A Guide to PC Hardware Maintenance and Repair

1
Chapter 10 Input Devices
2
Objectives

• To learn how a variety of common input devices
  work.
• To get a peek at the encoding mechanisms that are
  used by different devices.
• To see how devices can be input devices and
  output devices at the same time.

3
The Basic Keyboard

• The different parts of the keyboard
• How the keyboard works
• Keyboard Maintenance

4
Keyboard Parts

• Keycaps
• Theyre the actual buttons you push
• Are usually removable for maintenance
• Have specific size and spacing specifications

5
Keyswitches

• Provide the on/off contact to generate the
  various keyboard signals
• Range from the elegantly simple to the complex

6
Tactile Feel of the keyboard

• A function of the distance the keycap must travel
  to engage the keyswitch
• AND a function of the type of keyswitch used.

7
Mechanical Contact Switch

• Rarely (if ever) used any more
• Individual switches for each key
• Difficult to maintain, expensive and virtually
  impossible to repair

8
Foam and Foil Switch

• Keyboard presses onto plunger
• Plunger presses metallic foil into contact with
  circuit beneath foil
• Foil completes circuit and generates signal
• Mostly replaced by Rubber Dome Switch

9
Rubber Dome Switch
Rubber Domes

• Keycap presses down onto rubber dome.
• Rubber dome presses metallic button into circuit
  below.

Circuit Pad
10
Keyboard Circuitry

• Small microprocessor to keep track of keyboard
  grid pattern
• ROM-BIOS chip with embedded instructions

11
The Basics of Keyboard I/O

• Keyboard laid out in grid called the Key Matrix
• Each key is assigned a row and column number
• When a key is first pressed it generates a Make
  Code.
• When a key is released, it generates a Break
  Code.
• Keyboard processor uses the grid placement to
  generate unique make/break codes for each key.

12
The Keyboard Cable

• Four conductors
• 5V power
• Ground
• Data signal
• Clock signal

13
Keyboard Maintenance

• Prevent liquid spills
• Membrane covers available to help
• Keep debris out of the keyboard
• Occasionally pop off the keycaps and blow out the
  cracker crumbs and old staples
• Not much else you can do. When they break,
  replace them.

14
The Mouse

• Opto/Mechanical mouse
• Uses LED and perforated wheel
• Optical Mouse
• Uses LED and surface pattern

15
The Opto-Mechanical Mouse

• Three wheels
• One for North-South axis
• One for East-West axis
• One to maintain pressure of the ball against the
  other rollers
• A Mouse Ball
• So it can shoot a few hoops when its not moving
  the rollers
• A LED
• A perforated wheel for each axis

16
Two wheels track N/S and E/W travel of the mouse.
When wheel rotates, the perforated edge creates
light/shadow patterns that are converted to
electrical impulses.
17
The Optical Mouse

• Two LEDs
• Two reflection sensors
• Light from LED bounces off desk or mousepad
  surface
• Reflection sensor track motion of mouse

18
Data encoding and the Mouse

• Button state (on/off) for each button
• 0
• 1
• X-coordinate
• Y-coordinate
• X overflow indicates excessive movement
• Y overflow indicates excessive movement

19
(No Transcript)
20
Mouse Maintenance

• Erratic movement
• Generally caused by debris collected on ball
  and/or rollers. Clean with cotton swab LIGHTLY
  dampened in mild detergent solution.
• In severe cases debris might have to be scraped
  from rollers.
• Excessively fast or slow speed
• Adjust driver settings

21
Game Controllers

• Joystick
• One device on the system that doesnt require an
  IRQ
• Game Paddles
• Basically a mouse on steroids that you use with
  both hands
• Steering Wheels
• Right/left movement. Some add acceleration and
  braking functions. Others add triggers for firing
  virtual weapons.

22
Digital Cameras

• Less expensive or older cameras use a Charge
  Coupled Device (CCD) to convert an optical image
  created by the lens into a digital signal.
• Newer and more expensive cameras use a CMOS chip.

23
Digital Camera Images

• Resolution measured in mega-pixels
• Number derived from the number of total
  horizontal pixels time the number of vertical
  pixels generated by CCD or CMOS
• Color balance
• Warm shifting toward red
• Cool shifting toward blue

24
Touchscreen Monitors

• Surface of screen allows user to generate input
  by touching specific areas on screen.
• Touchscreen aware software converts the signal
  generated by touching the monitor into
  pre-programmed data.

25
Types of Touchscreen Monitor

• Analog-Resistive
• Special coating generates electrical charge when
  touched. Works with bare fingers, gloved hands or
  stylus tip
• Capacitive
• Voltage grid on surface determines where the
  monitor was touched. Only a bare finger or a
  conductive tip works
• Surface Acoustive Wave
• A coating on the surface converts the energy
  generated by the touch into sound waves