Wireless Home Automation Using Bluetooth

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CHAPTER 1
INTRODUCTION
1.1 GENERAL: Although home automation today is not a new thing but most
advanced home automation systems in existence today require a big and expensive
change of infrastructure. This means that it often is not feasible to install a home
automation system in an existing building.
“Homatic” is a wireless home automation application that is supposed to be
implemented in existing home environments, without any changes in the existing
infrastructure.
“Homatic” lets the user to control his home from his or her android smart
phone. In the smart phone application the user can select actions what should
happen with electrical and/or electronic devices in the network [2]. The Bluetooth
wireless technology is set to revolutionize the way people perceive digital devices
in our homes and office environment. Now they are no longer just theindividual
devices; instead, with the embedded Bluetooth technology, they form a network in
which appliances can communicate with each other. This wireless technology is
especially useful in home environment, where there exists hardly any infrastructure
to interconnect intelligent appliances.
1.2 BASIC CONCEPT: It could be suitably used for home automation in acost-
effective manner. Operating over unlicensed, universally available frequency of
2.4 GHz, it can link digital devices within a range of 10 m (expandable to 100
m[5], by increasing the transmitted power) at the speed of 1 Mbps.Building upon
this theme, we proposea home automation system based on Bluetooth technology.
There are certain issues involved in the design of a home automation system.
The system should be scalable, so that new device can easily be integrated into it.
It should provide a user-friendly interface on the host side, so that the devices can
be setup, monitored and controlled. The interface should also provide some
diagnostic services so those problems with the system, if any, can be tracked down.
The overall system should be fast enough to realize the true power of wireless

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technology. It should also be cost effective in order to justify its application in
home automation.
The system developed during the course of this research consists of a Host
Controller (HC) implemented on a Smart Phone, and a microcontroller based
temperature-sensor/fan-controller, that is able to communicate with the host
through the Bluetooth link. The system is based on Home Automation Protocol
(HAP), developed by the authors in order to facilitate the master–slave
communication in a home automation network . This protocol ensures a prioritized,
interlocked exchange of data.
It also supports dynamic addition and removal of devices on the network. A
user interface on the PC offers device registration, control as well as diagnostic
utilities[4]. Bluetooth development kit from Ericsson was used for the
development. A microcontroller was used as a device controller for client modules.

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1.3 COMPONENTS USED
Following components are used in this project:
1. Android Smart phone
2. Microcontroller IC(AT89S52)
3. Bluetooth Module(HC05)
4. Relays
5. Relay Control IC(ULN2003)
6. LED’s and Bulb's
7. Transformer(220/12V)
8. Diode Bridge
9. 7805 regulator IC
10.Resistors, Capacitors and Connecting Wires

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CHAPTER 2
LITRATURE REVIEW
2.1 Android Smart phone
Android has an active community of developers and enthusiasts who
use the Android Open Source Project (AOSP) source code to develop and
distribute their own modified versions of the operating system. Android is
everywhere. Present days Phones, Tablets, TVs and set-top boxes powered
by Google TV.
Android was originally created by Andy Rubin as an operating system
for mobile phone twenty-first century. In 2005, Google acquired Android
Inc[12], and made Andy Rubin the Director of Mobile Platforms for
Google. As we are very familiar with the various features of the android
smart mobile. transferring the data(Commands) through wireless medium in
one of it and the desired act.
These wireless connections could be established over:
 Internet
 WI-FI
 Bluetooth(Used in Project)
 Infrared
 RF Communication
To generate The Commands for the Microcontroller in order to get a load
start working an Application on Android Platform is mandatory. The
Application must be designed according to the loads are to be controlled.
To establish a connection make sure that the Bluetooth module over the
model is switched ON and then pair(Connect) any android mobile with the
module and then go the application and send the load control commands
from the Application desirably.

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2.2 Microcontroller IC(AT89S52)
2.2.1 Features:
It has following features
• Compatible with MCS®-51 Products
• 8KBs of ISP Flash Memory – Endurance: 10,000 Write/Erase Cycles
• 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 • FastProgramming Time
• Flexible ISP Programming (Byte and Page Mode)
• Green (Pb/Halide-free) Packaging Option
2.2.2 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 nonvolatile memory
technology and is compatible with the industry-standard 80C51 instruction set and
pin out[15]. The on-chip Flash allows the program memory to be reprogrammed
in-system or by a conventional nonvolatile 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-

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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
con-tents but freezes the oscillator, disabling all other chip functions until the next
interrupt or hardware reset.
FIG. 3

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2.2.3 Pin Configurations:
FIG. 4

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2.2.4 Pin Description:
 VCC: Supply voltage.
 GND: 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 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
sourcecurrent (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 1

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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 use 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 use 8-bit addresses (MOVX @
RI), [21]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.
sourcecurrent (IIL) because of the pull-ups.
Port 3 receives some control signals for Flash programming and
verification.Port 3 also serves the functions of various special features of the
AT89S52, as shown in the following table.
TABLE 2

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 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 98 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 weakly pulled high. Setting the ALE-
disable bit has no effect if the microcontroller is in external execution mode.
 PSEN: Program Store Enable (PSEN) is the read strobe to external program
memory[24]. 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.

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2.3 Bluetooth Module(HC05)
2.3.1 INTRODUCTION: HC-05 module is an easy to use Bluetooth SPP
(Serial Port Protocol) module, designed for transparent wireless serial
connection setup.
Serial port Bluetooth module is fully qualified Bluetooth V2.0+EDR (Enhanced
Data Rate) 3Mbps Modulation with complete 2.4GHz radio transceiver and
baseband[14]. It uses CSR Bluecore 04-External single chip Bluetooth system
with CMOS technology and with AFH(Adaptive Frequency Hopping Feature). It
has the footprint as small as 12.7mmx27mm. Hope it will simplify your overall
design/development cycle.
FIG. 6
2.3.2 Specifications:
a.Hardware features
Typical -80dBm sensitivity
Up to +4dBm RF transmit power
Low Power 1.8V Operation ,1.8 to 3.6V I/O
PIO control
UART interface with programmable baud rate
With integrated antenna
With edge connector

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b.Software features
Default Baud rate: 38400, Data bits:8, Stop bit:1,Parity:No parity, Data
control: has. Supported baud rate:
9600,19200,38400,57600,115200,230400,460800.
Given a rising pulse in PIO0, device will be disconnected.
Status instruction port PIO1: low-disconnected, high-connected;
PIO10 and PIO11 can be connected to red and blue led separately. When
master and slave are paired, red and blue led blinks 1time/2s in interval,
while disconnected only blue led blinks 2times/s.
Auto-connect to the last device on power as default.
Permit pairing device to connectas default.
Auto-pairing PINCODE:”0000” as default[16]..
Auto-reconnect in 30 min when disconnected as a result of beyond the range
of connection.
2.3.3 HARDWARE SIZE:
FIG. 7

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2.3.4 Pin Description
TABLE 3

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2.4 Relays
FIG. 8
2.4.1 INTRODUCTION: A relay is an electrically operated switch. Many
relays use an electromagnet to mechanically operate a switch, but other operating
principles are also used, such as solid-state relays. Relays are used where it is
necessary to control a circuit by a low-power signal (with complete electrical
isolation between control and controlled circuits)[6], or where several circuits must
be controlled by one signal. The first relays were used in long
distance telegraph circuits as amplifiers: they repeated the signal coming in from
one circuit and re-transmitted it on another circuit. Relays were used extensively in
telephone exchanges and early computers to perform logical operations.
A type of relay that can handle the high power required to directly control an
electric motor or other loads is called a contactor. Solid-state relays control power
circuits with no moving parts, instead using a semiconductor device to perform
switching. Relays with calibrated operating characteristics and sometimes multiple
operating coils are used to protect electrical circuits from overload or faults; in
modern electric power systems these functions are performed by digital
instruments still called "protective relays".
2.4.2 Basic design and operation:
A simple electromagnetic relay consists of a coil of wire wrapped around a soft
iron core, an iron yoke which provides a low reluctancepath for magnetic flux, a
movable iron armature, and one or more sets of contacts (there are two in the relay
pictured). The armature is hinged to the yoke and mechanically linked to one or
more sets of moving contacts[17]. It is held in place by a spring so that when the

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relay is de-energized there is an air gap in the magnetic circuit. In this condition,
one of the two sets of contacts in the relay pictured is closed, and the other set is
open. Other relays may have more or fewer sets of contacts depending on their
function. The relay in the picture also has a wire connecting the armature to the
yoke. This ensures continuity of the circuit between the moving contacts on the
armature, and the circuit track on the printed circuit board (PCB) via the yoke,
which is soldered to the PCB.
When an electric current is passed through the coil it generates a magnetic
field that activates the armature, and the consequent movement of the movable
contact(s) either makes or breaks (depending upon construction) a connection with
a fixed contact. If the set of contacts was closed when the relay was de-energized,
then the movement opens the contacts and breaks the connection, and vice versa if
the contacts were open. When the current to the coil is switched off, the armature is
returned by a force, approximately half as strong as the magnetic force, to its
relaxed position. Usually this force is provided by a spring, but gravity is also used
commonly in industrial motor starters. Most relays are manufactured to operate
quickly. In a low-voltage application this reduces noise; in a high voltage or
current application it reduces arcing.
When the coil is energized with direct current, a diode is often placed across the
coil to dissipate the energy from the collapsing magnetic field at deactivation,
which would otherwise generate a voltage spike dangerous
to semiconductor circuit components. Some automotive relays include a diode
inside the relay case[13]. Alternatively, a contact protection network consisting of
a capacitor and resistor in series (snubbercircuit) may absorb the surge. If the coil
is designed to be energized with alternating current (AC), some method is used to
split the flux into two out-of-phase components which add together, increasing the
minimum pull on the armature during the AC cycle. Typically this is done with a
small copper "shading ring" crimped around a portion of the core that creates the
delayed, out-of-phase component.

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2.4.3 Types:
Latching relay:
FIG. 9:Latching relay with permanent magnet
A latching relay (also called "impulse", "keep", or "stay" relays) maintains either
contact position indefinitely without power applied to the coil. The advantage is
that one coil consumes power only for an instant while the relay is being switched,
and the relay contacts retain this setting across a power outage. A latching relay
allows remote control of building lighting without the hum that may be produced
from a continuously (AC) energized coil.
In one mechanism, two opposing coils with an over-center spring or permanent
magnet hold the contacts in position after the coil is de-energized. A pulse to one
coil turns the relay on and a pulse to the opposite coil turns the relay off. This type
is widely used where control is from simple switches or single-ended outputs of a
control system, and such relays are found in avionics and numerous industrial
applications.
Another latching type has a remanent core that retains the contacts in the operated
position by the remanent magnetism in the core. This type requires a current pulse
of opposite polarity to release the contacts. A variation uses a permanent magnet
that produces part of the force required to close the contact; the coil supplies
sufficient force to move the contact open or closed by aiding or opposing the field
of the permanent magnet. A polarity controlled relay needs changeover switches or
an H bridge drive circuit to control it[19]. The relay may be less expensive than
other types, but this is partly offset by the increased costs in the external circuit.
In another type, a ratchet relay has a ratchet mechanism that holds the contacts
closed after the coil is momentarily energized. A second impulse, in the same or a
separate coil, releases the contacts. This type may be found in certain cars,
for headlamp dipping and other functions where alternating operation on each
switch actuation is needed.

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A stepping relay is a specialized kind of multi-way latching relay designed for
early automatic telephone exchanges.
An earth leakage circuit breaker includes a specialized latching relay.
Very early computers often stored bits in a magnetically latching relay, such as
ferreed or the later memreed in the 1ESS switch.
Some early computers used ordinary relays as a kind of latch—they store bits in
ordinary wire spring relays or reed relays by feeding an output wire back as an
input, resulting in a feedback loop or sequential circuit. Such an electrically-
latching relay requires continuous power to maintain state, unlike magnetically
latching relays or mechanically ratcheting relays.
In computer memories, latching relays and other relays were replaced by delay line
memory, which in turn was replaced by a series of ever-faster and ever-smaller
memory technologies.
Reedrelay:
FIG 10:Top, middle: reed switches, bottom: reed relay
A reed relay is a reed switch enclosed in a solenoid[2]. The switch has a set of
contacts inside an evacuated or inert gas-filled glass tube which protects the
contacts against atmospheric corrosion; the contacts are made of magnetic material
that makes them move under the influence of the field of the enclosing solenoid or
an external magnet.
Reed relays can switch faster than larger relays and require very little power from
the control circuit. However, they have relatively low switching current and
voltage ratings. Though rare, the reeds can become magnetized over time, which
makes them stick 'on' even when no current is present; changing the orientation of
the reeds with respect to the solenoid's magnetic field can resolve this problem.

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Mercury-wettedrelay:
FIG 11:A mercury-wetted reed relay that has AC/DC switching specifications of 100 W, 500 V,
2 A maximum
A mercury-wetted reed relay is a form of reed relay in which the contacts are
wetted with mercury. Such relays are used to switch low-voltage signals (one volt
or less) where the mercury reduces the contact resistance and associated voltage
drop, for low-current signals where surface contamination may make for a poor
contact, or for high-speed applications where the mercury eliminates contact
bounce. Mercury wetted relays are position-sensitive and must be mounted
vertically to work properly. Because of the toxicity and expense of liquid mercury,
these relays are now rarely used.
The mercury-wetted relay has one particular advantage, in that the contact closure
appears to be virtually instantaneous, as the mercury globules on each
contact coalesce. The current rise time through the contacts is generally considered
to be a few picoseconds, however in a practical circuit it will be limited by
the inductance of the contacts and wiring. It was quite common, before the
restrictions on the use of mercury, to use a mercury-wetted relay in the laboratory
as a convenient means of generating fast rise time pulses, however although the
rise time may be picoseconds, the exact timing of the event is, like all other types
of relay, subject to considerable jitter, possibly milliseconds, due to mechanical
imperfections.
The same coalescence process causes another effect, which is a nuisance in some
applications. The contact resistance is not stable immediately after contact closure,
and drifts, mostly downwards, for several seconds after closure, the change
perhaps being 0.5 ohm.

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Mercury relay:
A mercury relay is a relay that uses mercury as the switching element. They are
used where contact erosion would be a problem for conventional relay contacts.
Owing to environmental considerations about significant amount of mercury used
and modern alternatives, they are now comparatively uncommon[12].
Polarizedrelay:
A polarized relay places the armature between the poles of a permanent magnet to
increase sensitivity. Polarized relays were used in middle 20th Century telephone
exchange is to detect faint pulses and correct telegraphic distortion. The poles
were on screws[27], so a technician could first adjust them for maximum
sensitivity and then apply a bias spring to set the critical current that would operate
the relay.
Machine tool relay:
A machine tool relay is a type standardized for industrial control of machine
tools, transfer machines, and other sequential control. They are characterized by a
large number of contacts (sometimes extendable in the field) which are easily
converted from normally-open to normally-closed status, easily replaceable coils,
and a form factor that allows compactly installing many relays in a control panel.
Although such relays once were the backbone of automation in such industries as
automobile assembly, the programmable logic controller (PLC) mostly displaced
the machine tool relay from sequential control applications.
A relay allows circuits to be switched by electrical equipment: for example, a timer
circuit with a relay could switch power at a preset time. For many years relays
were the standard method of controlling industrial electronic systems. A number of
relays could be used together to carry out complex functions (relay logic). The
principle of relay logic is based on relays which energize and de-energize
associated contacts[16]. Relay logic is the predecessor of ladder logic, which is
commonly used in programmable logic controllers.
Coaxialrelay:
Where radio transmitters and receivers share one antenna, often a coaxial relay is
used as a TR (transmit-receive) relay, which switches the antenna from the receiver

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to the transmitter. This protects the receiver from the high power of the transmitter.
Such relays are often used in transceivers which combine transmitter and receiver
in one unit. The relay contacts are designed not to reflect any radio frequency
power back toward the source, and to provide very high isolation between receiver
and transmitter terminals. Thecharacteristic impedance of the relay is matched to
the transmission line impedance of the system, for example, 50 ohms.
Time delay:
Timing relays are arranged for an intentional delay in operating their 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[7]. 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; both air-filled and oil-filled dashpots are used. The
time period can be varied by increasing or decreasing the flow rate. For longer time
periods, a mechanical clockwork timer is installed. Relays may be arranged for a
fixed timing period, or may be field adjustable, or remotely set from a control
panel. Modern microprocessor-based timing relays provide precision timing over a
great range.
Some relays are constructed with a kind of "shock absorber" mechanism attached
to the armature which prevents immediate, full motion when the coil is either
energized or de-energized. This addition gives the relay the property of time-delay
actuation. Time-delay relays can be constructed to delay armature motion on coil
energization, de-energization, or both.
Time-delay relay contacts must be specified not only as either normally-open or
normally-closed, but whether the delay operates in the direction of closing or in the
direction of opening[6]. The following is a description of the four basic types of
time-delay relay contacts.
First we have the normally-open, timed-closed (NOTC) contact. This type of
contact is normally open when the coil is unpowered (de-energized). The contact is
closed by the application of power to the relay coil, but only after the coil has been
continuously powered for the specified amount of time. In other words, the
direction of the contact's motion (either to close or to open) is identical to a regular
NO contact, but there is a delay in closing direction. Because the delay occurs in
the direction of coil energization, this type of contact is alternatively known as a
normally-open, on-delay

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2.4.4 Contactor:
A contactor is a heavy-duty relay used for switching electric motors and lighting
loads, but contactors are not generally called relays. Continuous current ratings for
common contactors range from 10 amps to several hundred amps. High-current
contacts are made with alloys containing silver. The unavoidable arcing causes the
contacts to oxidize; however, silver oxide is still a good conductor.[5] Contactors
with overload protection devices are often used to start motors. Contactors can
make loud sounds when they operate, so they may be unfit for use where noise is a
chief concern.
A contactor is an electrically controlled switch used for switching a power circuit,
similar to a relay except with higher current ratings.[6] A contactor is controlled by
a circuit which has a much lower power level than the switched circuit.
Contactors come in many forms with varying capacities and features. Unlike
a circuit breaker, a contactor is not intended to interrupt a short circuit current.
Contactors range from those having a breaking current of several amperes to
thousands of amperes and 24 V DC to many kilovolts. The physical size of
contactors ranges from a device small enough to pick up with one hand, to large
devices approximately a meter (yard) on a side.
Solid-state relay:
FIG 12:Solid state relay with no moving parts
FIG 13:25 A or 40 A solid state contactors

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A solid state relay or SSR is a solid state electronic component that provides a
function similar to an electromechanical relay but does not have any moving
components, increasing long-term reliability[14]. A solid-state relay uses
a thyristor, TRIAC or other solid-state switching device, activated by the control
signal, to switch the controlled load, instead of a solenoid. An optocoupler (a light-
emitting diode (LED) coupled with a photo transistor) can be used to isolate
control and controlled circuits.
As every solid-state device has a small voltage drop across it, this voltage drop
limits the amount of current a given SSR can handle. The minimum voltage drop
for such a relay is a function of the material used to make the device. Solid-state
relays rated to handle as much as 1,200 amperes have become commercially
available. Compared to electromagnetic relays, they may be falsely triggered by
transients and in general may be susceptible to damage by extreme cosmic
ray and EMP episodes.
Solid state contactorrelay:
A solid state contactor is a heavy-duty solid state relay, including the necessary
heat sink, used where frequent on/off cycles are required, such as with electric
heaters, small electric motors, and lighting loads. There are no moving parts to
wear out and there is no contact bounce due to vibration. They are activated by AC
control signals or DC control signals from Programmable logic controller(PLCs),
PCs, Transistor-transistor logic (TTL) sources, or other microprocessor and
microcontroller controls.
Buchholz relay:
A Buchholz relay is a safety device sensing the accumulation of gas in large oil-
filled transformers, which will alarm on slow accumulation of gas or shut down the
transformer if gas is produced rapidly in the transformer oil. The contacts are not
operated by an electric current but by the pressure of accumulated gas or oil flow.
Forced-guidedcontacts relay:
A forced-guided contacts relay has relay contacts that are mechanically linked
together, so that when the relay coil is energized or de-energized, all of the linked
contacts move together[16]. If one set of contacts in the relay becomes

26
immobilized, no other contact of the same relay will be able to move. The function
of forced-guided contacts is to enable the safety circuit to check the status of the
relay. Forced-guided contacts are also known as "positive-guided contacts",
"captive contacts", "locked contacts", "mechanically-linked contacts", or "safety
relays".
These safety relays have to follow design rules and manufacturing rules that are
defined in one main machinery standard EN 50205 : Relays with forcibly guided
(mechanically linked) contacts. These rules for the safety design are the one that
are defined in type B standards such as EN 13849-2 as Basic safety principles and
Well-tried safety principles for machinery that applies to all machines.
Forced-guided contacts by themselves can not guarantee that all contacts are in the
same state, however they do guarantee, subject to no gross mechanical fault, that
no contacts are in opposite states. Otherwise, a relay with several normally open
(NO) contacts may stick when energised, with some contacts closed and others still
slightly open, due to mechanical tolerances. Similarly, a relay with several
normally closed (NC) contacts may stick to the unenergised position, so that when
energised, the circuit through one set of contacts is broken, with a marginal gap,
while the other remains closed. By introducing both NO and NC contacts, or more
commonly, changeover contacts, on the same relay, it then becomes possible to
guarantee that if any NC contact is closed, all NO contacts are open, and
conversely, if any NO contact is closed, all NC contacts are open. It is not possible
to reliably ensure that any particular contact is closed, except by potentially
intrusive and safety-degrading sensing of its circuit conditions[25], however in
safety systems it is usually the NO state that is most important, and as explained
above, this is reliably verifiable by detecting the closure of a contact of opposite
sense.
Forced-guided contact relays are made with different main contact sets, either NO,
NC or changeover, and one or more auxiliary contact sets, often of reduced current
or voltage rating, used for the monitoring system. Contacts may be all NO, all NC,
changeover, or a mixture of these, for the monitoring contacts, so that the safety
system designer can select the correct configuration for the particular application.
Safety relays are used as part of an engineered safety system.
Overloadprotection relay:
Electric motors need overcurrent protection to prevent damage from over-loading
the motor, or to protect against short circuits in connecting cables or internal faults

27
in the motor windings.[7] The overload sensing devices are a form of heat operated
relay where a coil heats a bimetallic strip, or where a solder pot melts, releasing a
spring to operate auxiliary contacts. These auxiliary contacts are in series with the
coil. If the overload senses excess current in the load, the coil is de-energized.
This thermal protection operates relatively slowly allowing the motor to draw
higher starting currents before the protection relay will trip. Where the overload
relay is exposed to the same environment as the motor, a useful though crude
compensation for motor ambient temperature is provided.
The other common overload protection system uses an electromagnet coil in series
with the motor circuit that directly operates contacts. This is similar to a control
relay but requires a rather high fault current to operate the contacts. To prevent
short over current spikes from causing nuisance triggering the armature movement
is damped with adashpot. The thermal and magnetic overload detections are
typically used together in a motor protection relay.
Electronic overload protection relays measure motor current and can estimate
motor winding temperature using a "thermal model" of the motor armature system
that can be set to provide more accurate motor protection. Some motor protection
relays include temperature detector inputs for direct measurement from
a thermocouple or resistance thermometer sensorembedded in the winding.
Vacuum relays:
A sensitive relay having its contacts mounted in a highly evacuated glass housing,
to permit handling radio-frequency voltages as high as 20,000 volts without
flashover between contacts even though contact spacing is but a few hundredths of
an inch when open.

28
2.4.5 Pole and throw:
FIG 14:Circuit symbols of relays. (C denotes the common terminal in SPDT and DPDT types.)
Since relays are switches, the terminology applied to switches is also applied to
relays; a relay switches one or more poles, each of whose contacts can
be thrown by energizing the coil.
Normally-open (NO) contacts connect the circuit when the relay is activated; the
circuit is disconnected when the relay is inactive. It is also called a "Form A"
contact or "make" contact. NO contacts may also be distinguished as "early-make"
or "NOEM", which means that the contacts close before the button or switch is
fully engaged[21].
Normally-closed (NC) contacts disconnect the circuit when the relay is activated;
the circuit is connected when the relay is inactive. It is also called a "Form B"
contact or "break" contact. NC contacts may also be distinguished as "late-break"
or "NCLB", which means that the contacts stay closed until the button or switch is
fully disengaged.
Change-over (CO), or double-throw (DT), contacts control two circuits: one
normally-open contact and one normally-closed contact with a common terminal.
It is also called a "Form C" contact or "transfer" contact ("break before make"). If
this type of contact has a "make before break" action, then it is called a "Form D"
contact.

29
The following designations are commonly encountered:
 SPST – Single Pole Single Throw. These have two terminals which can be
connected or disconnected. Including two for the coil, such a relay has four
terminals in total. It is ambiguous whether the pole is normally open or
normally closed. The terminology "SPNO" and "SPNC" is sometimes used to
resolve the ambiguity.
 SPDT – Single Pole Double Throw. A common terminal connects to either of
two others. Including two for the coil, such a relay has five terminals in total.
 DPST – Double Pole Single Throw. These have two pairs of terminals.
Equivalent to two SPST switches or relays actuated by a single coil. Including
two for the coil, such a relay has six terminals in total. The poles may be Form
A or Form B (or one of each).
 DPDT – Double Pole Double Throw. These have two rows of change-over
terminals. Equivalent to two SPDT switches or relays actuated by a single coil.
Such a relay has eight terminals, including the coil.
The "S" or "D" may be replaced with a number, indicating multiple switches
connected to a single actuator. For example 4PDT indicates a four pole double
throw relay that has 12 switch terminals.
EN 50005 are among applicable standards for relay terminal numbering; a typical
EN 50005-compliant SPDT relay's terminals would be numbered 11, 12, 14, A1
and A2 for the C, NC, NO, and coil connections, respectively[25].
DIN 72552 defines contactnumbers in relays for automotive use;
 85 = relay coil -
 86 = relay coil +
 87 = common contact
 87a = normally closed contact
 87b = normally open contact

30
2.4.6 Applications:
FIG 15:A DPDT AC coil relay with "ice cube" packaging
Relays are used wherever it is necessary to control a high power or high voltage
circuit with a low power circuit. The first application of relays was in
long telegraph systems, where the weak signal received at an intermediate station
could control a contact, regenerating the signal for further transmission. High-
voltage or high-current devices can be controlled with small, low voltage wiring
and pilots switches. Operators can be isolated from the high voltage circuit. Low
power devices such as microprocessors can drive relays to control electrical loads
beyond their direct drive capability. In an automobile, a starter relay allows the
high current of the cranking motor to be controlled with small wiring and contacts
in the ignition key.
Electromechanical switching systems including Strowger and Crossbar telephone
exchanges made extensive use of relays in ancillary control circuits. The Relay
Automatic Telephone Company also manufactured telephone exchanges based
solely on relay switching techniques designed by Gotthilf Ansgarius Betulander.
The first public relay based telephone exchange in the UK was installed
in Fleetwood on 15 July 1922 and remained in service until 1959.
The use of relays for the logical control of complex switching systems like
telephone exchanges was studied by Claude Shannon, who formalized the
application of Boolean algebra to relay circuit design in A Symbolic Analysis of
Relay and Switching Circuits. Relays can perform the basic operations of Boolean
combinatorial logic. For example, the boolean AND function is realised by
connecting normally open relay contacts in series, the OR function by connecting
normally open contacts in parallel. Inversion of a logical input can be done with a
normally-closed contact[21]. Relays were used for control of automated systems

31
for machine tools and production lines. The Ladder programming language is often
used for designing relay logic networks.
Early electro-mechanical computers such as the ARRA, Harvard Mark II, Zuse Z2,
and Zuse Z3 relays for logic and working registers. However, electronic devices
proved faster and easier to use.
Because relays are much more resistant than semiconductors to nuclear radiation,
they are widely used in safety-critical logic, such as the control panels of
radioactive waste-handling machinery. Electromechanical protective relays are
used to detect overload and other faults on electrical lines by opening and
closing circuit breakers.
Relay application considerations:
FIG 16:Several 30-contact relays in "Connector" circuits in mid 20th century1XB
switch and 5XB switch telephone exchanges; cover removed on one
Selection of an appropriate relay for a particular application requires evaluation of
many different factors:
 Number and type of contacts – normally-open, normally-closed, (double-throw)
 Contact sequence – "Make before Break" or "Break before Make"[18]. For
example, the old style telephone exchanges required Make-before-break so that
the connection didn't get dropped while dialing the number.
 Rating of contacts – small relays switch a few amperes, large contactors are
rated for up to 3000 amperes, alternating or direct current
 Voltage rating of contacts – typical control relays rated 300 VAC or 600 VAC,
automotive types to 50 VDC, special high-voltage relays to about 15,000 V

32
 Operating lifetime, useful life - the number of times the relay can be expected
to operate reliably. There is both a mechanical life and a contact life. The
contact life is affected by the kind of load being switched. Breaking load
current causes undesired arcing between the contacts, eventually leading to
contacts that weld shut or contacts that fail due erosion by the arc.[10]
 Coil voltage – machine-tool relays usually 24 VDC, 120 or 250 VAC, relays
for switchgear may have 125 V or 250 VDC coils, "sensitive" relays operate on
a few milliamperes
 Coil current - including minimum current required to operate reliably and
minimum current to hold. Also effects of power dissipation on coil temperature
at various duty cycles.
 Package/enclosure – open, touch-safe, double-voltage for isolation between
circuits, explosion proof, outdoor, oil and splash resistant, washable for printed
circuit board assembly
 Operating environment - minimum and maximum operating temperatures and
other environmental considerations such as effects of humidity and salt
 Assembly – Some relays feature a sticker that keeps the enclosure sealed to
allow PCB post soldering cleaning, which is removed once assembly is
complete.
 Mounting – sockets, plug board, rail mount, panel mount, through-panel mount,
enclosure for mounting on walls or equipment
 Switching time – where high speed is required
 "Dry" contacts – when switching very low level signals, special contact
materials may be needed such as gold-plated contacts
 Contact protection – suppress arcing in very inductive circuits
 Coil protection – suppress the surge voltage produced when switching the coil
current
 Isolation between coil contacts
 Aerospaceor radiation-resistant testing, special quality assurance[5]
 Expected mechanical loads due to acceleration – some relays used
in aerospace applications are designed to function in shock loads of 50 g or
more
 Size - smaller relays often resist mechanical vibration and shock better than
larger relays, because of the lower inertia of the moving parts and the higher

33
natural frequencies of smaller parts.[3] Larger relays often handle higher voltage
and current than smaller relays.
 Accessories such as timers, auxiliary contacts, pilot lamps, and test buttons
 Regulatory approvals
 Stray magnetic linkage between coils of adjacent relays on a printed circuit
board.
There are many considerations involved in the correct selection of a control relay
for a particular application. These considerations include factors such as speed of
operation, sensitivity, and hysteresis. Although typical control relays operate in the
5 ms to 20 ms range, relays with switching speeds as fast as 100 us are
available. Reed relays which are actuated by low currents and switch fast are
suitable for controlling small currents.
As for any switch, the current through the relay contacts (unrelated to the current
through the coil) must not exceed a certain value to avoid damage. In the particular
case of high-inductance circuits such as motors, other issues must be addressed.
When an inductance is connected to a power source, an input surge current or
electromotor starting current larger than the steady current exists. When the circuit
is broken, the current cannot change instantaneously, which creates a potentially
damaging spark across the separating contacts.
Consequently for relays which may be used to control inductive loads, we must
specify the maximum current that may flow through the relay contacts when it
actuates, the make rating; the continuous rating; and the break rating. The make
rating may be several times larger than the continuous rating, which is itself larger
than the break rating.

34
Derating factors:
Control relays should not be operated above rated
temperature because of resulting increased degradation
and fatigue. Common practice is to derate 20 degrees
Celsius from the maximum rated temperature limit.
Relays operating at rated load are also affected by their
environment. Oil vapors may greatly decrease the
contact tip life, and dust or dirt may cause the tips to
burn before their normal life expectancy. Control relay
life cycle varies from 50,000 to over one million cycles
depending on the electrical loads of the contacts, duty
cycle, application, and the extent to which the relay is
derated. When a control relay is operating at its derated
value, it is controlling a lower value of current than its maximum make and break
ratings. This is often done to extend the operating life of the control relay. The
table lists the relay derating factors for typical industrial controlapplications[13].
Undesired arcing:
Switching while "wet" (under load) causes undesired arcing between the contacts,
eventually leading to contacts that weld shut or contacts that fail due to a buildup
of contact surface damage caused by the destructive arc energy.[10]
Inside the 1ESS switch matrix switch and certain other high-reliability designs, the
reed switches are always switched "dry" to avoid that problem, leading to much
longer contact life.[11]
Without adequate contact protection, the occurrence of electric current
arcing causes significant degradation of the contacts in relays, which suffer
significant and visible damage. Every time a relay transitions either from a closed
to an open state (break arc) or from an open to a closed state (make arc & bounce
arc), under load, an electrical arc can occur between the two contact points
(electrodes) of the relay. In many situations, the break arc is more energetic and
thus more destructive, in particular with resistive-type loads. However, inductive
loads can engender more destructive make arcs: for example, with standard electric
motors, the start-up (inrush) current tends to be much greater than the running
current. This translates into enormous make arcs.
Type of load % of rated value
Resistive 75
Inductive 35
Motor 20
Filament 10
Capacitive 75

35
During an arcing event, the heat energy contained in the electrical arc is very high
(tens of thousands of degrees Fahrenheit), causing the metal on the contact surfaces
to melt, pool and migrate with the current. The extremely high temperature of the
arc cracks the surrounding gas molecules creating ozone, carbon monoxide, and
other compounds. The arc energy slowly destroys the contact metal, causing some
material to escape into the air as fine particulate matter[20]. This very activity
causes the material in the contacts to degrade quickly, resulting in device failure.
This contact degradation drastically limits the overall life of a relay to a range of
about 10,000 to 100,000 operations, a level far below the mechanical life of the
same device, which can be in excess of 20 million operations.
Protective relays:
For protection of electrical apparatus and transmission lines, electromechanical
relays with accurate operating characteristics were used to detect overload, short-
circuits, and other faults. While many such relays remain in use, digital devices
now provide equivalent protective functions.
Railway signaling:1
FIG 17:Part of a relay interlocking using UK Q-style miniature plug-in relays.
FIG 18:UK Q-style signalling relay and base.

36
Railway signalling relays are large considering the mostly small voltages (less than
120 V) and currents (perhaps 100 mA) that they switch[14]. Contacts are widely
spaced to prevent flashovers and short circuits over a lifetime that may exceed fifty
years. BR930 series plug-in relays[13] are widely used on railways following British
practice. These are 120 mm high, 180 mm deep and 56 mm wide and weigh about
1400 g, and can have up to 16 separate contacts, for example, 12 make and 4 break
contacts. Many of these relays come in 12V, 24V and 50V versions.
The BR Q-type relay are available in a number of different configurations:
 QN1 Neutral
 QL1 Latched - see above
 QNA1 AC-immune
 QBA1 Biased AC-immune - see above
 QNN1 Twin Neutral 2x4-4 or 2x6-2
 QBCA1 Contactor for high current applications such as point motors. Also DC
biased and AC immune.
 QTD4 - Slow to release timer
 QTD5 - Slow to pick up timer
Since rail signal circuits must be highly reliable, special techniques are used to
detect and prevent failures in the relay system. To protect against false
feeds, double switching relay contacts are often used on both the positive and
negative side of a circuit, so that two false feeds are needed to cause a false signal.
Not all relay circuits can be proved so there is reliance on construction features
such as carbon to silver contacts to resist lightning induced contact welding and to
provide AC immunity[18].
Opto-isolators are also used in some instances with railway signalling, especially
where only a single contact is to be switched.
Signalling relays, typical circuits, drawing symbols, abbreviations & nomenclature,
etc. come in a number of schools, including the United States, France, Germany,
and the United Kingdom.

37
2.4.7 History:
The American scientist Joseph Henry is often claimed to have invented a relay in
1835 in order to improve his version of the electrical telegraph, developed earlier
in 1831. However, there is little in the way of official documentation to suggest he
had made the discovery prior to 1837.
It is claimed that the English inventor Edward Davy "certainly invented the electric
relay" in his electric telegraph c.1835.
A simple device, which we now call a relay, was included in the original
1840 telegraph patent of Samuel Morse. The mechanism described acted as a
digital amplifier, repeating the telegraph signal, and thus allowing signals to be
propagated as far as desired. This overcame the problem of limited range of earlier
telegraphy schemes.
The word relay appears in the context of electromagnetic operations from 1860.

38
2.5 Relay Control IC(ULN2003)
A Relay driver IC is an electro-magnetic switch that will be used whenever we
want to use a low voltage circuit to switch a light bulb ON and OFF which is
connected to 220V mains supply. The required current to run the relay coil is more
than can be supplied by various integrated circuits like Op-Amp, etc.Relays have
unique properties and are replaced with solid state switches that are strong than
solid-state devices. High current capacities, capability to stand ESD and drive
circuit isolation are the unique properties of Relays[14]. There are various ways to
drive relays.Some of the Relay Driver ICs are as below.
 High side toggle switch driver
 Low side toggle switch driver
 Bipolar NPN transistor driver
 N-Channel MOSFET driver and
 Darlington transistor driver
 ULN2003 driver
2.5.1 RelayDriver IC Circuit
Relays are components that permit a low-power circuit to control signals or to
switch high current ON and OFF which should be electrically isolated from
controlling circuit.
The Required Components
 Zener Diode
 6-9V Relay
 9V Battery or DC Power Supply
 2N2222 Transistor
 1K Ohm Resistor
 Second Input Voltage Source

39
FIG 19:Relay Driver IC Circuit
In order to drive the relay, we use transistor and only less power can be possibly
used to get the relay driven. Since, transistor is an amplifier so the base lead
receives sufficient current to make more current flow from Emitter of Transistor to
Collector. If the base once gets power that is sufficient, then the transistor conduct
from Emitter to Collector and power the relay.
The Transistor’s emitter-to-collector channel will be opened even though no input
current or voltage is applied to Base lead of Transistor. Therefore, blocking current
flows through relay coil.
The emitter-to-collector channel will be opened and allows current to flow through
relay’s coil if enough current or voltage is applied as input to the base lead. AC or
DC Current can be used to power the relay and circuit.Relays are electromagnetic
devices which allow low-power circuit to switch a high current ON and OFF
switching devices with the help of an armature that is moved by an electromagnet.
Driver Circuit is used to boost or amplify signals from micro-controllers to control
power switches in semi-conductor devices. Driver circuits take functions that
include isolating the control circuit and the power circuit, detecting malfunctions,

40
storing and reporting failures to the control system, serving as a precaution against
failure, analyzing sensor signals and creating auxiliary voltages.
Driver Circuits:
A typical digital logic output pin supplies only tens of MA of current. External
devices such as high-power LEDs, motors, speakers, light bulbs, buzzers, solenoids
and relays can require hundreds of MA and they need same voltages. In order to
control small devices which use DC, a transistor-based driver circuit is used to
amplify current to the required levels[1]. If the voltage and current levels are in
perfect range, the transistor acts like a high-current switch controlled by the lower
current digital logic signal. A discrete BJT is used at times in place of MOSFET
transistor especially on older or low voltage circuits as shown below.
FIG 20:Driver Circuit
Basic Driver Circuit using a BJT Transistor PNP, NPN, or MOS transistors are
also be used. Transistor provides current gain. The resistor used on the base of the
transistor is 1K ohm. On inductive loads (i.e., motors, solenoids, relays), a diode is
often connected backwards across the load to suppress the voltage spikes (back
EMF) generated when turning devices OFF.
Inductor V = L* di/dt
A negative voltage spike is produced when turning the device OFF. A diode is
also connected across the transistor instead of the load sometimes in order to
protect the transistor. The 2N3904 shown below is a small discrete BJT transistor
is used for a driver circuit that required less than 200MA. In this circuit with BJTs,

41
Vcc – higher voltage supply than the logic power supply and 6 or 12V DC is
required for motors or relays.
The load is directly connected to battery power and cannot passed through the
voltage regulator in battery operated devices. Many devices such as motors have
more inflow current spike when they are first turned ON. Be cautious on maximum
current ratings.
FIG 21:Relay Driver Circuits
Advantages of Low Side Driver:
More interface options are available which includes popular ULN2003 driver.
 Easy to interface to low voltage logic circuitry.
 Fewer components are used.
 Less expensive NPN drive transistors.
 Relay power reduces load on voltage regulator.
 It uses more commonly obtained NPN drive transistors.
 It is easier to interface relay.
 It is economic.
 Uses Industry standard technique.
The ULN2003 has internal clamp diodes. While these work OK in non-critical
applications and it leads to rise of glitches.

42
Clamp Diode
The clamp, free-wheeling or commutation diode provides a path for the inductive
discharge current to flow when the driver switch is opened. If not provided, it will
generate an arc in the switch—while the arc will not generally damage a switch
contact, it will cause contact degradation over time—and yes, it will destroy
transistors—been there, done that. The diode requirements are non-critical and a
1N4148 signal diode will generally work OK in low power applications[23].
Avoid emitter follower drivers. If the relay is switched to OFF in 4007 diode
eliminates back e.m.f and safe guards the transistor. ON status of the relay is
indicated by LED.
DC RelayDriver IC Circuit
Let us see construction of relay driver circuit for relays that are operated from DC
power. In order to drive a DC relay, DC voltage is needed in required quantity to
rate a relay and a zener diode.Voltage is required for the relay to operate and to
open or close its switch in a circuit. Relays exist with a voltage rating. This is
known as relay’s datasheet to rate its coil voltage. For the function of relay, it must
receive this voltage at its coil terminals. Thus, if a relay has a rated voltage of
9VDC, it should get 9 volts of DC voltage for its working. In order to eliminate
voltage spikes from a relay circuit, a diode is required for its proper functioning.
The coil of a relay acts an Inductor.
FIG 22:DC Relay Driver Circuit

43
The inductors are electronic components which withstand changes in current and
also the inductors are coils of wires wrapped around a conductive core. Voltage
spikes damages all components in a circuit and also damages relay’s switch
contacts. To prevent these voltage spikes, a diode is kept reverse biased in parallel
with the relay which acts as a transient (spike) suppressor eliminates voltage spikes
by going into conduction before voltage is formed across the coil. A transient
suppressor suppresses these spikes. A diode conducts reverse bias current if
voltage reaches a certain threshold. The diode functions to shunt excess power to
ground, and the diodes conductif the voltage reaches breakdown voltage.
The Required Components
 DC Relay
 Zener Diode
 DC Voltage Source or a DC power supply.
The zener diode is placed reverse biased in parallel to the relay.
The Relay used in the above is rated for 9Volts. In this a 9V DC Voltage source
feeds the resistor. A Zener diode reverse biased is placed in order to suppress the
transients caused by opening and closing the relay. This shunts all excess power to
ground if it reaches a particular threshold. This is the process to operate a relay.
Driving the loads which were connected to the output taking required power the
relay will be closed.
AC RelayDriver IC Circuit
This AC Relay driver IC circuit is a relay that runs with AC power and cannot be
run with DC power. In order to run an AC relay, enough AC voltage is required tp
rate the relay and transient suppressor. In AC relay circuit we cannot use a diode to
remove voltage spikes. This diode conducts an alternate half-cycle with AC power.
We use an RC series network by placing across coil in parallel to form a working
transient voltage suppressor with an AC circuit. Capacitor absorbs charge which
comes excessively and resistor helps to control overflow.Components required to
form the circuit is as follows

44
FIG 23:AC Relay Driver Circuit
 AC Relay
 100 Ohm Resistor
 0.05 Micro Farad Capacitor
 AC Voltage Source
NOTE: AC voltage source may come out from plug that is inserted into US wall
outlet.
Be careful with AC Power that comes out directly from wall outlet as it causes
Shock. Consult a Professional before taking power from plug into wall outlet.
When we use a relay with rated voltage 110VAC, we should feed it with 110V
from an AC power source. To suppress voltage spikes, resistor and capacitor
connected in series acts as transient voltage suppressor[25].
2.5.2 RelayDriver IC ULN2003 PIN DIAGRAM
The relay driver uln2003 ic is a high voltage and current darlington array ic, it
comprises of 7-open collector darlington pairs with common emitters. A pair of
darlington is an arrangement of two bipolar transistors. This IC belongs to the
family of ULN200x ICs and various types of this family interface to various logic
families. This ULN2003 IC is for 5V TTL and CMOS logic devices. These ICs are
used as relay drivers as well as to drive a wide range of loads, line drivers, display
drivers etc. This IC is also normally used while driving Stepper Motors. The pairs
of darlington in ULN2003 is esteemed at 500mA and can withstand peak current of
600mA.In the pin layout, the i/ps & o/ps are provided reverse to each other. Each

45
driver also has a suppression diode to dissipate voltage spikes while driving
inductive loads
FIG 24:Relay Driver IC ULN2003
This project is designed for a three-phase-solid-state relay system. It incorporates
three single-phase units wherein each phase is controlled individually by power
TRIAC with RC snubber network for a zero-voltage switching (ZVS)[]17].
Opto-isolators are used in each phase to receive switching signals from
a microcontroller of the 8051 family, loads are connected in series with a set of
TRIACS driven by an opto-isolator. The microcontroller is designed to generate
output pulses after zero voltage pulse to ensure that the load gets switched on at
zero cross ofthe supply waveform.
The zero crossing feature of the TRIAC driver, (an opto-isolator) ensures low noise
generation thus avoiding sudden inrush of current on resistive and inductive loads.
In this project, two push buttons are used for generating the output pulses from the

46
microcontroller randomly, away from the ZVS ie not coinciding with zero voltage
supply voltage of the waveform.
FIG 25
The ULN2003A is a high-voltage, high-current Darlington transistor array.It
consists of seven NPN Darlington pairs that feature high-voltage outputs
with common-cathode flyback diodes for switching inductive loads. It is very
similar to the ULN2801A, ULN2802A, ULN2803A, ULN2804A, and
ULN2805A, only differing in logic input levels (TTL,CMOS, PMOS) and
number of inputs (8). The drivers can be paralleled for higher current
capability, even stacking one chip on top of another, both electrically and
physically has been done. Generally it can also be used for interfacing with
stepper motor, where the motor requires high ratings which cannot be
provided by other interfacing devices.

47
2.6 LED’s and Bulb's
2.6.1 INTRODUCTION: An LED lamp is a light-emitting
diode (LED) product that is assembled into a lamp (or light bulb) for use in
lighting fixtures. LED lamps have a lifespan and electrical efficiency that is
several times better than incandescent lamps, and significantly better than
most fluorescent lamps, with some chips able to emit more than 100 lumens
per watt.
FIG.26
Like incandescent lamps and unlike most fluorescent lamps (e.g. tubes
and compact fluorescent lamps or CFLs), LEDs come to full brightness without
need for a warm-up time; the life of fluorescent lighting is also reduced by frequent
switching on and off.[citation needed]Initial cost of LED is usually higher[15].
Degradation of LED dye and packaging materials reduces light output to some
extent over time.
Some LED lamps are made to be a directly compatible drop-in replacement for
incandescent or fluorescent lamps. An LED lamp packaging may show
the lumen output, power consumption in watts, color temperature in kelvins or
description (e.g. "warm white"), operating temperature range, and sometimes the
equivalent wattage of an incandescent lamp of similar luminous output.
Most LEDs do not emit light in all directions, and their directional characteristics
affect the design of lamps. Although through the progression of time,
omnidirectional lamps are becoming more common, allowing for 360° light
spread. The light output of single LEDs is less than that of incandescent and

48
compact fluorescent lamps; in most applications multiple LEDs are used to form a
lamp, although high-power versions (see below) are becoming available.
LED chips need controlled direct current (DC) electrical power; an
appropriate circuit is required to convert alternating current from the supply to the
regulated low voltage direct current used by the LEDs. LEDs are adversely
affected by high temperature, so LED lamps typically include heat
dissipation elements such as heat sinks and cooling fins.
2.6.2 DIAGRAM:
FIG. 27
FIG. 28

49
2.7 Transformer(230/12V)
FIG. 29
2.7.1 MODEL: RM0511
2.7.2 DESCRIPTION:AC - 230 V to AC - 12 V.
RM0513 is a general purpose chassis mounting mains transformer. Transformer
has 240 V primary windings and centre tapped secondary winding. The
transformer has flying colored insulated connecting leads ( Approx 100 mm long
)[4]. The Transformer act as step down transformer reducing AC - 240 V to AC - 6
V.
The Transformer gives two outputs of 6 V , 12 V and 0 V. The Transformer’s
construction is written below with details of Solid Core and Winding.
The transformer is a static electrical device that transfers energy by inductive
coupling between its winding circuits. A varying current in the primary winding
creates a varying magnetic flux in the transformer's core and thus a varying
magnetic flux through the secondary winding[4]. This varying magnetic flux
induces a varying electromotive force (E.M.F) or voltage in the secondary
winding. The transformer has cores made of high permeability silicon steel. The

50
steel has a permeability many times that of free space and the core thus serves to
greatly reduce the magnetizing current and confine the flux to a path which closely
couples the windings. The solid core uses one of the common design of laminated
core is made from interleaved stacks of E - shaped steel sheets capped with I -
shaped pieces, leading to its name of 'E - I transformer’. Such a design tends to
exhibit more losses, but is very economical to manufacture.
Windings are arranged concentrically to minimize flux leakage. The effect of
laminations is to confine eddy currents to highly elliptical paths that enclose little
flux, and so reduce their magnitude. Thinner laminations reduce losses, but are
more laborious and expensive to construct. Thin laminations are generally used on
high-frequency transformers, with some of very thin steel laminations able to
operate up to 10 KHz.
TABLE 4

51
2.8 Diode Bridge
2.8.1 INTRODUCTION: Full Wave Bridge Rectifier, This type of single
phase rectifier uses four individual rectifying diodes connected in a closed loop
“bridge” configuration to producethe desired output. The main advantage of this
bridge circuit is that it does not require a special centre tapped transformer, thereby
reducing its size and cost. The single secondarywinding is connected to one side
of the diode bridge network and the load to the other side as shown below.
FIG. 30
The four diodes labelled D1 to D4 are arranged in “series pairs” with only two
diodes conducting current during each half cycle. During the positive half cycle of
the supply, diodes D1 and D2 conduct in series while diodes D3 and D4 are
reverse biased and the current flows through the load as shown below[7].
2.8.2 The Positive Half-cycle
FIG. 31

52
During the negative half cycle of the supply, diodes D3 and D4 conduct in series,
but diodes D1 and D2switch “OFF” as they are now reverse biased. The current
flowing through the load is the same direction as before.
2.8.3 The Negative Half-cycle
FIG. 32
As the current flowing through the load is unidirectional, so the voltage developed
across the load is also unidirectional the same as for the previous two diode full-
wave rectifier, therefore the average DC voltage across the load is 0.637Vmax.
2.8.4 The Smoothing Capacitor
We saw in the previous section that the single phase half-wave rectifier produces
an output wave every half cycle and that it was not practical to use this type of
circuit to produce a steady DC supply. The full-wave bridge rectifier however,
gives us a greater mean DC value (0.637 Vmax) with less superimposed ripple
while the output waveform is twice that of the frequency of the input supply
frequency. We can therefore increase its average DC output level even higher by
connecting a suitable smoothing capacitor across the output of the bridge circuit as
shown below.

53
Full-wave Rectifier with Smoothing Capacitor
FIG. 33
The smoothing capacitor converts the full-wave rippled output of the rectifier into
a smooth DC output voltage. Generally for DC power supply circuits the
smoothing capacitor is an Aluminium Electrolytic type that has a capacitance value
of 100uF or more with repeated DC voltage pulses from the rectifier charging up
the capacitor to peak voltage.
However, their are two important parameters to consider when choosing a suitable
smoothing capacitor and these are its Working Voltage, which must be higher than
the no-load output value of the rectifier and its Capacitance Value, which
determines the amount of ripple that will appear superimposed on top of the DC
voltage.
Too low a capacitance value and the capacitor has little effect on the output
waveform. But if the smoothing capacitor is sufficiently large enough (parallel
capacitors can be used) and the load current is not too large, the output voltage will
be almost as smooth as pure DC[8]. As a general rule of thumb, we are looking to
have a ripple voltage of less than 100mV peak to peak.
The maximum ripple voltage present for a Full Wave Rectifier circuit is not only
determined by the value of the smoothing capacitor but by the frequency and load
current, and is calculated as:

54
2.8.5 Bridge Rectifier Ripple Voltage
Where: I is the DC load current in amps, ƒ is the frequency of the ripple or twice the
input frequency in Hertz, and C is the capacitance in Farads.
The main advantages of a full-wave bridge rectifier is that it has a smaller AC
ripple value for a given load and a smaller reservoir or smoothing capacitor than an
equivalent half-wave rectifier. Therefore, the fundamental frequency of the ripple
voltage is twice that of the AC supply frequency (100Hz) where for the half-wave
rectifier it is exactly equal to the supply frequency (50Hz).
The amount of ripple voltage that is superimposed on top of the DC supply voltage
by the diodes can be virtually eliminated by adding a much improved π-filter (pi-
filter) to the output terminals of the bridge rectifier. This type of low-pass filter
consists of two smoothing capacitors, usually of the same value and a choke or
inductance across them to introduce a high impedance path to the alternating ripple
component

55
2.9 VOLTAGE REGULATOR IC(7805)
2.9.1 INTRODUCTION: 7805 is a voltage regulator integrated circuit. It is a
member of 78xx series of fixed linear voltage regulator ICs. The voltage source in
a circuit may have fluctuations and would not give the fixed voltage output.
The voltage regulator IC maintains the output voltage at a constant value. The xx
in 78xx indicates the fixed output voltage it is designed to provide. 7805 provides
+5V regulated power supply. Capacitors of suitable values can be connected at
input and output pins depending upon the respective voltage levels.
This series of fixed-voltage integrated-circuit voltage regulators is designed for a
wide range of applications. These applications include on-card regulation for
elimination of noise and distribution problems associated with single-point
regulation. Each of these regulators can deliver up to 1.5 A of output current. In
addition to use as fixed-voltage regulators, these devices can be used with external
components to obtain adjustable output voltages and currents, and also can be used
as the power-pass element in precision regulators[4].
2.9.2PinDiagram:
FIG. 34

56
2.9.3 PIN DESCRIPTION
TABLE 5
2.9.4 ORDERING INFORMATION
TABLE 6

57
2.10 Resistors, Capacitors and Crystal Oscilator
2.10.1 RESISTOR:
A resistor is a two-terminal electrical or electronic component that opposes an
electric current by producing a voltage drop between its terminals in accordance
with Ohm's law: The electrical resistance is equal to the voltage drop across the
resistor divided by the current through the resistor while the temperature remains
the same. Resistors are used as part of electrical networks and electronic circuits.
Fig 35
Axial-lead resistors on tape. The tape is removed during assembly before the leads
are formed and the part is inserted into the board.
Fig 36
Three carbon composition resistors in a 1960s valve radio.
.
.

58
2.10.2 CAPACITOR
A capacitor is an electrical/electronic device that can store energy in the electric
field between a pair of conductors (called "plates"). The process of storing energy
in the capacitor is known as "charging", and involves electric charges of equal
magnitude, but opposite polarity, building up on each plate.
Capacitors are often used in electric and electronic circuits as energy-storage
devices. They can also be used to differentiate between high-frequency and low-
frequency signals. This property makes them useful in electronic filters.
Capacitortypes
Fig 37
Capacitors: SMD ceramic at top left; SMD tantalum at bottom left; through-hole tantalum at top
right; through-hole electrolytic at bottom right. Major scale divisions are cm.
Fig 38
Various types of capacitors. From left: multilayer ceramic, ceramic disc, multilayer polyester
film, tubular ceramic, polystyrene, metallized polyester film, aluminium electrolytic. Major scale
divisions are cm.

59
Fig 39
2.10.3 CRYSTALOSCILLATOR
Fig 40
A miniature 4 MHzquartz crystal enclosed in a hermetically sealed HC-49/US
package, used as the resonator in a crystal oscillator.A crystal oscillator is an
electronic circuit that uses the mechanical resonance of a vibrating crystal of
piezoelectric material to create an electrical signal with a very precise
frequency[24]. This frequency is commonly used to keep track of time (as in quartz
wristwatches), to provide a stable clock signal for digitalintegrated circuits, and to
stabilize frequencies for radio transmitters/receivers.
Fig 41
Inside construction of a modern high performance HC-49 package quartz crystal

60
CHAPTER 3
Result and Discussion
3.1 ADVANTAGES:
The main advantages of Bluetooth are:
 it is easily available and in reach of common people.
 It consumes very less battery power and requires less processing power for
processing.
 The synced bluetooth devices does not need clear line of sight between them
and the chances of other wireless networks interfering with bluetooth are
very low.
3.2 DISADVANTAGES:
 The disadvantage of bluetooth is that the battery usage during a single
transfer is negligible, but if Bluetooth is kept on whole day, then battery loss
is significant and because of this it inevitably eats into the battery of these
devices, and lowers the battery life considerably.
 The other disadvantage of bluetooth is that the security in Bluetooth is good
but it is much better in infrared technology.
3.3 RESULT:
this low cost system is designed to improve the standard living in home. The
remote control function by smart phone provides help and assistance especially to
disabled and elderly. In order to provide safety protection to the user, a low voltage
activating switches is replaced current electrical switches. Moreover,
implementation of wireless Bluetooth connection in control board allows the
system install in more simple way. The control board is directly installed beside
the electrical switches whereby the switching connection is controlled by relay.
Furthermore, flexible types of connections are designed as backup connections to
the system. The connected GUIs are synchronized to the control board. They
indicate the real-time switches status. The system is designed in user-friendly
interface. The easy to use interface on Window and Android GUI provides simple
control by the elderly and disabled people.

61
CHAPTER 4
CONCLUSION
The goal of this project research was to outline the design and implementation of
an embedded system which can easily interface with the existing home appliances
and communicate with a smart phone via bluetooth using serial interfacing. We
intended to create a home which more or less acts as a rational agent . This
research shows many types of applications for implementing home automation.
The applications are not limited to those discussed in this paper. The technology
discussed could be used in wide variety of applications that requires sensors and
appliances and can serve the society in a very instructive manner. Our goal should
not be limited to smart home technology but in future we should move past smart
homes that automate every task for us .
The smart home system was fully functional for the switching applications and as
the appliances are switched on the user interface is updated to reflect the current
status. The smart home system was also tested for intrusion and fire detection
whereby it successfully detected the respective events generating an email to the
user and turning on the siren. Figure 10 shows the email generated (due to a fire
detected in the kitchen) and received by the user on the mobile device and on the
desktop PC where email was configured on Microsoft outlook.
The proposed system has all the feature with respect to the project. On the other
hand, it also has security features such as user authentication for accessing the
smart home system, and intrusion and fire detection with alert notification. The
system does not require a dedicated PC or voice processing module for the voice
activation feature making it low costand affordable.
The group has some ideas for future study of the topics involved in this project.
For one, it would be interesting to see if, given what we now know about wireless
communication, obtaining feedback is possible. Future project groups may be able
to establish wireless communication faster than we did if they examine the steps
that we took.

62
CHAPTER 5
Future work Home Automation.
One of the things we talk about and have written about before is the reluctance of
home automation industry to adoptoff-the-shelf hardware as part of their offering.
Some argue that dedicated hardware, dedicated home automation controllers,
dedicated home automation touch panels, and in some cases, dedicated home
automation network cables are necessary to create a stable, high-quality
installation. While on the surface this argument holds true, it does ring a bit
hollow. It rings hollow because we tend to be very good at defending a point of
view where our income depends on it.
The truth is that these dedicated home automation instruments are extremely
expensive to the end-user and the business model of many a home automation
company depends on the fat hardware margins. So it makes one wonder if the
established automation vendors have a true interest to see alternatives from mass-
volume consumer electronics industry to work in the field of home automation?
Enter Apple and Google
Now there are exceptions to the statements above. Some consumer devices corner
such a huge following that installers have little to no choice but to accommodate
them. Apple iPod as storage for one's personal music collection has become a
central device in many people's lives. It's only logical for the user to resist having
to replicate his music collection somewhere else. So integrate we must the iPod
into the system. Then came the iPhone/iTouch with their beautiful touch screen
interfaces and now the latest gadget, the mighty iPad.
Our digital life-styles are being pushed more and more into mobile consumer
electronic devices. At the same time these devices are increasing their capabilities
by leaps and bounds. It is only natural for users to want devices that are central to
their lives to be part of their home automation as well, and on top of that, use these
same devices to controlthe automation in their homes.
We regularly see touch panel components sell on the market with price tags of
6000 to 7000 dollars or euros. It is difficult to justify prices like these for devices

63
that have the same functionality as a $700 device acquired elsewhere. Certainly,
they are dedicated home automation devices but does that really justify a ten-fold
price tag? We think not. Android from Google, promises to open wide the doors to
custom panels.
It's a Luxury Business
If you allow a localized analogy, Switzerland is a country with a thriving watch-
making industry. They produce the most beautiful, most intricately designed, most
perfect hand-made watches to the very high-end luxury market, and they sell for
several thousand to tens of thousands of dollars/euros/francs. It is the very best of
what the industry can offer, the perfect device to tell you what time of the day it is
by glancing at your wrist (and at the same time impressing your peers), and at least
for some watch-makers, a sustainable business. And while there is a consumer
demand for this market to keep it breathing, the truth is that the real revenues and
real profits the industry makes come from the mass market, from watches that
regular people can afford, from few hundred to couple of thousand in
USD/EUR/CHF.
And the same is true for home automation. It is and has been a luxury market.
There is room for a small number of specialists who cater for the very high-end
luxury market. But at the peak of this pyramid, there is very little space to breathe.
It is also this focus, and consequently the business models that have been built
around it, that prevents the industry from growing. There's a need for larger
audience in order to grow the revenues and profits, and that means catering more to
the masses with higher volumes but lower mean prices. And that means taking
benefit of the off-the-shelf products where possible.
Going generic
Off-the-shelf hardware is produced in huge mass volumes by the Apples, Intels,
Asuses, Acers, Dells and AMDs of the world. The competition drives the prices
down quickly and into margins that are fraction of what the luxury home
automation vendors might make on similar devices. Apart from the very high-end
luxury market, it seems necessary for automation vendors who want to expand
their audiences to co-optrather than compete with this trend.
Now, generic off-the-shelf hardware comes with its own set of trade-offs. It is not
dedicated for the automation domain so needs to be adapted accordingly. This
means new challenges in testing, quality assurance and certifying working

64
components and integration. Nevertheless, these challenges can be addressed and
have been done previously in other industries.
Another analogy we can use is the modern PC industry. While home computers
started as dedicated devices in 1980's with each vendor designing their hardware
and software from scratch - whether it was Atari, Commodore, Amstrad or any
other of the number of vendors designing their home computers - the real break-
through came when IBM PC was cloned and brought to mass market with a flood
of companies offering software and hardware components to this generic
computing platform. A whole ecosystem emerged and the industry took off. Since
then, various hardware and software certification processes have emerged to ensure
a smooth end-user experience. While niche markets still exist for dedicated
hardware, majority of today's home computers and all the way up to business
datacenters are built on this same generic PC computing device or some of its
offspring. IT professionals have learned how to build systems that we trust with
most critical business transactions despite of the sometimes "imperfect" foundation
of the technology. In home automation, we must do the same.
And Then There Was the Internet
Finally, the most fundamental technological change in the last 15 years has been
the Internet. There's hardly any industry not affected by it, and home automation is
no exception. Internet at home is now as central to media consumption as what TV
was before it, and radio before that. Music, video, photos, books and magazines are
distributed through it.
And because of that, the core of what makes the Internet work - the IP network - is
becoming as common a communication infrastructure in people's houses as the TV
cable or the phone line was before. Hardly any new buildings go up these days
without Internet cables and connectors installed into the walls.
This means homes are equipped with a communications infrastructure that is
usable for control and automation. And as with off-the-shelf hardware, vendors
who are looking to expand their markets towards a wider audience, must take
advantage of it.
Now, when talking about IP networks and home automation, people often confuse
this with an idea that every electric device must have an IP address bound to it and
must be connected to the IP network directly. This is not the case. There are areas
at home where IP network won't reach for some time to come (lighting for

65
example), and in some areas wireless sensor networks are a better alternative
(although we may eventually see Internet protocolon top of WSN).
What the prevalence of Internet and IP network means, however, is that the
backbone infrastructure of an automation network consumed by masses is likely to
be based on Internet protocol.
This in turn means dedicated gateways or translators that integrate the home's IP
network with the necessary protocols to automate all electric devices, be it serial
connections, infrared, Zigbee or Z-Wave, and so on. This is what we call the "last-
meter" connection between the IP network and the end-device.
It also means expanded know-how towards IP network setups and switches, such
as understanding virtual LAN setups to improve the end-user control experience.
This is part and parcel of IT professionals and network administrators today who
use IP networks for critical tasks in corporate environments and is a needed
transition for installers creating IP-based home automation setups as well.
The Changes Future Will Bring
Taken all the points together, what does this mean to home automation industry?
(1) Dedicated Home Automation Hardware Will Still Have Its Place
But the kind of dedicated home automation hardware that we are going to see are
the components usually hidden from the view of the home owner. Dedicated
gateway products that specialize on translating automation protocols to and from
the home IP network are still needed. The mass consumer electronics industry will
have little interest to target this area, at least not yet.
Expect to see less and less dedicated touch screens or dedicated home automation
controllers that are easily replaced with off-the-shelf products. Their pricing, and
therefore their utility, can only exist at the very peak of the luxury market,
targeting high-net-worth-individual homes, not the mass market. There's not much
space at the peak of the consumer pyramid, few vendors will survive in this
segment but most will need to adjust their business models to cater to a different
kind of home owner.
(2) IP networks Will Have an Increasing Role

66
As with the off-the-shelf hardware, IP networks are already in the homes, already
installed around the house in new buildings, and they are being used to transfer
media for user consumption. Undoubtedly, whether it is music, video, photos etc.
the distribution happens on an IP network. Media centers are enabled for IP based
controls. Web's HTTP protocol and Universal Plug'n'Play protocols are being used
over IP to control things.
This means the backbone communication and control infrastructure is often in
place already and it is IP-based. A fact that cannot be ignored by any vendor that
wishes to reach a wider market that demands lower initial investment to
experiment with the automation technology. What needs to be supported by
automation vendors is the "last-meter" of network integration between IP to
Infrared, IP to serial, IP to Z-Wave and so on.
(3) Increasing Need for Interoperability, Testing and Certification
Both off-the-shelf hardware and IP networks are generic technical solutions that
must be adapted to automation purposes accordingly.
IT industry today uses these same components to support critical functions in the
business enterprise. Same can be done for automation. But it requires establishing
new processes that tackles the challenges of quality assurance in testing
components, ensuring they work together and ultimately, certifying them as a
supported solution for an automation installation. Training programs will need to
be created and updated to include technical and configuration details of third party
components.
(4) Re-adjust Business Models
Home automation today is stuck in a deadlock that prevents growth. This is due to
several factors, including lack of standardization, proprietary systems, high cost of
integration and business models that target the very high-end of luxury market.
What we need to create is a virtuous cycle that fosters growth. This means
expanding the target market and enabling vendor ecosystem and partner network
growth. We can achieve this by using technologies that are open, adopting existing
de-facto standards and creating technical solutions that are available to all
participants.

67
Integration is a key here. Any solution looking for mass adoption must take into
account several market realities: existing investment in already installed systems,
the need to integrate with devices from mass consumer electronics market, the
dynamic nature of automation as more consumer devices become control-capable
at ever increasing pace and finally, the ability to provide the home owner with a
complete solution that adapts to their needs over time without a prohibitive cost
structure.
Needless to say, we at Open Remote believe Open Source plays a key part in this
picture as a growth catalyst. How this happens is worthy of a full article. What we
can achieve is to lower the cost of integration and enable integrators and installers
to expand to a larger market segment. We can enable integrators and installers to
deliver a complete solution to the home owner and we can help installers to
manage higher volume mass market (see the final point of this conclusion). This in
turn will mean higher revenues, and hopefully in the end, higher profit.
(5) New Kind of Installer
As with any change of status quo, the need for adjustment rises. None of the above
conclusions means installers will disappear or become obsolete. In fact, quite the
opposite. But change does mean some new knowledge must be acquired and some
existing knowledge may have less use in the future.
Ability to manage IP networks is a given. Not just installing a wireless hub in the
corner of a room but skills more akin to network administrators. Provisioning the
network bandwidth may be necessary. Understanding the required hardware,
switches and their configuration is very likely necessary.
At the same time, in order to facilitate higher volume customer relationship
management, tools need to exist to easily monitor, change and configure
installations. Minor changes and tweaks should be possibly to implement remotely.
Basic issue diagnostic should be possible remotely. The installer tools should drive
towards minimizing the cost of change for the installer. This simply due to the fact
that the installation environments are becoming ever more dynamic in the future.
We at OpenRemote want to bring such tools to integrators and installers. We are
preparing the next 2.0 version of our online tools which you can test drive
here:http://composer.openremote.org/demo (you will need to create a new
temporary account even if you have registered with us before).

68
The main aspect we've added for installers is the ability to dynamically change the
user interfaces and controller configuration online, using a shared account with the
customer. These changes can be automatically downloaded to OpenRemote
controller without additional on-site work (Internet connection assumed, of
course). You can read some more about features we've added here.

69
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72
Appendixes
Appendix A:
A. The Bluetooth APIs:
All of the Bluetooth APIs’ are available in the Android Bluetooth package.
The following is the overview of the classes needed during the application’s
development.
·BluetoothAdapter: Represents the local Bluetooth adapter (Bluetooth radio)
·BluetoothDevice: Represents a remote Bluetooth device, to query
information such as its name, address, class, and bonding state.
·BluetoothSocket: Represents the interface for a Bluetooth socket (similar to
a TCP Socket).
·BluetoothClass: Describes the general characteristics and capabilities of a
Bluetooth device.
B. Bluetooth Permissions:
In order to use Bluetooth features in an Android application, at least one of
two Bluetooth permissions:BLUETOOTH and BLUETOOTH_ADMIN are needed
to be declared. We declared the Bluetooth permission(s) in our application’s
AndroidManifest.xml as below:
<manifest ... >
<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
….
</manifest>

74
Appendix B
Complete Circuit Diagram
FIG. 42

75
Practical Implemented Model:
FIG. 43

Wireless Home Automation Using Bluetooth

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