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CHAPTER 2

COMPONENTS SPECIFICATIONS

Component Rating or IC no No. of Component

Micro- controller Atmel AT89C51 1

Seven Segment Common Cathode 4

Buzzer - 1

LED Yellow 5

Electrolyte

Capacitors10uF/50V 1

Ceramic Capacitor

33pF 2

105pF 2

Crystal Oscillator 11.0592 MHz 1

Diodes 1N4007 1

Resistors

10 K Ω 1

1.5 K Ω 28

Voltage Regulator 7805 1

Bread Board - 1

Battery 9 V 1

Battery Clip - 1

Table 2.1 Components detail



3

CHAPTER 3

DIGITAL ALARM USING 8051

The circuit diagram of Digital Alarm using 8051 System is shown in Figure 1. This circuit

contains 8051 microcontroller with its all basic components. Crystal oscillator is connected to

pin 18 and pin 19 for frequency oscillation of microcontroller. And two capacitors of ceramic

capacitor are connected in parallel with crystal oscillator as shown in figure 26.

Pin no. 31 of microcontroller is connected to power supply VCC. Pin no.9 i.e. reset pin of

microcontroller is connected to ground via a register as shown in figure 26. A capacitor is

connected in between the pin no. 9 and VCC. A reset switch is also connected in parallel with

this capacitor.

There are 4 seven segment common cathode is connected to micro controller which display the

time.



4

3.1 CIRCUIT DIAGRAM OF DIGITAL ALARM USING 8051 SYSTEM

Fig 3.1 Circuit diagram of Digital Alarm using 8051 System



5

3.2 CIRCUIT DESCRIPTION

Fig: 3.2 Pin configurations of 7805 and BC547

The circuit of the microcontroller-based clock. It comprises microcontroller AT89C2051 (IC1),

inverting buffer ULN2003 (IC2), real-time clock (RTC) DS1307 (IC3), regulator 7805 (IC4),

non-inverting source driver UDN2982 (IC5) and a few discrete components.

Microcontroller AT89C2051 is the heart of the clock. It is an 8-bit microcontroller with 2kB

Flash programmable and erasable read-only memory (PEROM), 128 bytes of RAM, 15

input/output (I/O) lines, two 16-bit timers/counters, a five-vector two-level interrupt architecture,

a full-duplex serial port, a precision analogue comparator, on-chip oscillator and clock circuitry.

Port pins P1.7 down through P1.1 of the microcontroller are pulled up with 10kΩ resistor

network RNW1 and connected to input pins 1 through 7 of inverting buffer IC2, respectively, to

provide segment data for the seven-segment display. The display shows the time as ‘hour

minute.’ Flashing of decimal point (dp) on DIS3 indicates the seconds. The decimal points for

DIS1 and DIS2 are not used here.

The selection of the four seven-segment displays is made by port pins P3.7, P3.4, P3.5 and P1.0

of the microcontroller. These pins drive the four non-inverting buffers of driver IC5 to provide

display-enable signal to the common-anode pin (either pin 3 or pin 8) of DIS1 through DIS4,

respectively. If



7

The display and alarm are con-trolled by microcontroller AT89C2051. Data is transferred

between microcontroller AT89C2051 and the RTC using two wires (which form the I2C bus),

one of which serves as the clock line (SCL) and the other as data line (SDA). The four

subroutines required for data transfer are the send-start condition, send-stop condition, read-a-

byte and write-a-byte. Using these subroutines, the time of the day can be written into internal

registers of the RTC at address locations 00H through 06H (refer the datasheet). The address of

the control register is 07H. If it is written with control word 10, a 1Hz square wave is available

from pin 7 of the RTC. The pulse output at pin 7 drives pin 5 (dp) of DIS3, which blinks every

second.

Fig 3.4 Component layout for the PCB

The RTC is driven by an external 32.768 kHz crystal. A 3V battery is connected at its pin 3 along

with 1μF capacitor for battery backup. Pins 5 and 6 are pulled up to 5V by resistors R5 and R4

and connected to pins P3.1 and 3.0 of the microcontroller, respectively, for serial communication

between the RTC and the microcontroller.

To derive the supply power for the circuit, the 230V, 50Hz AC mains is stepped down by

transformer X1 to deliver a secondary output of 9V, 500mA. The transformer’s output is rectified

by a full-wave bridge rectifier comprising diodes D1 through D4, filtered by capacitor C1 and



8

regulated by IC 7805 (IC4). Capacitor C2 bypasses the ripples present in the regulated output.

LED1 acts as the power indicator. Resistor R1 acts as the current-limiter for LED1.

An actual-size, single-side PCB for the microcontroller-based clock using DS1307 is shown in

Fig. 3.3 and its component layout in Fig. 3.4.

3.3 SETTING OF CURRENT TIME AND ALARM TIME

To set the alarm time, press switch S2 connected to pin P3.2 of the microcontroller and keep it

pressed until the display changes and reaches the required alarm time, say, 7:30. Now connect the

pole of SPDT switch S3 to Vcc momentarily (which makes pin P3.3 of the microcontroller high)

and bring it back to the initial position. Immediately, the alarm sounds for a minute. The alarm

time is thus set at 7:30.

To set the current time, keep switch S2 pressed until the time display reaches the current time.

Release it when the current time is set.

Once the time is set and the clock is working, there is no need to set the time again even after

switching off the circuit. This is because the RTC works off the 3V battery connected to its pin 3.

3.4 SOFTWARE

The source code is written in Assembly language and assembled using a cross-assembler

(ASM51). It is well-commented and easy to understand.

The program uses internal Timer 0 of the microcontroller for periodic data output to the LED

displays. Timer 0 is programmed as a 16-bit timer. The timer starts from F0FFH and overflows at

FFFFH. On every overflow, its interrupt function is enabled. The interrupt service routine

refreshes the display. For this, the minutes and hours data is read from the RTC and displayed on

the seven-segment display.

For setting the time when switch S2 is pressed, the time is incremented and stored into the RTC.

Set the alarm time by using switch S2 in combination with switch S3. The set time is stored in



9

the RTC in two RAM locations. Every time the clock-time changes, it is compared with the

stored alarm time value and if both are same, pin 7 of the microcontroller becomes high.

Transistor T1 conducts and piezo buzzer PZ1 sounds for a duration of one minute.



10

CHAPTER 4

POWER SUPPLY

4.1 BATTERY

Here we use 9V battery for supplying power followed by voltage regulator 7805. The most

common form of 9 volt battery is commonly called the transistor battery, introduced for the early

transistor radios. This is a rectangular prism shape with rounded edges and a polarized snap

connector at the top. This type is commonly used in pocket radios, smoke detectors, carbon

monoxide detectors, guitar effect units, and radio-controlled vehicle controllers.

Fig 4.1 Battery 9 Volt

They are also used as backup power to keep the time in certain electronic clocks. This format is

commonly available in primary carbon-zinc and alkaline chemistry, in primary lithium iron

disulfide, and in rechargeable form in nickel-cadmium, nickel-metal hydride and lithium-ion.

Mercury oxide batteries in this form have not been manufactured in many years due to their

mercury content.



11

Most 9 volt alkaline batteries are constructed of six individual 1.5V LR61 cells enclosed in a

wrapper. These cells are slightly smaller than LR8D425 AAAA cells and can be used in their

place for some devices, even though they are 3.5 mm shorter. Carbon-zinc types are made with

six flat cells in a stack, enclosed in a moisture-resistant wrapper to prevent drying.

4.2 CONNECTORS

The battery has both terminals in a snap connector on one end. The smaller circular (male)

terminal is positive, and the larger hexagonal or octagonal (female) terminal is the negative

contact. The connectors on the battery are the same as on the connector itself; the smaller one

connects to the larger one and vice versa. The same snap style connector is used on other battery

types in the Power Pack (PP) series. Battery polarization is normally obvious since mechanical

connection is usually only possible in one configuration. The clips on the 9 volt battery can be

used to connect several nine-volt batteries in series to create higher voltage.

4.3 REGULATOR

Fig 4.2 Voltage Regulator

Voltage regulator ICs are available with fixed (typically 5, 12 and 15V) or variable output

voltages. They are also rated by the maximum current they can pass. Negative voltage regulators

are available, mainly for use in dual supplies. Most regulators include some automatic protection

from excessive current ('overload protection') and overheating ('thermal protection').

Many of the fixed voltage regulator ICs has 3 leads and look like power transistors, such as the

7805 +5V 1A regulator shown on the right. They include a hole for attaching a heat sink if

necessary.

http://en.wikipedia.org/wiki/Battery_terminals

http://en.wikipedia.org/wiki/Power_Pack_%28battery_series%29

http://en.wikipedia.org/wiki/Power_Pack_%28battery_series%29

http://en.wikipedia.org/wiki/Battery_terminals



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4.4 POWER SUPPLY

Since in our circuit we need 5 V, thus we use a 9 V battery followed by Voltage regulator 7805.

The battery supplies 9 V and converts to 5 V by regulator which passes to the rest of circuit.



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CHAPTER 5

MICROCONTROLLER AT89C52 (8051 Family)

5.1 INTRODUCTION

A microcontroller AT89C52 (also microcomputer, MCU or µC and it is in family of 8051

controller) is a small computer on a single integrated circuit consisting internally of a relatively

simple CPU, clock, timers, I/O ports, and memory. There is a program memory in the form of

NOR flash or OTP ROM is also often included on chip, as well as a typically small amount of

RAM. Microcontrollers are designed for small or dedicated applications. Thus, in contrast to the

microprocessors used in personal computers and other high-performance or general purpose

applications, simplicity is emphasized. Some microcontrollers may use 4-bit words and operate

at clock rate frequencies as low as 4 KHz, as this is adequate for many typical applications,

enabling low power consumption (milliwatts or microwatts). They will generally have the ability

to retain functionality while waiting for an event such as a button press or other interrupt; power

consumption while sleeping (CPU clock and most peripherals off) may be just nano watts,

making many of them well suited for long lasting battery applications. Other microcontrollers

may serve performance-critical roles, where they may need to act more like a digital signal

processor (DSP), with higher clock speeds and power consumption.

Microcontrollers are used in automatically controlled products and devices, such as automobile

engine control systems, remote controls, office machines, appliances, power tools, and toys. By

reducing the size and cost compared to a design that uses a separate microprocessor, memory,

and input/output devices, microcontrollers make it economical to digitally control even more

devices and processes. Mixed signal microcontrollers are common, integrating analog

components needed to control non-digital electronic systems.

5.2 FEATURES

Compatible with MCS-51® Products

8K Bytes of In-System Programmable (ISP) Flash Memory – Endurance: 1000 Write/Erase

Cycles

http://en.wikipedia.org/wiki/Integrated_circuit

http://en.wikipedia.org/wiki/Crystal_oscillator

http://en.wikipedia.org/wiki/Watchdog_timer

http://en.wikipedia.org/wiki/NOR_flash

http://en.wikipedia.org/wiki/Programmable_read-only_memory

http://en.wikipedia.org/wiki/Microprocessor

http://en.wikipedia.org/wiki/Personal_computer

http://en.wikipedia.org/wiki/Clock_rate

http://en.wikipedia.org/wiki/Digital_signal_processor




http://en.wikipedia.org/wiki/Clock_rate

http://en.wikipedia.org/wiki/Personal_computer

http://en.wikipedia.org/wiki/Microprocessor

http://en.wikipedia.org/wiki/Programmable_read-only_memory

http://en.wikipedia.org/wiki/NOR_flash

http://en.wikipedia.org/wiki/Watchdog_timer

http://en.wikipedia.org/wiki/Crystal_oscillator

http://en.wikipedia.org/wiki/Integrated_circuit



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4.0V to 5.5V Operating Range

Fully Static Operation: 0 Hz to 33 MHz

Three-level Program Memory Lock

256 x 8-bit Internal RAM

32 Programmable I/O Lines

Three 16-bit Timer/Counters

Eight Interrupt Sources

Full Duplex UART Serial Channel

Low-power Idle and Power-down Modes

Interrupt Recovery from Power-down Mode

Watchdog Timer

Dual Data Pointer

Power-off Flag

5.3 DESCRIPTION

The AT89S52 is a low-power, high-performance CMOS 8-bit microcontroller with 8K bytes of

in-system programmable Flash memory. The device is manufactured using Atmel’s high-density

non-volatile memory technology and is compatible with the industry- standard 80C51 instruction

set and pin out. The on-chip Flash allows the program memory to be reprogrammed in-system or

by a conventional non-volatile memory programmer. By combining a versatile 8-bit CPU with

in-system programmable Flash on a monolithic chip, the Atmel AT89S52 is a powerful

microcontroller which provides a highly-flexible and cost-effective solution to many embedded

control applications. The AT89S52 provides the following standard features: 8K bytes of Flash,

256 bytes of RAM, 32 I/O lines, Watchdog timer, two data pointers, three 16-bit timer/counters,

a six-vector two-level interrupt architecture, a full duplex serial port, on-chip oscillator, and clock

circuitry. In addition, the AT89S52 is designed with static logic for operation down to zero

frequency and supports two software selectable power saving modes. The Idle Mode stops the

CPU while allowing the RAM, timer/counters, serial port, and interrupt system to continue

functioning. The Power-down mode saves the RAM contents but freezes the oscillator, disabling

all other chip functions until the next interrupt or hardware reset.



15

Fig 5.1 Block Diagram of 8051 Microcontroller



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5.4 PIN CONFIGURATIONS OF 8052

Fig 5.2 Pin Configuration of 8052 Microcontroller

5.4.1. PIN DESCRIPTION

VCC

Vcc is Supply voltage which is 5V for 8051 microcontroller

GND

Pin no. 20 is connected to ground.

Port 0

Port 0 is an 8-bit open drain bidirectional I/O port. As an output port, each pin can sink eight

TTL inputs. When 1s are written to port 0 pins, the pins can be used as high impedance inputs.

Port 0 can also be configured to be the multiplexed low order address/data bus during accesses to

external program and data memory. In this mode, P0 has internal pull-ups. Port 0 also receives



17

the code bytes during Flash programming and outputs the code bytes during program

verification. External pull-ups are required during program verification.

Port 1

Port 1 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 1 output buffers can

sink/source four TTL inputs. When 1s are written to Port 1 pins, they are pulled high by the

internal pull-ups and can be used as inputs. As inputs, Port 1 pins that are externally being pulled

low will source current (IIL) because of the internal pull-ups. In addition, P1.0 and P1.1 can be

configured to be the timer/counter 2 external count input (P1.0/T2) and the timer/counter 2

trigger input (P1.1/T2EX), respectively, as shown in the following table. Port 1 also receives the

low-order address bytes during Flash programming and verification.

Table 4.1 Port 1

Port 2



internal pull-ups and can be used as inputs. As inputs, Port 2 pins that are externally being pulled

low will source current (IIL) because of the internal pull-ups. Port 2 emits the high-order address

byte during fetches from external program memory and during accesses to external data memory

that uses 16-bit addresses (MOVX @ DPTR). In this application, Port 2 uses strong internal pull-

ups when emitting 1s. During accesses to external data

Memory that uses 8-bit addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special

Function Register. Port 2 also receives the high-order address bits and some control signals

during Flash programming and verification.



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Port 3



internal pull-ups and can be used as inputs.

As inputs, Port 3 pins that are externally being pulled low will source current (IIL) because of the

pull-ups. Port 3 also serves the functions of various special features of the AT89S52, as shown in

the following table. Port 3 also receives some control signals for Flash programming and

verification.

Table 4.2 Port 3

RST

Reset input. A high on this pin for two machine cycles while the oscillator is running resets the

device. This pin drives High for 96 oscillator periods after the Watchdog times out. The DISRTO

bit in SFR AUXR (address 8EH) can be used to disable this feature. In the default state of bit

DISRTO, the RESET HIGH out feature is enabled.

ALE/PROG

Address Latch Enable (ALE) is an output pulse for latching the low byte of the address during

accesses to external memory. This pin is also the program pulse input (PROG) during Flash

programming. In normal operation, ALE is emitted at a constant rate of 1/6 the oscillator

frequency and may be used for external timing or clocking purposes. Note, however, that one

ALE pulse is skipped during each access to external data memory.

If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH. With the bit set,

ALE is active only during a MOVX or MOVC instruction. Otherwise, the pin is



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PSEN

Program Store Enable (PSEN) is the read strobe to external program memory. When the

AT89S52 is executing code from external program memory, PSEN is activated twice each

machine cycle, except that two PSEN activations are skipped during each access to external data

memory.

EA/VPP

External Access Enable (EA) must be strapped to GND in order to enable the device to fetch

code from external program memory locations starting at 0000H up to FFFFH. Note, however,

that if lock bit 1 is programmed, EA will be internally latched on reset. EA should be strapped to

VCC for internal program executions. This pin also receives the 12-volt programming enable

voltage (VPP) during Flash programming.

XTAL1

Input to the inverting oscillator amplifier and input to the internal clock operating circuit.

XTAL2

Output from the inverting oscillator amplifier

OSCILLATOR CHARACTERISTICS

XTAL1 and XTAL2 are the input and output, respectively, of an inverting amplifier which can

be configured for use as an on-chip oscillator, as shown in Figure 10. Either a quartz crystal or

ceramic resonator may be used. To drive the device from an external clock source, XTAL2

should be left unconnected while XTAL1 is driven as shown in Figure 11.

Note: C1, C2 = 30 pF ± 10 pF for Crystals

= 40 pF ± 10 pF for Ceramic Resonators

Fig 5.3 Crystal Oscillator Connection



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CHAPTER 6

SEVEN SEGMENT

The 14.2 mm (0.56 inch) LED seven segment displays are designed for viewing distances up to 7

metres (23 feet). These devices use an industry standard size package and pinout. Both the

numeric and ±1 overflow devices feature a right hand decimal point. All devices are available as

either common anode or common cathode. A seven-segment display (SSD), or seven-segment

indicator, is a form of electronic display device for displaying decimal numerals that is an

alternative to the more complex dot matrix displays.

Seven-segment displays are widely used in digital clocks, electronic meters, and other electronic

devices for displaying numerical information.

Fig 6.1 Seven Segment

The seven elements of the display can be lit in different combinations to represent the arabic

numerals. Often the seven segments are arranged in an oblique (slanted) arrangement, which aids

readability. In most applications, the seven segments are of nearly uniform shape and size

(usually elongated hexagons, though trapezoids and rectangles can also be used), though in the

case of adding machines, the vertical segments are longer and more oddly shaped at the ends in

an effort to further enhance readability.

The numerals 6, 7 and 9 may be represented by two or more different glyphs on seven-segment

displays, with or without a 'tail'.



21

The seven segments are arranged as a rectangle of two vertical segments on each side with one

horizontal segment on the top, middle, and bottom. Additionally, the seventh segment bisects the

rectangle horizontally. There are also fourteen-segment displays and sixteen-segment displays

(for full alphanumerics); however, these have mostly been replaced by dot matrix displays.

The segments of a 7-segment display are referred to by the letters A to G, where the optional DP

decimal point (an "eighth segment") is used for the display of non-integer numbers.

6.1 FEATURES

Industry Standard Size

Industry Standard Pinout15.24 mm (0.6 in.) DIP Leads on 2.54 mm (0.1 in.) Centers

Choice of Colors

AlGaAs Red, High Efficiency Red, Yellow, Green

Excellent Appearance

Evenly Lighted Segments

Mitered Corners on Segments

Gray Package Gives Optimum Contrast

±50° Viewing Angle

Design Flexibility

Common Anode or Common Cathode

Single and Dual Digits

Right Hand Decimal Point

±1. Overflow Character

Categorized for Luminous Intensity

Yellow and Green Categorized for Color

Use of Like Categories Yields a Uniform Display

High Light Output

High Peak Current

Excellent for Long Digit String Multiplexing

Intensity and Color Selection Option

See Intensity and Color Selected Displays Data Sheet



22

6.2 CONTRAST ENHANCEMENT

The objective of contrast enhancement is to provide good display readability in the end use

ambient light. The concept is to employ both luminance and chrominance contrast techniques to

enhance the readability. This is accomplished by having the OFF dots blend into the display

background and the ON dots stand out vividly against this same background. Therefore, these

display devices are assembled with a gray package and matching encapsulating epoxy in the dots.



23

CHAPTER 7

BUZZER

A buzzer or beeper is an audio signalling device, which may be mechanical, electromechanical,

or piezoelectric. Typical uses of buzzers and beepers include alarm devices, timers and

confirmation of user input such as a mouse click or keystroke.

Fig 7.1 Buzzer

7.1 FEATURES

The PS series are high-performance buzzers that employ unimorph piezoelectric elements

and are designed for easy incorporation into various circuits.

They feature extremely low power consumption in comparison to electromagnetic units.



24

Because these buzzers are designed for external excitation, the same part can serve as both a

musical tone oscillator and a buzzer.

They can be used with automated inserters. Moisture-resistant models are also available.

The lead wire type (PS1550L40N) with both-sided adhesive tape installed easily is prepared.

7.2 SOUND MEASURING METHOD

Fig 7.2 Sound Measuring Method

7.3 SPECIFICATION

Table 7.1 Specification



25

CHAPTER 8

LED

Fig 8.1 Light Emitting Diode

A light-emitting diode (LED) is a semiconductor light source. LEDs are used as indicator lamps

in many devices and are increasingly used for other lighting. Appearing as practical electronic

components in 1962, early LEDs emitted low-intensity red light, but modern versions are

available across the visible, ultraviolet, and infrared wavelengths, with very high brightness.

8.1 Internal Description of LED

When a light-emitting diode is forward-biased (switched on), electrons are able to recombine

with electron holes within the device, releasing energy in the form of photons. This effect is

called electroluminescence and the color of the light (corresponding to the energy of the photon)

is determined by the energy gap of the semiconductor. An LED is often small in area (less than 1

mm2), and integrated optical components may be used to shape its radiation pattern.



26

Fig 8.2 Internal description of LED

LEDs present many advantages over incandescent light sources including lower energy

consumption, longer lifetime, improved physical robustness, smaller size, and faster switching.

LEDs powerful enough for room lighting are relatively expensive and require more precise

current and heat management than compact fluorescent lamp sources of comparable output.

Fig 8.3 Electronic Symbol of LED



27

CHAPTER 9

CAPACITOR

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

to store energy 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 separated by a thin layer of insulating film. Capacitors are

widely used as parts of electrical circuits in many common electrical devices.

Fig 9.1 Capacitors

When there is a potential difference (voltage) across the conductors, a static 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, measured in farads.This is the ratio of the electric charge on each conductor to the potential difference between

them. The capacitance is greatest when there is a narrow separation between large areas of

conductor, hence capacitor conductors are often called "plates," referring to an early means of

construction. In practice, the dielectric between the plates passes a small amount of leakage

current and also has an electric field strength limit, resulting in a breakdown voltage, while the

conductors and leads introduce an undesired inductance and resistance.



28

Fig 9.2 Varieties of Capacitors

Practical capacitors are available commercially in many different forms. The type of internal

dielectric, the structure of the plates and the device packaging all strongly affect the

characteristics of the capacitor, and its applications.

Capacitors are widely used in electronic circuits for blocking direct current while allowing

alternating current to pass, in filter networks, for smoothing the output of power supplies, in the



29

resonant circuits that tune radios to particular frequencies, in electric power transmission systems

for stabilizing voltage and power flow, and for many other purposes.

9.1 Theory of Operation

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.

Fig 9.3 Theory of Operation of Capacitor

A capacitor is assumed to be self-contained and isolated, with no net electric charge and no

influence from any external electric field. The conductors thus hold equal and opposite charges

on their facing surfaces, and the dielectric develops an electric field. In SI units, a capacitance of

one farad means that one coulomb of charge on each conductor causes a voltage of one volt

across the device.

The capacitor is a reasonably general model for electric fields within electric circuits. An ideal

capacitor is wholly characterized by a constant capacitance C, defined as the ratio of charge ±Q

on each conductor to the voltage V between them.



30

Sometimes charge build-up affects the capacitor mechanically, causing its capacitance to vary. In

this case, capacitance is defined in terms of incremental changes:

9.2 Energy of Electric Field

Work must be done by an external influence to "move" charge between the conductors in a

capacitor. When the external influence is removed the charge separation persists in the electric

field and energy is stored to be released when the charge is allowed to return to its equilibrium

position. The work done in establishing the electric field, and hence the amount of energy stored,

is given by:

9.3 Current-Voltage Relation

The current i(t) through any component in an electric circuit is defined as the rate of flow of a

charge q(t) passing through it, but actual charges, electrons, cannot pass through the dielectric

layer of a capacitor, rather an electron accumulates on the negative plate for each one that leaves

the positive plate, resulting in an electron depletion and consequent positive charge on one

electrode that is equal and opposite to the accumulated negative charge on the other.

Thus the charge on the electrodes is equal to the integral of the current as well as proportional to

the voltage as discussed above. As with any anti-derivative, a constant of integration is added to

represent the initial voltage v (t0). This is the integral form of the capacitor equation,

Taking the derivative of this, and multiplying by C, yields the derivative form



31

The dual of the capacitor is the inductor, which stores energy in a magnetic field rather than an

electric field. Its current-voltage relation is obtained by exchanging current and voltage in the

capacitor equations and replacing C with the inductance L.



32

CHAPTER 10

RESISTOR

A resistor is a passive two-terminal electrical component that implements electrical resistance as

a circuit element

Fig 10.1 Resistors

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 R is the resistance of the conductor in units

of ohms. The ratio of the voltage applied across a resistor's terminals to the intensity of current in

the circuit 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



33

as resistance wire (wire made of a high-resistivity alloy, such as nickel-chrome). Resistors are

also implemented within integrated circuits, particularly analog devices, and can also be

integrated into hybrid and printed circuits.

The electrical functionality of a resistor is specified by its resistance: common commercial

resistors are manufactured over a range of more than nine orders of magnitude. When specifying

that resistance in an electronic design, the required precision of the resistance may require

attention to the manufacturing tolerance of the chosen resistor, according to its specific

application. The temperature coefficient of the resistance may also be of concern in some

precision applications. Practical resistors are also specified as having a maximum power rating

which must exceed the anticipated power dissipation of that resistor in a particular circuit: this is

mainly of concern in power electronics applications. Resistors with higher power ratings are

physically larger and may require heat sinks. In a high-voltage circuit, attention must sometimes

be paid to the rated maximum working voltage of the resistor.

Practical resistors have a series inductance and a small parallel capacitance; these specifications

can be important in high-frequency applications. In a low-noise amplifier or pre-amp, the noise

characteristics of a resistor may be an issue. The unwanted inductance, excess noise, and

temperature coefficient are mainly dependent on the technology used in manufacturing the

resistor.

10.1 ELECTRONIC SYMBOLS AND NOTATION

The symbol used for a resistor in a circuit diagram varies from standard to standard and country

to country. Two typical symbols are as follows.



34

Fig 10.2 Electronic Symbols

10.2 THEORY OF OPERATION

Ohm's law

The behaviour of an ideal resistor is dictated by the relationship specified by Ohm's law:

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

constant of proportionality is the resistance (R). Equivalently, Ohm's law can be stated:

This formulation states that the current (I) is proportional to the voltage (V) and inversely

proportional to the resistance (R).



35

SERIES AND PARALLEL RESISTORS

In a series configuration, the current through all of the resistors is the same, but the voltage

across each resistor will be in proportion to its resistance. The potential difference (voltage) seen

across the network is the sum of those voltages, thus the total resistance can be found as the sum

of those resistances:

Resistors in a parallel configuration are each subject to the same potential difference (voltage),

however the currents through them add. The conductance of the resistors then add to determine

the conductance of the network. Thus the equivalent resistance (Req) of the network can be

computed:

Power Dissipation

The power P dissipated by a resistor (or the equivalent resistance of a resistor network) is

calculated as

The first form is a restatement of Joule's first law. Using Ohm's law, the two other forms can be

derived.

The total amount of heat energy released over a period of time can be determined from the

integral of the power over that period of time:

http://en.wikipedia.org/wiki/File:Resistors_in_series.svg







36

CHAPTER 11

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.

Fig 11.1 Switches

The momentary push-button switch is a type of biased switch. The most common type is a "push-

to-make" (or normally-open or NO) switch, which makes contact when the button is pressed and

breaks when the button is released. Each key of a computer keyboard, for example, is a normally-

open "push-to-make" switch. A "push-to-break" (or normally-closed or NC) switch, on the other

hand, breaks contact when the button is pressed and makes contact when it is released. An

example of a push-to-break switch is a button used to release a door held open by an



38

CHAPTER 12

LEARNINGS AND OUTCOMES

We have learned that Microcontroller AT89C2051 is the heart of the clock. It is an 8-bit

microcontroller with 2 kB Flash programmable and erasable read-only memory (PEROM), 128

bytes of RAM, 15 input/output (I/O) lines, two 16-bit timers/counters, a five-vector two-level

interrupt architecture, a full-duplex serial port, a precision analogue comparator, on-chip

oscillator and clock circuitry. Once the time is set and the clock is working, there is no need to

set the time again even after switching off the circuit.

We have learned about the Assembly language

Uses of a cross-assembler (ASM51).

It is well-commented and easy to understand

It gives the output accurately

A highly portable cost-effective multifunctional system has been made

Its accuracy is high



39

Conclusion

Micro-controller based Digital Clock Alarm was our Minor Project. It was beneficial for us both

in theoretical and practical knowledge. It improved our knowledge about languages used in the

Micro-controller 8051. These devices provides best accurate results. In the proposed design, a

simple, portable cost-effective multifunctional system has been developed and implemented to

show the time. Though simple hardware is used, its accuracy is high.



References

[1.] http://www.engineersgarage.com/microcontroller/8051projects/LCD-digital-alarm-clock-

AT89C51-circuit

[2.] www.electronics.howstuffworks.com

[3.] http://www.electronicsforu.com/

[4.] http://www.8051projects.info/threads/microcontroller-based-digital-clock-with-alarm.541/

[5.] http://electronicsforu.com/electronicsforu

http://www.engineersgarage.com/microcontroller/8051projects/LCD-digital-alarm-clock-AT89C51-circuit




http://www.electronics.howstuffworks.com/



http://www.electronicsforu.com/



http://www.8051projects.info/threads/microcontroller-based-digital-clock-with-alarm.541/



http://electronicsforu.com/electronicsforu









autopal project report

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