What is the working principle of the mouse?

Working principle of photoelectric mouse

The biggest difference between optical mouse and mechanical mouse lies in the different positioning methods.

The working principle of the optical mouse is that there is a light-emitting diode inside the optical mouse, and the light emitted by the light-emitting diode illuminates the bottom of the optical mouse (which is also the reason why the bottom of the mouse always shines). Then part of the light reflected from the bottom of the optical mouse passes through a group of optical lenses and is transmitted to the optical sensing device (micro imager) for imaging. In this way, when the optical mouse moves, its moving track will be recorded as a series of high-speed continuous images. Finally, the special image analysis chip (DSP, that is, digital microprocessor) in the optical mouse is used to analyze and process a series of images taken on the motion track, and the movement direction and distance of the mouse are judged by analyzing the position changes of feature points on these images, so as to complete 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.