Remote control
Last updated: June 19, 2007.

The way we love our remote controls,
you'd think our living rooms were the size of Texas! It's an awfully long way to
go, isn't it, to change the television
channel or pump up the volume on the
stereo? Remote controls are a perfect indulgence for couch potatoes
everywhere—but have you ever stopped to wonder how they work? How
come your TV remote doesn't trigger the video? Why do you have to
point it directly at the TV? And when you aim your remote at a
neighbor's house, does their TV channel change too? Let's take a
closer look at the mysteries of remote control!
Photo: A typical TV remote control unit.
How remote controls use infrared beams
The first thing you notice about a remote control
unit is that it has no wires, so it has to send signals to whatever
it's operating using electromagnetic waves.
Light, x-rays,
radio waves, and microwaves are all examples of electromagnetic
waves: vibrating packets of electrical and magnetic energy that
travel through the air at the speed of light. Most remote controls
send signals using infrared radiation (which is a kind of invisible
red light that hot objects give off and halogen
hobs use to
cook with), though some use radio waves instead.
Photo: The small infrared LED on the top of a
typical remote control.
If you look at the top of your remote control
unit, you'll see there's a small plastic light-emitting
diode (LED) where the infrared radiation comes out. Now take a look at your
TV or video. Somewhere on the front, there's a very small infrared
light detector. When you press the remote control, a beam of infrared
radiation travels from the remote to your TV at the speed of light
and the detector picks it up.
Human eyes can't detect infrared, so even if you
press the buttons on your remote and stare at the LED you won't see
anything happening. Some animals, including rattlesnakes, can detect infrared. Rattlesnakes have tiny
infrared detectors buried in pits near their eyes, which work
a bit like the infrared detectors on your TV.
By homing in on infrared heat, snakes can locate prey at night when
there's no
ordinary light to see by.
What would
happen if you pointed a TV remote control at a snake and pressed the
buttons? Maybe it would think you were a mouse and slither over to
eat you. It's unlikely you could control a rattlesnake with a TV
remote—and we don't recommend you try!
Photo: Rattlesnakes "speak" infrared, just like TV
sets.
Picture by courtesy of US Fish & Wildlife Service.
Remote control codes
It's no good the remote control just sending out a
burst of random infrared. Clearly if your remote control has 20 or
more buttons on it, it must have a way of sending out at least this
many signals—each one different enough for your TV to be able to
decode and understand it. When you press one of the buttons, the
remote generates a systematic series of on/off infrared pulses that
signal a binary code (a way
of representing any kind of information using only zeros and ones,
which computers use). So a short
pulse of infrared
could signal a 1 and no pulse could signal a 0. Sending many infrared
pulses, one after another, allows your remote to send whole strings
of zeros and ones. One code (maybe it's 101101) might mean "volume
up", while another (perhaps 11110111) could mean "mute sound."
As well as sending out pulses that tell the TV
what you want it to do, the remote also sends a short code that
identifies the product you're trying to control (for example, a
specific make and model of TV). That ensures your remote operates
only the TV, not the video, and not any other TVs that happen to be
nearby. Generally, this means each remote control unit can operate
only one appliance made by only one manufacturer. Of course if you
could discover the codes that different TVs and videos understand,
you could build a remote control that operated any appliance. This is
how universal remotes work. They let you
control any TV or
video and, instead of sending out only signals specific to one brand
of equipment, they can send out codes that any make or model can
understand. One inventor has even gone so far as to develop a remote
called TV-B-Gone
that systematically sends out a "switch TV off" signal using
every possible manufacturer's code. It's designed to allow TV haters
to switch off annoying TVs covertly as they wander through shopping
malls and department stores!
Radio control

Infrared remotes can operate TVs and videos only
over quite short distances. The infrared LED is quite small and
low-powered and the receiver on the TV or video is small too. This is
why you generally have to point the remote directly at the appliance
you're trying to control. Some remotes are more tolerant and it is
sometimes possible to bounce the infrared beam off a wall, mirror, or
picture and still change channel. Infrared remotes are no good for
controlling things over distances greater than a few meters (feet);
the infrared energy is too easily soaked up and dissipated along its
journey.
To control things over greater distances, you need to use a
different kind of system called radio control.
You operate
radio-controlled cars, trucks, boats, airplanes, and robots using a
handheld radio transmitter box that sends signals from an
antenna on
the top to a matching antenna on whatever you're interested in
controlling. Radio signals can travel much further than infrared ones
without interference, especially if the transmitters and antennas are
large and powerful.
Photo: A selection of radio-controlled airplanes.
You can see the control units on the right of the picture.
Picture by courtesy of NASA Dryden Flight Research Center.
Radio control isn't just used in toys; many of the
latest wireless gadgets use similar technology, including
Bluetooth®
(a convenient way of operating computer-based equipment without
wires), RFID (radio frequency identification)
technology used
in anti-shoplifting systems, and Wi-Fi, used in wireless Internet.
Even cellphones communicate using a
wireless system not unlike
radio control. So maybe remote control isn't just for couch potatoes
after all?