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 PWM value is reduced to a minimum to maximum, or when the alarm buzzer will