利用单片机定时器中断，通过按键控制定时器计数初值，从而调节程序进入定时器中断的频率，实现输出不同频率的脉冲信号，使蜂鸣器发出不同频率的声音~~简单有趣-Interruption of the use of single-chip timer, the timer counts through the buttons to control the initial value, thereby regulating the procedure to enter the timer interrupt