Have you ever wondered how it actually “reads” your movements?

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As a PC gamer it’s hard to think of a better fatigue partner than our mouse. Fifth-essential part of any desktop worth its salt, this peripheral has been with us for almost the entire history of the modern personal computer. Even more so from a player’s perspective, for the enormous influence of the mouse in the development of the video game in three dimensions.

And even with all its importance, everything named to praise the mouse, are few players who know how it works this quirky desktop rodent. There has been a long talk about the importance of its shape, its sensor, or its characteristics, but what we want to do today is tell how that mouse that you have on the side of your desk works.

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Your mouse inside: what parts are it?

Although there is a wide variety of mice on the market, as well as models with very different characteristics from each otherRegardless of its form factor, finishes, materials, and even dedicated uses, the modern mouse is usually made up of a series of very specific parts.

interior mouse modification

Interior of a modified mouse. Original image by Jeanbaptisteparis via Flickr.

However, the purpose of this entire set of parts is always the same: move the cursor around our screen, and the way in which it achieves it is also always the same: through a reading sensor, the main one in charge of discerning when we move our mouse.

This reading sensor may be based on various movement registration systems, giving each of these systems specific characteristics; whether it is driven in a mechanical part, based on advanced optics, or relies on laser technology for this registration.

Out of all of them, optics-based sensors They are the most common today for a series of reasons that we will not list now, but that we will say has a lot to do with their precision and speed. Let’s see how one of these sensors normally works in depth.

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A bit of optics, what does our sensor capture?

If we open the channel to our mouse we could verify that all the peripheral optics are composed of four main pieces, relatively simple in essence, but with a more intricate operation than it seems. These pieces are the Infrared LED transmitter, the prisms reflectors, the lens, Y the sensor CMOS that is responsible for capturing the information. All of them work together.

Sensor Optico

On some occasion we have talked about how the sensor of our mouse is a “camera” that captures the surface where we move it. This is true, but the images it captures are not the same as in a regular camera, rather they are an enlarged simplification of the surface where the mouse rests.

The emitting LED of our mouse, in conjunction with the prisms, illuminates at an angle the imperfections of the surface where our mouse rests, creating a kind of “noise map” of the surface that is magnified by the lens and reaches the eye of the CMOS sensor directly.

This sensor contains a network formed by a set of 40 x 40 pixels that collects the image of this mentioned noise map of less than an inch, and that contains all the information you need the electronics of the mouse to read the movement.

Noise Map

Reduced noise map

Obviously, this sensor does not take a single imageInstead, it does so consistently every second. A modern sensor typically takes about 16,000 shots per second (16: 1 ms) on a regular basis. Now it is time to wonder how our mouse detects movement with only images of a 40 x 40 pixel noise map, and this is where the electronics of the mouse come into play.

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The sensor is the true protagonist

Our mouse does not save any of the 16 captures It performs per millisecond of the surface it is on. It only keeps in memory the image immediately captured, and the image that the sensor itself is about to collect.

If we move our mouse during this process, the two images that the mouse holds should be different from each other, since surface imperfections They will have made this noise map that the sensor captures change, but, in itself, we cannot know what path the mouse has followed to take this new image.

Interpolation2

Pixel interpolation. Original from ResearchGate; modified for use.

This is where the sensor’s DSP Chip comes into play, the part in charge of the logical comparison of the two mentioned images. The DSP compares the texture of the new image with respect to the first, simulating its route until it finds an exact match; When this happens, it performs the same process in reverse, all in the interval that corresponds to the capture of two images.

When you have this reciprocity, the direction is determined on a standard two-dimensional axis and this information is transmitted from the mouse’s SoC to our computer, which represents it on the screen as accurately as possible. The number of points traveled determines, in theory, with a 4: 1 ratio depending on the size on a standard mouse.

Understanding all the above, it is easy to understand that one sensor will be more accurate than another simply because of the algorithm used, the optimization of the referred processes, or simply the use of more powerful hardware; Similarly, the use of techniques such as interpolation or the simulation of the movement can influence other elements, such as a sensor’s DPI count, its level of acceleration and other elements of interest.

In any case, we wish that this explanation, while somewhat convoluted in nature, was entertaining enough to understand how your desktop rodent works. We hope to meet you in these parts soon.

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