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MINI PROJECT REPORT

ON

INDUSTRIAL EQUIPMENT CONTROLLED WITH TEMPERATURE AND LDR

Submitted in partial fulfillment for the award of the Degree of  

Bachelor of Technology in Electrical and Electronics Engineering

Submitted By  

G.SWETHA (08281A0251) R.JYOTHIRMAI (08281A0261)

A.SURYA KIRAN (09285A0206)

Under the Guidance of  

Sri VIGNESH 

Assoc. /Asst. professor 

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

KAMALA INSTITUTE OF TECHNOLOGY AND SCIENCE

(Affiliated to J.N.T.U, Hyderabad)

SINGAPUR, KARIMNAGAR -505468

(2011-2012)

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Department of Electrical and Electronics Engineering

CERTIFICATE 

This is to certify that   Ms.G.SWETHA (08281A0251),

MS.R.JYOTHIRMAI (08281A0261) & MR. A.SURYA KIRAN (09285A0206) 

of final year B.Tech has satisfactorily completed the module of project entitled 

―INDUSTRIAL EQUIPMENT CONTROLLED WITH TEMPERATURE AND LDR” 

under my supervision and guidance towards partial fulfillment of requirements for the award of 

the degree of Bachelor of Technology in E.E.E to JNTU, Hyd, A.P. during the year 2010-2011. 

 MiniProject guide Head of the department

Sri VIGNESH Sri YOGESH.Y.PUNDLIK 

Assoc. professor, EEE Assoc.professor,EEE 

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ACKNOWLEDGEMENT

We express our deep sense of gratitude and sincere thanks to our project guide SriVIGNESH Assoc. Professor, EEE Department for his valuable guidance, inspiration and

constant encouragement throughout the course of this work. His exemplary patience, concern

and understanding have resulted in completion of this work to our fullest satisfaction.

We take this opportunity to express our gratitude to our Head of the Department 

Sri YOGESH.Y.PUNDLIK Assoc. Professor, for his interminable support and encouragement.

We endow our sincere thanks to our Principal Prof. K.SHANKAR who has always

been our backing force.

We express our sincere gratitude to all teaching and non-teaching staff of the department

of Electrical & Electronics Engineering who extended their help in making our project a possible

one.

We would also like to express our heartfelt thanks to all my friends for their valuable

ideas and insightful criticism on our project.

Finally, we take this opportunity to convey our sincere thanks to all those who directly or

indirectly contributed for the successful completion of our project.

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  Abstract 

The task of this project works with AC 230V, 50Hz power supply. The AC

230V converted into DC and the output of 12V DC source fed to the load via R1, R2,

R3 and PT100 thermostat. The entire module performs by the logic gates of 

Thermostat and LDR. Particularly the module works whenever the instructions to

be followed by the Industries according to the power sector rules. Similarly the

work men of the industry as well as the superior’s related to the management of the

plant followed by the above stated parameters

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  CONTENTS

1.  INTRODUTION

2.  OVERVIEW OF THE MINI PROJECT

3.  BLOCK DIAGRAM OF INDUSTRIAL EQUIPMENT

CONTROLLED WITH TEMPERATURE AND LDR

4.  CIRCUIT DIAGRAM

5.  OPERATION AND PROCEDURE

5.1. FIRST HALF CIRCUIT FUNCTIONING

5.2. ECOND HALF CIRCUIT FUNCTIONING

6.  COMPONENTS USED

6.1 PANEL INDICATORS

6.2 DIFFERENT TYPES OF DIODES

6.3 RHEOSTAT, POTENTIOMETER & PRESETS

6.4 RESISTORS, CAPACITORS & INDUCTORS

6.5 INTIGRATED CIRCUITS(IC NE 555)

6.6 THERMOSTAT /THERMOCOUPLE & THERMISTORS

6.7 LIGHT DEPENDENT RESISTORS (LDR)

6.8 RELAY COIL

6.9 BIPOLAR JUNCTION TRANSISTORS (BJT)

7.  CONCLUSION

i. 

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1. INTRODUCTION 

The main circuit breaker of the industry can be switched according to the set 

points of parameters of LDR and thermostat. Under the circumstances of the LDR

and Thermostat whenever it operates at the set point mode, soon the main circuit 

breaker will be getting off then the entire plant man power will go to their homes.

Accordingly every day the cycle will be repeated and remains off. Thus this

condition the energy will be saved.

1 

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2. OVER VIEW OF THE PROJECT

2 

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3. BLOCK DIAGRAM

3

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4. CIRCUIT DIAGRAM

4

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5. OPERATION & PROECEDURE

The AC 230V received from the terminal connector and given to the R1 via

Thermostat, the R1 output goes to step down Transformer and it is connected as DC

through the Bridge Rectifier and the Output connected to the Load via R2. And the same

supply fed to the R3 relay via Key Actuators.

5.1 FIRST HALF CIRCUIT FUNCTIONING: Here is the simple fire alarm circuit based timer ID NE555. The works

is simple, the lamp give light to the LDR (Light Depending Resistor) as light sensor. When the

light from the lamp covered with smoke then the LDR will change its resistance value and then

activated the alarm.

EXPLANATION:

Fire alarm circuit using LDR (Light Depending Resistor) as light sensor. It warns the user against

fire accidents. It relies on the smoke that is produced in the event of a fire. When this smoke

passes between a LED and an LDR, the amount of light falling on the LDR decreases. This causes

the resistance of LDR to increase and the voltage at the base of the transistor is pulled high due

to which the supply to NE555 then activated the alarm.

The thermistor offers a low resistance at high temperature and high resistance at low

temperature. This phenomenon is employed here for sensing the fire.

The IC1 (NE555) is configured as a free running oscillator at audio frequency. The transistors T1

and T2 drive IC1. The output (pin 3) of IC1 is couples to base of transistor T3 (SL100), which

drives the speaker to generate alarm sound. The frequency of NE555 depends on the values of 

resistances R5 and R6 and capacitance C2.When thermistor becomes hot, it gives a low-

resistance path for the positive voltage to the base of transistor T1 through diode D1 and

resistance R2. 

5

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Capacitor C1 charges up to the positive supply voltage and increases the the time for which thealarm is ON. The larger the value of C1, the larger the positive bias applied to the base of 

transistor T1 (BC548). As the collector of T1 is coupled to the base of transistor T2, the

transistor T2 provides a positive voltage to pin 4 (reset) of IC1 (NE555). Resistor R4 is selected

s0 that NE555 keeps inactive in the absence of the positive voltage. Diode D1 stops discharging

of capacitor C1 when the thermistor is in connection with the positive supply voltage cools out

and provides a high resistance path. It also inhibits the forward biasing of transistor T1.

5.2 SECOND HALF CIRCUIT FUNCTIONING:

Photo electric street light circuit:- This is basically a Schmitt Trigger circuit which receives

input from a cadmium sulfide photo cell and controls a relay that can be used to switch off and

on a street lamp at dawn and dusk. I have built the circuit with a 120 ohm/12 volt relay and

monitored performance using a lamp dimmer, but did not connect the relay to an outside light. 

6

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The photo cell should be shielded from the lamp to prevent feedback and is

usually mounted above the light on top of a reflector and pointed upward at the sky so the

lamp light does not strike the photo cell and switch off the lamp.

The photo cell is wired in series with a potentiometer so the voltage at the junction (and base

of transistor) can be adjusted to about half the supply, at the desired ambient light level. Thetwo PNP transistors are connected with a common emitter resistor for positive feedback so as

one transistor turns on, the other will turn off, and vice versa. Under dark conditions, the photo

cell resistance will be higher than the potentiometer producing a voltage at Q1 that is higher

than the base voltage at Q2 which causes Q2 to conduct and activate the relay.

The switching points are about 8 volts and 4 volts using the resistor values shown but could be

brought closer together by using a lower value for the 7.5K resistor. 3.3K would move the levels

to about 3.5 and 5.5 for a range of 2 volts instead of 4 so the relay turns on and off closer to the

same ambient light level. The potentiometer would need to be readjusted so that the voltage is

around 4.5 at the desired ambient condition. 

6. COMPONENTS:

6.1 PANEL INDICATORS:

(a)LED Indicator 

(b)Neon bulb Indicator 

(a)LED INDICATOR 

Abbreviation of light emitting diode is

LED. This is a semiconductor optical

illuminating device. LED operates at very low

voltage level. Hence it is used very much as

indicator. Although operating voltage level of 

LED is very less, but LED can be indication in

230V to 250V supply by reducing through

high value resistance 68K to 82K in series of LED. If LED is used at serially 6V, 12V or 2K2

resistance is used. At least 10M for illumination of LED.

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7

LED is available in red, green and yellow colors. Care is taken for polarity while

using in DC supply. If reverse DC supply is given at toppings of LED then LED not given

illumination LED has long leg anode point and short leg point.

(a) NEON BULB

It is ordinary indicator equipment. If is made by combining two electrodes in

glass cover filled with neon gas. One high value resistance from 470K to 1 ME is

connected in its series for operating at 230V supply. It is not essential to take care for

polarity of its points while using neon bulb. But this indicator not gives indication at low

voltage because neon gas conducts at potential difference of 90V and given

illumination. Neon bulbs are made set in plastic cover for using an indicator.

Transparent plastic is used for front of this cover, which is red, green or yellow color.

These are available in different designs.

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6.2 DIFFERENT TYPES OF DIODES:

8

DIODE:

In electronics, a diode is a two-terminal electronic component that conducts electric current

in only one direction. The term usually refers to a semiconductor diode, the most common type

today. This is a crystalline piece of semiconductor material connected to two electrical terminals.A vacuum tube diode (now little used except in some high-power technologies) is a vacuum tube

with two electrodes: a plate and a cathode.

The most common function of a diode is to allow an electric current to pass in one direction

(called the diode's forward direction) while blocking current in the opposite direction (the

reverse direction). Thus, the diode can be thought of as an electronic version of a check valve.This unidirectional behavior is called rectification, and is used to convert alternating current to

direct current, and to extract modulation from radio signals in radio receivers.

However, diodes can have more complicated behavior than this simple on-off action. This is due

to their complex non-linear electrical characteristics, which can be tailored by varying the

construction of their P-N junction. These are exploited in special purpose diodes that performmany different functions. For example, specialized diodes are used to regulate voltage (Zener

diodes), to electronically tune radio and TV receivers (varactor diodes), to generate radio

frequency oscillations (tunnel diodes), and to produce light (light emitting diodes). Tunnel diodesexhibit negative resistance, which makes them useful in some types of circuits.

Diodes were the first semiconductor electronic devices. The discovery of crystals' rectifying

abilities was made by German physicist Ferdinand Braun in 1874. The first semiconductordiodes, called cat's whisker diodes, developed around 1906, were made of mineral crystals such

as galena. Today most diodes are made of silicon, but other semiconductors such as germanium

are sometimes used.

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Thermionic and gaseous state diodes

Figure 4: The symbol for an indirect heated vacuum tube diode. From top to bottom, the components

are the anode, the cathode, and the heater filament.

9

Thermionic diodes are thermionic-valve devices (also known as vacuum tubes, tubes, or valves),

which are arrangements of electrodes surrounded by a vacuum within a glass envelope. Earlyexamples were fairly similar in appearance to

incandescent light bulbs.

In thermionic valve diodes, a current through the heater

filament indirectly heats the cathode, another internal

electrode treated with a mixture of barium and

strontium oxides, which are oxides of alkaline earth metals; these substances are chosen because

they have a small work function. (Some valves use direct heating, in which a tungsten filamentacts as both heater and cathode.) The heat causes thermionic emission of electrons into the

vacuum. In forward operation, a surrounding metal electrode called the anode is positivelycharged so that it electro statically attracts the emitted electrons. However, electrons are not

easily released from the unheated anode surface when the voltage polarity is reversed. Hence,

any reverse flow is negligible.

For much of the 20th century, thermionic valve diodes were used in analog signal applications,

and as rectifiers in many power supplies. Today, valve diodes are only used in niche applicationssuch as rectifiers in electric guitar and high-end audio amplifiers as well as specialized high-

voltage equipment.

Semiconductor diodes:

A modern semiconductor diode is made of a crystal of semiconductor like silicon that has impurities

added to it to create a region on one side that contains negative charge carriers (electrons), called n-

type semiconductor, and a region on the other side that contains positive charge carriers (holes), called

p-type semiconductor. The diode's terminals are attached to each of these regions. The boundary within

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the crystal between these two regions, called a PN junction, is where the action of the diode takes place.

The crystal conducts conventional current in a direction from the p-type side (called the anode) to the n-

type side (called the cathode), but not in the opposite direction. Another type of semiconductor diode,

the Schottky diode, is formed from the contact between a metal and a semiconductor rather than by a

p-n junction.

Current – voltage characteristic: A semiconductor diode‘s behavior in a circuit is given by itscurrent – voltage characteristic, or I – V graph (see graph below). The shape of the curve isdetermined by the transport of charge carriers through the so-called depletion layer or depletion

region that exists at the p-n junction between differing semiconductors. When a p-n junction is

first created, conduction band (mobile) electrons from the N-doped region diffuse into the P-

doped region where there is a large population of holes (vacant places for electrons) with which

the electrons ―recombine‖. When a mobile electron recombines with a hole, both hole andelectron vanish, leaving behind an immobile positively charged donor (dopant) on the N-side and

negatively charged acceptor (dopant) on the P-side. The region around the p-n junction becomes

depleted of charge carriers and thus behaves as an insulator.

10

However, the width of the depletion region (called the depletion width) cannot grow without

limit. For each electron-hole pair that recombines, a positively charged dopant ion is left behindin the N-doped region, and a negatively charged dopant ion is left behind in the P-doped region.

As recombination proceeds more ions are created, an increasing electric field develops through

the depletion zone which acts to slow and then finally stop recombination. At this point, there is

a ―built-in‖ potential across the depletion zone. 

If an external voltage is placed across the diode with the same polarity as the built-in potential,

the depletion zone continues to act as an insulator, preventing any significant electric currentflow (unless electron/hole pairs are actively being created in the junction by, for instance, light.

see photodiode). This is the reverse bias phenomenon. However, if the polarity of the external

voltage opposes the built-in potential, recombination can once again proceed, resulting insubstantial electric current through the p-n junction (i.e. substantial numbers of electrons and

holes recombine at the junction). For silicon diodes, the built-in potential is approximately 0.7 V

(0.3 V for Germanium and 0.2 V for Schottky). Thus, if an external current is passed through thediode, about 0.7 V will be developed across the diode such that the P-doped region is positive

with respect to the N-doped region and the diode is said to be ―turned on‖ as it has a forward 

bias.

A diode‘s ' I  – 

V characteristic' can be approximated by four regions of operation.

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At very large reverse bias , beyond the peak inverse voltage or PIV, a process called reverse breakdown

occurs which causes a large increase in current (i.e. a large number of electrons and holes are created

at, and move away from the pn junction) that usually damages the device permanently. The avalanche

diode is deliberately designed for use in the avalanche region. In the zener diode, the concept of PIV is

not applicable. A zener diode contains a heavily doped p-n junction allowing electrons to tunnel from

the valence band of the p-type material to the conduction band of the n-type material, such that the

reverse voltage is “clamped” to a known value (called the zener voltage), and avalanche does not occur.

Both devices, however, do have a limit to the maximum current and power in the clamped reverse

voltage region. Also, following the end of forward conduction in any diode, there is reverse current for a

short time. The device does not attain its full blocking capability until the reverse current ceases.

11

The second region, at reverse biases more positive than the PIV, has only a very small reversesaturation current. In the reverse bias region for a normal P-N rectifier diode, the current through

the device is very low (in the µA range). However, this is temperature dependent, and atsufficiently high temperatures, a substantial amount of reverse current can be observed (mA or

more).

The third region is forward but small bias, where only a small forward current is conducted.

As the potential difference is increased above an arbitrarily defined ―cut-in voltage‖ or ―on-

voltage‖ or ―diodeforward voltage drop

(Vd)‖, the diodecurrent becomes

appreciable (the levelof current considered

―appreciable‖ and thevalue of cut-in voltage

depends on the

application), and thediode presents a very

low resistance. The

current – voltage curveis exponential. In a

normal silicon diode at

rated currents, the arbitrary ―cut-in‖ voltage is defined as 0.6 to 0.7 volts. The value is different

for other diode types — Schottky diodes can be rated as low as 0.2 V, Germanium diodes 0.25-0.3 V, and red or blue light-emitting diodes (LEDs) can have values of 1.4 V and 4.0 V

respectively.

At higher currents the forward voltage drop of the diode increases. A drop of 1 V to 1.5 V is

typical at full rated current for power diodes.

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Shockley diode equation

The Shockley ideal diode equation or the diode law (named after transistor co-inventor William

Bradford Shockley, not to be confused with tetrode inventor Walter H. Schottky) gives the I – V

characteristic of an ideal diode in either forward or reverse bias (or no bias). The equation is:

Where  I is the diode current,

 I S is the reverse bias saturation current (or scale current),

V D is the voltage across the diode,

V T is the thermal voltage, and

n is the ideality factor , also known as the quality factor or sometimes emission coefficient . The

ideality factor n varies from 1 to 2 depending on the fabrication process and semiconductor

material and in many cases is assumed to be approximately equal to 1 (thus the notation n is

omitted).

The thermal voltage V T is approximately 25.85 mV at 300 K, a temperature close to “room

temperature” commonly used in device simulation software. At any temperature it is a known

constant defined by:

12

where k is the Boltzmann constant, T is the absolute temperature of the p-n junction, and q is themagnitude of charge on an electron (the elementary charge).

The Shockley ideal diode equation or the diode law is derived with the assumption that the only

processes giving rise to the current in the diode are drift (due to electrical field), diffusion, andthermal recombination-generation. It also assumes that the recombination-generation (R-G)

current in the depletion region is insignificant. This means that the Shockley equation doesn‘taccount for the processes involved in reverse breakdown and photon-assisted R-G. Additionally,

it doesn‘t describe the ―leveling off‖ of the I– V curve at high forward bias due to internalresistance.

Under reverse bias voltages (see Figure 5) the exponential in the diode equation is negligible,

and the current is a constant (negative) reverse current value of − I S. The reverse breakdown

region is not modeled by the Shockley diode equation.

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For even rather small forward bias voltages (see Figure 5) the exponential is very large because

the thermal voltage is very small, so the subtracted ‗1‘ in the diode equation is negligible and theforward diode current is often approximated as

The use of the diode equation in circuit problems is illustrated in the article on diode modeling.

Small-signal behavior

For circuit design, a small-signal model of the diode behavior often proves useful. A specific

example of diode modeling is discussed in the article on small-signal circuits.

Reverse-recovery effect

Following the end of forward conduction in a PN type diode, a reverse current flows for a short

time. The device does not attain its full blocking capability until the reverse current ceases.Theeffect can be significant when switching large currents very quickly (di/dt on the order of 100

A/us or more). A certain amount of "reverse recovery time" (t r) (on the order of tens of 

nanoseconds) may be required to remove the "reverse recovery charge" Q r (on the order of tensof nanoCoulombs) from the diode. During this recovery time, the diode can actually conduct in

the reverse direction! That is to say, current will effectively flow from the cathode to the anode!

In certain real-world cases it can be important to consider the losses incurred by this non-idealdiode effect. However, when the slew rate of the current is not so severe (di/dt on the order of 10

A/us or less), the effect can be safely ignored.For most applications, the effect is also negligible

for Schottky diodes.

13

Types of semiconductor diode

Figure 8: Several types of diodes. The scale is centimeters.

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There are several types of junction diodes, which either emphasize a different physical aspect of a diode often by geometric scaling, doping level, choosing the right electrodes, are just anapplication of a diode in a special circuit, or are really different devices like the Gunn and laser

diode and the MOSFET:

Normal (p-n) diodes, which operate as described above, are usually made of doped silicon or,more rarely, germanium. Before the development of modern silicon power rectifier diodes,

cuprous oxide and later selenium was used; its low efficiency gave it a much higher forwardvoltage drop (typically 1.4 – 1.7 V per ―cell‖, with multiple cells stacked to increase the peak inverse voltage rating in high voltage rectifiers), and required a large heat sink (often an

extension of the diode‘s metal substrate), much larger than a silicon diode of the same currentratings would require. The vast majority of all diodes are the p-n diodes found in CMOS

integrated circuits, which include two diodes per pin and many other internal diodes.

Avalanche diodes

Diodes that conduct in the reverse direction when the reverse bias voltage exceedsthe breakdown voltage. These are electrically very similar to Zener diodes, and are often

mistakenly called Zener diodes, but break down by a different mechanism, the avalanche effect.

This occurs when the reverse electric field across the p-n junction causes a wave of ionization,

reminiscent of an avalanche, leading to a large current. Avalanche diodes are designed to break

down at a well-defined reverse voltage without being destroyed. The difference between the

avalanche diode (which has a reverse breakdown above about 6.2 V) and the Zener is that the

channel length of the former exceeds the “mean free path” of the electrons, so there

arecollisions between them on the way out. The only practical difference is that the two types

have temperature coefficients of opposite polarities.

14

Cat‘s whisker or crystal diodes 

These are a type of point-contact diode. The cat’s whisker diode consists of a thin or

sharpened metal wire pressed against a semiconducting crystal, typically galena or a

piece of coal. The wire forms the anode and the crystal forms the cathode. Cat’s whisker

diodes were also called crystal diodes and found application in crystal radio receivers.

Cat’s whisker diodes are generally obsolete, but may be available from a few

manufacturers.

Constant current diodes

These are actually a JFET with the gate shorted to the source, and function like a two-

terminal current-limiter analog to the Zener diode, which is limiting voltage. They allow

a current through them to rise to a certain value, and then level off at a specific value.

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Also called CLDs, constant-current diodes, diode-connected transistors, or current-

regulating diodes.

Esaki or tunnel diodes

These have a region of operation showing negative resistance caused by quantum

tunneling, thus allowing amplification of signals and very simple bistable circuits. These

diodes are also the type most resistant to nuclear radiation.

Gunn diodes

These are similar to tunnel diodes in that they are made of materials such as GaAs or InP

that exhibit a region of negative differential resistance. With appropriate biasing, dipole

domains form and travel across the diode, allowing high frequency microwave

oscillators to be built.

Light-emitting diodes (LEDs)

In a diode formed from a direct band-gap semiconductor, such as gallium arsenide,

carriers that cross the junction emit photons when they recombine with the majority

carrier on the other side. Depending on the material, wavelengths (or colors) from the

infrared to the near ultraviolet may be produced. The forward potential of these diodes

depends on the wavelength of the emitted photons: 1.2 V corresponds to red, 2.4 V to

violet. The first LEDs were red and yellow, and higher-frequency diodes have been

developed over time. All LEDs produce incoherent, narrow-spectrum light; “white” LEDsare actually combinations of three LEDs of a different color,

15

or a blue LED with a yellow scintillator coating. LEDs can also be used as low-efficiency

photodiodes in signal applications. An LED may be paired with a photodiode or

phototransistor in the same package, to form an opto-isolator.

Laser diodes

When an LED-like structure is contained in a resonant cavity formed by polishing theparallel end faces, a laser can be formed. Laser diodes are commonly used in optical

storage devices and for high speed optical communication.

Thermal diodes

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This term is used both for conventional PN diodes used to monitor temperature due to

their varying forward voltage with temperature, and for Peltier heat pumps for

thermoelectric heating and cooling.. Peltier heat pumps may be made from

semiconductor, though they do not have any rectifying junctions, they use the differing

behaviour of charge carriers in N and P type semiconductor to move heat.

Photodiodes

All semiconductors are subject to optical charge carrier generation. This is typically an

undesired effect, so most semiconductors are packaged in light blocking material.

Photodiodes are intended to sense light(photodetector), so they are packaged in

materials that allow light to pass, and are usually PIN (the kind of diode most sensitive

to light). A photodiode can be used in solar cells, in photometry, or in optical

communications. Multiple photodiodes may be packaged in a single device, either as a

linear array or as a two-dimensional array. These arrays should not be confused withcharge-coupled devices.

Point-contact diodes

These work the same as the junction semiconductor diodes described above, but their

construction is simpler. A block of n-type semiconductor is built, and a conducting

sharp-point contact made with some group-3 metal is placed in contact with the

semiconductor. Some metal migrates into the semiconductor to make a small region of 

p-type semiconductor near the contact. The long-popular 1N34 germanium version is

still used in radio receivers as a detector and occasionally in specialized analog

electronics.

16

PIN diodes

A PIN diode has a central un-doped, or intrinsic, layer, forming a p-type/intrinsic/n-type

structure.[18] They are used as radio frequency switches and attenuators. They are also

used as large volume ionizing radiation detectors and as photodetectors. PIN diodes are

also used in power electronics, as their central layer can withstand high voltages.

Furthermore, the PIN structure can be found in many power semiconductor devices, 

such as IGBTs, power MOSFETs, and thyristors. 

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Schottky diodes

Schottky diodes are constructed from a metal to semiconductor contact. They have a

lower forward voltage drop than p-n junction diodes. Their forward voltage drop at

forward currents of about 1 mA is in the range 0.15 V to 0.45 V, which makes them

useful in voltage clamping applications and prevention of transistor saturation. They can

also be used as low loss rectifiers although their reverse leakage current is generally

higher than that of other diodes. Schottky diodes are majority carrier devices and so do

not suffer from minority carrier storage problems that slow down many other diodes — 

so they have a faster “reverse recovery” than p-n junction diodes. They also tend to

have much lower junction capacitance than p-n diodes which provides for high

switching speeds and their use in high-speed circuitry and RF devices such as switched-

mode power supply, mixers and detectors. 

Super barrier diodes

Super barrier diodes are rectifier diodes that incorporate the low forward voltage drop

of the Schottky diode with the surge-handling capability and low reverse leakage current

of a normal p-n junction diode.

Gold-doped diodes

As a dopant, gold (or platinum) acts as recombination centers, which help a fast

recombination of minority carriers. This allows the diode to operate at signal

frequencies, at the expense of a higher forward voltage drop. Gold doped diodes are

faster than other p-n diodes (but not as fast as Schottky diodes). They also have less

reverse-current leakage than Schottky diodes (but not as good as other p-n

diodes).[19][20]

 A typical example is the 1N914.

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Snap-off or Step recovery diodes

The term step recovery relates to the form of the reverse recovery characteristic of 

these devices. After a forward current has been passing in an SRD and the current is

interrupted or reversed, the reverse conduction will cease very abruptly (as in a step

waveform). SRDs can therefore provide very fast voltage transitions by the very sudden

disappearance of the charge carriers.

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Transient voltage suppression diode (TVS)

These are avalanche diodes designed specifically to protect other semiconductor

devices from high-voltage transients.[21]

 Their p-n junctions have a much larger cross-

sectional area than those of a normal diode, allowing them to conduct large currents to

ground without sustaining damage.

Varicap or varactor diodes

These are used as voltage-controlled capacitors. These are important in PLL (phase-

locked loop) and FLL (frequency-locked loop) circuits, allowing tuning circuits, such as

those in television receivers, to lock quickly, replacing older designs that took a long

time to warm up and lock. A PLL is faster than an FLL, but prone to integer harmonic

locking (if one attempts to lock to a broadband signal). They also enabled tunable

oscillators in early discrete tuning of radios, where a cheap and stable, but fixed-frequency, crystal oscillator provided the reference frequency for a voltage-controlled

oscillator. 

Zener diodes

Diodes that can be made to conduct backwards. This effect, called Zener breakdown,

occurs at a precisely defined voltage, allowing the diode to be used as a precision

voltage reference. In practical voltage reference circuits Zener and switching diodes are

connected in series and opposite directions to balance the temperature coefficient to

near zero. Some devices labeled as high-voltage Zener diodes are actually avalanche

diodes (see above). Two (equivalent) Zeners in series and in reverse order, in the same

package, constitute a transient absorber (or Transorb, a registered trademark).

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The Zener diode is named for Dr. Clarence Melvin Zener of Carnegie Mellon University,

inventor of the device.

Other uses for semiconductor diodes include sensing temperature, and computing analoglogarithms (see Operational amplifier applications#Logarithmic).

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DiodeZener

diode

Schottky

diode

Tunnel

diode

Light-emitting

diodePhotodiode Varicap Silicon controlled rectifier

PRESETS / VARIABLE RESISTORS

Variable resistors consist of a resistance track with connections at both ends and a

wiper which moves along the track as you turn the spindle. The track may be made from

carbon, cermet (ceramic and metal mixture) or a coil of wire (for low resistances). The track is

usually rotary but straight track versions, usually called sliders, are also available.

Variable resistors may be used as a rheostat with two connections (the wiper and just one end

of the track) or as a potentiometer with all three connections in use. Miniature versions called

presets are made for setting up circuits which will not require further adjustment.

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Variable resistors are often called potentiometers in books and catalogues. They are specified

by their maximum resistance, linear or logarithmic track, and their physical size. The standard

spindle diameter is 6mm.

The resistance and type of track are marked on the body:

4K7 LIN means 4.7 k linear track.

1M LOG means 1 M logarithmic track.

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Some variable resistors are designed to be mounted directly on the circuit board, but most are

for mounting through a hole drilled in the case containing the circuit with stranded wire

connecting their terminals to the circuit board.

Linear (LIN) and Logarithmic (LOG) tracks

Linear (LIN) track means that the resistance changes at a constant

rate as you move the wiper. This is the standard arrangement and

you should assume this type is required if a project does not specify the type of track. Presets

always have linear tracks.

Logarithmic (LOG) track means that the resistance changes slowly at one end of the track and

rapidly at the other end, so halfway along the track is not half the total resistance! This

arrangement is used for volume (loudness) controls because the human ear has a logarithmicresponse to loudness so fine control (slow change) is required at low volumes and coarser

control (rapid change) at high volumes. It is important to connect the ends of the track the

correct way round, if you find that turning the spindle increases the volume rapidly followed by

little further change you should swap the connections to the ends of the track.

6.3 RHEOSTATS, POTENTIOMETER & PRESETS:

Rheostat

This is the simplest way of using a variable resistor. Two terminals 

are used: one connected to an end of the track, the other to the

moveable wiper. Turning the spindle changes the resistance

between the two terminals from zero up to the maximum

resistance. Rheostats are often used to vary current, for example

to control the brightness of a lamp or the rate at which a capacitor charges.

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If the rheostat is mounted on a printed circuit board you may find that all three terminals are

connected! However, one of them will be linked to the wiper terminal. This improves the

mechanical strength of the mounting but it serves no function electrically.

Potentiometer 

Rheostat Symbol

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Variable resistors used as potentiometers have all three terminals 

connected.

This arrangement is normally used to vary voltage, for example to set

the switching point of a circuit with a sensor, or control the volume

(loudness) in an amplifier circuit. If the terminals at the ends of the

track are connected across the power supply then the wiper terminal will provide a voltage

which can be varied from zero up to the maximum of the supply.

Presets 

These are miniature versions of the standard variable resistor. They are

designed to be mounted directly onto the circuit board and adjusted only when

the circuit is built. For example to set the frequency of an alarm tone or the

sensitivity of a light-sensitive circuit. A small screwdriver or similar tool is

required to adjust presets. Presets are much cheaper than standard variable resistors so they

are sometimes used in projects where a standard variable resistor would normally be used.

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Multiturn presets: are used where very precise adjustments must be made. The screw

must be turned many times (10+) to move the slider from one end of the track to the other,

Potentiometer Symbol

Preset Symbol

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giving very fine control .

Preset

(open style)

Presets

(closed style)Multiturn preset

6.4 Resistors, capacitors and inductors:

It is sometimes not obvious whether a color coded component is a resistor, capacitor, or inductor,and this may be deduced by knowledge of its circuit function, physical shape or by measurement.

Resistor values are always coded in ohms (symbol Ω), capacitors in picofarads (pF), andinductors in micro henries (µH).

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One decade of the preferred E12 values (there are twelve preferred values per decade of 

values) shown with their electronic color codes on resistors. 

A 100 kΩ, 5% through-hole resistor.

A 0Ω resistor, marked with a single black band. 

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To distinguish left from right there is a gap between the C and D bands.

  band A is first significant figure of component value (left side)

  band B is the second significant figure

  band C is the decimal multiplier

  band D if present, indicates tolerance of value in percent (no color means 20%)

For example, a resistor with bands of   yellow, violet, red, and gold  will have first digit 4 (yellowin table below), second digit 7 (violet), followed by 2 (red) zeros: 4,700 ohms. Gold signifies thatthe tolerance is ±5%, so the real resistance could lie anywhere between 4,465 and 4,935 ohms.

Resistors manufactured for military use may also include a fifth band which indicates component

failure rate (reliability); refer to MIL-HDBK-199 for further details.

Tight tolerance resistors may have three bands for significant figures rather than two, and/or anadditional band indicating temperature coefficient, in units of ppm /K. 

All coded components will have at least two value bands and a multiplier; other bands are

optional (italicised below).

A resistor which (read left to right) displays the colors yellow, violet, yellow, brown. Thefirst two bands represent the digits '4, 7. The third band, another yellow , gives the multiplier 10

4.

The value is then 47 x 104 Ω , or 470 kΩ. The brown band is a s then a tolerance of ±1%. 

Resistors use Preferred numbers for their specific values, which are determined by their

tolerance. These values repeat for every decade of magnitude; 6.8, 68, 680, and so forth.

Zero ohm resistors are made as lengths of wire wrapped in a resistor-shaped body which can be

substituted for another resistor value in automatic insertion equipment. They are marked with a

single black band.The 'body-end-dot' or 'body-tip-spot' system was used for radial-lead composition resistors

sometimes found in vacuum-tube equipment; the first band was given by the body color, the

second band by the color of the end of the resistor, and the multiplier by a dot or band around the

middle of the resistor. The other end of the resistor was colored gold or silver to give thetolerance, otherwise it was 20%.

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Extra bands on ceramic capacitors will identify the voltage rating class and temperature

coefficient characteristics.[4]

 A broad black band was applied to some tubular paper capacitors toindicate the end that had the outer electrode; this allowed this end to be connected to chassis

ground to provide some shielding against hum and noise pickup.

Polyester film and "gum drop" tantalum electrolytic capacitors are also color coded to give thevalue, working voltage and tolerance.

Diode part number

The part number for diodes was sometimes also encoded as colored rings around the diode, using

the same numerals as for other parts. The JEDEC "1N" prefix was assumed, and the balance of the part number was given by three or four rings.

Postage stamp capacitors and war standard coding

Capacitors of the rectangular 'postage stamp" form made for military use during World War IIused American War Standard (AWS) or Joint Army Navy (JAN) coding in six dots stamped on

the capacitor. An arrow on the top row of dots pointed to the right, indicating the reading order.

From left to right the top dots were: black, indicating JAN mica or silver indicating AWS paper.

first and second significant figures. The bottom three dots indicated temperature characteristic,tolerance, and decimal multiplier. The characteristic was black for +/- 1000 ppm/ degree c,

brown for 500, red for 200, orange for 100, yellow for -20 to +1 — ppm/ degree c, and green for 0

to +70 ppm/degree C. A similar six-dot code by EIA had the top row as first, second and thirdsignificant digits and the bottom row as voltage rating (in hundreds of volts - no color indicated

500 volts), tolerance, and multiplier. A three-dot EIA code was used for 500 volt 20% tolerance

capacitors, and the dots signified first and second significant digits and the multiplier. Such

capacitors were common in vacuum tube equipment and in surplus for a generation after the warbut are unavailable now.

Mnemonics

Further information: List of electronic color code mnemonics

A useful mnemonic matches the first letter of the color code, by order of increasing magnitude. There are many variations:

The tolerance codes, gold, silver, and none, are not usually included in the mnemonics; one

extension that includes them is:

The colors are sorted in the order of the visible light spectrum: red (2), orange (3), yellow (4),

green (5), blue (6), violet (7). Black (0) has no energy, brown (1) has a little more, white (9) has

everything and grey (8) is like white, but less intense.

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Examples

Color coded resistors

From top to bottom:

  Green-Blue-Black-Black-Brown

o  560 ohms ± 1%

  Red-Red-Orange-Gold

o  22,000 ohms ± 5%

  Yellow-Violet-Brown-Gold

o  470 ohms ± 5%

  Blue-Gray-Black-Silvero  68 ohms ± 10%

The physical size of a resistor is indicative of the power it can dissipate, not of its resistance.

Printed numbers:

0Ω and 27Ω (27×100) surface-mount resistors.

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Color-coding of this form is becoming rarer. In newer equipment, most passive components come in

surface mount packages. Many of these packages are unlabeled and, those that are, normally use

alphanumeric codes, not colors. 

In one popular marking method, the manufacturer prints 3 digits on components: 2 value digitsfollowed by the power of ten multiplier. Thus the value of a resistor marked 472 is 4,700 Ω, acapacitor marked 104 is 100 nF (10x10

4pF), and an inductor marked 475 is 4.7 H

(4,700,000 µH). This can be confusing; a resistor marked 270 might seem to be a 270 Ω unit,when the value is actually 27 Ω (27×10

0). A similar method is used to code precision surface

mount resistors by using a 4-digit code which has 3 significant figures and a power of ten

multiplier. Using the same example as above, 4701 would represent a 470x101=4700 Ω, 1%

resistor. Another way is to use the "kilo-" or "mega-" prefixes in place of the decimal point:

1K2 = 1.2 kΩ = 1,200 Ω 

M47 = 0.47 MΩ = 470,000 Ω 

68R = 68 Ω 

For some 1% resistors, a three-digit alphanumeric code is used, which is not obviously related tothe value but can be derived from a table of 1% values. For instance, a resistor marked 68C is

499(68) × 100(C ) = 49,900 Ω. In this case the value 499 is the 68th entry of a table of 1% values

between 100 and 999.[citation needed ]

 

Transformer wiring color codes

Power transformers used in North American vacuum-tube equipment often were color-coded to

identify the leads. Black was the primary connection, red secondary for the B+ (plate voltage),red with a yellow tracer was the center tap for the B+ full-wave rectfier winding, green or brown

was the heater voltage for all tubes, yellow was the filament voltage for the rectifier tube (often a

different voltage than other tube heaters). Two wires of each color were provided for eachcircuit, and phasing was not identified by the color code.

Audio transformers for vacuum tube equipment were coded blue for the finishing lead of theprimary, red for the B+ lead of the primary, brown for a primary center tap, green for the

finishing lead of the secondary, black for grid lead of the secondary, and yellow for a tapped

secondary. Each lead had a different color since relative polarity or phase was more importantfor these transformers. Intermediate-frequency tuned transformers were coded blue and red for

the primary and green and black for the secondary.

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Other wiring codes

Wires may be color-coded to identify their function, voltage class, polarity, phase or to identifythe circuit in which they are used. The insulation of the wire may be solidly colored, or wheremore combinations are needed, one or two tracer stripes may be added. Some wiring color codes

are set by national regulations, but often a color code is specific to a manufacturer or industry.

Building wiring under the US National Electrical Code and the Canadian Electrical Code is

identified by colors to show energized and neutral conductors, grounding conductors and to

identify phases. Other color codes are used in the UK and other areas to identify building wiring

or flexible cable wiring.

Thermocouple wires and extension cables are identified by color code for the type of 

thermocouple; interchanging thermocouples with unsuitable extension wires destroys the

accuracy of the measurement.

Automotive wiring is color-coded but standards vary by manufacturer; differing SAE and DIN

standards exist.

Modern personal computer peripheral cables and connectors are color coded to simplify

connection of speakers, microphones, mice, keyboards and other peripherals, usually according

to the PC99 scheme. 

A common convention for wiring systems in industrial buildings is; black jacket - AC less than

1000 volts, blue jacket - DC or communications, orange jacket - medium voltage 2300 or 4160V, red jacket 13,800 volts or higher.

Local area network cables may also have jacket colors identifying, for example, process controlnetwork vs. office automation networks, or to identify redundant network connections, but these

codes vary by organization and facility

6.5 IC’s (INEGRATED CIRCUITS):

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Introduction about integrated circuits:

Integrated circuits were made possible by experimental discoveries which showed thatsemiconductor devices could perform the functions of vacuum tubes and by mid-20th-century

technology advancements in semiconductor device fabrication. The integration of large numbers

of tiny transistors into a small chip was an enormous improvement over the manual assembly of circuits using electronic components. The integrated circuit's mass production capability,

reliability, and building-block approach to circuit design ensured the rapid adoption of 

standardized ICs in place of designs using discrete transistors.

There are two main advantages of ICs over discrete circuits: cost and performance. Cost is low

because the chips, with all their components, are printed as a unit by photolithography ratherthan being constructed one transistor at a time. Furthermore, much less material is used to

construct a packaged IC die than a discrete circuit. Performance is high since the components

switch quickly and consume little power (compared to their discrete counterparts) because the

components are small and positioned close together. As of 2006, chip areas range from a fewsquare millimeters to around 350 mm2, with up to 1 million transistors per mm2

IC NE555:

The important features of the 555 timer are :

  It operates from a wide range of  power supplies ranging from + 5 Volts to + 18 Volts

supply voltage.

  Sinking or sourcing 200 mA of load current.

  The external components should be selected properly so that the timing intervals can be

made into several minutes Proper selection of only a few external components allows

timing intervals of several minutes along with the frequencies exceeding several

hundred kilo hertz.

  It has a high current output; the output can drive TTL.

  It has a temperature stability of 50 parts per million (ppm) per degree Celsius change in

temperature, or equivalently 0.005 %/  °C.

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  The duty cycle of the timer is adjustable with the maximum power dissipation per

package is 600 mW and its trigger and reset inputs are logic compatible.  

6.6 THERMOSTAT / THERMO COUPLE & THERMISTORS:

THERMOSTAT / THERMO COUPLE:

Definition : When the junction of two different metals is heated the electricity is

produced at the two ends of the metal strips. This source is used in the meters for measuring

the heat of furnaces. When two wires of different metals are joined together an e.m.f. exists

across the junction which is dependent on the types of metals or alloys used and also directlyproportional to the temperature of the junction. When one tries to measure this e.m.f. more

 junctions are to be made, which also will give rise to e.m.fs. When all the junctions are at the

same temperature, the resultant e.m.f. in the whole circuit will be zero. When one junction,

however, is at different temperature, the resultant e.m.f. will not be zero. This resultant e.m.f.

is proportional to the temperature difference of the junctions and is called thermoelectric

e.m.f.

The e.m.f. produced by a thermocouple is very small but it can be measured with

reasonable accuracy by a sensitive moving coil millivometer, which can be calibrated in terms of 

temperature. As mentioned earlier, thermocouples are made of different materials. The

materials to be used will depend upon the range of temperature to be measured.

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Materials used for thermocouples

Materials Temperature

Range (ºC) 

E.m.f. at 500ºC

mV

Copper/Constantan

Iron/Constantan

Nickel/Nickel chromium

Platinum/Platinumrhodium

-200 to 400

0 to 900

0 to 1100

500 to 1400

27.6

26.7

10.0

4.5

Thermocouples can be used for the measurement of temperature. Depending on the range of 

temperature to be measured, proper materials are to be chosen for a thermocouple. If one

 junction, called the cold junction, is held at a known constant temperature, the e.m.f. produced

becomes measure of the temperature of the other junction. This is the principle of the

thermocouple pyrometer.

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THERMISTORS:

Thermistors are thermally sensitive resistors and have, according to type, a negative (NTC), or

positive (PTC) resistance/temperature coefficient. Thermo metrics product portfolio comprises

a wide range of both types.

Manufactured from the oxides of the transition metals - manganese, cobalt, copper and nickel,

NTC thermistors are temperature dependant semiconductor resistors. Operating over a range

of -200°C to + 1000°C, they are supplied in glass bead, disc, chips and probe formats. NTCs

should be chosen when a continuous change of resistance is required over a wide temperature

range. They offer mechanical, thermal and electrical stability, together with a high degree of 

sensitivity.

The excellent combination of price and performance has led to the extensive use of NTCs in

applications such as temperature measurement and control, temperature compensation, surge

suppression and fluid flow measurement.

PTC thermistors are temperature dependent resistors manufactured from barium titanate and

should be chosen when a drastic change in resistance is required at a specific temperature or

current level. PTCs can operate in the following modes:

  Temperature sensing, switching at temperatures ranging from 60°C to 180°C, e.g.

protection of windings in electric motors and transformers.

  Solid state fuse to protect against excess current levels, ranging from several mA to

several A (25°C ambient) and continuous voltages up to 600V and higher, e.g. power

supplies for a wide range of electrical equipment.

  Liquid level sensor.

6.7 LIGHT DEPENDENT RESISTOR (LDR):

As the name indicates, the resistance of LDR depends on the amount of light falling on

to it. It consists of a sintered ceramic disc made mainly

from cadmium sulphide. Interleaved, comb like metallic

electrodes are then applied to the surface facing the

light, leads are attached to them and the whole

assembly suitably encapsulated.

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6.8 RELAY COIL:

A relay is an electrically operated switch. Current flowing through the coil of the relay creates

a magnetic field which attracts a lever and changes the switch contacts. The coil current can be

on or off so relays have two switch positions and most have double throw (changeover) switch

contacts as shown in the diagram.

Relays allow one circuit to switch a second circuit which can be completely separate from the

first. For example a low voltage battery circuit can use a relay to switch a 230V AC mains circuit.

There is no electrical connection inside the relay between the two circuits, the link is magnetic

and mechanical.

The coil of a relay passes a relatively large current, typically 30mA for a 12V relay, but it can be

as much as 100mA for relays designed to operate from lower voltages. Most ICs (chips) cannot

provide this current and a transistor is usually used to amplify the small IC current to the larger

value required for the relay coil. The maximum output current forthe popular 555 timer IC is 200mA so these devices can supply

relay coils directly without amplification.

Relays are usually SPDT or DPDT but they can have many more

sets of switch contacts, for example relays with 4 sets of 

changeover contacts are readily available. For further information

about switch contacts and the terms used to describe them please

see the page on switches. Most relays are designed for PCB

mounting but you can solder wires directly to the pins providing

you take care to avoid melting the plastic case of the relay. The

supplier's catalogue should show you the relay's connections. The coil will be obvious and it

may be connected either way round. Relay coils produce brief high voltage 'spikes' when they

are switched off and this can destroy transistors and ICs in the circuit. To prevent damage you

must connect a protection diode across the relay coil.

6.9 BIPOLAR JUNCTION TRANSISTORS: 

A bipolar (junction) transistor (BJT) is a three-terminal electronic device constructed of doped

semiconductor material and may be used in amplifying or switching applications. Bipolar transistors are

so named because their operation involves both electrons and holes. Charge flow in a BJT is due to

bidirectional diffusion of charge carriers across a junction between two regions of different charge

concentrations. This mode of operation is contrasted with unipolar transistors, such as field-effect

transistors, in which only one carrier type is involved in charge flow due to drift. By design, most of the

BJT collector current is due to the flow of charges injected from a high-concentration emitter into the

base where they are minority carriers that diffuse toward the collector, and so BJTs are classified as

minority-carrie devices.

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NPN TRANSISTOR:-

PNP TRANSISTOR:-

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7. CONCLUSION:

Hence this is a circuit which works with 230V, 50HZ supply occupying very less

space in the work environment because of its small size and compatibility. This

circuit works in accordance with temperature. When on button is pressed load is

connected through the relay and is energized. And when off button is pressed it gets

turned off. This is automatic in functioning the plant circuit breaker. By the usage of 

LEDs, transistors, IC1 NE 555 chip, thermistor and relays we can operate the

industrial equipment with low cost investment. Man power can also be reduced to a

very good extent. So the circuit operation is very beneficial and the speaker in the

circuit works as an alarm in emergency thus indicating the fault and also detects the

fire. Hence we can use it in real time applications.

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