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I just replaced my scroll wheel in my mouse, a one minute repair. But now I've seen something that can't be unseen.
Logitech scroll wheels apparently function using magic.
It freely rests on three buttons that detect left, right, and straight down presses. But the wheel itself is not electrically connected to anything whatsoever. It's plastic resting on a spring.
How does the mouse know when I'm scrolling? And why was it affected by dust and gunk?
Edit: and how does it detect which direction you are scrolling?
I don't know if this is the same for this mouse, but in the past, it was a laser that shines through the wheel, and inside the wheel were sparks (or whatever the word is, it has areas that are open and areas that are closed). If the laser was intercepted it could sense that it was scrolled and in which direction. – LPChip – 2017-11-23T21:30:21.880
2Look here. Each mouse setup is different, but based on the fact the pic you have posted shows clear mounts on the wheel implies there is an optical encoder at play. – JakeGould – 2017-11-24T02:58:31.597
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This might surprise you, but the old ball-mouse (not the modern laser-mouse) works exactly in the same way, except that it has 2 wheels -- for X and Y directions. If you manage to find and open one, you'll see that the ball is not attached to anything. Here's a pic: https://38.media.tumblr.com/7d0bb30a71fba01f9c191fc48ca457f5/tumblr_inline_mlrx4d0kts1qz4rgp.jpg
– dr01 – 2017-11-24T13:27:05.4132
The answers cover the way it's actually done; another possibility would be to use a Hall effect sensor, which basically counts electrical pulses generated by a magnet in the wheel passing a coil. Those are often used in power tools, car engines and other things that rotate quickly.
– David Richerby – 2017-11-25T14:25:50.823