Wireless mouse solution based on micro-electromechanical system

Where [ ] represents integer; a is the voltage output by the acceleration sensor, V. The maximum sampling rate of the ATmega 16L microcontroller can reach 15,000 times/second, and this article uses 1,000 times/second; that is, sampling once every 1ms, and reporting the relative displacement change to the computer once every 25ms to ensure the accuracy and smoothness of the mouse pointer movement on the screen, then each reported displacement change contains 25 acceleration sampling data. An approximate algorithm can be used to perform a secondary integration of the acceleration signal to obtain a displacement signal.

The purpose of encoding is to encode the displacement changes in the X and Y directions, together with the real-time information of the mouse buttons, in the format required by the standard Microsoft mouse protocol, so that the information finally sent to the host can be correctly recognized by the computer, so that the computer can correctly process the displacement signal sent to it to correctly control the movement of the mouse cursor and other actions. Table 1 shows the three-byte data packet format specified by the standard mouse protocol. The first byte records the information of the left and right buttons and the highest two bits of the mouse X and Y displacement. When the button is pressed, the corresponding position is 1, otherwise, it is set to 0; the second and third bytes record the lower 6 bits of the X and Y displacement data respectively. The displacement value ranges from -127 to +127, and any larger displacement change will automatically overflow.

Table 1 Microsoft standard mouse protocol data packet format

2 Specific design plan

2.1 Mouse Principle

At the heart of an optical mouse is a low-resolution mini camera called a sensor. A viewing LED illuminates a surface, and the light bounces off the surface and is collected by a lens. Most mouse manufacturers use visible red LEDs, and some also make mice that use infrared LEDs.

As the mouse moves, the sensor continuously photographs the surface and uses digital signal processing to compare the images to determine the distance and direction of movement. The results are sent back to the computer, and the cursor on the screen moves based on these results. Although optical mouse sensors can move over almost any surface, there are some surfaces that mouse sensors cannot navigate, such as mirrors, glass, glossy surfaces, magazines, and holographic surfaces.

According to Figure 1, the mouse can be divided into the following functional parts:

1) Displacement detection unit--X, Y dual-axis acceleration sensor;

2) Key detection unit;

3) Single chip microcomputer (MCU);

4) Bluetooth transmitter chip;

5) Bluetooth transceiver chip - as receiver (RX);

6) Microcontroller with USB interface (USB MCU).

Figure 1 Description of wireless mouse based on acceleration sensor

The specific working principle of the mouse is as follows: the single-chip microcomputer in the mouse monitors the movement and button status of the acceleration sensor in real time. When the state of the mouse changes, the single-chip microcomputer reads the button status and promptly obtains the current X/Y coordinate movement position; then the single-chip microcomputer packages the changed data according to the agreed communication protocol and sends it to the receiving end through wireless transceiver technology. The receiving end decodes the data packet that conforms to the mouse USB protocol to the USB port of the PC host through the single-chip microcomputer; the mouse driver in the PC receives the data packet from the port, decodes it and transmits it to the corresponding application software, thereby completing the detection and control process of the mouse.