Mice
Last updated: March 26, 2007.
Once upon a time, if you'd seen a mouse in
your room you might
have screamed and jumped up on the desk. Today, the mouse has jumped
on your desk instead: it's the handy little pointer that makes your
computer easy to use. The first mouse was made of wood and designed
over four decades ago in 1961. Today, mice sell by the million and
hardly a computer ships without one. They've changed quite a
bit in that time but they still work in much the same way. Let's take
a look inside!
How mice were born
For most of their history,
computers were the province of
egg-heads and boffins. You needed a maths degree just to understand
the manual and you could only tell them what to do by feeding in a
stack of index cards punched with holes. All that started to change
when a brilliant US computer scientist named
Douglas Engelbart (1925-) developed the computer mouse. Engelbart
realized computers were far too useful for boffins: he could see they
had the power to change people's lives. But he could also see that
they needed to be much easier to use. So, during the 1960s, he
pioneered most of the easy-to-use computer technologies that we now
take for granted, including on-screen word processing, hypertext (the
way of linking documents together used in web pages like these),
windows (so you can have more than one document or program in view at
a time), and video conferencing.
But he's still best known for inventing the mouse, or the “X-Y
Position Indicator” as it was originally known. That stuffy
name was dropped when someone spotted that the cable hanging out
looked just like a mouse's tail. From then on, Engelbart's invention
was known simply as the "mouse".
A mouse is something you push along your desktop to make a cursor
(pointing device) move on your screen. So what a mouse has to do is
figure out how much you're moving your hand and in which direction.
There are two main kinds of mice and they do this job in two
different ways.
Ball mouse
Traditional mice (like the one in our top photo up above) have a
heavy rubber ball inside them. Lift the lid and they look like this:
You can see the heavy ball clearly and
the spring
that keeps it in
position. As you move a mouse like this across the desk, the ball
rolls under its own weight and pushes against two plastic wheels.
One
of the wheels detects movements in an up-and-down direction (like the
y-axis on graph/chart paper); the other detects side-to-side
movements (like the x-axis on graph paper). As you move the mouse,
the turns one or both of the wheels. If you move the mouse straight
up, only the y-axis wheel turns; if you move to the right, only the
x-axis wheel turns. And if you move the mouse at an angle, the ball
turns both wheels at once. The amount by which each wheel turns is
measured by the chip at the front, which
sends details down the
cable
to your computer. Software in your computer moves the cursor on
your screen by a corresponding amount. Before we leave this photo,
notice the three tiny black switch buttons
at the
front. They detect the clicks you make with the much larger buttons
on the mouse case.
There are various problems with mice like this. You need a special
mouse mat for starters. But even if you have one, the rubber ball
gradually picks
up dirt, so the x- and y-axis wheels turn erratically and make the
pointer stutter across your screen. The
solution is to keep taking your mouse to pieces and cleaning it.
Or
you could buy yourself an...
Optical mouse
An optical mouse works in a completely different way. It shines a
bright line down onto your desk from an LED
(light-emitting
diode)
and then detects the reflected light with a photocell.
This is
what
it looks like underneath (note the lack of ball):
As you move your mouse, the pattern of reflected light changes—and
the mouse uses this to figure out how you're moving your hand.
Inside, an optical mouse is much more hi-tech than a ball mouse.
Where a ball mouse is almost entirely mechanical, an optical mouse is
almost entirely electronic. This is what it looks like if you take
off the cover:
In this mouse, there are two LEDs. The first one (marked here as
LED#1) shines down onto the desk. The light from that is picked up by
a photocell that has a lens mounted in front
of it. The lens
magnifies the
light bouncing off your desk and makes the mouse operate more
accurately. The second LED at the back (marked LED#2) lights up a red
plastic strip along the back of the mouse so you can see it's
working. This mouse also has a wheel at the
front so you can
scroll
pages on-screen much faster. Like the chip in a ball mouse, the chip
inside an optical mouse does all the measuring and sends details of
your movements to your computer.
Isn't it amazing how something so simple can make such a big difference
to our lives?
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