Rain sensor (FC-37 / YL-83)
Rain sensor plate and LM393 module pinout, analog and digital outputs, how to stop the plate corroding, and wiring on 3.3 V and 5 V boards.
Community draft — report a mistake
3.3 V or 5 V? AO and DO swing up to VCC. Power the module from 3.3 V on ESP32/Pico so AO stays within the ADC range.
The kit has two parts: a sensing plate with interleaved tracks, and a small LM393 comparator board. Water bridging the tracks lowers the resistance, so AO falls as the plate gets wetter, and DO switches at the threshold set by the pot.
It’s great for rain alarms, auto-closing windows and “irrigation skip” logic — but the bare copper tracks corrode quickly if powered all the time. Power it only while measuring.
The plate connects to the comparator board with two wires; polarity doesn’t matter.
Prices are indicative (Oct 2026) and vary by seller.
Pinout
| Pin | What it does |
|---|---|
VCC | 3.3–5 V supply — switch it from a GPIO to reduce corrosion |
GND | Ground |
DO | Digital output: changes state when water crosses the pot threshold |
AO | Analog output: lower with more water on the plate |
Use it with
Common errors
Plate turns green and stops working after weeks
Electrolysis: DC on a wet plate eats the tracks. Power the module from a GPIO only for the moment you read it (a few ms).
Reads “wet” for hours after the rain
Water sits on the plate. Mount it tilted so drops run off.
Values vary between modules
Uncalibrated by design. Record dry and wet readings and set your own thresholds.