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T he computer mouse has become an essential part of personal computing, allowing users to interact graphically, that is, with the aid of their eyes, with virtual objects. While scrolling through a website, editing a video or playing a videogame, a mouse works like an extension of the user’s hand, translating its movements to movements on screen. What kinds of mice are there? The common mouse is able to accept two kinds of input — button click and motion.
From their old bulky models to the ergonomic builds today, computer mice have undergone a significant evolution. These designs have mainly differed in how they translate a user’s movement of the mouse to that of a cursor on the screen. The buttons are fairly straightforward.
Each button is a switch in the mouse that completes a circuit when it is pressed, sending a signal to the computer to perform a certain action. The first stage in the mouse’s evolution was the trackball mouse whereas current models use lasers. How did the trackball mouse work? The ball mouse, also called a trackball or mechanical mouse, has a small ball on its underside that rotates when the user moves the mouse.
This ball exerts pressure on two rollers that are positioned at right angles to each other (see image). One roller detects movement along the Y-axis (forward-backward) and the other detects movement along the X-axis (left-right). A third roller, which is spring-loaded, pushes the ball against the two other rollers.
Each roller is linked to an encoder wheel with unique thunderbolt-shaped edges. A light source, like a small bulb, emits infrared radiation from behind the encoder wheel. A sensor on the other side receives this light.
When the user moves the mouse, the ball moves and rotates the rollers. This finally turns the encoder wheels, which interrupt the infrared light falling on the sensors as they move. The sensors translate this series of interruptions into a digital signal — 1 when it receives light and 0 when it doesn’t, resulting in a sequence of 0s and 1s.
Simple logic circuits figure out which way the wheel is rotating by examining these signals. Typically, the ball’s outer casing is made of steel while the ball is covered in a precisely moulded rubber surface. The weight of the ball is also adjusted to ensure it maintains reliable contact with the surface its moving on, guaranteeing accurate transmission from the mouse’s movement to the rollers and the cursor on the screen.
Elegant as the trackball mouse was, it had to be cleaned regularly to work properly. The optical mouse requires less maintenance. How does the optical mouse work? Microsoft invented the modern optical mouse in 1999 and called it the “IntelliMouse”.
Rather than a ball on the underside, this device had a laser pointer pointing down. The laser light would bounce off the surface on which the mouse moved and into a complementary metal-oxide semiconductor (CMOS) sensor inside the mouse. The CMOS sensor is like a camera that takes 1,500 to 6,000 images of the reflected light per second.
The images are passed to a digital signal processor. It detects patterns in each image and determines how far the mouse has moved since the previous image, and sends the corresponding coordinates to the computer. Aside from maintenance, the optical mouse is also more sensitive to small movements than the trackball mouse.
In the 1980s, Xerox developed another kind of optical mouse that had a low-resolution camera in place of the CMOS sensor. It didn’t catch on because it required more computational power to work. The humble computer mouse has come a long way since its early days.
But whether mechanical or optical, both types have banked on clever engineering to convert simple hand movements into precise on-screen interactions. Amartya Srinivasan is a Class XI student at P.S.
Senior Secondary School, Mylapore, Chennai. Published - March 12, 2025 08:30 am IST Copy link Email Facebook Twitter Telegram LinkedIn WhatsApp Reddit Text and Context / technology (general) / IT/computer sciences.
