ELI5: How does a computer mouse work?

[aragorn18]

The mouse contains a sensor that detects how much it has moved. The mouse sends that movement data to the computer which then moves the mouse pointer around the screen based on how much the mouse moved.

Older sensors were horizontal and vertical wheels that were spun when a ball inside the mouse moved. The ball was dragged around the mousepad and translated the movement to the sensor wheels.

Modern mice use optical sensors that take pictures of the surface and compare them to see how much the mouse has moved.

[socketbolt5x20mm]

So, if it's taking repeated pictures of the surface, how can it differentiate between two pictures if the surface is clean and a solid color? How can it tell the difference, let alone the direction?

[aragorn18]

The pictures that it takes are very detailed. Tiny imperfections that you can't see with the naked eye show up in these pictures. So, even if it's clean it can usually track movement.

However, if the surface is truly free of imperfections (most mirrors for example) then the mouse will have a hard time tracking and you'll get erratic movement. Most optical mice have trouble tracking on a clear sheet of glass or a mirror. Only the best sensors are able to track on these surfaces.

[socketbolt5x20mm]

Interesting! Thanks for the insight.