How computer mouse is made

Estelle Sidler

Background Designers in the computer industry seek not only to “build the better mousetrap” but to build the best mouse. The computer mouse is an accessory to the personal computer that has become an essential part of operation of the computer. The small device fits neatly in the curve of […]

Background

Designers in the computer industry seek not only to “build the
better mousetrap” but to build the best mouse. The computer mouse
is an accessory to the personal computer that has become an essential part
of operation of the computer. The small device fits neatly in the curve of
the user’s hand and enables the user, through very limited
movements of the hand and fingers to “point and click”
instructions to the computer. A rolling ball on the underside of the mouse
gives directions on where to move to the cursor (pointer) on the monitor
or screen, and one to three buttons (depending on design) allow the user
to say yes by clicking the buttons on the right instruction for the
computer’s next operation.

History

Dr. Douglas Engelbart, a professor with the Stanford Research Institute in
Menlo Park, California, developed the first device that came to be known
as the mouse in 1964. At that time, the arrow keys on the keyboard were
the only way of moving the cursor around on a computer screen, and the
keys were inefficient and awkward. Dr. Engelbart made a small, brick-like
mechanism with one button on top and two wheels on the underside. The two
wheels detected horizontal and vertical movement, and the unit was
somewhat difficult to maneuver. The unit was linked to the computer by a
cable so the motion signals could be electrically transmitted to the
computer for viewing on the monitor. One of Dr. Engelbart’s
co-workers thought the device with its long cable tail looked something
like a mouse, and the name stuck.

Other scientists, notably those at the National Aeronautics and Space
Administration (NASA), had also been seeking methods of moving cursors and
pointing to objects on the computer screen. They tried steering wheels,
knee switches, and light pens, but, in tests of these devices versus
Engelbart’s mouse, it was the mouse that roared. NASA’s
engineers were concerned, however, about the spacewalks the mouse would
take from its work surface in the weightlessness of space.

By 1973, the wheels on the mouse’s undercarriage had been replaced
by a single, free-rolling ball; and two more buttons (for a total of
three) had been added to the top. The creature was called both a mouse and
a pointing device, and Xerox combined it with its Alto computer, one of
the first personal computers. The Alto had a graphical user interface
(GUI); that is, the user pointed to icons, or picture symbols, and lists
of operations called menus and clicked on them to cause the computer to
open a file, print, and perform other functions. This method of operating
the computer was later adapted by Macintosh and Windows operating systems.

The development of the personal computer stimulated an explosion of
applications for the device that was small enough to be used at a number
of work stations. Engineers could develop computer-aided designs at their
own desks, and the mouse was perfect for drawing and drafting. The mouse
also began to generate offspring, collectively called input/output
devices, such as the trackball, which is essentially a mouse lying on its
back so the user can roll the ball instead of moving the entire unit over
a surface. The military, air traffic controllers, and video game players
now had a pet of their
own. Mechanical sensors in both types of devices were replaced by
optical-electronic sensor systems patented by Mouse Systems; these were
more efficient and lower in cost. An optical mouse with no moving parts
was developed for use on a special mouse pad with grid lines; light from
inside the mouse illuminates the grid, a photodetector counts the number
and orientation of the grid lines crossed, and the directional data are
translated into cursor movements on screen.

The mouse began to multiply rapidly. Apple Computers introduced the
Macintosh in 1984, and its operating system used a mouse. Other operating
systems like Commodore’s Amiga, Microsoft Windows,
Visicorp’s Vision, and many more incorporated graphical user
interfaces and mice. Improvements were added to make sensors less prone to
collecting dust, to make scrolling easier through an added wheel on the
top, and to make the mouse cordless by using radio-frequency signals
(borrowed from garage door openers) or infrared signals (adapted from
television or remote controls).

Mouse Anatomy


Body

The mouse’s “skin” is the outer, hard plastic body
that the user guides across a flat surface. It’s
“tail” is the electrical cable leading out of one end of the
mouse and finishing at the connection with the Central Processing Unit
(CPU). At the tail end, one to three buttons are the external contacts to
small electrical switches. The press of a button closes the switch with a
click; electrically, the circuit is closed, and the computer has received
a command.

On the underside of the mouse, a plastic hatch fits over a rubberized
ball, exposing part of the ball. Inside, the ball is held in place by a
support wheel and two shafts. As the ball rolls on a surface, one shaft
turns with horizontal motion and the second responds to vertical motion.
At one end of each of the two shafts, a spoked wheel also turns. As these
spokes rotate, infrared light signals from a light-emitting diode (LED)
flicker through the spokes and are intercepted by a light detector. The
dark and light are translated by phototransistors into electrical pulses
that go to the interface integrated circuit (IC) in the mouse. The pulses
tell the IC that the ball has tracked left-right and up-down, and the IC
instructs the cursor to move accordingly on the screen.

The interface integrated circuit is mounted on the printed circuit board
(PCB) that is the skeleton to which all the internal workings of the mouse
are attached. The integrated circuit, or computer chip, collects the
information from the switches and the signals from the phototransistors
and sends a data stream to the computer.


Brain

Each mouse design also has its own software called a driver. The driver is
an external brain that enables the computer to understand the
mouse’s signals. The driver tells the computer how to interpret the
mouse’s IC data stream including speed, direction, and clicked
commands. Some mouse drivers allow the user to assign specific actions to
the buttons and to adjust the mouse’s resolution (the relative
distances the mouse and the cursor travel). Mice that are purchased as
part of computer packages have the drivers built in or preprogrammed in
the computers.

Raw Materials

The mouse’s outer shell and most of its internal mechanical parts,
including the shafts and spoked wheels, are made of acrylonitrile
butadiene styrene (ABS) plastic that is injection-molded. The ball is
metal that is coated in rubber; it is made by a specialty supplier. The
electrical micro-switches (made of plastic and metal) are also
off-the-shelf items supplied by subcontractors although mouse designers
can specify force requirements for the switches to make them easier or
firmer to click. Integrated circuits or chips can be standard items,
although each manufacturer may have proprietary chips made for use in its
complete line of products. Electrical cables and overmolds (end
connectors) are also supplied by outside sources.

The printed circuit board (PCB) on which the electrical and mechanical
components are mounted is custom-made to suit the mouse design. It is a
flat, resin-coated sheet. Electrical resistors, capacitors, oscillators,
integrated circuits (ICs), and other components
are made of various types of metal, plastic, and silicon.

Design

Design of a new mouse begins with meetings among a product development
manager, designer, marketing representative, and consulting ergonomist (a
specialist in human motion and the effects various movements have on body
parts). A list of human factors guidelines is developed specifying size
range of hands, touch sensitivity, amount of work, support of the hand in
a neutral position, the user’s posture while operating the mouse,
finger extension required to reach the buttons, use by both left- and
right-handed individuals, no prolonged static electricity, and other
comfort and safety requirements; these can differ widely, depending on
whether the mouse is to be used in offices or with home computers, for
example. A design brief for the proposed mouse is written to describe the
purpose of the product and what it achieves; a look is also proposed in
keeping with the anticipated market.

The design team returns to the table with foam models; scores of different
shapes may be made for a single mouse design. User testing is done on
these models; the engineers may do this preliminary testing themselves, or
they may employ focus groups as typical users or observe one-on-one
testing with sample users. When the selection of models is narrowed down,
wooden models that are more refined and are painted are made of the
winning designs. Input is gathered again on the feel, shape, and look of
the models; the ergonomist also reviews the likely designs and confirms
that the human factors guidelines have been achieved.

When the optimal model is chosen, the engineering team begins to design
the internal components. A three-dimensional rendering is
computer-generated, and the same data are used to machine-cut the shapes
of the exterior shell with all its details. The mechanical and electronics
engineers fit the printed circuit board (and its electronics) and the
encoder mechanism (the ball, shafts, wheels and LED source and detector)
inside the structure. The process of fitting the workings to the shell is
iterative; changes are made, and the design-and-fit process is repeated
until the mouse meets its design objectives and the design team is pleased
with the results. Custom chips are designed, produced on a trial basis,
and tested; custom electronics will help the design meet performance
objectives and give it unique, competitive, and marketable
characteristics.

The completed design diagrams are turned over to the project tooler who
begins the process of modifying machines to produce the mouse. Tooling
diagrams are generated for injection-molding the shell, for example. The
size, shape, volume of the cavity, the number of gates through which the
plastic will be injected into the mold, and the flow of the plastic
through the mold are all diagramed and studied. After the final tooling
plan is reviewed, tools are cut using the computer-generated data. Sample
plastic shells are made as “try shots” to examine actual
flow lines and confirm that voids aren’t induced. Changes are made
until the process is perfect. Texture is added to the external appearance
of the shell by acid etching or by sand blasting.

In the meantime, the engineering team has set up the assembly line for the
new mouse design and conducted trial assemblies. When the design details
are finalized, tools have been produced, and test results have met the
design team’s objectives and standards, the mouse is ready for mass
production.

The Manufacturing

Process

To make the computer mouse, several manufacturing processes are performed
simultaneously to make different pieces of the unit. These processes are
described in the first three steps below. The pieces are then brought
together for final assembly, as described in steps 4 through 7.

  1. In one of the sets of manufacturing and assembling steps, the printed
    circuit board (PCB) is cut and prepared. It is a flat, resin-coated
    sheet that can be of surface-mount design or through-hole design. The
    surface-mount version is assembled almost entirely by machine. A
    computer-controlled automatic sequencer places the electrical components
    in the proper order onto the board in a prescribed pattern.

    For through-hole PCB assembly, attachment wires of the electronic
    components are inserted in holes in the PCB. Each assembly line worker
    has a drawing for part of the board and specific units to add. After
    all the components are mounted on the board, the bottom surface of the
    board is passed through molten lead solder in a wave soldering
    machine. This machine washes the board with flux to remove
    contaminants, then heats the board and the components it carries by
    infrared heat to lessen the possibility of thermal shock. As the
    underside of the board flows over the completely smooth, thin liquid
    sheet of molten solder, the solder moves up each wire by capillary
    action, seals the perforations, and fixes the components in place. The
    soldered boards are cooled. The PCB is visually inspected at this
    stage, and imperfect boards are rejected before the encoder mechanism
    is attached.

  2. The encoder mechanism (including the rubber-covered ball, the support
    wheel, both spoked wheels and their axles, the LED, and its detector) is
    assembled as a separate unit. The plastic parts were also manufactured
    by injection-molding in accordance with proprietary specifications and
    trimmed of scrap plastic. After the mechanism is assembled, the unit is
    fastened to the PCB using either clips or screws. The board is now
    completely assembled and is subjected to an electronics quality control
    test.
  3. The mouse’s tail—its electrical cable—has also been
    manufactured using a set of wires, shielding, and the rubber cover. The
    cable has two additional pieces of molded rubber called overmolds. These
    are strain relief devices that prevent the cable from detaching from the
    mouse or its connector plug if the cable is tugged. Mouse makers
    typically design their own shapes for overmolds. The near-mouse overmold
    is hooked to the housing, and, at the opposite end of the tail, the
    connector is soldered to the wires and the connector overmold is popped
    into place.
  4. The pieces of the outer shell are visually inspected after molding,
    trimming, and surface (finish) treatment and prior to assembly. The
    outer shell is assembled in four steps. The completed PCB and encoder
    assembly is inserted into the bottom of the shell. The buttons are
    snapped into the top part of the housing, the cable is attached, and the
    top and bottom are screwed together using automated screwdrivers.
  5. The final electronics and performance quality check is performed when
    assembly is essentially complete. Rubber or neoprene feet with adhesive
    sheeting pre-applied to one side are added to the underside of the
    mouse.
  6. While the tooling designs and physical assembly described above have
    been in progress, a programming team has been developing, testing, and
    reproducing the mouse driver firmware. The firmware so-called because it
    lies in the realm between software and hardware consists of a
    combination of codes in the integrated circuit and the translation of
    the mouse’s directional movements and micro-switch signals that
    the receiving computer needs to understand when the mouse is attached.
    When the driver has been developed, the manufacturer’s own
    testers run it through rigorous trials, and both the Federal
    Communications Commission (FCC) and the European Commission
    (CE—an organization that governs radio emissions and
    electrostatic discharge) also approve the electronics. Approved driver
    data is encoded and mass-produced on diskettes.
  7. The FCC requires that signaling or communications devices including the
    mouse bear labels identifying the company and certain product
    specifications. The labels are preprinted on durable paper with strong
    adhesive so they cannot easily be removed. A label is pasted on the
    mouse bottom, and the mouse is bagged in plastic. The device, its driver
    diskette, and an instruction booklet with registration and warrantee
    information are boxed and prepared for shipment and sale.

Quality Control

Use of computer-generated designs builds quality and time savings into the
product. Data can be stored and modified quickly, so experiments with
shapes, component layouts, and overall look can be attempted and iterative
adjustments can be made. Computer-aided design data also speeds review of

Beneath the outer, hard plastic body that the user maneuvers across a
mouse pad is a rubberized ball that turns as the mouse moves. The ball
is held in place by a support wheel and two shafts. As it rolls, one
shaft turns with horizontal motion and the second responds to vertical
motion. At one end of each of the two shafts, a spoked wheel also
turns. As these spokes rotate, infrared light signals from a
light-emitting diode (LED) flicker through the spokes and are
intercepted by a light detector. The dark and light are translated by
phototransistors into electrical pulses that go to the interface
integrated circuit (IC) in the mouse. The pulses tell the IC that the
ball has tracked left-right and up-down, transmits the command through
the cable to the Central Processing Unit (CPU), and instructs the
cursor to move accordingly on the screen.

parts specifications, the tooling process, and design of assembly
procedures so the opportunity for conflicts is small.

At least three quality control steps are performed during assembly. An
electronics check is carried out on the PCB after its components are
attached (and soldered into place if through-hole assembly methods are
used) and before any of the plastic mechanism is attached. The plastic
parts (the encoder mechanism and the outer shell) are visually inspected
when they are complete but before they are connected to the board and
electronics; this prevents disassembly or wasting electronics due to a
defective shell, for example. Finally, the completely assembled device is
subjected to another electronics and performance check; 100% of the mice
manufactured by Kensington Technology Group are plugged into operating
computers and tested before they are packaged. As noted above, both the
FCC and CE regulate aspects of mouse operations, so they also test and
approve driver data.

Byproducts/Waste

Computer mice makers do not generate byproducts from mouse manufacture,
but most offer a range of similar devices for different applications.
Compatible or interchangeable parts are incorporated in new designs or
multiple designs whenever possible to avoid design, tooling, and assembly
modification costs.

Waste is minimal. The mouse’s ABS plastic skin is highly recyclable
and can be ground, molded, and reground many times. Other plastic and
metal scrap is produced in minute quantities and can be recycled or
disposed.

The Future

Devices that are modifications of mice are currently on the market. The
Internet mouse inserts a scrolling wheel between the two buttons to make
scrolling of web pages easier; a still more sophisticated version adds
buttons that can be programmed by the user to perform Internet functions,
like moving back or forward, returning to the home page, or starting a new
search. One mouse version has returned to the floor where two foot pads or
pedals replace the ball and buttons; one pedal is pushed to relocate the
cursor and the second clicks. Cordless mice that communicate with radio
signals are available, and the mouse has been disposed of altogether by
the touchpad. The user runs a finger across the touchpad to reposition the
cursor, and web pages can be scrolled and advanced by other, specific
moves. Many of these adaptations are designed to eliminate repetitive
stress ailments and save forearm strain.

The mouse’s inventor, Dr. Engelbart, never believed the mouse would
reach thirty-something or retain its nontechnical name. In fact, both the
mouse and its trackball offspring are increasingly popular as shapes
become more comfortable, less cleaning and maintenance are required, and
reliability and longevity improve. Future developments in mice will follow
the evolution of the Internet and include more options for
programmability, such as switching hands to double the number of available
functions. The mouse may become extinct someday, and the most likely
candidate to replace it is a device that tracks the eye movement of the
computer user and follows it with appropriate cursor motions and function
signals.

Where to Learn More


Books

Ed., Time-Life

Books. Input/Output: Understanding Computers.

Alexandria, VA: Time-Life Books, 1990.


Periodicals

Alexander, Howard. “Behold the Lowly Mouse: Clever Technology
Close at Hand.”

New York Times

(October 1, 1998): D9.

“The Mouse.”

Newsweek

(Winter 1997): 30.

Randall, Neil.

PC Magazine

(January 5, 1997): 217.

Terrell, Kenneth. “A new clique of mice: designers turn the
computer mouse on its head; some cut its tail.”

U.S. News & World Report

(March 23, 1998): 60+.


Other

Kensington Technology Group.

http://www.kensington.com/

(June 7, 1999).

Logitech.

http://www.logitech.com/

(June 7, 1999).

Microsoft Corporation.

http://www.microsoft.com/

(June 7, 1999).

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