ORCAD Training Report

8/11/2019 ORCAD Training Report

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Guru Nanak Institute of Technology, 2011-15

I

Infrared Motion Detector

A TRAINING REPORT

SUBMITTED TOWARDS THE PARTIAL FULFILLMENT OF

REQUIREMENTS FOR THE AWARD OF DEGREE OF

Bachelor of Technology

in

Electronics and Communication Engineering

Submitted By:

Ankur Gupta

6311220

Department of Electronics and Communication Engineering

Guru Nanak Institute of Technology, MullanaAffiliated to Kurukshetra University

(2011-2015)


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II

ACKNOWLEDGEMENT

I am highly grateful to Gaurav Sharma, HOD ECE, Guru Nanak Institute of Technology,

Mullana, for providing this opportunity to carry out the six week summer training with INIT

Call Technologies.

I would like to express my gratitude to other faculty members of Electronics and

Communication Engineering department of GNIT, Mullana for providing academic inputs,

guidance & encouragement throughout the training period.

I would also like to express my gratitude to Mr. Sahil Gupta, Incharge of INIT Call

technologies, without whose permission, wise counsel and able guidance, it would not have

been possible to pursue my training in this manner.

The help rendered by Mr Shivam Tayal for experimentation is greatly acknowledged.

Finally, I express my indebtedness to all who have directly or indirectly contributed to the

successful completion of my summer training.

ANKUR GUPTA


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1. INTRODUCTION


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2.ORCAD

2.1INTRODUCTION

OrCAD is a proprietary software tool suite used primarily for electronic design automation.

The software is used mainly by electronic design engineers and electronic technicians to

create electronic schematics and electronic prints for manufacturing printed circuit boards.

Figure 2.1: ORCAD Logo

The name OrCAD is a portmanteau, reflecting the company and its software's origins: Oregon

+ CAD. Oregon is a state in the Pacific Northwest region of the United States while CAD

stands for Computer Aided Designing.

Founded in 1985 by John Durbetaki, Ken and Keith Seymour as OrCAD Systems

Corporation in Hillsboro, Oregon, the company became a supplier of desktop electronic

design automation (EDA) software. The company's first product was SDT (Schematic Design

Tools), which shipped first late in 1985. The flagship SDT product was soon followed with a

digital simulator, VST (Verification and Simulation Tools) and printed circuit board (PCB)

layout tools. Over time, OrCAD's product line broadened to include Windows-based software

products to assist electronics designers in developing field-programmable gate arrays (FPGAs),

including complex programmable logic devices (CPLDs). The latest iteration of OrCAD CIS

schematic capture software has the ability to maintain a database of available integrated

circuits. This database may be updated by the user by downloading packages from component

manufacturers, such as Analog Devices and others.


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2.2PARTS OF ORCAD

The major parts of the ORCAD product suite are: -

i. Capture CIS

ii. OrCAD PCB Editoriii. PSpice

iv. Layout Plus

2.2.1 CAPTURE CIS

OrCAD Capture CIS is a software tool used for circuit schematic capture. It is part

of the OrCAD circuit design suite.

Capture CIS is nearly identical to the similar OrCAD tool, Capture. The difference

between the two tools comes in the addition of the component information system

(CIS). The CIS links component information, such as printed circuit board package

footprint data or simulation behavior data, with the circuit symbol in the schematic.

When exported to other tools in the OrCAD design suite, the data stored in the CIS

is also transferred to the other tool. Thus, when a design engineer exports a

schematic to the circuit board layout utility, the majority of the circuit elements

have footprints linked to them. This saves time for the design engineer.

Capture CIS has the ability to export netlists, representative of the circuit schematic

which is currently open, to the OrCAD simulation utility, PSpice. Capture CIS also

exports a simulation configuration file, accessible through the simulation toolbar.

This, coupled with the CIS, allows for quick simulations with data representative of

how the circuit will behave. Capture may also export a netlist to the SPICE

simulation utility.

Capture may export a hardware description of the circuit schematic that is currently

open, either in Verilog or VHDL.

Capture also has the ability to export netlists to several different circuit board layout

utilities, such as OrCAD Layout, Allegro, and others. When combined with the CIS,

circuit board footprints are linked to this netlist. This, combined with the pin to pin

interconnect description of the netlist, will open the correct part footprints, and, if

the CIS data that CIS exported is correct, will connect all of the pads together with


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representative lines. This feature makes the circuit board design process easier for

the design engineer.

Recent versions of capture also include a TCL/TK scripting functionality that

allows users to execute a command through a command prompt. The command can

be stored and replayed later. This allows users extensive customization and scripts

can be written to automate any task possible though the graphical interface.

The latest version of OrCAD also includes a marketplace much like the Android or

iPhone app stores. This enables customers to get on-demand access to information,

design data, and resources from across the Web, and apps both free and paid,

written in TCL/TK which can be used to customize the design environment and get

features and capabilities not supported by the tool.

2.2.2 OrCAD PCB EDITOR

PCB Editor contains full-featured PCB editor based on Allegro technology; its

extensive feature set addresses a wide range of todays design challenges and

manufacturability concerns.

Cadence OrCAD PCB Editor is an intuitive, easy-to-use, constraint-driven

environment for creating and editing simple to complex PCBs. It contains a fully

integrated design flow that includes a constraint manager, design capture

technology, component tools, a PCB editor, an auto/interactive router, and

interfaces for manufacturing and mechanical CAD. OrCAD PCB Editor provides

powerful, features that deliver controlled automation to maintain user control, while

maximizing routing productivity. It also provides a powerful and flexible set of

floorplanning tools, and etch creation/editing in a highly productive interconnect

environment. The software can generate a full suite of phototooling, bare-board

fabrication and test outputs.

2.2.3 PSpice

PSpiceis a SPICE analog circuit and digital logic simulation program for Microsoft

Windows. The name is an acronym for Personal SPICE - SPICE itself being an

acronym for Simulation Program with Integrated Circuit Emphasis.


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PSpice was initially developed by MicroSim and is used in electronic design

automation. The company was bought by OrCAD, which was subsequently

purchased by Cadence Design Systems.

PSpice was the first version of UC Berkeley SPICE available on a PC, having been

released in January 1984 to run on the original IBM PC. This initial version ran

from two 360 KB floppy disks and later included a waveform viewer and analyser

program called Probe. Subsequent versions improved on performance and moved to

DEC/VAX minicomputers, Sun workstations, Apple Macintosh, and Microsoft

Windows.

During its development, PSpice has evolved into an analog mixed signal simulator.

The software, now developed towards more complex industry requirements, is

integrated in the complete systems design flow in OrCAD and Cadence Allegro. It

includes features such as analysis of a circuit with automatic optimization,

encryption, a model editor, support for parametrized models, auto-convergence and

checkpoint restart, several internal solvers, a magnetic part editor, and support for

Tabrizi core model for non-linear cores.

(a)PSpice BASICS

In PSpice, the circuit is first described to a computer by using a file called

circuit file. It contains the circuit details, viz., the information about source and

commands for what to do and what to display as output. The PSpice accepts

circuit file as an input and after executing commands, creates and outputs file to

store results. However, the circuit to be analyzed is specified in terms of element

names, element values different sources (voltage or current) and different

parameters. PSpice calculates all nodal voltages and branch currents over a

range of time interval by giving the output of their instantaneous values. It can

also perform other operations as will be evident later. For circuits with variable

frequency sources, AC analysis is used. Each circuit element is connected

between two nodes. All nodes must be connected to at least two elements and

therefore appear twice at least. The node O is predefined as ground.

PSpice is a computer program itself so one need not have to do programming

to use this software. The job is just to prepare the circuit file that instructs

SPICE what to do. The circuit file consists of statements describing the circuit,specifying the analysis to be performed and statements to control the output


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formats and variables. PSpice is to do the simulation called for in the circuit file

and stores the result in an output file. The results may be displayed and or

printed.

(b)TYPES OF ANALYSIS

The type of simulation performed by PSpice depends on the source

specifications and control statements. The types of analysis usually executed in

the PSpice program are as follows:

DC Analysis: - it is used for circuits with time invariant sources (e.g., steady

state dc sources). It calculates all nodal voltages and branch currents over a

range of values. The types of analysis and their corresponding. (dot) commands

are described below:-

Transient Analysis: - It is used for circuits with time variant sources (e.g., ac

sources/switched dc sources). It calculates all nodes voltages and branch

currents over a time interval and their instantaneous values are the outputs. The

corresponding. (dot) commands are as follows:-

AC Analysis: - It is used for small signal analysis of circuits with sources of

varying frequencies. It also calculates all nodal voltages and branch currents

(over a range of frequencies) and their magnitudes and phase angles.


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3.INFRARED RADIATION

Infrared radiation exists in the electromagnetic spectrum at a wavelength that is longer

than visible light. It cannot be seen but it can be detected. Objects that generate heat

also generate infrared radiation and those objects include animals and the human body

whose radiation is strongest at a wavelength of 9.4um. Infrared in this range will not

pass through many types of material that pass visible light such as ordinary window

glass and plastic. However it will pass through, with some attenuation, material that is

opaque to visible light such as germanium and silicon. An unprocessed silicon wafer

makes a good IR window in a weatherproof enclosure for outdoor use. It also provides

additional filtering for light in the visible range. 9.4um infrared will also pass through

polyethylene which is usually used to make Fresnel lenses to focus the infrared

onto sensor elements. Infrared(IR) light is electromagnetic radiation with

longer wavelengths than those of visible light, extending from the nominal red edge of

the visible spectrum at 700 nanometres (nm) to 1 mm. This range of wavelengths

corresponds to a frequency range of approximately 430 THz down to 300 GHz and

includes most of the thermal radiation emitted by objects near room temperature.

Infrared light is emitted or absorbed by molecules when they change their rotational-

vibrational movements. The existence of infrared radiation was first discovered in 1800by astronomer William Herschel

Slightly more than half of the energy from the Sun arrives on Earth in the form of

infrared radiation. The balance between absorbed and emitted infrared radiation has a

critical effect on Earth's climate. Slightly more than half of the energy from the Sun

arrives on Earth in the form of infrared radiation. The balance between absorbed and

emitted infrared radiation has a critical effect on Earth's climate.

Infrared energy elicits vibrational modes in a molecule through a change in the dipole

moment, making it a useful frequency range for study of these energy states for

molecules of the proper symmetry. Infrared spectroscopy examines absorption and

transmission of photons in the infrared energy range.

Infrared light is used in industrial, scientific, and medical applications. Night-vision

devices using active near-infrared illumination allow people or animals to be observed

without the observer being detected. Infrared astronomy uses sensor-

equipped telescopes to penetrate dusty regions of space; such as molecular clouds detect

objects such as planets, and to view highly red-shifted objects from the early days of


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the universe. Infrared thermal-imaging cameras are used to detect heat loss in insulated

systems, to observe changing blood flow in the skin, and to detect overheating of

electrical apparatus


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4.INFRARED MOTION DETECTOR

The Infrared Motion Detector can be used to sense intrusions in the range of the

detector. The detector is capable of sensing any motion in its area. It uses a transmitter

circuit and a receiver circuit for its operation. The transmitter circuit will send Infra red

rays. The infra red rays reflected from a static object will be in one phase while the infra

red rays reflected by a moving object will be in another phase. The infra red motion

detector applies this principle to sense every motion in its area.

Before I elaborate further on the working of the Infrared motion detector, I would shed

some light on motion detectors.

4.1 BACKGROUND

Motion detection is the action of sensing physical movement in a given area. Motion

can be detected by measuring change in speed or vector of an object in the field of view.

This can be achieved either by mechanical devices that physically interact with the field

or by electronic devices that quantifies and measures changes in the given environment.

There are two device of motion detection which is the mechanical device, and the other

one is electronic device. In the mechanical device, a tripwire is a simple form of motion

detection. If a moving objects steps into the tripwire's field of view then a simple sound

device like bells may alert the user. Mechanical motion detection devices can be simple

to implement, but at the same time, it can be defeated easily by interrupting the devices'

mechanics like "cutting the wire. While in electronic device, the electronic motion

sensing such as motion detectors, can prevent such mechanical intervention. The

principal methods by which motion can be electronically identified are optical detection

and acoustical detection. Infrared light or laser technology may be used for optical

detection. Motion detection devices, such as motion detectors, have sensors that detect

movement and send a signal to a sound device that produces an alarm or switch on an

image recording device. There are motions detector which employ cameras connected to

a computer which stores and manages captured images to be viewed over a computer

network. The applications for such detection are detection of unauthorized entry,

detection of cessation of occupancy of an area to extinguish lighting, and detection of a

moving object which triggers a camera to record subsequent events. The motion

detector is thus a basic idea of electronic security systems.


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4.2 MOTION DETECTORS

A motion detector is a device that detects moving objects, particularly people. A motion

detector is often integrated as a component of a system that automatically performs a

task or alerts a user of motion in an area. Motion detectors form a vital component of

security, automated lighting control, home control, energy efficiency, and other useful

systems.

An electronic motion detector contains a motion sensor that transforms the detection of

motion into an electric signal. This can be achieved by measuring optical changes in the

field of view. Most motion detectors can detect up to 1525 meters (4080ft).

A motion detector may be connected to a burglar alarm that is used to alert the homeowner or security service after it detects motion. Such a detector may also trigger a red

light camera. Motion detectors have found great application in domestic and

commercial applications. Some of these applications include motion-activated outdoor

lighting systems, motion sensor street lamps and motion sensor lanterns.

4.2.1 TYPES OF MOTION DETECTORS

i.

Infrared motion detectorsii. Ultrasonic motion detectors

iii. Microwave motion detectors

iv. Tomographic motion detectors

4.3 INFRARED MOTION DETECTORS

An infrared motion detector is used to sense movement of people, animals, or other

objects. They are commonly used in burglar alarms and automatically-activated lightingsystems.


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Fig 4.1: An Infrared Motion detector used to control an outdoor, automatic light

4.3.2 Operation

What is actually detected is the broken field for a normal temperature. The sensor detects the

change in the infrared radiation and triggers an alarm if the gradient of the change is higher

than a predefined value. Thus the field does not have to be broken by an object with a different

temperature in order to register change, as sensors will activate from the configuration change

of the environment.

Fig 4.2: Infrared motion detector sensing operation


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4.4 CIRCUIT

The circuit used for my project is given below. This circuit has been used to build the InfraredMotion Detector that is capable of sensing intrusions in its range.

Fig 4.3: Circuit Diagram of Infrared Motion Detector

The following components have been used in this project:

(i) Resistors

(ii) Capacitors

(iii)

Potentiometers

(iv)

IC 555

(v) IR Diode

(vi)

Infrared Transistor L14F

(vii) LM1458

(viii) 1N4148

(ix) Buzzer

I would now describe all these components in detail before explaining the operation and

working of the circuit.


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4.4.1 RESISTORS

A resistoris a passive two-terminal electrical component that implements electrical resistance

as a circuit element. The current through a resistor is in direct proportion to the voltage across

the resistor's terminals. This relationship is represented by Ohm's law:

where I is the current through the conductor in units of amperes, V is the potential difference

measured across the conductor in units of volts, and Ris the resistance of the conductor in units

of ohms. Fig 4.4 shows the symbol used for resistances in electrical circuits.

Fig 4.4: Electrical Symbol of resistor

The ratio of the voltage applied across a resistor's terminals to the intensity of current in thecircuit is called its resistance, and this can be assumed to be a constant (independent of the

voltage) for ordinary resistors working within their ratings. Resistors are common elements of

electrical networks and electronic circuits and are ubiquitous in electronic equipment. Practical

resistors can be made of various compounds and films, as well as resistance wire (wire made of

a high-resistivity alloy, such as nickel-chrome).

Different types of resistors are shown in Fig 4.5.


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Fig 4.5: Different types of resistors

Resistance is measured in OHMS (the Greek letter - called Omega). Higher resistance values

are represented by "k" (kilo-ohms) and M (megs-ohms).

4.4.1.1TYPES OF RESISTORS

(i) CARBON COMPOSITION RESISTORS

Carbon composition resistors consist of a solid cylindrical resistive element with embedded

wire leads or metal end caps to which the lead wires are attached. The body of the resistor is

protected with paint or plastic. Early 20th-century carbon composition resistors had uninsulated

bodies; the lead wires were wrapped around the ends of the resistance element rod and

soldered. The completed resistor was painted for color-coding of its value.

Fig 4.6: Carbon Composition resistors in a vaccum tube radio

(ii) CARBON PILE RESISTORS

A carbon pile resistor is made of a stack of carbon disks compressed between two metal contact

plates. Adjusting the clamping pressure changes the resistance between the plates. These


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resistors are used when an adjustable load is required, for example in testing automotive

batteries or radio transmitters. A carbon pile resistor can also be used as a speed control for

small motors in household appliances (sewing machines, hand-held mixers) with ratings up to a

few hundred watts.

(iii) CARBON FILM RESISTORS

A carbon film is deposited on an insulating substrate, and a helix is cut in it to create a long,

narrow resistive path. Varying shapes, coupled with the resistivity of amorphous carbon

(ranging from 500 to 800 m), can provide a variety of resistances. Compared to carbon

composition they feature low noise, because of the precise distribution of the pure graphite

without binding.Carbon film resistors feature a power rating range of 0.125 W to 5 W at 70 C.

Resistances available range from 1 ohm to 10 megohm.

Fig 4.7: Partially exposed Tesla TR-212 1 k carbon film resistor

(iv)

PRINTED CARBON RESISTORS

Carbon composition resistors can be printed directly onto printed circuit board (PCB)

substrates as part of the PCB manufacturing process. Whilst this technique is more common

on hybrid PCB modules, it can also be used on standard fibreglass PCBs. Tolerances are

typically quite large, and can be in the order of 30%. A typical application would be non-

critical pull-up resistors.

(v) THICK AND THIN FILM RESISTORS

Thick film resistors became popular during the 1970s, and most SMD (surface mount

device) resistors today are of this type. The resistive element of thick films is 1000 times

thicker than thin films,but the principal difference is how the film is applied to the cylinder

(axial resistors) or the surface (SMD resistors).Thin film resistors are made by sputtering (a

method of vacuum deposition) the resistive material onto an insulating substrate. The film is

then etched in a similar manner to the old (subtractive) process for making printed circuit

boards; that is, the surface is coated with a photo-sensitive material, and then covered by a


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pattern film, irradiated with ultraviolet light, and then the exposed photo-sensitive coating is

developed, and underlying thin film is etched away. Thick film resistors are manufactured

using screen and stencil printing processes.

(vi)

METAL FILM RESISTORS

A common type of axial resistor today is referred to as a metal-film resistor. Metal electrode

leadless face (MELF) resistors often use the same technology, but are a cylindrically shaped

resistor designed for surface mounting. Note that other types of resistors (e.g., carbon

composition) are also available in MELF packages. Metal film resistors are usually coated

with nickel chromium (NiCr), but might be coated with any of the cermet materials listed

above for thin film resistors. Unlike thin film resistors, the material may be applied using

different techniques than sputtering (though that is one such technique). Also, unlike thin-

film resistors, the resistance value is determined by cutting a helix through the coating rather

than by etching.

(vii) METAL OXIDE FILM RESISTORS

Metal-oxide film resistors are made of metal oxides such as tin oxide. This results in a

higher operating temperature and greater stability/reliability than Metal film. They are used

in applications with high endurance demands.

(viii) WIREWOUND RESISTORS

Wirewound resistors are commonly made by winding a metal wire, usually nichrome,

around a ceramic, plastic, or fiberglass core. The ends of the wire are soldered or welded to

two caps or rings, attached to the ends of the core. The assembly is protected with a layer of

paint, molded plastic, or an enamel coating baked at high temperature. These resistors are

designed to withstand unusually high temperatures of up to +450 C. Because wirewound

resistors are coils they have more undesirable inductance than other types of resistor,

although winding the wire in sections with alternately reversed direction can minimize

inductance.

4.4.2 CAPACITORS

A capacitor (originally known as a condenser) is a passive two-terminal electrical

component used to store energy electrostatically in an electric field. The forms of practical

capacitors vary widely, but all contain at least two electrical conductors separated by a

dielectric (insulator); for example, one common construction consists of metal foils


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separated by a thin layer of insulating film. Capacitors are widely used as parts of electrical

circuits in many common electrical devices.

When there is a potential difference across the conductors, an electric field develops across

the dielectric, causing positive charge to collect on one plate and negative charge on the

other plate. Energy is stored in the electrostatic field. An ideal capacitor is characterized by a

single constant value, capacitance. This is the ratio of the electric charge on each conductor

to the potential difference between them. The SI unit of capacitance is the farad, which is

equal to one coulomb per volt.

A capacitor consists of two conductors separated by a non-conductive region. The non-

conductive region is called the dielectric. In simpler terms, the dielectric is just an electrical

insulator. Examples of dielectric media are glass, air, paper, vacuum, and even a

semiconductor depletion region chemically identical to the conductors.

An ideal capacitor is wholly characterized by a constant capacitance C, defined as the ratio

of charge Qon each conductor to the voltage Vbetween them:

Because the conductors (or plates) are close together, the opposite charges on the conductors

attract one another due to their electric fields, allowing the capacitor to store more charge for

a given voltage than if the conductors were separated, giving the capacitor a large

capacitance.

Fig 4.8: Different Type of Capacitors


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4.4.2.1TYPES OF CAPACITORS

The major types of capacitors are:

(i) Ceramic capacitors

(ii)

Aluminum electrolytic capacitors

(iii) Film capacitors and paper capacitors

(iv) Tantalum electrolytic capacitors

(v) Super Capacitors

(vi)

Silver Mica Capacitors

(vii) Glass Capacitors

(viii) Vacuum Capacitors

4.4.3 POTENTIOMETERS

A potentiometer, informally a pot, is a three-terminal resistor with a sliding contact that

forms an adjustable voltage divider. If only two terminals are used, one end and the

wiper, it acts as a variable resistor or rheostat. A potentiometer measuring instrument is

essentially a voltage divider used for measuring electric potential (voltage); the

component is an implementation of the same principle, hence its name.

Potentiometers are commonly used to control electrical devices such as volume controls

on audio equipment. Potentiometers operated by a mechanism can be used as position

transducers, for example, in a joystick. Potentiometers are rarely used to directly control

significant power (more than a watt), since the power dissipated in the potentiometer

would be comparable to the power in the controlled load. Fig 4.9 shows the symbol

used for a potentiometer in electrical circuits.

Fig 4.9 Electrical Symbol of a Potentiometer

Potentiometers comprise a resistive element, a sliding contact (wiper) that moves along

the element, making good electrical contact with one part of it, electrical terminals at

each end of the element, a mechanism that moves the wiper from one end to the other,

and a housing containing the element and wiper.

Many inexpensive potentiometers are constructed with a resistive element formed into

an arc of a circle usually a little less than a full turn, and a wiper rotating around the arc

and contacting it. The resistive element, with a terminal at each end, is flat or angled.


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The wiper is connected to a third terminal, usually between the other two. On panel

potentiometers, the wiper is usually the center terminal of three. For single-turn

potentiometers, this wiper typically travels just under one revolution around the contact.

A typical single turn potentiometer is shown in Fig 4.8.

Fig 4.8: A Typical Single Turn Potentiometer

Potentiometers are rarely used to directly control significant amounts of power (more

than a watt or so). Instead they are used to adjust the level of analog signals (for

example volume controls on audio equipment), and as control inputs for electronic

circuits. For example, a light dimmer uses a potentiometer to control the switching of a

TRIAC and so indirectly to control the brightness of lamps. Preset potentiometers are

widely used throughout electronics wherever adjustments must be made during

manufacturing or servicing.

Fig 4.9: Inside View of a Potentiometer


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4.4.4 IC 555

The 555 timer IC is an integrated circuit (chip) used in a variety of timer, pulse

generation, and oscillator applications. The 555 can be used to provide time delays, as

an oscillator, and as a flip-flop element. Derivatives provide up to four timing circuits in

one package.

Fig 4.10: A NE555 Timer IC

4.4.4.1 DESIGN

Depending on the manufacturer, the standard 555 package includes 25 transistors, 2

diodes and 15 resistors on a silicon chip installed in an 8-pin mini dual-in-line package

(DIP-8). Variants available include the 556 (a 14-pin DIP combining two 555s on one

chip), and the two 558 & 559s (both a 16-pin DIP combining four slightly modified

555s with DIS & THR connected internally, and TR is falling edge sensitive instead of

level sensitive).

The NE555 parts were commercial temperature range, 0 C to +70 C, and the SE555

part number designated the military temperature range, 55 C to +125 C. These

were available in both high-reliability metal can (T package) and inexpensive epoxy

plastic (V package) packages. Thus the full part numbers were NE555V, NE555T,SE555V, and SE555T. It has been hypothesized that the 555 got its name from the

three 5 k resistors used within,but Hans Camenzind has stated that the number was

arbitrary.

Low-power versions of the 555 are also available, such as the 7555 and CMOS

TLC555. The 7555 is designed to cause less supply noise than the classic 555 and the

manufacturer claims that it usually does not require a "control" capacitor and in many

cases does not require a decoupling capacitor on the power supply. Such a practice

should nevertheless be avoided, because noise produced by the timer or variation in


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power supply voltage might interfere with other parts of a circuit or influence its

threshold voltages.

4.4.4.2 PIN DESCRIPTION OF 555 TIMER IC

The connection of the pins for a DIP package is as follows:

Pin Name Purpose

1 GND Ground reference voltage, low level (0 V)

2 TRIGThe OUT pin goes high and a timing interval starts when this input falls below

1/2 of CTRL voltage (which is typically 1/3 of VCC, when CTRL is open).

3 OUT This output is driven to approximately 1.7V below+VCCor GND.

4 RESET

A timing interval may be reset by driving this input to GND, but the timing does

not begin again until RESET rises above approximately 0.7 volts. Overrides

TRIG which overrides THR.

5 CTRL Provides "control" access to the internal voltage divider (by default, 2/3 VCC).

6 THRThe timing (OUT high) interval ends when the voltage at THR is greater than

that at CTRL (2/3 VCCif CTRL is open).

7 DISOpen collector output which may discharge a capacitor between intervals. In

phase with output.

8 VCCPositive supply voltage, which is usually between 3 and 15 V depending on the

variation.

Pin 5 is also sometimes called the CONTROL VOLTAGE pin. By applying a voltage to the

CONTROL VOLTAGE input one can alter the timing characteristics of the device. In most

applications, the CONTROL VOLTAGE input is not used. It is usual to connect a 10 nF

capacitor between pin 5 and 0 V to prevent interference. The CONTROL VOLTAGE input can

be used to build an astable with a frequency modulated output.
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4.4.4.3 MODES OF OPERATION

The 555 times IC works in three different modes. The modes of operation of a 555 IC are:

i. MONOSTABLE MODE:

In this mode, the 555 functions as a "one-shot" pulse generator. Applications include

timers, missing pulse detection, bouncefree switches, touch switches, frequency divider,

capacitance measurement, pulse-width modulation (PWM) and so on.

ii. ASTABLE MODE

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