How does a REMOTE control work !?

active member عدد الرسائل : 40 تاريخ التسجيل : 12/06/2008

I am always curious how I can control a TV from my couch. How does a remote control work?

Most
remote controls rely on low-frequency light waves to send out signals.
Since the early 1980’s, remote controls have generally used light in
the infrared range, which has such a low frequency that your eyes can’t
see it. The remote control sends a different flashing light message,
like Morse code, for each job you want done.

You press a
button on your remote control. That push tells a tiny computer
processor to trigger a light-emitting device called a “diode” at the
front of the remote. The diode then flashes an infrared signal to a
light-sensitive area – called a “photocell” – on your TV. The signal is
different depending on which button you push – say, the volume control
or the channel-changer. To make sure your TV gets the message, these
light signals are repeated five times a second. Nowadays, some remote
controls can handle as many as fifty different commands. Now if only
you could remember where you left it!

Infrared Remote Controls: The Process

Pushing a button on a remote control sets in motion a series of events
that causes the controlled device to carry out a command. The process
works something like this:

You push the "volume up" button on your remote control, causing it to touch the contact beneath it and complete the "volume up" circuit on the circuit board. The integrated circuit detects this.
The integrated circuit sends the binary "volume up" command to the LED at the front of the remote.
The LED sends out a series of light pulses that corresponds to the binary "volume up" command.

One example of remote-control codes is the Sony Control-S
protocol, which is used for Sony TVs and includes the following 7-bit
binary commands:

Button	Code
1	000 0000
2	000 0001
3	000 0010
4	000 0011
Channel up	001 0000
Channel down	001 0001
Power on	001 0101
Power off	010 1111
Volume up	001 0010
Volume down	001 0011
Source: ARRLWeb

The remote signal includes more than the command for "volume up,"
though. It carries several chunks of information to the receiving
device, including:

a "start" command
the command code for "volume up"
the device address (so the TV knows the data is intended for it)
a "stop" command (triggered when you release the "volume up" button)

So when you press the "volume up" button on a Sony TV remote, it sends out a series of pulses that looks something like this:

How does a REMOTE control work !? Remote-control-7

Sony TV remotes use a space-coding method in which the length of the spaces between pulses of light represent a one or a zero.

When the infrared receiver on the TV picks up the signal from the
remote and verifies from the address code that it's supposed to carry
out this command, it converts the light pulses back into the electrical
signal for 001 0010. It then passes this signal to the microprocessor,
which goes about increasing the volume. The "stop" command tells the
microprocessor it can stop increasing the volume.
Infrared remote controls work well enough to have stuck around
for 25 years, but they do have some limitations related to the nature
of infrared light. First, infrared remotes have a range of only about 30 feet (10 meters), and they require line-of-sight.
This means the infrared signal won't transmit through walls or around
corners -- you need a straight line to the device you're trying to
control. Also, infrared light is so ubiquitous that interference can be a problem with IR remotes. Just a few everyday infrared-light sources include sunlight, fluorescent bulbs
and the human body. To avoid interference caused by other sources of
infrared light, the infrared receiver on a TV only responds to a
particular wavelength of infrared light, usually 980 nanometers. There
are filters on the receiver that block out light at other wavelengths.
Still, sunlight can confuse the receiver because it contains infrared
light at the 980-nm wavelength. To address this issue, the light from
an IR remote control is typically modulated to a frequency not present
in sunlight, and the receiver only responds to 980-nm light modulated
to that frequency. The system doesn't work perfectly, but it does cut
down a great deal on interference.
While infrared remotes are the dominant technology in
home-theater applications, there are other niche-specific remotes that
work on radio waves instead of light waves. If you have a garage-door
opener, for instance, you have an RF remote.

The world's first remote controls were radio-frequency devices that
directed German naval vessels to crash into Allied boats during WWI. In
WWII, remote controls detonated bombs for the first time. The end of
the great wars left scientists with a brilliant technology and nowhere
to apply it. Sixty years later, some of us spend an hour looking for
the remote before we remember there are buttons on the TV.
In this article, we'll examine the infrared technology used in most
home theaters, look at the difference between IR and RF remotes, find
out the difference between a "universal" and a "learning" remote and
check out some of the other high-tech features you can find on remotes
today, like PC connectivity, RF extenders and macro commands..

Remote controls of a tv work by emitting patterns of infrared light.
Infrared is a form of light in the portion of the electromagnetic
spectrum above the visible red color. The tv set picks up the infrared
emitions and translates the pattern it received into what button you
pressed and performs that activity.

Other remote controls such as for rc cars or rc airplanes use radio waves instead of infrared light.

in another words it sends pulses of infrared light out like a little old-school LED
light. We can't see them because infrared light is too low in
frequency. A detector on the device can detect them and recognize the
frequency.

It uses an Infrared LED to transmit a code to whatever you are
controlling. Every device is assigned a certain code, and if it
recieves a signal on that code, it can decode and carry out the
instructions

http://electronics.howstuffworks.com

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