说明：  程序功能：接收PWM控制信号，将其转换成对应的控制目标角度，A/D采样回馈得到当前摇臂的角度，最后在程序中采用PID控制输出，是摇臂到达预定目标。
(Program features: PWM control signal received, which was converted to the corresponding control target angle, A/D sampling to obtain the current angle of the swing arm back. Finally, the PID control output of the program, the arm reaches the target.)