If you are like
most Americans, you probably pick up a TV remote control at
least once or twice a day. Let's look inside and see how they
work. Here is the remote we will be dissecting today:
The remote control's job is to wait for you to press a key,
and then to translate that key-press into infrared (pronounced
"infra-red") light signals that are received by the TV. When
you take off the back cover of the control you can see that
there is really just 1 part visible: a printed circuit
board that contains the electronics and the battery
contacts.
The components that you see here are typical for most
remotes. You can see an integrated circuit (also known
as a chip) labeled "TA11835". The chip is packaged in
what is known as an 18 pin Dual Inline Package, or a
DIP. To the right of the chip you can see a diode, a
transistor (black, with three leads), a resonator (yellow),
two resistors (green) and a capacitor (dark blue). Next to the
battery contacts there is a resistor (green) and a capacitor
(tan disk). In this circuit, the chip can detect when a key is
pressed. It then translates the key into a sequence something
like morse code, with a different sequence for each different
key. The chip sends that signal out to the transistor to
amplify the signal and make it stronger.
The Circuit Board
When you unscrew the circuit board and take it out, you can
see that the circuit board is a thin piece of fiber glass that
has thin copper "wires" etched onto its surface. Electronic
parts are assembled on printed circuit boards because they are
easy to mass produce and assemble. In the same way that it is
relatively inexpensive to print ink onto a sheet of paper, it
is inexensive to "print" copper wires onto a sheet of fiber
glass. It is also easy to have a machine drop the parts (the
chips, transistors, etc.) onto the sheet of fiberglass and
then solder them on to connect them to the copper wires.
When you look at the board, you can see a set of contact
points for the buttons. The buttons themselves are made of a
thin rubbery sheet. For each button there is a black
conductive disk. When the disk touches the contacts on the
printed circuit board, it connects them and the chip can sense
that connection.
At the end of the circuit board there is an infrared
LED, or Light Emitting Diode. You can think of an
LED as a small light bulb. Many LEDs produce visible light,
but a remote's LED produces infrared light that is invisible
to the human eye. It is not invisible to all eyes, however.
For example, if you have a camcorder it can see the infrared
light. Point your remote at the camera and push a button. You
will be able to see the infrared light flashing in the
viewfinder. The receptor in the TV is able to see infrared
light as well.
So the basic operation of the remote goes like this: You
press a button. When you do that you complete a specific
connection. The chip senses that connection and knows what
button you pressed. It produces a morse-code-line signal
specific to that button. The transistors amplify the signal
and send them to the LED, which translates the signal into
infrared light. The sensor in the TV can see the infrared
light and "seeing" the signal reacts appropriately.
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