Controlling Electrical Appliances through TV Remote

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Controlling Electrical Appliances

through TV

Remote

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Controlling Electrical Appliances through TV Remote

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Abstract:

Wired or wireless remote control devices including Infrared (IR) or RF

transmitter for remotely operating AC powered electrical appliances such as television

receivers, home heaters, air conditioners, motorized curtains, lighting and other

electrical appliances in homes, apartments, offices and buildings in general are

switched on and off by a one way control or command signal, with the person

operating the remote control device verifying the on or off status of the operated

device by visual means, such as the TV is on, or the lights are off, or the air condition

unit is activated or not, by being at the site of the operated appliance.

Most of the remote control devices, including IR or wireless remote control

devices use the same power key to switch the appliance on and off, therefore without

the operating person's self verification on site, with most of currently available remote

control devices it is impossible to positively verify the on-off power status without

being at the appliance site.


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CHAPTER 1


POWER SUPPLY:

The input to the circuit is applied from the regulated power supply. The a.c. input i.e.,

230V from the mains supply is step down by the transformer to 12V and is fed to a

rectifier. The output obtained from the rectifier is a pulsating d.c voltage. So in order to get a

pure d.c voltage, the output voltage from the rectifier is fed to a filter to remove any a.c

components present even after rectification. Now, this voltage is given to a voltage regulator

to obtain a pure constant dc voltage.

Transformer:

Usually, DC voltages are required to operate various electronic equipment and these

voltages are 5V, 9V or 12V. But these voltages cannot be obtained directly. Thus the

a.c input available at the mains supply i.e., 230V is to be brought down to the required

voltage level. This is done by a transformer. Thus, a step down transformer is

employed to decrease the voltage to a required level.

Rectifier:


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The output from the transformer is fed to the rectifier, It converts A.C. into pulsating

D.C. The rectifier may be a half wave or a full wave rectifier. In this project. a bridge

rectifier is used because of its merits like good stability and full wave rectification.

Filter:

Capacitive filter is used in this project. It removes the ripples from the output of

rectifier and smoothens the D.C. Output received from this filter is constant until the

mains voltage and load is maintained constant. However, if either of the two is varied.

D.C. voltage received at this point changes. Therefore a regulator is applied at the

output stage.

Voltage regulator:

As the name itself implies, it regulates the input applied to it. A voltage regulator is an

electrical regulator designed to automatically maintain a constant voltage level. In this

project, power supply of 5V and I 2V are required. In order to obtain these voltage

levels. 7805 and 7812 voltage regulators are to be used. The first number 78

represents positive supply and the numbers 05, 12 represent the required output

voltage levels.

Necessity of regulated power supply:

The DC level of an ordinary power supply changes due to the following reasons.

Variations in AC mains voltage: the permissible variation in the mains voltage as per

Indian electricity rules is +1- 6% of its rated value. But in India the variation in

voltage is much more than its rated value. That is why the DC voltage of an ordinary

power supply changes to such an extent that the electronic device refuses to work

satisfactorily. Voltages drop in internal resistance: the internal resistance of an

ordinary power supply is very large. Therefore output voltage changes to an extent

when load is connected across it. Some it reduces to very low extent due to which the

electronic component refuses to work.

INTRODUCTION TO IR:

One of the advantages of infrared remote is that there is no radio signal for crooks to

monitor and record for use against you later on. Instead, there is a beam of invisible

infrared light which comes from a standard hand-held remote control unit. So from

that point of view, it is pretty secure. There is, though, an enormous variety of tasks to


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which you could put the unit. Just think of the myriad of things in your home these

days which use infrared remote to turn things on and off, change levels, open and

close.


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CHAPTER 2

WHAT IS INFRARED?

Infra Red is a energy radiation with a frequency below our eyes sensitivity, so

we cannot see it. Even that we cannot “see” sound frequencies, we know that it exist,

we can listen them

Even that we cannot see or hear infrared, we can feel it at our skin temperature

sensors. When you approach your hand to fire or warm element, you will “feel” the

heat, but you can’t see it. You can see the fire because it emits other types of

radiation, visible to your eyes, but it also emits lots of infrared that you can only feel

in your skin.

INFRAREDINELECTRONICS

Infra-Red is interesting, because it is easily generated and doesn’t suffer

electromagnetic interference, so it is nicely used to communication and control, but it

is not perfect, some other light emissions could contains infrared as well, and that can

interfere in this communication. The sun is an example, since it emits a wide spectrum

or radiation. The adventure of using lots of infra-red in TVNCR remote controls and

other applications, brought infra-red diodes (emitter and receivers) at very low cost at

the market.


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From now on you should think as infrared as just a “red” light. This light can means

something to the receiver, the “on or off” radiation can transmit different meanings.

Lots of things can generate infrared, anything that radiate heat do it, including out

body, lamps, stove, oven, friction your hands together, even the hot water at the

faucet. To allow a good communication using infra-red, and avoid those “fake”

signals. it is imperative to use a “key” that can tell the receiver what is the real data

transmitted and what is fake. As an analogy, looking eye naked to the night sky you

can see hundreds of stars, but you can spot easily a far away airplane just by its

flashing strobe light. That strobe light is the “key”, the “coding” element that alerts

us.

Similar to the airplane at the night sky, our TV room may have hundreds of

tinny IR sources, our body, and the lamps around, even the hot cup of tea. A way to

avoid all those other sources, is generating a key, like the flashing airplane.

So, remote controls use to pulsate its infrared in a certain frequency. The IR

receiver module at the TV, VCR or stereo “tunes” to this certain frequency and

ignores all other IR received. The best frequency for the job is between 30 and 60kHz,

the most used is around 36kHz So, remote controls use the 36kHz (or around) to

transmit information. Infrared light emitted by IR Diodes is pulsated at 36 thousand

times per second, when transmitting logic level“1”andsilencefor“0”.

IR Generation:

To generate a 36 kHz pulsating infrared is quite easy, more difficult is to

receive and identify this frequency. This is why some companies produce infrared

receives, that contains the filters, decoding circuits and the output shaper, that delivers

a square wave, meaning the existence or not of the 36kHz incoming pulsating

infrared. It means that those 3 dollars small units, have an output pin that goes high

(+5V) when there is a pulsating 36kHz infrared in front of it, and zero volts when

36kHz there is not this radiation.


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A square wave of approximately 27uS (microseconds) injected at the base of a

transistor, can drive an infrared LED to transmit this pulsating light wave. Upon its

presence, the commercial receiver will switch its output to high level (+5V).

If you can turn on and off this frequency at the transmitter, your receiver’s output will

indicate when the transmitter is on or off.

Those IR demodulators have inverted logic at its output, when a burst of IR is sensed

it drives its output to low level, meaning logic level = 1

The TV, VCR, and Audio equipment manufacturers for long use infra-red at their

remote controls. To avoid a Philips remote control to change channels in a Panasonic

TV, they use different codification at the infrared, even that all of them use basically

the same transmitted frequency, from 36 to 50 kHz. So, all of them use a different

combination of bits or how to code the transmitted data to avoid interference.


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CHAPTER 3

DECODING IR SIGNAL WITH A MICROCONTROLLER

To receive this signal using a microcontroller follows the timing from the

figure below. Note that the Infrared Receiver invert the bit signal, low level means bit

ON.

During Inactivity (no Infrared present) the output of the Infrared receiver is

UP (bit zero). You can connect the IR receiver output to any input port pin or

interrupt pin of your microcontroller, and keep polling it or prepare the interrupt

routine to trigger your reading after the first low level sensed. When you press a key

at the remote, it transmits the train of pulses, and your microcontroller will receive bit

#1 first. It will be sensed right after the middle of the bit when it changes from high to

low level to means bit “1”. This is the first time that your microcontroller will “see”

the incoming IR signal. You don’t need to decode those first two bits, not even the

CHK bit (except if you want to control as the TV do and described above), so you can

skip those 3 bits and start to receive the ADDRESS bits. To do that, you need to skip

2.75 bits time, and you will be exactly at the middle of the right level of the first

ADDRESS bit to be read (non inverted level).

So, upon sensing the first low level, your software should wait 4.752

milliseconds and then start to read the next 11 bits spaced 1.728ms each. The first 5

bits are Address and the next 6 bits are Command, logic correct level, LOW = 0,


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HIGH = 1. At your bit reading routine use an available microcontroller port pin and

generate a fast pulse UP and DOWN, then use one scope channel to display this pulse,

and the other scope channel to show the incoming signal.

Blue: Check bit (flipping)

White: Address (00)

Green: Command

IR RECEIVER:

Description:

The TSOPI7 series are miniaturized receivers for infrared remote control systems.

PIN diode and preamplifier are assembled on lead frame; the epoxy package is

designed as IR filter.

The demodulated output signal can directly be decoded by a microprocessor. TSOP17

is the standard IR remote control receiver series, supporting all major transmission

codes.

Features:

Photo detector and preamplifier in one package

Internal filter for PCM frequency


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Improved shielding against electrical field disturbance

TTL and CMOS compatibility

Output active low

Low power consumption

High immunity against ambient light

Continuous data transmission possible (up to 2400 bps)

Suitable burst length .10 cycles/burst

BLOCK DIAGRAM


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RELAY:

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

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

close one or many sets of contacts. It was invented by Joseph Henry in 1835. Because

a relay is able to control an output circuit of higher power than the input circuit, it can

be considered, in a broad sense, to be a form of electrical amplifier.

Operation:

When a current tiows through the coil, the resulting magnetic field auracts an

armature that is mechanically linked to a moving contact. The movement either makes

or breaks a connection with a fixed contact. 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 is 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 is to reduce noise. In a high voltage or high

current application, this is to reduce arcing.

lithe coil is energized with DC, a diode is frequently installed across the coil, to

dissipate the energy from the collapsing magnetic field at deactivation, which would

otherwise generate a spike of voltage and might cause damage to circuit components,

If the coil is designed to be energized with AC, a small copper ring can be crimped to

the end of the solenoid. This “shading ring” creates a small out-of-phase current,

which increases the minimum pull on the armature during the AC cycle.

By analogy with the functions of the original electromagnetic device, a solid-state

relay is made with a thyristor or other solid-state switching device. To achieve

electrical isolation, a light-emitting diode (LED) is used with a photo transistor.


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CONCLUSION:

Most of the remote control devices, including IR or wireless remote control

devices use the same power key to switch the appliance on and off, therefore without

the operating person's self verification on site, with most of currently available remote

control devices it is impossible to positively verify the on-off power status without

being at the appliance site.

Documents

Controlling Electrical Appliances through TV Remote