ESP32 - Soil Moisture Sensor
This tutorial instructs you how to use ESP32 to read the soil moisture from sensor. In detail, we will learn:
- Capacitive Moisture Sensor vs Resistive Moisture Sensor
- How to use ESP32 to read the value from a capacitive moisture sensor
- How to calibrate a capacitive moisture sensor
- How ESP32 determines if the soil is wet or dry
Hardware Used In This Tutorial
1 | × | ESP-WROOM-32 Dev Module | |
1 | × | Micro USB Cable | |
1 | × | Capacitive Soil Moisture Sensor | |
1 | × | Jumper Wires | |
1 | × | (Optional) 5V Power Adapter | |
1 | × | (Optional) DC Power Jack | |
1 | × | (Optional) ESP32 Screw Terminal Adapter |
Introduction to Soil Moisture Sensor Sensor

There are two types of moisture sensors:
- Resistive moisture sensor
- Rapacitive moisture sensor.
Both sensors output the soil moisture value. However, their working principles are different. We highly recommend using the capacitive moisture sensor, because of the following reasons:
- The resistive soil moisture sensor corrodes over time. The electrical current that flows between the sensor's probes causes electrochemical corrosion.
- The capacitive soil moisture sensor does NOT corrode over time. The sensor's electrodes are not exposed and no electrical current folows between them.
The below image shows the correction on a resistive soil moisture sensor.

The rest of this tutorial uses the capacitive soil moisture sensor.
Capacitive Soil Moisture Sensor Pinout
A capacitive soil moisture sensor has three pins:
- GND pin: connect this pin to GND (0V)
- VCC pin: connect this pin to VCC (5V or 3.3v)
- AOUT pin: Analog signal output pin outputs the voltage in direct proportion to the soil moisture level. Connect this pin to an ESP32's analog input pin.

How It Works
The more the water presents in the soil, the higher the voltage in the AOUT pin is
Wiring Diagram

This image is created using Fritzing. Click to enlarge image
ESP32 Code
Quick Instructions
- Copy the above code and paste it to Arduino IDE
- Click Upload button on Arduino IDE to upload code to ESP32 board
- Plant the moisture sensor into the soil
- Irrigate the soil slowly
- See the result on Serial Monitor. It looks like the below:
Calibration for Capacitive Soil Moisture Sensor
The measured value from the moisture sensor is relative. It depends on the soil's composition and water. In practice, we need to do calibration to determine a threshold that is a border between wet and dry.
How to do calibration:
- Run the above code on ESP32
- Plant the moisture sensor into the soil
- Plant the moisture sensor into the soil
- Irrigate the soil slowly
- Watch Serial Monitor.
- Write down a value at the time you feel that the soil changes its moisture from dry to wet. This value is called THRESHOLD.
Determine if the soil is wet or dry
After the calibration, update the THRESHOLD value you wrote down to the below code. The below code determines if the soil is wet or dry
The result on Serial Monitor.
Video Tutorial
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