Chapter - Copy

CHAPTER-1

OFFICE MONITORING SYSTEM

1.1 DESCRIPTION

The “Office Monitoring System” consists of a voltage regulator (7805), eight-input priority

encoder (CD4532), shift register (74LS96), triple three-input OR gate (CD4075), BCD to seven

segment decoder (74LS47), common anode seven segment display (LTS542), melody generator

(UM66), and a speaker along with some discrete components.

The block diagram is as follows,

Fig.1.1 Block Diagram Of Office Monitoring System

The circuit can be divided into four sections. They are:

Power Supply Section

Input Logging Section

Register and Control Section

Display and Melody Section

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POWER SUPPLY

SECTION

INPUT LOGGING SECTION

REGISTER AND

CONTROL SECTION

DISPLAY SECTION

MELODY SECTION

POWER SUPPLY SECTION: The circuit requires a 5V power supply. Hence to drive the power

supply for the circuit a 9V battery with a voltage regulator 7805 is used. The IC 7805 is used to

regulate the 9V supply to the 5V since it is a 5V voltage regulator. The regulated 5V obtained is

used to power the circuit.

INPUT LOGGING SECTION: Switches S1 through S7 are interfaced as input to the system

through IC 4532. For loading the input data through switches to the IC2, enable interrupt (EI)

pin5 of IC2 must be high.

REGISTER AND CONTROL SECTION: It is used to store the binary output of the encoder until

it is reset. To reset the data stored on the shift register, press reset switch S8 momentarily. For

controlling the input data, a three-input OR gate IC CD4075 is used. The high output of IC4 is

used for switching transistors T1 and T3. Transistor T3 is used to control the display LTS542

(DIS1) and transistor T1 is used to latch input data by keeping pin 5 of IC2 LOW.

DISPLAY AND MELODY SECTION: It is built around decoder driver 74LS47, a common anode

seven-segment display LTS542 and melody generator IC UM66. DIS1 is driven by IC5. The

input of a particular location is shown on DIS1. IC6 and transistor T2 are used to drive the loud-

speaker. The audio output is obtained from the loud-speaker when we press any switch from S1

through S7.

1.2 WORKING

The working of the circuit is simple. When any of the seven callers presses the switch (S1

through S7), respective binary code is generated at the output of IC2 which is further given to

IC3. These binary codes at data pins 2, 3 and 4 of IC3 ensure that at least one of its output pins

13, 14 or 15 is high. This makes the output pin 6 of OR gate (N1) high, which performs three

tasks:

1. Provides power supply to seven-segment display DIS1 to display caller’s number

through transistor T3.

2. Blocks the acceptance of further input due to low voltage at EI pin 5 of encoder IC2,

as transistor T1 conducts.

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3. Provides input power supply to IC4 to produce sound to alert the attendant.

After the attendant responds and presses reset switch S8 momentarily, all the outputs IC2 go low.

This makes the output of OR gate IC4 low. This, in turn, results in cutting off the power supply

to the seven-segment display and melody generator IC6. The encoder IC2 is permitted to accept

next input through switches S1 trough S7 by providing high voltage to its EI pin 5.

The circuit diagram is as follows,

Fig.1.2 Circuit Diagram Of Office Monitoring System

1.3 APPLICATIONS

This system can be used in offices or hotels to call an attendant from seven different

locations. Hence the manual energy can be saved. In offices in order to call for an attendant this

system is used so that the attendant responds quickly and the work can be done without delay.

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1.4ADVANTAGES AND DISADVANTAGES

ADVANTAGES

There are some advantages for this system. They are:

With the help of this system the response of the attender is fast and exact to the

particular initializer.

The major advantage is there won’t be any misplacements occur because this system

is completely electronic.

The cost for this system is less when compared to other facilities regarding this field

like intercom.

The equipment required is also less as it requires only one system and the number of

switches increases if the number of locations increases.

DISADVANTAGES

Not only advantages there are some disadvantages to this system as following:

If the display and the melody generator are not working properly, then there won’t be

any indication for the attender. Hence care should be taken while choosing the

components to avoid such problems.

CHAPTER-2

4

POWER SUPPLY SECTION

This section mostly consists of a 9V battery and a 5V voltage regulator. The circuit

requires 5V hence the generated by a 9V battery is regulated to a 5V by using a 7805 Voltage

regulator. This 5V power is used for the circuit operation.

2.1 VOLTAGE REGULATOR (7805)

Voltage Regulator usually having three legs converts varying input voltage and produces

a constant regulated output voltage. They are available in a variety of outputs. It is an electrical

regulator designed to automatically maintain a constant voltage level. It may use an

electromechanical mechanism, or passive or active electronic components. Depending on the

design, it may be used to regulate one or more AC or DC voltages. The 78XX series of voltage

regulators are designed for positive input. And the 79XX series is designed for negative input.

Examples:

5V DC Regulator Name: LM7805 or MC7805

-5V DC Regulator Name: LM7905 or MC7905

6V DC Regulator Name: LM7806 or MC7806

-9V DC Regulator Name: LM7909 or MC7909

Fig.2.1 Voltage Regulator IC

In this project we have used a LM7805 voltage regulator in order to have 5v constant dc

voltage supply. The LM78XX series typically has the ability to drive current up to 1A. For

application requirements up to 150mA, 78XX can be used. As mentioned above, the component

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has three legs: Input leg which can hold up to 36V DC common leg (GND) and an output leg

with the regulator’s voltage. For maximum voltage regulation, adding a capacitor in parallel

between the common leg and the output is usually recommended. Typically a 4.7uF capacitor is

use. This eliminates any high frequency AC voltage that could otherwise combine with the

output voltage.

2.1.1 TYPES OF REGULATORS

Linear regulators exist in two basic forms:

Series Regulators

Shunt Regulators

Series regulators are the more common form. The series regulator works by providing

path from the supply voltage to the load through a variable resistance (the main transistor is in

the “top half” of the voltage divider). The power dissipated by the regulating device is equal to

the power supply output current times the voltage drop in the regulating device.

The shunt regulator works by providing a path from the supply voltage to ground through

a variable resistance (the main transistor is in the “bottom half” of the voltage divider). The

current through the shunt regulator is diverted away from the load and flows uselessly to ground,

making this form even less efficient than the series regulator. It is, however, simpler, sometimes

consisting of just a voltage reference diode, and is used in very low-powered circuits where the

wasted current is too small to be of concern. This form is very common for voltage reference

circuits.

All linear regulators require an input voltage at least some minimum amount higher than

the desired output voltage. That minimum amount is called the “drop-out voltage”. For example,

a common regulator such as the 7805 has an output voltage of 5V, but can only maintain this if

the input voltage remains above about 7V. Its drop-out voltage is therefore 7V – 5V = 2V. When

the supply voltage is less than about 2V above the desired output voltage, as is the case in low-

voltage is low-voltage microprocessor power supplies, so-called low dropout regulators (LDOs)

must be used.

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2.1.1.1 SIMPLE ZENER REGULATOR

The image shows a simple zener voltage regulator. It is a shunt regulator and operates by

way of the zener diode’s action of maintaining a constant voltage itself when the current through

it is sufficient to take it into the zener breakdown region. The resistor R1 supplies the zener

current Iz as well as the load current IR2(R2 is the load). R1 can be calculated as

R1 = (VS - Vz)/(Iz + IR2)

Where, Vz is the zener voltage, and IR2 is the required load current.

Fig.2.2 Simple Zener Voltage Regulator

This regulator is used for very simple low power applications where the currents involved

are very small and the load is permanently connected across the zener diode (such as voltage

reference or voltage source circuits). Once R1 has been calculated, removing R2 will cause the

full load current (plus the zener current) to flow through the diode and may exceed the diode’s

maximum current rating thereby damaging it. The regulation of this circuit is also not very good

because the zener current (and hence the zener voltage) will vary depending on V s and inversely

depending on the load current.

2.1.1.2 SIMPLE SERIES VOLTAGE REGULATOR

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Adding an emitter follower stage to the simple zener regulator forms a simple series

voltage regulator and substantially improves the regulation of the circuit. Here, the load current

IR2 is supplied by the transistor whose base is now connected to the zener diode. Thus the

transistor’s base current (IB) forms the load current for the zener diode and is smaller than the

current through R2. This regulator is classified as “series” because the regulating element, viz.,

the transistor, appears in series with the load. R1 sets the zener current (IZ) and is determined as

R1 = (VS – VZ)/(IZ+K.IB)

Where, VZ is the zener voltage, IB is the transistor’s base current and K = 1.2 to 2 (to

ensure that R1 is low enough for adequate IB).

IB = IR2/hFE(min)

Where, IR2 is the required load current and is also the transistor’s emitter current (assumed

to be equal to the collector current) and hFE(min) is the minimum acceptable DC current gain for

the transistor.

Fig.2.3 Simple Series Voltage Regulator

This circuit has much better regulation than the simple zener regulator, since the base

current of the transistor forms a very light load on the zener, thereby minimizing variation in

zener voltage due to variation in the load. Note that the output voltage will always be about

0.65V less than the zener due to the transistor’s VBE drop. Although this circuit has good

regulation, it is still sensitive to the load and supply variation. It also does not have the capability

to be adjustable. Both these issues can be resolved by incorporating negative feedback circuitry

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into it. This regulator is often used as a “pre-regulator” in move advanced series voltage

regulator circuits.

7805 INTERCONNECTIONS

Fig.2.4 7805 Interconnections

2.1.2 ADVANTAGES AND DISADVANTAGES

ADVANTAGES

The 7805 series has several key advantages over many other voltage regulator circuits

which have resulted in its popularity:

7805 series ICs do not require any additional components to provide a constant, regulated

source of power, making them easy to use, as well as economical, and also efficient uses

in circuit board real estate. By contrast, most other voltage regulators require several

additional components to set the output voltage level, or to assist in the regulation

process. Some other designs (such as a switching power supply) can require not only a

large number of components but also substantial engineering expertise to implement

correctly as well.

78XX series ICs have built-in protection against a circuit drawing too much power. They

also have protection against overheating and short-circuits, making them quite robust in

most applications. In some cases, the current-limiting features of the 78XX devices can

provide protection not only for the 78XX itself, but also for other parts of the circuit it is

used in preventing other components from being damaged as well.

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DISADVANTAGES

The 78XX devices have a few drawbacks which can make them unsuitable or less

desirable for some applications:

The input voltage must always be higher than the output voltage by some minimum

amount (typically 2V). This can make these devices unsuitable for powering some

devices from certain types of power sources.

As they are based on a linear regulator design, the input current required is always the

same as the output current. As the input voltage must always be higher than the output

voltage, this means that the total power going into the 78XX will be more than the output

power provided. The extra input power is dissipated as heat. This means both that for

some applications an adequate heat sink must be provided, and also that a portion of the

input power is wasted during the process, rendering them less efficient than some other

types of power supplies. When the input voltage is significantly higher than the regulated

output voltage (for example, powering a 7805 using a 24 volt power source), this

inefficiency can be a significant issue.

Even in larger packages, 78XX integrated circuits cannot supply as much power as many

designs which use discrete components, and therefore are generally not appropriate for

applications which require more than a few amperes of current.

CHAPTER-3

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INPUT LOGGING SECTION

This section mostly consists of an encoder 4532. This encoder is used to generate a

binary output.

3.1 8-INPUT PRIORITY ENCODER (4532)

3.1.1 DESCRIPTION

The HCC4532B (extended temperature range) and HCF4532B (intermediate temperature

range) are monolithic integrated circuit, available in 16-lead dual in-line plastic or ceramic

package and plastic micro package.

The HCC/HCF4532B consists of combinational logic that encodes the highest priority

input to a 3-bit binary code. The eight inputs, I7 through I0 , each have an assigned priority. I7 is

the highest priority and I0 is the lowest. The priority encoder is inhibited when the chip-enable

input EI is low. When EI is high, the binary representation of the highest priority input appears

on output lines O2-O0, and the group select line GS is high to indicate that priority inputs are

present. The enable-out (EO) is high when no priority inputs are present. If anyone input is high,

EO is low and all cascaded lower-order stages are disabled.

Fig.3.1 Pin Diagram Of 4532

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In this project, 4532B is in usage with considering 7 inputs D1 through D7 of pins 11, 12,

13, 1, 2, 3, 4 and pins 6, 7, 9 as 3 outputs and 5th pin is the EI pin. Along with these pins 16 and 8

are also must as power supply and ground connections are must for operation of an IC

3.1.2 LOGICAL FUNCTIONING

The logical diagram is as follows,

Fig.3.2 Logic Diagram Of 4532

Truth Table:

Here, in the above truth table

H = High State(more positive voltage)

L = Low State(low positive voltage)

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X = State is immaterial

Logic Equations:

3.1.3 APPLICATIONS

The 8-input priority encoder is having some applications. The 4532 IC is also used to build the

following circuits:

0 to 9 key board encoder

16-level priority encoder

Digital to Analog converter

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CHAPTER-4

REGISTER AND CONTROL SECTION

This section mostly consists of a shift register 74LS96 and a 3-input OR gate (4075). The

shift register is used to store the binary output of the encoder until it is reset. For controlling the

input data, a three-input OR gate IC CD4075 is used

4.1 SHIFT REGISTER (74LS96)

There are several families of logic ICs numbered from 74XX00 onwards with letters

(XX) in the middle of the number to indicate the type of circuitry, e.g. 74LS00 and 74HC00. The

original family had no letters, e.g. 7400. The 74LS and 74HCT families require a 5V supply so

they are not convenient for battery operation.

The “74LS”(Low-power Schottky) family uses TTL(Transistor-Transistor Logic)

circuitry which is fast but requires more power than later families. The 74 series is often still

called the ‘TTL series’ even though the latest ICs do not use TTL. The “74HC” family has High-

speed CMOS circuitry, combining the speed of TTL with the very low power consumption of the

4000 series. They are CMOS ICs with the same pin arrangement as the older 74LS family. Note

that 74HC inputs cannot be reliably driven by 74LS outputs because the voltage ranges used for

logic 0 are not quite compatible, use 74HCT instead. The 74HCT family is a special version of

74HC with 74LS TTL compatible inputs so 74HCT can be safely mixed with 74LS in the same

system.

4.1.1 DESCRIPTION

The ’96 is a 5-bit shift register with both serial and parallel data entry. Since the ’96 has

the output of each stage available as well as D-type serial input and ones transfer inputs on each

stage, it can be used in 5-bit serial-to-parallel, serial-to-serial and some parallel-to-serial data

operations.The ’96 is five master/slave flip-flops connected to perform right shift. The flip-flops

change state on the LOW-to-HIGH transistion of the clock. The serial input is edge-triggered and

must be stable only one set-up time before the LOW-to-HIGH clock transistion.

The pin configuration is as follows,

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Fig.4.1 Pin Diagram Of 7496

In this project, 74LS96 is used with 2,3,4 pins as inputs and 13,14, 15 pins are outputs.

The 8th pin is the preset enable (PE) and the 16th pin is the clear. Along with these pins power

supply and ground are must, here 5th is the supply and 12 th pin is the ground.

4.1.2 LOGIC DIAGRAM

Each flip-flop has asynchronous set inputs, allowing them to be independently set HIGH.

The set inputs are controlled by a common active HIGH Preset Enable (PE) input. The PE input

is not buffered, and care must be taken not to overload the driving element. When the PE is

HIGH, a HIGH on the preset (A-E) inputs will set the associated flip-flops HIGH. A LOW on

the A-E inputs will cause “no change” in the appropriate flip-flops.

The asynchronous active LOW clear is buffered. When LOW, the clear overrides the

clock and clears the register if the PE is not active. The Preset inputs override the clear, forcing

the flip-flops HIGH if both are activated simultaneously. However, for predictable operation,

both signals sould not be deactivated simultaneously.

The logic diagram is as follows,

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Fig.4.2 Logic Diagram Of 74LS96

4.1.3 FEATURES

74LS family and its TTL characteristics are:

1. Supply to this chip must be in range 5V+0.25V. It must be very smooth, a regulated

supply is best.

2. In addition to the normal supply smoothing, a 0.1uF capacitor should be connected across

the supply near the IC to remove the ‘spikes’ generated as it switches state, one capacitor

is needee for every 4 ICs.

3. Inputs float high to logic 1 if unconnected, but do not rely on this in a permanent circuit

because the inputs may pick up electrical noise. 1mA must be drawn to hold inputs at

logic 0.

4. Outputs can sink up to 16mA, but they can source only about 2mA. To switch largaer

currents you can connect a transistor.

5. Fan-out: one output can drive up to 10 74LS inputs, but many more 74HCT inputs.

6. Gate propagation time: about 10ns for a signal to travel through a gate.

7. Frequency is up to about 35MHz.

8. Power consumption is a few Mw

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4.2 THREE INPUT OR GATE (CD4075)

4.2.1 DESCRIPTION

The CD4075 IC provides the positive triple 3-input OR function. The outputs are fully

buffered for highest noise immunity and pattern insensitivity of output impedance.

The pin configuration is as follows,

Fig.4.3 Pin Diagram Of CD4075

In this project, CD4075 IC is used with 3,4,5 pins as input pins and the 6 th pin as output

pin. Along with these pins the 14th and 7th pins are the must which are the power supply and

ground pins respectively.

The logic diagram of 3-input OR gate consists of a NOR gate followed by an inverter. It

is having three inputs and one output. The logic diagram is as follows,

Fig.4.4 Logic Diagram Of 3-Input OR Gate

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4.2.2 FEATURES

IC CD4075 is having the following features:

High-Voltage Types (20V Rating)

Medium speed operation: -tPHL, tPLH = 60ns at 10V

100% Tested for quiescent current at 20V

Maximum Input Current of 1uA at 18V over full package temperature range; 100nA at

18V and +250C

Standardized symmetrical output characteristics

Noise Margin (Over Full Package Temperature Range):

- 1V at VDD = 5V

- 2V at VDD = 10V

- 2.5V at VDD = 15V

5V, 10V and 15V Parametric Ratings

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CHAPTER-5

DISPLAY AND MELODY SECTION

This section mostly consists of a seven segment decoder, a seven-segment display and a

melody generator.

5.1 SEVEN SEGMENT DECODER (74LS47)

5.1.1 DESCRIPTION

The 74LS47 are Low Power Schottky BCD to 7-Segment Decoder consisting of NAND

gates, input buffers and seven AND-OR-INVERT gates. They offer active LOW, high sink

current outputs for driving indicators directly. Seven NAND gates and one driver are connected

in pairs to make BCD data and its complement available to the seven decoding AND-OR-

INVERT gates. The remaining NAND gate and three input buffers provide lamp test, blanking

input/ripple-blanking output and ripple-blanking input.

The circuits accept 4-bit binary-coded-decimal (BCD) and, depending on the state of the

auxiliary inputs, decodes this data to drive a 7-segment display indicator. The relative positive-

logic output levels, as well as conditions required at the auxiliary inputs, are shown in the truth

tables. Output configurations of the 74LS47 are designed to withstand the relatively high

voltages required for 7-segment indicators.

These outputs will withstand 15V with a maximum reverse current of 250uA. Indicator

segments requiring up to 24mA of current may be driven directly from the 74LS47 high

performance output transistors. Display patterns for BCD input counts above nine are unique

symbols to authenticate input conditions.

The 74LS47 incorporates automatic leading and/or trailing-edge zero-blanking control

(RBI and RBO). Lamp test(LT) may be performed at any time which the BI/RBO node is a

HIGH level. This device also contains an overriding blanking input (BI) which can be

used to contrel the lamp intensity by varying the frequency and duty cycle of the BI input signal

or to inhibit the outputs.

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Lamp Intensity Modulation Capability (BI/RBO)

Open Collector Outputs

Lamp Test Provision

Leading/Trailing Zero Suppression

Input Clamp Diodes Limit High-Speed Termination Effects

The pin configuration is as follows,

Fig.5.1 Pin Diagram Of 74LS47

In this project, 74LS47 IC is used with 7,1,2 as input pins where 9,10,11,12,13,14,15 pins

are the output pins. Other than these pins the 16th and 8th pins are must which are the supply and

ground pins respectively. As we are using only 3 inputs the other input pin i.e., 6 th pin is also

grounded.

5.1.2 FUNCTIONING

The 74LS47 decodes the input data in the pattern indicated in the truth table and the

segment identification illustration. If the input data is decimal zero, a LOW signal applied to the

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RBI blanks the display and causes a multi digit display. For example, by grounding the RBI of

the highest order decoder and connecting its BI/RBO to RBI of the next lowest order decoder,

etc., leading zeros will be suppressed. Similarly, by grounding RBI of the lowest order decoder

and connecting its BI/RBO to RBI of the next highest order decoder, etc., trailing zeros will be

suppressed.

Leading and trailing zeros can be suppressed simultaneously by using external gates, i.e.

by driving RBI of a intermediate decoder from an OR gate whose inputs are BI/RBO of the next

highest and lowest order decoders. BI/RBO also serves as an unconditional blanking input. The

internal NAND gate that generates the RBO signal has a resistive pull-up, as opposed to a totem

pole, and thus BI/RBO can be forced LOW by external means, using wired-collector logic. A

LOW signal thus applied to BI/RBO turns off all segment outputs. This blanking feature can be

used to control display intensity by varying the duty cycle of the blanking signal. A LOW signal

applied to LT turns on all segment outputs, provided that BI/RBO is not forced LOW.

The logic diagram is as follows,

Fig.5.2 Logic Diagram Of 74LS47

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NUMERICAL DESIGNATIONS-RESULTANT DISPLAYS

5.2 SEVEN-SEGMENT DISPLAY

5.2.1 DESCRIPTION

A seven segment display or seven segment indicator is a form of electronic display

device for displaying decimal numerals. A seven-segment display may have 7,8, or 9 leads

on the chip. Usually leads 8 and 9 are decimal points. The figure below is a typical

component and pin layout for a seven segment display.

Fig.5.3 Pin Diagram Of 7-Segment Display

The light emitting diodes in a seven-segment display are arranged in the figure below

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Fig.5.4 Diode Placement In 7-Segment Display

There are two types of displays available. They are:

Common Anode

Common Cathode

The wiring for a common anode is shown below,

Fig.5.5 Common Anode Internal Wiring

The wiring for a common cathode is shown below,

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Fig.5.6 Common Cathode Internal Wiring

Here in our project we are using common anode seven segment display.

5.2.2 APPLICATIONS

Seven-segment displays are having many applications as follows:

They are widely used in digital clocks, electronic meters, and other electronic devices to

display numerical information.

A seven-segment display illuminated by incandescent bulbs was used on a power-plant

boiler room signal panel.

5.3 MELODY GENERATOR (UM66)

5.3.1 DESCRIPTION

The UTC UM66TXXL series are CMOS LSI designed for using in door bell, telephone

and toy application. It is an on-chip ROM programmed for musical performance. Produced by

CMOS technology, the device results in very low power consumption. Since the UTC

UM66TXXL series include oscillatiom circuits a compact melody module can be constructed

with only a few additional components.

The pin configuration of UM66 is as follows,

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Fig.5.7 Pin Diagram Of UM66

The UM66 is a 3 pinned IC. In this the 1st pin is the output pin, 2nd pin is the input pin

where as the 3rd pin acts as common pin and given to the ground.

The melody generator gives beautiful tune through 4Ω or 8Ω speaker. This UM66 IC

looks like a transistor, but its CMOS type IC. So that reason it uses very less power. It has been

consist of a Read Only Memory (ROM). This is main part of tone generator and Music tone is

stored in there. Q1 transistor is use as an output amplifier. You can give dc power supply

between 1.5V to 4.5V, but don’t exceed 4.5V. Don’t connect directly low impedance speakers to

output pins of IC, it’s harmful to your IC. Use good quality PCB to build this circuit for best

performance.

Now, you can select your IC using this song list of UM66 IC.

IC No Song

UM66T05L Home sweet home

UM66T19L For Alice

UM66T32L Coo Coo Waltz

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5.3.2 FEATURES

The following are the features of an UM66 IC:

64-Note ROM memory.

1.5V-4,5V power supply and low power consumption.

Dynamic speaker can be driven with external NPN transistor.

OSC resistor hold mode.

Power on reset:melody begins from the first note.

Built in level hold mode.

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CHAPTER-6

ELECTRONIC COMPONENTS

An electronic component is a basic electronic element and may be available in a discrete

form having two or more electrical terminals. A component may be classified as active or

passive.

Passive components are ones which cannot introduce net energy into the circuit they are

connected to. They also cannot rely on a source of power except for what is available from the

AC circuit they are connected to. These components include two-terminal components such as

resistors, capacitors, inductors e.t.c.

Active components rely on a source of energy and are usually able to inject power into a

circuit although this is not part of the definition. This includes amplifying components such as

transistors, tunnel diodes e.t.c

The major electronic components we used in our project are speaker, diodes, transistors,

switches.

6.1 SPEAKER

A loudspeaker (or "speaker") is an electro acoustic transducer that produces sound in

response to an electrical audio signal input. Non-electrical loudspeakers were developed as

accessories to telephone systems, but electronic amplification by vacuum tube made

loudspeakers more generally useful. The most common form of loudspeaker uses a paper cone

supporting a voice coil electromagnet acting on a permanent magnet, but many other types exist.

Where accurate reproduction of sound is required, multiple loudspeakers may be used, each

reproducing a part of the audible frequency range. Miniature loudspeakers are found in devices

such as radio and TV receivers, and many forms of music players. Larger loudspeaker systems

are used for music, sound reinforcement in theatres and concerts, and in public address systems.

6.1.1 TYPES OF SPEAKERS

There are different types of speakers in usage. They are:

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Horn loudspeakers Piezoelectric speakers Magnetostrictive speakers Electrostatic loud speakers Ribbon and planar magnetic loudspeakers Bending wave loudspeakers Flat panel loudspeakers Plasma arc speakers Digital speakers

Speakers are divided into 3 categories based on frequency ranges. They are:

Full-range: A full-range driver is designed to have the widest frequency response possible. These drivers are small, typically 3 to 8 inches (7.6 to 20 cm) in diameter to permit reasonable high frequency response, and carefully designed to give low-distortion output at low frequencies, though with reduced maximum output level. Full-range drivers are most commonly heard in public address systems, in televisions, small radios, intercoms, some computer speakers, etc. In hi-fi speaker systems, the use of wide-range drive units can avoid undesirable interactions between multiple drivers caused by non-coincident driver location or crossover network issues

Mid-range: A mid-range speaker is a loudspeaker driver that reproduces middle frequencies.

Tweeter: A tweeter is a high-frequency driver that reproduces the highest frequencies in a speaker system. Many varieties of tweeter design exist, each with differing abilities with regard to frequency response, output fidelity, power handling, maximum output level, etc. Soft-dome tweeters are widely found in home stereo systems, and horn-loaded compression drivers are common in professional sound reinforcement.

In our project we used a round speaker which is of diameter 30mm, power 0.5w and 4 ohm impedance.

Fig.6.1 Speaker

6.1.2 FEATURES

The following are the features of a round speaker which we used in the project:

Its impedance is of 4 ohms. The related power is 0.5w.

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The shape of the speaker is round. Its diameter is 30mm. Its resonant frequency is around 1000+20%Hz.

6.2 DIODES

Diodes were the first semiconductor electronic devices. A diode is a type of two-terminal electronic component with nonlinear resistance and conductance (i.e., a nonlinear current-voltage characteristic), distinguishing it from components such as two-terminal linear resistors which obey Ohm’s law. A semiconductor diode, the most common type today, is a crystalline piece of semiconductor material connected to two electrical terminals.

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 value. This unidirectional behavior is called rectification, and is used to convert alternating current to direct current, these diodes are forms of rectifiers.

Fig.6.2 PN Junction Diode Structure

6.2.1 TYPES OF DIODES

There are different types of diodes. They are:

Junction diode Zener diode Tunnel diode Schottky diode Varactor diode DIAC (Diode A.C. Switch) TRIAC (Triode A.C. Switch) SCR Light emitting diode Photo diode

In our project we used a 1N4148 diode and a 3.1V zener diode.

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1N4148 Diode:

The 1N4148 diode is a fast, standard small signal silicon diode with high conductance

used in signal processing. The diode 1N4148 is very useful at high frequencies with a reverse

recovery time of no more than 4ns. This permits rectification and detection of radio frequency

signals very effectively, as long as their amplitude is above the forward conduction threshold of

silicon (around 0.7V) or the diode is biased.

Fig.6.3 1N4148 Symbol

The following are the characteristics of a diode,

Fig.6.4 Characteristics Of A Diode

Zener diode

A Zener Diode is a special kind of diode which permits current to flow in the forward direction as normal, but will also allow it to flow in the reverse direction when the voltage is above a certain value - the breakdown voltage known as the Zener voltage.

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Fig.6.5 Zener Diode Symbol

The Zener voltage of a standard diode is high, but if a reverse current above that value is allowed to pass through it, the diode is permanently damaged. Zener diodes are designed so that their zener voltage is much lower. When a reverse current above the Zener voltage passes through a Zener diode, there is a controlled breakdown which does not damage the diode. The voltage drop across the Zener diode is equal to the Zener voltage of that diode.

Fig.6.6 VI-Characteristics Of Zener Diode

With a zener diode connected in the forward direction, it behaves exactly the same as a standard diode with current flowing through pretty much unrestricted. In the reverse direction however there is a very small leakage current between 0V and the Zener voltage - i.e. just a tiny amount of current is able to flow. Then, when the voltage reaches the breakdown voltage, suddenly current can flow freely through it.

Since the voltage dropped across a Zener Diode is a known and fixed value, Zener diodes are typically used to regulate the voltage.

6.2.2 APPLICATIONS

A diode can be used in several applications. Some of them are mentioned below:

A diode is used in a rectifier circuit. It rectifies an ac voltage, so that it can be smoothed and converted into a dc voltage.

A zener diode is used in a voltage regulator. It is connected in parallel to the load and is used to keep the output voltage of a circuit at a constant value.

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It is also used in the clamper circuits where it is used to add a dc voltage level to a signal.

6.2.3 SAFETY PRECAUTIONS

The following is a list of some of the special safety precautions that should be taken into consideration when working with diodes:

Never remove or insert a diode into a circuit with voltage applied. When testing a diode, ensure that the test voltage does not exceed the diode’s maximum

allowable voltage. Ensure a replacement diode into a circuit is in the correct direction.

6.3 TRANSISTOR (BC547)

A transistor is a semiconductor device used to amplify and switch electronic signals and

power. It is composed of a semiconductor material with at least three terminals for connection to

an external circuit. A voltage or current applied to one pair of the transistor's terminals changes

the current flowing through another pair of terminals. Because the controlled (output) power can

be much more than the controlling (input) power, a transistor can amplify a signal. The transistor

is the fundamental building block of modern electronic devices.

6.3.1 TYPES OF TRANSISTORS

There are different types of transistors. Some of them which are mostly used are mentioned

below:

1. Bipolar Junction Transistor

Hetero Junction Bipolar Transistor

Schottky Transistor

Avalanche Transistor

Darlington Transistor

Insulated Gate Bipolar Transistor

Photo Transistor

2. Field-Effect Transistors

Junction Field Effect Transistor (JFET)

Metal Oxide Semiconductor Field Effect Transistor (MOSFET)

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Inverted-T Field Effect Transistor (ITFET)

3. Diffusion transistor

4. Uni-Junction Transistors

In our project we used a BC547 transistor, which is a common transistor used in almost every

circuit. The pin diagram of transistor is as follows,

Fig.6.7 Pin Diagram Of A Transistor

6.3.2 APPLICATIONS

Transitors are having several applications as they play a major role in the operation of a

particular circuits:

In some cases transistors acts as a switch

It is also used as an amplifier

Transistors are used in receiver circuits

They are also used in regenerative circuits

6.4 SWITCH

In electronics, a switch is an electrical component that can break an electrical circuit, interrupting the current or diverting it from one conductor to another.

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The most familiar form of switch is a manually operated electromechanical device with one or more sets of electrical contacts, which are connected to external circuits. Each set of contacts can be in one of two states: either "closed" meaning the contacts are touching and electricity can flow between them, or "open", meaning the contacts are separated and the switch is non -conducting. The mechanism actuating the transition between these two states (open or closed) can be either a "toggle" (flip switch for continuous "on" or "off") or "momentary" (push-for "on" or push-for "off") type.

A switch may be directly manipulated by a human as a control signal to a system, such as a computer keyboard button, or to control power flow in a circuit, such as a light switch. Automatically operated switches can be used to control the motions of machines.

Switch is a component that can pass current or break the flow of current.

Switch- manually operated switch.

Electrical description: SPST, SPDT, DPST, DPDT, NPNT(general) Technology: slide switches, toggle switches, rocker switches, rotary switches,

pushbutton switches.

Keypad- array of pushbutton switches DIP switch- small array of switches for internal configuration settings Footswitch- foot-operated switch Knife switch- switch with unenclosed conductors Micro switch- mechanically activated switch with snap action Limit switch- mechanically activated switch to sense limit of motion Mercury switch- switch sensing tilt Centrifugal switch- switch sensing centrifugal force due to rate of rotation Relay- electrically operated switch Reed switch- magnetically activated switch Thermostat- thermally activated switch Humidistat- humidity activated switch Circuit breaker- switch opened in response to excessive current, a resettable fuse

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RESULTS

OFFICE MONITORING SYSTEM CIRCUIT

BEFORE PRESSING THE SWITCH

AFTER PRESSING THE SWITCH

OFFICE MONITORING SYSTEM

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CONCLUSION

Our project Office Monitoring System is a system which is of low cost and an easy way

to call an attendant from different locations. The equipment used is less and the circuit is also

less complex. So, the misplacements in the circuit can be easily rectified.

FUTURE SCOPE

By using this circuit, one can call an attendant from different locations. This is mostly

used in offices and hotels. In this circuit we used a melody generator to give an audio indication

through speaker and a seven-segment display to give a video indication of the particular location.

We can expand this circuit in future by using an LED instead of a seven-segment display. Using

the LED display we can display the name of the particular person who is calling the attendant

where as this seven-segment display displays only the number alloted to that particular location.

This case is mostly useful when the number of locations are increased and it will be easy to

identify by displaying the name.

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REFERENCES

www.datasheet4u.com

www.circuitstoday.com

www.freewebs.com

www.forum.allaboutcircuits.com

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