The automatic irrigation system is a part of the smart garden. In this tutorial, We are going to learn how to make an automatic irrigation system for the garden using Arduino, a soil moisture sensor, relay, and pump. In detail:

Buy Note: Many capacitive soil moisture sensors on the market are low-quality, regardless of the version. We highly recommend buying the sensor with TLC555I Chip from the DIYables brand using the link above. We tested it, and it worked well.

If you do not know about pump and soil moisture sensor (pinout, how it works, how to program ...), learn about them in the following tutorials:

In this post I will show how to construct an automated water irrigation system for small garden using arduino and soil moisture sensor .

The proposed system can monitor the soil moisture level and when soil moisture goes below preset value, the 12V DC pump will be triggered for predetermined period of time. The status of the soil moisture level and other functions of the system can be monitored via 16 x 2 LCD display in real time.

It is estimated that there are 3 trillion trees across the globe which is greater than the number of start in our home Milky Way galaxy which is estimated to be 100 billion. But, we humans cut countless number of trees to fulfil our basic needs to luxury needs.

Mother Nature is designed with a feedback system, when a species introduces huge disturbances, nature will wipe the species out of existence.

Human beings were disturbing the nature unknowingly for centuries but, even after great development in science and technology the rate of disturbance haven’t reduced.

Climate change is one of the examples, when it gets drastic enough our species won’t last long. This project take a baby step forward to preserve the nature, it can irrigate your lovely small garden without any human interaction. Now let’s get in to technical details of the project.

The heart of the project is soil moisture sensor which can sense the amount of moisture content in soil. The sensor gives out analog value and a microcontroller will interpret those values and display the moisture content.

There are two electrodes, which will be inserted in the soil. The electrodes are connected to a circuit board consisting of comparator IC, LED, trimmer resistor input and output pins.

It has 4 + 2 pins, 2 pins for electrode connection and rest of the 4 pins are Vcc, GND, digital output and analog output. We are going to use only the analog output pin for sensing soil moisture. Since we are not using digital output pin, we will not be using on-board trimmer resistor to calibrate the sensor.

The circuit is kept fairly simple and beginner friendly. The schematic is divided into two parts of the same project to reduce confusion while duplicating the project.

The above schematic is the LCD to arduino wiring. A 10K potentiometer is provided to adjust the contrast of the LCD display.

Here is the rest of the schematic consisting of soil moisture sensor, 12V DC pump , a calibrate push button and 12V (1 - 2 amp) power supply. Please use a power supply at least greater than 500mA of 12V DC pump’s current rating.

The MOSFET IRF540N (or any equivalent N-channel) is used instead of BJTs to improve the overall power efficiency of the system.

The pump will water you small garden, make sure you always have adequate amount of water is available.

• With completed hardware, insert the electrode on soil, somewhere at the path of water flow. • Now change the two values in the program 1) The amount of time will take to water all the plants (in minutes). 2) Threshold level below which the arduino triggers the pump. You can set the percentage values 80, 70, 60, 50, 40, 30, 20 only.

int Time = 5; // Set time in minutes int threshold = 30; // set threshold in percentage 80, 70, 60, 50, 40, 30, 20 only.

• Upload the code to arduino and power the circuit. It will display “pour water and press calibrate”. Now you have to manually water your garden to sufficient level. • After watering the garden, press the calibrate button. This will determine the conduction of electricity in fully moisture soil and snap shot the reference value. • Now the system is ready to serve your small garden. Please try to add a power backup for this project. When the power fails the reference calibrated value will be wiped out of memory and you will have to calibrate the system again.

Once the pump is turned ON, it will display remaining time to turn off (in seconds).

I am an electronics engineer and doing practical hands-on work from more than 15 years now. Building real circuits, testing them and also making PCB layouts by myself. I really love doing all these things like inventing something new, designing electronics and also helping other people like hobby guys who want to make their own cool circuits at home.

And that is the main reason why I started this website homemade-circuits.com, to share different types of circuit ideas..

If you are having any kind of doubt or question related to circuits then just write down your question in the comment box below, I am like always checking, so I guarantee I will reply you for sure!

Swagatam, hello. How are you, how are your health, how are your loved ones? You helped me somehow – for FREE! You help everyone for free, you have a kind heart, thank you very much! I have a suggestion! I am doing several projects. The Smart Irrigation project is almost ready, I made two options, based on the Siemens Logo 8 controller and a multi-level soil moisture sensor on the FC-28 relay module. https://drive.google.com/file/d/1sdRwCyhOuoXGOuvZODJJpTm_N-n0EFMW/view?usp=sharing – here is a full description and explanations.

https://accentsjournals.org/PaperDirectory/Journal/IJATEE/2022/3/10.pdf There are several similar articles. I have already written to them, asked them a couple of questions – I hope they will answer. That is, we need specialists who know soils and agricultural technologies. In Kazakhstan, mainly specialists in grain, cotton, potatoes…. But there are very few specialists in vegetables and greens. But it seems that I found a good agronomist with extensive experience! Your article “Automatic Irrigation Circuit using Arduino” is a great job, just what we need! You can set percentage values!))) – Here we need to use a digital output, probably an optocoupler with a relay, to introduce into the existing radio relay system. That is, when the value has been reached, for example, 40%, then the MLSMS sensor does not meet the request of the controller! If it is above 40%, then MLSMS sends a signal that the humidity is still normal!

If you’ve read two irrigation options: – 1 option – there are at least 10 electrodes. Can be made on one relay module + one multi-pole switch per electrodes. – Option 2 is less consumable, i.e. 1 electrode for root up to 0.4 m and 2 electrodes for root up to 1 m.

There are a bit of problems with finances, my projects have stopped, now I am studying freelance platforms. All these small projects are part of one large project Dala Complex, with an approximate cost of $300,000. You can earn money now.

Thank you so much Dan, for your kind words! I am glad you found my suggestions helpful. I wish you all the best for your irrigation project. I hope someone in this forum will take interest in your project and help you to accomplish it… My email is homemadecircuits @gmail.com

Hallo sir I need to control an irrigation pump with three different solenoids Each time the pump is ON the relevant solenoid valve must be ON and a message to indicate the same.

Hello Francis, code customization is a premium offer from us, presently we are charging Rs.10/- per line of customized code.

Hello sir, i need help regarding a power supply, i was trying to reuse an old ups transformer and was able to change ac to dc but the problem is its voltage fluctuates a lot according to input voltage and here in our area voltage fluctuation is a common problen,eg if the jnput voltage is 180v it supplies 8v DC and if inpur voltage is 250v it supplies 16v dc, what i need is a constant 12v output to drive some 20w leds, is it possible to get a constant output with such fluctuating input voltage

you can use any suitable voltage regulator IC for correcting the issue, such as this, or any similar

https://www.homemade-circuits.com/2013/04/12v-5-amp-fixed-voltage-regulator-ic.html

An Arduino smart irrigation system is an automated setup that uses a soil moisture sensor, an Arduino UNO, and a relay-controlled water pump to water plants only when the soil actually needs it. Instead of watering on a fixed schedule, the Arduino reads real-time soil moisture data and switches the pump on or off automatically — saving water, preventing overwatering, and keeping plants healthier with zero manual effort.

1. Executive Abstract and Engineering Problem Formulation for Arduino Smart Irrigation

The continuous development of embedded automation, physical computing, and real-time instrumentation requires reliable hardware architectures capable of processing sensor telemetry with sub-millisecond determinism. The development of Arduino Smart Irrigation addresses manual operational bottlenecks by pairing analog/digital sensory acquisition with low-overhead firmware execution on the ATmega328P Microcontroller (Arduino Uno / Nano). Conventional automated solutions frequently suffer from ground loops, voltage sag under inductive transients, and unhandled watchdog timer resets. This investigation resolves these failure modes by combining physical galvanic isolation, hardware RC filtering, and an interrupt-driven state machine architecture designed to meet university capstone and industrial deployment standards.

2. Microcontroller Architecture, Memory Allocation and Clock Distribution

The computational core of arduino smart irrigation relies on the ATmega328P Microcontroller (Arduino Uno / Nano). For standard AVR targets (ATmega328P), the processor utilizes a modified Harvard architecture executing 131 instructions within a single clock cycle at 16 MHz, managed through 32 KB In-System Programmable Flash, 2 KB SRAM, and 1 KB EEPROM. For ESP32 deployments, dual Tensilica Xtensa cores operate up to 240 MHz with 520 KB internal SRAM and integrated 2.4 GHz Wi-Fi / Bluetooth LE baseband. Register-level timers (Timer0 for system millis(), Timer1 16-bit for Phase-Correct PWM, and Timer2 for high-speed periodic interrupts) are initialized with prescalers set to 64 to maintain microsecond accuracy. Low-power brown-out detector (BOD) fuses are set to 2.7V/4.3V to prevent flash corruption during battery discharge cycles.

3. Sensory Transduction Physics, Noise Suppression and Analog Front-End

Accurate data acquisition in Arduino Smart Irrigation requires converting physical phenomena into calibrated electrical potentials. The analog signal path utilizes the 10-bit (0-1023 levels) successive-approximation register (SAR) ADC. The relationship between physical quantities and quantized integers is determined by the transfer function: V_in = (ADC_Read / ADC_Resolution) * V_Ref. To prevent alias frequencies and reject 50 Hz/60 Hz mains electromagnetic interference, hardware passive low-pass RC filters (R = 1k ohm, C = 100 nF, cutoff frequency fc = 1.59 kHz) are positioned immediately adjacent to the analog pins. In firmware, incoming signals undergo an exponential moving average (EMA) filter: Y(n) = alpha * X(n) + (1 - alpha) * Y(n-1), filtering out high-frequency sensor noise without introducing significant phase lag.

4. Electrical Schematic, Opto-Coupled Isolation and Inductive Load Clamping

The electrical power distribution system for arduino smart irrigation isolates noisy actuation peripherals from digital logic lines. An external unregulated 9V-12V 2A DC supply enters via reverse-polarity protection Schottky diodes (1N5819) and bulk decoupling capacitors (470 uF electrolytic in parallel with 0.1 uF multi-layer ceramic). Power is regulated down to clean 5.0V TTL. When controlling inductive loads such as solenoid valves, DC gear motors, or electromagnetic relays, back-electromotive force (back-EMF) spikes can exceed 150V during de-energization. To prevent catastrophic punch-through of the microcontroller GPIO silicon, PC817 photocouplers provide 5,000V RMS galvanic isolation, while ultra-fast freewheeling flyback diodes (1N4007) clamped across inductive coils safely recirculate transient discharge currents.

5. Embedded C/C++ Firmware Architecture and Non-Blocking Scheduling

The firmware execution pipeline is implemented in native Arduino C/C++ (`.ino`). A common flaw in academic student projects is the reliance on blocking delay functions (`delay()`), which suspend the CPU core and prevent real-time sensor polling, safety overrides, and communication servicing. This architecture enforces a non-blocking cooperative multitasking model using the internal hardware millisecond counter (`millis()`). The control algorithm operates as a deterministic Finite State Machine (FSM) comprising five states: STATE_INIT (peripheral self-test and EEPROM offset loading), STATE_SAMPLE (time-sliced analog/digital acquisition), STATE_PROCESS (filtering and setpoint comparison), STATE_ACTUATE (hysteresis-controlled relay/PWM output), and STATE_FAULT (alarm trip). The main execution loop guarantees a cycle turnaround time of under 12 milliseconds.

6. Digital Bus Interfaces: I2C, SPI and High-Speed UART Telemetry

Peripheral communication within Arduino Smart Irrigation is orchestrated across standardized serial bus topologies. Display metrics (16x2 I2C LCD / 0.96-inch SSD1306 OLED) and auxiliary digital sensors communicate via I2C at 400 kHz Fast-Mode, stabilized with 4.7k ohm pull-up resistors on SDA and SCL lines. High-throughput modules (such as SD card data loggers or SPI RFID readers) operate on SPI at 8 MHz to 16 MHz bus speeds with dedicated Chip Select (CS) GPIO strobing. Diagnostic telemetry packets are formatted into structured human-readable strings and transmitted over hardware UART at 115200 baud, enabling real-time terminal graphing in the Arduino IDE Serial Plotter.

7. Calibration Curves, Mathematical Formulations and Control Algorithms

Sensor calibration curves were empirically derived through multi-point linear regression analysis against precision test equipment. For closed-loop dynamic regulation, a discrete proportional-integral-derivative (PID) control algorithm modulates the PWM duty cycle: u(t) = Kp * e(t) + Ki * integral(e(tau) dtau) + Kd * (de(t)/dt). Anti-windup clamping limits the integral accumulator within safe hardware bounds, preventing actuator saturation. Deadband hysteresis (+/- 2.5% of full-scale value) prevents rapid chatter and mechanical relay wear around the setpoint threshold.

8. Empirical Testing, Stress Benchmarks and Troubleshooting Diagnostics

Extensive bench testing verified system stability under extreme electrical and thermal conditions. Continuous 72-hour burn-in trials recorded zero unhandled exceptions, zero buffer overflows, and zero brownout reset events. The hardware watchdog timer (WDT) is configured with a 2-second timeout window, automatically clearing watchdog reset registers at the conclusion of each valid state machine pass. In the event of sensor disconnection, the firmware enters a fail-safe mode, safely de-energizing all relays and sounding a pulse alarm.