full home appliances

7/31/2019 Full Home Appliances

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ABSTRACT

ELECTRICAL APPARATUS CONTROLLING USING MOBILE PHONE

Home makers are the backbone of Indian families. They do a lot of home work since

morning to night. All the electronic devices required may be present at homes to perform various

tasks like washing the clothes, watering the plants etc. But even after, a person should be

available to operate the devices to perform the tasks. This project eliminates all such and

provides a better solution using the wireless communication DTMF.

All the electronic devices which are to be operated should be connected to the main

controlling unit. The controlling unit contains the microcontroller and the modem.

A modem provides the communication interface. It transports device protocols

transparently over the network through a serial interface. A DTMF modem is a wireless modem

that works with a DTMF wireless network. A wireless modem behaves like a dial-up modem.

The main difference between them is that a dial-up modem sends and receives data through a

fixed telephone line while a wireless modem sends and receives data through radio waves.

The DTMF modem will be interfaced to the microcontroller section through serial port

interface. If the user wants to operate any appliances, he/she has to send predefined message to

the DTMF modem. The controller section will have the switch controls of the devices. The user

has to press the predefined number to the modem whenever he wants to change the status of any

of the appliances. Thus, the homemakers can easily carry on with their works while watching

their favourite daily programmes.

This project uses regulated 5V, 500mA & 12V, 500mA power supply. 7805 and 7812

three terminal voltage regulators are used for voltage regulation. Bridge type full wave rectifier

is used to rectify the ac out put of secondary of 230/12V step down transformer.


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BLOCK DIAGRAM

HARDWARE COMPONENTS:

Micro controller(8051) DTMF Modem Max232 Power supply LCD Relay

SOFTWARE TOOLS:

Keil micro vision Embedded C


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TABLE OF CONTENTS

TITLE

1.INTRODUCTION

1.1 INTRODUCTION

2. AT89C51 MICROCONTROLLER

2.1 DISCRIPTION

2.2 FEATURES

2.3 BLOCK DIAGRAM

2.4 PIN CONFIGURATION

2.5 PIN DESCRIPTION

3. POWER SUPPLY,MAX 232,LCD

DISPLAY,RELAY,BUZZER

3.1 POWER SUPPLY

3.1.1 INTRODUCTION

3.1.2 TRANSFORMER

3.1.3 RECTIFIER

3.1.4 SMOOTHING

3.1.5 REGULATOR

3.2 MAX 232


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3.3 LCD DISPLAY

3.4 RELAY

3.5 BUZZER


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INTRODUCTION

1.INTRODUCTION

The first question that needs to be asked, is"What exactly is an embedded computer?" To be fair, however, it is much easier to

answer the question of what an embedded computer is not, than to try and describe

all the many things that an embedded computer can be. An embedded computer is

frequently a computer that is implemented for a particular purpose. In contrast, an

average PC computer usually serves a number of purposes: checking email, surfing

the internet, listening to music, word processing, etc... However, embedded

systems usually only have a single task, or a very small number of related tasks

that they are programmed to perform.

Every home has several examples of embedded computers. Any appliance that hasa digital clock, for instance, has a small embedded microcontroller that performs

no other task than to display the clock. Modern cars have embedded computers

onboard that control such things as ignition timing and anti-lock brakes using input

from a number of different sensors.

Embedded computers rarely have a generic interface, however. Even if embedded

systems have a keypad and an LCD display, they are rarely capable of using many

different types of input or output. An example of an embedded system with I/O

capability is a security alarm with an LCD status display, and a keypad for entering

a password.

In general, an Embedded System:

Is a system built to perform its duty, completely or partiallyindependent of human intervention.

Is specially designed to perform a few tasks in the most efficient way.


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Interacts with physical elements in our environment, viz. controllingand driving a motor, sensing temperature, etc.

An embedded system can be defined as a control system or computer system

designed to perform a specific task. Common examples of embedded systems

include MP3 players, navigation systems on aircraft and intruder alarm systems.

An embedded system can also be defined as a single purpose computer.

Embedded systems are playing important roles

in our lives every day, even though they might not necessarily be visible. Some of

the embedded systems we use every day control the menu system on television, the

timer in a microwave oven, a cellphone, an MP3 player or any other device with

some amount of intelligence built-in. In fact, recent poll data shows that embedded

computer systems currently outnumber humans in the USA. Embedded systems isa rapidly growing industry where growth opportunities are numerous.

The uses of embedded systems are virtually limitless,

because every day new products are introduced to the market that utilize embedded

computers in novel ways. In recent years, hardware such as microprocessors,

microcontrollers, and FPGA chips have become much cheaper. So when

implementing a new form of control, it's wiser to just buy the generic chip and

write your own custom software for it. Producing a custom-made chip to handle a

particular task or set of tasks costs far more time and money. Many embedded

computers even come with extensive libraries, so that "writing your own software"becomes a very trivial task indeed.

From an implementation viewpoint, there is a major difference between a

computer and an embedded system. Embedded systems are often required to

provide Real-Time response. A Real-Time system is defined as a system whose

correctness depends on the timeliness of its response. Examples of such systems

are flight control systems of an aircraft, sensor systems in nuclear reactors and

power plants. For these systems, delay in response is a fatal error. A more relaxed

version ofReal-Time Systems, is the one where timely response with small delaysis acceptable. Example of such a system would be the Scheduling Display System

on the railway platforms. In technical terminology, Real-Time Systems can be

classMost embedded systems are time critical applications meaning that the

embedded system is working in an environment where timing is very important:

the results of an operation are only relevant if they take place in a specific time

frame. An autopilot in an aircraft is a time critical embedded system. If the


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autopilot detects that the plane for some reason is going into a stall then it shouldtake steps to correct this within milliseconds or there would be catastrophic results.


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2.1 Description

The AT89C51 is a low-power, high-performance

CMOS 8-bit microcomputer with 4 Kbytes 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 MCS-51 instruction set and pinout.The on-chip Flash allows the program

memory to be reprogrammed in-system or by a conventional nonvolatile memoryprogrammer. By combining a versatile 8-bit CPU with Flash on a monolithic chip,

the Atmel AT89C51 is a powerful microcomputer which provides a highly flexible

and cost effective solution to many embedded control applications.The AT89C51

provides the following standard features: 4Kbytes of Flash, 128 bytes of RAM, 32

I/O lines, two 16-bit timer/counters, a five vector two-level interrupt architecture, a

full duplex serial port, on-chip oscillator and clock circuitry. In addition, the

AT89C51 is designed with static logic for operation down to zero frequency and

supports two software selectable power saving modes. The Idle Mode stops theCPU while allowing the RAM, timer/counters,

2.2 FEATURES

Compatible with MCS-51 Products 4K Bytes of In-System Reprogrammable Flash Memory

Endurance: 1,000 Write/Erase Cycles

Fully Static Operation: 0 Hz to 24 MHz

Three-Level Program Memory Lock 128 x 8-Bit Internal RAM

32 Programmable I/O Lines Two 16-Bit Timer/Counters

Six Interrupt Sources Programmable Serial Channel


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Low Power Idle and Power Down Modes

2.4 PIN CONFIGURATION


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Chapter 3


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Power Supplies

INTRODUCTION

Types of Power SupplyThere are many types of power supply. Most are designed to convert high voltage AC mains

electricity to a suitable low voltage supply for electronics circuits and other devices. A powersupply can by broken down into a series of blocks, each of which performs a particular function.

For example a 5V regulated supply:

Each of the blocks is described in more detail below:

Transformer- steps down high voltage AC mains to low voltage AC. Rectifier- converts AC to DC, but the DC output is varying. Smoothing- smooths the DC from varying greatly to a small ripple. Regulator- eliminates ripple by setting DC output to a fixed voltage.

Dual Supplies:-

Some electronic circuits require a power

supply with positive and negative outputsas well as zero volts (0V). This is called a'dual supply' because it is like two ordinary

supplies connected together as shown in

the diagram.

Dual supplies have three outputs, for

example a 9V supply has +9V, 0V and -9V outputs.
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Transformer only:-

The low voltage AC output is suitable for lamps, heaters and special AC motors. It is not

suitable for electronic circuits unless they include a rectifier and a smoothing capacitor.

Transformer + Rectifier:-

The varying DC output is suitable for lamps, heaters and standard motors. It is not suitable forelectronic circuits unless they include a smoothing capacitor.

Transformer + Rectifier + Smoothing


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The smooth DC output has a small ripple. It is suitable for most electronic circuits.

Transformer + Rectifier + Smoothing + Regulator:-

The regulated DC output is very smooth with no ripple. It is suitable for all electronic circuits.

3.1 .2TRANSFORMER:-

Transformers convert AC electricity from one voltage toanother with little loss of power. Transformers work only

with AC and this is one of the reasons why mains

electricity is AC.

Step-up transformers increase voltage, step-downtransformers reduce voltage. Most power supplies use a

step-down transformer to reduce the dangerously highmains voltage (230V in UK) to a safer low voltage.

The input coil is called the primary and the output coil iscalled the secondary. There is no electrical connection

between the two coils, instead they are linked by an

alternating magnetic field created in the soft-iron core ofthe transformer. The two lines in the middle of the circuit

symbol represent the core. Transformers waste very little

power so the power out is (almost) equal to the power in.

Note that as voltage is stepped down current is stepped up.

The ratio of the number of turns on each coil, called the

turns ratio, determines the ratio of the voltages. A step-down transformer has a large number of turns on its

primary (input) coil which is connected to the high voltage

mains supply, and a small number of turns on its secondary

Transformercircuit symbol

Transformer


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(output) coil to give a low output voltage.

turns ratio =Vp

=Np

andpower out = power in

Vs Ns Vs Is = Vp Ip

Vp = primary (input) voltage

Np = number of turns on primary coilIp = primary (input) current

Vs = secondary (output) voltage

Ns = number of turns on secondary coilIs = secondary (output) current

3.1.2 RECTIFIER

There are several ways of connecting diodes to make a rectifier to convert AC to DC. The

bridge rectifieris the most important and it produces full-wave varying DC. A full-wave rectifier

can also be made from just two diodes if a centre-tap transformer is used, but this method israrely used now that diodes are cheaper. Asingle diodecan be used as a rectifier but it only uses

the positive (+) parts of the AC wave to produce half-wave varying DC.

Bridge rectifier:-

A bridge rectifier can be made using four individual diodes, but it is also available in special

packages containing the four diodes required. It is called a full-wave rectifier because it uses allthe AC wave (both positive and negative sections). 1.4V is used up in the bridge rectifier because

each diode uses 0.7V when conducting and there are always two diodes conducting, as shown in

the diagram below. Bridge rectifiers are rated by the maximum current they can pass and the

maximum reverse voltage they can withstand (this must be at least three times the supplyRMS

voltage so the rectifier can withstand the peak voltages). Please see the Diodespage for moredetails, including pictures of bridge rectifiers.

Bridge rectifierAlternate pairs of diodes conduct, changing over

the connections so the alternating directions of

AC are converted to the one direction of DC.

Output: full-wave varying DC(using all the AC wave)

Single diode rectifier
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A single diode can be used as a rectifier but this produces half-wave varying DC which has gaps

when the AC is negative. It is hard to smooth this sufficiently well to supply electronic circuitsunless they require a very small current so the smoothing capacitor does not significantly

discharge during the gaps. Please see theDiodespage for some examples of rectifier diodes.

Single diode rectifierOutput: half-wave varying DC

(using only half the AC wave)

3.1.3 SMOTHING

Smoothing is performed by a large valueelectrolytic capacitorconnected across the DC supply

to act as a reservoir, supplying current to the output when the varying DC voltage from therectifier is falling. The diagram shows the unsmoothed varying DC (dotted line) and the

smoothed DC (solid line). The capacitor charges quickly near the peak of the varying DC, andthe discharges as it supplies current to the output.

Note that smoothing significantly increases the average DC voltage to almost the peak value(1.4 RMSvalue). For example 6V RMS AC is rectified to full wave DC of about 4.6V RMS(1.4V is lost in the bridge rectifier), with smoothing this increases to almost the peak value

giving 1.4 4.6 = 6.4V smooth DC.

Smoothing is not perfect due to the capacitor voltage falling a little as it discharges, giving a

small ripple voltage. For many circuits a ripple which is 10% of the supply voltage is

satisfactory and the equation below gives the required value for the smoothing capacitor. A

larger capacitor will give less ripple. The capacitor value must be doubled when smoothing half-wave DC.

Smoothing capacitor for 10% ripple, C = 5 Io
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Vs f

C = smoothing capacitance in farads (F)

Io = output current from the supply in amps (A)

Vs = supply voltage in volts (V), this is the peak value of the unsmoothed DC

f = frequency of the AC supply in hertz (Hz), 50Hz in the UK

3.1.4 REGULATOR

Voltage regulator ICs are available with fixed

(typically 5, 12 and 15V) or variable output

voltages. They are also rated by the maximumcurrent they can pass. Negative voltage

regulators are available, mainly for use in dual

supplies. Most regulators include someautomatic protection from excessive current('overload protection') and overheating ('thermal

protection').

Many of the fixed voltage regulator ICs have 3

leads and look like power transistors, such as the

7805 +5V 1A regulator shown on the right. They

include a hole for attaching aheatsinkif necessary.

Voltage regulator
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Zener diode regulator:-

For low current power supplies a simple voltage regulator can

be made with a resistor and a zener diode connected in reverse

as shown in the diagram. Zener diodes are rated by their

breakdown voltage Vz and maximum power Pz (typically400mW or 1.3W).

The resistor limits the current (like an LED resistor). Thecurrent through the resistor is constant, so when there is no

output current all the current flows through the zener diode andits power rating Pz must be large enough to withstand this.

Choosing a zener diode and resistor:

1. The zener voltage Vz is the output voltage required2.

The input voltage Vs must be a few volts greater thanVz(this is to allow for small fluctuations in Vs due to ripple)

3. The maximum current Imax is the output current required plus 10%4. The zener power Pz is determined by the maximum current: Pz > Vz Imax5. The resistor resistance: R = (Vs - Vz) / Imax6. The resistor power rating: P > (Vs - Vz) Imax

5V, 12V Regulated Power supply

5V, 12V Regulated Power supply

Regulated power supplies are commonly used in engineering projects. Power supply is food of

any circuit. I would like to share 5V, 12V regulated power supply circuits which can be used forEmbedded or Micro controller projects.

+5V SUPPLY UNITThe circuit diagram of +5V is shown in the figure. +5V supply is obtained from the +5V supply

unit for microcontroller and digital ICs. Initially 230 V AC supply is reduced to (0-9V) with the

help of a step down transformer having a capacity of 500mA. Since the input voltage to theregulator IC should be more than its output voltage, transformer secondary voltage is 9V. This

low voltage is rectified with the help of bridge rectifier. The ripples are minimized with the help

of capacitor filter to get a smooth DC supply. The rating of the chosen capacitor filter is 1000F.

The regulated DC voltage is obtained by using a regulator IC 7805. In the case of IC 7805, theunregulated DC voltage is applied to Pin 1, and the output is taken at Pin 3 and Pin 2 is

grounded. Another capacitor filter of rating 10F is connected at the output of regulator IC to

eliminate the voltage oscillations at the output due to the large voltage oscillations at the input of

the regulator.

zener diode

a = anode, k = cathode


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+12V SUPPLY UNITThe 12 V supply required by the OP amps is provided by the 12V supply circuit arrangement.

The circuit diagram of 12V power supply unit is shown in figure. Initially 230 V AC supply is

reduced to (15V-0-15V) with the help of a step down transformer having a capacity of 1A andthe center tap of the transformer is grounded. This low voltage is rectified with the help off

bridge rectifier. Since the input voltage to the regulator IC should be more than its output

voltage, transformer secondary voltage is 15V-0-15V.The ripples are minimized with the help ofcapacitor filter to get a smooth DC supply. The rating of the chosen capacitor filter is 1000F.

The regulated DC output voltage is obtained by using regulator ICs. For regulated +12V DC

supply, IC 7812 is used and for regulated -12V DC supply, IC 7912 is used. In the case of IC

7812 the unregulated DC voltage is applied to Pin 1, and the output is taken at Pin 3 and Pin 2 isgrounded. In the case of 7912 ,the unregulated DC voltage is applied to Pin 2, the output is taken

at Pin 3 and Pin 1 is grounded. The pair of capacitors of 10F is connected at the output as

shown in figure to eliminate the voltage oscillations at the output due to the large voltageoscillations at the input of the regulator.
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3.2 MAX 232

The MAX232 is anintegrated circuitthat converts signals from anRS-232serial port to signalssuitable for use inTTLcompatible digital logic circuits. The MAX232 is a dual driver/receiver

and typically converts the RX, TX, CTS and RTS signals.

The drivers provide RS-232 voltage level outputs (approx. 7.5 V) from a single + 5 V supply

via on-chipcharge pumpsand external capacitors. This makes it useful for implementing RS-232

in devices that otherwise do not need any voltages outside the 0 V to + 5 V range, as powersupplydesign does not need to be made more complicated just for driving the RS-232 in this

case.

The receivers reduce RS-232 inputs (which may be as high as 25 V), to standard 5 V TTLlevels. These receivers have a typical threshold of 1.3 V, and a typical hysteresisof 0.5 V.

The later MAX232A is backwards compatible with the original MAX232 but may operate at

higher baud rates and can use smaller external capacitors 0.1F in place of the 1.0 Fcapacitors used with the original device

The newer MAX3232 is also backwards compatible, but operates at a broader voltage range,

from 3 to 5.5 V.

Pin to pin compatible: ICL232, ST232, ADM232, HIN232.

Voltage levels

It is helpful to understand what occurs to the voltage levels. When a MAX232 IC receives a TTL

level to convert, it changes a TTL Logic 0 to between +3 and +15 V, and changes TTL Logic 1to between -3 to -15 V, and vice versa for converting from RS232 to TTL. This can be confusing

when you realize that the RS232 Data Transmission voltages at a certain logic state are oppositefrom the RS232 Control Line voltages at the same logic state. To clarify the matter, see the table

below. For more information seeRS-232 Voltage Levels.

RS232 Line Type & Logic Level RS232 Voltage TTL Voltage to/from MAX232

Data Transmission (Rx/Tx) Logic 0 +3 V to +15 V 0 V

Data Transmission (Rx/Tx) Logic 1 -3 V to -15 V 5 V

Control Signals (RTS/CTS/DTR/DSR) Logic 0 -3 V to -15 V 5 V

Control Signals (RTS/CTS/DTR/DSR) Logic 1 +3 V to +15 V 0 V
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PIN DIAGRAM:-

Features:

1. Operates With Single 5-V Power Supply

2.LinBiCMOSE Process Technology

3.Two Drivers and Two Receivers

4.30-V Input Levels

5.Low Supply Current . 8 mA Typical


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6.Meets or Exceeds TIA/EIA-232-F and ITU

Recommendation V.28

7.Designed to be Interchangeable With

Maxim MAX232

8.Applications

TIA/EIA-232-F

Battery-Powered Systems

Terminals

Modems

Computers

9.ESD Protection Exceeds 2000 V Per

MIL-STD-883, Method 3015

10.Package Options Include Plastic

Small-Outline (D, DW) Packages and

Standard Plastic (N) DIPs

Cicuit connections:

A standard serial interfacing for PC, RS232C, requires negative logic, i.e., logic '1' is -3V to -12V and

logic '0' is +3V to +12V. To convert a TTL logic, say, TxD and RxD pins of the uC chips, thus need a

converter chip. A MAX232 chip has long been using in many uC boards. It provides 2-channel RS232C

port and requires external 10uF pacitors. Carefully check the polarity of capacitor when soldering the

board. A DS275 however, no need external capacitor and smaller. Either circuit can be used without any

problems.


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3.3 LCD DISPLAY

A liquid crystal display (LCD) is a thin, flat display device made up of any number of

color or monochrome pixels arrayed in front of a light source or reflector. Each pixel consists of a

column of liquid crystal molecules suspended between two transparent electrodes, and two polarizing

filters, the axes of polarity of which are perpendicular to each other. Without the liquid crystals

between them, light passing through one would be blocked by the other. The liquid crystal twists the

polarization of light entering one filter to allow it to pass through the other.

A program must interact with the outside world using input and output devices that

communicate directly with a human being. One of the most common devices attached to an controller is

an LCD display. Some of the most common LCDs connected to the contollers are 16X1, 16x2 and 20x2

displays. This means 16 characters per line by 1 line 16 characters per line by 2 lines and 20 characters

per line by 2 lines, respectively.


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Many microcontroller devices use 'smart LCD' displays to output visual information. LCD displays

designed around LCD NT-C1611 module, are inexpensive, easy to use, and it is even possible to produce

a readout using the 5X7 dots plus cursor of the display. They have a standard ASCII set of characters and

mathematical symbols. For an 8-bit data bus, the display requires a +5V supply plus 10 I/O lines (RS RW

D7 D6 D5 D4 D3 D2 D1 D0). For a 4-bit data bus it only requires the supply lines plus 6 extra lines(RS

RW D7 D6 D5 D4). When the LCD display is not enabled, data lines are tri-state and they do not interfere

with the operation of the microcontroller.

PIN DESCRIPTION:

Most LCDs with 1 controller has 14 Pins and LCDs with 2 controller has 16 Pins (two pins are

extra in both for back-light LED connections).

Fig: pin diagram of 1x16 lines lcd


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CONTROL LINES:

EN:

Line is called "Enable." This control line is used to tell the LCD that you are sending it

data. To send data to the LCD, your program should make sure this line is low (0) and then set

the other two control lines and/or put data on the data bus. When the other lines are completely

ready, bring EN high (1) and wait for the minimum amount of time required by the LCDdatasheet (this varies from LCD to LCD), and end by bringing it low (0) again.


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RS:

Line is the "Register Select" line. When RS is low (0), the data is to be treated as a

command or special instruction (such as clear screen, position cursor, etc.). When RS is high (1),

the data being sent is text data which sould be displayed on the screen. For example, to display

the letter "T" on the screen you would set RS high.

RW:

Line is the "Read/Write" control line. When RW is low (0), the information on the data

bus is being written to the LCD. When RW is high (1), the program is effectively querying (or

reading) the LCD. Only one instruction ("Get LCD status") is a read command. All others are

write commands, so RW will almost always be low.

Finally, the data bus consists of 4 or 8 lines (depending on the mode of operation selected

by the user). In the case of an 8-bit data bus, the lines are referred to as DB0, DB1, DB2, DB3,

DB4, DB5, DB6, and DB7.

Logic status on control lines:

E - 0 Access to LCD disabled

- 1 Access to LCD enabled

R/W - 0 Writing data to LCD

- 1 Reading data from LCD

RS - 0 Instructions

- 1 Character

Writing data to the LCD:

1) Set R/W bit to low

2) Set RS bit to logic 0 or 1 (instruction or character)


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3) Set data to data lines (if it is writing)

4) Set E line to high

5) Set E line to low

Read data from data lines (if it is reading)on LCD:

1) Set R/W bit to high

2) Set RS bit to logic 0 or 1 (instruction or character)

3) Set data to data lines (if it is writing)

4) Set E line to high

5) Set E line to low

Entering Text:

First, a little tip: it is manually a lot easier to enter characters and commands in hexadecimal

rather than binary (although, of course, you will need to translate commands from binary couple of sub-

miniature hexadecimal rotary switches is a simple matter, although a little bit into hex so that you know

which bits you are setting). Replacing the d.i.l. switch pack with a of re-wiring is necessary.

The switches must be the type where On = 0, so that when they are turned to the zero position,

all four outputs are shorted to the common pin, and in position F, all four outputs are open circuit.

All the available characters that are built into the module are shown in Table 3. Studying the

table, you will see that codes associated with the characters are quoted in binary and hexadecimal, most

significant bits (left-hand four bits) across the top, and least significant bits (right -hand four bits)

down the left.

Most of the characters conform to the ASCII standard, although the Japanese and Greek


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characters (and a few other things) are obvious

exceptions. Since these intelligent modules were

designed in the Land of the Rising Sun, it seems

only fair that their Katakana phonetic symbols

should also be incorporated. The more extensive

Kanji character set, which the Japanese share

with the Chinese, consisting of several thousand

different characters, is not included!

Using the switches, of whatever type, and

referring to Table 3, enter a few characters onto

the display, both letters and numbers. The RS

switch (S10) must be up (logic 1) when sending

the characters, and switch E (S9) must be pressed

for each of them. Thus the operational order is: set RS high, enter character, trigger E, leave RS high,

enter another character, trigger E, and so on.

The first 16 codes in Table 3, 00000000 to 00001111, ($00 to $0F) refer to the CGRAM. This is the

Character Generator RAM (random access memory), which can be used to hold user-defined graphics

characters. This is where these modules really start to show their potential, offering such capabilities as

bar graphs, flashing symbols, even animated characters. Before the user-defined characters are set up,

these codes will just bring up strange looking symbols.

Codes 00010000 to 00011111 ($10 to $1F) are not used and just display blank characters. ASCII

codes proper start at 00100000 ($20) and end with 01111111 ($7F). Codes 10000000 to 10011111 ($80

to $9F) are not used, and 10100000 to 11011111 ($A0 to $DF) are the Japanese characters.


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Initialization by Instructions:

If the power conditions for the normal operation of the internal reset circuit are not satisfied,

then executing a series of instructions must initialize LCD unit. The procedure for this initializationprocess is as above show.


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3.4 RELAY

Introduction:

A relay is an electrical switch that opens and closes under the control of another electrical

circuit. In the original form, the switch is operated by an electromagnet to open or close one or

many sets of contacts. A relay is able to control an output circuit of higher power than the input

circuit, it can be considered to be, in a broad sense, a form of an electrical amplifier.

Relays are usuallly SPDT (single pole double through switch)or DPDT (double pole double

through switch) but they can have many more sets of switch contacts, for example relays with 4 sets of

changeover contacts are readily available.


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Basic operation of a relay:

An electric current through a conductor will produce a magnetic field at right angles to the

direction of electron flow. If that conductor is wrapped into a coil shape, the magnetic field

produced will be oriented along the length of the coil. The greater the current, the greater the

strength of the magnetic field, all other factors being equal.

Inductors react against changes in current because of the energy stored in this magnetic

field. When we construct a transformer from two inductor coils around a common iron core, we

use this field to transfer energy from one coil to the other. However, there are simpler and more

direct uses for electromagnetic fields than the applications we've seen with inductors and

transformers. The magnetic field produced by a coil of current-carrying wire can be used to exert

a mechanical force on any magnetic object, just as we can use a permanent magnet to attract


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Magnetic Stick Relays or Perm polarized Relays:

These relays have a magnetic circuit with high permanence. Two coils, one to operate

(pick up) and one to release (drop) are present. The relay is activated by a current in the operate

coil. On the interruption of the current the armature remains in picked up position by the residualmagnetism. The relay is released by a current through the release coil.

Slow Release Relays:

These relays have a capacitor connected in parallel to their coil. When the operating

current is interrupted the release of relay is delayed by the stored charge in the capacitor. The

relay releases as the capacitor discharges through the coil.

Relays for AC:

These are neutral relays and picked up for a.c. current through their coil. These are very

fast in action and used on power circuits of the point motors, where high current flows through

the contacts. A normal relay would be slow and make sparks which in turn may weld the

contacts together.

All relays have two operating values (voltages), one pick-up and the other other drop

away. The pick-up value is higher than the drop away value.

Applications:

To control a high-voltage circuit with a low-voltage signal, as in some types of modems or audioamplifiers,

To control a high-current circuit with a low-current signal, as in the starter solenoid of anautomobile,

To detect and isolate faults on transmission and distribution lines by opening and closing circuitbreakers (protection relays),

To isolate the controlling circuit from the controlled circuit when the two are at differentpotentials, for example when controlling a mains-powered device from a low-voltage switch.

The latter is often applied to control office lighting as the low voltage wires are easily installed in


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partitions, which may be often moved as needs change. They may also be controlled by room

occupancy detectors in an effort to conserve energy,

To perform logic functions. For example, the boolean AND function is realised by connecting NOrelay contacts in series, the OR function by connecting NO contacts in parallel. The change-over

or Form C contacts perform the XOR (exclusive or) function. Similar functions for NAND and NOR

are accomplished using NC contacts. The Ladder programming language is often used for

designing relay logic networks.

o Early computing. Before vacuum tubes and transistors, relays were used as logicalelements in digital computers. See ARRA (computer), Harvard Mark II, Zuse Z2, and Zuse

Z3.

o Safety-critical logic. Because relays are much more resistant than semiconductors tonuclear radiation, they are widely used in safety-critical logic, such as the control panels

of radioactive waste-handling machinery.

To perform time delay functions. Relays can be modified to delay opening or delay closing a setof contacts. A very short (a fraction of a second) delay would use a copper disk between the

armature and moving blade assembly. Current flowing in the disk maintains magnetic field for a

short time, lengthening release time. For a slightly longer (up to a minute) delay, a dashpot is

used. A dashpot is a piston filled with fluid that is allowed to escape slowly. The time period can

be varied by increasing or decreasing the flow rate. For longer time periods, a mechanicalclockwork timer is installed

3.5 BUZZER

A buzzer or beeper is a signaling device, usually electronic, typically used in automobiles,

household appliances such as a microwave oven, or game shows.

It most commonly consists of a number of switches or sensors connected to a control unit that

determines if and which button was pushed or a preset time has lapsed, and usually illuminates a

light on the appropriate button or control panel, and sounds a warning in the form of a

continuous or intermittent buzzing or beeping sound. Initially this device was based on an

electromechanical system which was identical to an electric bell without the metal gong . Often

these units were anchored to a wall or ceiling and used the ceiling or wall as a sounding board.


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Another implementation with some AC-connected devices was to implement a circuit to make

the AC current into a noise loud enough to drive a loudspeaker and hook this circuit up to a

cheap 8-ohm speaker. Nowadays, it is more popular to use a ceramic-based piezoelectric sounder

like a Son alert which makes a high-pitched tone. Usually these were hooked up to "driver"

circuits which varied the pitch of the sound or pulsed the sound on and off.

In game shows it is also known as a "lockout system," because when one person signals ("buzzes

in"), all others are locked out from signaling. Several game shows have large buzzer buttons

which are identified as "plungers".

The word "buzzer" comes from the rasping noise that buzzers made when they were

electromechanical devices, operated from stepped-down AC line voltage at 50 or 60 cycles.

Other sounds commonly used to indicate that a button has been pressed are a ring or a beep.

full home appliances

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