How Computer Mice Work

It is amazing how simple and effective a mouse is, and it is also amazing how long it took mice 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, a couple of decades passed before mice became mainstream.

In the beginning, there was no need to point because computers used crude interfaces like teletype machines or punch cards for data entry. The early text terminals did nothing more than emulate a teletype (using the screen to replace paper), so it was many years (well into 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 humans the first way to point.

Light pens were used on a variety of machines as a pointing device for many years, and graphics tablets, joy sticks and various other devices were also popular in the 1970s. None of these really took off as the pointing device of choice, however.

When the mouse hit the scene -- attached to the Mac, it was an immediate success. There is something about it that is completely natural. Compared to a graphics tablet, mice are extremely inexpensive and they take up very little desk space. In the PC world, mice took longer to gain ground, mainly 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 PC-human interface of choice very quickly.

The main goal of any mouse is to translate the motion of your hand into signals that the computer can use. Let's take a look inside a track-ball mouse to see how it works:

In this optomechanical arrangement, the disk moves mechanically, and an optical system counts pulses of light. On this mouse, the ball is 21 mm in diameter. The roller is 7 mm in diameter. The encoding disk has 36 holes. So if the mouse moves 25.4 mm (1 inch), the encoder chip detects 41 pulses of light.

You might have noticed that 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. It is visible in this photo:

This piece of plastic provides a window through which the infrared sensor can "see." The window on one side of the disk is located slightly higher than it is on the other -- one-half the height of one of the holes in the encoder disk, to be exact. That difference causes the two infrared sensors to see pulses of light at slightly different times. There are times when one of the sensors will see a pulse of light when the other does not, and vice versa. This page offers a nice explanation of how direction is determined.

Most mice on the market today use a USB connector to attach to your computer. USB is a standard way to connect all kinds of peripherals to your computer, including printers, digital cameras, keyboards and mice. See How USB Ports Work for more information about this technology.

­ Some older mice, many of which are still in use today, have a PS/2 type connector. Instead of a PS/2 connector, a few other older mice use a serial type of connector to attach to a computer. See How Serial Ports Work for more information.

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­ Developed by Agilent Technologies and introduced to the world in late 1999, the optical mouse­ actually uses a tiny camera to take thousands of pictures every second.

Able to work on almost any surface without a mouse pad, most optical mice use a small, red light-emitting diode (LED) that bounces light off that surface onto a complimentary metal-oxide semiconductor (CMOS) sensor. In addition to LEDs, a recent innovation are laser-based optical mice that detect more surface details compared to LED technology. This results in the ability to use a laser-based optical mouse on even more surfaces than an LED mouse.

Here's how the sensor and other parts of an optical mouse work together:

Optical mice have several benefits over track-ball mice:

A number of factors affect the accuracy of an optical mouse. One of the most important aspects is resolution. The resolution is the number of pixels per inch that the optical sensor and focusing lens "see" when you move the mouse. Resolution is expressed as dots per inch (dpi). The higher the resolution, the more sensitive the mouse is and the less you need to move it to obtain a respon­se.

Most mice have a resolution of 400 or 800 dpi. However, mice designed for playing electronic games can offer as much as 1600 dpi resolution. Some gaming mice also allow you to decrease the dpi on the fly to make the mouse less sensitive in situations when you need to make smaller, slower movements.

Historically, corded mice have been more responsive than wireless mice. This fact is changing, however, with the advent of improvements in wireless technologies and optical sensors. Other factors that affect quality include:

Most wireless mice use radio frequency (RF) technology to communicate information to your computer. Being radio-based, RF devices require two main components: a transmitter and a receiver. Here's how it works:

Many electronic devices use radio frequencies to communicate. Examples include cellular phones, wireless networks, and garage door openers. To communicate without conflicts, different types of devices have been assigned different frequencies. Newer cell phones use a frequency of 900 megahertz, garage door openers operate at a frequency of 40 megahertz, and 802.11b/g wireless networks operate at 2.4 gigahertz. Megahertz (MHz) means "one million cycles per second," so "900 megahertz" means that there are 900 million electromagnetic waves per second. Gigahertz (GHz) means "one billion cycles per second." To learn more about RF and frequencies, see How the Radio Spectrum Works.

Unlike infrared technology, which is commonly used for short-range wireless communications such as television remote controls, RF devices do not need a clear line of sight between the transmitter (mouse) and receiver. Just like other types of devices that use radio waves to communicate, a wireless mouse signal can pass through barriers such as a desk or your monitor.

RF technology provides a number of additional benefits for wireless mice. These include:

As with most mice on the market today, wireless mice use optical sensor technology rather than the earlier track-ball system. Optical technology improves accuracy and lets you use the wireless mouse on almost any surface -- an important feature when you're not tied to your computer by a cord.

Pairing and Security

In order for the transmitter in the mouse to communicate with its receiver, they must be paired. This means that both devices are operating at the same frequency on the same channel using a common identification code. A channel is simply a specific frequency and code. The purpose of pairing is to filter out interference from other sources and RF devices.

Pairing methods vary, depending on the mouse manufacturer. Some devices come pre-paired. Others use methods such as a pairing sequence that occurs automatically, when you push specific buttons, or when you turn a dial on the receiver and/or mouse.

To protect the information your mouse transmits to the receiver, most wireless mice include an encryption scheme to encode data into an unreadable format. Some devices also use a frequency hopping method, which causes the mouse and receiver to automatically change frequencies using a predetermined pattern. This provides additional protection from interference and eavesdropping.

One of the RF technologies that wireless mice commonly use is Bluetooth. Bluetooth technology wirelessly connects peripherals such as printers, headsets, keyboards and mice to Bluetooth-enabled devices such as computers and personal digital assistants (PDAs). Because a Bluetooth receiver can accommodate multiple Bluetooth peripherals at one time, Bluetooth is also known as a personal area network (PAN). Bluetooth devices have a range of about 33 feet (10 meters).

Bluetooth operates in the 2.4 GHz range using RF technology. It avoids interference among multiple Bluetooth peripherals through a technique called spread-spectrum frequency hopping. WiFi devices such as 802.11b/g wireless networks also operate in the 2.4 GHz range, as do some cordless telephonescordless telephones and microwave ovens. Version 1.2 of Bluetooth provides adaptive frequency hopping (AFH), which is an enhanced frequency-hopping technology designed to avoid interference with other 2.4 GHz communications.

The other common type of wireless mouse is an RF device that operates at 27 MHz and has a range of about 6 feet (2 meters). More recently, 2.4 GHz RF mice have hit the market with the advantage of a longer range -- about 33 feet (10 meters) and faster transmissions with less interference. Multiple RF mice in one room can result in cross-talk, which means that the receiver inadvertently picks up the transmissions from the wrong mouse. Pairing and multiple channels help to avoid this problem.

Typically, the RF receiver plugs into a USB port and does not accept any peripherals other than the mouse (and perhaps a keyboard, if sold with the mouse). Some portable models designed for use with notebook computers come with a compact receiver that can be stored in a slot inside the mouse when not in use.

As with many computer-related devices, mice are being combined with other gadgets and technologies to create improved and multipurpose devices. Examples include multi-media mice, combination mice/remote controls, gaming mice, biometric mice, tilting wheel mice and motion-based mice. To learn more about innovations in mouse technology, let's start with multi-media mice and combination mice/remote controls.

­Multi-Media Mouse and Combination Mouse/Remote

These types of mice are used with multimedia systems such as the Windows XP Media Center Edition computers. Some combine features of a mouse with additional buttons (such as play, pause, forward, back and volume) for controlling media. Others resemble a television/media player remote control with added features for mousing. Remote controls generally use infrared sensors but some use a combination of infrared and RF technology for greater range.

Gaming Mice

­ Gaming mice are high-precision, optical mice designed for use with PCs and game controllers. Features may include:

Motion-Based Mice

Yet another innovation in mouse technology is motion-based control. With this feature, you control the mouse pointer by waving the mouse in the air.

The technology patented by one manufacturer, Gyration, incorporates miniature gyroscopes to track the motion of the mouse as you wave it in the air. It uses an electromagnetic transducer and sensors to detect rotation in two axes at the same time. The mouse operates on the principle of the Coriolis Effect, which is the apparent turning of an object that's moving in relation to another rotating object. The device and accompanying software converts the mouse movements into movements on the computer's screen. The mice also include an optical sensor for use on a desktop.

Biometric mice add security to your computer system by permitting only authorized users to control the mouse and access the computer. Protection is accomplished with an integrated fingerprint reader either in the receiver or the mouse. This feature enhances security and adds convenience because you can use your fingerprint rather than passwords for a secure login.

To use the biometric feature, a software program that comes with the mouse registers fingerprints and stores information about corresponding authorized users. Some software programs also let you encrypt and decrypt files. For more information about biometric fingerprint technology, see How Fingerprint Scanners Work.

A more recent innovation in mouse scrolling is a tilting scroll wheel that allows you to scroll onscreen both horizontally (left/right) and vertically (up/down). The ability to scroll both ways is handy when you are viewing wide documents like a Web page or spreadsheet.

To navigate both horizontally and vertically, the scroll wheel is positioned on a combination fulcrum and lever. This is the design used by the Logitech Cordless Click! Plus mouse.

Another method for vertical and horizontal scrolling is a touch scroll panel that responds to your finger sliding horizontally and vertically, as employed by the Logitech V500 Cordless Notebook Mouse.