按K1，PWM值增加，则占空比减小,LED 灯渐暗。按K2，PWM值减小，则占空比增加,LED 灯渐亮。当PWM值增加到最大值或减小到最小值时，蜂鸣器将报警-By K1, PWM value is increased, the duty cycle decreases, LED lights dimming. By K2, PWM value is reduced, then the duty cycle increases, LED lights before dawn. When the P