Smart Agriculture: Automated Soil Irrigation System with Arduino

Prevent under-watering or over-watering of plants. In this guide, we will assemble a fully automated soil watering system using an Arduino microcontroller, a moisture detector probe, and a 5V relay module to trigger a mini submersible water pump.

Introduction & Concept

The resistance of soil changes depending on moisture density. A resistive soil moisture sensor measures this change as an analog voltage level. The Arduino continuously reads the voltage. If the reading rises above a set dry threshold, indicating dry soil, the microcontroller switches a 5V relay module to turn on the water pump. Once the soil becomes moist again, the pump is shut down.

Required Electronic Components

Component Name	Purpose	Store Link
Arduino Uno R3	Microcontroller processor to track sensor values.	Buy Arduino Uno
Soil Moisture Sensor Module	Probes to detect volumetric water content in soil.	Buy Soil Sensor
4-Channel 5V Relay Module	Acts as an electronic switch to safely power the water pump.	Buy 5V Relay Module

Wiring Connections Diagram

   +-------------+           +-------------------+
   | Arduino Uno |           | Soil Moist Probe  |
   |          5V |---------->| VCC               |
   |         GND |---------->| GND               |
   |          A0 |<----------| Analog Out (AO)   |
   |             |           +-------------------+
   |             |           +-------------------+
   |       Pin 7 |---------->| Relay IN1         |
   |          5V |---------->| Relay VCC         |
   |         GND |---------->| Relay GND         |
   +-------------+           +---------+---------+
                                       |
                                       v
                             [Relay Switch Loop]
               External 6V (+) ---> COM | NO ---> Pump (+)
               External 6V (-) -----------------> Pump (-)
          

Step-by-Step Installation

1. Sensor Setup: Connect the soil moisture probe to the amplifier breakout board. Insert the probe pins directly into plant soil.
2. Relay Integration: Route the digital signal from Arduino Pin 7 to the Relay input. Connect the pump positive line to the Normally Open (NO) terminal and the power positive line to the Common (COM) terminal.
3. Arduino Code Configuration: Upload the code below, and adjust the threshold limit according to your soil texture.

Control Code

const int sensorPin = A0;
const int relayPin = 7;
const int dryThreshold = 700; // Trigger threshold (0 is wet, 1023 is bone dry)

void setup() {
  Serial.begin(9600);
  pinMode(relayPin, OUTPUT);
  digitalWrite(relayPin, HIGH); // Turn off pump (Active Low relay)
}

void loop() {
  int sensorValue = analogRead(sensorPin);
  Serial.print("Soil Moisture Value: ");
  Serial.println(sensorValue);
  
  if (sensorValue > dryThreshold) {
    digitalWrite(relayPin, LOW); // Turn on water pump
  } else {
    digitalWrite(relayPin, HIGH); // Turn off water pump
  }
  delay(2000);
}