Soil Moisture Sensor - Wiring and Calibration

💧 Soil Moisture Sensor - Complete Guide for Smart Irrigation

💧 What You'll Learn:

🔌 Wire capacitive and resistive soil moisture sensors to ESP32
📊 Calibrate your sensor (DRY_VALUE and WET_VALUE)
💧 Make automated irrigation decisions (water when dry)
💰 Save 30-40% of water while improving crop yields

Soil moisture sensors are the most important sensors for smart irrigation. They can save 30-40% of water while improving crop yields. A $10 sensor can save thousands of liters of water annually.

🔌 Wiring Instructions

Capacitive Soil Moisture Sensor     ESP32
═══════════════════════════════     ════
VCC (3.3-5V)               ─────►   3.3V
GND                        ─────►   GND
AO (Analog Output)         ─────►   GPIO32

⚠️ Resistive sensors use same wiring but corrode faster (months vs years)

💡 Capacitive vs Resistive:

Capacitive ($8-12): Lasts years, no corrosion, more accurate ✅ BEST
Resistive ($2-3): Corrodes in 3-6 months, less accurate ❌ AVOID for farming

📊 Calibration Process (CRITICAL!)

// Step 1: Find DRY_VALUE
// Place sensor in dry air for 1 minute
// Record the reading (typically 3500-4095 on ESP32)

// Step 2: Find WET_VALUE
// Submerge sensor completely in water for 1 minute
// Record the reading (typically 1000-2000)

// Step 3: Update code with YOUR values
const int DRY_VALUE = 3800;   // ← YOUR dry reading
const int WET_VALUE = 1500;   // ← YOUR wet reading

// Step 4: Calculate percentage
int raw = analogRead(SOIL_PIN);
int moisture = map(raw, DRY_VALUE, WET_VALUE, 0, 100);
moisture = constrain(moisture, 0, 100);

📖 Complete Working Code

#define SOIL_PIN 32

// CALIBRATE THESE VALUES FOR YOUR SENSOR!
const int DRY_VALUE = 3800;   // Reading in dry air
const int WET_VALUE = 1500;   // Reading in water

void setup() {
    Serial.begin(115200);
    pinMode(SOIL_PIN, INPUT);
    Serial.println("💧 Soil Moisture Monitor Started");
}

void loop() {
    int raw = analogRead(SOIL_PIN);
    int moisture = map(raw, DRY_VALUE, WET_VALUE, 0, 100);
    moisture = constrain(moisture, 0, 100);
    
    Serial.println("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━");
    Serial.printf("📊 Raw ADC: %d\n", raw);
    Serial.printf("💧 Soil Moisture: %d%%\n", moisture);
    
    // Irrigation decision
    if (moisture < 30) {
        Serial.println("⚠️ SOIL IS DRY - Start watering!");
        // digitalWrite(RELAY_PIN, LOW);  // Turn pump ON
    } else if (moisture > 80) {
        Serial.println("✅ Soil is wet - Stop watering");
        // digitalWrite(RELAY_PIN, HIGH); // Turn pump OFF
    } else if (moisture < 50) {
        Serial.println("💡 Soil is drying - Monitor closely");
    } else {
        Serial.println("✅ Soil moisture adequate");
    }
    Serial.println("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━\n");
    
    delay(60000);  // Read every minute
}

📖 Success Story - Kenyan Tomato Farm:

A tomato farmer installed capacitive soil moisture sensors on 2 hectares:

💧 Before: Watered daily at 6 AM regardless of soil condition
💧 After: Only watered when moisture dropped below 35%
📊 Result: 38% less water used, 28% higher tomato yield
💰 Savings: $45/month on water bills + higher quality fruit

⚠️ Common Mistakes:

❌ Not calibrating: Every sensor is different! Always calibrate yours.
❌ Using resistive sensors: They corrode in months. Buy capacitive sensors.
❌ Reading too often: Every minute is fine. Every second will overload your sensor.
❌ Wrong depth: Insert sensor at root depth (10-20cm), not surface.

🎯 Key Takeaways:

✅ Capacitive sensors last YEARS (resistive fails in months)

✅ Calibration is MANDATORY for accurate readings

✅ Water when moisture < 30%, stop when > 80%

✅ Read every 15-60 minutes (not constantly)

✅ A $10 sensor can save thousands of liters of water annually

💡 Key Takeaways:

Apply these concepts directly to your farm or project.

Take notes on important details for the quiz.

Use the button below to track your progress.

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