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Input Device :keyboard
Types of key switch
Components of Keyboard
Keyboard switches
Keyboard processor or circuitry
Key matrix
Types of key Switches
Capacitive switch
Hall effect switch
Opto electronic switch
Membrane switch
Mechnical switch
Types of key switch
Capacitive 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.
Based on the switch open/close voltage is received
this voltage is converted into proper signals to inform
Lifespan 20 millon key strokes.
Capacitive key switch
Types of key switch
Hall effect switch:
magnetic field is applied
to any device the
resistance of device will
starts flowing)
 This allow current flow
Lifespan 100 million
Types of key switch
have LED light generate light
when electric power is
current to flow in the
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 output Vout
Membrane switch
membrane switch: it is
multi layered plastic or
rubberuses the row and
colum conductor sheets.
Mechanical switch: it
uses two metal pieces or
contacts .
Rubber dome:madeup of
polyester domes
Mechanical switch
Keyboard Interfaces
Connects to PC
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
Interface between keyboard and pc
– AT keyboard connector(DIN5)
– PS2 keyboard connector or(MIN-DIN6)
– USB connector
AT keyboard connector(DIN5)
– Uses
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,
Keyboard working:key is pressed it pushes down the rubber
Dome tuches a pair of conductive lines on circuit
Allow current flow
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.
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
Mouse types
Each roller attached to encoder.
Each time a contact bar touches a point an electrical signal.
Signals generated are sent to PC over the mouse cables
And number of mouse time mouse button is clicked.
2. Optical 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.
Each roller connected to wheel these rollers are rotated by
movement of rollers.
Wheel rotate pair of LED and photo detectors
Signals sent to PC through mouse connectors
Opto mechnical mouse
Mouse types
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.
Optical mouse
Installing Mouse
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.