Radio remote doorbell circuit schematic

Photocoupler

This example presents a radio remote-controlled doorbell system named "Ding Dong," which utilizes the TWH630/631 remote control module. When a visitor arrives, pressing the doorbell button on the door frame triggers a crisp and melodic bird call, notifying those inside about an arrival. For homeowners, simply pressing the remote control switch in their pocket will produce a "beep" sound from the doorbell. This setup is particularly convenient for families with school-aged children, as they do not need to carry keys; instead, they can wear a compact remote control and press it upon returning home, allowing parents to easily track their child's return.

The child has returned home safely.

Working Principle

The remote doorbell comprises two main components: a transmitter and a receiver. The circuit schematics for these components are illustrated in Figures a and b, respectively.

The transmitter primarily consists of a TWH630 miniature radio transmitter that broadcasts high-frequency signals into the air via its built-in antenna when the transmit button SB1 is pressed. The modulation oscillator uses a common 555 timer integrated circuit, which is connected to a self-excited multivibrator. The output square wave frequency is f = 1.44 / (R1 + 2R2)C1, calculated to be approximately 1 kHz based on the data provided in Figures a and b. This square wave signal is applied through resistor R3 to the input terminal IN of TWH630, thereby modulating the radiated high-frequency signal.

The receiver includes a TWH631 radio receiver, LM567 audio decoder, and KI-156 ASIC. The TWH631 captures the signal from the transmitter module and amplifies it before decoding it using the LM567. The center frequency of the decoder is primarily determined by RRP + R4 and C4, with Opf = 1.1 / (RRP + R4)C4. Adjusting the potentiometer RP ensures the center frequency matches the modulation frequency of the transmitter, which is 1 kHz. At this point, the 8-pin output of the integrated block outputs a low level, which is applied to the low-trigger terminal TG2 of IC5, triggering it to emit a "Ding Dong" signal that is then amplified by the transistor VT to drive the speaker BL to produce sound. IC5 is a "Ding Dong-Bird" music integrated circuit, featuring two trigger terminals: one is the high-level trigger terminal TG1, which triggers the OUT terminal to produce a bird call signal when activated by a high level; the other is the low-level trigger terminal TG2, which triggers the OUT terminal to produce a "Ding Dong" signal when activated by a low level. The SB2 is a button mounted on the door frame. When pressed by a visitor, it triggers the low-level trigger terminal TG2, causing the speaker BL to emit a "bird" sound.

Component Selection

IC1 can use NE555, SI555, or any equivalent 555 timer IC; IC2 and IC3 should use TWH630/631 type radio transmitting and receiving modules; IC4 is an LM567 audio decoder; IC5 is a KD-156 "Ding Dong-Bird" specialized music integrated circuit, which is packaged in black paste. Resistors R6-R8, capacitor C5, and transistor VT can be soldered onto the small printed circuit board of the chip. VD1 and VD2 are common 1N4148 silicon switching diodes. Their function is to use the forward diode voltage drop to ensure the KD-156 operates under normal voltage.

VT can use a 9013 type silicon NPN transistor, requiring a current amplification factor β > 100.

RP is best suited for a WSW organic solid trimmer potentiometer. Other RC components have no specific requirements, except that their sizes should be smaller.

G1 is best suited for a 12V battery dedicated to electronic lighters. G2 is connected in series by four 5th dry batteries, providing a voltage of 6V.