Wireless mouse solution based on micro-electromechanical system

1 System Principle and Design

1.1 Detection Principle

At present, there are two common types of mice, wheel type and photoelectric type. The wheel type mouse relies on the transmission of the wheel to drive the decoding wheels on the X and Y axes to rotate to sense the change of mouse displacement; the photoelectric mouse uses a photoelectric sensor with its own light source. The core of the photoelectric mouse, DSP, identifies the direction and displacement of movement by comparing the differences between these snapshots.

The wireless mouse based on MEMS technology uses a micro-acceleration sensor to measure the acceleration of the mouse movement in real time, which is converted into a displacement signal after two integrations and transmitted to the host to control the movement of the cursor, thereby realizing the function of the mouse.

1.2 Hardware Design

As shown in FIG1 , the entire wireless mouse system is divided into two subsystems, the remote subsystem and the host subsystem.

Figure 1 Wireless mouse system structure diagram

The remote subsystem consists of a micro-accelerometer, a microcontroller and an nRF2401 radio frequency transceiver. The micro-accelerometer uses the ADXL203 microsensor produced by the American AD company, and the microcontroller uses the ATmega 16L microcontroller produced by Atmel. The microcontroller is equipped with an 8-channel 10-bit programmable A/D conversion circuit, which can convert the acceleration analog signal output by the ADXL203 acceleration sensor into an acceleration digital signal in real time.

The output voltage of the ADXL203 accelerometer is 2.5V when the acceleration is 0. To improve the accuracy of A/D conversion, this paper uses the built-in differential amplifier function of ATmega 16L to filter out the 2.5V voltage with the differential signal, and amplifies the differential voltage signal to match the reference voltage of A/D conversion. The system is powered by a 9V battery commonly used in electrical appliances, and a LM78M05 voltage regulator is connected to obtain a constant 5V voltage for use by each module.

The host terminal system consists of an nRF2401 RF transceiver, a serial transmission interface chip and another ATmega 16L microcontroller. The RS232 serial communication interface chip uses the MAX233 chip from Maxim2IC, which converts the 5V TTL/CMOS level output by the microcontroller into the EIA/TIA-232-E level for serial (RS232) communication with the computer host.

1.3 Software and Algorithm Design

When the mouse moves under human control, the micro-acceleration sensor will output the acceleration and direction of the mouse movement in real time. The range of the ADXL203 sensor is ±1.7gn, and the voltage sensitivity is 1000mV/gn. After the voltage signal is differentially amplified by 5.0/1.7 times, it is converted into a digital signal corresponding to the acceleration through the microcontroller A/D conversion function. After two integrations, the acceleration becomes the displacement signal of the mouse movement, and then it is encoded and transmitted through the nRF2401 RF transceiver.

When the output voltage of the acceleration sensor is a, the digital value obtained by A/D conversion is