Automate plant watering using a capacitive soil moisture sensor and DHT11 climate sensor to control a relay-switched pump that turns on only when soil is dry and temperature is suitable.
Explore more projects
View All ProjectsLearning Objectives
India loses billions of litres of water annually to inefficient irrigation. Your Smart Irrigation System uses a soil moisture sensor, a DHT11 climate sensor, and a relay-controlled pump to water a plant automatically — only when the soil is dry and temperature conditions are suitable.
Good to Know
Commercial smart irrigation products like the Rachio and B-Hyve use this exact principle but connect to weather APIs via Wi-Fi to skip watering on rainy days. Your project is the foundational prototype of this ₹5,000-crore market.
| Component | Qty | Notes |
|---|---|---|
| Arduino Uno R3 | 1 | _ |
| Capacitive Soil Moisture Sensor v1.2 | 1 | Preferred over resistive (no corrosion) |
| DHT11 Temperature & Humidity Sensor | 1 | ±2 °C, ±5% RH accuracy |
Good to Know
Relay and Water Safety: The relay module in this project switches a low-voltage DC pump (safe). Never use this relay to switch mains (230 V AC) electricity unless you are trained and supervised by a qualified electrician. Water and high voltage are extremely dangerous. Keep all electronics away from standing water.
| Sensor Pin | Arduino Pin | |-----------|-------------| | VCC | 3.3 V (NOT 5 V — protects the sensor) | | GND | GND | | AOUT | A0 |
| DHT11 Pin | Arduino Pin | |-----------|-------------| | VCC | 5 V | | GND | GND | | DATA | Pin 7 |
Add a 10 kΩ pull-up resistor between DATA and VCC.
| Relay Pin | Arduino Pin | |----------|-------------| | VCC | 5 V | | GND | GND | | IN | Pin 8 |
Connect the pump's positive wire to the relay's COM terminal and the relay's NO (Normally Open) terminal back to the pump power supply positive.
Install the DHT sensor library by Adafruit from Library Manager first.
// Smart Irrigation System
#include <DHT.h>
#define DHTPIN 7
#define DHTTYPE DHT11
#define SOIL_PIN A0
#define RELAY_PIN 8
DHT dht(DHTPIN, DHTTYPE);
// Thresholds (calibrate for your soil type)
const int DRY_THRESHOLD = 600; // ADC value — adjust after calibration
const int WET_THRESHOLD = 300;
Two-Point Soil Calibration
DRY_THRESHOLD.WET_THRESHOLD.Watering Cycle Analysis
Run the system for 24 hours with a potted plant. Copy Serial Monitor data to a spreadsheet. Plot soil moisture (ADC) vs. time. Identify:
WET_THRESHOLD?DRY_THRESHOLD?| 5 V Single-Channel Relay Module | 1 | 10 A / 250 VAC capacity |
| Mini Submersible Water Pump | 1 | 3–5 V DC, ~1 W |
| Small Container + Tubing | 1 | Water reservoir + 30 cm silicone tube |
| Potted Plant or Soil Sample | 1 | For testing |
| Jumper Wires | 12+ | _ |