What is a light detection chip?

Let’s talk about the principle first:

The working principle of the optical mouse is that there is a light-emitting diode inside the mouse. The diode emits light to illuminate the contact surface at the bottom of the mouse, and at the same time, the contact surface reflects back part of the light. , after the reflected light passes through a set of optical lenses, it is imaged in a CMOS sensor.

When the mouse moves, the movement trajectory will be recorded as a set of coherent images shot at high speed, and there is a dedicated DSP image analysis chip inside the mouse to analyze the captured images on the movement trajectory. A series of images are analyzed and processed, and the movement direction and distance of the mouse are determined by analyzing the changes in the position of the feature points on these images, thereby completing the positioning of the cursor.

An optical mouse usually consists of the following parts: optical sensor, optical lens, light-emitting diode, interface microprocessor, touch buttons, scroll wheel, connection, PS/2 or USB interface, shell, etc. The following are introduced separately:

Optical sensor

The optical sensor is the core of the optical mouse. Currently, there are only three manufacturers that can produce optical sensors: Agilent, Microsoft and Logitech. Among them, Agilent's optical sensors are widely used. Except for all Microsoft and some Logitech optical mice, other optical mice basically use Agilent's optical sensors.

Optical mouse control chip

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

There is a very important concept here that everyone should know, which is the impact of dpi on mouse positioning. DPI is used to measure the number of points that can be detected per inch of mouse movement. The smaller the DPI, the fewer the points used for positioning, and the lower the positioning accuracy; the larger the DPI, the more points used for positioning, and the lower the positioning accuracy. high.

Normally, the scanning accuracy of traditional mechanical mice is below 200dpi, while the optical mouse can reach 400 or even 800dpi. This is the main reason why the optical mouse can easily surpass the mechanical mouse in positioning accuracy. reason.

Optical lens assembly

The optical lens assembly is placed at the bottom of the optical mouse. It can be clearly seen from Figure 5 that the optical lens assembly consists of a prism mirror and a circular Made up of shaped lenses. Among them, the prism is responsible for transmitting the light emitted by the light-emitting diode to the bottom of the mouse and illuminating it.

The circular lens is equivalent to the lens of a camera. This lens is responsible for transmitting the illuminated bottom image of the mouse to the small hole at the bottom of the optical sensor. By looking at the back shell of the optical mouse, we can see that the circular lens is much like a camera. Through the test, the author concluded that whether blocking the light path of the prism mirror or the circular lens will immediately cause the optical mouse to become "blind" . The result is that the optical mouse cannot be positioned, which shows the importance of the optical lens assembly.

Light-emitting diode

The optical sensor needs to continuously "take pictures" of the bottom of the mouse that lacks light, so the support of a "photographic light" is naturally indispensable. Otherwise, the image taken from the bottom of the mouse will be dark. Dark images cannot be compared, and of course optical positioning cannot be performed.

Usually, the light-emitting diodes used in optical mice (as shown in Figure 7) are red (some are blue) and are highly bright (in order to obtain sufficient illumination). Part of the red light emitted by the light-emitting diode illuminates the bottom of the mouse through the optical lens (the prism) at the bottom of the mouse; the other part is transmitted directly to the front of the optical sensor. In one sentence, the function of the light-emitting diode is to generate the light source required for the operation of the optical mouse.

Touch buttons

It is unimaginable to have a mouse without buttons, so even an ordinary optical mouse will have at least two touch buttons. There are three touch buttons welded on the PCB of the Founder optical mouse (Figure 8). In addition to the left and right buttons, the middle button is assigned to the page turning wheel. Advanced mice usually have two page turning wheels, X and Y, but most optical mice only have one page turning wheel like this Founder optical mouse. When the page turning wheel scrolls up and down, the "document" or "webpage" being viewed will scroll up and down. When the scroll wheel is pressed, the "middle button" on the PCB will work. Note: The actions generated by the "middle key" can be defined by the user according to their own needs.

When we remove the page-turning roller, we can see that there is a pair of photoelectric "transmitting/receiving" devices "hidden" in the position of the roller. There is a grid on the "roller". Because the grid can "block" the light path of the pair of photoelectric "transmitting/receiving" devices at intervals, a page turning pulse signal can be generated. This pulse signal is transmitted to the Windows operation through the control chip. The system can generate page turning action.

In addition to the above, what else does an optical mouse include? It also includes connecting cables, PS/2 or USB interfaces, housings, etc. Since these parts are not much different from a mechanical mouse, they will not be explained here.

Continue to introduce several important technical parameters of the optical mouse:

CPI: The imaging principle of the optical engine is actually microscopic photography, and its CPI level is equivalent to the amplification of photographic details. Clarity. Obviously, this magnification resolution has nothing to do with the size of the photo. It only depends on the magnification of the optical component. That is to say, even if you change the COMS to half the original size, it will only make the sampled image smaller. , but the detail and clarity won't change.

Resolution is usually expressed by 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 (count per inch) statement. Most optical mice on the market have 400 CPI, which means they return 400 coordinates for every inch they move.

Sampling rate: This is a unique technical parameter of the optical mouse. It represents the number of times the CMOS sensor "shoots" the sampling surface per second and the corresponding processing power of the DSP chip per second. Early optical mice had serious frame loss problems when moving at high speeds. Why does this problem occur? Because when the mouse moves at high speed, it is very likely that the images taken twice by the CMOS sensor do not have any identical sampling points. Without different sampling points, there is no way to compare the movement directions, which causes the DSP chip to be unable to process normally, thus generating a large number of error signals.

Let’s talk about the mouse pad:

The advantage of the mouse pad is that we hope to use additional tools to give the mouse a pure and smooth moving friction surface, so as to effectively avoid complicated problems during actual use. Moving the surface brings you a bad mood. For example, in the now very popular team-based FPS game CS, think about yourself, not because of technology, but because the player encountered a small protrusion on the desktop during the movement. If your crosshair fails to reach the target position in time and gets a headshot, will it make you furious? For enthusiast-level FPS and other gamers, the mouse pad may be helpful for the movement and positioning performance of the mouse in terms of movement smoothness and feel. Enthusiastic players always hope to improve their actual level with the help of some tools under the existing conditions. Making an excellent mouse pad has naturally become the goal of these players.

Although the current mouse products have completed the transformation from mechanical to optical, they still cannot do without movement, but the focus of attention has shifted from the rolling ball to the foot pads. Although manufacturers have considered many aspects when designing the mouse, due to the differences in habits among users, the mouse pad still has its practical significance. Looking at the current mouse pad product market, there are a lot of products made of various materials, and because good mouse pads have been specially treated, they are very equal in terms of surface uniformity and roughness, and there will be no high-speed movement and Abnormal obstructions and other phenomena in situations such as high-precision positioning, but it cannot be used with just a mouse pad. Some users may prefer a softer one, while others prefer a rougher one.

So how many common types of mouse pads are there on the market now?