Computer Mice

Optical Mouse

Track-Ball Mouse

(By, Kevin Le)

Contrary to common belief, Steve Jobs did not invent the mouse – Xerox did.  What Steve Jobs did do was make a practical and cheaper mouse which greatly differed from the clunky and expensive ($300) mouse developed by Xerox.  The mouse, the perfect pointing device, advanced computer technology by making Graphical User Interfaces (GUI’s) a standard in the computer world.  Without the mouse, computers would not have reached the stage it is in now.  But because of how common computer mice are, they are often taken for granted.  The main goal of a mouse is to translate the motion of a user’s hand into commands and signals that the computer can understand and use, which of course everyone knows.  Yet, not everybody knows how the computer mouse works, but for a device so influential in the history of computers, it ought to be known by everyone.

There are five main components of a typical track-ball mouse.  A ball inside the mouse correlates with the desktop, and rolls when the mouse rolls.  Two separate rollers touch the ball, and correspond to two different degrees of linear motion: x and y.  When the ball rolls, the computer either detects the ball travelling across the x-axis roller or the y-axis roller.  Each roller is attached to a shaft, and the shaft spins a disk with holes punched into it.  When the roller rolls, so do the shaft and disk.  The disk acts as an optical encoder, and usually has 36 holes in it.  The optical encoder works like so: on either side of each disk, there is an infrared LED and an infrared sensor.  As the disk spins, it breaks up the infrared light and the sensor sees pulses of infrared light beaming towards it.  Since the disk spins as the track-ball moves, the rate of the pulse is directly related to the speed of the mouse and how far the mouse is travelling.  An onboard processor chip then reads the infrared pulses and converts the pulses into binary data which is sent to the computer and used to calculate the movement of the cursor on the screen.

Optical mice are a little bit more complicated.  Introduced in 1999 by Agilent Technologies, optical mice use a tiny camera to take thousands of pictures per second.  Unlike the track-ball mice, optical mice do not need a mouse pad and use a small red light-emitting diode (LED) which bounces light off the surface below it onto a complimentary metal-oxide semiconductor (CMOS) sensor.  The CMOS sensor then sends image to the digital signal process (DSP) for analysis.  The DSP analyzes the images for patterns in how the mouse is moving, and based on these changes, the DSP is able to interpret where the mouse has moved, how far it has moved, and how quickly the mouse has moved.  Then, the DSP sends the coordinates of the mouse’s movement to the computer, which translates the motion towards the cursor on the desktop.  Incredibly, this process happens hundreds of times each second and makes the cursor appear to move smoothly.

In the end, the computer mouse – the unassuming servant of the desktop – is much more complex than it appears.  Nowadays, there are many types of mice ranging from the traditional track-ball mouse to laser optical and Bluetooth mice.  The mouse may be unappreciated, but sometimes ingenuity and engineering greatness lie in the most humble of places.


Posted in How Things Work