Computer Mice

Mice first broke onto the public stage with the introduction
of the Apple Macintosh in 1984, and since then they have
helped to completely redefine the way we use computers.

Every day of your computing life, you reach out for your
mouse whenever you want to move your cursor or activate
something. Your mouse senses your motion and your clicks and
sends them to the computer so it can respond appropriately.

Evolution of the Computer Mouse

It is amazing how simple and effective a mouse is, and it is
also amazing how long it took mice to become a part of
everyday life. Given that people naturally point at things --
usually before they speak -- it is surprising that it took so
long for a good pointing device to develop. Although
originally conceived in the 1960s, a couple of decades passed
before mice became mainstream.

In the beginning, there was no need to point because
computers used crude interfaces like teletype machines or
punch cards for data entry. The early text terminals did
nothing more than emulate a teletype (using the screen to
replace paper), so it was many years (well into the 1960s and
early 1970s) before arrow keys were found on most terminals.
Full screen editors were the first things to take real
advantage of the cursor keys, and they offered humans the
first way to point.

Light pens were used on a variety of machines as a pointing
device for many years, and graphics tablets, joy sticks and
various other devices were also popular in the 1970s. None of
these really took off as the pointing device of choice,
however.

When the mouse hit the scene -- attached to the Mac, it was
an immediate success. There is something about it that is
completely natural. Compared to a graphics tablet, mice are
extremely inexpensive and they take up very little desk
space. In the PC world, mice took longer to gain ground,
mainly because of a lack of support in the operating system.
Once Windows 3.1 made Graphical User Interfaces (GUIs)
a standard, the mouse became the PC-human interface of choice
very quickly.

Inside a Mouse
The main goal of any mouse is to translate the motion of your
hand into signals that the computer can use. Let's take
a look inside a track-ball mouse to see how it works

A ball inside the mouse touches the desktop and rolls when
the mouse moves.

Two rollers inside the mouse touch the ball. One of the
rollers is oriented so that it detects motion in the X
direction, and the other is oriented 90 degrees to the first
roller so it detects motion in the Y direction. When the ball
rotates, one or both of these rollers rotate as well.

The rollers each connect to a shaft, and the shaft spins
a disk with holes in it. When a roller rolls, its shaft and
disk spin.

On either side of the disk there is an infrared LED and
an infrared sensor. The holes in the disk break the beam of
light coming from the LED so that the infrared sensor sees
pulses of light. The rate of the pulsing is directly related
to the speed of the mouse and the distance it travels.

An on-board processor chip reads the pulses from the infrared
sensors and turns them into binary data that the computer can
understand. The chip sends the binary data to the computer
through the mouse's cord.

In this optomechanical arrangement, the disk moves
mechanically, and an optical system counts pulses of light.
On this mouse, the ball is 21 mm in diameter. The roller is
7 mm in diameter. The encoding disk has 36 holes. So if the
mouse moves 25.4 mm (1 inch), the encoder chip detects 41
pulses of light.

You might have noticed that each encoder disk has two
infrared LEDs and two infrared sensors, one on each side of
the disk (so there are four LED/sensor pairs inside a mouse).
This arrangement allows the processor to detect the disk's
direction of rotation. There is a piece of plastic with
a small, precisely located hole that sits between the encoder
disk and each infrared sensor.

This piece of plastic provides a window through which the
infrared sensor can "see." The window on one side of the disk
is located slightly higher than it is on the other --
one-half the height of one of the holes in the encoder disk,
to be exact. That difference causes the two infrared sensors
to see pulses of light at slightly different times. There are
times when one of the sensors will see a pulse of light when
the other does not, and vice versa.

Connecting Computer Mice

Most mice on the market today use a USB connector to attach
to your computer. USB is a standard way to connect all kinds
of peripherals to your computer, including printers, digital
cameras, keyboards and mice.

Some older mice, many of which are still in use today, have
a PS/2 type connector. Instead of a PS/2 connector, a few
other older mice use a serial type of connector to attach to
a computer.