Input devices

To have detailed knowledge about the input devices.


The following are the commonly used input devices.

c.Image scanners
d.Touch panels
e.Light pen
f.Voice systems
g.Track ball and space ball
i.Data Glove


An alphanumeric keyboard is used as a device for entering text strings.
Function keys allow users to enter frequently used operations in a single
keystroke and cursor control keys can be used to select displayed objects or
coordinates portions by positioning the screen cursor.

A numeric keypad is included on the keyboard for fast entry of numeric


A mouse is small handled box used to position the screen cursor.Wheels or
rollers on the bottom of the mouse can be used to record the amount and
direction of movement.Optical sensor is also used to detect mouse
movement. It detects movement across the lines in the grid.

Image scanners

Drawing graphs,color and black-and-white photos, or text can be stored
for computer processing with an image scanner by passing an optical scanning
mechanism over the information to be stored.

The gradations of gray scale or color are recorded and stored in an array.
After getting the internal representation of the picture, we can apply
transformation to rotate ,scale or crop the picture to a particular screen

Various image processing methods can also be applied to modify the array
representation of the picture. For scanned text input,various editing
operations can be performed on the stored documents.

Touch panels

Touch panels allow displayed objects or screen positions to be selected
with the touch of the finger. The touch panel is used to select the
processing options that are represented with graphical icons.

The touch panels system can be adapted for touch input by fitting a
transparent device with a touch sensitive mechanism over the video monitor
screen. Touch input can be recorded using optical, electrical, or acoustical methods.

Optical touch panels

Optical touch panels employ a line of infrared light emitting diodes along
one vertical edge and along horizontal edge of the frame.
The opposite vertical and horizontal edges contain light detectors.These
detectors are used to record which beams are interrupted when the panel is
touched. The crossing beams that are interrupted identify the horizontal and
vertical coordinates of the screen position selected.Positions can be
selected.Positions can be selected with an accuracy of about 1/4 inch.

With closely spaced LED's it is possible to break into horizontal or two
vertical beams simultaneously. In this case an average positions between the
two interrupted beams is recorded. The LEDs operate at infrared
frequencies,So that the light is not visible to the user.

Electrical touch panels

An electrical touch panel is constructed with two transparent plates
separated by a small distance.One of the plate is coated with conducting
material,and the other plate is coated with the resistive material.

When the outer plate is touched, it is forced into contact with the inner
plate.This contact creates a voltage drop across the resistive plate that
is converted to the coordinate values of the selected screen positions.

Acoustical touch panels

In acoustical touch panels,high frequency sound waves are generated in the
horizontal and vertical directions across the glass plate.

Touching the screen causes part of each wave to be reflected from the
finger to the emitter. The screen position at the point of contact is
calculated from a measurement of the time interval between the transmission
of each wave and its reflection to the emitter.

Light Pens

Pencil shaped device are used to select screen positions by detecting the
light coming from points on the CRT screen.
They are sensitive to the short burst of light emitted from the phosphor
coating at the instant the electron beam strikes a particular point. Other
light sources as background light in the room are not detected by a light

An activated light pen generates an electrical pulse that causes the
coordinate position of the electron beam to be recorded. The recorded light
pen coordinates can be used to position an object or to select a processing option.

Voice systems

Speech recognizers are used to accept voice commands as inputs. The
voice systems input can be used to initiate graphics operations or to enter
data. These systems operate by matching an input against a predefined
dictionary of words and phrases.

When a voice command is given,the systems searches the dictionary for a
frequency pattern match.Voice input is typically spoken into a microphone
mounted on a headset.The microphone is designed to minimize input of other
background sounds.

Track ball and Space ball

A track ball is a ball that can be rotated with the fingers or palm to
produce screen cursor movement.potentiometers attached to the ball, measure the amount and direction of rotation.Trackballs can be mounted on keyboards or other devices such as the z mouse.

Space balls are used for three dimensional positioning and selection
operations in virtual reality systems,modelling ,animation , CAD and other


A joystick consists of a small, vertical lever mounted on a base that is
used to steer the screen cursor around.Some joysticks mounted on a
keyboard,others function as stand alone units.

Most joysticks select screen positions with actual stick movement, others
respond to pressure on the stick.The distance that the stick is moved in any direction from its center position corresponds to screen cursor movement in that direction.

Data Glove

The glove is constructed with a series of sensors that detect hand and
finger motions.Electro magnetic coupling between transmitting antennas and
receiving antennas is used to provide information about the position and
orientation of the hand.


A common device for drawing,painting or interactively selecting coordinate
positions on an object is digitizer.These devices can be used to input
coordinate values in either a two-dimensional or a three-dimensional space.

One type digitizer is the graphic tablet which is used to input
two-dimensional coordinates by activating a hand cursor or styles positions on a flat surface.


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