🔌 Measuring Soil Temperature with DS18B20

🛠️ Why DS18B20 is Best for Soil

• ✅ Waterproof probe
  Can be buried directly in soil — no special enclosure needed!
• ✅ Digital output
  No calibration required — reads accurate temperature immediately
• ✅ Accurate to ±0.5°C
  Range: -55°C to +125°C (works in all farming climates)
• ✅ Multiple sensors on one wire
  One GPIO pin can read 10+ sensors (OneWire protocol)
• ✅ Very affordable
  Only $4-6 per sensor — monitor multiple zones cheaply

🔗 Wiring the DS18B20

DS18B20 Waterproof Sensor (colors may vary):
═══════════════════════════════════════════════════════════════
Red wire (VDD)     → ESP32 3.3V (or 5V for ESP8266)
Black wire (GND)   → ESP32 GND
Yellow/White (DATA)→ ESP32 GPIO4

⚠️ CRITICAL: 4.7kΩ pull-up resistor required!
   Connect between DATA (GPIO4) and 3.3V

Diagram:
       4.7kΩ
GPIO4 ──█/\/\/\█── 3.3V
   │
   └── DS18B20 DATA (yellow)

Multiple sensors: Connect all DATA wires to same GPIO4!
    

📖 Reading Soil Temperature (Basic Code)

#include <OneWire.h>
#include <DallasTemperature.h>

#define ONE_WIRE_BUS 4

OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature sensors(&oneWire);

void setup() {
    Serial.begin(115200);
    sensors.begin();
    Serial.println("🌡️ DS18B20 Soil Temperature Sensor Ready");
    Serial.println("========================================");
}

void loop() {
    sensors.requestTemperatures();
    float soilTemp = sensors.getTempCByIndex(0);
    
    if (soilTemp == -127.0) {
        Serial.println("❌ Sensor error! Check wiring.");
    } else {
        Serial.printf("🌡️ Soil Temperature: %.1f°C\n", soilTemp);
        
        if (soilTemp < 10) {
            Serial.println("⚠️ TOO COLD! Do not plant sensitive crops.");
        } else if (soilTemp > 35) {
            Serial.println("⚠️ TOO HOT! Increase irrigation, provide shade.");
        } else {
            Serial.println("✅ Soil temperature is within good range.");
        }
    }
    
    delay(60000);
}
    

📖 Advanced Code (Multiple Sensors)

#include <OneWire.h>
#include <DallasTemperature.h>

#define ONE_WIRE_BUS 4

OneWire oneWire(ONE_WIRE_BUS);
DallasTemperature sensors(&oneWire);
int sensorCount = 0;

void setup() {
    Serial.begin(115200);
    sensors.begin();
    sensorCount = sensors.getDeviceCount();
    Serial.printf("🔍 Found %d DS18B20 sensor(s)\n", sensorCount);
}

void loop() {
    sensors.requestTemperatures();
    
    for (int i = 0; i < sensorCount; i++) {
        float temp = sensors.getTempCByIndex(i);
        
        if (temp != -127.0) {
            Serial.printf("🌡️ Sensor %d: %.1f°C\n", i + 1, temp);
            
            if (temp < 12) {
                Serial.printf("   Zone %d: Too cold for germination\n", i + 1);
            } else if (temp > 32) {
                Serial.printf("   Zone %d: Heat stress — water more\n", i + 1);
            } else {
                Serial.printf("   Zone %d: Optimal temperature\n", i + 1);
            }
        }
    }
    
    delay(300000);
}
    

📊 Interpreting Soil Temperature Data

• ❄️ Below 10°C
  → Too cold for most crops — delay planting
  🌱 Seeds won't germinate. Roots stop growing below 8°C.
• 🌿 10-15°C
  → Cold-tolerant crops only (wheat, onions, peas, lettuce)
  🌱 Germination is slow but possible for cold-season crops.
• ✅ 15-25°C
  → Ideal for most vegetables (tomatoes, peppers, cucumbers)
  🌱 Optimal root growth, nutrient uptake, and microbial activity.
• 🌞 25-35°C
  → Good for tropical crops (maize, sorghum, okra, eggplant)
  🌱 Warm-season crops thrive, but monitor moisture closely.
• 🔥 Above 35°C
  → Heat stress — increase watering, provide shade, mulch heavily
  🌱 Root death above 40°C. Immediate action required!

// Add to your monitoring code
float soilTemp = sensors.getTempCByIndex(0);

if (soilTemp < 12 && month == 3) {  // March planting season
    Serial.println("⚠️ Soil too cold! Delay planting by 2 weeks.");
} else if (soilTemp > 18 && month == 3) {
    Serial.println("✅ Soil ready for planting tomatoes and peppers.");
}

if (soilTemp > 35) {
    Serial.println("⚠️ CRITICAL: Soil overheating! Water immediately.");
}