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Techno Page - By Harendra Alwis - email: technopage_lk@yahoo.com How the mouse
evolved The computer mouse was first introduced with the Apple Macintosh in 1984, and since then it has helped to completely redefine the way we use computers. Every day of your computing life, you reach for your mouse whenever you want to move your cursor or activate something. Your mouse senses your motion and your clicks and sends them to the computer so it can respond appropriately. It is amazing how simple and effective a mouse is, and it is also amazing how long it took to become a part of everyday life. Given that people naturally point at things usually before they speak it is surprising that it took so long for a good pointing device to develop. Although originally conceived in the 1960s, it took quite some time to implement the idea. In the early days there was no need to point because computers used rudimentary interfaces like teletype machines or punch cards for data entry. The text terminals did nothing more than emulate a teletype (using the screen to replace paper), so it was the 1960s and early 1970s before arrow keys were found on most terminals. Full screen editors were the first things to take real advantage of the cursor keys, and they offered the first crude way to point. Light pens were used on many machines as a pointing device for a number of years, and graphics tablets, joy sticks and various other devices were also popular in the 1970s. But when the mouse hit the scene attached to the Mac, it was an immediate success. There was something about it that was completely natural. Compared to a graphics tablet, The mouse is extremely inexpensive and takes up very little desk space. In the PC world however, it took longer to gain popularity because of a lack of support in the operating system. Once Windows 3.1 made Graphical User Interfaces (GUIs) a standard, the mouse became the main PC human interface. The main goal of any mouse is to translate the motion of your hand into signals that the computer can use. Almost all today do the translation using five components. A ball inside the mouse touches the desktop and rolls when the mouse moves. Two rollers inside the mouse touch the ball. One of the rollers is oriented so that it detects motion in the X direction, and the other is oriented 90 degrees to the first roller so it detects motion in the Y direction. When the ball rotates, one or both of these rollers rotate as well. The rollers each connect to a shaft, and the shaft spins a disk with holes in it. When a roller rolls, its shaft and disk spin with it. On either side of the disk there is an infrared LED and an infrared sensor. The holes in the disk break the beam of light coming from the LED so that the infrared sensor sees pulses of light. The rate of the pulsing is directly related to the speed of the mouse and the distance it travels. An on-board processor chip reads the pulses from the infrared sensors and turns them into binary data that the computer can understand. The chip sends the binary data to the computer through the mouse's cord. Each encoder disk has two infrared LEDs and two infrared sensors, one on each side of the disk (so there are four LED/sensor pairs inside a mouse). This arrangement allows the processor to detect the disk's direction of rotation. There is a piece of plastic with a small, precisely located hole that sits between the encoder disk and each infrared sensor. With advances in mouse technology, the wheeled mouse is in danger of extinction. The preferred device for pointing and clicking now is the optical mouse. Developed in the late 1999, the optical mouse actually uses a tiny camera to take 1,500 pictures every second. Able to work on almost any surface, the mouse has a small, red light-emitting diode (LED) that bounces light off that surface onto a complimentary metal-oxide semiconductor (CMOS) sensor. The CMOS sensor sends each image to a processor (DSP) for analysis. The DSP, operating at 18 MIPS (million instructions per second), is able to detect patterns in the images and see how those patterns have moved since the previous image. Based on the change in patterns over a sequence of images, the DSP determines how far the mouse has moved and sends the corresponding coordinates to the computer. The computer moves the cursor on the screen based on the coordinates received from the mouse. This happens hundreds of times each second, making the cursor appear to move very smoothly. Although the LED-based optical mouse is fairly recent, another type of optical mouse has been around for over a decade. The original optical-mouse technology bounced a focused beam of light off a highly-reflective mouse pad onto a sensor. The mouse pad had a grid of dark lines. Each time the mouse was moved, the beam of light was interrupted by the grid. Whenever the light was interrupted, the sensor sent a signal to the computer and the cursor moved a corresponding amount. This kind of optical mouse was difficult to use, requiring that you hold it at precisely the right angle to ensure that the light beam and sensor aligned. Also, damage to or loss of the mouse pad rendered the mouse useless until a replacement pad was purchased. Today's LED-based optical mouse is far more user-friendly and reliable. Most in use today use the standard PS/2 type connector. The data is sent from the mouse to the computer serially on the data line. The PS/2 mouse sends on the order of 1,200 bits per second. That allows it to report mouse position to the computer at a maximum rate of about 40 reports per second. If you are moving the mouse very rapidly, the mouse may travel an inch or more in one-fortieth of a second. That, just about
wraps it up. (I guess it was a good mouse hunt). So keep clicking
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