Ding dong doorbell switch s1 is push button switch on the door, without press the switch, the capacitance cannot be connected is not recharged, and capacitance voltage of 0 v, the reset has been in a low level condition, leading to the speaker doesn't work. When closed switch s1, the VCC current through the diode for capacitor charging, make its both ends of the voltage, and reset voltage also began to rise gradually. When the voltage of the capacitance increased to higher levels, namely the reset input port is the high level, the timer starts, composed of resistance, capacitance and diode oscillator start work, output frequency for f1.When disconnecting switch s1, resistance and capacitance circuit, capacitor began to discharge. At the same time composed of resistance, capacitance and diode oscillator start work, output frequency for ` 2 f.Restore low level is reset when the capacitor discharge end, timer stop working.

Model Number: NE555

Package Include: 1 x Dingdong Doorbell Kit