Interfacing Capacitive Soil Moisture Sensor with ESP32 DOIT DevKit v1

Introduction

The Capacitive Soil Moisture Sensor is widely used in smart farming and gardening projects. Unlike the resistive type, it does not corrode easily, making it more durable for long-term use. The sensor measures the dielectric constant of soil: wetter soil has a higher dielectric constant, which changes the sensor’s output voltage.

The sensor provides an analog output, which we can read using the ESP32’s ADC pin (GPIO 32 in our setup). By reading these values, we can determine whether the soil is dry, moist, or wet and then automate irrigation systems accordingly.

Components Required

• ESP32 DOIT DevKit v1
• Capacitive Soil Moisture Sensor
• Breadboard & jumper wires
• USB cable

Circuit Diagram

• Sensor VCC → 3.3V
• Sensor GND → GND
• Sensor AO (Analog Output) → GPIO 32

Arduino Code

// Capacitive Soil Moisture Sensor with ESP32 DOIT DevKit v1
#define SOIL_PIN 32  // Analog pin connected to sensor

void setup() {
  Serial.begin(115200);
  Serial.println("Capacitive Soil Moisture Sensor with ESP32");
}

void loop() {
  int soilValue = analogRead(SOIL_PIN); // Read analog value (0 - 4095)
  Serial.print("Soil Moisture Value: ");
  Serial.println(soilValue);

  // Simple soil condition check
  if (soilValue > 3000) {
    Serial.println("Soil is DRY");
  } else if (soilValue > 1500) {
    Serial.println("Soil is Moist");
  } else {
    Serial.println("Soil is WET");
  }

  delay(2000); // Wait 2 seconds
}

Step-by-Step Code Explanation

Define Sensor Pin

#define SOIL_PIN 32

The sensor is connected to GPIO 32 (ADC pin).

Setup

Serial.begin(115200);

Initializes serial communication for monitoring.

Read Analog Value

int soilValue = analogRead(SOIL_PIN);

Reads soil moisture level as a raw ADC value (0–4095).

Print Values

Serial.print("Soil Moisture Value: ");
Serial.println(soilValue);

Displays sensor readings on Serial Monitor.

Soil Condition Check

if (soilValue > 3000) { ... }  

Uses threshold values to categorize soil as Dry, Moist, or Wet.

Output

Capacitive Soil Moisture Sensor with ESP32
Soil Moisture Value: 3500
Soil is DRY
Soil Moisture Value: 2200
Soil is Moist
Soil Moisture Value: 900
Soil is WET

Real-Life Applications

• Smart Irrigation Systems → Automatically water plants when soil is dry.
• Greenhouse Monitoring → Maintain soil moisture for crops.
• Home Gardening → Monitor houseplants with IoT dashboards.
• Agriculture IoT Projects → Send soil data to the cloud for analysis.

Troubleshooting

Problem	Cause	Solution
Readings always high	Wrong wiring	Check VCC, GND, AO connections
Fluctuating values	Poor power supply	Use stable 3.3V / external regulated supply
Dry/Wet threshold not accurate	Soil type variation	Calibrate values for your soil
No data in Serial Monitor	Wrong baud rate	Set Serial Monitor to 115200