Rain Drop Detection Sensor Module
PCB-based rain and moisture detection board.
A conductive-trace PCB that detects rainfall or spilled liquid, commonly paired with servo-driven window/roof closers in weather projects. The sensing board is a grid of exposed parallel copper traces whose resistance drops sharply when bridged by water droplets, and a companion driver board (usually built around an LM393 comparator) converts that resistance change into both a digital threshold output and a proportional analog signal — a simple, low-cost way to detect the presence and rough intensity of rain or spilled liquid.
Specifications
| Sensor type | Conductive-trace rain/moisture sensing PCB with LM393 comparator driver board |
| Operating voltage | 3.3V–5V DC |
| Operating current | ~15-20 mA typical |
| Digital output (DO) | Goes LOW when water bridges enough traces to cross the threshold set by the onboard potentiometer (HIGH when dry, on most boards) |
| Analog output (AO) | Continuous voltage proportional to how much of the sensing grid is wetted — lower resistance (more water) gives a lower/higher voltage depending on wiring convention |
| Sensitivity adjustment | Onboard trimmer potentiometer sets the digital-output trigger threshold |
| Interface | 1 digital pin (threshold trigger) + 1 analog pin (intensity reading) |
| Durability note | Exposed copper traces will oxidize/corrode with repeated wetting over time — treat as a low-cost, semi-consumable sensor rather than a permanent outdoor fixture |
Pinout
| Pin | Name | Description |
|---|---|---|
| 1 | VCC | Power, 3.3–5V DC |
| 2 | GND | Ground |
| 3 | DO | Digital output — threshold-triggered rain/no-rain signal |
| 4 | AO | Analog output — proportional to how wet the sensing grid is |
Mount the sensing board at a slight tilt so water can run off rather than pool on the traces, which extends its usable life and reduces false lingering triggers after rain has stopped. Because the exposed copper traces corrode over repeated exposure to water, expect to eventually replace the sensing board itself in long-term outdoor installations, even though the separate driver board typically remains fine.
Variants
The bundled conductive-trace rain sensor is the cheapest and most common option for a hobby weather-response project, accepting that the sensing PCB is a semi-consumable part. For a longer-lasting, corrosion-free design, an optical windshield-style rain sensor costs more but avoids exposed metal traces entirely.
| Variant | Temp range | Hum range | Accuracy | Protocol | Price |
|---|---|---|---|---|---|
| Rain sensor (board + LM393 driver) | ~$1-3 | ||||
| Capacitive soil moisture sensor | ~$2-4 | ||||
| Optical rain sensor (windshield-style) | ~$10-20 |