Soil Moisture Sensor Arduino — Wiring, Code & Simulation

A Soil Moisture Sensor Arduino setup lets an Arduino Uno read how wet the soil is around a plant and switch a pump or relay automatically. In this tutorial we cover wiring, calibration and the full soil moisture sensor Arduino code so you can build a reliable auto-watering system that doesn't over-water your plants.

Welcome to this beginner-friendly Arduino tutorial on the soil moisture. By the end of the guide, you'll wire the module to an Arduino UNO, flash a short sketch, and read live values on the Serial Monitor — no prior electronics experience required.

Need this built for you? I do custom Arduino, ESP32 and Proteus projects from $15.

What you'll learn

• How the module works in plain language
• The exact parts you need and how to wire them safely
• The full Arduino IDE sketch with comments
• Common issues and how to fix them

Arduino code

Open the Arduino IDE, paste the sketch below into a new file, install any libraries the sketch #includes (Tools → Manage Libraries), select your board and COM port, then click Upload.

// Sensor pins pin D6 LED output, pin A0 analog Input
#define ledPin 6
#define sensorPin A0

void setup() {
  Serial.begin(9600);
  pinMode(ledPin, OUTPUT);
  digitalWrite(ledPin, LOW);
}

void loop() {
  Serial.print("Analog output: ");
  Serial.println(readSensor());
  delay(500);
}

//  This function returns the analog data to calling function
int readSensor() {
  int sensorValue = analogRead(sensorPin);  // Read the analog value from sensor
  int outputValue = map(sensorValue, 0, 1023, 255, 0); // map the 10-bit data to 8-bit data
  analogWrite(ledPin, outputValue); // generate PWM signal
  return outputValue;             // Return analog moisture value
}

How it works

The sketch initialises serial communication and the soil moisture driver in setup(), then in loop() it samples the sensor at a regular interval and prints the result to the Serial Monitor at 9600 baud. Open the Serial Monitor (Ctrl+Shift+M) after upload to see live readings.

Troubleshooting checklist

• No readings: verify the baud rate in Serial Monitor matches the sketch (usually 9600).
• Garbage characters: wrong baud rate or loose GND wire.
• Library not found: install the exact library referenced in the #include line via Library Manager.
• Sensor not detected (I²C): run an I²C scanner sketch to confirm the address.

What to build next

Once the basic readout works, try logging values to an SD card, sending them over Wi-Fi with an ESP32, or pushing them to a Blynk IoT dashboard. Pair this module with our simulator round-up to prototype the circuit before soldering.

Stuck on your own build? Send me your Arduino / ESP32 / Proteus project on Fiverr — from $15, you don't pay if it doesn't work.