Figure show the timer circuit with delay to light . The circuit consists of a single stable delay circuit , driving circuit , buzzer , LED and other components. The 555 and R1, C3 forms a monostable delay circuit composed of the output signal control circuit work behind . Light on the direction of light from the circuit after the relay power through the diode is increased to 555 , so that capacitor C3 to charge through R1 . With the charge of conduct , the low potential increases in potential when the signal rise up 2/3VDD ( about l -minute delay ), the 555 overturns , the output pin low so that BG conduction . Corresponding drive LED light , buzzer sound , the sound and light signal lights in time to remind drivers . Circuit lights the length of time that corresponds to the circuit delay time can be adjusted to change the time constant R1C3 . The circuit in the driver forgot to lock the direction of light , the time to remind drivers to turn off the power .