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CONTENTS
Page No
CHAPTER-1 MICROCONTROLLER 1
1.1 Architecture of Microcontroller 1
1.2 PIN description Of AT89C51 4
1.3 Memory Organization 13
CHAPTER-2 POWER SUPPLY 17
2.1 Step down transformer 172.2 Bridge Rectifier 19
2.3 Voltage Regulators 23
CHAPTER-3 RS232 25
CHAPTER-4 MAX232 28
CHAPTER-5 PROJECT DESCRIPTION 31
5.1. Block diagram 31
5.2. Description 31
5.3. Working 32
CONCLUSION 33
BIBLIOGRAPHY 34
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CHAPTER-1
MICROCONTROLLER
1.1 Architecture of Microcontroller:
Most microcontrollers today are based on the Harvard architecture, which clearly defined
the four basic components required for an embedded system. These include a CPU core, memory
for the program (ROM or Flash memory), memory for data (RAM), one or more timers
(customizable ones and watchdog timers), as well as I/O lines to communicate with external
peripherals and complementary resources all this in a single integrated circuit. Figure shows the
block diagram of a general microcontroller. A microcontroller differs from a general-purpose CPUchip in that the former generally is quite easy to make into a working computer, with a minimum
of external support chips. The idea is that the microcontroller is placed in the device to be
controlled, hooked up to power and any information it needs, and that's that.
A traditional microprocessor does not allow you to do this. It requires all of these additional
tasks to be handled by other chips. For example, a number of RAM or Flash memory chips must be
added. The amount of memory provided is more flexible in the traditional approach, but at least a
few external memory chips must be provided, which requires numerous connections to pass the
data back and forth to them.
For instance, a typical microcontroller will have a built in clock generator and a small
amount of RAM and ROM (or EPROM, EEPROM or Flash memory), meaning that to make it
work, all that is needed is the control software and a timing crystal (though some even have
internal RC clocks). Microcontrollers also usually have a variety of input/output devices, such as
analog-to-digital converters, timers, UARTs or specialized serial communications interfaces like
IC, Serial Peripheral Interface and Controller Area Network. Often these integrated devices can be
controlled by specialized processor instructions.
Originally, microcontrollers were only programmed in assembly language, or later in C code.
Recent microcontrollers integrated with on-chip debug circuitry accessed by In-circuit emulator via
JTAG enables a programmer to debug the software of an embedded system with a debugger.
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More recently, however, some microcontrollers have begun to include a built-in high-level
programming language interpreter for greater ease of use. BASIC is a common choice, and is used
in the popular BASIC Stamp MCUs.
Microcontrollers trade away speed and flexibility to gain ease of equipment design and low cost.
There is only so much room on the chip to include functionality, so for every I/O device or
memory increase the microcontroller includes, some other circuitry has to be removed.
Figure: The architecture of the microcontroller
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Finally, it must be mentioned that microcontroller architectures are available from many
different vendors in so many varieties that they could rightly belong to a category of their own.
Chief among these, are the 8051, Z80 and ARM derivatives.
The microcontroller used in this application is 8051. The 8051 has the widest range of
variants of any embedded controller on the market and there are many manufacturers like Intel,
Siemens, Atmel, Marta etc manufacturing it. some of the 8051 variants are
89C51,89C1051,89C2051 etc from Atmel, MCS251,87C51GB etc from Intel, 80C517A,80515
from Siemens etc. 89c51 from Atmel Company is used for this application. 89c51 has 40 pins, it
has 256Kbytes of RAM, and it is fast.
AT89C51 Microcontroller Features:
Compatible with MCS-51 Products
8K Bytes of In-System Reprogram able Flash Memory
Endurance: 1,000 Write/Erase Cycles
Fully Static Operation: 0 Hz to 24 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
Programmable Serial Channel
Low-power Idle and Power-down Modes
AT89C51 General Description:
The AT89c51 is a low-power, high-performance CMOS 8-bit microcomputer with 8K
bytes of Flash programmable and erasable read only memory (PEROM). The device is
manufactured using Atmels high-density nonvolatile memory technology and is Compatible with
the industry-standard 80C51 and 80C52 instruction set and pin out. The on-chip Flash allows the
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program memory to be reprogrammed in-system or by a conventional nonvolatile memory
programmer. By combining a versatile 8-bit CPU with Flash on a monolithic chip, the Atmel
AT89c51 is a powerful microcomputer that provides a highly flexible and cost-effective solution to
many embedded control applications.
1.2 Pin Diagram of AT89C51:
Fig: Pin Diagram of ATMEL89c51 Microcontroller
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Pin Description
Port 0: -
Port 0 is an 8-bit open drain bi-directional 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 may 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 the code bytes during Flash programming, and outputs the code bytes during program
verification. External pull-ups are required during program verification. Below table 4.1 indicates
pin connections of port 0 in the PLC Motherboard circuit.
Port0 Pin Connection Dtails
Port 1: -
6
Port Pin Connected to
P0.0 Toggle switch 1
P0.1 Toggle switch 2
P0.2 Toggle switch 3
P0.3 Toggle switch 4
P0.4 Toggle switch 5
P0.5 Toggle switch 6
P0.6 Toggle switch 7
P0.7 Toggle switch 8
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Port 1 is an 8-bit bi-directional 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. Port 1 also receives the low-order
address bytes during Flash programming and verification. Below table 4.2 indicates pin
connections of port 1 in the PLC Motherboard circuit.
Port Pin Connected to
P1.0 D0 of LCD
P1.1 D1 of LCD
P1.2 D2 of LCD
P1.3 D3 of LCD
P1.4 D4 of LCD
P1.5 D5 of LCD
P1.6 D6 of LCD
P1.7 D7 of LCD
Port 1Pin Connection details
Port 2: -
Port 2 is an 8-bit bi-directional 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. Below table 4.3 indicates pin
connections of port 2 in the PLC Motherboard circuit.
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Port Pin Connected to
P2.0 IN1 pin of ULN 2803.
P2.1 IN2 pin of ULN 2803.
P2.2 IN3 pin of ULN 2803.
P2.3 IN4 pin of ULN 2803.
P2.4 IN5 pin of ULN 2803.
P2.5 IN6 pin of ULN 2803.
P2.6 IN7 pin of ULN 2803.
P2.7 IN8 pin of ULN 2803.
Port 2 Pin Connection Details
Port 3: -
Port 3 is an 8-bit bi-directional 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. Below table 4.4 indicates pin connections of
port 3 in the PLC Motherboard circuit.
Port Pin Connected to
P3.0 No Connection
P3.1 No Connection
P3.2 E pin of LCD
P3.3 R/W pin of LCD
P3.4 RS pin of LCD
P3.5 INCR key
P3.6 DECR key
P3.7 ENTER key
Port 3 Pin Connection Details
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VCC - Supply voltage (+5V).
RST: -
Reset input. A high on this pin for two machine cycles while the oscillator is running resets
the device.
ALE/PROG: -
Address Latch Enable 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 weakly pulled high. Setting the ALE-disable bit has no effect if
the Microcontroller is in external execution mode.
PSEN: -
Program Store Enable is the read strobe to external program memory. When the AT89c51
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. A should be strapped to VCC
for internal program executions. This pin also receives the 12-volt programming enable voltage
(VPP) during Flash programming when 12-volt programming is selected.
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XTAL1: - Input to the inverting oscillator amplifier and input to the internal clock operating
circuit.
XTAL2: -Output from the inverting oscillator amplifier.
Crystals for timing purposes:
A crystal is a solid in which the constituent atoms, molecules, or ions are packed in a
regularly ordered, repeating pattern extending in all three spatial dimensions.
Almost any object made of an elastic material could be used like a crystal, with
appropriate transducers, since all objects have natural resonant frequencies of vibration. For
example, steel is very elastic and has a high speed of sound. It was often used in mechanical filters
before quartz. The resonant frequency depends on size, shape, elasticity and the speed of sound in
the material. High-frequency crystals are typically cut in the shape of a simple, rectangular plate.
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Low-frequency crystals, such as those used in digital watches, are typically cut in the shape of a
tuning fork. For applications not needing very precise timing, a low-cost ceramic resonator is often
used in place of a quartz crystal.
When a crystal of quartz is properly cut and mounted, it can be made to bend in an electric
field, by applying a voltage to an electrode near or on the crystal. This property is known as
piezoelectricity. When the field is removed, the quartz will generate an electric field as it returns to
its previous shape, and this can generate a voltage. The result is that a quartz crystal behaves like a
circuit composed of an inductor, capacitor and resistor, with a precise resonant frequency.
Quartz has the further advantage that its size changes very little with temperature.
Therefore, the resonant frequency of the plate, which depends on its size, will not change much,
either. This means that a quartz clock, filter or oscillator will remain accurate. For critical
applications the quartz oscillator is mounted in a temperature-controlled container, called a crystal
oven, and can also be mounted on shock absorbers to prevent perturbation by external mechanical
vibrations.
Quartz timing crystals are manufactured for frequencies from a few tens of kilohertz to tens
of megahertz. More than two billion (2109) crystals are manufactured annually. Most are small
devices for consumer devices such as wristwatches, clocks, radios, computers, and cell phones.
Quartz crystals are also found inside test and measurement equipment, such as counters, signal
generators, and oscilloscopes.
CRYSTALS AND FREQUENCY:
Schematic symbol and equivalent circuit for a quartz crystal in an oscillator
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The crystal oscillator circuit sustains oscillation by taking a voltage signal from the quartz
resonator, amplifying it, and feeding it back to the resonator. The rate of expansion and contraction
of the quartz is the resonant frequency, and is determined by the cut and size of the crystal.
A regular timing crystal contains two electrically conductive plates, with a slice or tuning
fork of quartz crystal sandwiched between them. During startup, the circuit around the crystal
applies a random noise AC signal to it, and purely by chance, a tiny fraction of the noise will be at
the resonant frequency of the crystal. The crystal will therefore start oscillating in synchrony with
that signal. As the oscillator amplifies the signals coming out of the crystal, the crystal's frequency
will become stronger, eventually dominating the output of the oscillator. Natural resistance in the
circuit and in the quartz crystal, filter out all the unwanted frequencies.
One of the most important traits of quartz crystal oscillators is that they can exhibit very
low phase noise. In other words, the signal they produce is a pure tone. This makes them
particularly useful in telecommunications where stable signals are needed and in scientific
equipment where very precise time references are needed.
The output frequency of a quartz oscillator is either the fundamental resonance or a
multiple of the resonance, called an overtone frequency.
A typical Q for a quartz oscillator ranges from 104 to 106. The maximum Q for a high stability
quartz oscillator can be estimated as Q = 1.6 107/f, where f is the resonance frequency in
megahertz.
Environmental changes of temperature, humidity, pressure, and vibration can change the
resonant frequency of a quartz crystal, but there are several designs that reduce these
environmental effects. These include the TCXO, MCXO, and OCXO (defined below). These
designs (particularly the OCXO) often produce devices with excellent short-term stability. The
limitations in short-term stability are due mainly to noise from electronic components in the
oscillator circuits. Long term stability is limited by aging of the crystal.
Due to aging and environmental factors such as temperature and vibration, it is hard to keep eventhe best quartz oscillators within one part in 1010 of their nominal frequency without constant
adjustment. For this reason, atomic oscillators are used for applications that require better long-
term stability and accuracy.
Although crystals can be fabricated for any desired resonant frequency, within
technological limits, in actual practice today engineers design crystal oscillator circuits around
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relatively few standard frequencies, such as 3.58MHz, 10 MHz, 14.318, 20 MHz, 33.33 MHz, and
40 MHz . The vast popularity of the 3.58MHz and 14.318MHz crystals is attributed initially to low
cost resulting from scale of economy resulting from the popularity of television and the fact that
this frequency is involved in synchronizing to the color burst signal necessary to display color on
an NTSC or PAL based television set. Using frequency dividers, frequency multipliers and phase
locked loop circuits; it is possible to synthesize any desired frequency from the reference
frequency.
Care must be taken to use only one crystal oscillator source when designing circuits to
avoid subtle failure modes of metastability in electronics. If this is not possible, the number of
distinct crystal oscillators, PLLs, and their associated clock domains should be rigorously
minimized, through techniques such as using a subdivision of an existing clock instead of a new
crystal source. Each new distinct crystal source needs to be rigorously justified, since each one
introduces new, difficult to debug probabilistic failure modes, due to multiple crystal interactions,
into equipment.
Specifications:
Frequency range: 1.50MHz to 160MHz
Frequency range: 1.50MHz to 160MHz
Frequency tolerance: +/-10ppm to +/-30ppm (at 25 degree Celsius)
Frequency stability +/-10ppm to +/-30ppm
Operating temperature range: -20 to +70 degrees Celsius
Load capacitance: 10pF to 32pF, series or special
Shunt capacitance: 7pF maximum
Drive level: 100uw to 1000uw
Oscillation mode: fundamental, 3rd and 5th overtone
Measure instrument: S and A 250 A system
Equivalent series resistance
Oscillation mode: fundamental
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Frequency/HC-49/U (ohms maximum):
1.5 to 1.99/700 ohms
2.0 to 2.99/500 ohms
3.0 to 3.19/300 ohms
3.2 to 3.99/150 ohms
4.0 to 4.49/90 ohms
4.5 to 4.99/70 ohms
5.0 to 6.99/50 ohms
7.0 to 9.99/35 ohms
10.0 to 36.0/25 ohms
Oscillation mode: 3rd overtone
Frequency/HC49/U (ohm maximum):
20.0 to 24.99/45 ohms
25.0 to 90.9/40 ohms
Oscillation mode: 5th overtone
Frequency/HC-49/U (ohm maximum):
70.0 to 160.0/70 ohms
1.3 Memory Organization:
The 8051 architecture provides the user with three physically distinct memory spaces
which can be seen in Figure A - 1. Each memory space consists of contiguous addresses from 0 to
the maximum size, in bytes, of the memory space. Address overlaps are resolved by utilizing
instructions which refer specifically to a given address space. The three memory spaces function as
described below.
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The CODE Space
The first memory space is the CODE segment in which the executable program resides.
This segment can be up to 64K (since it is addressed by 16 address lines). The processor treats this
segment as read only and will generate signals appropriate to access a memory device such as an
EPROM. However, this does not mean that the CODE segment must be implemented using an
EPROM. Many embedded systems these days are using EEPROM which allows the memory to be
overwritten either by the 8051 itself or by an external device. This makes upgrades to the product
easy to do since new software can be downloaded into the EEPROM rather than having to
disassemble it and install a new EPROM.
The DATA Space
The second memory space is the 128 bytes of internal RAM on the 8051, or the first 128
bytes of internal RAM on the 8052. This segment is typically referred to as the DATA segment.
The RAM locations in this segment are accessed in one or two cycles depending on the instruction.
This access time is much quicker than access to the XDATA segment because memory is
addressed directly rather than via a memory pointer such as DPTR which must first be initialized.
Therefore, frequently used variables and temporary scratch variables are usually assigned to the
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DATA segment. Such allocation must be done with care, however, due to the limited amount of
memory in this segment.
Variables stored in the DATA segment can also be accessed indirectly via R0 or R1. The
register being used as the memory pointer must contain the address of the byte to be retrieved or
altered. These instructions can take one or two processor cycles depending on the
source/destination data byte.
Special Function Registers
Control registers for the interrupt system and the peripherals on the 8051 are contained in
internal RAM at locations 80 hex and above. These registers are referred to as special functionregisters (or SFRs for short). Many of them are bit addressable. The bits in the bit addressable
SFRs can either be accessed by name, index or bit address. Thus, you can refer to the EA bit of the
Interrupt Enable SFR as EA, IE.7, or 0AFH. The SFRs control things such as the function of the
timer/counters, the UART, and the interrupt sources as well as their priorities. These registers are
accessed by the same set of instructions as the bytes and bits in the DATA segment.
The IDATA Space
Certain 8051 family members such as the 8052 contain an additional 128 bytes of internal
RAM which reside at RAM locations 80 hex and above. This segment of RAM is typically
referred to as the IDATA segment. Because the IDATA addresses and the SFR addresses overlap,
address conflicts between IDATA RAM and the SFRs are resolved by the type of memory access
being performed, since the IDATA segment can only be accessed via indirect addressing modes.
The final 8051 memory space is 64K in length and is addressed by the same 16 address
lines as the CODE segment. This space is typically referred to as the external data memory space
(or the XDATA segment for short). This segment usually consists of some sort of RAM (usually
an SRAM) and the I/O devices or external peripherals to which the 8051 must interface via its bus.
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Read or write operations to this segment take a minimum of two processor cycles and are
performed using either DPTR, R0, or R1. In the case of DPTR, it usually takes two processor
cycles or more to load the desired address in addition to the two cycles required to perform the
read or write operation. Similarly, loading R0 or R1 will take minimum of one cycle in addition to
the two cycles imposed by the memory access itself. Therefore, it is easy to see that a typical
operation with the XDATA segment will, in general, take a minimum of three processor cycles.
Because of this, the DATA segment is a very attractive place to store any frequently used
variables. It is possible to fill this segment entirely with 64K of RAM if the 8051 does not need to
perform any I/O with devices in its bus or if the designer wishes to cycle the RAM on and off
when I/O devices are being accessed via the bus.
CHAPTER-2
POWER SUPPLY
POWER SUPPLY MODULES:
STEP DOWN TRANSFORMER
BRIDGE RECTIFIER WITH FILTER
VOLTAGE REGULATORS
2.1 STEP DOWN TRANSFORMER:
A transformer is an electrical device that transfers energy from one circuit to another by
magnetic coupling, without requiring relative motion between its parts. A transformer comprises
two or more coupled windings, and, in most cases, a magnetic core to concentrate magnetic flux. A
changing voltage applied to one winding creates a time-varying magnetic flux in the core, which
induces a voltage in the other windings.
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Transformers come in a range of sizes from a thumbnail-sized coupling transformer hidden
inside a stage microphone to huge gigawatt units used to interconnect large portions of national
power grids. All operate with the same basic principles and with many similarities in their parts.
A transformer transfers electrical energy from a high-current, low-voltage circuit to a lower-
current, higher-voltage circuit.
Coupling by mutual induction:
The principles of the transformer are illustrated by consideration of a hypothetical ideal
transformer. In this case, the core requires negligible magneto motive force to sustain flux, and all
flux linking the primary winding also links the secondary winding. The hypothetical ideal
transformer has no resistance in its coils. A simple transformer consists of two electrical
conductors called the primary winding and the secondary winding. Energy is coupled between
the windings by the time varying magnetic flux that passes through (links) both primary and
secondary windings. Whenever the amount of current in a coil changes, a voltage is induced in the
neighboring coil. The effect, called mutual inductance, is an example of electromagnetic induction.
Fig: An ideal step-down transformer showing flux in the core
If a time-varying voltage is applied to the primary winding of turns, a current will flow
in it producing a magneto motive force (MMF). Just as an electromotive force (EMF) drives
current around an electric circuit, so MMF tries to drive magnetic flux through a magnetic circuit.
The primary MMF produces a varying magnetic flux in the core, and, with an open circuit
secondary winding, induces a back electromotive force (EMF) in opposition to . In accordance
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with Faradays law of induction, the voltage induced across the primary winding is proportional to
the rate of change of flux:
and
where
vPand vS are the voltages across the primary winding and secondary winding,
NPandNS are the numbers of turns in the primary winding and secondary winding,
dP / dtand dS / dtare the derivatives of the flux with respect to time of the primary
and secondary windings.
In the hypothetical ideal transformer, the primary and secondary windings are perfectly coupled,
or equivalently, . Substituting and solving for the voltages shows that:
Where
vp and vs are voltages across primary and secondary,
Np andNs are the numbers of turns in the primary and secondary, respectively.
Hence in an ideal transformer, the ratio of the primary and secondary voltages is equal to
the ratio of the number of turns in their windings, or alternatively, the voltage per turn is the same
for both windings. The ratio of the currents in the primary and secondary circuits is inversely
proportional to the turns ratio.
The EMF in the secondary winding will cause current to flow in a secondary circuit. The
MMF produced by current in the secondary winding opposes the MMF of the primary winding and
so tends to cancel the flux in the core. Since the reduced flux reduces the EMF induced in the
primary winding, increased current flows in the primary circuit. The resulting increase in MMF
due to the primary current offsets the effect of the opposing secondary MMF. In this way, the
electrical energy fed into the primary winding is delivered to the secondary winding. In addition,
the flux density will always stay the same as long as the primary voltage is steady.
Step-down: The secondary has fewer turns than the primary i.e. it converts higher voltage at the
input side to a lower voltage at the output.
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2.2 BRIDGE RECTIFIER:
A diode bridge orbridge rectifier is an arrangement of four diodes connected in a bridge
circuit as shown below, that provides the same polarity of output voltage for any polarity of the
input voltage. When used in its most common application, for conversion of alternating current
(AC) input into direct current (DC) output, it is known as a bridge rectifier. The bridge recitifier
provides full wave rectification from a two wire AC input (saving the cost of a center tapped
transformer) but has two diode drops rather than one reducing efficiency over a center tap based
design for the same output voltage.
Fig: Schematic of a diode bridgeThe essential feature of this arrangement is that for both polarities of the voltage at the bridge
input, the polarity of the output is constant.
Basic operation:
When the input connected at the left corner of the diamond is positive with respect to the one
connected at the right hand corner, current flows to the right along the upper colored path to the
output, and returns to the input supply via the lower one.
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When the right hand corner is positive relative to the left hand corner, current flows along the
upper colored path and returns to the supply via the lower colored path.
fig: AC, half-wave and full wave rectified signals
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In each case, the upper right output remains positive with respect to the lower right one.
Since this is true whether the input is AC or DC, this circuit not only produces DC power when
supplied with AC power: it also can provide what is sometimes called "reverse polarity
protection". That is, it permits normal functioning when batteries are installed backwards or DC
input-power supply wiring "has its wires crossed" (and protects the circuitry it powers against
damage that might occur without this circuit in place).
Output smoothing:
For many applications, especially with single phase AC where the full-wave bridge serves to
convert an AC input into a DC output, the addition of a capacitor may be important because the
bridge alone supplies an output voltage of fixed polarity but pulsating magnitude (see figure
below).
The function of this capacitor, known as a 'smoothing capacitor' is to lessen the variation in
(or 'smooth') the raw output voltage waveform from the bridge. One explanation of 'smoothing' is
that the capacitor provides a low impedance path to the AC component of the output, reducing the
AC voltage across, and AC current through, the resistive load. In less technical terms, any drop in
the output voltage and current of the bridge tends to be cancelled by loss of charge in the capacitor.
This charge flows out as additional current through the load. Thus the change of load current and
voltage is reduced relative to what would occur without the capacitor. Increases of voltage
correspondingly store excess charge in the capacitor, thus moderating the change in output
voltage / current.
The capacitor and the load resistance have a typical time constant = RCwhere CandR
are the capacitance and load resistance respectively. As long as the load resistor is large enough so
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that this time constant is much longer than the time of one ripple cycle, the above configuration
will produce a well smoothed DC voltage across the load resistance. In some designs, a series
resistor at the load side of the capacitor is added. The smoothing can then be improved by adding
additional stages of capacitorresistor pairs, often done only for sub-supplies to critical high-gain
circuits that tend to be sensitive to supply voltage noise.
CHARACTERISTICS OF BRIDGE RECTIFIER:
EFFICIENCY:
It is defined as the ratio of output DC power to input AC power.
Its efficiency is 81.2%, which is same as that of a full wave rectifier.
RIPPLE FACTOR:
It is defined as the ratio of RMS voltage of the AC component to the DC component.
For bridge rectifier it is 0.48, which is same as full wave rectifier.
In bridge rectifier the bulky center tapped transformer is not used which is a great
advantage.
The peak inverse voltage (PIV) of the diodes is half that of the PIV of the diodes in a full
wave rectifier.
The transformer utilization factor (T.U.F) is high i.e. 0.812, as the current flowing in the
transformer secondary is fully utilized.
2.3 VOLTAGE REGULATORS:
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A
voltage regulator 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.
With the exception of shunt regulators, all voltage regulators operate by comparing the
actual output voltage to some internal fixed reference voltage. Any difference is amplified and
used to control the regulation element. This forms a negative feedback servo control loop. If the
output voltage is too low, the regulation element is commanded to produce a higher voltage. For
some regulators if the output voltage is too high, the regulation element is commanded to producea lower voltage; however, many just stop sourcing current and depend on the current draw of
whatever it is driving to pull the voltage back down. In this way, the output voltage is held roughly
constant. The control loop must be carefully designed to produce the desired tradeoff between
stability and speed of response.
Voltage Regulator(7805 +5v regulator, 1 Amp rated output) :
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In this project, we need a stable, constant 5-volt DC supply. It's the job of a voltage
regulator IC to take the variable; unregulated DC input and turns it into a constant supply
we can use. Two common families of fixed voltage regulator exist - the 78xx series for positive
voltages, and the 79xx series for negative voltages. The rest of the part number consists of the
output voltage, i.e. 7805 for +5 volts, 7812 for +12 volts. There are other regulators rated for
different currents are available, such as 7xLxx series (e.g. 79L05) for 0.1 Amps and 7xSxx series
(e.g. 78S12) for 2 Amps.
CHAPTER-3
RS-232
RS-232 is simple, universal, well understood and supported but it has some serious
shortcomings as a data interface. The standards to 256kbps or less and line lengths of 15M (50 ft)
or less but today we see high speed ports on our home PC running very high speeds and with high
quality cable maxim distance has increased greatly. The rule of thumb for the length a data cable
depends on speed of the data, quality of the cable.
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Electronic data communications between elements will generally fall into two broad
categories: single-ended and differential. RS232 (single-ended) was introduced in 1962, and
despite rumors for its early demise, has remained widely used through the industry.
Independent channels are established for two-way (full-duplex) communications. The
RS232 signals are represented by voltage levels with respect to a system common (power / logic
ground). The "idle" state (MARK) has the signal level negative with respect to common, and the
"active" state (SPACE) has the signal level positive with respect to common. RS232 has numerous
handshaking lines (primarily used with modems), and also specifies a communications protocol.
The RS-232 interface presupposes a common ground between the DTE and DCE. This is a
reasonable assumption when a short cable connects the DTE to the DCE, but with longer lines and
connections between devices that may be on different electrical busses with different grounds, this
may not be true.
RS232 data is bi-polar.... +3 TO +12 volts indicates an "ON or 0-state (SPACE) condition"
while A -3 to -12 volts indicates an "OFF" 1-state (MARK) condition.... Modern computer
equipment ignores the negative level and accepts a zero voltage level as the "OFF" state. In fact,
the "ON" state may be achieved with lesser positive potential. This means circuits powered by 5
VDC are capable of driving RS232 circuits directly; however, the overall range that the RS232
signal may be transmitted/received may be dramatically reduced.
The output signal level usually swings between +12V and -12V. The "dead area" between
+3v and -3v is designed to absorb line noise. In the various RS-232-like definitions this dead area
may vary. For instance, the definition for V.10 has a dead area from +0.3v to -0.3v. Many
receivers designed for RS-232 are sensitive to differentials of 1v or less.
This can cause problems when using pin powered widgets - line drivers, converters,
modems etc. These types of units need enough voltage & current to power them self's up. Typical
URART (the RS-232 I/O chip) allows up to 50ma per output pin - so if the device needs 70ma to
run we would need to use at least 2 pins for power. Some devices are very efficient and only
require one pin (some times the Transmit or DTR pin) to be high - in the "SPACE" state while idle.
An RS-232 port can supply only limited power to another device. The number of output
lines, the type of interface driver IC, and the state of the output lines are important considerations.
Data is transmitted and received on pins 2 and 3 respectively. Data Set Ready (DSR) is an
indication from the Data Set (i.e., the modem or DSU/CSU) that it is on. Similarly, DTR indicates
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to the Data Set that the DTE is on. Data Carrier Detect (DCD) indicates that a good carrier is being
received from the remote modem. Pins 4 RTS (Request To Send - from the transmitting computer)
and 5 CTS (Clear To Send - from the Data set) are used to control. In most Asynchronous
situations, RTS and CTS are constantly on throughout the communication session. However where
the DTE is connected to a multipoint line, RTS is used to turn carrier on the modem on and off. On
a multipoint line, it's imperative that only one station is transmitting at a time (because they share
the return phone pair). When a station wants to transmit, it raises RTS. The modem turns on
carrier, typically waits a few milliseconds for carrier to stabilize, and then raises CTS. The DTE
transmits when it sees CTS up. When the station has finished its transmission, it drops RTS and the
modem drops CTS and carrier together. Clock signals (pins 15, 17, & 24) are only used for
synchronous communications. The modem or DSU extracts the clock from the data stream and
provides a steady clock signal to the DTE. Note that the transmit and receive clock signals do not
have to be the same, or even at the same baud rate. Note: Transmit and receive leads (2 or 3) can
be reversed depending on the use of the equipment - DCE Data Communications Equipment or a
DTE Data Terminal Equipment.
Sub-D15 Male Sub-D15 Female
This is a standard 9 to 25 pin cable layout for async data on a PC AT serial cable
Description Signal 9-pin DTE 25-pin DCE Source DTE or DCE
Carrier Detect CD 1 8 from Modem
Receive Data RD 2 3 from Modem
Transmit Data TD 3 2 from Terminal/Computer
Data Terminal Ready DTR 4 20 from Terminal/Computer
Signal Ground SG 5 7 from Modem
Data Set Ready DSR 6 6 from ModemRequest to Send RTS 7 4 from Terminal/Computer
Clear to Send CTS 8 5 from Modem
Ring Indicator RI 9 22 from Modem
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CHAPTER-4
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MAX-232
Features:
Operates With Single 5-V Power Supply
LinBiCMOS Process Technology
Two Drivers and Two Receivers
30- V Input Levels
Low Supply Current . . . 8 mA Typical
Meets or Exceeds TIA/EIA-232-F and ITU
Recommendation V.28
Designed to be Interchangeable With
Applications:
TIA/EIA-232-F
Battery-Powered Systems
Terminals
Modems
Computers
ESD Protection Exceeds 2000 V Per
MIL-STD-883, Method 3015
Package Options Include Plastic
Small-Outline (D, DW) Packages and
Standard Plastic (N) DIPs
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Absolute maximum ratings
Input supply voltage range, VCC : 0.3 V to 6 V
Positive output supply voltage range:VS+ VCC 0.3 V to 15 V
Negative output supply voltage range: VS0.3 V to 15 V
Input voltage range, VI: Driver:0.3 V to VCC + 0.3 V
Receiver: 30 V
Output voltage range, VO: T1OUT, T2OUT VS 0.3 V to VS+ + 0.3 V
R1OUT, R2OUT : 0.3 V to VCC + 0.3 V
Short-circuit duration: T1OUT, T2OUT: Unlimited
Package thermal impedance, D package :113C/W
DW package : 105C/W
N package : 78C/W
Storage temperature range, Tstg : 65C to 150C
Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds: 260 C
Stresses beyond those listed under absolute maximum ratings may cause permanent
damage to the device. These are stress ratings only and functional operation of the device at these
or any other conditions beyond those indicated under recommended operating conditions is not
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implied. Exposure to absolute-maximum-rated conditions for extended periods may affect device
reliability. NOTE 1: All voltage values are with respect to network ground terminal.2. The package
thermal impedance is calculated in accordance with JESD 51, except for through-hole packages,
which use a trace length of zero description
MAX 232 Interfacing with RS232 and 89C51 microcontroller
The MAX232 device is a dual driver/receiver that includes a capacitive voltage
generator to supply EIA-232 voltage levels from a single 5-V supply. Each receiver converts EIA-
232 inputs to 5-V TTL/CMOS levels. These receivers have a typical threshold of 1.3 V and a
typical hysterics of 0.5 V, and can accept 30-V inputs. Each driver converts TTL/CMOS input
levels into EIA-232 levels. The driver, receiver, and voltage-generator functions are available as
cells in the Texas
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CHAPTER-5
PROJECT DESCRIPTION
5.1. Block diagram:
5.2. Description:
In this project we are controlling the appliances connected to the microcontroller. A
command is passed to the microcontroller through pc. That command is first given to the RS-232
and then passed to max-232 that converts the logic levels of RS-232 to microcontroller logic
levels. According to the command received by the microcontroller the appliances connected to the
driver ULN 2804, which drives the relay, are controlled.
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Hype
r
termin
PC
Straigh
t
cable
Max-
232
ATMEL
ULN
DRIVER
RelayControlling
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5.3. Working:
After the connections are made as per circuit diagram the user has to enter the
commands in the hyper terminal of PC using keyboard to control the appliances.
When a command is entered, the command is passed to the microcontroller throughRS-232 and max-232.
Now the microcontroller checks the command. That is it compares the received
command with the commands that are already stored in the controller.
If the command is A then the controller activates device 1.
If the command is B it deactivates the device 1.
If the command is C it activates the device 2.
If it is D it deactivates the device 2.
Each device is activated and deactivated through relay that is driven by ULN 2804.
It also shows the status of the devices for each command.
If the controller receives other than these commands it waits till the proper
command is received.
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CONCLUSION
Industrial Automation has been taken into a new dimension. We have clearly demonstrated
that Automation is the birth of a brand new era open to endless possibilities. Automation can be
applied for your convenience. For example, living in a city such as London where the temperature
can greatly vary between the morning and the evening, Automation can be very beneficial. Say you
leave to work in the morning on a hot summery day and during the day you start to realize that the
temperature aiming to go below freezing; you can then remotely turn on the heating at your home.
This document presents a user-friendly approach to the available home automation
systems. It is real-time monitor-able and remote controllable which simplifies the users indoor life
and their interaction with home and industry. This system can easily be implemented because of its
no necessity to wiring between the appliances. PC controls every data bit by bit, which results in
preventing the disorder between different home appliances.
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BIBLIOGRAPHY
1. THE 8051 MICRO-CONTROLLER AND EMBEDDED SYSTEMS
a. MOHAMMAD ALI MAZIDI.
b. JANICE GILLISPE.
2. PROGRAMMINIG AND CUSTOMIZING WITH 8051
a. MYKE PREDKO
3. WWW.EMBEDDED.COM
4. EMBEDDED SYSTEMS: ARCHITECTURE AND DESIGNING
a. VAHID & GIVARGIS
5. 8051 BY AYALA
http://www.embedded.com/http://www.embedded.com/