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Peripheral Devices. 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
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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
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
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
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
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
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
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
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
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
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
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
