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Input & Output
devices
Input Device :keyboard
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a keyboard is an input device, partially modeled after the
typewriter keyboard, which uses an arrangement of buttons or
keys, to act as mechanical levers or electronic switches.
A keyboard is also used to give commands to the operating
system of a computer.
Connectors to keyboard AT(DIN-5) PS2 andUSB.
XT with 83 keys,At with 84 keys, 104 keys by adding window
keys.
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Keys includes: Typing keys numeric keypad,function
keys,control keys
Virtual Laser Keyboard(sensor,Signalsto computer)
Input Device :keyboard
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Components of Keyboard
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Keyboard switches
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Keyboard processor or circuitry
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Key matrix
Types of keySwitches
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Capacitive switch
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Hall effect switch
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Opto electronic switch
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Membrane switch
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Mechnical switch
Input Device :keyboard
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Key matrix: keyboard matrix is the arrangement of circuit
connections between the keyboard controller and all the keys.
Key switch: The main component of any keyboard is the key
switch. These switches generate typical codes of signal when
they are depressed and it is used for interfacing with computer
system
Input Device :keyboard
Input Device :keyboard
Input Device :keyboard
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Key matrix: keyboard matrix is the arrangement of circuit
connections between the keyboard controller and all the keys.
each key is placed at the intersection of a matrix row and a
matrix column. The keyboard repeatedly applies current to
each column in turn, and checks to see which rows output
current. From this, the keyboard can deduce which keys in
that column have been depressed.
Input Device :keyboard
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Capcitive switch:two plates of the capacitor are brought
closer when the key is pressed.
Change in capacitance of switch changes and change in
capacitance is detected in terms of voltage.
Basedon the switch open/close voltage is recived thisvoltage
is converted into proper signals to inform CPU.
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Lifespan 20 millonkey strokes.
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Hall effect switch:
magnetic field is applied to any device the resistance of device
will be increases or decresed(current starts flowing)
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This allow current flow
Lifespan 100 million keystrokes
Input Device :keyboard
Input Device :keyboard
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opto-electronic switch: have LED light generate light when
electric power is applied.uses photo- transistor which allow
current to flow in the circuit.
When key is pressed not pressed the light from LED falls onto
photo-transistor
When key is pressed the value will be produced at the ouput
Vout
membrane switch:it is multi layered plastic or rubberuses the
row and colum conductor sheets.
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Mechanical switch: it uses two metal pieces or contacts .
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Rubber dome:madeup of polyester domes
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Refered as direct switches.
Input Device :keyboard
opto-electronic
switch
membrane
switch
Input Device :keyboard
Mechanical
switch
Keyboard Interfaces
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Connects to PC
– KEYBOARD
– KEYBOARD CONNECTOR
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Inside keyboard a processor and circuit which carry information
to or from that processor.
Keyboard controller is single chip contains memory RAM,
processor ROM(control operations of keyboard)
Key matrix: row and columns made up wires and each key act
like switch
Key matrix is grid of circuits when key is pressed the row wire
makes contact with colmn wire and completes the circuit . KM
passes current to keyboard controller .
Keyboard controller will detects the closed circuit and registers
the key press and controller read the key pressed.
Keyboard Interfaces
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KEYBOARD CONNECTOR
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Interface between keyboard and pc
– AT keyboard connector(DIN5)
– PS2 keyboard connector or(MIN-DIN6)
– USB connector
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AT keyboard connector(DIN5)
– Uses
5
pins:
KBDCLK(provide
clock
pulse),
KBDAT(send/recive data),KBRST (reset keyboardinternal
buffer),GND(ground),VCC(+5v provides power to keyboard)
PS2 keyboard connector or(MIN-DIN6): With 6 pins
USB keyboard connector:
USB keyboard connector : uses 4 pins VDC(+5V),DATAcarries -ve data signal,DATA+it carries +ve data Signal,
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Keyboard working:key is pressed it pushes down the rubber
dome
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Dome tuches a pair of conductive lines on circuit
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Allow current flow
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Mouse:
Mechanical Mouse : Mechanical Mouse uses ball for the
movement of cursor on thecomputer screen. When the ball is
rolled in any direction, a sensor of the mouse detects it and also
moves the mouse pointer in the same direction.
Optical Mouse : Optical Mouse uses Laser rays for the
movement of cursor on the computer screen. It is an advanced
pointing device. Movement is detected by sensing changes in
the reflected light rather than the motion of a rolling sphere.
Cord-Less Mouse : Cord-Less Mouse is battery driven and does
not need any wire for the physical connection with the
motherboard. It transmits data through infrared or radio signal.
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Mechanical
mouse
Mouse types
1.Mechanical mouse: a rubber ball rolls as the mouse is moved
across table top or mouse pad.
The wheels are referred as encoders have tiny metal contact
points on rims
Location of mouse is identified by how many times the contact
points have touched the bars.
mouse moved across flat surface.
As balls rotate it touches and turns two rollers inside the mouse
Two rollers are used for vertical and horizontal movements of
cursor
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Mouse types
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Each roller attached to encoder.
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Each time a contact bar touches a point an electrical signal.
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Signals generated are sent to PC over the mouse cables
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And number of mouse time mouse button is clicked.
2. Optical-mechanical mouse:
When mouse moves the ball of mouse moves and two separate
rollers fixed at 90 degree to each other one roller is for vertical
and horizontal movement of cursor.
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Each roller connected to wheel these rollers are rotated by
movement of rollers.
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Wheel rotate pair of LED and photo detectors
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Signals sent to PC through mouse connectors
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Mouse types
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Optical mouse:
LED produces a red light that is emitted onto surface the
light reflected back to CMOS sensor then to DSP(digital
signal processor) for analysis
DSP analysis the signal and and patterns and
determines mouse movements.
Along with coordinates are received by computer and will
show mouse movement on screen.
Installing Mouse
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Locate the mouse port(USB,PS/2 COM1/COM2) on computer
system back.
Plug the mouse carefully on the mouse port of computer.
Turn on system.
Installing of mouse driver software
window have built in drivers
Insert driver CD
Run the dialog box displayed on screen.
Fallow installation instruction
Restart computer.
END