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The Ding dong doorbell switch s1 is a push button switch on the door, without pressing 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, makes both ends of the voltage and reset voltage also began to rise gradually. When the voltage of the capacitance increases 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 s
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NE555 Doorbell Suite Electronic