autopal project report
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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
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CHAPTER 3
DIGITAL ALARM USING 8051
The circuit diagram of Digital Alarm using 8051 System is shown in Figure 1. This circuit
contains 8051 micro- controller 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.
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3.1 CIRCUIT DIAGRAM OF DIGITAL ALARM USING 8051 SYSTEM
Fig 3.1 Circuit diagram of Digital Alarm using 8051 System
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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
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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
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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
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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.
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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.
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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.
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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
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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.
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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
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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
Port 2 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 2 output buffers can
sink/source four TTL inputs. When 1s are written to Port 2 pins, they are pulled high by the
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
Port 3 is an 8-bit bidirectional I/O port with internal pull-ups. The Port 3 output buffers can
sink/source four TTL inputs. When 1s are written to Port 3 pins, they are pulled high by the
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'.
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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
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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.
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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.
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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
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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.
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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
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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.
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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
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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.
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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
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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.
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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
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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.
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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).
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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:
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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
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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
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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.
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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
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