Radio remote control doorbell circuit b

Using the remote control circuit composed of TDC1808 and TDC1809 dedicated radio remote control transmitting/receiving modules, the doorbell can be remotely controlled and
the circuit can be simplified. cut costs. The remote control distance is between 15-60m, especially suitable for high-rise buildings.
  (1) Working principle
  1) Transmitting circuit: Figure a shows the circuit principle of the remote control transmitter. Transistors VT1 and rr2 form a multivibrator, which
generates a 20kHz/2.5V square wave signal at the c pole of VT2. After being limited by Rs, it is sent to the input end of the remote control transmitting module IC (TDC1808), and
is processed Pulse modulation, and finally the 300MHz radio wave is emitted by the internal antenna.
    2) Receiving circuit: The receiving circuit is shown in Figure 18-2b. When the receiver remote control receiving module ICl (T DC 1809) receives
the radio wave from the transmitter, the internal circuit demodulates the received signal into a square wave signal, and sends it from its output terminal ① pin to the ③ pin of IC2, and then
Frequency selection decoding is performed by IC2. When the time constant of the external resistor Ri and capacitor C3 connected to pins ⑤ and ⑤ is consistent with the frequency of the square wave sent, pin ③
changes from high level to low level, triggering the dual-tone doorbell integrated circuit IC3 (KD-156) @ pin, the IC3 output signal is amplified by VT and drives the speaker to make
a "ding dong" sound or a "bird call".
    3) Musical KD-156. KD156 is an integrated circuit music chip produced by Zhejiang Xiaoshan Jinglong Electronics Co., Ltd. Its circuit structure
is shown in Figure 18-2c. Interested readers can assemble a musical doorbell that does not require a remote control. When the two buttons are pressed respectively, they will make a "ding-dong" sound
and a "bird call" sound.