Peripheral DevicesPeripheral Devices

KeyboardsKeyboards Keyswitch Keyboards- employ an individual switch under each key- a Keyswitch Keyboards- employ an individual switch under each key- a

plunger moves downward in response to a key press, making a connection plunger moves downward in response to a key press, making a connection between two signal lines coming from the keyboard controllerbetween two signal lines coming from the keyboard controller InexpensiveInexpensive Simple to makeSimple to make Simple to serviceSimple to service Bounce led to duplicate letters, but decreased tension leads to finger Bounce led to duplicate letters, but decreased tension leads to finger

fatiguefatigue BulkyBulky Require Voltage to operateRequire Voltage to operate

Second effort employed an electric controller to constantly scan for Second effort employed an electric controller to constantly scan for keystrokes, ignoring those which are not present for a second scankeystrokes, ignoring those which are not present for a second scan

Capacitive KeyboardsCapacitive Keyboards

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

Keyboard ConnectorsKeyboard Connectors

DIN 5-DIN 5- standard on the IBM PC or XT/AT standard on the IBM PC or XT/AT form factor machinesform factor machines

Mini- PS/2-Mini- PS/2- smaller then the DIN 5- so named smaller then the DIN 5- so named because it was initially introduced on the IBM because it was initially introduced on the IBM PS/2PS/2

Cleaning KeyboardsCleaning Keyboards

Remove it from the computer and soak it in distilled, Remove it from the computer and soak it in distilled, demineralized water as soon as a spill occursdemineralized water as soon as a spill occurs A dry spill is much harder to cleanA dry spill is much harder to clean Running keyboard through the dishwasher is not Running keyboard through the dishwasher is not

recommended recommended Be sure the keyboard is completely dry before reconnecting Be sure the keyboard is completely dry before reconnecting

it and using itit and using it Disassemble and use a special keyboard cleanerDisassemble and use a special keyboard cleaner

Due to the amount of time this method requires, it is Due to the amount of time this method requires, it is cheaper to simply buy a new keyboardcheaper to simply buy a new keyboard

The MouseThe Mouse

GUIGUI- Graphical User Interface- the use of - Graphical User Interface- the use of pictures to represent computer entities or basic pictures to represent computer entities or basic commands (i.e.- save, exit)commands (i.e.- save, exit)

MouseMouse- a device specifically designed to - a device specifically designed to interact with the pictures represented in a GUI interact with the pictures represented in a GUI interface- translates moves on a horizontal interface- translates moves on a horizontal surface into movements of a pointer on the surface into movements of a pointer on the screenscreen

Types of MiceTypes of Mice

Opto-mechanical- Opto-mechanical- contains a round ball that makes contains a round ball that makes contact with two internal rollers representing the x contact with two internal rollers representing the x and y axis respectively- optical sensors interpret light and y axis respectively- optical sensors interpret light patterns as speed and direction of movement and send patterns as speed and direction of movement and send those to the mouse control software on the computerthose to the mouse control software on the computer

An An OpticalOptical Mouse has no ball- rather it uses a special Mouse has no ball- rather it uses a special mouse pad and a beam of laser light- the pad reflects mouse pad and a beam of laser light- the pad reflects the laser back to a sensor in the mouse that detects the laser back to a sensor in the mouse that detects movement and directionmovement and direction Will not work without the special mouse padWill not work without the special mouse pad

Mouse InterfacesMouse Interfaces

Serial –Serial – the first major mouse interface was a the first major mouse interface was a DB9 serialDB9 serial Major disadvantage was the use of a COM portMajor disadvantage was the use of a COM port

Bus Interface-Bus Interface- an expansion card with a PS/2 an expansion card with a PS/2 connector connector Did not take up a COM port, but it does use an Did not take up a COM port, but it does use an

interrupt interrupt PS/2 Mouse InterfacePS/2 Mouse Interface- the same PS/2 - the same PS/2

connector integrated on the motherboardconnector integrated on the motherboard

Cleaning the MouseCleaning the Mouse

1. Turn the mouse upside down and remove the ball by 1. Turn the mouse upside down and remove the ball by rotating the retaining ringrotating the retaining ring

2. Flip the mouse upright so the ball will fall out2. Flip the mouse upright so the ball will fall out

3. Use a small eyeglass screwdriver to remove the circular 3. Use a small eyeglass screwdriver to remove the circular accumulation of dust and dirt on the rollersaccumulation of dust and dirt on the rollers

4. If needed, soak in isopropyl alcohol to loosen4. If needed, soak in isopropyl alcohol to loosen

5. Reassemble5. Reassemble

Other Pointing DevicesOther Pointing Devices TrackballsTrackballs- essentially an upside-down mouse- the ball moves while the - essentially an upside-down mouse- the ball moves while the

casing is stationary- typical trackballs are large desktop style- portable casing is stationary- typical trackballs are large desktop style- portable trackballs are more compact and may be held in the handtrackballs are more compact and may be held in the hand

Drawing TabletsDrawing Tablets- a sheet of plastic with a rubberized coating on which a - a sheet of plastic with a rubberized coating on which a user my use a stylus to “draw” imagesuser my use a stylus to “draw” images

Electromagnetic Tablets-Electromagnetic Tablets- tablet has a grid of wires across which an electrical 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 pulse is sent at regular intervals- a sensor in the stylus translates the signals to x and y coordinatesand y coordinates

Resistive TabletsResistive Tablets- have a resistive surface under the rubberized coating that - have a resistive surface under the rubberized coating that induces variable current at different spots on the x and y axis translating to induces variable current at different spots on the x and y axis translating to specific coordinatesspecific coordinates

Acoustic TabletsAcoustic Tablets- stylus has a small spark which activates at the press of a - 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 button- microphones on the x and y axis translate the coordinates into values for the computerfor the computer

Touch Screens-Touch Screens- a screen which is sensitive to touch a screen which is sensitive to touch OpticalOptical- the physical touch breaks a beam of light emanating from the screen - the physical touch breaks a beam of light emanating from the screen

to determine x and y coordinates\to determine x and y coordinates\ Capacitive screens-Capacitive screens- like the keyboards, employ two sheets of clear plastic like the keyboards, employ two sheets of clear plastic

separated by a layer of air- touching a particular spot changes the total separated by a layer of air- touching a particular spot changes the total capacitance and translates to an x, y coordinatecapacitance and translates to an x, y coordinate

ScannersScanners Flatbed ScannersFlatbed Scanners- resemble the top half of a photocopier- they - resemble the top half of a photocopier- they

employ a charge coupled device, a motorized carriage, and a employ a charge coupled device, a motorized carriage, and a light source to convert images in to computerized files light source to convert images in to computerized files Usually SCSI Usually SCSI Can be manufacturer proprietaryCan be manufacturer proprietary

Handheld ScannersHandheld Scanners- contain all the same components in a - contain all the same components in a smaller enclosure with wheelssmaller enclosure with wheels InexpensiveInexpensive Decent CapabilitiesDecent Capabilities SlowSlow Quality Depends Largely on UserQuality Depends Largely on User

Scanners may be cleaned carefully with glass cleanerScanners may be cleaned carefully with glass cleaner

ModemsModems Modem Modem actually stands for Modulator/Demodulator- digital actually stands for Modulator/Demodulator- digital

signals can lose strength over long distances- analog signals signals can lose strength over long distances- analog signals may get weaker, but the may get weaker, but the soundsound does not degrade- therefore, does not degrade- therefore, analog signals are a better choice for communication over a analog signals are a better choice for communication over a telephone line. The modem translates the digital signals from telephone line. The modem translates the digital signals from the computer to analog signals for transmission and visa versathe computer to analog signals for transmission and visa versaModem Signal AbbreviationsModem Signal Abbreviations

OH- Off the HookOH- Off the HookSD(TX) Transmit DataSD(TX) Transmit DataRD(RX) Receive DataRD(RX) Receive DataAA Auto AnswerAA Auto Answer