利用51单片机内置的定时器控制I/O口输出占空比不同的波形，使蜂鸣器产生不同的震动频率，实现唱歌。-The use of 51 single-chip built-in timer, control I/O output, duty cycle of different waveforms, so that the buzzer has a different frequency of vibration, to achieve the singing