Peripheral Devices

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Peripheral Devices
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Keyboards

• Keyswitch Keyboards- employ an individual switch
  under each key- a plunger moves downward in
  response to a key press, making a connection
  between two signal lines coming from the keyboard
  controller
• Inexpensive
• Simple to make
• Simple to service
• Bounce led to duplicate letters, but decreased
  tension leads to finger fatigue
• Bulky
• Require Voltage to operate
• Second effort employed an electric controller to
  constantly scan for keystrokes, ignoring those
  which are not present for a second scan

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Capacitive Keyboards

• Placed two sheets of semi-conductive materials
  separated by a thin sheet of Mylar inside the
  keyboard- a key press creates contact between the
  sheets changing the capacitance- the controller
  is aware of which key is pressed by reading a
  scan code
• You cannot repair capacitive switch keyboards
• Durable
• Inexpensive

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Keyboard Connectors

• DIN 5- standard on the IBM PC or XT/AT form
  factor machines
• Mini- PS/2- smaller then the DIN 5- so named
  because it was initially introduced on the IBM
  PS/2

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Cleaning Keyboards

• Remove it from the computer and soak it in
  distilled, demineralized water as soon as a spill
  occurs
• A dry spill is much harder to clean
• Running keyboard through the dishwasher is not
  recommended
• Be sure the keyboard is completely dry before
  reconnecting it and using it
• Disassemble and use a special keyboard cleaner
• Due to the amount of time this method requires,
  it is cheaper to simply buy a new keyboard

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The Mouse

• GUI- Graphical User Interface- the use of
  pictures to represent computer entities or basic
  commands (i.e.- save, exit)
• Mouse- a device specifically designed to interact
  with the pictures represented in a GUI interface-
  translates moves on a horizontal surface into
  movements of a pointer on the screen

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Types of Mice

• Opto-mechanical- contains a round ball that makes
  contact with two internal rollers representing
  the x and y axis respectively- optical sensors
  interpret light patterns as speed and direction
  of movement and send those to the mouse control
  software on the computer
• An Optical Mouse has no ball- rather it uses a
  special mouse pad and a beam of laser light- the
  pad reflects the laser back to a sensor in the
  mouse that detects movement and direction
• Will not work without the special mouse pad

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Mouse Interfaces

• Serial the first major mouse interface was a
  DB9 serial
• Major disadvantage was the use of a COM port
• Bus Interface- an expansion card with a PS/2
  connector
• Did not take up a COM port, but it does use an
  interrupt
• PS/2 Mouse Interface- the same PS/2 connector
  integrated on the motherboard

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Cleaning the Mouse

• 1. Turn the mouse upside down and remove the
  ball by rotating the retaining ring
• 2. Flip the mouse upright so the ball will fall
  out
• 3. Use a small eyeglass screwdriver to remove
  the circular accumulation of dust and dirt on the
  rollers
• 4. If needed, soak in isopropyl alcohol to
  loosen
• 5. Reassemble

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Other Pointing Devices

• Trackballs- essentially an upside-down mouse- the
  ball moves while the casing is stationary-
  typical trackballs are large desktop style-
  portable trackballs are more compact and may be
  held in the hand
• Drawing Tablets- a sheet of plastic with a
  rubberized coating on which a user my use a
  stylus to draw images
• Electromagnetic Tablets- tablet has a grid of
  wires across which an electrical pulse is sent at
  regular intervals- a sensor in the stylus
  translates the signals to x and y coordinates
• Resistive Tablets- have a resistive surface under
  the rubberized coating that induces variable
  current at different spots on the x and y axis
  translating to specific coordinates
• Acoustic Tablets- stylus has a small spark which
  activates at the press of a button- microphones
  on the x and y axis translate the coordinates
  into values for the computer
• Touch Screens- a screen which is sensitive to
  touch
• Optical- the physical touch breaks a beam of
  light emanating from the screen to determine x
  and y coordinates\
• Capacitive screens- like the keyboards, employ
  two sheets of clear plastic separated by a layer
  of air- touching a particular spot changes the
  total capacitance and translates to an x, y
  coordinate

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Scanners

• Flatbed Scanners- resemble the top half of a
  photocopier- they employ a charge coupled device,
  a motorized carriage, and a light source to
  convert images in to computerized files
• Usually SCSI
• Can be manufacturer proprietary
• Handheld Scanners- contain all the same
  components in a smaller enclosure with wheels
• Inexpensive
• Decent Capabilities
• Slow
• Quality Depends Largely on User
• Scanners may be cleaned carefully with glass
  cleaner

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Modems

• Modem actually stands for Modulator/Demodulator-
  digital signals can lose strength over long
  distances- analog signals may get weaker, but the
  sound does not degrade- therefore, analog signals
  are a better choice for communication over a
  telephone line. The modem translates the digital
  signals from the computer to analog signals for
  transmission and visa versa
• Modem Signal Abbreviations
• OH- Off the Hook
• SD(TX) Transmit Data
• RD(RX) Receive Data
• AA Auto Answer