The Design And Research Of Vehicle Air Quality Monitoring System Based On CAN

With the development of the automobile electronic technology, all kinds of vehicle electronic control unit were developed, in order to improve the vehicle’s performance, comfort and safety. In-car air pollution causes serious damage to health and life of drivers and passengers. So the design of safe and convenient, multi-function car air quality monitoring system is of great significance.First of all, this paper realizes overall scheme design of monitor. Monitor can be divided into the monitoring unit and the execution unit, they can communicate on CAN bus. Monitoring unit collects pollutants’ concentration, then sents them to execution unit. If concentration of pollutants more than set point, execution unit will drive motor rotation to drive the fan to discharge pollutants. In the hardware design, monitor selects the STM32 microcontroller and MQ138 air pollutant concentration sensor, STM32 carries the CAN and ADC controller. monitoring unit includes the MQ138 signal acquisition, CAN communication, download debugging and touch screen circuit; Execution unit includes the CAN communication, dc motor drive, speed feedback, serial interface hardware circuit. In the software design of monitoring unit, transplants the μC/OS-II real-time kernel into the STM32 microcontroller, then creates related tasks to realize functions of monitoring unit.Secondly, this paper implements function of execution unit through model based design, to realize PID control of speed. Driver code of microcontroller MCU is encapsulated into simulink’s library module, in the model file, builds simulink block diagram to realize algorithm design of speed feedback, makes use of automatic code generation tool to download algorithm into the MCU to obtain speed’s response, then estimates the motor’s transfer function, in order to realize adjustment of PID parameters, last downloads simulink block diagram of PID algorithm design into MCU to run. Serial port realizes the cooperation of MATLAB and MCU, so real-time and convenient join debugging of the software and hardware becomes so easy.Finally, developed the monitor model, and completed the experiment research. The experimental results show that when the air pollutant concentration more than the set value, execution unit will output the corresponding PWM of duty cycle. PID control of Motor can make the velocity error within ±0.3 r/min, the accuracy is 0.3%, a good control performance.