SENSORS/ACTUATORS

INTERNET OF THING (IoT)

ESP32 - Rain Sensor

The rain sensor is capable of detecting and measuring rain/snow level. The rain sensor provides two outputs: a digital output (LOW/HIGH) and an analog output.

In this tutorial, we will learn how to use an ESP32 and an rain sensor to detect and measure the rain. Specifically, we will cover the following:

How to connect the rain sensor to an ESP32.
How to program the ESP32 to detect the rain by reading the digital signal from the rain sensor.
How to program the ESP32 to measure the rain level by reading the analog signal from the rain sensor.

Afterward, you can modify the code to activate a motor or warning when it detects rain./snow

Hardware Used In This Tutorial

1	×	ESP-WROOM-32 Dev Module
1	×	USB Cable Type-C
1	×	Rain Sensor
1	×	Breadboard
1	×	Jumper Wires
1	×	(Recommended) Screw Terminal Expansion Board for ESP32

Or you can buy the following sensor kits:

1	×	DIYables Sensor Kit (30 sensors/displays)
1	×	DIYables Sensor Kit (18 sensors/displays)

Disclosure: some of these links are affiliate links. We may earn a commission on your purchase at no extra cost to you. We appreciate it.

Introduction to Rain Sensor

The rain sensor can be utilized to detect the presence of rain or measure the level of water dropped by the rain. The rain sensor provides two options via a digital output pin and analog output pin.

The rain sensor includes two parts:

The sensing pad
The electronic module

image source: diyables.io

The sensing pad

The sensing pad is placed outside that can face with rain/snow (e.g. the roof). The sensing pad has a series of exposed copper traces, devided into two groups: power traces and sense traces. These power traces and sense traces are not connected unless they are bridged by water or snow. There is no differences between the power trace and sense trace. You can pick one as power trace and the other wil be come the sense trace

The electronic module

The The electronic module of rain sensor converts the signal from the sensing pad to analog or digital value that can be read by ESP32. It includes four pins:

VCC pin: It needs to be connected to VCC (3.3V to 5V).
GND pin: It needs to be connected to GND (0V).
DO pin: It is a digital output pin. It is HIGH if the rain is not detected and LOW if detected. The threshold value for rain detection can be adjusted using a built-in potentiometer.
AO pin: It is an analog output pin. The output value decreases as the water in the sensing pad is increased, and it increases as water in the sensing pad is decreased.

Furthermore, it has two LED indicators:

One PWR-LED indicator for power.
One DO-LED indicator for the rain state on the DO pin: it is on when rain is present.

How It Works

For the DO pin:

The module has a built-in potentiometer for setting the threshold (sensitivity).
When the intensity is above the threshold value, the rain is detected, the output pin of the sensor is LOW, and the DO-LED is on.
When the intensity is below the threshold value, the rain is NOT detected, the output pin of the sensor is HIGH, and the DO-LED is off.

For the AO pin:

The more water in the sensing pad, the lower the value read from the AO pin.
The less water in the sensing pad, the higher the value read from the AO pin.

Note that the potentiometer does not affect the value on the AO pin.

Wiring Diagram

As mentioned above, the VCC pin of the sensor should be connected to the 3.3V or 5V. If we connect this pin directly to 3.3V or 5V pin of ESP32, the lifespan of sensor will be shorten because of electrochemical corrosion. The best way is to connect the the VCC pin of the rain sensor to an output pin of ESP32, We can program that pin to power the rain sensor when reading only. This can mimimize the impart of the electrochemical corrosion.

Since the rain sensor module has two outputs, you can choose to use one or both of them, depending on what you need.

How to connect ESP32 and rain sensor using breadboard

The rain sensor module offers two outputs. You can use either one or both as required.

This image is created using Fritzing. Click to enlarge image

How to connect ESP32 and rain sensor using screw terminal block breakout board

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 - Read value from DO pin

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-rain-sensor */ #define POWER_PIN 19 // ESP32's pin GPIO19 that provides the power to the rain sensor #define DO_PIN 21 // ESP32's pin GPIO21 connected to DO pin of the rain sensor void setup() { // initialize serial communication Serial.begin(9600); // initialize the Arduino's pin as an input pinMode(POWER_PIN, OUTPUT); // configure the power pin pin as an OUTPUT pinMode(DO_PIN, INPUT); } void loop() { digitalWrite(POWER_PIN, HIGH); // turn the rain sensor's power ON delay(10); // wait 10 milliseconds int rain_state = digitalRead(DO_PIN); digitalWrite(POWER_PIN, LOW); // turn the rain sensor's power OFF if (rain_state == HIGH) Serial.println("The rain is NOT detected"); else Serial.println("The rain is detected"); delay(1000); // pause for 1 sec to avoid reading sensors frequently to prolong the sensor lifetime }

Quick Instructions

If this is the first time you use ESP32, see how to setup environment for ESP32 on Arduino IDE
Copy the above code and open with Arduino IDE
Click Upload button on Arduino IDE to upload code to ESP32
Drop some water to the rain sensor
See the result on Serial Monitor.

COM6

Send

The rain is NOT detected The rain is NOT detected The rain is NOT detected The rain is detected The rain is detected The rain is detected The rain is detected The rain is detected The rain is NOT detected The rain is NOT detected The rain is NOT detected

Autoscroll Show timestamp

Clear output

9600 baud

Newline

Please keep in mind that if you notice the LED status remaining on constantly or off even when the sensor faces to a rain, you can adjust the potentiometer to fine-tune the sensitivity of the sensor.

ESP32 Code - Read value from AO pin

/* * This ESP32 code is created by esp32io.com * * This ESP32 code is released in the public domain * * For more detail (instruction and wiring diagram), visit https://esp32io.com/tutorials/esp32-rain-sensor */ #define POWER_PIN 19 // ESP32's pin GPIO19 that provides the power to the rain sensor #define AO_PIN 36 // ESP32's pin GPIO36 connected to AO pin of the rain sensor void setup() { // initialize serial communication Serial.begin(9600); // set the ADC attenuation to 11 dB (up to ~3.3V input) analogSetAttenuation(ADC_11db); pinMode(POWER_PIN, OUTPUT); // configure the power pin pin as an OUTPUT } void loop() { digitalWrite(POWER_PIN, HIGH); // turn the rain sensor's power ON delay(10); // wait 10 milliseconds int rain_value = analogRead(AO_PIN); digitalWrite(POWER_PIN, LOW); // turn the rain sensor's power OFF Serial.println(rain_value); // print out the analog value delay(1000); // pause for 1 sec to avoid reading sensors frequently to prolong the sensor lifetime }

Quick Instructions

Copy the above code and open with Arduino IDE
Click Upload button on Arduino IDE to upload code to ESP32
Drop some water to the rain sensor
See the result on Serial Monitor.

COM6

Send

225 2426 236 563 687 959 975 1009 1017 1053 1078 841 743 440 279

Autoscroll Show timestamp

Clear output

9600 baud

Newline

※ NOTE THAT:

This tutorial uses the analogRead() function to read values from an ADC (Analog-to-Digital Converter) connected to a rain sensor. The ESP32 ADC is good for projects that do NOT need high accuracy. However, for projects that need precise measurements, please note:

The ESP32 ADC is not perfectly accurate and might need calibration for correct results. Each ESP32 board can be a bit different, so you need to calibrate the ADC for each individual board.
Calibration can be difficult, especially for beginners, and might not always give the exact results you want.

For projects that need high precision, consider using an external ADC (e.g ADS1115) with the ESP32 or using an Arduino, which has a more reliable ADC. If you still want to calibrate the ESP32 ADC, refer to ESP32 ADC Calibration Driver

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Function References

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