Musical doorbell without buttons

This article introduces a musical doorbell that does not require buttons. As long as the visitor stands in front of the doorbell, the doorbell will automatically sound. The circuit principle of the musical doorbell is shown in the attached figure. IC1 and other components form an infrared emission circuit. IC1, RP, R1, and C1 form a multivibrator frequency. According to the component data shown in the figure, the oscillation frequency is about 40kHz and the output current is 100--200mA. It can drive the infrared light-emitting diode D1 to emit 40kHz Modulated infrared pulses. IC2 is an infrared receiving chip with high sensitivity, high gain, good output waveform, and frequency identification function. After the infrared receiving tube D2 receives the infrared pulse with a frequency of 40kHz, it is converted into an electrical signal and sent to the ⑦ pin of IC2. After amplification, C5, L tuning, and IC2 internal circuit detection and shaping, the pulse signal is output from the ① pin. Normally, IC2 pin ① outputs low battery, D3 is cut off, music integrated circuit IC3 has no trigger pulse, does not generate music signal output, and speaker B does not produce sound. When someone stands in front of the door and blocks the infrared signal emitted by D1, the potential of IC2 pin ① instantly changes from low level to high level, and IC3 is triggered by D3 to output a music signal, which is amplified by V to drive the speaker to sound. IC1 uses NE555, IC2 uses μPC1373, and IC3 uses 9300 series music integrated circuits. D1 can use SE303A or LM66R 5mm round infrared light-emitting diode, and D2 can use PH302 square infrared receiving diode. V is 9013NPN tube, β≥100. B selects YD58--1 type, 8Ω/0.25W small diameter speaker. L uses 0.08mm high-strength enameled wire and tightly wraps 30 turns on the intermediate frequency transformer frame of the small transistor radio.