Rain Sensor (FC-37/YL-83)

The FC-37 (also sold as YL-83) rain sensor module detects the presence and intensity of water droplets on its sensing pad. It uses an LM393 comparator to provide both a digital (rain/no-rain) and an analog (intensity) output, making it useful for rain detection, irrigation control, and weather monitoring.

For this interfacing you need the following components:

• Arduino board (Uno, Nano, Mega, etc.)
• FC-37 / YL-83 rain sensor module (sensing pad + control board)
• Breadboard and jumper wires (female-to-female for the sensor)
• USB cable to connect Arduino to your computer

Schematic

The sensor module has two parts: the sensing pad and the control board. Connect the control board to the Arduino as follows:

Control Board         Arduino
-------------         -------
VCC           -->     5V
GND           -->     GND
DO            -->     Digital Pin 2
AO            -->     Analog Pin A0

Connect the sensing pad to the control board using the female-to-female jumper wires. The control board has a potentiometer that adjusts the digital output threshold — rotate it with a screwdriver to set the sensitivity.

Pin Map

Control Board

Sensing Pad

Install necessary Library

No external library is required — rain detection uses standard digitalRead() and analogRead() functions built into Arduino.

Code with complete explanation

This sketch reads both the digital (rain detected or not) and analog (rain intensity) outputs, printing the values to the Serial Monitor.

const int digitalPin = 2; // DO pin
const int analogPin  = A0; // AO pin

void setup()
{
  Serial.begin(9600);
  pinMode(digitalPin, INPUT);
}

void loop()
{
  int digitalValue = digitalRead(digitalPin); // LOW = rain detected
  int analogValue  = analogRead(analogPin);   // 0–1023 (lower = more water)

  Serial.print("Digital: ");
  Serial.print(digitalValue);
  Serial.print(" (");

  if (digitalValue == LOW)
  {
    Serial.print("RAIN DETECTED");
  }
  else
  {
    Serial.print("NO RAIN");
  }

  Serial.print(")  Analog: ");
  Serial.print(analogValue);
  Serial.print(" (");

  // Interpret analog value
  if (analogValue < 200)
  {
    Serial.print("Heavy rain");
  }
  else if (analogValue < 500)
  {
    Serial.print("Light rain");
  }
  else if (analogValue < 800)
  {
    Serial.print("Damp / humid");
  }
  else
  {
    Serial.print("Dry");
  }

  Serial.println(")");
  delay(500);
}

Code breakdown

• digitalRead(digitalPin) — reads the DO pin. The LM393 comparator drives this pin LOW when water is detected above the threshold set by the potentiometer. It is HIGH when dry.
• analogRead(analogPin) — reads the AO pin (0–1023). A lower value means more water on the pad, as water creates a conductive path that reduces resistance.
• The digital output provides a simple rain/no-rain boolean. The analog output provides granular intensity data, useful for differentiating between mist, light rain, and heavy rain.

Steps to perform this interfacing

1. Connect the sensing pad to the control board via the spring terminals.
2. Connect the control board to the Arduino as shown in the schematic.
3. Copy the code into the Arduino IDE.
4. Select the correct board and port (Tools > Board and Tools > Port).
5. Upload the sketch to the Arduino.
6. Open the Serial Monitor (Tools > Serial Monitor, set baud rate to 9600).
7. Place a drop of water on the sensing pad and observe the readings change.
8. Adjust the sensitivity potentiometer on the control board with a screwdriver to change the digital trigger point.

Caution

• The sensing pad is NOT corrosion-proof. Prolonged exposure to moisture and DC current causes electrolysis that degrades the copper traces over time. Consider applying a conformal coating or using the sensor only for short measurement bursts (power it through a MOSFET or transistor when not actively reading).
• Do not power the sensing pad continuously. Turn on VCC only when taking a reading (via a digital pin controlling a transistor) to extend the pad’s lifespan.
• The sensor does not differentiate between rain and other conductive liquids (tap water, salt water, condensation). False triggers can occur in high-humidity environments.
• Keep the control board dry — only the sensing pad should be exposed to the elements.
• Clean the sensing pad periodically with isopropyl alcohol to remove oxidation and residue.