In this paper, a calibrated liquid level sensor transducer for detecting rainfall of botanic garden is newly proposed. The output signal is a pulse stream, it could be easily sent over a wide range of transmission media, such as package switch network, radio, optical, infrared, ultrasonic, and so on. Another innovation is that a calibration method is proposed to easily adjust parameters to calibrate various liquid level sensors. By collocating with a liquid level sensor that has a range of 3.97 to 123.34 mm, the corresponding output frequency ranges from 3.12 to 57.25 kHz. After calibration, the measured maximum frequency error is 1.46%. Measurement results have successfully verified all the functions and performance of the proposed calibrated liquid level sensor transducer and confirmed it to be applied on detecting rainfall of botanic garden. The proposed calibrated liquid level sensor transducer is suitable for devices of detecting liquid level.Index Terms-Rainfall, liquid level sensor, liquid level sensor transducer.