用单片机控制DAC0832芯片输出电流，让发光二级管D12由灭均匀变到最亮，再由最亮均匀熄灭。在最亮和最暗时使用蜂鸣器分别警报一声，完成整个周期时间控制在5S左右，循环变化。-DAC0832 chip microcontroller to control the output current, light emitting diode D12 from off the uniform change to the brightest, and then goes out from the brig