The working principle of the inductive doorbell

5.1 Inductive Automatic Doorbell

The inductive automatic doorbell does not need to install a doorbell button on the outside of the door, but relies on the human body sensors to trigger the door to sound. When there is a guest outside the door, the inductive automatic doorbell will automatically send out the "Ding Dong" sound to notify the owner to open the door to welcome the guest.

5.1.1 Circuit working principle

Figure 5-1 shows the circuit diagram of the inductive automatic doorbell. It is mainly composed of three major components: First, by the pyroelectric infrared detector BH9402 (1Q) composed of the detection circuit; Second, by the "Dingdong" doorbell integrated circuit KD-253B (1C2) and other components of the audio signal source circuit; Third, by the transistor VTl, VT2 and speaker B and other components of the amplifier circuit. The power supply uses two No. 5 batteries. Because the work of the doorbell is characterized by the need for long-term standby, so this circuit does not set the power switch. When not in use for a long time, remove the batteries can be.

(1) Detection circuit Pyroelectric infrared detector head is a passive infrared detection device, can be detected in a non-contact way of infrared radiation emitted by the human body, and will be converted into electric