SparkFun Qwiic Soil Moisture Sensor - Resistivity-Based Probe

The sensor is designed to operate from a 3.3V to 5V DC power supply, making it directly compatible with most Arduino boards, Raspberry Pi GPIO (using 3.3V), ESP32, and other common microcontroller platforms without requiring a level shifter.

For the simplest connection, use a Qwiic cable to link the sensor's connector to another Qwiic-enabled device (like a SparkFun RedBoard Qwiic). This establishes I2C communication. Alternatively, you can use the breakout pins: connect VCC to 3.3V/5V, GND to ground, and the SIG pin to an analog input pin on your microcontroller to read the raw resistive output.

The Electroless Nickel Immersion Gold (ENIG) plating on the PCB's exposed pads and traces provides superior corrosion resistance compared to standard solder finishes. This is critical for a sensor constantly exposed to damp soil and electrolytes, as it significantly slows oxidation, prolonging the sensor's operational lifespan and maintaining measurement accuracy.

While the ENIG finish improves durability, permanent burial is not recommended for long-term industrial use. For extended projects, periodic inspection and cleaning are advised. For best results, consider using it in a protected housing or as part of a system where the sensor PCB itself is not in constant, direct contact with saturated soil.

The SIG pin provides an analog voltage that correlates with the resistance between the probe pads. Higher moisture (lower resistance) results in a higher output voltage. Calibration involves taking readings in "dry" and "water-saturated" soil conditions specific to your medium to map the sensor's output range to a meaningful moisture percentage or index for your application.