How Computer Mouse Work – Explained

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how computer mouse work

The mouse is one of the most overused and underappreciated devices today. They are so common that we do not even think about them. From outside they may seem like simple plastic pieces but actually, they have quite interesting technology inside.

The journey of the computer mouse has not been so easy, they have gone through some major development and innovations. In this article, we will try to understand how a computer mouse works. We would also take a brief look at how it came into existence and its development over the years.

How it came to Spotlight? (History of Mouse)

history of the computer mouse

Although the computer mouse has been in the existence from quite a while, Apple is the company who made it popular.

The early development of the mouse started as a part of British military project to better interact with computing devices. It consisted of a solid base with a tracking ball on top (top left image). Later improvements were made into the design and various other models were developed.

Being the part of the military project, it was considered a secret and kept away from the public uses.

The first mouse developed for commercial use was made by Stanford University. It consisted of two horizontally and vertically aligned rolling wheels (top right image) fixed at the bottom which rotated in the direction of motion. These were better than previous trackballs but were restricted in movement as they could only move in front and sideways direction.

ball mouse
Ball Mouse

Due to these primitive designs with movement restrictions, tech companies started developing a new kind of mice. Making an omnidirectional mouse was their target and that is how the ball mouse came into existence. The new design allowed it to work in front, sideways and across the surface.

How did ball mice work

The ball mice had many similarities with previous generation mice. For example, it also had two rolling wheels which touched the rubber ball, instead of directly touching the surface as in earlier generation mice.

The horizontal movement was measured by one wheel while vertical was measured by the other. In case of lateral movement “across” the surface, the movement of both the wheels was calculated.

This technology was quickly adopted by other companies like Microsoft and Apple and since then it had become the most popular input device. Later the need of a scrolling button was felt and the scroll wheel was introduced.

Although the ball mouse seemed to work properly but on prolonged uses, it collected a lot of dirt and grease. This made the mouse to skid which affected its readings. Sometimes the ball use to get stuck and have to be cleaned to make it usable again. The need for better technology was felt.

optical mouse imageOptical mouse was commercially introduced in the late 90s to address the issues with the traditional ball mouse. The newer optical mouse had better accuracy, lighter weight and needed almost no maintenance. As years went by the design of the optical mouse was improved to provide better performance. Later the line laser mouses were introduced for high-end gaming and graphics related uses.

How Optical Mouse works

how an optical mouse worksA mouse is a device which translates hand movements to the digital signals. Below is the list of parts inside a mouse which work together to achieve this physical to digital movement conversion.

A typical mouse consist of these main parts :-

  1. LED Light
  2. Prism
  3. CMOS Light sensor
  4. DSP Chip
  5. Scroll Wheel
  6. Rotary Encoder
  7. Switch Buttons
  8. USB Outlet

How Motion is Tracked in Mouse

how motion is tracked in mouse-01LED – It is used to illuminate the surface below the sensor. The cheaper mouse in the market uses traditional LEDs which emits red or blue light. Many of the mice come with an infrared LED whose lights are not visible to the human eye but can be seen by mouse sensor. The mouse which uses LEDs as light sourcew are called optical mouse.

From last few years, laser mouse is getting popular. They use a laser diode instead of the traditional LED. These mice are said to work on any surface including glass and are used in the high-end gaming mouse.

click here to know more about optical mouse and laser mouse.

Prism – The main job of the prism is to prevent the light source and other electronics to be exposed outside. The light from the LEDs strikes the prism. The prism reflects the beam and guides it to the surface below the sensor.

CMOS Sensor – When the light illuminates the surface, the CMOS sensor receives the reflected light and tries to measure the movements of the mouse.

The working of (CMOS) Light Sensor in mouse

The CMOS (complementary metal-oxide semiconductor) sensor sits at the bottom of the mice circuit. CMOS is a Photographic Sensor which is used in most of the modern day Smart-phone cameras and DSLR’s. It receives light signals and converts them into digital signals to make a digital photograph.

how does it measure the movement?

The CMOS Sensors used in computer mice are specifically designed to be used in them. It Takes the pictures of the surface at very high frame rates ranging from 1500 to 6000 images per second. After taking these pictures it sends them to the DSP chip for further processing.

DSP Chip – DSP (Digital Signal Processor) is an IC (Integrated Circuit) whose main job is to process information. It is like the brain of the mouse and responsible for all the calculations.

After receiving images from the CMOS sensor it performs a lot of tests. It compares multiple images and looks for changes in the pattern of the surface. Then it calculates the direction and speed of the mouse based on those patterns and sends those movements as a digital signal of the corresponding cursor coordinates to the computer through the USB Outlet.

Working of Scroll Wheel

The scroll wheel is a very convenient addition to the mouse. Before the introduction of the scroll wheel, arrow keys were used to scroll up and down the page. The use of arrow keys slowed down the workflow and was very inconvenient to interact with them to the computer.

As we all know the Scroll Wheel performs two functions one of scroll wheel and second as a button. The device which measures the forward or backward motion and speed of that motion is called rotary encoder. The rotary encoder has a three-terminal resistor and measures the speed and direction by analyzing the change in voltage across its three terminals. Then it interprets the signal and sends them to the computer.

Some mouse optical encoder instead of a rotary encoder to measure scroll data.

Optical Encoders

Optical encoders work in a very different manner than the scroll wheel with rotary encoder. In optical encoder based mice an LED placed at one side of scroll wheel produces a beam of light. The light passes through the scroll wheel and makes a shadow on other end. The light and shadow pattern is picked up by an optical encoder to produce scroll movement data. In these types of mouse the scroll wheel has spokes to make clear light and shadow patterns.

Check out the video below for better understanding.

Buttons/Switch – Switches are simples devices which activates a response when a user clicks them. As mouse button is clicked thousands of times, so switches are specifically designed to handle that abuse. These switches are generally rated for millions of clicks and can be swapped with another one in some of the high-end gaming mouse.

USB Outlet – All the data generated in the mouse goes into the computer through the USB outlets. Many a times wires are the first things which gets damaged in the mouse. So the companies started making kevlar wires which were more robust and improved the longevity.


Overall, the mouse is more complex than what most people think. here is the quick overlook at how it works.

It all starts with LED lights illuminating the surface. The lights are picked up by CMOS sensor – which is essentially a camera. Then it goes to Digital Signal Processing chip which figures out the movement and path. The scrolling wheel uses a device called “rotary encoder” to measure its movement. The collected data is then sent to the computer along with click and scroll data.


Todd Davis

Contributor at Essentialpicks, Todd Davis likes all things tech. He has a master's degree in electronics and a deep understanding of underlying technologies used inside tech products. He likes to travel and fly his drone around. He can often be found on the trails of California.

This Post Has 2 Comments

  1. John

    isn’t the CMOS sensor used in smartphones…

    1. Kabir

      yes, that’s true…
      the same technology is used in the mouse…

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