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Optical sensor in the mouse, how it works and what types exist

Optical mice have a number of benefits compared to conventional ball-based mice. By not relying on mechanical parts there is a lower probability of failure, but at the same time this reduces the ability to be repaired. Nor do we have to worry about the annoying dirt that accumulates on the mouse and for performance they are much more accurate when it comes to capturing speed changes and do not require the use of special mats.

What is an optical sensor?

In order to understand how mice with optical sensors work, then the first thing we will have to know is the operation of this type of sensors. As for its simplified description, the only thing an optical sensor does is convert the light rays into an electronic signal that a processor can measure. Optical sensors are not only used in mice, for example the automatic brightness system of your smartphone uses one of these sensors to automatically lower the brightness of the screen.

Optical sensors have many more uses beyond their use in PC mice. Among its utilities are photocopiers and document scanners, and also to detect the presence of moving objects. The latter are used for alarm systems and automatic photography, especially to detect the presence of animals in the wild.

But what interests us is how these types of sensors work in the mice that we use every day on our PCs, since since the launch of Microsoft’s Intellimouse in 1999 these mice have been displacing the classic ball mice and have seen the appearance of a second type of mouse based on laser illumination, where the first of them in history was the MX 1000 from Logitech.

The optical sensor in PC mice

optical sensor mouse LED

In the case of optical mice, these do not emit any type of light, so the mouse is usually accompanied by a light emitter, usually an LED light, although it can also be a laser, with which the surface on which it is placed is illuminated. move the mouse. When in the specifications of a mouse they are not saying that its sensor has a certain amount of IPS, they are actually talking about the amount of images per second that is made by the photodetector.

Said information is processed by a processor that can be digital signal, DSP, or be a fixed function unit. His homework? Compare the images with each other to see if there has been a displacement. For this, an internal mesh is used in which all the “pixels” of the image are aligned and given an identification. When there has been a shift in the next image, the DSP knows it by comparing the position of each pixel from one image to the other.

optical sensor operation

It must be taken into account that by knowing the displacement between two points and taking time into account, it is possible to know the displacement speed of a body and also the acceleration. Once the DSP has processed the data, the conclusion of the same is sent to the PC. This is done at very high speed and therefore at a time when the user sees a direct movement correlation between movement with their mouse and the screen cursor. Reality? It is an illusion produced by the high frequency at which the optical sensor works and the images it captures are processed.

LED versus laser lighting

A laser mouse is the same as an optical mouse, its working principle is the same, but they differ in the type of light used to illuminate the surface. In the case of LED lighting, this has the problem that it cannot penetrate many surfaces. The consequences of it? If it turns out that you are using the mouse on a highly reflective surface, such as a glass table, then what will happen is that the pattern that the optical sensor picks up will be wrong.

That is why mice with an optical sensor that make use of a laser to illuminate have greater precision than those that use LED lighting, although such precision can be counterproductive, since they can capture useless over-information, leading to errors in its interpretation by part of the DSP. What causes the movement with the mouse not to be interpreted correctly and this can lead to errors in programs such as graphic design, where great precision is required with the mouse.

So there are situations in which an optical sensor with LED lighting is better than a laser one, the cost being the greatest of them, but also the fact that a laser is a much more sensitive part to break than an LED light. Also, the only handicap is its use on highly reflective surfaces.

Laser or LED, which technology is better?

DSP optical sensor

Before this question, each manufacturer will give a different answer, some will tell you that an optical sensor with LED light is much better and others one with laser. The former are usually recommended for conventional uses unless you move the mouse over glass or a highly reflective surface. On the other hand, lasers are usually used in professional gaming mice and hence these tend to be generally much more expensive.

It must be taken into account that an important part of the process is based on how the DSP integrated in the mouse interprets the captured images. This is crucial and different brands of mice develop their own proprietary technologies, which are based on the use of their own DSPs. After all, the photodetector of the optical sensor, the laser, the LED light and the rest of the components of the different types of mice are quite standard, with the DSP being the most unknown and at the same time the most important piece of hardware of an optical mouse. .