ESP32 - Rain Sensor - Relay

We are going to learn how to program ESP32 to activate the relay if the rain is detected.

Connecting the relay to a motor or actuator allows us to utilize the rain sensor for seamless control of the motor or actuator.

Hardware Used In This Tutorial

1×ESP-WROOM-32 Dev Module
1×USB Cable Type-C
1×Rain Sensor
1×Jumper Wires
1×(Optional) Solenoid Lock
1×(Optional) 12V Power Adapter
1×(Optional) DC Power Jack
1×(Recommended) ESP32 Screw Terminal Adapter

Or you can buy the following sensor kits:

1×DIYables Sensor Kit (30 sensors/displays)
1×DIYables Sensor Kit (18 sensors/displays)
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Introduction to Relay and Rain Sensor

Unfamiliar with relay and rain sensor, including their pinouts, functionality, and programming? Explore comprehensive tutorials on these topics below:

Wiring Diagram

ESP32 Rain Sensor Relay Wiring Diagram

This image is created using Fritzing. Click to enlarge image

If you're unfamiliar with how to supply power to the ESP32 and other components, you can find guidance in the following tutorial: How to Power ESP32.

ESP32 Code

/* * This ESP32 code is created by * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit */ #define RAIN_SENSOR_PIN 25 // The ESP32 pin GPIO25 connected to the sound sensor #define RELAY_PIN 26 // The ESP32 pin GPIO26 connected to the relay int rain_state = LOW; // current state of rain sensor's pin int prev_rain_state = LOW; // previous state of rain sensor's pin void setup() { Serial.begin(9600); // initialize serial pinMode(RAIN_SENSOR_PIN, INPUT); // set ESP32 pin to input mode pinMode(RELAY_PIN, OUTPUT); // set ESP32 pin to output mode } void loop() { prev_rain_state = rain_state; // store old state rain_state = digitalRead(RAIN_SENSOR_PIN); // read new state if (prev_rain_state == LOW && rain_state == HIGH) { // pin state change: LOW -> HIGH Serial.println("Rain detected!"); digitalWrite(RELAY_PIN, HIGH); // turn on } else if (prev_rain_state == HIGH && rain_state == LOW) { // pin state change: HIGH -> LOW Serial.println("Rain stopped!"); digitalWrite(RELAY_PIN, LOW); // turn off } }

Quick Instructions

  • If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE.
  • Do the wiring as above image.
  • Connect the ESP32 board to your PC via a micro USB cable
  • Open Arduino IDE on your PC.
  • Select the right ESP32 board (e.g. ESP32 Dev Module) and COM port.
  • Connect ESP32 to PC via USB cable
  • Open Arduino IDE, select the right board and port
  • Copy the above code and open with Arduino IDE
  • Click Upload button on Arduino IDE to upload code to ESP32
Arduino IDE Upload Code
  • Move your hand in front of sensor
  • See the change of relay's state

Code Explanation

Read the line-by-line explanation in comment lines of source code!

Video Tutorial

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