solder remover wick (copper braid)

Apply both the end of the wick and the tip of your soldering iron to the joint. As the solder melts most of it will flow onto the wick, away from the joint. Remove the wick first, then the soldering iron. Cut off and discard the end of the wick coated with solder. After removing most of the solder from the joint(s) you may be ab le to remove the wire or component lead straight away (allow a few seconds for it to cool). If the joint will not come apart easily apply your soldering iron to melt the remaining traces of solder at the same time as pulling the joint apart, taking care to avoid burning yourself.

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Chapter 6 Safe Meter Usage

Using an electrical meter safely and efficiently is perhaps the most valua ble skill an electronics technician can master, both for the sake of their own personal safety and for proficiency at their trade. It can be daunting at first to use a meter, knowing that you are connecting it to live circuits which may harbor life-threatening levels of voltage and current. This concern is not unfounded, and it is always best to proceed cautiously when using meters. Carelessness more than any other factor is what causes experienced technicians to have electrical accidents. The most common piece of electrical test equipment is a meter called the multimeter . Multimeters are so named because they have the ability to measure a multiple of variables: voltage, current, resistance, and often many others. In the hands of someone ignorant and/or careless, however, the multimeter may become a source of danger when connected to a "live" circuit.

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You will notice that the display of this meter is of the "digital" type: showing numerical values using four digits in a manner similar to a digital clock. The rotary selector switch (now set in the Off position) has five different measurement positions it can be set in: two "V" settings, two "A" settings, and one setting in the middle with a funny-looking "horseshoe" symbol on it representing "resistance." The "horseshoe" symbol is the Greek letter "Omega" (Ω), which is the common symbol for the electrical unit of ohms. Of the two "V" settings and two "A" settings, you will notice that each pair is divided into unique markers with either a pair of horizontal lines (one solid, one dashed), or a dashed line with a squiggly curve over it. The parallel lines represent "DC" while the squiggly curve represents "AC." The "V" of c ourse stands for "voltage" while the "A" stands for "amperage" (current). The meter uses different techniques, internally, to measure DC than it uses to measure AC, and so it requires the user to select which type of voltage (V) or current (A) is to be measured. Although we haven't discussed alternating current (AC) in any technical detail, this distinction in meter settings is an important one to bear in mind. There are three different sockets on the multimeter face into which we can plug our test leads. Test leads are nothing more than specially-prepared wires used to connect the meter to the circuit under test. The wires are coated in a color-coded (either black or red) flexible insulation to prevent the user's hands from contacting the bare conductors, and the tips of the probes are sharp, stiff pieces o f wire:

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The black test lead always plugs into the black socket on the multimeter: the one marked "COM" for "common." The red test lead plugs into either the red socket marked for voltage and resistance, or the red socket marked for current, depending on which quantity you intend to measure with the multimeter. To see how this works, let's look at a couple of examples showing the meter in use. First, we'll set up the meter to measure DC voltage from a battery:

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Note that the two test leads are plugged into the appropriate sockets on the meter for voltage, and the selector switch has been set for DC "V". Now, we'll take a look at an example of using the multimeter to measure AC voltage from a household electrical power receptacle (wall socket):

The only difference in the setup of the meter is the placement of the selector switch: it is now turned to AC "V". Since we're still measuring voltage, the test leads will remain plugged in the same sockets. In both of these examples, it is imperative that you not let the probe tips come in contact with one another while they are both in contact with their respective points on the circuit. If this happens, a short-circuit will be formed, creating a spark and perhaps even a ball of flame if the voltage source is capable of supplying enough current! The following image illustrates the potential for hazard:

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This is just one of the ways that a meter can become a source of hazard if used improperly. Also, it must be remembered that digital multimeters usually do a good job of discriminating between AC and DC measurements, as they a re set for one or the other when checking for voltage or current. As we have seen earlier, both AC and DC voltages and currents can be deadly, so when using a multimeter as a safety check device you should always check for the presence of both AC and DC, even if you're not expecting to find both! Also, when checking for the presence of hazardous voltage, you should be sure to check all pairs of points in question. Using a multimeter to check for resistance is a much simpler task. The test leads will be kept plugged in the same sockets as for the voltage checks, but the selector switch will need to be turned until it points to the "horseshoe" resistance symbol. Touching the probes across the device whose resistance is to be measured, the meter should properly display the resistance in ohms:

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One very important thing to remember about measuring resistance is that it must only be done on de-energized components! When the meter is in "resistance" mode, it uses a small internal battery to generate a tiny current through the component to be measured. By sensing how difficult it is to move this current through the component, the resistance of that component can be determined and displayed. If there is any a dditional source of voltage in the meter-lead-component-lead-meter loop to either aid or oppose the resistance-measuring current produced by the meter, faulty readings will result. In a worse-case situation, the meter may even be damaged by the external voltage. The "resistance" mode of a multimeter is very useful in de termining wire continuity as well as making precise measurements of resistance. When there is a good, solid connection between the probe tips (simulated by touching them together), the meter shows almost zero Ω. If the test leads had no resistance in them, it would read exactly zero:

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If the leads are not in contact with each other, or touching opposite ends of a broken wire, the meter will indicate infinite resistance (usually by displaying dashed lines or the abbreviation "O.L." which stands for "open loop"):

Another potential hazard of using a multimeter in its current-measuring ("ammeter") mode is failure to properly put it back into a voltage-measuring configuration before measuring voltage with it. The reasons for this are specific to ammeter design and operation. When measuring circuit current by placing the meter directly in the path of current, it is best to have the meter offer little or no resistance against the flow of electrons. Otherwise, any additional resistance offered by the meter would impede the electron flow and alter the circuit's operation. Thus, the multimeter is designed to have practically zero ohms of resistance between the test probe tips when the red probe has been plugged into the red "A" (current-measuring) socket. In the voltage-measuring mode (red lead plugged into the red "V" socket), there are many mega-ohms of resistance

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between the test probe tips, because voltmeters are designed to have close to infinite resistance (so that they don't draw any appreciable current from the circuit under test). When switching a multimeter from current- to voltage-measuring mode, it's easy to spin the selector switch from the "A" to the "V" position and forget to correspondingly switch the position of the red test lead plug from "A" to "V". The result -- if the meter is then connected across a source of substantial voltage -- will be a short-circuit through the meter!

To help prevent this, most multimeters have a warning feature by which they beep if ever there's a lead plugged in the "A" socket and the selector switch is set to "V". As convenient as features like these are, though, they are still no substitute for clear thinking and caution when using a multimeter. All good-quality multimeters contain fuses inside that are engineered to "blow" in the even of excessive current through them, such as in the case illustrated in the last image. Like all overcurrent protection devices, these fuses are primarily designed to protect the equipment (in this case, the meter itself) from excessive damage, and only secondarily to protect the user from harm. A multimeter can be used to check its own current fuse by setting the selector switch to the resistance position and creating a connection between the two red sockets like this:

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A good fuse will indicate very little resistance while a blown fuse will always show "O.L." (or whatever indication that model of multimeter uses to indicate no continuity). The actual number of ohms displayed for a good fuse is of little consequence, so long as it's an arbitrarily low figure. So now that we've seen how to use a multimeter to measure voltage, resistance, and current, what more is there to know? Plenty! The value and capabilities of this versatile test instrument will become more evident as you gain skill and familiarity using it. There is no substitute for regular practice with complex instruments such as these, so feel free to experiment on safe, battery-powered circuits.

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Chapter 7 Using Digital Multimeter for Measurement and Testing of Electronic Components Digital multimeter and digital volt-ohm-miliamperemeter are terms commonly used for electronic high-impedance test meter. High-impedance meters, required for measuring computer circuits. All digital meters contain a battery to power the display so they use virtually no power from the circuit under test. This means that on their DC voltage ranges they have a very high resistance (usually called inp ut impedance) of 1M or more, usually 10M, and they are very unlikely to affect the circuit under test.

7.1. Measuring Voltage A voltmeter measures potential of electricity in a units of volts. A v oltmeter is connected to a circuit in parallel. All voltmeters have a large internal resistance so that the current flow through the meter will not effect the circuit being tested. 7.2. Measuring Resistance An ohmmeter measures the resistance in ohms of a component or circuit section when no current is flowing through the circuit. An ohmmeter contains a battery, when the leads are connected to a component, current flows through the test leads and the difference in voltage (voltage drop) between the lead is measured as resistance. Zero ohms on the scale mean no resistance between test leads, indicating that there is continuity path for the current to flow in a closed circuit. Infinity means no connection, is an open circuit. To summarize, open and zero readings are as follows: 0.0 Ω = zero resistance OL = an open circuit (no current flows) 7.3. Measuring Amperes An ammeter measures the flow of current through a complete circuit in unit of amperes. The ammeter has to be installed in the circuit (in series) so that it can measure all the current flow in that circuit, just as a water flow meter wou ld measure the amount of water flow. Caution: An ammeter must be installed in series with the circuit to measure the current flow in the circuit. If a meter set to read amperes is connected in parallel, such as across a battery, the meter or the leads may be destroyed or the fuse will blow by the current available across the battery.

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7.4. Testing Electronic Components 7.4.1. Testing diode and Transistor with a multimeter When using an analog instrument to test a diode, diode is ok if it's resistance value is very small in one, and very high in other direction. According to 11.2, positive end of the diode is connected to one probe and negative end to the other probe (11.2a), and then it is turned around (11.2b). In the first case, value should be very low, and in the other it should be very high. When the multimeter shows low value, diode's anode is conne cted to the positive probe of the meter (red probe). If the value is equal to or near equal, either low or high in both directions, diode is faulty, and should be replaced.

Digital instrument has another method to test the diodes. It has it's own switch position, as shown on 11.1b. When we connect probes to each other, multimeter should sound a buzz which signals a short circuit, and display tells 0. When we distance the probes, buzzing stops, and a symbol for open circuit is displayed (this can be either 0L or 1).

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Now we conenct probes to the diode (11.3a). Then we rotate the diode and connect it again (11.3b). If the measured diode was ok, one of the two measurements would have shown a value which represents a minimum voltage that could be conducted through the diode (between 400mV and 800mV), and the anode is the end of the diode which is connected to probe A (red one). Diode is faulty if you hear a buzz (closed circuit) or some value which represents infinity.

Transistors are tested in a similar fashion, since they act as two connected diodes. Both diodes should be tested in described way, and if both of them are functional – transistor is functional as well. According to 11.4b, positive probe is connected to base, and the negative probe is first at the collector and then emitter afterwards, in both cases resistance should be low. After that, you do the same thing, only with switched probes, negative probe is connected to the base and you test collector and emitter with a positive probe, both cases should produce a high value on the meter. When testing PNP transistors, all steps are the same, but the measurements should be opposite: on 11.4a they are high, and on 11.4c they are low.

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If you test transistors using a digital instrument, process remains similar to the one with diodes. Each diode should produce a value between 400mV and 800mV. Many modern day digital multimeters have a tool for direct transistor check. There is, as displayed on 11.5, a special plug where low and medium power transistors fit nicely. In case when there is a need to test high power transistors, thin wires (0.8mm will do fine) should be soldered to transistor's pins and then plugged into the instrument. As displayed on 11.5, transistor is plugged into specified slot according to it's type (PNP or NPN) and the switch on the instrument is brought into position with a hFE marking. In case transistor works, display shows a value which represents the current amplification coefficient. If, for example, transistor BC140 is tested, and the display shows 74, this means that the collector current is 74 times higher than the ba se current.

7.4.3. Transformers and coils Grid transofrmers are tested by measuring the resistance of the copper wire on the primary and secondary coil. Since the primary coil has more curls than the secondary one, and is wound using a thinner wire, it's resistance is higher, and it's value lays in range between several tens of ohms (in high power transofrmers) to several hundreds of ohms, even to kiloohms (in low power transformers). Secondary resistance is lower and is in range between several ohms to several tens of ohms, where the principle of inverse relations is still in place, high power means low resistance. In case an instrument shows an infinite value, it is a certain sign that the coil is either poorly connected or the curls are disconnected at some point. Coils can be tested in the same way as transformers – through their resistance. All principles remain the same as with transformers. Infinite resistance still means disconnected coil. 7.4.4. Capacitors DC capacitors should produce an infinite value on the instrument. Eexceptions are electrolithic and very high value block capacitors. When the positive end of an electrolithic capacitor is connected to a positive probe of an analog instrument, and a

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negative end to a negative probe, needle jumps to the lowest value and then gradually comes back towards infinity. This is a proof that the capacitor is ok, and the needle's movement is the charge stored in the component being discharged. (Even small capacitance components get charged while testing, but their discharge time is very short, so the needle doesn't have the time to move.) Variable capacitors are tested by connecting an ohm-meter to them, and turning the rotor. Needle should point infinity at all times, because any other value is a certain signal that the plates of the rotor and stator are connected which means that the component doesn't work. There are digital instruments that have the a bility to measure capacitance, which simplifies the process to comparing the value on the capacitor to the one on the display, any other value means that the component is faulty. With this said, it is worth mentionig that the capacitors have considerably wider tolerance than resistors, which goes even to 20%. 7.4.5. Potentiometers To test a potentiometer, or a pot, or a variable resistor, process is rather simple – you connect the component to probes of an ohm-meter and turn the shaft, and values should do what component's name says – vary. Of course, this behavior should be linear – jumps and twitches in values mean that the component is not working as supposed to. If that component was to be used in some audio amplifier, speakers would produce loud noise or no sound at all while pot is being turned. (“Noisy” pot can be repaired using a special spray, or oil or even a graphite pencil, but this is not a good solution since it is weak and short-lived, and should be practiced only if there is no replacement for that potentiometer) 7.4.6 Speakers, headphones and microphones When testing speakers, their variable coil has either 4 or 8Ohms in most cases, and the meter should show those values. When using an analog instrument on the speakers, not much of attention is being paid to the value shown on the actual instrument, because by only connecting the probes there should be a short noise heard. If there is no noise, speaker is broken. Same goes for headphones and dynamic microphones. Electret microphones don't produce the noise. And another source of trouble could be the built-in FET amplifier. 7.4.7. Other Semiconductor Devices To test diodes using this circuit, we fall back to the diode theory of operation: when anode is positive comparing to the cathode (red probe on anode, black on cathode), whole diode acts as a low value resistor, which means that speaker sound is higher than usual. On the other hand, in the opposite direction, sound is lower because in that direction diode acts as a high value resistor. Testing process is shown on 12.4.

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DC transistor acts in the same fashion as two connected diodes (11.4a). If both diodes are functional, transistor is functional as well as shown on 12.5. As you can see, probe A is connected to the base, and then probe B is connected first to the emitter, and then to the collector. In both cases, if the transistor is ok, “music” would have been heard. We then switch probe connections, A goes where B was connected to and vice versa, if there is no music now, everything is in order. So, transistor is faulty if speaker remains silent in the first two measurements, or if it “plays” in one of the second two measurements. FET testing is done in similar fashion as testing the bipolar transistors, which is shown on 12.6.

One principle that is applicable when testing the photo resistors, photo transistors and diodes is NL-NM (or, No Light – No Music). Probe A is connected to the collector of the transistor, or diode's anode or one side of the photo resistor, and the other one is connected to transistor's emitter or diode's cathode or the other resistor's side and some kind of sound should be heard from the speaker. If this continues when the component is shadowed using your palm, everything is in functional order. We displayed graphically the method of testing photo sensitive components on 12.7.

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7.4.8. Checking other components Many other components may be tested using this instrument. Base rule is: if component is intended to conduct electricity, sound will be heard. This is the case with resistors, coils, transformers, fuses, closed switches. If component doesn't conduct electricity, like capacitors, or open switches, or two copper wires on the circuit board which shouldn't be connected, then music would have not been heard. When testing different resistors, it is apparent that different resistance values give different output sound. So with some experience using this instrument on various resistors it will be possible to tell the resistance of the resistor in question from only the generated sound. This may be easier and more accurately done using regular ohmmeter on your multimeter, but your nerd level will certainly rise sky high if you are able to tell resistor's value from bare sound. Components which have coils in them, like different electro motors, headphones, speakers, transformers and such conduct electricity, so absence of sound while testing tells of some coil connection failure. With transformers with several secondary coils there is a possibility to find beginning and the end of each of them. And from the sound frequency one is possible to tell which coil is primary and which is secondary.

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Basic Electronics Book

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