A39 Raindrop Detection Sensor Module – Digital and Analog Output, LM393 Comparator

The A39 Raindrop Module is a rain and water-drop detection module designed to sense the presence and relative intensity of water on its sensing surface. It combines a nickel-plated FR-04 double-sided sensor board with a separate comparator board built around the LM393 dual differential comparator. When water droplets bridge the exposed traces on the sensor board, the board’s resistance changes, and the LM393 converts this change into two output signals: a digital switching output (DO) and an analog voltage output (AO).

In operation, the digital output remains high (1) when the sensing surface is dry. When a sufficient amount of water is present, the DO pin switches to low (0), and the onboard indicator LED lights up. The sensitivity threshold for this digital switching is set by a small potentiometer on the comparator board, allowing the module to be adapted to different rain intensities or mounting positions. The analog output provides a voltage that varies continuously with the amount of water on the sensor, so a microcontroller’s ADC can be used to estimate rainfall intensity rather than just detecting a yes/no condition.

The module operates from a DC supply of 3.3V to 5V, making it compatible with 3.3V and 5V microcontrollers including Arduino, ESP32, and Raspberry Pi. The comparator output has a clean waveform and a driving capability exceeding 15mA. The sensing area measures 5.0 × 4.0cm, while the comparator board measures 32 × 14mm, and the module weighs approximately 10g. Fixed bolt holes on the board allow straightforward mounting, and the sensor board is connected to the comparator board by a detachable cable. The nickel plating is specifically intended to improve oxidation resistance and extend service life in outdoor or humid environments.