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 frequency, the realization of the output pulse signals of different frequencies, so that different frequency buzzer sound ，interesting ~ ~ simply