Reflection Light Barrier With Delay

TABLE OF CONTENTS

TABLE OF CONTENTS..............................................................i

LIST OF TABLES....................................................................iii

LIST OF FIGURES...................................................................iii

1 . INTRODUCTION..............................................................1

1.1 Introduction.........................................................................11.2 Components Used:..............................................................2

2 . BLOCK DIAGRAM............................................................3

3 . OPTICAL SENSOR – CNY 70.............................................4

3.1 Optical Sensor:....................................................................43.2 CNY 70:................................................................................53.3 Features:-............................................................................63.4 Applications of CNY 70:.......................................................73.5 Object Detection using CNY 70:..........................................7

4 . INTEGRATED CIRCUITS...................................................9

4.1 Integrated circuit:................................................................94.2 Introduction to Timers:......................................................104.3 Schematic diagram:..........................................................114.4 Pin diagram of 555 Timer:.................................................124.5 Functional Block Diagram of 555 Timer:...........................134.6 Definition of Pin Functions:................................................134.7 Astable Multivibrator:........................................................154.8 Monostable Multivibrator:..................................................204.9 LM 393...............................................................................224.10 Equivalent Circuit of LM 393..............................................234.11 Pin Configuration of LM 393..............................................234.12 Advantages of LM 393.......................................................23

5 . RESISTORS AND CAPACITORS.......................................24

5.1 Resistors:...........................................................................245.2 Theory:..............................................................................255.3 Capacitors:........................................................................265.4 Capacitor types:................................................................27

6 . CIRCUIT DESCRIPTION AND WORKING...........................31

6.1 Circuit Diagram:................................................................316.2 Operation:.........................................................................316.3 Design of Astable Multivibrator:........................................32

7 . CIRCUIT TESTING AND RESULTS....................................33

7.1 Testing Procedure:............................................................337.2 Results...............................................................................34

8 . TIME AND COST ANALYSIS............................................35

8.1 Time Analysis....................................................................358.2 Cost Analysis.....................................................................36

9 . CONCLUSION AND FUTURE SCOPE.................................37

9.1 Conclusion.........................................................................379.2 Applications.......................................................................379.3 Future Modifications..........................................................37

APPENDIX 38

DATASHEETS...............................................................................38

LIST OF TABLES

Table 5-1 Specifications of different types of capacitors................29

Table 7-1 Astable multivibrator output...........................................33

Table 7-2 Reflector distance vs Potentiometer resistance..............33

Table 8-1 TIME ANALYSIS................................................................34

Table 8-2 COST ANALYSIS...............................................................35

ii

LIST OF FIGURES

Figure 2.1 Block Diagram..................................................................3

Figure 3.1 Electronic symbol.............................................................5

Figure 3.2 Reflective Type Sensor....................................................6

Figure 3.3 CNY 70 Schematic............................................................6

Figure 3.4 CNY 70 operation principle..............................................7

Figure 3.5 Collector Current vs. Distance.........................................8

Figure 3.6 Forward Current vs. Forward Voltage..............................8

Figure 4.1 Integrated Circuit.............................................................9

Figure 4.2 Schematic of IC 555.......................................................11

Figure 4.3 Pin configuration of IC 555.............................................12

Figure 4.4 Functional Block Diagram of 555...................................13

Figure 4.5 Astable circuit................................................................15

Figure 4.6 Table of different frequencies of 555 Timer...................17

Figure 4.7 Output voltage waveforms.............................................18

Figure 4.8 Wave forms representing duty cycle.............................19

Figure 4.9 Monostable Circuit.........................................................20

Figure 4.10 Input and output voltage waveforms...........................21

Figure 4.11 Equivalent circuit of LM 393.........................................23

Figure 4.12 Pin configuration of LM 393.........................................23

Figure 5.1 resistor code..................................................................24

Figure 5.2 Resistor color code.........................................................25

Figure 5.3 Capacitor........................................................................27

Figure 5.4 Types of capacitors........................................................29

Figure 5.5 Symbols for different type of capacitors........................30

Figure 6.1 Circuit Diagram..............................................................31

iii

Reflection Light Barrier With Delay

1. INTRODUCTION

1.1 Introduction

The aim of this project is to design an automatic fridge door alarm circuit,

which beeps when the refrigerator door is open for more than predefined time

interval. The motivation for doing this project is the fact that the energy consumption

in our house to be made more efficient. If the door of the refrigerator is open for long

period then the coolness inside the fridge reduces for time lapse. Refrigerator consists

of a temperature sensor that maintains a constant temperature value inside the

refrigerator.

Usually the condenser in the refrigerator is on only for some time and is

switched off when the required coolness in the refrigerator is achieved. A closed loop

circuit consisting of temperature sensors, senses and regulates the temperature control

in the refrigerator. If the refrigerator door is open for long period then the condenser is

on for long duration of time and hence consumes more power. Hence, by keeping the

refrigerator door open for long time the losses incurred are :-

1. The refrigerator condenser consumes more power and hence electricity bill is

more.

2. Coolness of the refrigerator is lost soon.

3. Consumes more time to reach the required level of coolness inside the

refrigerator.

4. Energy efficient utilization factor is reduced.

5. Vegetables in the refrigerator (especially leafy vegetables) are spoiled soon

due to water generated by the exposure of cool vegetables to normal

temperature.

Hence, to overcome all these losses we design a small, simple and low power

circuit that generates an alarm when the refrigerator door is open. The alarm from the

circuit is generated after a fixed amount of time.

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1.2 Components Used:

1. Photo Transceiver – CNY70

2. Dual op-amp IC – LM393

3. Timer IC – NE555

4. Resistors – 1MΩ (1)

470kΩ (1)

100kΩ (2)

47kΩ (2)

1kΩ (1)

5. Potentiometer – 1MΩ (1)

6. Capacitors – 220µF (3)

1µF (1)

100nF (2)

7. Electronic Buzzer – 1

8. DC Battery – +9V (1)

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2. BLOCK DIAGRAM

As shown in block diagram there are mainly five blocks: Sensor, comparator,

Low Pass Filter, Timer Circuit, Buzzer Block.

Figure 2.1 Block Diagram

The Basic Blocks are explained below:

Reflection barrier device : This block senses the input light and generates the

corresponding voltage signal which will drive the comparator.

Comparator: This block compares the reference signal and the input signal

and produces the corresponding voltage.

Active low pass filter: This block consists of active low pass filter designed

by operational amplifier which removes any pips present in the comparator

output and maintains stable output at input of the timer.

Timer circuit: The timer circuit acts as an astable multivibrator which

produces square pulse as output and this train of pulses are fed to the output

load.

Buzzer O/P: The load connected at the output stage is buzzer. This buzzer

produces sound when train of pulses is given as input from the astable

multivibrator.

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3. OPTICAL SENSOR – CNY 70

3.1 Optical Sensor:

Sensor is a physical device which senses and measures physical quantities and converts them into electrical signals. Optical sensors are electronic detectors that convert light, or a change in light, into an electronic signal.

The optical sensor used in this project is reflective optical sensor with

transistor output type. CNY 70 is an example for reflective optical sensor with

transistor type device. CNY 70 consists of

1. IR led (Emitter)

2. Transistor type photo detector (Detector)

Infrared LEDs :-

A light-emitting diode (LED) is a semiconductor light source. An IR LED,

also known as IR transmitter, is a special purpose LED that transmits infrared rays in

the range of 760 nm wavelength. Such LEDs are usually made of gallium arsenide or

aluminum gallium arsenide. They, along with IR receivers, are commonly used as

sensors.

The appearance is same as a common LED. Since the human eye cannot see

the infrared radiations, it is not possible for a person to identify whether the IR LED is

working or not, unlike a common LED. To overcome this problem, the camera on a

cellphone can be used. The camera can show us the IR rays being emanated from the

IR LED in a circuit.

The IR LED emits 760nm wavelength,

has radiant power output 16mW at 100ma

(max 1.2A), forward voltage 1.2V, and

viewing angle to 1/2 intensity 45°.

Figure 2. IR – LED

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Figure 3.2 Electronic symbol

Detector :-

Photo detectors are sensors of light or other electromagnetic energy that can

provide an electrical response that is a useful measure of incident electromagnetic

radiation. A photodiode is a p-n junction or PIN structure. When a photon of

sufficient energy strikes the diode, it excites an electron, thereby creating a free

electron (and a positively charged electron hole).

This mechanism is also known as the inner photoelectric effect. If the

absorption occurs in the junction's depletion region, or one diffusion length away

from it, these carriers are swept from the junction by the built-in field of the depletion

region. Thus holes move toward the anode, and electrons toward the cathode, and

a photocurrent is produced.

A phototransistor is in essence a bipolar transistor encased in a transparent

case so that light can reach the base-collector junction. The electrons that are

generated by photons in the base-collector junction are injected into the base, and this

photodiode current is amplified by the transistor's current gain β.

3.2 CNY 70:

The CNY70 is a reflective sensor that includes an infrared emitter and

phototransistor in a leaded package which blocks visible light. Reflective sensors

incorporate an infrared emitter and photo detector adjacent to each other as shown in

Figure 2.3. The IC and its schematic is shown in fig. 2.4.

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Figure 3.3 Reflective Type Sensor

Figure 3.4 CNY 70 Schematic

The emitted light is reflected back towards the photo detector, and when the

reflector moves towards the front face of the CNY 70 the amount of light energy

reaching the detector increases. This change in light energy or photo current is used as

input signal in the application.

3.3 Features:-

• Package type: leaded

• Detector type: phototransistor

• Dimensions (L x W x H in mm): 7 x 7 x 6

• Peak operating distance: < 0.5 mm

• Operating range within > 20 % relative collector current: 0 mm to 5 mm

• Typical output current under test: IC = 1 mA

• Emitter wavelength: 950 nm

• Daylight blocking filter

• Lead (Pb) free soldering available

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3.4 Applications of CNY 70:

• Optoelectronic scanning and switching devices i.e., index sensing, coded disk

scanning etc. (optoelectronic encoder assemblies).

3.5 Object Detection using CNY 70:

The basic idea is to send infrared light through IR-LEDs, which is then reflected

by any object in front of the sensor. Then all you have to do is to pick-up the reflected

IR light. For detecting the reflected IR light, we are going to use a very original

technique: we are going to use another IR-LED, to detect the IR light that was emitted

from another led of exact same type.

This is an electrical property of Light Emitting Diodes (LEDs) which is the

fact that an LED produces a voltage difference across its leads when it is subjected to

light, as if it was a photo-cell, but with much lower output current. In other words, the

voltage generated by the LEDs can't be - in any way - used to generate electrical

power from light. It can barely be detected. That’s why as we use a Op-Amp

(operational Amplifier) to accurately detect very small voltage changes.

The pictorial representation of operation of CNY 70 is shown in fig. 2.5

Figure 3.5 CNY 70 operation principle

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Figure 3.6 Collector Current vs. Distance

Figure 3.7 Forward Current vs. Forward Voltage

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4. INTEGRATED CIRCUITS

4.1 Integrated circuit:

In electronics, an integrated circuit (also known as IC, chip, or microchip) is a

miniaturized electronic circuit (consisting mainly of semiconductor devices, as well as

passive components) that has been manufactured in the surface of a thin substrate of

semiconductor material. Integrated circuits are used in almost all electronic equipment

in use today and have revolutionized the world of electronics. Computers, cellular

phones, and other digital appliances are now inextricable parts of the structure of

modern societies, made possible by the low cost of production of integrated circuits.

A hybrid integrated circuit is a miniaturized electronic circuit constructed of

individual semiconductor devices, as well as passive components, bonded to a

substrate or circuit board. A monolithic integrated circuit is made of devices

manufactured by diffusion of trace elements into a single piece of semiconductor

substrate, a chip.

Figure 4.8 Integrated Circuit

Integrated circuits were made possible by experimental discoveries which

showed that semiconductor 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 circuits mass production capability, reliability, and building-block approach

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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 and not constructed as one transistor at a time. Furthermore,

much less material is used to construct a circuit as a packaged IC die than as 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

close together.

4.2 Introduction to Timers:

The 555 timer is an integrated circuit (chip) implementing a variety of timer

and Multivibator applications. It was produced by Signetics Corporation in early

1970. The original name was the SE555/NE555 and was called "The IC Time

Machine". The 555 gets its name from the three 5-KΩ resistors used in typical early

implementations. It is widely used because of its ease to use, low price and reliability.

It is one of the most popular and versatile integrated circuits which can be used

to build lots of different circuits. It includes 23 transistors, 2 diodes and 16 resistors

on a silicon chip installed in an 8-pin mini dual-in-line package (DIP-8).

The 555 Timer is a monolithic timing circuit that can produce accurate and

highly stable time delays or oscillations. The timer basically operates in one of the

two modes—monostable (one-shot) multivibrator or as an astable (free-running)

multivibrator. In the monostable mode, it can produce accurate time delays from

microseconds to hours. In the astable mode, it can produce rectangular waves with a

variable duty cycle. Frequently, the 555 is used in astable mode to generate a

continuous series of pulses, but you can also use the 555 to make a one-shot or

monostable circuit.

The 555 can source or sink 200 mA of output current, and is capable of driving

wide range of output devices. The output can drive TTL (Transistor-Transistor Logic)

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and has a temperature stability of 50 parts per million (ppm) per degree Celsius

change in temperature, or equivalently 0.005 %/°C. Also available are ultra-low

power versions of the 555 such as the 7555 and TLC555.

The 555 IC has three operating modes:

Monostable mode:

In this mode, the 555-timer functions as "one-shot". Applications include

timers, missing pulse detection, bounce free switches, touch switches, Frequency

Divider, Capacitance Measurement, Pulse Width Modulation (PWM) etc.

Astable mode:

Free Running mode: the 555 can operate as an oscillator. Uses include LED

and lamp flashers, pulse generation, logic clocks, tone generation, security alarms,

pulse position modulation, etc.

Bistable mode:

The 555 can operate as a flip-flop, if the DIS pin is not connected and no

capacitor is used. Uses include bounce free latched switches, etc.

4.3 Schematic diagram:

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Figure 4.9 Schematic of IC 555

4.4 Pin diagram of 555 Timer:

Figure 4.10 Pin configuration of IC 555

The connection of the pins is as follows:

1. GND Ground, low level

2. TR A short pulse high → low on the trigger starts the timer

3. Q During a timing interval, the output stays at +VCC

4. R A timing interval can be interrupted by applying a reset pulse to low

(0V)

5. CV Control voltage allows access to the internal voltage divider

(2/3 VCC)

6. THR The threshold voltage (Upper threshold → 2/3 VCC)

7. DIS Connected to a capacitor whose discharge time will influence the

timing interval.

8. VCC The positive supply voltage which must be between 5 and 15V

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4.5 Functional Block Diagram of 555 Timer:

Figure 4.11 Functional Block Diagram of 555

4.6 Definition of Pin Functions:

Pin 1 (Ground): The ground (or common) pin is the most-negative supply potential of

the device, which is normally connected to circuit common (ground) when operated

from positive supply voltages.

Pin 2 (Trigger): This pin is the input to the lower comparator and is used to set the

latch, which in turn causes the output to go high. The external trigger pulse is applied

to this pin. The output of the timer is low if the voltage at this pin is greater than 2/3

Vcc. If a negative going pulse of amplitude larger than 1/3 Vcc is applied to this pin, the

output of comparator 2 becomes low, which in turn makes the output of the timer

high. The output remains high as long as the trigger terminal remains at low voltage.

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One precaution that should be observed with the trigger input signal is that it must not remain lower than 1/3 V+ for a period of time longer than the timing cycle.

A second precaution with respect to the trigger input concerns storage time in

the lower comparator. This portion of the circuit can exhibit normal turn-off

delays of several microseconds after triggering; that is, the latch can still have

a trigger input for this period of time after the trigger pulse.

Pin 3 (Output): There are two ways a load can be connected to the output terminal

either between pin 3 and ground (pin 1) or between pin 3 and the supply voltage +

VCC (pin 8). When the output is low, the load current flows through the load

connected between pin 3 and pin 8 into the output terminal and is called the sink

current.

However, the current through the grounded load is zero. Therefore, the load

between pin 3 and + VCC is called “normally on load” and that connected between

pin 3 and ground is called “normally off load”. On the other hand, when the output is

high, the current through the load connected between pin 3 and + VCC (“normally on

load”) is zero. However, the output terminal supplies current to the “normally off

load”. This current is called the source current. The maximum value of sink or source

current is 200 mA.

Pin 4 (Reset): The 555 timer can be reset or disabled by applying a negative pulse to

this pin. When not in use, this pin is connected to +VCC to avoid possibility of false

triggering. This pin is also used to reset the latch and return the output to a low state.

The reset voltage threshold level is 0.7 volt, and a sink current of 0.1mA from this pin

is required to reset the device.

Pin 5 (Control Voltage): An external voltage may be applied to this terminal to

change the threshold as well as the trigger voltage. The pulse width of the output

waveform is hence dependent on it. By applying a voltage to this pin, it is possible to

vary the timing of the device independently of the RC network. When not in use, the

control pin should be bypassed to ground with a 0.01 μF capacitor.

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Pin 6 (Threshold): This is the non-inverting input terminal of the comparator 1.

When the voltage at this pin becomes greater than or equal to the threshold voltage

2/3 VCC, the output of this comparator becomes high, which in turn, switches the

output of the timer low. The action of the threshold pin is level sensitive, allowing

slow rate-of-change waveforms.

Pin 7 (Discharge): This pin is connected internally to the collector of a transistor Q1.

When the output of the timer is high, Q1 is off and acts as an open circuit to an

external capacitor C connected across it. On the other hand, when the output of the

timer is low, Q1 is saturated and acts as a short circuit, shorting C to ground. Usually

the timing capacitor is connected between pin 7 and ground and is discharged when

the transistor turns "on".

Pin 8 (+Vcc ): Vcc is the positive supply voltage terminal of the 555 timer IC. The

supply voltage of +5 V to + 18 V is applied to this pin with respect to ground (pin 1).

4.7 Astable Multivibrator:

An astable multivibrator is a wave-generating circuit in which neither of the

output levels is stable. If we rearrange the circuit slightly so that both the trigger and

threshold inputs are controlled by the capacitor voltage, we can cause the 555 to

trigger itself repeatedly. In this case, we need two resistors in the capacitor charging

path so that one of them can also be in the capacitor discharge path.

Figure 4.12 Astable circuit

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The time period (T) of the square wave is the time for one complete cycle, but

it is usually better to consider frequency (f) which is the number of cycles per second.

T = 0.7 × (R1 + 2R2) × C1 and f = 1.4

(R1 + 2R2) × C1

Where,

T = Time period in seconds(s)

f = Frequency in hertz (Hz)

R1 = Resistance in ohms (Ω)

R2 = Resistance in ohms (Ω)

C1 = Capacitance in farads (F)

The time period can be split into two parts:

T = Tm + Ts

Mark time (output high):

Tm = 0.7 × (R1+R2) × C1

Space time (output low):

Ts = 0.7 × R2 × C1

Many circuits require Tm and Ts to be almost equal; this is achieved if R2 is

much larger than R1.

For a standard astable circuit Tm cannot be less than Ts, but this is not too

restricting because the output can both sink and source current. For example an LED

can be made to flash briefly with long gaps by connecting it (with its resistor)

between +Vs and the output. This way the LED is on during Ts, so brief flashes are

achieved with R1 larger than R2, making Ts short and Tm long.

Choosing R1, R2 and C1:

R1 and R2 should be in the range 1kΩ to 1MΩ. It is best to choose C1 first

because capacitors are available in just a few values.

Choose C1 to suit the frequency range you require (use the table as a guide).

Choose R2 to give the frequency (f) you requires. Assume that R1 is much

smaller than R2 (so that Tm and Ts are almost equal), then you can use:

R2 = 0.7/f×C1

Choose R1 to be about a tenth of R2 (1kΩ min.) unless you want the mark

time Tm to be significantly longer than the space time Ts.

If you wish to use a variable resistor it is best to make it R2.

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If R1 is variable it must have a fixed resistor of at least 1kΩ in series

(this is not required for R2 if it is variable).

555 astable frequencies

C1R2 = 10kΩ

R1 = 1kΩ

R2 = 100kΩ

R1 = 10kΩ

R2 = 1MΩ

R1 = 100kΩ

0.001µF 68kHz 6.8kHz 680Hz

0.01µF 6.8kHz 680Hz 68Hz

0.1µF 680Hz 68Hz 6.8Hz

1µF 68Hz 6.8Hz 0.68Hz

10µF 6.8Hz 0.68Hz (41 per min.) 0.068Hz (4 per min.)

Figure 4.13 Table of different frequencies of 555 Timer

Figure 4.5 shows 555 timer connected as an astable multivibrator. Pin 5 is

bypassed to ground through a 0.01 μF capacitor. The power supply (+VCC) is

connected to common of pin 4 and pin 8 and pin 1 is grounded. If the output is high

initially, capacitor C starts charging towards VCC through Ra and Rb. As soon as the

voltage across the capacitor becomes equal to 2/3 VCC , the upper comparator triggers

the flip-flop, and the output becomes low.

The capacitor now starts discharging through RB and transistor Q1. When the

voltage across the capacitor becomes 1/3 VCC , the output of the lower comparator

triggers the flip-flop, and the output becomes high. The cycle then repeats. The output

voltage and capacitor voltage waveforms are shown in Figure 4.7.

In this mode, the initial pulse when power is first applied is a bit longer than

the others, having duration of T=

1 .1( Ra+Rb )∗C

.

However, from then on, the capacitor alternately charges and discharges

between the two comparator threshold voltages. When charging, C starts at (1/3) V cc

and charges towards VCC. However, it is interrupted exactly halfway there, at (2/3)

Vcc. Therefore, the charging time,

t1=0.693( Ra+Rb )∗C

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Figure 4.14 Output voltage waveformsWhen the capacitor voltage reaches (2/3) Vcc, the discharge transistor is

enabled (pin 7), and this point in the circuit becomes grounded. Capacitor C now

discharges through Rb alone. Starting at (2/3)VCC, it discharges towards ground, but

again is interrupted halfway there, at (1/3)Vcc. The discharge time,

t2=0.693 Rb∗C

The total period of the pulse train is

t1+t2=0.693( Ra+2 Rb )∗C

The output frequency of this circuit is the inverse of the period,

f = 1 . 45( Ra+2 Rb )∗C

Note that the duty cycle of the 555 timer circuit in astable mode cannot reach

50%. On time must always be longer than off time, because Ra must have a resistance

value greater than zero to prevent the discharge transistor from directly shorting VCC

to ground. Such an action would immediately destroy the 555 IC.

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Duty cycle:

The duty cycle of an astable circuit is the proportion of the complete cycle for

which the output is high (the mark time). It is usually given as a percentage.

For a standard 555/556 astable circuit the mark time (Tm) must be greater than

the space time (Ts), so the duty cycle must be at least 50%:

Duty cycle = Tm

= R1 + R2

Tm + Ts R1 + 2R2

To achieve a duty cycle of less than 50% a diode can be added in parallel with

R2 as shown in the diagram. This bypasses R2 during the charging (mark) part of the

cycle so that Tm depends only on R1 and C1:

Tm = 0.7 × R1 × C1 (ignoring 0.7 V across diode)

Ts = 0.7 × R2 × C1 (unchanged)

Duty cycle with diode = Tm

= R1

Tm + Ts R1 + R2

Figure 4.15 Wave forms representing duty cycle

Applications of Astable 555 Timer:

Modulate transmitters such as ultrasonic and IR transmitters.

Create an accurate clock signal.

Turn on and off an actuator at set time intervals for a fixed duration.

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4.8 Monostable Multivibrator:

A monostable multivibrator is a pulse-generating circuit having one stable and

one quasi-stable state. Since there is only one stable state, the circuit is known as

‘monostable multivibrator’. The duration of the output pulse is determined by the RC

network connected externally to the 555 timer. The stable state output is

approximately zero or at logic-low level. An external trigger pulse forces the output to

become high or approximately.

After a predetermined length of time, the output automatically switches back

to the stable state and remains low until a trigger pulse is again applied. The cycle

then repeats. That is, each time a trigger pulse is applied, the circuit produces a single

pulse. Hence, it is also called ‘one-shot multivibrator’.

Figure 4.16 Monostable Circuit

The circuit has an external resistor and capacitor. The voltage across the

capacitor is used for the threshold to pin 6. When the trigger arrives at pin 2, the

circuit produces output pulse at pin 3.

Initially, if the output of the timer is low, that is, the circuit is in a stable state,

transistor Q1 is on and the external capacitor C is shorted to ground. Upon application

of a negative trigger pulse to pin 2, transistor Q1 is turned off, which releases the

short circuit across the capacitor and as a result, the output becomes high.

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The capacitor now starts charging up towards Vcc through R1. When the

voltage across the capacitor equals 2/3 Vcc, the output of comparator 1 switches from

low to high, which in turn makes the output low via the output of the flip-flop. Also,

the output of the flip-flop turns transistor Q1 on and hence the capacitor rapidly

discharges through the transistor.

The output of the monostable Multivibator remains low until a trigger pulse is

again applied. The cycle then repeats. Figure 8 shows the trigger input, output

voltage, and capacitor voltage waveforms.

Figure 4.17 Input and output voltage waveforms

As shown, the pulse width of the trigger input must be smaller than the

expected pulse width of the output waveform. Moreover, the trigger pulse must be a

negative-going input signal with amplitude larger than 1/3 Vcc. The time for which the

output remains high is given by,

tp = 1.1 R1C1

where R1 is in ohms, C1 in farads and tp in seconds.

Once the circuit is triggered, the output will remain high for the time interval

tp. It will not change even if an input trigger is applied during this time interval. One

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interesting and very useful feature of the 555 timer in either mode is that the timing

interval for either charge or discharge is independent of the supply voltage, VCC. This

is because the same VCC is used both as the charging voltage and as the basis of the

reference voltages for the two comparators inside the 555.

Thus, the timing equations above depend only on the values for R and C in

either operating mode.

4.9 LM 393

LM 393 is Low Power Low Offset Voltage Dual Comparator consists of two

independent precision voltage comparators with an offset voltage specification as low

as 2.0 mV max for two comparators which were designed specifically to operate from

a single power supply over a wide range of voltages.

These comparators also have a unique characteristic in that the input common-

mode voltage range includes ground, even though operated from a single power

supply voltage. Application areas include limit comparators, simple analog to digital

converters; pulse, square wave and time delay generators; wide range VCO; MOS

clock timers; multivibrators and high voltage digital logic gates. The LM393 series

was designed to directly interface with TTL and CMOS. When operated from both

plus and minus power supplies, the LM393 series will directly interface with MOS

logic where their low power drain is a distinct advantage over standard comparators.

The LM393 series are high gain, wide bandwidth devices which, like most

comparators, can easily oscillate if the output lead is inadvertently allowed to

capacitively couple to the inputs via stray capacitance. This shows up only during the

output voltage transition intervals as the comparator change states. Power supply

bypassing is not required to solve this problem. Standard PC board layout is helpful as

it reduces stray input-output coupling.

The output of the LM393 series is the uncommitted collector of a grounded-emitter

NPN output transistor. Many collectors can be tied together to provide an output

OR’ing function. An output pull-up resistor can be connected to any available power

supply voltage within the permitted supply voltage range and there is no restriction on

P a g e | 22


this voltage due to the magnitude of the voltage which is applied to the V+ terminal of

the LM393 package.

4.10 Equivalent Circuit of LM 393

Figure 4.18 Equivalent circuit of LM 393

4.11 Features:

Wide supply

o --- Voltage range: 2.0V to 36V

o --- Single or dual supplies: ±1.0V to ±18V

Very low supply current drain (0.4mA) --- independent of supply voltage

Low input biasing current: 25nA

Low input offset current: ±5nA

Maximum offset voltage: ±3mV

Input common-mode voltage range includes ground

Different input voltage range equal to the power supply voltage

Low output saturation voltage: 250mV at 4mA

Output voltage compatible with TTL,DTL,ECL,MOS and CMOS logic

systems

Available in the 8-BUMP(12 mil) micro SMD package

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4.12 Pin Configuration of LM 393

Figure 4.19 Pin configuration of LM 393

4.13 Advantages of LM 393

I. High precision comparators

II. Reduced VOS drift over temperature

III. Eliminates need for dual supplies

IV. Allows sensing near ground

V. Compatible with all forms of logic

VI. Power drain suitable for battery operation

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5. RESISTORS AND

CAPACITORS

5.1 Resistors:

Introduction

A resistor is a two-terminal electronic component that produces a voltage

across its terminals that is proportional to the electric current through it in accordance

with Ohm's law:

V = IR

Resistors are elements of electrical networks and electronic circuits and are

ubiquitous in most 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).

Figure 5.20 resistor code

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The primary characteristics of a resistor are the resistance, the tolerance, the

maximum working voltage and the power rating. Other characteristics include

temperature coefficient, noise, and inductance. Less well-known is critical resistance,

the value below which power dissipation limits the maximum permitted current, and

above which the limit is applied voltage. Critical resistance is determined by the

design, materials and dimensions of the resistor.

Resistors can be integrated into hybrid and printed circuits, as well as

integrated circuits. Size, and position of leads (or terminals), are relevant to

equipment designers; resistors must be physically large enough not to overheat when

dissipating their power.

Figure 5.21 Resistor color code

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5.2 Theory:

Ohm's law

The behavior of an ideal resistor is dictated by the relationship specified in Ohm's

law:

Ohm's law states that the voltage (V) across a resistor is proportional to the

current (I) through it where the constant of proportionality is the resistance (R).

Equivalently, Ohm's law can be stated:

This formulation of Ohm's law states that, when a voltage (V) is maintained across a

resistance (R), a current (I) will flow through the resistance.

This formulation is often used in practice. For example, if V is 12 volts and R is 400

ohms, a current of 12 / 400 = 0.03 amperes will flow through the resistance R.

5.3 Capacitors:

A capacitor is an electrical device that can store energy in the electric field

between a pair of closely spaced conductors (called 'plates'). When current is applied

to the capacitor, electric charges of equal magnitude, but opposite polarity, build up

on each plate.

Capacitors are used in electrical circuits as energy-storage devices. They can

also be used to differentiate between high-frequency and low-frequency signals and

this makes them useful in electronic filters.

Capacitors are occasionally referred to as condensers. This is now considered

an antiquated term. The capacitor's capacitance (C) is a measure of the amount of

charge (Q) stored on each plate for a given potential difference or voltage (V) which

appears between the plates:

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C=Q/V

In SI units, a capacitor has a capacitance of one farad when one coulomb of

charge is stored due to one volt applied potential difference across the plates. Since

the farad is a very large unit, values of capacitors are usually expressed in microfarads

(µF), nanofarads (nF), or picofarad (pF).

The capacitance is proportional to the surface area of the conducting plate and

inversely proportional to the distance between the plates. It is also proportional to the

permittivity of the dielectric (that is, non-conducting) substance that separates the

plates.

Figure 5.22 Capacitor

5.4 Capacitor types:

Vacuum:

Two metal, usually copper, electrodes are separated by a vacuum. The

insulating envelope is usually glass or ceramic. Typically of low capacitance - 10 -

1000 pF and high voltage, up to tens of kilovolts, they are most often used in radio

transmitters and other high voltage power devices. Both fixed and variable types are

available. Variable vacuum capacitors can have a minimum to maximum capacitance

ratio of up to 100, allowing any tuned circuit to cover a full decade of frequency.

Vacuum is the most perfect of dielectrics with a zero loss tangent. This allows very

high powers to be transmitted without significant loss and consequent heating.

Air:

Air dielectric capacitors consist of metal plates separated by an air gap. The

metal plates, of which there may be many interleaved, are most often made of

aluminum or silver-plated brass. Nearly all air dielectric capacitors are variable and

are used in radio tuning circuits.

P a g e | 28


Metalized plastic film:

Made from high quality polymer film (usually polycarbonate, polystyrene,

polypropylene, polyester (Mylar), and for high quality capacitors polysulfone), and

metal foil or a layer of metal deposited on surface. They have good quality and

stability, and are suitable for timer circuits suitable for high frequencies.

Mica:

Similar to metal film capacitors, these are often high voltage capacitors,

suitable for high frequencies having excellent tolerance. These are fast and stable for

HF and low VHF RF circuits, but expensive.

Paper:

Used for relatively high voltages. Common in antique radio equipment, paper

dielectric and aluminum foil layers rolled into a cylinder and sealed with wax. Low

values up to a few μF, working voltage up to several hundred volts, oil-impregnated

bathtub types to 5 kV used for motor starting and high-voltage power supplies, and up

to 25 kV for large oil-impregnated energy discharge types.

Glass:

Used for high voltages, expensive, stable temperature coefficient in a wide

range of temperatures.

Ceramic:

Chips of alternating layers of metal and ceramic. Depending on their

dielectric, their degree of temperature/capacity dependence varies. They often have

high dissipation factor, high frequency coefficient of dissipation, their capacity

depends on applied voltage, and their capacity changes with aging. However they find

massive use in common low-precision coupling and filtering applications.

Aluminum electrolytic:

Polarized, constructionally similar to metal film, but the electrodes are made

of etched aluminum to acquire much larger surfaces. The dielectric is soaked with

liquid electrolyte. They can achieve high capacities but suffer from poor tolerances,

high instability, gradual loss of capacity especially when subjected to heat, and high

leakage. Tend to lose capacity in low temperatures. Bad frequency characteristics

make them unsuited for high-frequency applications

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Tantalum electrolytic:

Similar to the aluminum electrolytic capacitor but with better frequency and

temperature characteristics, high dielectric absorption, high leakage. Has much better

performance in low temperatures.

Super capacitors:

Made from carbon aerogel, carbon nanotubes, or highly porous electrode

materials. Extremely high capacity and can be used in some applications instead of

rechargeable batteries.

Gimmick capacitors:

These are capacitors made from two insulated wires that have been twisted

together. Each wire forms a capacitor plate. Gimmick capacitors are also a form of

variable capacitor. Small changes in capacitance (20 percent or less) are obtained by

twisting and untwisting the two wires.

Varicap capacitors:

These are specialized, reverse-biased diodes whose capacitance varies with

voltage. Used in phase-locked loops.

Figure 5.23 Types of capacitors

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Figure 5.24 Symbols for different type of capacitors

Table 5-1 Specifications of different types of capacitors

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6. CIRCUIT DESCRIPTION AND WORKING

6.1 Circuit Diagram:

Figure 6.25 Circuit Diagram

6.2 Operation:

The power supply for the circuit requires about 12 mA at 12 V. Potentiometer

P1 adjusts the sensitivity of the sensor. Normally the potentiometer is adjusted to the

maximum value to get proper sensitivity of the device. Sensitivity of the device is

stated as the small variation in the distance which changes the output of the circuit.

The sensor works reliably from a distance of one centimeter. If the current through the

LED is increased, the distance can be increased a little. The delay can be adjusted

with capacitor C3. C4 provides extra filtering for the reference voltage. R6 and R7

should be in the range 1kΩ to 1MΩ. It is best to choose C5 first because capacitors are

available in just a few values. The capacitor and resistor values are designed in such a

way that the circuit acts as astable multivibrator with a frequency of square wave

P a g e | 32


output as 10Hz and a duty cycle of 60%.The buzzer would switch on with a ‘chirping’

sound when its input is train of pulses obtained from the astable multivibrator circuit.

The well-known IC NE-555 timer is used as astable multivibrator. The buzzer may

also be driven with a duty cycle of 2:1, which improves the audibility.

6.3 Design of Astable Multivibrator:

We have also taken value of capacitor C=1μF and R1=R2=47k.

Frequency of output pulse

f = 1 . 45( R1+2 R2 )∗C

Putting the values of f, R1 and C1

f = 1. 453∗47000∗0 .000001

Therefore,

f = 10.283 Hz

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7. CIRCUIT TESTING AND

RESULTS

7.1 Testing Procedure:

As in any technical project, it is necessary to test the work carried out.

Here also we carried out various tests on our project. We assembled the circuit in

section by section manner, tested the individual section and if required the section

component values were modified depending upon requirements. The overall testing

and calibration is divided into following steps.

1) Testing of astable multivibrator Circuit.

2) Testing of entire circuit by connection other blocks to astable multivibrator.

TESTING OF ASTABLE MULTIVIBRATOR CIRCUIT:

1) Connect the circuit connection.

2) Connect the power supply to the ICs from the linear regulator circuit

3) Observe the wave-form at PIN-3 of IC 555. Measure each output

voltage for each case in observation table shown in table 7.1

4) Change the reset pin from high to low and observe the change in the

output of the circuit.

TESTING OF VARIATION IN BUZZER SOUND WITH CHANGE IN

DISTANCE OF THE REFLECTOR:

1) Keep supply voltage at its nominal value.

2) Observe the output variation of buzzer with reflector door closed by

varying the potentiometer. Observe the sensitivity of the circuit.

3) Keep the potentiometer fixed to its maximum position and gradually

increase the distance between the reflector and the sensor and find the

distance at which alarm is obtained.

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4) Now by keeping the potentiometer at different resistance values note

the distance at which alarm is obtained.

7.2 Results

WAVE-FORM OBSERVATION

Sr.

No.PIN NO

TYPE OF WAVE-

FORMINFERENCE

1.

AT

PIN NO 3

OF IC 555

Square-wave of voltage

+8v, -8v

Operation of OP-AMP in saturation region

alternatively

Table 7-2 Astable multivibrator output

DISTANCE OF REFLECTOR Vs POTENTIOMETER

Sr. No. Potentiometer ValueDistance of reflector at which

buzzer is obtained

1. 1MΩ

2. 800kΩ

3. 500kΩ

Table 7-3 Reflector distance vs Potentiometer resistance

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8. TIME AND COST

ANALYSIS

8.1 Time Analysis

SR. NO. TASK

TIME

REQUIRED

(IN WEEKS)

1 Selection of project 1

2 Study of fundamental theory 2

3Design of overall circuitry and component selection and

purchasing components1

4Testing of individual sections (on GP Board) and making

necessary modifications2

5Integrated testing of the project (on GP Board) and

making necessary modifications1

6 Assembling and testing of the project on final GP Board 1

7 Writing Project report 1

8 Computerization of the report ( including figures) 1

Total Time Required in Weeks 10

Table 8-4 TIME ANALYSIS

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8.2 Cost Analysis

SR. NO. WORK / COMPONENTCOST

Rs.

1 IC 555 & LM 393 (4 each) 40

2 RESISTORS 10

3 CAPACITORS 15

4 CNY 70 (Two) 160

5 BREAD BOARD 70

6 GENERAL PURPOSE PRINTED CIRCUIT BOARD 40

7 BUZZER, SOLDERING WIRE AND OTHER COMPONENTS 100

8PROJECT REPORT DATA ENTRY, PRINTING , XEROXING

AND BINDING CHARGES600

TOTAL COST OF THE PROJECT 700

Table 8-5 COST ANALYSIS

Page | 37


9. CONCLUSION AND FUTURE

SCOPE

9.1 Conclusion

From the project work, following points can be concluded.

1. It fulfills all the requirements for its application.

2. The buzzer responds to the changes of the distance between the reflector and the optical

sensor.

3. Changing the duty-cycle of the pulse to a ratio of 2:1 improves the audibility of the circuit.

9.2 Applications

The project can be used as:

1. Fridge door alarm.

2. Car boot door alarm.

9.3 Future Modifications

Following are the possible future modifications in our project work.

1. The output values of the circuit are not that accurate. To improve the accuracy we can

model the same circuit using a microcontroller.

2. Programming the delay of the circuit becomes flexible by using a microcontroller or a

PIC.

Page | 38


APPENDIX

DATASHEETS

Page | 39

Documents

Reflection Light Barrier With Delay