Sonic's Desktop

The computer mouse

The silent rodent of the computer world

In our last edition, we broke up the hardware components of the total computer system as input devices, output devices, system unit and secondary storage. Therefore, in today's edition, and in the future editions, let's go into details of these divisions.

By now, you will be aware that it is through input devices that we feed in any relevant data to the computer. With the development of multimedia, now there is a host of various input devices. For a start, let us explore the key input device which is the mouse. Sonic will present you some important facts about this small device.

Evolution

The mouse came into existence as a result of the need for a pointing device which would enable easy navigation in the Graphical User Interface provided by new operating systems.

This was invented by Douglas Engelbart of the Stanford Research Institute in 1964. It used two wheels which are perpendicular(at 90 degrees) to each other, and the position of the cursor (the arrow in the desktop) was determined by how far one wheel has gone in one direction and how far the other wheel has moved in the perpendicular direction.

Thereafter, it evolved rapidly as explained hereafter.

Different types and how they work

* Mechanical mice

These detect movement by inspecting the movement in parts of the mouse. The first mouse itself was a mechanical mouse since it detected the motion of two wheels.

Thereafter, it was improved by replacing the two wheels with a ball and the movement of the cursor was determined by checking the beams of light coming through the chopper wheels (wheels with holes around the edge) which were in contact with the ball.

The same was further improved by using two rollers to be in contact with the ball. These too had chopper

 wheels at the ends of the rollers and the position of the cursor was determined by checking the rotation of these rollers where each was mapped to a movement along the X and Y axes respectively. This is the ball mouse that you often see in your computers nowadays.

* Optical mice

Optical mice detect movement of the mouse by inspecting the surface which the mouse is moved on.

These came into being in the 1980s and there were two ways by which the movement of the mouse was detected. In one method, an infra-red LED was used along with an infra-red sensor and the movement was determined by inspecting the grid lines that were marked on the surface on which the mouse was moved.

This method required a special mouse pad with gridlines. In the other method, a visible-light image sensor tracked the motion of light dots in a dark field of a printed paper or similar mouse pad.

As technology developed, the optical mouse was improved by using optoelectronic sensors, which determine the motion by taking images of the surface at a fast rate and analysing them using the image processing chips in the mouse.

The difference in successive pictures are mapped on to a movement along X and Y axes. This approach doesn't require a special mouse pad as primitive optical mice. These mice are really handy since the nature of the surface does not affect the cursor movement a lot like in the mechanical mouse.

But, these do not work on reflective surfaces since it will be capturing the same image all the time, which is the underside of the mouse itself. Try using an optical mouse on a mirror and see for yourself.

* Laser mice

This is quite similar to the optical mouse, but the LED of the normal optical mouse is replaced by an infra-red laser. This is done in order to increase the sensitivity to the movement, and it has been improved about twenty times more than the conventional optical mice. This can be used on shiny surfaces to a certain extent than optical mice, due to its high sensitivity.

* Inertial mice

This uses accelerometers to detect movement along the axes supported. An accelerometer is an

 electromechanical device that will measure acceleration forces.

These forces may be static, like the constant force of gravity pulling at your feet, or they could be dynamic like when moving the accelerometer. This is considered to consume less power than a normal optical mouse and the performance is better.

* Tactile mice

Tactile refers to the sense of touch as used in Braille. The tactile mouse was mainly developed to provide access for blind people to obtain graphical information on the computer screen. It consists of an ordinary computer mouse with a small tactile display unit on its top.

The combined effect of the movement of the hand and the tactile response to the fingers makes users feel as if they were exploring touchable drawings.

See you next week with more interesting facts about computer 'mice' and other pointing devices.

Signing out for now, Aravinda Dassanayake