Arduino Nano - Soil Moisture Sensor
This tutorial instructs you how to use a moisture sensor with Arduino Nano. Specifically, we will look at:
- The differences between a resistive and capacitive moisture sensor
- How to program Arduino Nano to read the value of the moisture sensor using Arduino Nano
- How to use Arduino Nano to calibrate the moisture sensor
- How Arduino Nano determines if the soil is wet or dry
|USB A to Mini-B USB cable
|Capacitive Soil Moisture Sensor
|(Optional) 9V Power Adapter for Arduino Nano
|(Recommended) Screw Terminal Adapter for Arduino Nano
Or you can buy the following sensor kit:
|DIYables Sensor Kit 30 types, 69 units
Buy Note: Many soil moisture sensors available in the market are unreliable, regardless of their version. We strongly recommend buying the sensor from the DIYables brand using the link provided above. We tested it, and it worked reliably.
Overview of Soil Moisture Sensor Sensor
There are two types of moisture sensors:
- The resistive moisture sensor
- The capacitive moisture sensor.
Both sensors offer soil moisture information. However, their working principles are different. We strongly suggest utilizing the capacitive moisture sensor due to the following:
- The resistive soil moisture sensor is prone to corrosion over time. This is because electrical current passes between its probes, leading to electrochemical corrosion.
- The capacitive soil moisture sensor corrodes with time much slower than the resistive soil moisture sensor. This is because its electrodes are not exposed and are comparatively more resistant to corrosion.
This is an illustration of a resistive soil moisture sensor that has been damaged due to corrosion over time.
The remainder of this tutorial will utilize the capacitive soil moisture sensor.
Capacitive Soil Moisture Sensor Pinout
The capacitive soil moisture sensor has three pins:
- GND pin: This should be connected to the GND (0V)
- VCC pin: This should be connected to VCC (5V or 3.3v)
- AOUT pin: This analog signal output pin will produce a voltage that is proportional to the soil moisture level. This should be connected to an Arduino's analog input pin.
How It Works
The AOUT pin has a higher voltage when there is more water in the soil.
This image is created using Fritzing. Click to enlarge image
Arduino Nano Code for reading value from soil moisture sensor
- Copy the code above and open it with the Arduino IDE.
- Click the Upload button on the Arduino IDE to compile and upload the code to the Arduino Nano.
- Insert the moisture sensor into the soil.
- Gently pour water into the soil.
- Check out the result on the Serial Monitor.
Calibration for Capacitive Soil Moisture Sensor
The value obtained from the moisture sensor is not absolute. It depends on the soil's composition and amount of water present. In order to accurately determine a boundary between wet and dry, calibration must be done.
Instructions for calibration:
- Execute the code on Arduino Nano
- Place the moisture sensor in the soil
- Gradually add water to the soil
- Check out the Serial Monitor
- Record the value when the soil changes from dry to wet. This is referred to as the THRESHOLD.
Arduino Nano determines if the soil is wet or dry
Once the calibration is complete, update the THRESHOLD value that you noted down into the code below. This Arduino Nano code will decide whether the soil is wet or dry.
The output displayed on the Serial Monitor.