A wireless doorbell circuit

This wireless doorbell is an electronic product analyzed by the author.

The wireless doorbell button, together with the transmitter, is embedded in the wall beside the door. The receiver can receive the sound at a distance of more than 10m indoors. The transmitter uses a 9V laminated battery and the receiver uses three AA batteries. The standby current of the receiver is only 0.5mA and the working current is 140mA, as shown in Figure 1 and Figure 2.

Transmitter In the circuit shown above, A, B, resistor R2, crystal JT1 and other components of the CD4069 six-phase inverter form a high-frequency oscillator, and C, D, E, and F form shaping and driving circuits respectively. The signal is amplified by transistor 9018 and then transmitted into the air after resonance by L2, C2, and C3.

Receiving part As shown in the figure below, after the external signal is received by the loop antenna L3, the super regenerative detector is composed of VTl and other components, VT2, VT3, A, B, C are used for voltage amplification, VD3, VD4 and other components are used for large signal detection (this is designed for anti-interference), and finally the detection signal passes through D, E, F, and outputs square wave signals at pins (10) and (12), triggering pin (4) of the dedicated doorbell chip KD-0A. At this time, the speaker will emit a loud "ding dong" or "hello, please open the door" call sound. In the figure, L2 and L3 are made of copper foil to form an "Ω"-shaped loop antenna.