💧 Soil Moisture Sensor Complete Guide for Raspberry Pi Pico W

Soil moisture sensors help you water only when needed, saving 30-40% of water while improving crop yields. The Pico W's built-in ADC makes it perfect for analog sensors.

🔌 Wiring Diagram

═══════════════════════════════════════════════════════════════════════════════
                    SOIL MOISTURE SENSOR TO PICO W
═══════════════════════════════════════════════════════════════════════════════

    Capacitive Sensor                    Raspberry Pi Pico W
    ┌─────────────────┐                  ┌─────────────────┐
    │ VCC (3.3-5V)    │ ───────────────► │ 3.3V (Pin 36)   │
    │ GND             │ ───────────────► │ GND (Pin 38)    │
    │ AO (Analog Out) │ ───────────────► │ GP26 (Pin 31)   │
    └─────────────────┘                  └─────────────────┘

    ⚠️ Note: Pico W ADC pins are GP26, GP27, GP28 only!
    GP26 = ADC0, GP27 = ADC1, GP28 = ADC2

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📖 Complete MicroPython Code

from machine import Pin, ADC
import time

# ADC on GP26 reads 0-3.3V -> 0-65535
moisture = ADC(Pin(26))

# ========== CALIBRATION VALUES ==========
# CALIBRATE THESE FOR YOUR SPECIFIC SENSOR!
DRY_VALUE = 60000    # Value in dry air (calibrate this!)
WET_VALUE = 20000    # Value in water (calibrate this!)

def read_moisture():
    """Read soil moisture and return percentage 0-100%"""
    raw = moisture.read_u16()
    
    # Convert raw value to percentage
    # Higher raw = drier, lower raw = wetter
    percent = 100 - ((raw - WET_VALUE) * 100 / (DRY_VALUE - WET_VALUE))
    percent = max(0, min(100, percent))  # Clamp between 0-100
    
    return raw, percent

def get_recommendation(percent):
    """Get irrigation recommendation based on moisture level"""
    if percent < 20:
        return "🚨 CRITICAL: Soil extremely dry! Water immediately!"
    elif percent < 30:
        return "⚠️ SOIL IS DRY - Water within 24 hours"
    elif percent < 45:
        return "💡 Soil slightly dry - Monitor closely"
    elif percent <= 70:
        return "✅ OPTIMAL - Soil moisture adequate"
    elif percent <= 85:
        return "💧 Soil moist - Reduce irrigation"
    else:
        return "⚠️ Soil too wet - Risk of root rot!"

print("Soil Moisture Monitor Started")
print(f"Calibration: Dry={DRY_VALUE}, Wet={WET_VALUE}\n")

while True:
    raw, percent = read_moisture()
    
    print("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━")
    print(f"📊 Raw ADC: {raw}")
    print(f"💧 Soil Moisture: {percent:.1f}%")
    print(f"🎯 {get_recommendation(percent)}")
    print("━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━\n")
    
    time.sleep(60)  # Read every minute