🔷 Overview

A soil moisture sensor module measures the water content in soil by detecting changes in electrical conductivity, based on the Electrical Conductivity principle.
It typically consists of:

A probe (two metal electrodes) inserted into soil
A control module with signal conditioning and comparator
⚙️ Electrical Specifications
Operating Voltage: 3.3V – 5V DC
Operating Current: ~5 mA – 35 mA
Output Signals:
Analog (A0): continuous voltage
Digital (D0): HIGH/LOW threshold output
Comparator IC: LM393
📊 Measurement Specifications
Moisture Detection Range:
Dry soil → Low conductivity (high resistance)
Wet soil → High conductivity (low resistance)
Output Voltage Range (Analog): 0V – VCC
Sensitivity: Adjustable via onboard potentiometer
Response Time: < 1 second
🔌 Module Interface
📍 Pin Configuration (4-pin module)
VCC – Power supply (3.3V–5V)
GND – Ground
A0 – Analog output (moisture level)
D0 – Digital output (threshold detection)
🧠 Working Principle
The probe is inserted into the soil
Water in the soil conducts electricity between the probes
The module measures resistance/conductivity
The signal is converted into:
Analog voltage (moisture level)
Digital signal (wet/dry threshold)
🌡️ Environmental Specifications
Operating Temperature: −10°C to +60°C
Humidity: Suitable for soil environments (non-corrosive recommended)
📐 Physical Specifications
Probe (YL-69 / FC-28)
Material: Copper traces (often nickel-plated)
Length: ~60 mm
Width: ~20 mm
Control Module
Size: ~30 mm × 16 mm × 7 mm
Weight: ~5–10 g
Indicators:
Power LED
Output status LED
🔗 Compatibility

Works with:

Arduino (Uno, Nano, Mega)
ESP32 / ESP8266
Raspberry Pi (ADC required for analog)
Other microcontrollers
⚡ Key Features
Dual output (analog + digital)
Adjustable sensitivity
Low cost and easy to use
Real-time soil moisture monitoring
⚠️ Limitations
Corrosion Issue:
Probe can corrode over time due to electrolysis
Not highly precise (gives relative moisture, not exact %)
Affected by:
Soil type
Salinity
Temperature
🔄 Common Types
Resistive (YL-69 / FC-28) – low cost, prone to corrosion
Capacitive Soil Moisture Sensor – more durable, less corrosion