What is the working principle of optical mouse? What does it have to do with the mouse pad?

The working principle of optical mouse is that there is a light-emitting diode inside the mouse to illuminate the contact surface at the bottom of the mouse, and at the same time, the contact surface will reflect some light, and the reflected light will be imaged in a CMOS sensor after passing through a group of optical lenses.

When the mouse moves, the moving track will be recorded as a series of continuous images taken at high speed. There is a special DSP image analysis chip inside the mouse to analyze and process a series of images taken on the motion track. By analyzing the changes of feature points on these images, we can judge the moving direction and distance of the mouse, thus completing the positioning of the cursor.

Optical mouse usually consists of the following parts: optical sensor, optical lens, light emitting diode, interface microprocessor, touch button, wheel, cable, PS/2 or USB interface, shell and so on. The following are introduced respectively:

optical sensor

Optical sensor is the core of optical mouse. At present, only Agilent, Microsoft and Romania have the skills to produce optical sensors. Among them, Agilent's optical sensors are widely used. Except for all optical mice from Microsoft and some from Logitech, all other optical mice basically use Agilent optical sensors.

Optical mouse control chip

The control chip is responsible for coordinating the work of various components in the optical mouse, and communicating (bridging) with external circuits and sending and receiving various signals. We can understand it as the "housekeeper" in the optical mouse.

There is a very important concept that everyone should know, that is, the influence of dpi on mouse positioning. Dpi is used to measure the number of points that the mouse can detect per inch. The smaller the dpi is, the fewer points are used for positioning, and the positioning accuracy is low. The larger the dpi, the more points used for positioning, and the higher the positioning accuracy.

Usually, the scanning accuracy of the traditional mechanical mouse is below 200dpi, while the photoelectric mouse can reach 400 or even 800dpi, which is the main reason why the photoelectric mouse can easily surpass the mechanical mouse in positioning accuracy.

Optical lens assembly

The optical lens assembly is placed at the bottom of the optical mouse. As can be clearly seen from fig. 5, the optical lens assembly consists of a prism and a circular lens. Among them, the prism is responsible for transmitting the light emitted by the LED to the bottom of the mouse and illuminating it.

The circular lens is equivalent to the camera lens, which is responsible for transmitting the illuminated mouse bottom image to the small hole at the bottom of the optical sensor. By observing the back shell of the optical mouse, we can see that the circular lens is like a camera that has passed the test. The author concludes that blocking the optical path of prism or circular lens will immediately lead to the "blindness" of optical mouse. As a result, the optical mouse cannot be positioned, which shows the importance of the optical lens assembly.

Light Emitting Diode(LED)

Optical sensors need the support of "photographic lights" to continuously "photograph" the bottom of the mouse without light. Otherwise, the image taken from the bottom of the mouse will be very dark, and the dark image can't be compared, let alone optically positioned.

Usually, the light emitting diodes (LEDs) used in optical mice (as shown in Figure 7) are red (some are blue) and highlighted (in order to get enough illumination). Part of the red light emitted by the LED illuminates the bottom of the mouse through the optical lens (i.e. prism) at the bottom of the mouse; The other part is directly transmitted to the front of the optical sensor. In a word, the function of light-emitting diode is to generate the light source needed when the photoelectric mouse works.

Touch key

A mouse without buttons is unimaginable, so there will be at least two light touch buttons on an ordinary photoelectric mouse. There are three touch buttons welded on the PCB of Founder Optical Mouse (Figure 8). In addition to the left and right keys, the middle key is assigned to the page turning wheel. Advanced mice usually have two page turning wheels, X and Y, but most optical mice still have only one page turning wheel, just like this Founder optical mouse. When the page turning wheel scrolls up and down, it will make the "document" or "web page" you are reading scroll up and down. When the wheel is pressed, the "middle button" on the PCB will work. Note: the action generated by "middle key" can be defined by the user according to his own needs.

When we remove the page turning wheel, we can see a pair of photoelectric "transmitting/receiving" devices hidden in the position of the wheel. There is a grid on the wheel. Because the grid can "block" the optical path of the photoelectric "transmitting/receiving" device at intervals, it can generate a page-turning pulse signal, which is transmitted to the Windows operating system through the control chip, thus generating a page-turning action.

Besides the above, what else does the optical mouse include? It also includes connecting cable, PS/2 or USB interface, shell and so on. Because these components are not much different from mechanical mice, they will not be explained here.

Continue to introduce several important technical parameters of optical mouse:

CPI: The imaging principle of optical engine is actually microphotography, and its CPI level is equivalent to the magnification and clarity of photographic details. Obviously, this magnification definition has nothing to do with the size of the photo, but only depends on the magnification of the optical element. That is to say, even if you change COMS to half the original size, it will only make the sampled image smaller, but the details and definition will not change.

The resolution is usually expressed in DPI (dots per inch), which can measure the accuracy of the mouse. In fact, it may be more correct to use Agilent Technologies' original CPI statement. Most optical mice on the market are 400 CPI, which means that every inch of movement will return 400 coordinates.

Sampling rate: this is a unique technical parameter of optical mouse, which represents the number of times that CMOS sensor "shoots" the sampling surface per second and the corresponding processing capacity of DSP chip per second. When the early optical mouse was moving at high speed, there was a serious frame loss problem. Why is there such a problem? Because when the mouse moves at high speed, there is probably no same sampling point in the images taken by CMOS sensor twice. Without the same sampling points, it is impossible to compare the motion directions, which leads to the failure of DSP chip to process normally, resulting in a large number of error signals.

In addition, the mouse pad:

The advantage of the mouse pad is that we hope to give the mouse a pure and smooth moving friction surface with the help of additional tools, so as to effectively avoid the bad mood brought by the complicated moving surface in the actual use process. For example, the popular team FPS game CS, think about yourself, not because of technology, but because you met a small protrusion on the desktop during the moving process, so that the player's line of sight did not reach the target position in time and was hit on the head. Does it make you angry? For gamers with a fever level like FPS, the mouse pad may contribute to the mobile positioning performance of the mouse in terms of mobile fluency and feel. Fever players always want to improve their actual level with some tools under the existing conditions, so making excellent mouse pads naturally becomes the goal of these players.

Although the current mouse product has completed the transformation from mechanical to photoelectric, it is still inseparable from movement, but the focus of attention has shifted from rolling ball to foot pad. Although the manufacturer has considered many aspects from the beginning of mouse design, the mouse pad still has its practical significance because of the habit differences between users. Look at the current market of mouse pad products. Products made of various materials are very rich, and because good mouse pads have been specially treated, the surface uniformity and roughness are equal, and there will be no abnormal obstacles such as high-speed movement and high-precision positioning, but one mouse pad cannot be used. Some users may prefer soft ones, while others prefer rough ones. So how many kinds of mouse pads are there on the market now?